Thermal characteristics and intermetallic compounds formed at Sn-9Zn-0.5Ag/Cu interface

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 179.5similar to191.0, 195.5similar to208.1 and 220.4similar to227.8degreesC, and the heats of fusion are 104.2, 163.9 and 151.0J/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 196.7degreesC, but the melting range and heat of fusion decrease from 12.6 to 11.3degreesC 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.