Effect of foam porosity on microstructure and grain refinement by using composite solder

Due to the development of power devices, the preparation of high reliability Cu joints using high-performance lead-free solder is an effective way to address issues. In this paper, different porosity Cu-Ni foam reinforced Sn composite solder were successfully prepared. The results shown that the alloying treatment significantly improved the tensile strength of composite solder. The solid-phase transformation of (Cu,Ni)
6
Sn
5
to (Ni,Cu)
3
Sn
4
occurs in joint with the decrease of Cu-Ni foam porosity, and the growth of Cu
3
Sn layer was inhibited, thus achieving the refinement of the intermetallic compound in the joint. The mutual encouragement of phase change and grain structure led to the fast transformation of (Cu,Ni)
6
Sn
5
to (Ni,Cu)
3
Sn
4
. As the porosity of the Cu-Ni foam decreased, the Cu joint's strength steadily rose. And the soldering time was prolonged, the joint’s shear strength initially rose and subsequently fell. The shear strength of the Cu joint employing composite solder reinforced by Cu-Ni foam with a 60 percent porosity bonded for 60 minutes, reaching a maximum value of 79.9Mpa.