A high-remelting-point interconnect method based on porous copper and Sn42Bi58 solder

Step soldering is typically employed during the packaging process for some electronic components. In conventional step soldering, the melting point is controlled by adjusting the composition of the alloy to ensure a sufficient temperature gap, resulting in a complex process. In addition, components requiring low-temperature soldering are difficult to achieve step soldering by this method. In this study, a novel interconnect method based on porous copper and Sn42Bi58 solder was proposed to resolve these problems. The joints were soldered at 160 °C for 10 min, but their remelting point exceeded 138 °C. The submicron porous copper was infiltrated by the Sn-Bi solder, and the Cu skeleton reacted with the Sn phase to form Cu-Sn IMC. Due to the enormous specific surface area of the porous copper, the Sn phase was consumed rapidly. The joint is mainly composed of Cu6Sn5 phase, Bi phase and a small amount of Cu phase. The shear strength of the joint at 150°C can reach 15 MPa, and the fracture mode is brittle fracture. Thus, this work demonstrates the feasibility of interconnection methods based on porous copper and Sn-Bi solder for step soldering applications.