Pressureless die attach by transient liquid phase sintering of Cu nanoparticles and Sn-58Bi particles assisted by polyvinylpyrrolidone dispersant

Highly reliable bonding materials have attracted tremendous interest due to a growing demand for high-temperature electronics. We developed a fluxless and binder-free paste comprising Cu nanoparticles (NPs), Sn-58Bi (SnBi) particles, and polyvinylpyrrolidone (PVP) dispersing agent, which enables pressureless, low-temperature (190–250 °C) formation of robust joints (over 7 MPa) by means of transient liquid phase sintering (TLPS). Microstructural evolution of the joint was investigated under variations in PVP molecular weight (MW; 10,000, 55,000, 360,000, or 1,300,000) and bonding conditions including temperature and time. In a die-shear test, the joint formed with PVP MW 360,000 was the strongest due to its proper particle dispersion and the formation of intermetallic compounds (IMCs). Conditions of excessive PVP MW, bonding temperature, and time impeded the bonding characteristics of the TLPS joint, with formation of voids and increasing brittleness. TLPS bonding with the optimal dispersing agent enabled pressureless die attach without chip damage, demonstrating applicability as a simple, robust interconnection for high-temperature electronics.