Characterization and reliability analysis of wire bonds inside a package subjected to cyclic loading.

摘要

This study predicts analytically and determines experimentally the mechanical effects on the wire bonds caused by the ultrasonic welding process performed to hermetically seal the lid to the LDMOS housing base. The first task was to perform a finite element analysis and understand the response of the system under the conditions set by the experimental apparatus. The natural frequencies of the model containing a quarter-LDMOS housing base with one die and one wire were determined under a modal analysis. Stresses and displacements at both wire bond locations were analyzed, plotted and compared to the ultimate yield stress of gold material. The finite element results demonstrated that an equivalent cyclic load applied to the lip of the LCP wall can cause failure on the wire bonds due to high stresses at some of the resonant frequencies of the system. It was also shown that the resonant frequencies associated with the motion of the wire caused the highest stresses on the wire bonds. Finally, the experimental work agreed with the theoretical prediction. Both visual inspection and the bond pull test performed after exposure of the wires to ultrasonic welding showed a considerable number of wires that broke off or yielded low bond strength results at the same predicted locations. Such observations resulted in concluding that wires can be damaged by the ultrasonic welding process and recommendations were generated for future research.