Effectors of high temperature reliability in epoxy encapsulated devices

Ball shear testing of devices encapsulated with a variety of molding compounds after aging at either 200°C/dry or 158°C/85% R.H. has shown comparable or faster failure rates for the 158°C/85% R.H. parts than for the 200°C/dry parts, in most cases. Slight or no corrosion of the bond pad was observed under either of these conditions, suggesting that loss of ball shear strength with wet aging (like dry aging) results from chemical weakening of the ball/intermetallic interface. Molding compounds without Sb₂O₃, and containing an ion scavenger performed the best. Electrical testing was also carried out on three different types of logic devices with either pure aluminum, aluminum+copper, or aluminum+copper+silicon metallization, built with three different molding compounds and three different die attach materials, under the more traditional high temperature (190°C) dry conditions (High Temperature Storage Life Test). The most improved reliability found was for devices with pure aluminum pad metallization encapsulated with non-Sb₂O₃ molding compounds of high catalyst level and using a low Cl ion die attach. Among the identified effectors of high temperature reliability, the presence of moisture and the type of molding compound used, are the most important