Absorption of Ag3Sn on Cu6Sn5 intermetallic compounds at Sn-3.5Ag-xCu/Cu interfaces

The absorption behavior of Ag₃Sn particles on the surface of intermetallic compounds (IMCs) formed at Sn-3.5Ag-xCu/Cu (x=0, 0.7, 1.5 wt. %) interfaces was studied. The Sn-3.5Ag-xCu/Cu solder joints were prepared by reflow soldering at 260degC for different time. The X-ray diffraction results showed that the dominant IMCs formed at Sn-3.5Ag-xCu/Cu interfaces were Cu₆Sn₅. For Sn-3.5Ag/Cu and Sn-3.5Ag-0.7Cu/Cu joints, when the reflow time reached 120 s and 60 s respectively, besides Cu₆Sn₅, Ag₃Sn particles were also found at the interface. While for all the reflow time in this study, the Ag₃Sn particles were always detected at Sn-3.5Ag-1.5Cu/Cu interfaces. To observe the morphology of the interfacial IMCs, scanning electron microscope were performed. It was found that with the increase of the grain size of Cu₆Sn₅ the amount of absorbed Ag₃Sn particles increased. During the solidification, the Ag₃Sn particles could play the role of surface energy reducer for the interfacial Cu₆Sn₅ grains. There should be a critical grain size at which the absorption behavior of Ag₃Sn particles on Cu₆Sn₅ grains happened. According to this study, the critical grain size was determined to be about 2 mum.