ESD worksurfaces are typically an integral part of the ESD workstation, particularly in areas where hand assembly occurs. The purpose of the ESD worksurface is two-fold:
(1) To provide a surface with little to no charge on it.
(2) To provide a surface that will remove ElectroStatic charges from conductors (including ESD Susceptible devices and assemblies) that are placed on the surface.
For an electronics manufacturing environment, the worksurface resistance point-to-point (Rtt) and point-to-ground (Rtg) of 1.0 x 106 to less than 1.0 x 109 ohms is recommended(ANSI/ESD S4.1). Worksurfaces can be defined as any surface that un-packaged ESD susceptible devices or assemblies placed in direct contact with. Worksurfaces can include, mats, laminates, trays, carts, shelves, and other storage or handling devices that do not have an ESD shielding function. A ground wire from the mat should connect to the common point ground which is connected to ground, preferably equipment ground.
All ESD worksurfaces should be systematically tested for Rtg using a resistance megohmmeter with a 5 lb. electrodes. This should become part of a regular compliance verification plan. Surfaces should be confirmed at least two to four times per year and whenever a workstation or bench is moved or installed. ESD mats where the Rtg measures > 5 x 108 or greater should be considered for replacement before they are out of spec.
The worksurface must be maintained and should be cleaned with an worksurface ESD cleaner. Regular cleaners typically contain silicone. They should never be used on an ESD worksurface because the silicone will add an insulating layer. The ESD control plan should require testing the resistance to ground periodically.
For more information on best practices for establishing and ESD workstation, contact Desco.