123697.fig.003
Figure 3: Scheme of the interfacial reaction of SAC305/Cu during solder reflow: (a) dissolution of the Cu substrate, (b) supersaturation of the molten solder layer with Cu, (c) formation of the scallop-type Cu6Sn5 at the interface, and (d) Cu3Sn emerges between Cu6Sn5/Cu with prolonged soldering.