An assessment of the reliability of a new soldering process for automotive power module

This paper presents a reliability study of power assemblies based on the correlation between finite element simulations and experimental results. This study is a part of the European PIDEA project called PEPPER (Power Electronics Packaging Providing system integration and Extended Reliability). The new process developed in the PEPPER project allows to solder bare dice on a copper lead frame by using a local heating source. We used a methodology based on the evaluation of the strain energy density (S.E.D.) accumulated in the solder joint during the lifetime of the assembly. The study was also carried out on different kind of solders (lead contain and leadfree). Thanks to finite element simulations, we have made an evaluation of the influence of this reflow process on the reliability of the assembly before ageing tests. Accelerated ageing tests have been carried out on representative test vehicles, in order to evaluate the lifetime of the assembly. We used liquid/liquid thermal shocks between -55deg C and +125deg C. During the ageing, the thermal impedance characteristic of the assembly was monitored. The strain energy density leading to failure is then computed by simulating those thermal shocks. On the other hand, simulation of a realistic mission profile is also carried out. By correlation, we evaluated the lifetime of the assembly in real operating conditions. The results indicate that the lifetime of the assembly using a local heating process is about the same as a classical process.