Ultrasonic-Assisted Soldering of Sn-Based Solder Alloys to Form Intermetallic Interconnects for High Temperature Application

Wide band gap semiconductors, such as SiC, GaN, etc. can provide power electronic systems with increased power densities, high reliability in extreme environments and higher integration density, and have been receiving considerable attentions to replace Si power semiconductor devices. High power, high service temperature are the characteristics of these semiconductors, however, these make big challenges for the interconnections between the semiconductor die and the substrate. Novel interconnection materials without lead have been developing, including novel solder alloys, such as Au-Sn, Au-Ge, Bi-Ag, Zn-Al, etc. and metallic nanoparticles (NPs), such as Ag NPs, Cu NPs, etc. Corresponding interconnection methods can be divided into soldering, transient liquid phase (TLP) bonding and sintering. Indeed, materials research and development obviously is effective for solving the present challenges. Novel techniques are another important way for wide band gap semiconductors packaging. Thus, different from the traditional Sn-based soldering (commonly resulting in an interconnect possessing a low-melting temperature similar to the soldering temperature), this work reports a fabrication method of forming intermetallic compound (IMC) interconnect through ultrasonic-assisted soldering with traditional Sn-0.7wt.%Cu solder alloy. A (Cu, Ni) 6Sn5 ternary IMC joint was fabricated at 250°C for 10s. The thermal conductivity of the IMC joint was 75.8W/(m·K), which was approximately 3 times higher than the joint obtained by traditional reflow [20W/(m·K)]. The IMC joint can be served at the temperature less than 332°C (0.8 times of the melting point).