Morphology and adhesion strength of the Sn–9Zn–3.5Ag/Cu interface after aging

Abstract

The microvoids formation and morphology of intermetallic compounds formed at the Sn–9Zn/Cu interface with and without Ag addition have been investigated by scanning electron microscopy and energy dispersive spectrometry and pull-off test. The microvoids are formed at the Sn–9Zn/Cu interface after aging at 180°C for 100h and at the Sn–9Zn–3.5Ag/Cu interface after aging at the same temperature for 1000h. The formation of the microvoids is inhibited by Ag addition. After aging at 180°C for 1000h, the planar Cu6Sn5 and scallop-shaped Cu6Sn5 are observed at the Sn–9Zn/Cu and Sn–9Zn–3.5Ag/Cu interfaces, respectively. The decomposition rate of the Cu5Zn8 and the growth rate of the Cu6Sn5 at 180°C at the Sn–9Zn/Cu interface are determined as 2.22 × 10−9 and 6.80 × 10−10ms−1/2, respectively, and those at the Sn–9Zn–3.5Ag/Cu interface are determined as 8.61 × 10−10 and 5.40 × 10−9ms−1/2, respectively. The adhesion strength of the Sn–9Zn–3.5Ag/Cu interface increases from 5.76 ± 0.77 to 14.19 ± 0.75MPa when aging time increases from 0 to 1000h and shows a better solder joint reliability than the Sn–9Zn solder alloy.