Study of New Types Lead-Free Solder Alloys of Sn-Ag-Cu-Al-Ni and Sn-Zn-Bi-In-P

Sn-Ag-Cu lead-free solder alloy is the most potential substitute for Pb-Sn solder, while it still has problems because of its high melting point and poor application properties. We have developed new types lead-free solder alloys of Sn-Ag-Cu-Al-Ni and Sn-Zn-Bi-In-P. The properties of anti-oxidization and stability are enhanced by adding Ni, Al and P. The new Sn-Zn-Bi-In-P lead-free solder has good solderability, low melting point and the same reflow profile as the Sn-37Pb eutectic solder. The bonding strength of the Sn-Zn-Bi-In-P solder joint is 1.5 times higher than that of the Sn-37Pb solder joint. After thermal fatigue, the fatigue life of the former is 25% more than that of the latter. The microstructure and composition of the solder joint interface are also studied. A Zn-rich layer is found at the interface which can prevent the diffusion of Sn and Cu atoms, consequently decrease the thickness of the intermetallic compound layer. The results of EDX and TEM indicate that the intermetallic compound is Cu₅Zn₈ . The solder paste has been produced and tested on the production line to evaluate its performance