Evaluation of Stiffness-Reduced Joints by Transient Liquid-Phase Sintering of Copper-Solder-Resin Composite for SiC Die-Attach Applications

Transient liquid-phase sintering (TLPS) using a Cu-solder-resin composite for the die-attach application of high-temperature silicon carbide (SiC) power modules was evaluated with the goal of controlling the joint stiffness. The Cu-solder-resin composite mainly contains Cu particles, Sn–3Ag–0.5Cu solder particles, and polyimide-type thermosetting resin. Microstructural observations, shear strength tests, and thermal cycling tests of the SiC die-attached specimens bonded through the pressureless reflow process at 250 °C for 1 min were carried out after preheating at 100 °C for 60 min in a nitrogen atmosphere. A skeleton-shaped microstructure, consisting of Cu and Cu–Sn intermetallic compounds (IMCs) partially filled with polyimide resin, was observed in the joints, which exhibited shear strengths exceeding 12 MPa. The thermal cycling tests revealed that the TLPS specimens showed a superior reliability through 1200 thermal cycles in the temperature range from −55 °C to 175 °C. These experimental results were supported by mechanical finite-element (FE) simulations of simplified models that consist of the skeleton-shaped microstructure between the SiC chip and the substrate against an external force to mimic the shear test condition. The FE analyses proved that the stiffness of the composite joints strongly depends on the interconnection density that results from the formation of IMCs between the particles.