Comparison and Optimization of SLID Bonding for Die Attach on Various Substrate Types in Power Module Packaging Applications

As advancing power electronic modules increasingly operate at higher power densities, thermally and thermomechanically stable die-attach materials are required to ensure their thermal performance and reliability. This study conducted finite element (FE) simulations and substrates characterization, followed by low-temperature (LT) solid-liquid interdiffusion (SLID) bonding experiments. FE simulations qualitatively compared the thermal performance of Sn-Ag-Cu (SAC) solder, sintered Ag, and Cu-Sn SLID bonds, while additionally analyzing thermomechanical stress development during Cu-Sn SLID cooling phases. Three types of substrates were characterized in terms of warpage and surface roughness. Additionally, Cu-Sn-In LT SLID bonding process was applied to achieve thin die-attach layers. Dummy Si chips of varying sizes were bonded to the direct copper bonding (DCB) and active metal brazing (AMB) substrates, with bonded area percentage quantified by scanning acoustic microscope (SAM). Furthermore, large-sized functional insulated-gate bipolar transistor (IGBT) chips achieved up to 93% bonded area on insulated metal substrates (IMSs) with the LT SLID die-attach process. Microstructure analysis confirmed stable phase and reduced crack formation located at the corners of the LT bonded samples. The simulation and experimental results demonstrate that LT SLID bonding enables a thin die-attach layer with low thermal resistance and high melting point. However, the substrate technology improvements on warpage and surface roughness reduction remain necessary for implementing the new die-attach method in novel power modules.