Effect of nano-Cr particles on solder joint properties of Sn-Zn-Bi-In/Cu brazing

Abstract

The new composite solder Sn-5Zn-10Bi-10In-xCr (x=0%, 0.1%, 0.3%, 0.5%, mass fraction) was made by adding different contents of nano-Cr particles to the Sn-Zn-Bi-In solder. The effect of nano-Cr particles on the microstructure, element distribution, phase composition and mechanical properties of brazing joints before and after aging was studied. The results show that the addition of nano-Cr particles can inhibit the growth of intermetallic compounds (IMCs) in the solder joints. With the increase of the content of nano-Cr particles, the thickness of the IMCs diffusion layer is gradually decreased; the IMCs diffusion layer at the interface near the base material Cu is Cu5Zn8 phase, and the side close to the solder zone is the Cu6Sn5 phase; as the aging time increases, the Cu5Zn8 compound on the solder side grows and is decomposed, and the Cu3Sn phase is formed; the nano-Cr particles inhibit the further growth of the IMCs diffusion layer during the aging process; as the content of Cr particles increases, the shear strength and microhardness of the solder joints increase first and then decrease. The shear strength and hardness of the Sn-5Zn-10Bi-10In-0.3Cr/Cu solder joints are the highest; the shear strength is lower than before aging, but the addition of nano-Cr particles keeps the solder joints with good shear strength. After aging, the microhardness of the solder area of the solder joints increases compared with that before aging, but it has always been maintained at below 30HV0.1.

Keywords

• lead-free solder
• wettability
• imcs
• aging
• shear strength