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Question Are there any hard and fast requirements for control of relative humidity in ESD Protected Areas now that MIL-STD-1695 has been cancelled without replacement. If not, where can I find what specific additional ESD controls should be placed in effect when RH drops below 20%? Thank you for any guidance you can provide. - Anonymous, Austin, TX
Answer The standard, ANSI/EIA-625-1994, section 11.2 recommends a minimum humidity of 40% R.H. Since tribocharging will be producing higher voltages it’s critical for the user to obtain high compliance to a rigid ESD control program. Items that might be employed in any environment would be essential in an environment below 20% RH, such as: Use of static shielding bags which create a Faraday cage to protect ESD sensitive components at all times when they are stored or being transported; Overhead and Bench Ionizers to neutralize static charges from insulators; Use of Continuous Monitors to ensure that workstations, both ESD mat and wrist strap, are properly grounded. Note: continuous monitors require utilizing worksurface resistance to ground (RTG) of 5 x 10^8 ohms or below. If periodic testing is utilized, workers should check their wrist straps and foot grounders at least twice a day. Mat and surfaces must be cleaned with a silicone-free ESD Cleaner. Silicone is an insulator and will prevent mats from properly draining away static charges. Coil cords should be of durable single-wire designed utilizing contoured supported banana plugs to improve reliability preventing breaks in grounding circuit. Use of dissipative smocks or lab coats to provide a Faraday Cage around static charges generated by movement of worker’s clothing. Use of dissipative floor finish and two foot grounders per person to reduce tribocharging from movement across the floor, and ensure the proper draining of static charges from personnel, carts, etc. An alternative is the use of dissipative or conductive floor mats that are permanently attached to a proper ground. Removal of all non-essential items from the ESD work area. Any tapes, clip boards, binders, document carriers, waste can liners used should be anti-static versions. Topical antistat treatment should be sprayed on all non-static surfaces. Use of CD ROM and other training tools to ensure worker understanding of Compliance efforts should be increased using Test Equipment to ensure that flooring and mats have proper electrical properties.
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