Sn-0.7Cu-10Bi Solder Modification Strategy by Cr Addition

Abstract

The application of Sn-0.7Cu-based composite solder in electronic packaging is limited due to its high melting point, poor wettability and low mechanical properties. Herein, we propose a strategy of adding Bi and Cr to improve the solderability of Sn-0.7Cu lead-free solder. The results show that the addition of Bi reduces the melting point of the composite solder. Moreover, the Cr particles adsorb at the interface between solder and substrate, thereby reducing the wetting angle of the composite solder. The wetting angle reaches a minimum value of 25.84° when the content of Cr is 0.2 wt.%. The addition of Bi and Cr changes the microstructure of the composite solder. The nucleation rate of β-Sn rises with the increase of Cr content, thus decreasing the size of β-Sn. Furthermore, the addition of Bi and Cr reduces the thickness of the intermetallic compounds (IMCs). This is due to the adsorption of Bi and Cr at the interface of IMCs hinders the atomic diffusion channels and inhibits the growth of IMCs.