Solution of Wire Creep Rupture Problem in a Thick-Film Power Hybrid

Surviving 2000 thermal shock cycles from 0 to 125°C without bonding wire deterioration in a plastic-encapsulated power hybrid requires judicious selection of materials and processes. Power hybrid modules under development had reached the preproduction and qualification test phase and began exhibiting wire failure within 200 thermal shock cycles. The wire failures occurred within two to three wire diameters above the ball in thermosonic bonded 0.025- and 0.051-mm wire. The problem was determined to be one of creep rupture wherein the wire was being subjected to repeated thermal and mechanical stressing during assembly and test. The module, the materials of construction, and the methods whereby the problem was identified and resolved are · described.