Tag Archives: Clean Rooms

Avoiding contaminant build-up is critical for controlling electrostatic charge

By Jim Curtis, ITW Simco, and Howard Siegerman, PhD, ITW Texwipe

Emitter electrodes in ionizing systems for electrostatic charge control will become contaminated with environmental residues over time and these residues will compromise performance by reducing ion density and by generating particles. This article describes why this is the case and how it can be avoided.

The production of semiconductors, flat-panel displays, disk drives, and medical devices involves a series of complex manufacturing processes, many of which require non-conductive materials and isolated conductors. These materials generate and retain large charge potentials. Electrostatic charge is one variable found throughout the process that, if left uncontrolled, affects both the yield rate and the quality of finished product. Control of electrostatic charge (static) in cleanroom manufacturing processes is therefore critical.

Ionizers add molecules to the air that have the ability to carry charge. These charged air molecules are able to neutralize electrostatic charge on both insulators and conductors.

Corona ionization

Electrically based, corona technology is the most widely used ion generation method for electrostatic charge control. Several types of commercial electrical ionizers are currently in use and all operate on the corona principle. Electrical ionizers generate ions by concentrating an electric field on a point. The three common types of corona ionizers are: AC, Steady State DC, and Pulsed DC.

Negative ions are produced in close proximity to emitter points driven by a negative power supply. Ions are generated in the plasma of the corona around the emitter. In the corona region, weakly bound electrons are driven from orbit and attach to a molecular cluster. The resulting negative molecule is repelled from the like-charged emitter.

Positive ions are produced in the area around emitter points driven by a positive power supply. The free electron is attracted back to the positive polarity emitter point. In this case, the resulting positive molecular cluster accelerates away from the like-charged electric field of the emitter electrode.

Ion current strength is a function of applied voltage, emitter geometry, and conductivity. Duration of applied voltage influences the ion current strength and the distance the ions are capable of traveling.

Ion current is affected by environmental conditions such as temperature, humidity, atmospheric pressure, and proximity to ground planes. Closely controlled environments such as minienvironments and cleanrooms eliminate much of the environmental variance concern for ionization.


Figure 1. Deposits appear as a white substance at the end of the emitter electrode and are commonly referred to as white “fuzz.”
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A great deal of activity takes place at the emitter of an ionizer. The corona region at the tip of the emitter is a field of complex chemical reaction that results in the creation of ions, but also causes precipitation of trace elements from the environment onto the emitter. These deposits appear as a white substance at the end of the emitter electrode and are commonly referred to as white “fuzz” (see Fig. 1).

In a paper titled “Clean Corona Ionization” (Hobbs, Gross, Murray, 1990), researchers found that the overwhelming percentage of particles identified on ionizer emitter tips was ammonium nitrate (NH4NO3). In the same study, it was demonstrated that contamination problems could be avoided by isolating emitter electrodes in an environment of clean, dry air. The primary cause of emitter electrode contamination was found to be the result of inter-actions between the ionizers concentrated high voltage field and ambient humidity.

Reduction in emitter performance

The build-up of deposits on the emitter electrode impacts ionizer performance. Deposits cause an increase in the emitter electrical resistance. Without a means of compensation, this condition will cause a reduction in ion emission and ionizer efficiency (see Table 1).


Run time 300+ hours. Ionizer utilizing current-controlled closed-loop feedback.
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Ionizers designed with active feedback and control systems are capable of compensating for dirty emitters. And, to a point, deposition on the emitter will have no measurable performance impact. The better ionizers on the market today contain an active feedback system to control output. A number of methods are used but the better methods function to maintain the selected output current level. As resistance increases on the pin, the measured output current drops and the ionizer power supply must increase voltage in order to maintain the selected output current level. Both the chemistry of the deposits and the increased drive level experienced by the emitter will nevertheless result in a shortened life. A dirty emitter condition causes accelerated emitter wear.


Figure 2. Emitter tips should be cleaned at regular intervals to maintain optimum system performance. One convenient method is to use a pre-wetted swab (shown here), which is shipped with a protective sleeve covering the white foam swab end. The swab incorporates an inner glass vial of alcohol inside a plastic tube.
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The problem escalates when the power supply is running at its highest output level and is no longer capable of maintaining the selected output current. At or near this point, a properly designed ionizer will issue a fault condition warning. This is a condition the user should avoid by properly cleaning and maintaining the emitter pins. Emitter tips should be cleaned once per quarter at a minimum. Consider more frequent cleaning if significant residues accumulate between cleanings.

Jim Curtis is a business unit manager for ITW Simco (Hatfield, PA). He can be reached via e-mail at [email protected].

Howard Siegerman, PhD, is director of technology for ITW Texwipe (Mahwah, NJ). He can be reached via e-mail at [email protected].

Working group aims to develop uniformity in FFU testing parameters and reporting data

By Monroe A. Britt, Clarcor Air Filtration Products, Inc., and Chair, Working Group CC036

Fan filter units (FFUs) are being used more frequently for air recirculation systems in cleanrooms and minienvironments. These units are usually easily installed and allow for control of local air cleanliness and/or air velocities within a large cleanroom or in groupings of cleanrooms, which may be used for various functions and require different filtration efficiencies (i.e., HEPA or ULPA). In certain circumstances, these units also provide the most energy-efficient means of maintaining air control and cleanliness within a given workspace. Fan filter units can also be easily added or moved if the cleanroom requires minor changes or major modifications.

An FFU is a self-contained module consisting of a small fan, a HEPA or ULPA filter, and some means of controlling the speed of the fan, thereby controlling the airflow. These units are typically designed to be installed directly in the cleanroom ceiling grid and provide a downward airflow with velocities ranging from 60 to 100 fpm. These units can also be designed to meet specific requirements for minienvironments and tool enclosures. Some FFUs allow for roomside replacement of the filter. Also, the fan’s speed control may be mounted on the top side of the unit, the roomside of the unit, or it may be remotely located.

FFUs are manufactured by several companies and performance data are provided by each company in their unique formats and contain individual operational claims. Usually, test methods used to determine the airflow, power requirements, and sound data are not stated in the manufacturer’s literature. The lack of uniformity in test methods and in the presentation of performance data has made it difficult to compare the true performance of FFUs from different manufacturers.

IEST Working Group (WG) CC036 was formed to produce a recommended practice (RP) to provide a means for cleanroom industries to identify or develop uniform test methods for significant performance parameters of FFUs and to provide a reporting data format that allows a clear comparison of the performance of FFUs provided by various companies. During the formative meetings of this new WG, members identified airflow volume, external available pressure, power requirements, sound power levels, airflow uniformity, and FFU housing vibration as the parameters that were most important for inclusion in this new RP. Various methods of testing for each of these parameters have been fully discussed in several meetings. Approximately fifty percent of attendees of these meeting have been first-time attendees and, consequently, there have been wide discussions of various testing techniques and protocols. It is believed that, at this time, the WG has received sufficient guidance and information on testing methods from the contamination control industry and is ready to formalize the procedures. This RP will recommend only the test methods for measuring the individual performance parameters and will not contain recommended performance values.

The first major parameter to be measured is the airflow volume exiting the filter surface of the FFU. The WG has chosen to measure flow volume, rather than measuring the air velocity exiting the filter surface and converting it to volume. One method discussed was the use of airflow hoods, which are used widely in the cleanroom industry, to measure the airflow exiting ceiling grid filters. The method selected, however, was the use of an airflow chamber, which is widely described in the existing standard test methods of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE; www.ashrae.org) and the Air Movement & Control Association International (AMCA; www.amca.org). An airflow chamber consists of a fan for moving the air through an air-control damper; airflow distribution screens; an American Society of Mechanical Engineers (ASME; www.asme.org) airflow-measuring orifice; and the FFU under test. The FFU is the last stage of the test apparatus and the airflow is exhausted into the test room at atmospheric conditions. This technology is well recognized and will provide accurate data. The airflow volume at various fan speed settings can be measured using the airflow chamber. The maximum possible airflow can be determined, as well as the minimum airflow with the fan speed reduced to its lowest setting.

During the airflow volume tests, the available external pressure can also be determined for any selected FFU airflow. The static pressure at the inlet to the FFU is monitored and modulated by adjustment of the chamber damper while measuring the airflow through the ASME orifice. This test method allows the FFU user to know the amount of static pressure that is available for use in cleanroom/minienvironment pressurization, for airflow through additional duct work and through prefilters, and for the increase in pressure drop of the HEPA/ULPA filter as the filter collects contaminants.

The electrical power will also be measured during the airflow and external pressure tests. The power parameters at each test condition will be measured and reported. Important parameters include line voltage, current, watts, and power factor. These values, in conjunction with the airflow and pressure data, allow potential users to readily determine the performance capabilities and the energy merits of FFUs from different manufacturers.

