Enhancing Properties of Low-temperature Pressureless Ag Sinter-joining by Optimizing Solvents and Hybrid Particles

Wide bandgap semiconductors attract increasing attention in power modules of electric vehicles, wind energy, and high-voltage power transmission because they support higher switching frequency, higher voltage and power capability, and higher junction temperature than traditional silicon semiconductors. The high-temperature working condition (even up to 200 °C) makes traditional solder unsuitable for wide-bandgap semiconductors. Sintered Ag is considered to be reliable packaging material due to its high-temperature reliability and great electrical and thermal conductivity. Micron-Ag particles are considered to be more valuable for development due to their lower cost than nano-Ag particles. However, the low sintering driving force of micron Ag flakes makes its sintering behavior inferior to that of nano-Ag particles. This paper intends to investigate the effects of solvent and hybrid particles on the sintering behavior of micron Ag paste. It is found that the volatility, viscosity, and wettability of the solvent to the Ag powder will have an obvious effect on the electrical and mechanical properties of the Ag paste. In addition, it is proved that adding submicron particles to micron Ag flakes can reduce the porosity of sintered Ag and improve its conductivity and bonding strength. By optimizing the solvent and adjusting the content of submicron particles, the resistivity of micron Ag paste is only about 6.8 μΩ•cm and the shear strength exceeds 60 MPa after pressureless sintering at 250 °C for 30 min. The research results provide technical support for the application of micron Ag pastes.