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Question ANSI/ESD 520.20-1999,Table I states the work surface resistance of ESD mats should have a resistively of 10 (9) ohms. Has this requirement been changed ? Most of our ESD mats have resistively of between 10(8) to 10(12) ohms. The mats we have bought recently are also within the range. Are mats to the new requirement available? Anonymous, Middletown, CT
Answer ANSI/ESD S20.20-1999 for the Development of an Electrostatic Discharge Control Program for - Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices) was approved in 1999. It is the recognized general document to provide ESD control guidance particularly for manufacturers assembling and handling products containing ESD susceptible electronic components. Prior to S20.20, the best general document was ANSI EIA-625-1994 which is still useful.

As you note, S20.20 requires work surfaces to be less than 1 x 10^9 ohms in an ESD protected area. EIA-625 recommends work surfaces in the dissipative range greater or equal to 10^5 ohms to less than 10^10 ohms. We strongly recommend ESD work surfaces in the dissipative range, using both specifications: 10^6 to 10^8 ohms.

Measuring resistance to ground or RTG, over 10^10 ohms is insulative as should not be used as it may not reliably provide a path to ground.
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