The WG has agreed that sound power levels are required and should be measured and reported instead of sound pressure levels. The FFU power levels can be used in conjunction with sound data from other equipment and the physical characteristics of the cleanroom to predict the expected sound pressure levels in the work environment. Sound power levels will be measured in 1/3-octave bands, using the sound intensity method as described in ANSI S12.12-1992. The FFU will be tested in an area with minimum background noise. The airflow volume of the FFU, the external available pressure, and electrical parameters will be reported with the sound power levels.

The velocity distribution of the airflow exiting the filter surface is important in many cleanroom applications. The velocity distribution below the filter will be measured and reported. The filter surface will be divided into 6-inch by 6-inch grids and the velocities will be measured 6 inches below the surface of the filter by suitable hot-wire anemometers. Measurements will be taken at each grid point. The purpose of these measurements is to determine the true velocity distribution, not the average over several locations.

Another extremely important parameter is the degree of vibration that is transmitted from the FFU fan/motor through the housing to the FFU mounting surface. Frequently, a soft gasket is used between the typical ceiling grid and the FFU housing to serve as an air seal. This gasket can help diminish the vibration passed to the mounting grid. More discussions within the WG are required before the proper test method is finalized for this parameter. Several approaches have been suggested and it is expected that the group can reach consensus at the next meeting of WG CC036 to be held at 8:00 a.m. on November 5, 2006, at the IEST Fall Conference (November 5-9, 2006, at the Hilton Garden Inn, Hoffman Estates, Illinois). More information is available at www.iest.org.

Attendance and active participation are encouraged for all interested parties. It is anticipated that the new RP can be ready for acceptance/vote by the IEST fall meeting.

Monroe Britt is manager of research and technology for Clarcor Air Filtration Products (CLC Air). He holds a bachelor’s degree in mechanical engineering from Georgia Tech and has been associated with essentially all phases of air filtration and air filter testing for more than thirty years. CLC Air’s air filter product areas include cleanrooms, commercial and industrials markets, dust control, gas turbine intakes and residential use. Mr. Britt can be contacted at (502) 810-5742 or via e-mail at [email protected].

Increased attention to microbiological contamination forces a greater focus on air sampling technology

By Christopher Mach, Pall Life Sciences

Improvements in environmental air monitoring technology are becoming increasingly important to the pharmaceutical industry. The latest ISO 14698 standards have served to underline the increased focus on air monitoring being shown by regulatory bodies around the world. Current monitoring technologies do not, for the most part, meet these challenges because their efficiency-the number of microbial particles they capture compared to those that are actually present-isn’t high enough to meet the new ISO standards. Another concern with existing technology is its inability to distinguish between contaminants captured from cleanroom air and those from externally introduced sampling. These increasing requirements have intensified the attention paid to advancements in air sampling technology. This article will outline some of the basic issues involved.

Increased focus on air monitoring

The increasing emphasis on environmental air monitoring in aseptic processing areas was apparent even before the British Medicines and Healthcare products Regulatory Agency (MHRA) suspended manufacturing at Chiron’s plant in Liverpool, England, for five months in 2004 and 2005. Chiron had been expected to produce half of the United States’ 100-million-dose flu vaccine supply for the 2004-05 season but the MHRA suspended the plant’s manufacturing license because of contamination issues. Inspectors found bacterial contamination of vaccine batches, microbial growths on equipment used to fill vaccine vials, high levels of bacterial toxins in vaccine preparations and contaminant in viral seed cultures, among other issues. Chiron’s shares fell more than 30 percent with news of the plant suspension and its 2004 earnings fell by half from the previous year.

Similar concerns have caused regulators around the world to focus increasing amounts of attention on ensuring that airborne microorganisms are within acceptable levels. Tight control over the cleanroom used for aseptic processing of pharmaceutical products is the primary safeguard against contamination. Nearly as important is the ability to evaluate bacterial contamination associated with airborne particles so that manufacturing personnel can promptly intervene in the event that values outside acceptable levels are detected. The increased awareness of microbiological contamination has forced a greater focus than ever before on bioaerosol sampling technology designed to accurately quantify the total number of viable microorganisms per unit volume of air.

The attention being paid to air sampling is further amplified by the Food and Drug Administration’s Process Analytical Technology (PAT) initiative, which aims to spearhead a shift from reliance on final product quality control to in-process control at key points in the manufacturing process. The ability to monitor quality and identify microbial contamination events during processing enables companies to diagnose root causes and take preventive action quickly in order to ensure product safety and avoid economic losses.

Limitations of conventional methods

As pharmaceutical manufacturers have begun focusing more attention in this area, the limitations of conventional bioaerosol sampling methods have become more apparent. The basic challenge of bioaerosol sampling is the trade-off that is required between particle collection efficiency, which requires moving microorganisms at high speed into the sampler, and avoiding severely stressing the microorganisms during the sampling process, which can conceal air contamination. This trade-off has become more challenging than ever since ISO released the 14698-1:2003 standard, which establishes tough sampling efficiency requirements that cannot be achieved by the vast majority of existing bioaerosol samplers. Another critical concern is the ability of the sampler to distinguish between contamination of the cleanroom air and random contamination from other sources such as the assay media. Finally, the critical locations in which samplers are placed lead to the requirement that they must not contaminate the environment.

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The new ISO standard highlights the limitations of traditional sedimentation technology, which, because of its simplicity, has long been the most popular environmental air sampling method. Sedimentation sampling relies on the force of gravity and air currents to cause airborne microorganisms to settle onto plates filled with media. After exposure, the plates are incubated. The problem with this method is that its efficiency is low and it is particularly inefficient at capturing smaller particles, which constitute a relatively high proportion of microbiological contaminants. For these reasons, Annex A.3.3 of the ISO standard states that settle plates should not be used to attempt to measure the total number of viable particles in the air but should be limited to measuring the rate at which particles settle on surfaces. The standard explicitly describes the use of active sampling methods in risk zones as essential to the accurate measurement of microbiological air quality.

Movement towards active methods

For these reasons, there has been steady movement in the industry towards active sampling methods. Impingement methods entrap airborne microorganisms in a liquid medium as the air is transmitted through the fluid. Centrifugal samplers spin an aerosol at a high rate of speed and rely on centrifugal force to propel particles against the settling plate. Filtration samplers collect airborne microorganisms by impelling air against a filter, such as gelatin membranes or cellulose fibers, that can then be placed onto an agar surface for quantification. Impaction samplers utilize a vacuum to draw microorganisms onto an agar surface. All active samplers must overcome the difficult trade-off between efficiency and overstressing organisms to comply with ISO standards. High air velocity runs the risk of overstressing microorganisms to the point they will not be detectable, while low air velocity reduces collection efficiency.

But even the vast majority of active air samplers are incapable of meeting the ISO standards, which enumerate several important factors to consider in selection of an air sampler. The effective sampling rate of the instrument, duration of sample acquisition and physical attributes of the sampling device all have the ability to strongly influence the viability of the microorganisms that are collected. Since there are many microbial air sampling systems available on the market today, ISO 14698-1 recommends users consider, as a minimum:

type and size of viable particles to be sampled

sensitivity of the viable particles to the sampling procedure

expected concentration of viable particles

capability of detecting high or low levels of biocontamination

appropriate culture media

time and duration of sampling

ambient conditions in the environment being sampled

disturbance of unidirectional airflow by the sampling apparatus

How active samplers work

Understanding these requirements demands an examination of the complicated physical forces that affect the motion of microbial particles in air. The force of gravity causes particles to accelerate based on their weight. Brownian motion causes random movements. Bioparticles have an electrical charge that influences their velocity and is strongly influenced by humidity. Vapors are absorbed on the surface of biological particles, which may cause coagulation of proteins. Acoustic forces may exert accelerations depending on their frequency and intensity. Adhesion forces are also important in determining particle behavior. For particles of 10 microns and below, Van der Waals forces are dominant. However, as particle size approaches 100 microns, gravity becomes the dominant force.

Inertial impact samplers have benefited from some of the most significant technical advances made in recent years. An inertial sampler is based upon the principle that when a stream of gas undergoes a sharp change in direction, the particles it transports will tend to continue in their original direction to a degree that is proportional to the ratio of their mass to their linear dimensions. Particles that have different dimensions and densities will follow different trajectories and can be collected separately. Inertial impact samplers capture particles by accelerating a jet of air in a nozzle. The particles transported in the jet are carried at the same speed as the fluid and follow its flow lines. Then, at the nozzle output, the fluid flow lines rapidly change direction, while particles tend to run in a straight line-into a surface to which they adhere-and are captured.

The impact efficiency (in other words, the probability that the particle will be captured by the impact plane) depends upon the particle linear dimensions, particle speed at the acceleration nozzle output, air viscosity, impactor geometry, and adhesion of the particle to the impact plane. Particle efficiency can be expressed in terms of a dimensionless parameter called the Stokes number, which takes into account the physical laws that govern the motion of the particles moving in a fluid under laminar flow conditions. These methods make it possible to calculate the efficiency of a given impactor design.

