Static Control in Desiccator Cabinets
Why all the Static?
How are Electrostatic Charges Generated?
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.
How Do Electrostatic Charges Damage Sensitive Devices?
Manufacturers have taken steps to combat these problems throughout the manufacturing process, but until recently, little was done to ensure static-free storage. Desiccator cabinets provide protection against contaminants, but nearly all are made of acrylic, one of the most prolific generators of ESD.
Why Use Acrylic in Desiccator Manufacturing?
Acrylic features many attractive characteristics: it allows easy and inexpensive fabrication, permits optimal viewing of stored parts, and stands up to the most rugged manufacturing and stockroom conditions. Yet it also generates static charges. Not only does this static generation threaten sensitive components, but it also makes your desiccator a dust magnet. Particles that cling to charged acrylic surfaces threaten parts, diminish visibility, and are difficult to remove.
Hence, acrylic desiccators can be a dangerous place to store microelectronic parts. For this reason, transparent static-dissipative plastics (such as Terra's static-dissipative PVC) are becoming the industry standard in cleanroom applications.
How Can Electrostatic Discharge be Controlled?
Once a nonconductive surface has obtained a charge, the only way it can be neutralized is by means of an ion source. Both positive and negative surface charges are eliminated on nonconductive surfaces by ions of the opposite polarity which neutralize surface charges. Static decay times are directly related to the number of airborne ions; the more negative ions, the faster the decay time for positive charges (and vice versa).
For conductive materials, Terra's Faraccator™ concept guarantees 100% ESD protection within a storage area.
Terra has developed a complete line of noncontaminating stainless steel shelves, trays, and drawers that guarantee the absolute conductivity required for a Faraday cage. These durable units come in standard sizes to fit all of our desiccator cabinets and provide organized storage—both inside and outside the desiccator.
Do these Units Provide the Same Static-Proof Protection when Removed?
Terra also offers a full line of Faraccator™ storage cabinets that incorporate slide-out conductive drawers and stainless steel inlays. Like the trays and shelves, these drawers continue to shield against ESD when removed and used as carrying containers.
Can Terra Desiccators be Retrofitted to Deliver the ESD-Free Protection of a Faraccator™?
Our GroundWatch™ device helps to enhance this protection by continuously monitoring the integrity of the ground connection of an indefinite number of desiccators. The minute a ground line is disrupted, visible and audible alarms alert you to the problem before stored parts can be damaged.
Which Method of ESD Control is Best Today?
If stored material is nonconductive (plastic boxes, nonconductive waffle packs, etc.), or
If stored material is already charged and must be neutralized, we recommend ionizing equipment in addition to the safety measures listed above. For additional protection, use conductive trays in conjunction with ionizing nozzles whenever possible.