Even the slightest static discharge can spell disaster for today’s delicate components. Because the dangers of ESD (electrostatic discharge) are amplified in a low humidity environment, Terra strongly urges that you consider these measures as part of your static control program.
Static electricity is an excess or deficiency of electrons on a surface. The total number of deficient or excess electrons determines the charge on that surface. A surface exhibiting an excess of electrons is charged negatively, and an electron-deficient surface is charged positively.
Although static electricity has plagued the semiconductor manufacturing industry ever since the advent of integrated circuitry, its effects pose especially serious problems to today’s miniaturized, sophisticated, and expensive components. These devices can be seriously damaged or destroyed by charges much smaller than a person can typically detect.
How are Electrostatic Charges Generated?
Electrostatic charges are usually generated by friction between and/or separation of two dissimilar materials, at least one of which is a nonconductor or a poor conductor of electricity. The accumulated charge (static) resides on the surface of, rather than within, the charged nonconductive object.
Electrostatic discharge (ESD) occurs when an accumulated charge (which may be present on an operator, the operator’s clothing, or on any other non-conductive object) is discharged through a conductor (which may be part of a wafer, a chip, or a packaged device), and it may occur whenever the electrostatic potential corresponding to accumulated charge is great enough.
Acrylic or Static-Dissipative PVC Shell
Acrylic, the most common plastic used in storage enclosures, is a prolific static generator. The act of cleaning an acrylic desiccator with a cleanroom wiper is enough to generate surface charges that can discharge onto semiconductor components. One way to avoid potentially disastrous static damage is to select Static-Dissipative PVC.
This material not only dissipates static charges safely, but it also eliminates the particle attraction that static charges create. Surfaces stay clean, inside and out, making this material perfect for use in Class 1 cleanrooms.
Because static-dissipative PVC is transparent and highly durable, it can be used in place of acrylic in nearly any application, desiccators included. It features a surface resistivity of approximately 107 ohms per square, placing it in the “dissipative range”. It is completely noncontaminating—with no measurable outgassing—and it resists a wide range of chemicals.
Note: To protect Static-Dissipative PVC surfaces, desiccators made of this material must include stainless steel shields installed at the bottom of each chamber.
Fabricated of clear acrylic or Static-Dissipative PVC, Faraccator™ Storage Systems provide full 360-degree viewing of stored components. Solvent-welding and contamination-free materials guarantee a clean environment free of outgassing. Faraccator™ cabinets house from one to four compartments of two different widths (see dimensional chart). Because Faraccator™ components are standardized, you can easily replace a damaged door.
Stainless Steel Slide-Out Drawers and Runners
The system's 304 stainless steel trays create a Faraday cage that shields stored materials against electro-static discharge (ESD). They can be easily removed and used as handling trays, eliminating the need to touch—and possibly to contaminate—sensitive microelectronic components.
The trays mount easily into the system's runners to become slide-out drawers. Runners feature an easy-glide suspension system that supports up to 40 lbs (18.1 kg). when fully extended and allows full access to every inch of drawer space. Two-drawer compartments provide 5.25" (133 mm) of clearance and include 5”-deep (127mm) trays suitable for 4" (102 mm) waffle packs; three-drawer compartments provide 3.1875" (81 mm) of clearance and are available with 2”-deep or 3”-deep trays, suitable for 2" (51 mm) waffle packs.
Stainless steel inlays, included in Faraccators with 2”-deep trays, are slotted every .375” (10 mm) to permit easy insertion of stainless steel dividers (order separately). Inlay packages allow front-to-back storage of up to 192 2-inch waffle packs (with retaining dividers) in small trays, and up to 240 2-inch waffle packs in large trays.
For enhanced static-control, select a Faraccator made of static-dissipative PVC, which dissipates surface charges that can attract and hold particles.
Although the Faraccator configuration does not form the closed box that Faraday described, both shield and tray are at the same potential and no electric field can exist within the volume they enclose. This effect can be demonstrated simply by directing an electrical discharge at the opening between the shield and the tray. The discharge never enters the cavity, and any stored materials inside remain completely shielded from the effects of the discharge.
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