CΦpDp2V

Stokes = —- C

9µW

C = pressure dependent correction factor (atmospheric pressure C=1)

Φp = particle density

Dp = particle equivalent diameter

V= particle speed at nozzle output

μ= air viscosity

W= slot width for rectangular slot impactors

Improving sampler design

There are two potential problems that must be considered in the design of the impact surfaces. If the particles do not adhere well to the impact surface, they can be resuspended in the fluid owing to the motion of the air. On the other hand, if the impact with the impact plane is elastic, particles may bounce off it and fall back into the fluid or break up. In order to avoid these potential problems, the impact surface must be able to absorb the particle’s kinetic energy and the kinetic energy imparted to the particle must be minimized.


Figure 2. BioCapt Impactor on the Pall-Ascotec* Microbiological Remote Air Monitoring System. With this technology, air is pulled downward through the slits using a vacuum, and an internal gas filter scrubs the air before it leaves the system. A stand-alone unit includes an aspiration mechanism with a pump and can be used as a portable sampler. A remote unit allows simultaneous or sequential sampling on multiple independent pneumatic lines connected to a single sampler.
*The Ascotec brand is owned by Biotrace International Plc
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One new design approach is to use laser technology to form rectangular slits that serve as nozzles to improve collection efficiency while avoiding severe stress to microorganisms. The slits also create a recognizable pattern of microorganisms on the assay media surface, which makes it possible to distinguish between microbial contamination in the clean air and particles introduced from other sources (see Fig. 2).

Evaluating sampler performance

New-design test samplers operating at 25 and 50 liters per minute were evaluated for physical and biological efficiency using the techniques described in ISO 14698. A conventional slit sampler was operated at 30 liters per minute during the biological and background efficiency testing for comparison purposes. Physical efficiency measures the sampler’s ability to collect various sizes of particles regardless of their nature. Biological efficiency goes one step further by measuring the ability of the sampler to capture viable particles-that is, particles that contains one or more living microorganisms-by taking into account the survival of the microorganisms during the collection process and the ability of the collection medium to support their growth. Viable particles generally range in size from 0.2 micron to 30 microns.


Figure 3. Settle plate exposed to ambient on left; plate used with the new-design impact sampling system on right.
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The physical efficiency of the sampler was measured through the particle range of 1 to 10 microns by creating aerosols of an aerostable bacterial spore Bacillus subtilis var. niger. The size of the spores containing particles was varied by aerosolizing them from a range of concentrations of potassium iodide solution. Physical efficiency testing was carried out in a cleanroom with 28 cubic meters of volume, supplied with a horizontal flow of clean air through HEPA filter banks. During aerosol sampling, the ventilation was switched off. A spinning top aerosol generator (STAG) was used to generate aerosol drops. A peristaltic pump was used to supply the STAG with the spray suspension at a flow rate of 0.5 mL/min. The STAG was placed above a standard room ventilation fan to allow dissemination of the aerosol. The samplers were placed 1.0 meter from the STAG next to the two filter samplers. The microbial aerosol was generated in on/off pulses of ten seconds each while the samplers were operated.


Figure 4. Impacted media plate with colonies defined in the impaction plane. The circled colony represents false positive growth outside the impaction area
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At the same time, a Cascade sampler was operating to measure the particle size of the aerosols used in the physical efficiency testing. The final particle size was controlled by the use of 80 percent ethanol as a solvent to allow rapid evaporation of the fluid, and potassium iodide as a bulking agent to govern the final size. A three-jet nebulizer was used to generate the mixed microbial aerosol for biological efficiency testing.

Comparing efficiency to conventional sampler

The biological efficiency of the sampler was compared to a standard slit sampler using mixed aerosols of the aerostable spore and a common air contaminant, Staphylococcus epidermidis. The ratio of the number of S. epidermidis cells collected to the aerostable spore gives an indication of the biological efficiency of the sampler. This microorganism was chosen as a test strain because, being derived from human skin cells, it is a common contaminant in cleanroom air. The biological efficiency testing was undertaken in a Class III microbiological safety cabinet with an internal volume of 0.865 cubic meters. The cabinet generates six air changes per minute when the fan unit is operated. The spray suspension was aerosolized for 30 seconds and then the samplers were operated for one minute. After 24 hours of incubation, the colonies of S. epidermidis and B. subtilis var niger were counted individually.

In the physical efficiency tests, the 50 LPM model was shown to have a d50 (smallest particle size of which it can capture 50 percent or more) of less than 1 micron. The 25 LPM model had a d50 value of less than 2 microns. The 50 LPM sampler collected 79 percent of spores aerosolized from 0.0 percent potassium iodide compared to 54 percent reported by Benbough et al. (1993) for an earlier model. The submicron d50 values of the 50 LPM sampler are considerably lower than d50 values reported in the past (Lach, 1985). The 50 LPM sampler had an average biological efficiency of 95.3 percent and 82.4 percent for a one-minute and 20-minute sampling period respectively, which is higher than a conventional slit sampler. The total net impact surface is less than 1 percent of the total plate surface. This implies that false positives can be excluded with a statistical probability exceeding 99 percent.

The efficiency and reliability of environmental air monitoring systems need to increase in order to address the requirements of pharmaceutical manufacturers as they move to meet the increasing scrutiny of regulatory agencies, as well as the challenges of the new ISO standard. Advanced air monitoring technologies are the key to gaining tighter control over manufacturing processes and providing greater assurance of product safety. The performance of microbiological air samplers plays an important role in the environmental monitoring program. The latest ISO 14698 standards provide a needed impetus for improvements by providing techniques for the evaluation and qualification of the efficiency of air samplers.

References

1. International Organization for Standardization. ISO 14698-1:200i, Cleanrooms and associated controlled environments-Biocontamination control.

2. International Organization for Standardization. ISO 14698-2:2003, Evaluation and interpretation of biocontamination data.

3. Benbough, J.E., A.M. Bennett, and S.R. Parks. “Determination of the collection efficiency of a microbial sampler,” Journal of Applied Bacteriology, 74: 170-173, 1993.

4. Lach, V. “Performance of the Surface Air System air samplers,” Journal of Hospital Infection, Vol. 6, pp. 102-107, 1985.

Christopher Mach is a biotechnology marketing manager for Pall Life Sciences. He can be reached at [email protected].

By Robert McIlvaine and Karen Vacura, The McIlvaine Company

The world market for cleanroom consum-ables in 2007 will be over $5 billion, while the amount spent on new rooms will be $3.6 billion (see Table 1). Both of these sectors will represent growth over 2006 and records for the industry. The consumables market grew 9 percent in 2006 and is expected to grow 11 percent in 2007. This is in inflated dollars. The market adjusted for inflation is expected to grow by 7 percent. While this is good in many industries, it is below the double-digit growth rate enjoyed by the cleanroom industry in the 1980s and 1990s.

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Gloves will be the largest single segment of the market, at 21 percent. Laundry revenues will constitute 19 percent of the market. Garment rental can be derived by combining reusable clothing and laundry revenues. Paper, supplies, and packaging are included in the “Other” segment (see Fig. 1).

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The semiconductor industry will by far be the largest purchaser of consumables, with a 41 percent market share, followed by the disk drive manufacturing industry (see Fig. 2).

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Semiconductor industry

The semiconductor industry had a big year in 2006, with sales of semiconductor equipment rising 18 percent above 2005 figures. Performance in 2007 is expected to be equally good, with the likelihood of double-digit growth again in 2008. Growth in the semiconductor industry will be driven by new applications, a growing economy and the continued transition to 300 mm wafers. Microsoft’s new Vista operating system and increased cell phone functionality are two specific drivers.

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In 2007, Japan will install almost a quarter of the world’s new semiconductor cleanrooms, followed by North America, Taiwan and South Korea (see Fig. 3).

Pharmaceutical industry

Facing increased competition, some U.S. and European producers are responding by building a manufacturing presence in Asia through partnerships or greenfield facilities. India and China are attractive because of the size of the potential markets.

The Chinese pharmaceutical industry will ultimately be a major market for cleanroom products and services, but presently it is not. Intellectual property protection remains a major concern in China and this has slowed construction of facilities by international pharmaceutical companies. Nevertheless, China has a growing number of domestic research institutions that must build new biopharmaceutical facilities in order to manufacture emerging products. With these developments, China is beginning to position itself as a significant competitor in the world biopharmaceutical production market.

Medical device industry

The medical device market in China is the fastest growing in the world and is expected to sustain a growth rate of 10 to 15 percent over the next ten years. This will mean that, by 2010, China will be the third largest medical device market, and will rival the Japanese market as the second largest by 2020.

Flat-panel display industry

The market for flat-panel cleanroom products is largely confined to three Asian countries. Taiwan will be the leading purchaser in 2007, with Japan in second place (see Table 2).

