Effect of Thermal Treatment on the Intermetallic Compounds Formed at Sn-9Zn-1.5Ag-xBi (x = 0 and 1) Lead-Free Solder/Cu Interface

Abstract

The formation of Intermetallic compounds (IMCs) at the interface between an Sn-9Zn-1.5Ag-xBi solder alloy and a Cu substrate dipped at 250 C and heat-treated at 150 C for various times has been investigated by an optical microscope (OM), an X-ray diffractometer (XRD) and a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS). The OM result shows the flat and smooth surface for the Sn9Zn-1.5Ag-1Bi solder alloy and Cu substrate after dipping at 250 C. The phases of IMCs formed are Cu 6 Sn 5 and Cu 5 Zn 8 for both lead-free solder alloys. After thermal treatment at 250 C for 200 h, the phases of IMCs are Cu 6 Sn 5 , Cu 5 Zn 8 and Ag 3 Sn. The Cu 6 Sn 5 has a scallop morphology, and is located at the interface between the solder and Cu substrate. The adhesion strength for the Sn-9Zn-1.5Ag-1Bi lead-free solder alloy is higher than the Sn-9Zn-1.5Ag solder alloy. After being heat-treated at 150 C, the adhesion strength of the Sn-9Zn-1.5Ag-1Bi solder alloy decreases from 12:67 AE 0:45 to 6:92 AE 0:38 MPa after thermal treatment for 200 h.