Electro-thermal-mechanical modeling of wire bonding failures in IGBT

In power electronic module (PEM), IGBT (Isolated Gate Bipolar Transistor) is a high electrical power device and control wide power range from micro-voltage-ampere to mega-voltage-ampere. In addition, IGBT device usually operates in high-temperature environment, such as engine of automobile. As a result, the thermal problem is one of main concern regardless of the influence from dissipated power or environmental temperature. This paper discusses temperature distribution and mechanical behavior of wire bonding in IGBT based on finite element method. The purpose of this research would focus on the interface of wire bonding and connection substrate. Because the material of wire and substrate are different, it would result in CTE mismatch. Due to thermal damage, it could cause failure in the interface, e.g. wire bond lift off and heel crack. Among these, wire bond lift off is a critical failure and even lead to the degradation of IGBT. In order to simulate electro-thermal-mechanical behavior, two analytical methods are adopted in this research, one is electro-thermal analysis; the other is thermal-mechanical analysis. In this paper, we would use ANSYS software to analyze electro-thermal-mechanical behavior of wire bonding structure, furthermore, the wire bonding structure we build up is symmetrical, so only half of model is analyzed to save more time and reduce computational complexity. In electro-thermal analysis, we would show the temperature distribution in wire bonding structure when electric current is applied to wire. Furthermore, the natural convection and forced convection are taken into consideration in order to correspond to the realistic operational situation. The temperature change is dominated by Joule heating caused by the magnitude of electric current. For the purpose of obtaining the relation between temperature and electric current, nonlinear transient finite element simulation is proposed in this research. The analytical results show that the temperature would change along electric current and there is nearly temperature distribution in wire bonding structure after stopping applying electric current for a period of time. In thermal-mechanical analysis, we would adopt indirect coupling method, that is, use the results obtained from electro-thermal analysis as thermal load to thermal-mechanical analysis. According to analysis, the maximum von-Mises stress occurs in the heel of wire bonding due to CTE mismatch and high Joule heating. Besides, the displacement of wire bonding structure has upward direction, namely, the warpage phenomenon would occur due to temperature change. Under continuing of temperature change, it would bring fatigue failure in the interface of wire bonding and connection substrate. The objective in this research is to improve and increase the mechanical strength of wire bonding by discussing the relation of electro-thermal-mechanical behavior.