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China, while not a large purchaser of cleanroom products in 2007, will see an increase in manufacturing in future years. According to China’s Ministry of Information Industry, around 80 percent of flat-panel TVs in the China market are currently imported from foreign countries and the ministry is working on developing the local flat-panel display industry. Domestic sales and exports of Chinese-made LCD TVs rose six-fold last year to over 4 million units.

TFT-LCD producer Chi Mei Optoelectronics Corp, AU Optronics Corp., LCD-polarizer maker Optimax Technology, and Sony Corp. are some companies expanding their production facilities in China to take advantage of lower wages and proximity to China’s growing TV-manufacturing industry. The manufacturers are also trying to attract suppliers to the area.

Disk drive industry

The global hard disk drive industry will expand to over 700 million units by 2010, driven by increasing usage in multiple markets including computers, consumer electronics, mobile phones and automobiles. Consumer applications represent one of the fastest-growing segments within the hard drive industry.

Nanotechnology

Ultimately, huge new cleanroom markets will be created by the manufacture of nanomaterials and nanodevices. But in 2007, the cleanroom opportunities will be mostly for research establishments. The federal government is spending more than $1 billion per year on the White House National Science and Technology Council’s National Nanotechnology Initiative. The National Science Foundation is distributing much of that money to fund research projects ranging from semiconductor nanocrystals and nanoelectromechanical sensors to new materials for propellants, explosives, and nanoparticles. The Department of Defense has a large nanotechnology program for military purposes, and the Department of Energy is focusing on new fuels and energy sources that incorporate nanotechnology.

Despite the growth of a few large players, such as ITW, the cleanroom industry remains fragmented with a few exceptions. Suppliers of filter media are mostly international, and several major filter-media manufacturers are now producing their products in China for both the local market and export.

The suppliers of rooms, devices, panels and other components are typically small companies with an industry or geographic focus. Suppliers of garments, gloves and other consumables are also not global in their reach. With the growth of the industry in Asia, there are more companies being created than are being absorbed through acquisitions, so fragmentation will accelerate in the near term.

In general, 2007 will be a good year for suppliers of cleanroom hardware and disposables. However, it will not show the double-digit growth that the industry has historically achieved.

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Robert McIlvaine is president and founder of The McIlvaine Company in Northfield, IL. He can be reached at [email protected].

Karen Vacura is the air filtration market editor for The McIlvaine Company. She can be reached at [email protected].

AC control options and networked solutions offer advantages and cost savings

By J. Fishbein, AirCare Automation Inc.

Cleanrooms utilizing fan filter units (FFUs) have experienced rapid growth. Enabling this growth has been the flexibility to provide controls to clean environments, from minienvironments as small as workbenches to ballroom-sized clean spaces. Higher purity work areas are also being incorporated within larger cleanrooms, adding further complexity to controls and systems implementation.

The evolution of low-cost AC fan controls has improved the performance and reduced the cost of AC fan-driven FFU systems. This article will identify key AC control options and trade-offs, as well as additional advantages and cost savings that are realized by incorporating “smart” networked solutions.

AC control options

When it comes to controlling cleanroom AC FFU fan speeds, there are a number of approaches available including: powering the motor directly off the AC line, autotransformer control, inverter drive control, “dimmer-switch type” 2- or 3-wire TRIAC control, and networked 2- and 3-wire TRIAC control.

The most basic control is powering directly off the AC line, where the control is based on the motor being fully on (high speed) or incorporating a multitap winding together with a switch to enable selection of a discrete high or low, or a high/medium or low, setting. Another simple approach is to use autotransformers to adjust the motor speeds.

In terms of more classical electronic control, inverter control and TRIAC control techniques are most commonly incorporated. Inverter control, or variable frequency drive (VFD), provides a true frequency control solution allowing “overdrive” and is usually sophisticated enough to be included in a networked solution. TRIAC control, which makes use of a phase control technique, can be implemented through either a manual dimmer-switch approach where the switch controls can be wall mounted, or through remote controller modules that can be mounted anywhere, but are usually located near the motor. Adjustment of the remote controller modules can be accomplished via a speedpot or can be operated in a closed-loop mode. Smart controller modules can also be integrated into a networked addressable system.

AC control approach attributes

Powering the motor directly from the AC line provides the lowest initial cost solution and allows for FFU operation at full speed. It may also allow for predetermined lower speed or speeds if the FFU contains tapped motor windings and a switch. With the controls on the FFU housing, however, adjustments to the FFU often require breaching the cleanroom ceiling. As a result, the FFU motors are often simply set to full speed, which unnecessarily increases energy cost and reduces filter life.

Autotransformer control is typically placed on the AC breaker line to vary the voltage to a bank of FFUs. However, although the use of an autotransformer eliminates the low frequency harmonics, it also adjusts all FFUs on the line to the same speed, which can prove expensive if used with too few FFUs.

The use of an inverter VFD control both eliminates the low frequency harmonics and reduces FFU power consumption. And, as will be shown later, this approach provides reduced power consumption compared to TRIAC control, at least at lower speeds. However, special consideration must be given to radio frequency interference (RFI) and power factor (PF), as VFD controls can create problems in these areas. Additionally, inverter drives require the use of more expensive inverter-grade motors to eliminate pitting of the motor bearings and motor insulation breakdown. Thus far, inverter drives have not experienced broad usage in cleanroom applications.

Dimmer-switch type 2- or 3-wire TRIAC control, similar to that used for lighting control, provides wall-mountable variable-speed control capability for FFUs. The 3-wire TRIAC control, as will be explained in more detail later, provides improved efficiency, as well as reduced harmonics and mechanical noise, or hum.

Networkable 2- and 3-wire TRIAC control units can incorporate a soft-start feature to limit high motor currents at start-up and, when operated in 3-wire mode, provide the same advantages as dimmer-switch control. Speed control can be achieved individually by connecting and varying a 10kΩ potentiometer, or the controllers can be operated individually in a closed-loop mode using a reference and a differential input to maintain variables such as pressure, temperature or airflow. It is advantageous to maintain a constant pressure in workstations, such as laminar-flow stations within cleanrooms, where doors can be opened during operation, resulting in pressure drop. Likewise, new developments aimed at maintaining constant airflow can have major ramifications in helping to maintain cleanroom integrity over changes in such variables as line voltage and the condition of the filter media.1

Network architecture

Smart controllers can also be networked using a single console to access each controller (see Fig. 1) The controllers are addressable FFU TRIAC drivers that control the FFU motors. The primary function of the console is to provide system control by communicating with all FFU controllers to set speed and monitor performance. Networking through a console also allows for a global setback (reduced speed) to further reduce energy consumption during nonwork times.


Figure 1. This example of an AC cleanroom network control system contains a low-cost, wall-mountable, fully programmed console with access control. The console can be a single-zone, 10-, 25-, 50-, or 125-address unit, or a multizone with up to four separate zones of 125 addresses each (500 total). Also included are the smart TRIAC controller modules with soft-start and a memory function that remembers the last speed setting in power failures and will continue to operate if the network connection is broken. This network system can be used in 115 V, 230 V, 277 V, 50 or 60 Hz applications at current levels up to 20 A.
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The network system console can also be used in closed-loop systems to provide the reference input with a digital readout, eliminating the need for a separate reference at each controller, and may incorporate other features such as shutdown or alarm in an emergency situation such as a fire or release of a toxic gas. A network solution can be implemented via a fully programmed console, a programmable logic controller (PLC) console, or a computer.

Technical advantages of TRIAC controls

The only two types of control that can be categorized as electronic controls are the inverter and TRIAC controls. Both control topologies can be integrated into network systems and the inverter drive can provide overdrive capability and additional efficiency improvements, at least at the lower FFU fan speeds (see Fig. 2). However, the higher cost of the inverter controls and the inverter-grade motors has thus far greatly limited their usage in AC cleanrooms.

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TRIAC type control, both wall-mountable, dimmer-switch TRIAC controls and the smarter networkable module type, provide more cost-effective AC control. Both can also provide 2- or 3-wire capability when connecting to the permanent split capacitor (PSC) motor commonly used in AC cleanrooms. The 2- and 3-wire wiring connections are shown in Figures 3 and 4, respectively.

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Implementing the 3-wire connection requires splicing the additional connection to the motor capacitor, thereby providing a separate drive to the auxiliary winding of the motor. For the 2-wire connection, both the main winding and the auxiliary winding are driven from the same source. Incorporating the 3-wire approach, whether with the dimmer switch or the networkable module approach, reduces power consumption, harmonics and noise. Figure 5 compares the harmonic content of a motor operating in the 2- and 3-wire modes. Of particular interest is the reduction in the third harmonic, which contains, by far, the highest amount of harmonic content.

