Control of interfacial reaction layers formed in Sn–3.5Ag–0.7Cu/electroless Ni–P solder joints

This study investigated a method for controlling the interfacial reaction between a Sn–3.5Ag–0.7Cu (wt.%) solder and an electroless nickel-immersion gold-plated Cu substrate through heat treatment. The interfacial reaction layer was controlled by heat treating of the electroless Ni–P plated layer. By applying a heat treatment, the thickness of the reaction layer (intermetallic compounds, P-rich Ni layer) was observed to be reduced. The formation of Ni2SnP, which significantly affects the mechanical reliability of solder joints, was suppressed.