Ionization Technologies at the Crossroads: High Voltage Corona vs. Alpha Emissions

Ionization Technologies at the Crossroads: High Voltage Corona vs. Alpha Emissions

By Susan English

Industry concern about particulates–especially those generated by ionizers–has spurred researchers to develop new systems and tools to cope with the new demands for ionization products in disk drives and storage media. According to Gopalan Vijayakumar, director of research and engineering at Ion Systems (Berkeley, CA), insulators such as plastic, quartz, ceramics and glass–used frequently in the manufacture of disk drives–are easily charged and retain their charge for long periods of time. These insulators can induce charges and cause an electrostatic discharge (ESD) event that can vaporize fine metal circuitry on magneto-resistive (MR) heads or cause damage to insulating films. Often discovered during post-production inspection steps, the losses can add up: damaged products and lost production time.

These new applications may even d zmand taking a new look at a venerable old technology: radioisotope nuclear ionization. Already in widespread use in volatile atmospheres and highly sensitive, high performance applications, nuclear ionizers use a naturally occurring radioisotope like polonium-210, which emits alpha particles that strip electrons from air molecules, creating free positive and negative ions. In fact, polonium generates a positive ion for every negative ion produced. Because electrostatic charge attracts ions of the opposite polarity, air ionizers can deliver ions to neutralize the charge, producing negatively charged ions for positively charged surfaces, and vice versa. The ions then interact with the charge, allowing for exchange of electrons, which creates a neutral state. The advantages are fairly obvious: alpha emissions create ions without creating particulate (independent test data shows virtually no particles greater than 0.03 &#181m), and since ion production is generated completely by the alpha emission process, no external energy source is required. Also, because positive and negative air ions are continuously produced in constant balance, the nuclear units do not require maintenance or calibration.

Radioisotope ionizers

NRD (Grand Island, NY) manufactures alpha energy ionizers using polonium-210. The ISO-certified nuclear ionizers are encapsulated into a solid foil made of precious metals. NRD Product Manager, Jim Curtis, says: “In the last year or so, we`ve noticed a dramatic increase in concern about small particles and especially those generated by ionizers. There`s a higher level of interest because part of the problem is that static charge will attract particles, and the new MR heads and storage media are highly sensitive to static charge.” Curtis says the increase in ESD-sensitive devices will mean multiple applications for ionization products in cleanroom environments. The other advantage the technology offers, he says, relates to the “balance issue.” Some manufacturers are trying to maintain charge levels below 5 V–critical tolerance for an ionizer–which, he claims, cannot really be maintained through the use of an electric-powered ionization system. “They talk about their units being in balance, but they`re really talking about a range that they determine: between &#17710 V or 20 V, or whatever the spec is for that particular manufacturer.”

The NRD product line includes Nuclestat Linear Air Ionizers, combination bar, induction static eliminator, ionizer guns and blowers. For use in space-limited and hand-held applications, there is the Nuclespot P-2042, a small, self-powered static control device. Other accessories and hardware include ion air curtains, in-line ionizers, electrostatic fieldmeters, packaging, wrist/heel strap testers, sole grounders, and other grounding equipment.

High voltage corona ionization systems

But manufacturers of high voltage corona ionization systems are meeting the challenges of the new ESD-sensitive devices, offering virtually particle-free emitter head material, improved balance capabilities and even lower voltage solutions. The concept of equipment ionization was pioneered by Ion Systems in 1993 with the introduction of the 4210, an in-line air/nitrogen ionizer that delivers ionized gas inside production equipment. Since then, the company has initiated joint development programs with several equipment makers to produce static-free production tools. Last September, the company`s new ionizing blower, designed for operation in disk drive assembly operations, made its disk drive industry debut at the DISKCON trade show in San Jose, CA. Called the Precision SC, the unit was developed specifically to address ESD damage to MR heads and other components in disk drive manufacturing, devices which can be up to 10 times more susceptible to ESD than semiconductor devices, according to Gopalan Vijayakumar. The steady-state DC unit also features long-term balance.

Cleanroom engineered, the Precision SC delivers ionized air through sealed air ducts to ensure no particles are introduced from the unit`s electrical circuitry. The ionizer also features machined titanium emitter points. According to Ion Systems` Arnie Steinman, “Emitter points are silicon and don`t contribute metallic contamination to the fab. We`ve developed new emitter point materials to deal with contamination from ionizers as cleanrooms have changed and their requirements for allowable contamination levels have changed.” He adds that a “properly designed” in-line corona ionizer will produce particle levels equally as low as a nuclear ionizer. “It`s not a case of whether one is better than the other; it`s that each has its own applications. If you had an application that dealt with explosive environments, then a nuclear ionizer would be the product of choice. However, in most applications in the semiconductor industry, you`re not dealing with explosive environments, and a corona ionizer appears to be the product of choice there because you don`t have to deal with the logistics` hassle of owning a radioactive source.” Those “hassles” include replacing the nuclear source every 13 to 16 months and having to return it to the manufacturer, in keeping with Nuclear Regulatory Commission regulations. “When you own a corona ionizer, with very minimal maintenance, you own it for five years or more,” Steinman says.

Ion Systems manufactures a variety of emitter point materials for specialized applications. Single-crystal silicon emitter points, specifically developed for ultraclean semiconductor environments, far exceed Class 1 cleanliness requirements, according to the company, and unlike metallic, coated and polysilicon points, they produce no particle bursts. For Class 1 or better cleanroom applications in which silicon is not appropriate, machined titanium emitter points are available. For Class 10 and higher cleanrooms, tungsten alloy emitter points are available.