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Over the usable speed range of about 60 to greater than 90 percent of full speed, the 3-wire approach reduces overheating, which is prevalent in many PSC motors, by reducing the motor power consumption by 10 to 20 percent typically (see Fig. 6). It is important to not run the motor at too low a speed because of the risk of stalling, at which point the motor will tend to draw more current and can be damaged by excess heat. Smart controllers contain a minimum speed setting to prevent operating the motor at too low a speed.

Networked TRIAC control advantages

Traditionally, network solutions for cleanrooms have been used in higher-end cleanrooms that use programmed, DC brushless motors to drive the FFU fans. Networking is accomplished either via computer control as part of a building management system or through the use of a programmed PLC unit. Also included are interface control boards that allow the user to vary fan motor speeds remotely, making changes by adjusting up or down their preprogrammed speed and torque curve. More recently, menu-driven, lower-cost, easy-to-install, stand-alone consoles with displays have been added to the tools to adjust the smart DC motors.

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These consoles also mate with some inverter drives as well as smart TRIAC controllers for use in network solutions in more cost-sensitive AC cleanrooms. TRIAC control of fan motor speed is accomplished via a phase control technique, which essentially is turning off the voltage to the motor for a portion of the AC cycle (in the U.S., there are 60 cycles per second). However, as shown in Figure 7, the phase angle varies nonlinearly over the cycle. This means that, when adjusting the dimmer-switch type TRIAC control, there can be a large amount of adjustment of the control with very little effect on FFU fan speed over part of the cycle, followed by large speed changes with smaller adjustments of the dimmer switch. This phenomenon complicates adjusting the FFU fan speed.

Figure 7 also illustrates that using a smart controller facilitates achieving linear speed control and, by incorporating a network solution, provides a visual display of the speed and ease of adjustment. It also allows for adjusting all fans from a single convenient location, as opposed to performing the adjustments at each FFU. Often, when smart control is not used, the FFU fans are simply set to maximum speed, which certainly is more costly in terms of energy consumption. Operating at full speed also reduces the FFU filter media life.

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To illustrate the energy cost savings that can be realized, two examples have been included in Tables 1 and 2. Both examples are for a 50 FFU cleanroom, comparing a 2-wire vs. a 3-wire system to a reference system being operated at full speed on a 24/7 basis.

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The assumptions have been taken from an actual application that was field retrofitted. The system in Table 1 included TRIAC controllers, but was not in a network solution and thus did not take advantage of the setback mode during nonwork time. If this system had been implemented using the 3-wire approach, the annual energy savings would have been over $3,200/yr, double the savings of the 2-wire approach.

The energy-savings results for the actual system, which is a networked, 3-wire control solution utilizing setback, are documented in Table 2. The network solution provided annual energy savings of over $5,500/yr, or about 70 percent more than if the non-network, 3-wire approach had been implemented. These annual energy savings are realized year after year for the life of the cleanroom.

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In addition to the energy cost savings, there are also installation cost savings that can be realized. For example, the 3-wire approach reduces the current draw at speeds less than full speed (see Fig. 8). At reduced speeds, the 2-wire approach results in elevated currents even though, as was shown in Fig. 6, the power consumption does decrease. The reduced currents with the 3-wire topology, along with reduced start-up currents (if the smart controllers contain a soft-start capability, which can limit peak start-up currents by up to about 50 percent), can result in being able to run more FFUs per circuit breaker, decreasing the number of circuit breakers required. There is an installation cost of some hundreds of dollars per breaker line installed. Thus, the cost savings will depend on the number of breaker lines that can be eliminated. Additionally, going to a network system will certainly reduce balancing costs by so many minutes per FFU. The reduction of circuit breaker lines installed and balance of time saved will vary.2

Conclusion

Despite all the advantages cited in this article, there remains one major obstacle to more broad-based implementation of network controls in AC cleanrooms: the ongoing short-term (and maybe shortsighted) requirement from the end customer for the lowest initial cost cleanroom. Cleanroom suppliers are often pushed for lowest cleanroom cost and are often competing for the job based upon that cost. Also, some larger companies utilize different personnel or departments for capital acquisitions, such as cleanrooms, and for managing operating costs. These, coupled with the fact that network control providers have been remiss in quantifying cost savings, have all been impediments to implementation. More recently, however, as this information is being distributed, some companies are even performing field retrofits to achieve the benefits, even though field retrofits are more expensive than including network control initially.

References

1. Abramowitz, H. “New Closed Loop Controls For Minienvironments,” Controlled Environments, February 2006.

2. Schwartz, J., et al. “Utilizing Lower-Cost ‘Smart’ FFU Systems,” Controlled Environments, November 2005.

Jeff Fishbein holds a BSEE and has over twenty years of experience in power electronics engineering, most of which was spent at Bell Laboratories and International Rectifier. He has held a number of positions in design and applications engineering, as well as in engineering management. For the past three years, he has been working with AirCare Automation (www.aircareautomation.com) as an applications engineering manager.

Defect analyzer


October 1, 2006

Engineers need to analyze defects and other failures during microfabrication in order to troubleshoot, adjust, and improve microfabrication processes. Unfortunately, the defect characterization provided by conventional systems (e.g., optical inspection tools) is typically inadequate. The defect analysis process is typically slow and manual, and is often performed in a laboratory located outside of the cleanroom environment. Also, when a wafer is taken for detailed defect analysis, in many cases the wafer must be discarded after it has been analyzed for fear of contamination, even though only a small part of the wafer is destroyed by the analysis. With ever increasing wafer sizes and material process complexities, such losses can result in significant financial hardships.

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The present invention provides methods, devices, and systems for analyzing defects in an object such as a semiconductor wafer. The process is partially or fully automated and can be done in the wafer fabrication facility to provide rapid feedback.

In this embodiment, a defect analysis system (A) is connected to remote interface computers (B) through a network (C). The defect analysis system generally includes a defect analyzer computer (D) connected to (or integrated with) a dual-beam defect analyzer (E) and database system (F).

The dual-beam system uses an ion beam that is either normal or tilted by a few degrees to the plane of the work piece surface and an electron beam having an axis that is also tilted (e.g., 52 degrees from the axis of the ion beam). The ion beam is typically used to image and machine the work piece, and the electron beam is used primarily for imaging but can also be used for some modification of the work piece. The electron beam will typically produce an image of a higher resolution than the ion beam image, and it will not damage the viewed surface. The image formed by the two beams can look different, and the two beams can therefore provide more information than a single beam.

The DA computer and dual-beam system use software (G) for implementing defect analysis and characterization. The software includes: user interface components (H), which generate screen interfaces for presenting to users controllable access to the functions provided by the other components; a defect analyzer application/system (I), which controls the overall operation of the defect analyzer system and invokes the various other applications and tool components upon receiving requests from users; a job builder application (J), which allows users to create “jobs” that define the defect analysis and review the tasks to be performed on defect sites within one or more wafers; a sequencer application (K), which triggers the defect analysis system to perform the job tasks on the designated defect sites; a defect explorer application (L), which allows users to selectively review images and data obtained from the defect analysis; and tool components (M).

Any suitable software applications, modules, and components may be used for implementing the software.

Patent number: 7,103,505

Date: September 5, 2006

Inventors: Janet Teshima (Hillsboro, OR); Daniel E. Partin

For a detailed description of this invention, visit the U.S. Patent and Trademark Office Web site at www.uspto.gov.

Understanding total costs early on is key to successful cost control

By Dana Watts, AIA, and Mark O’Brien, PE, Symmes Maini & McKee Associates, Inc.

Managing the design, construction, and operations costs of microelectronics, MEMS, and nanotechnology facilities is never easy. But it is likelier to be achieved if all stakeholders-owner, user, operator, design team, and builder-understand the total cost story early in the game. Four essential elements of cost control understanding and success are:

Knowing the true cost of a facility, considering not only initial costs, but also life cycle costs

Understanding the design drivers and their effect on cost

Understanding the impact of systems on cost

Developing a cost strategy for making effective budget decisions

True costs

With unpredictable materials and labor costs being the norm today, the challenge of setting a predictable budget grows tougher. Knowing where the costs fall is an essential first step in overcoming the challenge, and first costs and life costs both merit attention.

Decisions made in the planning and design stages not only affect initial cost, but also have a much greater impact on the overall cost of operating the facility over time.

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During a twenty-year use period the operational cost of an advanced technology facility may approach seven times the cost of initial construction (see Fig. 1). As the diagram illustrates, operational costs, along with building maintenance, account for much of the true cost. By contrast, initial design and construction represent only roughly ten percent of the true life cycle costs. Clearly, the greatest opportunity for savings rests in the building systems operation and maintenance. Making the right design decisions up front will reduce the overall life cycle costs of a facility.

Many of these decisions relate to engineering systems. Cost data analyzed from several advanced technology facilities reveal that the preponderance of a project’s initial costs are in mechanical, electrical and process systems, and to a lesser degree in cleanroom construction. These critical decision areas have the greatest impact on the lifetime cost of the facility.

