2004 Volume 45 Issue 3 Pages 606-613
The thermal characteristics of various Sn-based solder alloys and intermetallic compounds (IMCs) formed at the Sn-9Zn-0.5Ag/Cu interface have been investigated by using differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy, energy dispersive spectrometry, transmission electron microscopy and electron diffraction. The melting ranges of the Sn-37Pb, Sn-9Zn and Sn-3.5Ag alloys are 179.5∼191.0, 195.5∼208.1 and 220.4∼227.8°C, and the heats of fusion are 104.2, 163.9 and 151.0 J/g, respectively. When 0.5 mass% Ag is added to the Sn-9Zn alloy, the melting temperature of the solder alloy increases from 195.5 to 196.7°C, but the melting range and heat of fusion decrease from 12.6 to 11.3°C and 163.9 to 74.7 J/g, respectively. The IMCs formed at the Sn-9Zn-0.5Ag/Cu interface are determined as a scallop-shaped Cu6Sn5 near the solder alloy, a flat Cu5Zn8 close to the Cu substrate and Ag3Sn particles between the Cu substrate and Cu5Zn8 layer. The Cu6Sn5 is bi-structural, namely, hexagonal and monoclinic, which is caused by the Ag dissolution in the Cu6Sn5 layer.