ESD Systems - Questions And Answers

What is the relevence of the parameter “point to point resistance” of an ESD protective mat when the distance between two test points is not mentioned? How is it related to the surface resistivity of the mat? Which parameter among these two ( surface resistivity and point to point resistance ) is important to be known while procuring the ESD protective material? -Anonymous

Point-to-point measurements (known unofficially as RTT) are dependent on the application, floor or bench top. There are two standards, ANSI/ESD S7.1 for floors and ESD S4.1 for worksurfaces which describes the positioning, spacing and proper technique for making these measurements. This is a surface resistance measurement which is a function of distance (location) if the material is homogeneous. Surface resistivity is a characteristic of a material and is independent of location if the material is homogeneous. Typically, for concentric ring probes, the surface resistivity is about a factor of 10 greater than surface resistance. Both measurements are in ohms. The ESDA is moving away from using surface resistivity measurements because this information is not very relevant to ESD Control and it is confusing to most users. Surface resistivity is really a materials characteristic used primarily to characterize the ability of semiconductors to conduct ions or electrons or the base material (SiO2 wafer) and primarily used in Fab labs (Semiconductor Fabrication Laboratories). The most important resistance measurement you can make is a resistance from point to ground or RTG. An RTG measurement tells you how well the material conducts charges to ground and that the material is or can be grounded (depending on where you place the electrode to ground).

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