Numerical material design for reliable power electronics with cement-based encapsulation

Abstract:
The introduction of novel encapsulation materials is one opportunity to enhance the thermal, mechanical and thermomechanical performance of power electronic devices and modules. Because of the increased heat conductivity and low thermal expansion properties of cement-based materials they are potential candidates for further enhancement of reliability properties or miniaturization approaches. For a defined material design of these encapsulation materials multiple variations of the cement compositions, as well as different filler materials or filler contents are available, resulting in a wide range of available material properties after the hydration process. In order to allow a target-oriented material design, a microstructural and reliability driven simulation approach is presented. Therefore, the influence of the microstructure composition related to major engineering properties is studied by numerical approaches. In addition, the influence of the cement encapsulation on typical failure modes of an “Econo3” power module under power cycling conditions was analyzed and compared to common silicone gel encapsulation. The analyzed failure modes include bond wire fatigue, solder fatigue and fracture modes related to chip- or substrate failure. In order to verify the outcomes of the finite element modelling, also the local load distribution using these new encapsulation materials was compared exemplarily with finding from destructive failure analysis like cross sections of the solder interface and bond wires.