Modeling of the HPC infiltration process by means of the lattice Boltzmann method

The requirements for next-generation power electronic modules and devices imply enhanced energy densities, i.e., interconnection packaging technologies have to guarantee enhanced ampacity and robustness with respect to thermo-mechanical loads. Particularly, the interconnection layers of semi-conductor devices (e.g. MOSFET, IGBT, diodes) play a predominant role in the robustness of power electronic modules. Diffusion soldering (aka "HotPowCon", HPC) is a promising alternative with respect to the above mentioned requirements. HPC consists in the infiltration of a solder alloy melt into a porous copper matrix. The resulting intermetallic phases between copper and the soldering alloy have a melting point high above the standard processing and operating temperatures, and hence, a thermo-mechanically stable interconnection layer is formed. A simulation of this infiltration process requires the modeling of wetting dynamics in complex porous structures for which classical computational fluid dynamics (CFD) is limited with respect to computational efficiency. In contrast, the so-called lattice Boltzmann method (LBM), which is an indirect solver of the Navier-Stokes equations based on statistical physics, is numerically far more efficient. In this article, we present a simulation approach based on the LBM in order to model the response of infiltration rates on crucial HPC process parameters like viscosity and wettability of the liquid solder alloy, as well as porosity and geometrical properties of the copper matrix. The simulation results show consistency with the analytic Lucas-Washburn law for capillarity-driven flows in porous media. This can be seen as a proof of concept for the application of the LBM on the HPC infiltration process, and thus, the LBM might be the key-component of a future tool-chain for infiltration process optimization with respect to large-scale production demands.