Effect of Ni concentration on solderability, microstructure and hardness of SAC0705-xNi solder joints on Cu and graphene-coated Cu substrates

In this paper, solderability, microstructure and hardness of SAC0705-xNi solder joints on Cu and graphene-coated Cu (G-Cu) substrates were studied. As Ni content increases in the solder, the solderability improves gradually on both the Cu and G-Cu substrates. The solderability of SAC0705-xNi is better on G-Cu substrate than that on Cu substrate. The increasing Ni content in the solder has a positive effect on the microstructure refinement of both the kinds of substrates. Such effect is more significant on G-Cu substrate than that on Cu substrate. With the increase of Ni content, the thickness of the interfacial intermetallic compound (IMC) shows an increasing trend first and then decreasing trend on the two kinds of substrates. Since the graphene layer works as a diffusion barrier, the IMC on G-Cu is thinner than that on Cu substrate. The addition of Ni leads to the strengthening of the microstructure and thus increases the hardness of the solder bulks.