At the Ohio State University, a call for more than 19,000 square feet of cleanroom and research facilities was made after construction had begun on a new building. The fit-up would be used in the research of bio-MEMS devices for drug delivery within the human body to combat cancer and diabetes. The elements of the building included:

Two-story facility, all-steel structure, slab on grade

Masonry, glass, and metal panel exterior skin

4,100-square-foot laboratory, 3,200-square-foot office area on the first floor

7,300-square-foot bay-and-chase Class 100 (ISO Class 5) cleanroom suite on the second floor

Rooftop, steel-grillage-supported make-up air and recirculating air-handling units, in addition to process exhaust fans

Acceleration of a future 10,615-square-foot addition that would be utilized as a central utility plant

Facility costs for this project, completed in 2005, are summarized in Table 1, relative to total project budget.

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Over 50 percent of the first cost of advanced technology facilities is tied up in HVAC, process piping, plumbing and electrical construction. These systems also represent close to 100 percent of the operating cost for the facility.

Design drivers

Managing the cost of engineering systems and beginning the process of cost control require the planning team to gain control over critical design drivers.

Process

The research and/or manufacturing process that the facility is being designed to achieve determines the required level of cleanliness and the necessary sophistication of mechanical and process systems. They in turn drive design and cost.

Programming

A successful programming process is a powerful cost control tool. By developing a clear definition of the project’s requirements, and advancing that definition to a set of consensus-driven solutions, the essential cost areas become known while the nonessential ones can be eliminated.

Budget

Techniques for establishing a budget vary greatly depending on project size, complexity and timing. The sooner a budget reflects a clear picture of the full scope and detail of what is to be built, the more valuable it is as a cost control tool.

The budgeting process is likelier to be a more effective design driver if it includes:

Rolling cost estimates or models that are detailed by specific items of materials and installation scopes of work, consistently updated for each phase of the design process

Engagement of cost consultants, outside estimators, or construction managers to develop and check estimates

Operating cost data to assist in the decision-making process

Necessary soft costs

Allowance for cost escalation on projects that have a significant construction timeline

Budgeting can rely on a variety of approaches, with the differences among these approaches determined by the level of detail applied. The broad-brush approach, and typically the least valuable for clean facilities, applies a cost-per-square-foot formula based on historic data. More detail is brought to light in a space-type model, in which specific types of space-such as cleanrooms and labs-are studied for specific cost impact. A detailed budget model, one using a line-item format covering every element, is the only way to establish a true picture of cost.

Codes/safety

Building codes and regulatory requirements also drive design. Zoning laws, environmental regulations, fire protection standards, local ordinances, insurance regulations, and other external requirements can vary significantly from one state or city to the next.

Micro- and nanotechnology facilities, while not necessarily hazardous themselves, often use hazardous production materials in their research or fabrication processes, triggering additional code applications. Building codes can limit the facility’s size or its internal egress travel distance, and they can expand requirements for fire and life-safety protection.

Systems impact on facility cost

Architectural and engineering fees for a typical advanced technology facility represent just a tenth of one percent of its 20-year life cycle cost. Critical decisions made by the team during the design process will dictate the cost of production, utilities, and operations/maintenance costs long after the ribbon is cut.

Energy and water costs

Most of the operations cost is attributed to energy consumption: gas, oil and electricity. Power costs are directly related to HVAC equipment, process equipment/tools, interior lighting, and site lighting, determined by user needs and by design.

The expense of water, the other major contributor to the operational cost, has risen dramatically in most regions. In advanced technology facilities, water demands are high due to the need to supply DI systems and provide cooling tower make-up. Even a small DI system with a 100-gallon-per-minute (gpm) recirculating flow rate will use approximately 1.3 million gallons per year, depending upon process tool requirements.

Cooling tower make-up accounts for approximately 3 to 5 percent of recirculated water flow. On a 600-ton tower/cooling load, the peak make-up water flow, due to drift and evaporation, is 72 gpm. This can translate into substantial annual water costs in regions with high water and sewer rates.

Decisions about utilities require project teams to look beyond first costs of equipment and systems, and to evaluate the long-term costs and/or savings of each system option.

Environment control

The level of cleanliness and specifications for humidity and temperature control of a facility impact both first cost and long-term costs.

A conventional bay-and-chase design provides multiple bays with discrete environments. Each bay can have its own cleanliness level and spec for temperature and humidity. This approach is especially effective for uses and functions that demand environments at Class 1,000 (ISO Class 6) and below.

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A microenvironment design (see Fig. 2) is an option for functions requiring over Class 1,000 (ISO Class 6), and often for cleaner environments as well. In a microenvironment, the higher cleanliness level is contained within a larger, less clean space. This approach provides the owner with a lower operating cost for the critical clean space by piggybacking on the required pressurization, temperature, and humidity control of the larger area.

Knowing the options for cleanliness level, and working to ensure the selection of the appropriate level, helps avoid both first-cost and long-term-cost overruns.

Infrastructure

As noted earlier, more than half the first cost and almost all the operating cost of an advanced tech facility are attributable to engineering systems.

Capacity was a critical element during the renovation of an existing microelectronics fabrication facility for Analog Devices. The result was a savings in both first cost and long-term operations costs. By focusing on use-specific requirements, rather than on industry metrics, the design team was able to reduce the size of a make-up air unit from 50,000 cfm to 30,000 cfm. Because this was a 100 percent outdoor unit in the Northeast, the total reduction in cooling capacity was approximately 200 tons. First-cost savings from the reduction included:

$100,000 for the make-up air unit

$50,000 for the smaller chiller and cooling tower

$50,000 for a smaller boiler plant

By reducing the size by 20,000 cfm, this single design modification provided the owner with an immediate cost avoidance of $200,000. Smaller yet tangible savings would be realized in pump sizes and piping/insulation costs.

Long-term, the energy savings from downsizing the chiller alone was projected to be 10 percent per year, based on the use of a fully loaded 400-ton chiller as opposed to a partially loaded 600-ton machine.

Infrastructure location also affects cost. Make-up air units, recirculation units, exhaust fans and abatement devices, such as fume scrubbers, all require regular maintenance. It is important to determine a convenient location and assess the cost impact of that location.

Placing equipment on the roof is acceptable in some climates. However, in northern climates, performing regular maintenance in harsh winter conditions is difficult.

On the other hand, the cost of constructing a fan-deck level into a building is considerably more expensive than a rooftop location. First cost and ease of maintenance must be carefully weighed.

Building energy management systems can be designed to improve operations and energy efficiency. Direct Digital Control (DDC) performs the control logic, but these systems can be complex and proprietary.

Because the DDC control system will represent a first cost of approximately 15 to 20 percent of the HVAC system costs, partnering with a qualified DDC vendor during the design process is recommended. The vendor should be one that is either familiar with the owner’s facilities or one interviewed and selected by the project stakeholders. The cost benefits of this partnership are reflected both in first costs and in long-term costs. The owner’s facilities group develops an ongoing understanding of the DDC system they will operate, minimizing their learning curve. In addition, the DDC vendor brings added operational-cost-saving ideas to the table during design.

Future flexibility

Designing flexibility into a facility can reduce future design and construction burdens, but can add considerably to the first cost.

Frequently considered approaches to flexibility include:

Adding a general/unassigned clean bay to accommodate future expansion

Building a Class 1,000 (ISO Class 6) space now that can be upgraded to a Class 100 (ISO Class 5), should process needs change

Providing N+1 redundancy on many systems

Because such ambitious flexibility options, especially those involving unassigned space, fall victim to cost cutting, it’s important during cost modeling to be thorough and to project all future cost savings of these features as accurately as possible.

Not all flexibility approaches are expensive, however. Installing two 100 percent capacity supply fans in a make-up air unit, operating both of them normally, and allowing one to ramp up in case the other fails, provides an affordable redundancy. Similarly, installation of certain construction elements, such as required roof penetrations or valved and capped hydronic services, are low first-cost elements that will ease future fit-up changes and save time.

Strategies for true control

Several key strategies aid in accurately predicting the cost of the project, including stakeholder involvement and schedule acceleration.

Stakeholder involvement

Involving as many stakeholders as possible in the development of the cost model increases the relevance and acceptability of the cost model itself.

The owner, user, the architect/engineer, and construction manager develop a clear definition of the project’s requirements, advance that definition to a set of consensus-driven solutions, identify essential cost areas, and eliminate nonessential ones. The team creates the cost model, refines previous assumptions, and tests the results against what they know about the project’s business purpose.

All other key stakeholders need to be brought into the cost model process. With each new participant, the specificity, and hence the value, of the model increases. Such players include:

End users

Facility maintenance staff

Subcontractors (especially mechanical and electrical)

Commissioning agent

The use of detailed cost models dictates a vigilant approach, and the recommended strategy of team member involvement promotes the idea behind the strategy: to be as detailed as possible within the limits of available information.

