Interfacial reactions between Bi-Ag high-temperature solders and metallic substrates

This study investigated the interfacial morphology and tensile properties of the joints between Bi-Ag solders and two metallic substrates, Cu and Ni. Instead of forming intermetallic compounds, grooving occurred at the intersections of Cu grain boundaries with the Bi-Ag/Cu interface and thus provided mechanical bonding. As for the Ni substrate, cellular NiBi3 was observed at the interface and also, massive NiBi3 in the form of long blades emanating from the interface was located within the solder region. A thin NiBi layer formed through a solid-state reaction between NiBi3 and the solder. The formation of those Ni-Bi intermetallics had a strong influence on the tensile strength and fracture morphology of the Bi-Ag/Ni joints.

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