Thermal behavior and microstructure of the intermetallic compounds formed at the Sn–3Ag–0.5Cu/Cu interface after soldering and isothermal aging

The thermal behavior and microstructure of the intermetallic compounds formed at the Sn–3Ag–0.5Cu/Cu interface after soldering at 250 °C for 60 s and aging at 150 °C for various times have been investigated by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and pull-off testing. The DSC result shows that the solidus and liquidus temperatures of the Sn–3Ag–0.5Cu solder alloy are 217 and 221 °C, respectively. The melting range of the Sn–3Ag–0.5Cu is 4 °C smaller than 8.5 °C for the Sn–37Pb solder alloy. The major intermetallic compounds are monoclinic η′-Cu6Sn5, hexagonal η-Cu6Sn5 and Ag3Sn when aged at 150 °C for 0–300 h. When aged for 100–300 h, the morphology of Cu6Sn5 transforms from scallop-shaped to planar. The thickness of Cu6Sn5 increases from 4.1±0.4 to 7.8±0.3 μm when aging time increases from 0 to 300 h. The maximum and minimum adhesion strengths are 12.44±0.53 and 2.22±0.46 MPa, respectively, for as-soldered and aged (150 °C for 300 h) ones.