The second part of this strategy is to continually review and update the cost model as more accurate and better developed information becomes available. At each review milestone, the team must take the time to make sure the cost model remains appropriate and accurate for the current stage. These reviews also help to ensure that all project stakeholders are buying in. Questions that should be addressed at each review include:

Is the scope of work correct and up-to-date?

Is the quality level of the specified materials appropriate?

Are changes in materials or equipment being consistently worked into the model?

Schedule acceleration

The saying “Time is money” is never more applicable than in the construction industry. Different systems can be used to accelerate the project’s delivery and therefore reduce costs. There are, however, risks involved with each modification to the delivery method. The greater the opportunity to save time, the greater the risk to be managed. Keys to controlling cost from a scheduling perspective include:

Developing a detailed schedule for the design phase and construction phase together

Consistently monitoring and updating the schedule as the project progresses

Summary

Every project presents the possibility of both achieving cost control and meeting the exacting needs of advanced technology clients. By understanding where the most significant costs truly lie, and by working collaboratively with all stakeholders on a sustained cost management mission, the resulting facility can perform as needed on its opening day and on into a long life cycle-without inflating the project budget.

Dana Watts, AIA, is a principal at SMMA. He has overall responsibility for the architectural/engineering design and production team, from conceptual to final design and through construction administration.

Mark O’Brien, PE, is an associate principal and chief mechanical engineer at SMMA. He provides engineering and design services through all project phases for SMMA’s Corporate/Commercial, Science Technology + Health, and Institutional practice groups.

By Hank Hogan

It was after production units started shipping that the contamination problems cropped up, says Kimberly Subrahmanyan, engineering director for the semiconductor link processing group at Electro Scientific Industries, Inc. (ESI; Portland, OR). ESI’s first ultraviolet, laser-based link-processing offering was intended to allow its customers to manufacture advanced memory products, those with links spaced more closely together than possible with the company’s existing infrared laser-based systems.

The engineering prototypes had worked well. That was also the case with the production units-at least initially. Then the contamination-related issues started to appear.

“We were finding organics on the lenses. We were losing transmission through the optical path of our system,” recalls Subrahmanyan. “We were seeing some of the contaminants, like particles and such, burned onto the lenses.”

In switching from a light source with a wavelength longer than red to one with a wavelength shorter than blue, ESI’s engineering team thought they’d accounted for the contamination control challenge. The problem, though, had proven to be more difficult than they’d anticipated.

So they revamped their entire manufacturing process, cleaning it up in multiple ways. As a result, they succeeded in fixing the problem and now ship UV systems routinely. That effort carried with it some lessons, tips that could be of use as ultraviolet lasers and light sources work their way into more and more cleanrooms and a wider number of manufacturing steps or processes.

Contamination brought to light

In ESI’s case, the manufacturing changeover began because the company wanted to satisfy its customers’ needs. ESI’s systems “blow” links, which are found in semiconductor memory chips. These links electrically switch in spare good-memory locations for those with defects, allowing memory manufacturers to repair less-than-perfect product and improve yield. The technique is widely used in the industry and, in ESI’s products, involves firing a laser at the link.

The company had been doing this with infrared lasers operating at wavelengths of 1,300 and 1,064 nanometers, well above the 700 nm of the visible color red. Due to the fundamentals of optics, the spot size that a laser can be focused down to is a function of the wavelength. The shorter the wavelength, the smaller the spot created. As features on chips became smaller, memory manufacturers wanted to have the links take up less space and that meant ESI had to make some changes. “In support of shrinking structures, we needed to go down to smaller spot sizes in order to blow the links,” says Subrahmanyan.

The company chose to go to a laser operating at 355 nm, in the ultraviolet below the 400 nm visible to the eye. In doing so, the spot size decreased by the same ratio as the wavelength.

However, the energy of those photons rose similarly. Thus, while a 1,064 nm photon had energy of 1.2 electron volts (eV), one at 355 nm packed 3.5 eV. Because of the increased energy of UV photons, chemical reactions happen upon exposure to UV that don’t take place when visible or infrared light is involved. The engineering staff at ESI knew this and they therefore changed handling procedures during their manufacturing process to reduce contamination.

Although this worked with the prototype, it wasn’t successful when production ramped up. Bryan Bolt, manager of strategic technology development at ESI, had some previous experience with UV at 257 nm, where the energy climbs to 4.8 eV. He knew that optics failing in three weeks would, with 90 percent contamination reduction, not see their service life lengthen similarly and hit 11 months out of a 12 month target. “It may only increase service life to eight weeks or so,” he says. “That last 10 percent makes a big difference.”

As for what is considered a problem, Bolt points to anything in a vapor phase, such as heavy hydrocarbon chains and acid gases. These condense on the lens and photopolymerize into a film when the UV hits, thereby degrading the optics.

Coming clean

To eliminate the problem, ESI first ensured that they weren’t introducing contaminants into the process by their choice of materials. They then instituted a number of handling and cleaning procedures, such as using an ultrasonic clean followed by a vacuum bake of parts prior to assembly to remove any contaminants. Finally, they upgraded their research and development cleanroom as part of an overall remodeling process (see Figs. 1 and 2). They used this to prove out the revamped process. For production, they built a new cleanroom.


Cleanroom entrance at ESI headquarters’ R&D center. Photo courtesy of Electro Scientific Industries, Inc.
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According to Brian Green, semiconductor link processing group product manager at ESI, the new cleanroom will go live this month. It will include a 4,200-square-foot area that’s ISO Class 5, equivalent to the old Class 100 standard, and another 6,400 square feet that’s ISO Class 6 (Class 1,000). Those area figures include production, gowning, pass-through, and materials-handling space. The more sensitive components, such as those that experience the full intensity of the laser, will be assembled in the cleaner section. The Class 6 area uses HEPA filters, while the Class 5 area uses ULPA filters.

Green noted that in designing and building the new cleanroom, the team had to consider more than just the particulate load. “We had to take into account the molecular risk,” he says.


Testing room at ESI headquarters’ R&D center. Photo courtesyof Electro Scientific Industries, Inc.
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Heavier hydrocarbons, those with more than six carbons in them, were among the chemical constituents that concerned them. Green reports that so far everything appears to be in good shape, with the design and construction helping the cleanroom to hit its contamination control goal.

The combination of changes in materials, cleaning procedures, and manufacturing process paid off. ESI now consistently delivers its UV product to customers, with good field results.

Twenty or forty to one

The ESI story is one that may be repeated, in different forms, over and over as semiconductor technology advances. The ITRS roadmap, which the industry jointly produces to highlight future manufacturing needs, calls for widespread use of UV lasers for defect inspection, feature size and other measurement, via drilling and chip dicing. The wavelengths mentioned range from 355 to 266 to 193 nm (see Table). At the latter two wavelengths, light hydrocarbons and a host of other airborne contaminants become a problem.

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An example of what’s to come can be found in Applied Materials (Santa Clara, CA) UVision system, which uses a 266 UV laser for illumination. The company claims the device can spot critical defects as small as 30 nm, which will be needed for manufacturing of 65 nm and smaller processes. It’s able to do so, in part, because it uses a UV light source.

The contamination control challenge presented by such systems isn’t just in the construction of the laser-driven products. It’s also in their use, which can be in less-than-pristine areas. The link blowers that ESI makes, for instance, are typically found in test and assembly areas and not ultraclean semiconductor front ends.

So far, most of the deep UV lasers, those below 266 nm, have been in lithography steppers, but that won’t be the case in the future. Joe LaChapelle, CEO and chairman of Deep Photonics (Corvallis, OR), notes that there were 20 to 40 inspection stations for every lithography machine. Deep Photonics, a start-up, hopes to use some advanced technology it’s developed to provide relatively inexpensive solid state deep UV lasers that operate at 266 nm and below. The company claims its products will have longer lifetimes and will offer higher power than what’s currently available.

If Deep Photonics succeeds in bringing these products to market, the use of UV may become more prevalent. In particular, LaChapelle says a 266 nm source would make various materials-processing tasks easier, not only in semiconductor but also in electronics manufacturing. Printed circuit boards via holes, for example, can be drilled more easily with a 266 nm source than one at 355 nm.

However, he acknowledged that the new technology won’t get around the basic contamination control problem. “There’s no question that cleanliness, both during the assembly and manufacturing of our laser heads and then also in their implementation to the OEM capital equipment, is absolutely critical for maintaining lifetime and stable power,” he said.

Deep Photonics assembles its laser heads in a cleanroom. Then they’re nitrogen-purged to remove trace contaminants, and hermetically sealed. Because of the wavelength of the light, that discipline might have to be extended to the work area, with nitrogen-purging and other measures to reduce contamination. That’s particularly true if the intended use is not in a typical semiconductor front-end cleanroom.

