Assessment of Silicone Encapsulation Materials: Screening Techniques

Silicone encapsulants have been investigated under conditions for forming migrative resistive shorts (MGRS). The kinetics of moisture penetration and general techniques for assessing hybrid package susceptibility to MGRS failures have been determined. Using a temperature cycle of -10°C to +100°C, MGRS formation was observed at moisture levels of .9 to 1.2% V/V for Cl-, I-, K+ and Na+ ion contaminated environments. Dendritic growth has been found to occur when threshold water and ion levels were exceeded. A technique for measuring the kinetics of moisture penetration through encapsulants is described. The method consists of utilizing moisture microsensors bonded within the candidate hybrid package; followed by micro-spot AES, EDXA analysis of ionic contamination. The test results from the hybrid moisture microsensors are compared with kinetics data obtained by measuring surface currents on thermal SiO2. Measured moisture and ionic contamination levels and the formation of MGRS in the presence of Na, I, Br, Cl, S ion are summarized.