Evaluation of high-temperature long-term reliability of transient liquid phase bonded joints using etched Cu foam/Sn–3.0Ag–0.5Cu composite solder preform

This study was aimed at examining the applicability of Cu–Sn system transient liquid phase (TLP) bonding using Cu foam to high-temperature operating devices. A composite solder preform was fabricated using etched Cu foam and Sn–3.0Ag–0.5Cu (SAC305) solder alloy to facilitate TLP bonding. Subsequently, isothermal aging treatment was performed at 200 °C for up to 1000 h. Immediately after bonding process, the joint was mostly composed of Cu–Sn intermetallic compounds and residual Cu skeleton. The changes in the microstructure and mechanical properties of the joint subjected to isothermal aging treatment were examined. During the aging process, the quantity of shrinkage voids increased with the formation of Cu₃Sn owing to the continuous reaction between Cu and Cu₆Sn₅. As the reaction progressed, the Cu skeleton was continuously consumed, and its proportion in the joint decreased. Consequently, the shear strength decreased with increase in the aging time. However, despite its reduction owing to the formation of shrinkage voids and consumption of the Cu skeleton, the shear strength of the joint remained over 30 MPa even after 1000 h of aging.