Advances in cleanroom garment systems
Garment manufacturers are challenged with adopting consistent and realistic testing methods and procedures and educating users in the proper care and handling of cleanroom garments.
By Carolyn T. Mathas
Until recently, human sources were thought to be responsible for more than 20 percent of cleanroom contamination. Based in large part on improvements in fabrics and garments, that number is reported today to be less than five percent, possibly as low as two percent. To date, the industries that depend on cleanroom garments to preserve the integrity of their products evolve rapidly, demanding their suppliers not only remain fleet-of-foot to stay abreast of industry changes, but actually attempt to stay ahead of them.
One of the first fabrics designed for fuel handling in and around the space shuttle featured static-dissipative flame-retardant Nomex yarn. The fabric soon found its way into an industry experiencing equally serious problems with static — the burgeoning semiconductor industry. Semiconductor manufacturers remain a major customer of cleanroom garments in an attempt to keep static and particulates away from amazingly miniaturized products. Employees in such industries as pharmaceutical, biotech, critical assembly, automotive, food, wineries, distilleries, hospitals and paint manufacturers are also donning cleanroom garments, and the garment system industry continues to grow as companies begin to appreciate the correlation between contamination control concepts and product quality.
Taffeta weaves and herringbone coveralls with brass zippers, snap wrists and cuffs were standard fare in cleanrooms 25 to 30 years ago. Today, a myriad of colors and variety of garments dot the cleanroom landscape. High-density fabrics, barrier fabrics, static-dissipative qualities, coil zippers, gamma-compatible components, a variety of knit cuffs and conductive-molded boot soles are but a few of the changes in the garment system industry`s recent past. And, although the number and types of choices are evidence of an industry serious about the rapidly-evolving needs of its customers, challenges continue to face the young garment system industry.
Application-specific cleanroom garments
Two factors influence advances in garment systems — comfort and the underlying application for their use. In cleanroom environments — 70 degrees Fahrenheit and 45 percent humidity — comfort is critical. Fabrics need to be a barrier to protect the product while “breathing” sufficiently to ensure wearer comfort. Employees are spending eight- to 12-hour shifts in the garments. “Any time you put a hood on, and a face mask, it`s automatic discomfort — not just from the build up of body heat, but the natural claustrophobic feeling. The winner in the cleanroom garment industry will be the one to put comfort into garments without sacrificing the integrity of the product,” says John Smith, Precision Fabric`s (Greensboro, NC) marketing manager for Integrity fabrics.
According to Chuck Berndt, president of C.W. Berndt Associates Ltd. (Highland Park, IL), “When you`re packaging people up, you can have the greatest fabrics in the world all the way up to membranes such as Gortex, but, if you don`t follow well thought out and defined contamination control practices, the best and most expensive fabrics in the world won`t help you to control contamination effectively.”
Although several industries are beginning to show an interest in cleanroom garments, pharmaceuticals and semiconductors still represent the largest market segments. Within the pharmaceutical industry, focus is on high-density weaves and barrier fabrics. Today, even the pharmaceutical industry is looking at static-dissipative garments. Although they don`t face ESD concerns, they are concerned about microbial filtration — bacterial contamination. When polyester garments build up an electric charge, they attract particles — and bacteria. In response, barrier ESD garments developed in the past two years specifically target the pharmaceutical industry.
Examples of fabric technology innovation for the pharmaceutical industry include:
Precision Fabric`s Integrity1800, which features Teflon to impart fluid and splash resistance to chemicals used in pharmaceutical manufacturing, and a durable non-migrating, anti-microbial material called MicrobeShield to inhibit bacterial growth.
Stern and Stern`s (New York, NY) ChemStat 969+, which features anti-microbial yarns woven directly into the weave, compared to industry-standard anti-microbial finishes directly on the fabric.
Burlington Industries` (Greensboro, NC) Maxima ESD, which is a carbon stripe specifically targeting pharmaceutical industry cleanrooms.
Similarly, for the semiconductor industry, garments in demand feature high-density weaves with static-dissipative qualities. Grid fabrics afford better ESD protection, and offer twice the amount of carbon fiber over stripe garments. As advances in the semiconductor industry see micron levels move from 0.5 to 0.35 and even 0.l8, requirements will likely become increasingly stringent in terms of static control and static decay.
Strides in semiconductor fabrics include:
Precision`s Integrity 2000 and Integrity 1700 products with Teflon and MicrobeShield, which target Class 1 through Class 100, and Class 100 through Class 1,000, respectively.
Stern and Stern`s Chemstat 909A+, which targets Class 1 and Class 10 and features over 21,000 fiber filaments per square inch and a raised grid format — an increase of 25 percent greater efficiency based on company claims.
Burlington`s recently introduced C3+, which combines enhanced particulate filtration with breathability of fabric for worker comfort. It is specifically designed to deliver higher filtration efficiencies at less than 0.5 sub-micron level.
Susan Routt, president of Fibrotek (Longmont, CO) says, “one of the challenges is the number of fabrics, designs, and styles available. There is an even greater challenge to have the right mix of products to produce apparel.” Her solution is to ensure that programs are created jointly with customers that support what is needed at the moment, as well as where that customer is going in the near and long term.
