Abstract
Power module with high power density and high heat dissipation structure has been developed because of increasing requirement for high-power electric products. Nowadays, most power modules use metal wire as interconnection, which results in the limited heat dissipation capability. The heat generated by the power chip directly affects the reliability of the wire; thus, the failure mode of bonding wire is essential investigated. Along with continuously increasing power load, chip temperatures have gradually increased. Therefore, the double-sided power module was further proposed to solve the thermal issue. However, the exceeding high chip temperature bring about that the common solder unable sustain its function. Thus, the bonding materials with high-temperature resistant characteristics are highly demanded when chip temperatures are continuously increasing. The study aims to predict the electro-thermo-mechanical coupling behavior of high-power module and determine the failure behavior of bonding wire. A joint material with high-temperature resistance capability is also proposed. Its mechanical characteristics at the intended application temperatures were examined by shear test and tensile test. A three-dimensional (3D) finite element (FE) model based on an actual power module was established to predict the electro-thermal coupling effect and thermal mechanical behavior by numerical analysis. The maximum current density and the corresponding current crowding effect were generated at the interface between the insulated gate bipolar transistor (IGBT) chip and bonding wire. Meanwhile, the current load induces the maximum temperature gradient at the power chip and affects the structure thermal stress. The analysis result was validated with the measurement temperatures of IGBT chip to confirm that the numerical methodology is reliable. The thermal-mechanical behavior and failure mode of the bonding wire were also investigated. The parametric design of bonding wire was analyzed to predict the coupling behavior as well as further estimate their heat dissipation capabilities. An Au-20Sn eutectic solder with a high melting point was used as the bonding material, which further determines its mechanical characteristics. Experiments showed that the Au-20Sn solder transforms into intermetallic compound (IMC) materials with higher melting points (AuSn and Au5Sn), which meet the high temperature requirements. A shear test was used to analyze joint microstructure variations with regard to the influence of corresponding material strength at various thermal treatment conditions. Mechanical strength of joint at different application temperatures was also examined to assess the temperature resistant capabilities. The joint failure mode was analyzed to observe the initial break location and failure path, which means likely to cause the joint damage in advanced package structure. Nonlinear material properties of Au-20Sn solder were measured at various strain rates and temperature loads by tensile test. The strain rate and temperature effects on the influence of material strength were examined to accomplish the stress-strain curve for the Au-20Sn solder. The experimental results showed that the material strength declined when the treatment duration increased, when the temperature increased, and when the strain rate decreased. Finally, the temperature dependent material properties for Au-20Sn was established, which can be applied in FE model as nonlinear parameters and can accurately assess the reliability of high-power module.