Effects of trace amount addition of rare earth on properties and microstructure of Sn-Ag-Cu alloys

摘要

Ternary lead free solder alloys Sn-Ag-Cu were considered as the promising alternatives to conventional SnPb alloys comparing with other solders. In the present work, effects of trace amounts of rare earth Ce on the wet-tability, mechanical properties and microstructure of Sn-Ag-Cu solder have been investigated by means of scanning electron microscopy and energy dispersive X-ray analysis systematically. The results indicate that adding trace amount of rare earth Ce can remarkably improve the wettability, mechanical strength of Sn-Ag-Cu solder joint at different temperature, especially when the content of rare earth Ce is at about 0.03%, the tensile strength will be 110% times or more than that of the lead free solder joint without rare earth Ce addition. Moreover, it was observed that the trace amount of rare earth Ce in Sn-Ag-Cu solder may refine the joint matrix microstructure, modify the Cu_6Sn_5 intermetallic phase at the copper substrate/solder interface, and the intermetallic compound layer thickness was reduced significantly. In addition, since rare earth Ce possesses a higher affinity to Sn in the alloy, adding of rare earth Ce can also lead to the delayed formation and growth of the intermetallic compounds of Ag_3Sn and Cu_6Sn_5 in the alloy.