THE ELECTROSTATICS OF STATIC-DISSIPATIVE WORK-SURFACES

Static-dissipative worksurfaces must dissipate their own charge, remove chaage from objects on the surface, and limit induction charging to values which do not damage charged electronic devices which are dropped on the surface. In this paper, all of these requirements are expressed in terms of electrostatic charge decay models, which are then used to formulate the decay times for various practical situations. These decay times are compared to the times available in a typical electronics assembly situation to set limits for the volume resistivity and the surface resistivity of the work-surface. The preferred worksurface, from an electrostatic point of view, is composed of a material with a volume resistivity θ ≤ 1011 ω cm, and bonded on the bottom to a grounded conductor. The effective surface resistance should also be Rs ≥ 105 ω/square to avoid damaging charged devices through induction charging of the worksurface. In addition, the worksurface material should be soft enough to conform to objects placed on the worksurface, in order to reduce the contact resistance between it and charged objects placed on the surface. © 1990.