Effect Of Soh On The Interfacial Reaction And Reliability Of The Sn-Bi-Ag Solder Joint

Miniaturization of electronic products accelerates the process of the stand-off height (SOH) of solder joints decreasing. But due to IMCs (Intermetallic compound) intrinsic brittleness, thicker interfacial IMCs will degrade the reliability of the solder joint. So studying the interfacial reaction and the reliability of the solder joint is very important. This project comes from the National Natural Science Foundation of China, mainly investigate the effect of different SOH (100μm, 50μm, 20μm and 10μm) on the interfacial reaction and reliability.In the paper, Sn-4.8Bi-2Ag alloy was used as the lead-free solder. A high-precision device was used to control the SOH of the solder joint between two copper needles. The copper needles were connected by the reflow process. Then the specimens were aged at 150℃for different time. The effect of SOH on the reliability, which reflects by the changes of the intermetallic compound (IMC), such as the organization, morphology and the proportion of interfacial IMC layer were investigated. And the effect of the aging time (100h, 300h, 500h) on the reliability under a fixed SOH was studied too. Tensile test was also used to study the tensile strength of the solder joints.It is found that with the decreasing of the SOH, the thickness of interfacial IMC shows a slight decrease trend, and the proportion of interfacial IMC layer increases. When the SOH is 10μm, the proportion of interfacial IMC layer is 100%. With the aging time increasing, the thickness of interfacial IMC gradually increases.It is also found that with the stand-off height of the solder joint decreases, the maximum tensile strength of the solder joints decreases. When the SOH of the solder joints are 100μm, 50μm and 20μm, the tensile strength changes a little as the aging time increases. When the SOH is 10μm, tensile strength decreases with the aging time increases. In additional, with the aging time increasing and the SOH reducing, the fracture of the solder joints is firstly observed at one side of the interface between IMC and solder body, then it tends to appear at two sides of the interface between IMC and solder body, and ultimately it occur at the interface between Cu6Sn5 phase and Cu3Sn phase.