Assessment of Silicone Encapsulants for Hybrid Integrated Circuits (HIC)

A silicone encapsulant has been investigated as to its effectiveness in preventing migrated gold resistive shorts (MGRS). Using a temperature cycle of -10°C to +100°C, MGRS formation was observed at moisture levels of 0.9 to 1.2 percent V/V for Cl
^-
, 1
^-
, K
⁺
, and Na
⁺
ion contaminated environments. The results indicate that water molecules and halogen, Na
⁺
and K
⁺
ions will be readily transmitted through the silicone material. 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 mi-. crosensors bonded within the candidate hybrid package; followed by microspot 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 SiO
2
. Measured moisture and ionic contamination levels and the formation of MGRS in the presence of Na, I, K, Cl, S ions are summarized.