Authors: C. Hager, Y. Tronel and W. Fichtner
Affilation: ETH-EPFL, Switzerland
Pages: 163 - 167
Keywords: wire bonding, electro-thermo-mechanical simulations, finite element simulations
Finite-element simulations have been performed on aluminum wires as used in modern IGBT (Insulated Gate Bipolar Transistor) power modules. These wires were ultrasonically bonded to thin molybdenum plates and the influence of different origins of the mechanical stresses on the bond interface has been studied. The stress origins considered were: 1. heating and expansion of the bond wire due to an electric current, 2. the thermal expansion of a heated base plate and 3. the heating of the interface of the two materials with different thermal expansion coefficients. The geometries under investigation were: a) Wedge bonds on both ends and b) a wedge bond on one end and a ball bond on the other end. It was found that the stresses at the interface are dominated by the different thermal expansion coefficients of the aluminum bond wire and the molybdenum bond pad material. These main stresses at the interface are localized within a layer of about 50 m and are generally lower for the ball bond connection than for the wedge bond geometry.