Effect of Aluminum Clad Cu Wire Bonds on Power Cycle Lifetime for High Current Density Power Module Packages

Abstract

Significant growth of the Electric Vehicle (EV) market i s making a valuable contribution to the efficient reduction of CO 2 emissions. Application of power semiconductors in EVs is attracting a lot of attention, since many silicon (Si) power semiconductor chips, packages and modules are implemented in the main traction inverter, electric power steering system (EPS) , battery management system, and other motor drivers that are key components for EVs. Recently, silicon Carbide (SiC) power devices are promising alternatives, and with a view to achieving the superior semiconductor performance, the transition from Si power devices to SiC devices is underway. The maximum operating temperature of Si power devices is around 175℃, that of SiC devices is expected to be as high as 250℃, taking advantage of their wide bandgap characteristics, which induces high thermal stress around a SiC chip owing to a Coefficient of Thermal Expansion (CTE) mismatch and deteriorates the power module reliability. Al wire bond interconnections damage rapidly due to a thermal strain between the SiC chip and the wire material, which accelerates failures near the interface of the wire bonds in the power module, due to the T j changes caused by higher current loads. In this study, Al-Clad Cu (AlCu) wire bonding structure on a thick ion-plated Cu over-pad metallization (OPM) layer is proposed. To demonstrate the power cycling durability, SiC-Schottky barrier diodes (SBD) with AlCu wire bonds on a 25 m-thick Cu-OPM layer were assembled into the test vehicles. Applying finite element method (FEM) analysis, the reliability of AlCu wire bonds on Cu-OPM was demonstrated.The lifetime during power cycling tests of AlCu wire bonds on a 25 m-thick Cu-OPM layer was 14-times longer than that of Al wire bonds on an Al pad at ΔT j = 75℃. In light of inelastic stress-strain analysis, the lifetimes of the AlCu wire bonds on a 100 μmthick and a 300 μm-thick Cu-OPM layer during power cycling tests were predicted to be 42-times and 1,600 times longer than that of Al wire bonds on an Al pad, respectively.