The study on low temperature reflow of antioxidant multicomponent solder paste on copper substrates

Low-temperature solder joints play a critical role in advanced packaging technologies by minimizing heat input and expanding the processing window for assembly. The low-temperature solder paste consisting of SnBiIn-based solder nanoparticles is particularly promising due to its reflow temperatures as low as 100 °C. However, these nanoparticles are highly prone to oxidation. To mitigate this issue, high Gibbs free energy elements, such as Ag and Zn, were mixed into the original SnBiIn nanoparticles in this work. The oxide film thickness of SnBiInZnAg nanoparticles oxidized at 45 °C for 1h can decrease to 3.88 ± 0.32 nm, indicating the doping of Ag and Zn will lead to a 20% reduction in oxidation rate for SnBiInZnAg nanoparticles compared to the unmodified SnBiIn nanoparticles. EPMA and TEM results confirm that the interfacial IMCs are η′-Cu 6 (Sn, In) 5 doped with Zn and Ag. The doped IMCs have two morphologies during the reflow process, short whisker-like and long hexagonal rods-like. The hardness of (Ag, Zn)-doped Cu 6 (Sn, In) 5 is measured at 4.72 ± 0.37 GPa, which shows good mechanical properties. Therefore, the mix of high Gibbs free energy elements (Ag and Zn) into SnBiIn nanoparticles significantly reduces oxidation, improves the reflow process, and produces in solder joints with good mechanical properties, demonstrating promising application potential in advanced packaging technologies.