Comparative study of wire bond degradation under power and mechanical accelerated tests

Abstract

Degradation of wire bonds under accelerated power cycling tests is compared to that caused by mechanical high-frequency cycling for commercial power devices. Using micro-sectioning approach and optical microscopy it is found that the bond fracture under the mechanical cycling follows the same tendencies as that found under power cycling. Results of shear tests of the mechanically cycled bonds also agree well with the bond cracking tendencies observed by optical microscopy investigations. It is found that reduction of contact area of the wire at the bond/metallization interface due to the crack development follows the Paris-Erdogan law, which defines the degradation rate leading to wire lift-off. The results obtained on mechanical cycling in the current work also show good agreement with literature data on wire bond fracture under power cycling proving that main mechanism for wire lift-off failure is related to the mechanical stress development at the interface with metallization layer. The carried out study also creates a potential to further develop a high-frequency mechanical cycling into an alternative for reliability analysis of wire bonds. However, more studies have to be performed to compare degradation mechanisms occuring under power and mechanical accelerated tests.