The characterisation of antistatic materials: An alternative approach.

In the past, the typical characterisation of antistatic materials has been specified by different definitions of resistances, depending on the application of the material. Bulk and surface resistances are specified in standards. Typically for antistatic boxes, a kind of surface resistance is given, including point-to-point measurements. Even recently, IEC standards have been published in this domain. Most of these methods are only related to prevent charging up of materials by their handling. Also, it has been recognised by different researchers that this way of characterising antistatic materials is not correlating with the antistatic behaviour of these materials under practical circumstances. This holds especially for all materials based on a technology of fiber injection in plastics, where the surface resistance is no measure for the overall conductivity of the material. And furthermore, electronic design engineers are not interested in this surface resistance as such, but will ask for the ESD shielding behaviour of an enclosure, in relation with the immunity standard EN 61000-4-2 concerning ESD testing of systems. This paper presents an alternative method of characterising the ESD shielding behaviour of antistatic materials, that can be used for the manufacturing of enclosures. It is based on the recording of a typical ESD discharge in the frequency domain, and by careful analysis of the resulting spectrum. This analysis can be used to rank the materials under test according to an ESD shielding effectiveness. The results will be compared with the results of other measuring methods.