Choosing Cleanroom Cabinets and Shelves
With cleanroom space at a premium, the cost of maintaining supporting storage areas and systems can bust all but the biggest budget.
By Susan English
For many manufacturers in the microelectronics, pharmaceutical and related industries, automated storage/retrieval (AS/R) systems have proved to be an innovative and cost-effective approach to organizing high-volume inventory. Evolving from spruced-up filing systems to genuinely cleanroom-compatible storage, the new generation of AS/R systems not only have the capability to keep stored parts clean and organized, but also to guard against defects related to moisture and electrostatic discharge. Added to this are the important security benefits offered through software innovations–such as lock-out codes for selectable stock areas and bar-coded error warnings.
Rethinking racks
One company that has re-thought traditional racks for space-sensitive cleanrooms is Terra Universal (Anaheim, CA). Its newly designed automated storage systems provide an alternative to wick racks and work-in-progress racks for cleanrooms with severe space restrictions. Also, they can be installed in a chase area outside the cleanroom. Dual opposing-access doors with interlocks facilitate pass-through stocking and retrieval from either the clean or dirty side. The company`s FreeFlow or ASD units are available in heights of up to 20 feet and can even extend above a false ceiling. The shelf design makes it possible to store large inventories of reticle trays, wafer lot boxes, tote boxes, or other sensitive packages, while occupying a relatively small area.
Terra Universal manufactures three AS/R systems designed to accommodate specific environmental requirements. FreeFlow Systems provide laminar-flow storage inside the cleanroom. The open-cage design allows the vertical flow of clean air emanating from the cleanroom ceiling filters to pass through the storage area and exit either through a perforated base or side vents. Parts are stored on as many as 36 shelves that rotate on a carousel. For Class 10 environments, shelves are manufactured of electropolished stainless steel, and the open-cage design minimizes turbulence, while preserving enough rigidity to support loads of up to 600 lbs. each.
Material alternatives
According to Terra Universal`s Mike Buckwalter, the move to cleaner, more corrosion-resistant materials means, “more and more of our customers are requiring electropolished materials in Class 10 or better cleanrooms, whereas, five years ago, a plated or a standard stainless steel surface was adequate. We now manufacture more and more electropolished shelving, gowning benches, workbenches, etc.”
On the other hand, less expensive alternatives may be appropriate where cleanroom processes do not involve corrosive agents, says Carl Dymond, product manager for InterMetro Industries Corp. (Wilkes-Barre, PA), a leading wire shelving and storage equipment manufacturer. Two newcomers to the market–chrome-plated open-wire shelving and open-grid polymer shelving–have proven very effective in eliminating corrosion while maintaining stringent durability requirements, says Dymond — and at approximately one-third the cost of stainless steel.
However, Dymond cautions that furnishings within a cleanroom should always be appropriate to the design of the cleanroom, the tasks performed, and the degree of protocol. Since air filtration is key to maintaining required cleanliness levels, furnishings should not obstruct airflow and reduce operating efficiency or increase the risk of contamination. “Cleanrooms with vertical airflow, therefore, require furniture with open surfaces, such as open-wire, perforated or louvered steel and open-grid polymer furnishings,” he says.
Cleanroom compatibility
If cleanroom activities involve the use of corrosive agents, non-reactive shelf material should be selected for shelf surfaces. Dymond suggests selecting equipment that resists poor protocol practice. “Plated or stainless steel storage fixtures are better than powder-coated or pebble-grained polymer fixtures in a fab where repetitive pick-and-place operations are commonplace, for example,” he says. On the other hand, a black powder-coated shelf surface would readily expose the contaminants and residue resulting from poor gowning procedure.
Usually, the first question to arise during the process of selecting cleanroom furnishings is cleanroom compatibility. Dymond frequently receives calls asking if the company`s products are certified for use in a cleanroom. He points out that Federal Standard 209E does not define a certification process for equipment used within a controlled environment.
Although 209E does not define certification, some manufacturers have contracted independent test labs or engineers to certify that the introduction of a product into a cleanroom–usually Class 10 or 100–does not negatively affect the particle count within that environment. The inference here, says Dymond, is that since the particle count did not rise with the introduction of the product being evaluated, it will not contribute enough particulate to invalidate the room`s current classification. As logical as that sounds, he counters, it should be remembered that such “tests” are usually conducted in a dormant environment with the largest particle generators– personnel– absent from the cleanroom. He suggests that consumers ask for detailed test criteria before finalizing any purchases of cleanroom furniture. “The bottom line is common sense,” he says.
