Power Modules with Increased Power Density and Reliability Using Cu Wire Bonds on Sintered Metal Buffer Layers

This publication presents the results of investigations of Cu wire bonded power modules with Danfoss Bond Buffer Technology (DBB). Thermal and mechanical behaviour of state-of-the-art power modules in comparison with DBB modules will be presented. Using Cu wire bonds in combination with bond buffer layers on the semiconductors leads to better thermal performance of the power modules particularly to better thermal impedance (Zth) and thermal resistance (Rth). The Cu bond buffer on the power semiconductors increases their thermal capacity and thereby improves the Zth of the power modules without increasing their Rth. Furthermore, sintering of the die decreases their Rth and thus reduces the operation temperature of the semiconductors. The thickness of the Cu foil influences shear stresses in the sinter layer and is another parameter to optimise the properties of the power module. Cu wire bonds on sintered bond buffer significantly improve the reliability of the power modules. The power cycling test @130K ?T has shown at least a factor of twenty better results than standard technology. To perform the sintering process on the top of the die, commercially available metallization systems with noble metal finish (e. g. NiAu or NiAg) have been used. The availability of different semiconductors (diode, IGBT, MOSFET) combinable with bond buffer layers leads to a high design flexibility and to high yielding manufacturing processes of outstandingly reliable power modules.