Optimization of 2 Mil Al Wire Wedge Bond of D-PAK

Wire bonding is the most critical process in package assembly manufacturing. Among the wire bond-related failure mechanisms wedge bond heel crack is quite common and critical in the semiconductor industry. This paper focuses on enhancing the robustness of Al wire wedge bond heel in D-PAK under the reliability test of temperature cycling. The Al wire wedge bond shape can be approximately described by the wedge bond cross section, bond length and wire loop profile. To understand the impact of these 3 parameters, an orthogonal test is designed with three factors and two levels. The wedge bond cross section is screened out as the most important factor from the simulation results by the nonlinear FE code ANSYSreg. Then, detailed DOE simulations on the wedge bond cross section are conducted to obtain the optimal one. According to this guidance, practical tests based on the shape of bond cross section under temperature cycling are carried out experimentally. Packages with two different bond cross sections of Al wire are tested in the reliability lab under temperature cycling. It is found that packages with the recommended Al wire bond cross section are more robust, which confirms the simulation results