Instrumentation and standards for testing static control materials

The design, operation, and performance capabilities of an instrument that assesses insulating and semi-insulating materials by measuring of static charge decay are described. A patch of charge is deposited on the surface, and a fast-response electrostatic fieldmeter is used for direct, noncontact observation of the rate of charge dissipation. Comments are made on a proposed IEC standard incorporating the above method for assessing insulating materials. It is proposed that materials used in proximity to sensitive semiconductors should be of the static dissipative type with decay time constants at surface potentials in the 50 to 100 V range between 10 and 500 ms. The shortest decay time avoids the risk of spark-type electrical discharges to the surface, and the longer time is adequately short compared to normal manual actions likely to be involved in triboelectric charging. Examples of decay curves are given.<>