EVALUATION OF POLYMERIC COATINGS FOR MCM APPLICATIONS

An effort was initiated under the Reliability without Hermeticity (Rwo H) project to evaluate the performance of nonhermetic coatings for mul tichip module (MCM) applications. As a means of selecting coating mate rials, Sandia ATC01 test chips, with and without chip passivation (SiN ), were coated with three nonhermetic polymer materials: a silicone ge l, a filled epoxy, and a polyimide. Some of the coated parts were prec onditioned (500 temperature cycles and 96 h of salt spray), and some w ere not. The coated parts were subjected to either pressure cooker tes t (PCT-121 degrees C, 99.6%RH, no bias) or temperature-humidity-bias ( THB-85 degrees C, 85%RH, 40 V bias) tests, for 7000 and 10 000 h, resp ectively. In this paper, the moisture protection performance of the co atings on nonpassivated test chips is presented in detail. In addition , some overall comparisons of the failures in passivated and nonpassiv ated chips are given. For the preconditioned parts, THE median lives ( times to 50% failures) in excess of 10 000 h were obtained for the epo xy and the gel coatings. Polyimides exhibited a THE median life of 695 0 h. In PCT, the three coatings exhibited similar median lives in the range of 350-400 h, but, much different failure kinetics. Based on ear lier published studies, these median lives are representative of good coating performance. The failures in the nonpreconditioned coated part s were much lower (20-50%) for the gel and the polyimide coatings, at the end of THE tests. Epoxies on the other hand did not exhibit such i nfluence of preconditioning steps on failures. The comparison of passi vated and nonpassivated coated ATC01's revealed that the presence of p assivation enhances the moisture protection performance of all three c oatings. This effect was especially pronounced for the silicone gel.