Abstract
Due to development of technology and the users demand, power modules are widely used with the characteristic that it can promote energy transfer efficiency. Nowadays, high power and high integrated are the modern trends in development of power modules. Conventional power modules utilize bonding wire for interconnection and dissipate heat mainly based on forced cooling system. However, with the rising of working power, it is necessary to create power modules which can solve high junction temperature and effort high working current. Double-sided power modules are one of the structures which can realize high power module application with reducing junction temperature efficiently and providing more heat dissipation path. According to the research results of Tsing Hwau-Delta project, using bump interconnection can control the current density and design the DNP position of bumps freely, so that it is more flexible in the view of design than face-to-face solder interconnection which is utilized in existing double-sided power module. This research is focus on double-sided power module with bump interconnection and investigating reliability of the bump. When the power modules are subjected to the cyclic power load, the junction temperature varies significantly; the thermal stress and strain resulting from the mismatch between the coefficients of thermal expansion of materials causes the bumps to failure. This research will construct finite element models to conduct electro-thermal and thermal-mechanical analysis in aforementioned structure by commercial software ANSYS, and to simulate the mechanical behaviors of bump interconnection under power cycling. By using this simulation method, an analysis of the reliability of bump interconnection when it is in different cooling conditions and subjected to several power cycles is achieved. The area there the bumps will easily failure is discussed, and proposing methods to enhance its reliability with concepts used in advanced packaging. Finally, parameter analysis of IMC structure in bump interconnection is also executed to understand the effect of design parameters of IMC. From results of simulation, double-sided power module with double-sided cooling can get lower junction temperature and better reliability of copper bump. However, the structure in this condition possesses worse IMC reliability and this disadvantage can be improved by enlarging the corner bumps which have the largest DNP. In addition, under the premise that the bumps can keep complete joint, the thickness of IMC should be reduced as possible as it can, and the reliability of IMC will be increased. The bump interconnection used in this research is joined by Cu/Sn IMC, and it is needed that to get a credible value of the failure strength of the IMC material. Moreover, when the power module works, the junction temperature will reach 200 °C. Hence, the failure strength of IMC measured at room temperature is not suitable for the reliability analysis in this condition. This research proposes a recommended experiment design to investigate the failure strength of Cu/Sn IMC. Using thermal aging treatment to control the growth of IMC and utilizing shear test with heating module to measure its failure strength at high temperature.