A Moisture Protection Screening Test for Hybrid Circuit Encapsulants

An empirical comparative screening test for polymeric encapsulants reported here has been used to indicate how well different materials prevent unwanted leakage curents between closely spaced biased metal lines in integrated circuits (IC´s) and hybrid integrated circuits (HIC´s). It is not a reliability test. The screening test circuit, test procedure, and test conditions are described. This test and measurement equipment were developed earlier by N. L. Sbar and R. P. Kozakiewicz. Data for two silicone coatings and one epoxy coating are compared with data for our standard encapsulant, Dow Corning 3-6550 RTV. Also, interesting results are shown for layers of two different polymer coatings. A general conclusion drawn from these and other similar studies is that coatings of the same general polymer type can vary quite dramatically in performance in this screening test.