Although the advent of minienvironments will have an adverse impact on the number of employees used in cleanroom settings, and therefore on the garment industry itself, few within the industry are concerned. The consensus is that as other industries continue to find benefit in cleanroom practices to protect product quality, there is adequate oppor tunity to grow.
Innovations in garment systems
At first blush, it`s hard to see much progress in garment systems over the past two decades. Indeed, Berndt`s opinion is that “garment construction hasn`t advanced that much, other than in how seams are sewn, or in attempts to achieve a continuous electrical field.”
Others in the industry would argue that there have been plenty of advances in garment systems.
Fibrotek`s Routt points to footwear options as one of the major innovations, indicating items such as the Aussie cup sole and dedicated footwear, which have gone far to improve fit, safety, durability and footwear contamination concerns.
Jean Witt, sales manager at Hi-Tec Garments (Chatsworth, CA), cites design improvements. “Brass zippers that didn`t fit snug gave way to those made of double coil polyester with a very snug, but easy-to-maneuver fit. Knit cuffs are replacing snap cuffs for comfort and ESD qualities.” Witt agrees that advances in footwear options are extremely important. “There were several problems with the green vinyl sole, although it was an industry standard for years,” says Witt. “It didn`t hold up to abrasive or raised grid floors, and had a slippage factor in terms of safety. Today`s alternatives are non-skid and have carbon embedded in the injection molding process to address static concerns of the semiconductor market.”
Most garment manufacturers follow such industry construction practices as:
preserging components with overlock stitching to avoid fraying;
using like materials throughout garments including bias material;
maintaining a one-to-one ratio with thread and needle hole sizes;
clipping threads to 0.125-inch; and
inspecting 100 percent of garments.
Routt maintains there are several levels of sewing technique quality that set manufacturers apart. “Garment durability involves how machines are set, the types of equipment used — a lot can be preset for different operations to eliminate the `creative license` of human operators. In the garment industry, the more automation, the better,” says Routt.
Hi-Tec Garments believes in automation as well and is the first to invest in a unit mover — an efficient means of delivering work to its garment workers. The unit mover is an overhead rail system that delivers a complete coverall unit without the product dragging on the floor collecting debris. Completely computerized, work flow can be monitored on a screen, resulting in earlier problem detection and worker scheduling.
Bob Spector, group manager for cleanroom garment services at Prudential Cleanroom Services (Irvine, CA), takes the industry to task for, “spending an inordinate amount of time sewing things onto garments rather than worrying about closure and containment capabilities of the basic garment itself. Why for instance, is it necessary to wear a pager at work level?” Spector asks, referring to a garment tab to hold the pager. “Have you ever tested the particles generated by a vibrating pager? And, how many of the personnel who insist on wearing pagers wipe them down before they enter a cleanroom?”
Serving a clientele where change occurs so rapidly, there are bound to be challenges to suppliers of those clients — and cleanroom garment suppliers are no exception. The challenges include adopting consistent and realistic testing methods and procedures, educating users in the proper care and handling of cleanroom garments, and educating users on how to be informed users of garments, truly understanding what it is they are buying — and why.
While Berndt insists that end users “need to hold their suppliers` feet to the fire” to promote industry improvement, Spector says, “they don`t know what to hold them there for.” Spector encourages users to consider garments an integral part of the users` processes and operations. Minimally, Spector recommends users know what they`re buying, what it`s supposed to do, how it works and how to extract the best service and longevity from the product.
Spector also points out that, for the end user, education is the answer to using garments correctly. The person making the purchasing decision also needs to know what the inherent product weaknesses are. “Contamination is most critical where the product is most vulnerable. If purchasing garments is a non-production function, how is that person going to know where the product is most vulnerable?”
The Institute of Environmental Sciences and Technology (IEST/Mount Prospect, IL) issues recommended practices as the basis of cleanroom operations. Document IES-RP-CC003.2 Garment System Considerations for Cleanrooms and Other Controlled Environments is currently being updated specifically to recommend new test methodology specific and pertinent to the industry. “Testing garments in terms of contamination control is often not pertinent to what is trying to be accomplished,” says Berndt. “For instance, when measuring moisture vapor transmission, the current test is designed to measure moisture vapor transmission through insulation material used for the building industry. The test has been borrowed for adaptation to garments so as to measure comfort based on the rate of water vapor transmission which is expressed as grams per square meter per 24 hours.”
Global tests differ as well. “In Europe, American Society for Testing and Materials (ASTM) 5168 is performed differently than in the U.S.,” says Smith of Precision. “Instead of taking a microscope and counting particles they vacuum off, the test method is modified to pull the sample into a particle counter and actually count the number of particles by size. And, in the area of particle penetration, instead of pulling local dirty ambient air through fabric, they actually charge the atmosphere with particles of known size distribution, run it, and count particles.”