Cabinet/shelf variety
Several companies provide all types of shelving and cabinets. Storage cabinets in laminate, polypropylene and stainless steel, with adjustable shelves and hanger tubes, are available from Connecticut Clean Room Corp. (Bristol, CT). All cabinets have fully gasketed lexan doors with locking twist-turn handles. The shelving is available in solid and open-wire styles in stainless steel and chrome, free-standing, on casters, or wall-mounted in a variety of lengths and widths.
Southwest Machine and Fabrication, Inc. (Los Lunas, NM) has a glove dispenser cabinet constructed with electropolished stainless steel and clear Plexiglass. Two hinged doors allow easy loading. In addition, the company carries a variety of other cleanroom cabinets for storage of wet wipes and water bottles.
Air Control, Inc.`s (Henderson, NC) clean storage cabinets are specially designed for the protection, storage or transfer of delicate parts, sub-assemblies, or mixtures. For piping of inert gases or other controlled atmospheres, gas nipples can be installed in each storage area. Standard units are available in clear acrylic, ultra-violet-shielding amber, or clear ESD-PVC, and in one, two or three compartments with doors on one side or two sides for pass-thru applications. The company`s Microvoid HEPA- or ULPA-filtered portable storage cabinets are fabricated of white stress-relieved polypropylene with stainless steel hinged doors in ESD-PVC, or clear acrylic, and feature removable stainless steel shelves.
Eagle MHC`s (Clayton, DE) Quik-Set shelving includes a comprehensive line of solid, louvered and embossed shelving products constructed in either 14- or 16-gauge Type 304 stainless steel, or 14- or 16-gauge galvanized steel coated with an epoxy finish. The units are available in widths from 14 to 24 in., and in all standard matrices from 24 to 60 in. Post heights range from 14- to 86-in. high, 1.25-in. diameter and are available in two finishes: Type 304 stainless steel or zinc-chromate with baked-on clear epoxy coating for use in wet and dry applications.
Contamination Control Products, Inc. (Marlboro, NJ) offers cleanroom-grade shelving in electropolished stainless steel wire, solid stainless steel, chrome-plated wire or solid laminate surfaces. Wire shelves are designed with heavier gauge truss wires to provide up to 25 percent added strength. Calibrated posts in 1-in. increments and bottom levelers allow for level storage.
Servicor, Inc. (San Carlos, CA), carries a line of stainless steel or baked polyurethane enamel steel cleanroom benches and garment racks. Polyurethane has been shown to be more resistant to chemicals than epoxy, and the 450° baking process provides a chip-resistant, porcelain-like surface. Servicor produces all-welded furniture–no assembly is required in most cases. Benches are either flow-through, perforated or solid and can be bolted to the floor of the cleanroom. Garment racks hold chrome hangers captive to the rod, which can be individually numbered for garment assignment.
Advance Tabco (Edgewood, NY) offers both wall-mounted and free-standing stainless steel gowning racks in 4-, 5-, 6- and 8-ft. lengths. Stainless steel hardware for assembly and 12 electropolished stainless steel hangers are provided for each rack. Hangers also come boxed in dozens and are available separately.n
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Air Control`s amber storage cabinet is specially designed for the protection, storage or transfer of delicate parts, sub-assemblies, or mixtures.
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NTA Industries` #304 stainless steel rod security cleanroom cabinet features the company`s Ultracln electropolished finish, making it suitable for sub-Class 1 environments. The cabinet carries a lifetime warranty against manufacturing defects.
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Liberty Industries` HEPA-filtered garment cabinets bathe garments in Class 100 air. Manufactured in either metal or 3/4-in. novaply plastic laminated board, cabinets have Plexiglass doors. Also, prefilters are 35-percent efficient ASHRAE-rated. A direct-drive motor at 115V, 1-phase 60-Hz features a high-capacity forward curve blower.
“As logical as that sounds, he counters, it should be remembered that such “tests” are usually conducted in a dormant environment with the largest particle generators– personnel– absent from the cleanroom”
I disagree
Herta