Doors and pass-throughs


October 1, 2006

The transfer of product or equipment from one area to another presents a prime opportunity for a contamination event to occur. Doors and pass-throughs specifically designed for clean processing environments can help maintain necessary cleanliness levels.

Compiled by Angela Godwin

Pass-throughs and trolley hatches

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The PBSC pass-through chamber is used for passing product, equipment or even paperwork between sterile/clean areas and nonsterile/dirty areas. PBSC’s use of innovative materials and construction techniques makes these transfer hatches cost-effective for all manner of contamination-sensitive environments. Transfer hatches come in both stainless-steel and phenolic resin construction. The design includes a flush interior to the hatch and the company’s unique mechanical interlock system, which aids in the reduction of cross-contamination between clean and dirty areas. The absence of internal protruding or recessed areas helps eliminate possible bacterial growth and ensures complete sterilization during clean-down. The toughened plate-glass doors ensure minimal pressure is lost when passing product between sterile and nonsterile areas. PBSC trolley hatches are suitable for applications where the ground transfer by trolley of heavy, sensitive or fragile product or equipment is an absolute necessity in terms of convenience and satisfaction of even the most stringent health and safety regulations. The hatches are floor-mounted to allow transfer of heavy or dangerous substances in an efficient and easy manner, without having to load and unload trolleys. PBSC also offers a tested and certified 1-hour fire-rated transfer hatch, made of stainless-steel construction, complete with stainless-steel door and vision panel. The hatches are also available in PVC, phenolic resin or 304/316 grade stainless-steel construction.

PBSC Ltd.
West Yorkshire, U.K.
www.pbsc.co.uk

Stainless-steel pass-throughs

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Pass-throughs from Laminar Flow, Inc. (LFI) feature all-stainless-steel construction of either 304 or 316L. The company’s Posi-Lok interlock system is available in a mechanical or electronic version with a battery back-up system. Several configurations are available, including two- or three-door versions, floor-mounted, wall-mounted, or walk-through types. Solid or framed laminated safety-glass doors are standard, as is interior all-welded construction, which ensures quality and durability. Available in any size or configuration, options include: UV lighting, Class 10 or Class 100 (ISO 4 or 5) compliance, and once-through or recirculating flow. In addition, each pass-through contains a hermetically sealed gasket on the door to ensure a leak-free door seal.

Laminar Flow, Inc.
Ivyland, PA
www.laminarflowinc.com

Pass-through air locks

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Clean Air Products introduces Series 18 Pass Thru Air Locks. Designed to transfer parts and equipment into and out of cleanrooms, they significantly reduce potential contamination by decreasing the number of people entering and exiting the cleanroom. The new units are available in white polypropylene or optional stainless steel. Standard models are constructed of half-inch sheets of solid polypropylene welded together, providing a solid-plastic air lock entry system that resists deterioration. Stainless-steel versions also come welded together for a strong, durable, easily cleanable, and pleasing appearance. The air lock doors are made with a heavy-duty stainless-steel frame, stainless-steel continuous hinges, a plexiglass viewing window, closed-cell PVC door gasket and a 90-degree turn-knob latch. Larger units have a cam-action chrome-plated latch. The stainless-steel door frame adds strength, prevents long-term warping, and prevents cracks in the plexiglass door. Mechanical door interlocks are available to prevent both doors from being opened at the same time, thus avoiding depressurization and contamination infiltration. Additional options include include: wall or floor mount; perimeter frame; special sizes; fixed or adjustable shelves; viewing windows made of amber plex, lexan, safety glass or conducive PVC; UV light; HEPA filters; and air shower parts cleaning.

Clean Air Products
Minneapolis, MN
www.cleanairproducts.com

Stainless-steel pharmaceutical doors

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Rytec’s line of Pharma-Doors™ are designed, with input from pharmaceutical engineers in the U.S. and Europe, to meet cGMP guidelines and to be tight-sealing, reliable, high-performance pharmaceutical doors. The Pharma-Seal™ high-speed roll door is suitable for cleanroom applications or wherever an affordable stainless-steel package is desired. This door provides effective environmental control plus all the benefits of a high-speed door. Removable stainless-steel side-column covers allow for easy and thorough cleaning. The Pharma-Seal is for non-wash-down applications, or where hygienic needs are less stringent. The door opens at 42 inches per second, increasing productivity while providing a fast-closing, tight barrier. The door is extremely durable and designed for heavy traffic. Like all Rytec doors, Pharma-Seal doors feature the Break-Away™ bottom bar that allows the door to withstand the impact of a forklift and be quickly reset without tools. Anodized aluminum ribs provide resistance to negative pressure while allowing easy replacement of panels, including the standard 31-inch-high, full-width vision window.

Rytec Corporation
Jackson, WI
www.rytecdoors.com

High-speed, roll-up door

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The DYNACO M2 Cleanroom Door has been rated for inside environments from Class 10,000 to 100,000 (ISO 7 and 8), specifying a limitation of the leak flow at a difference in pressure up to 0.82 pounds per square foot. The door provides a full-parameter seal to minimize manufacturers’ concerns about contamination. M2 Cleanroom doors can be built to standard dimensions of up to 18 x 18 feet, and are gear-driven without ballast. They open at 4 feet per second, with faster speeds available upon request. The door is made of an upgraded, reinforced, PVC vinyl, and comes in colors and vision to fit custom needs. It is also available with an optional FDA-approved curtain material. Like all DYNACO doors, the M2 boasts a safety system with infrared side-guide sensors that stop the door instantly, and a bottom-edge detector that instantly reverses the door if it comes in contact with any object. The door features the company’s proprietary technology that allows the door to dislodge from the side guides when it is accidentally impacted, and then to instantly reinsert itself with the unique DYNACO re-inserting mechanism. Suitable for pharmaceutical, electronic, hospital, laboratory or other contamination-sensitive applications.

DYNACO USA Inc.
Northbrook, IL
www.dynacodoor.us

Cleanroom pass-through chambers

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Terra Universal’s BioSafe™ Pass-Through Chambers meet requirements for clean, aseptic processing in biotech, pharmaceutical, medical device, and other critical applications. Like Terra’s other BioSafe environments, these 304/316 stainless-steel chambers feature continuous-seam welded, ultrasmooth interior surfaces, eliminating cracks and seams that can harbor microbes and other contaminants. Rounded corners simplify disinfection, and electropolishing and antimicrobial surface treatments are available for optimal cleanliness. All hardware is designed to support clean, aseptic operation. High-reliability mechanical interlocks, which prevent the chance of cross-contamination when a “dirty”-side access door is opened, are isolated in a separate housing external to the pass-through chamber. Cam-style LiftLatches™ eliminate rotary stress on hinges and ensure an effective seal. One-piece molded gaskets are mechanically attached to door frames without adhesives to eliminate the chance of slipping or chemical outgassing. These ultraclean chambers are available in many standard sizes or can be specified in custom sizes and configurations. Options include an ULPA-filtered ventilation module for contaminant removal, UV-C lighting for sterilization, a refrigeration module for temperature conditioning, and several mounting packages that accommodate a variety of cleanroom or laboratory walls, including Terra’s BioSafe Modular Cleanroom.

Terra Universal
Fullerton, CA
www.TerraUniversal.com

The Trelleborg Group, developer of high-performance sealing and damping solutions, recently inaugurated its newly constructed manufacturing facility in Shanghai, China. According to the company, the increased production capacity from this state-of-the-art plant will allow Trelleborg to meet increasing demand from industry in China and the rest of Asia.


Trelleborg recently inaugurated its new manufacturing facility (shown here) in Shanghai.
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Many of Trelleborg’s proprietary high-technology sealing products will be produced at the over 100,000-square-foot (10,000 m2) facility, which has been designed to meet stringent environmental standards. On-site will be a 1,000-square-foot (100 m2) Class 100 (ISO 5) cleanroom for the manufacture of the company’s Isolast® perfluoroelastomer (FFKM) seals.

The chemical- and thermal-resistant seals operate in temperatures ranging from cryogenic up to 617°F (325°C) and seal effectively under pressure or in a vacuum. According to the company, the seals provide nearly universal chemical resistance to withstand aggressive fluids such as acids, bases, solvents, and gases, as well as autoclaving. The material formulations are USDA, FDA, and USP Class VI compliant and help to reduce downtime and improve production efficiency by extending seal life, while minimizing the risk of contamination and bacterial ingress. Applicable industries include medical, food, beverage, and pharmaceutical processing.

In addition to its manufacturing operations, the Shanghai facility will provide a range of services, including technical support for design and product development, and research and testing for both local and international customers. The company expects to have about 100 employees at the new facility by the end of the year.

According to Claus Barsøe, president of the Trelleborg sealing solutions business area, “We now have a best-in-class facility with enough capacity to meet growing demand. This marks another stage in strengthening our position in China.”