Long-term storage life prediction and growth kinetics of intermetallic compounds in 62Sn36Pb2Ag solder joints

Tin-based alloy solder joints are an indispensable key part of electronic products and the basis of realizing the functionalization of electronic components. The failure of an electronic product is often caused by solder joint damage. Life prediction of the solder joint is of great significance for the reliability research of electronic products. The intermetallic compound (IMC) thickness is an important parameter to evaluate the quality of solder joints. This study takes the thickness of the IMC layer and the assembly solder joints of the 62Sn36Pb2Ag QFP device as the key performance degradation parameter and the research object, respectively. After the reflowing process, Cu₆Sn₅ and Cu₃Sn IMC phases were observed at the copper lead side, and the (Cu_xNi_1-x)₆Sn₅ phase was observed at the PCB side. The evolution of interfacial microstructures was observed by a scanning electron microscope (SEM). The thickness of the IMC layer after storage at 94, 120, and 150 °C for different periods (1, 4, 9, 16, 25, 36, 49 days) was monitored. The growth process of the IMC is controlled by diffusion. As the storage time increases, the thickness of the IMC layer gradually increases. The growth rate of the IMC layer increases with the increase of the storage temperature because of the higher diffusion coefficient. Based on the Arrhenius equation, the growth kinetics model of the IMC with a bilateral interface is established. The failure density function is obtained by fitting the initial IMC thickness with a normal distribution, and the reliability function is then obtained to predict the long-term storage failure life of QFP assembly solder joints. Finally, this work calculates the median life and characteristic life of QFP assembly solder joints to be 16092 years and 17471 years, respectively. These results are expected to provide a new way to predict the life of solder joints stored for a long time and provide experimental and data support for the reliable application of the 62Sn36Pb2Ag solder.