Investigation on the Lifetime of Copper Wire Bonds in Electronic Packages under Thermal and Mechanical Cyclic Loading

In this study, the results of simulative and experimental investigations regarding thermal cycling (TC) of a LQFP (Low Profile Quad Flat Exposed Pad) with embedded copper wire bonds are discussed. The focus of this study is to analyze cyclic thermal and mechanical loading at high plastic strain in the heat affected zone (HAZ) above the nail-head, which may lead to fatigue failure of wire bonds in the packages. Thereby, a comparison with multiaxial mechanical test results obtained in a previous study will be drawn [1]. Indeed, the lifetime diagrams for these two methods show a clear correlation. Convincing agreement was found on experimental and on theoretical level. The described accelerated test method can be used as a rapid test for the determination of the lifetimes of wire bonds at various positions on the chip. Moreover, our testing method leads to conclusions, which enable improvements of package design.