Elimination of pores in Ag–Sn TLP bonds by the introduction of dissimilar intermetallic phases

Abstract

Low-temperature transient liquid phase (TLP) bonding is a very promising technology for achieving die attachment in high-temperature power devices. However, the Ag–Sn TLP-bonded joint has high sensitivity to shrinkage pores, which will lead to the deterioration of mechanical, thermal, and electrical properties. In this study, we have proposed two novel methods to solve the problem of pores in Ag–Sn TLP bonding through the introduction of second phases. The first method is replacing Ag substrate on one side with Cu substrate to create dual layers of dissimilar intermetallic compounds (IMCs). Consequently, the dual layers of Cu6Sn5 (or Cu3Sn) and Ag3Sn IMCs emerge on the cross-sections of bonded joint, resulting in the effective elimination of pores, which can be attributed to the change of the microstructure and the interface migration between two dissimilar IMC layers (e.g., Cu6Sn5/Ag3Sn). The second method is coating a thin Cu film on the Ag substrate to introduce Cu–Sn IMC particles. As a result, a great number of Cu6Sn5 particles disperse in the middle of the Ag3Sn layer, filling the micropores efficiently, such that a significant decrease in shrinkage pores is achieved. Both methods have been experimentally verified to improve the mechanical properties, and they have high potential to be implemented in other TLP systems.