Its 5000 series ionization system modular air ionization system includes ceiling emitters for open spaces; flowbars for minienvironments and flow hoods; and controllers, facility monitoring system links and software for system adjustment and monitoring. Ionizers feature both pulsed DC and steady-state DC ion emission. The company`s patented sequenced bipolar technology is a form of pulsed DC ionization, which sequentially produces balanced quantities of positive and negative ions. After installation and calibration, sequenced bipolar ionizers maintain a uniform level of static control over long periods. For close proximity applications, steady-state DC bars are available. The steady-state bars incorporate Ion Systems` patented IsoStat technology for intrinsically balanced ionization with no need for calibration.

Low-voltage solutions

Many ionization systems use a central power supply or a transformer to produce the high voltage required for ionization. Much of the power produced must be used to overcome losses and leakages in the high voltage cabling that distributes power to the emitter bars or grids. In addition, the stress on cabling increases the risk of high voltage arcing, which can result in system failure and shock hazards. Ion Systems uses power supplies located within each unit. 5000 series ionizers operate on 24 Vac, eliminating the stress problems associated with strings of continuous high-voltage cabling. Local power supplies and the resulting low-emitter-output current virtually eliminate shock hazards, ozone, EMI and contamination caused by emitter point erosion, according to the company. Enhanced (e) models monitor and regulate their own ion output using patented current regulation. If environmental or emitter point conditions change, internal feedback circuits adjust positive and negative output levels to enhance ionization effectiveness and consistency.

Ionization kit for Delta Flex test handling systems

An easy-to-install ionization kit for Delta Flex test handling systems is the first product offering of Ion Systems` Equipment Ionization Program, an initiative launched last July to develop solutions that will enable manufacturers to control static charges inside industrial equipment. The kit consists of an Ion Systems 4052 controller with alarm, Adjustable Ion Source, 6420 blower, special high temperature, high voltage cabling and detailed installation instructions. It is designed around a new Ion Systems technology which enables consistent high performance ionization in confined areas. This technology will be applicable to other in-tool ionization applications, said Larry Levitt, company director of technology development and program coordinator.

SIMCO`s (Hatfield, PA) Aerostat Guardian, PC and XC ionizing air blowers offer inherent balance at &#1775 V, rapid static decay rates, a patented built-in emitter point cleaner, ionization indicator and AC technology for stable balance and consistent performance. The Aerostat Guardian overhead ionizing blower requires no maintenance and features an integrated heater and two compact fluorescent lights. Variable air volume output range is 150 cfm to 300 cfm (combined three-fan output). The Aerostat PC (personalized coverage) ionizing air blower provides static charge decay rates over a targeted work surface area. The PC unit offers adjustable heated air flow for operator comfort and an ionization status light. The Aerostat XC (extended coverage) blower features a benchtop stand, optional pedestal mount, or it can be permanently mounted on a wall or an overhead shelf. The XC provides extended coverage and rapid decay times at all twelve test points.

Bench top/table top ionizers

ElectroStatics, Inc. (Harleysville, PA) makes a table top ionizing transport system. The Model IT-7000 is a self-contained, compact table-top ionizer capable of producing both positive and negative ions. The two-speed fan permits a gentle flow of ionized air, reaching a distance of six feet. A charged object, when passed through the ionization field, becomes neutral instantaneously. Inherently balanced, the Ion Transport System has a fail-safe balance indicator to assure proper ionization output. The company has also introduced a new ion transport system, the Model FGS Flow Gauge Ionizer, designed to prevent static electricity in desiccator boxes. A direct replacement for the standard flow gauge commonly used in desiccator boxes, the FGS neutralizes static electricity by ionizing dry nitrogen.

The Desco (Walnut, CA) A60457 Chargebuster Jr. High Output is compact (3 in. &#165 6.25 in. &#165 7 in.) including stand. Completely self-contained, the auto-balancing bench-top ionizer features closed-loop monitoring and visual balance alarm. The active feedback balancing circuitry automatically maintains the unit`s ion balance, despite variations in line voltage, air speed or the condition of emitter electrodes. The ionizer`s feedback circuit gives a visual alarm indication when the unit is out of balance and maintenance is required. An ionizing arm is also offered for mounting the unit off the bench to save valuable work bench space.

An ESD Certification Program for training and certifying employees in the proper handling of static-sensitive devices, in accordance with Mil-Std-1686 guidelines, is also offered by the company. The self-paced software program runs on a multimedia PC under Windows. A built-in Administrator`s Module keeps track of students` ESD training records. n

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Ion Systems` Precision SC Overhead Ionizing Blower protects static-sensitive devices and was designed and tested to meet Class 100 cleanroom requirements. Each fan is sealed and isolated from the rest of the chassis, ensuring that no particles are introduced into the airstream.

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The Model IT-7000 Table Top Ionizing Transport System from ElectroStatics Inc., is a self-contained, compact table-top ionizer capable of producing copious amounts of both positive and negative ions. The two-speed fan sends a flow of ionized air up to six feet.

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SIMCO`s Aerostat Guardian, PC, and XC Ionizing Air Blowers offer inherent balance at &#1775 V, rapid static decay rates, a patented built-in emitter point cleaner, ionization indicator and AC technology for stable balance and consistent performance.


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