Effect of zinc particle mixing on properties of copper–nanoparticle/bismuth–tin solder hybrid joints

The effects of Zn particle mixing into a Cu–nanoparticle/Bi–Sn solder hybrid bonding were examined. The bonding strength of an SiC/direct-bonded-copper joint exhibited limited dependence on the Zn mixing ratio, whereas that of an SiC/Cu joint increased with the Zn mixing ratio, up to 20 wt%. In the samples, Zn was present throughout the entire bonding layer, except for the Bi phase region. Bi segregation at the interface region, which occupies more volume in the SiC/Cu joints and impairs the bonding strength, reduced with the mixing ratio of Zn. Simultaneously, the volume fraction of the intermetallic compound involving Sn in the bonding layer increased. These phenomena could increase the interfacial strength, which reflects the bonding strength. However, at a Zn mixing ratio exceeding 20 wt%, the bonding strength decreased with increased Zn mixing ratio, independent of the joint structure, because of the increasing number of micro-voids generated in the bonding layer. The findings of this study indicate that mixing Zn powder into a Cu–nanoparticle/Bi–Sn solder hybrid bonding enables high bonding strength, even in joints composed of substances having strongly different thermal expansion coefficients, such as SiC and Cu.