Effect of microstructural evolution on electrical property of the Sn-Ag-Cu solder balls joined with Sn-Zn-Bi paste

Sn-8Zn-3Bi solder paste and Sn-3.2Ag-0.5Cu solder balls were reflowed simultaneously on Cu/Ni/Au metallized ball grid array (BGA) substrates. The correlation between microstructural evolution and the electrical resistance of the joints under various testing conditions of reflow cycles and heat treatment was investigated. The electrical resistance of the Sn-Ag-Cu joints without Sn-Zn-Bi was also conducted for comparison. The average resistance values of Sn-Ag-Cu and Sn-Ag-Cu/Sn-Zn-Bi samples changed, respectively, from 7.1 (single reflow) to 7.3 (10 cycles) mO and from 7.2 (single reflow) to 7.6 (10 cycles) mO. Furthermore, the average resistance values of Sn-Ag-Cu and Sn-Ag-Cu/Sn-Zn-Bi samples changed, respectively, from 7.1 (aging 0 h) to 7.8 (aging 1000 h) mO and from 7.2 (aging 0 h) to 7.9 (aging 1000 h) mO. It was also noticeable that the average resistance values of Sn-Ag-Cu/Sn-Zn-Bi samples were higher than those of Sn-Ag-Cu samples in each specified testing condition. The possible reasons for the greater resistance exhibited by the Sn-Zn-Bi incorporated joints were discussed.