Shear Mode Wire Failures in Plastic-Encapsulated Transistors

During the development of a wire-bonded plasticencapsulated transistor, it was found that the usual wire pull technique for measuring bond strength was not adequate for optimization of the bonding process and did not correlate with the observed failures which were caused by shear forces. A shear testing technique and apparatus are presented which were developed to quantitatively describe the quality of the wire bonds. It was also found that there is an interaction between the wire bonds and the particular molding compound and process used. By employing a suitable molding system and optimized bonding process, the frequency of occurrence of marginal bonds was reduced to an acceptable level as determined by qualification tests which included temperature cycling and elevated temperature parametric testing.