Effect of 0.5 wt% Cu in Sn-3.5%Ag Solder to Retard Interfacial Reactions With the Electroless Ni-P Metallization for BGA Solder Joints Application

摘要

Among the most advanced microelectronic packages, ball-grid-array (BGA) technology are expected to have increasing applications because of their higher input—output connection density achieved through area-array solder joints. In this study, the role of 0.5 wt % Cu in the interfacial reaction between the Sn-3.5%Ag solder and the electroless Ni-P metallization on the BGA substrate was investigated. Sn-3.5%Ag and Sn-3.5% Ag-0.5%Cu solders were reflowed on the electroless Ni-P layer at the peak temperature of 240 $^{circ}$C and the duration above 220 $^{circ}$C was 0.5 min. After reflowing, the samples were aged at 150 $^{circ}$C temperature for different times ranging from 24 h to 400 h. It was found that Cu addition retards the reaction rate with the electroless Ni-P layer significantly—especially during reflow soldering. However, among different layers formed by interfacial reactions, the P-rich Ni layer grew at a slower rate when Cu was present in the solder. Higher solder reaction rate for the Cu free alloys was explained in term of higher Ni dissolution and rapid formation of Ni $_{3}$Sn$_{4}$ .