Few companies conduct testing in the same way. This seems particularly true in the electro-static area where two testing methods are used — Fed-Std 101, 4046.1 or the newly released ESD Association Standard 2.1. It falls on users to test, and they do, often taking as long as two years to evaluate fabrics they may want to adopt. It would seem that the garment industry might reduce the purchasing cycles of its products by adopting standard testing methodology.
Stern and Stern`s marketing and sales manager, Tom Hogan, says “ASTM has very stringent procedures to qualify test methods. Their guidelines should be followed first rather than trying to introduce tests through IEST or any other body.
Spector points out that “ASTM does not provide a complete series of tests that apply exclusively to cleanroom garments. Therefore, there must be a merging of documents from different organizations to accomodate the needs of the document users. ASTM does not provide a test method for counting submicron particles, which is critical to a great many users.”
Burlington Industries is taking testing one step further. Creating a test facility in its Hurt, VA, lab, the facility will include a Class 10 cleanroom laundry to assist the company in evaluating its products as well as competitive products, conducting enhanced R & D, and performing quality control research. “This is an enormous commitment,” says Jeff Peck, business manager for Burlington`s uniform barrier products. “It will allow us to develop new products, more accurately test current ones, and lend services to our customers — garment manufacturers, cleanroom laundries themselves, and end users.”
The new facility is expected to be operational in September 1998.
“Worldwide, it`s one big industry now,” says Smith. “For example, you have Hyundai, Samsung, and Siemens building facilities in the U.S. Motorola and AMD are building in Germany. Motorola is also building in China and using contamination control people from the U.S. to start up the facility. Western Digital (Irvine, CA) and Seagate have huge facilities in Singapore and Malaysia — and there`s a lot of transfer of information within the worldwide network.”
Several countries and regions of the world have different opinions as to what should constitute cleanroom garments. In Europe, for example, a large number of semiconductor manufacturing operations do not use booties — preferring ESD shoes, and leaving garments open at the leg rather than attached to a high boot. The rationale — air is pulled down into the floor taking contaminants with it. In France, predictably, cleanroom garments are cut with more style. Throughout Asia, there is a mixture of Japanese, European and American influences. Typically, Japan prefers stripe to grid. Asia also uses regional fabrics that are different than those created in the U.S.
At Western Digital`s Singapore facility, the company reports that fit is a problem. Knit cuffs must fit snugly to ensure proper contact for ESD purposes. Yet, operators in the Singapore facility have slimmer wrists than do the American workers for whom the garments are sized.
“This is an important issue. I`ve been a strong proponent of standardized sizes in this industry since the inception of Fibrotek,” says Routt. “We were willing to invest the dollars necessary to change our own business to conform to whatever sizing method would be adopted by the industry. Our IEST committee has so far been able to standardize the way things are measured.” Routt suggests that all companies in the cleanroom garment industry opt for maintaining three or four size standards to address global implementation issues.
A view from the cleanroom floor
“The basic problem we see in garments involves the contact of garments to the skin, especially at the cuff area,” says Julius Turangan, ESD program manager at Western Digital`s Class 10 facility in San Jose, CA. “As soon as you lose contact, garments build up a substantial charge — as much as 150 volts — and will retain voltage for quite some time — a situation extremely detrimental to ESD-sensitive end products.”
An example is readily seen in the company`s experience with knit cuffs. Western connects wrist straps to two garment ribbons on the body that make conductive contact with the garment`s cuffs, and to the receptacle and monitor. The cuffs are relied on for contact to the skin. If the cuff is loose, a monitor alarms. “Through wear and washing, we see the cuff start to stretch out and no longer fit the operator`s wrist,” says Turangan. “Since we`ve been using garments with these cuffs for the past year, our experience is that they last from four to six months before they begin to fail.”
Because Western makes magneto-resistive storage products extremely sensitive to ESD, it maintains a very low static threshold level — sensors near each station set off alarms when sensing more than 20 volts. When an alarm sounds, station operators stop working, identify the problem, and are replaced by a roving operator — representing downtime for Western. And, the problem is occurring at not only the R & D facility in San Jose, but in its Class 100 manufacturing facilities in Singapore and Malaysia.
Western Digital is also working closely with its supplier to add ribbon contacts to booties, and enable operators to undo garment snaps without undue force. “We`ve come up with stricter garment criteria than most industries,” says Turangan, “but we`re confident we`re approaching it the correct way for us.”
Turangan admits substantial progress is being made to not only fix current problems, but in cleanroom garments themselves. “At one time garments accounted for 25 percent of our static problems — today I`d estimate it`s less than 10 percent,” adds Turangan.
Carolyn Mathas is principal of Mathas Communications, a public relations consultancy service for semiconductor, telecom and software companies (Jacksonville, OR). She is also a freelance writer. She can be reached at [email protected].
Unit movers (left, above) at Hi-Tec Garments deliver complete garments to the assembler.
The ChemStat 929 face mask and nose bridge (left) and the ChemStat 939 Plus InStep sole from Stern + Stern.
Cleanroom garments from Vidaro incorporate polyester taffetas and herringbone fabrics. (left)
Vidaro shoe covers feature static dissipative sole materials and resistance to skidding. (above)