Sn-Based Solder Joints Property And Life Prediction In Extremely Low Temperature

With the development of China’s aerospace industry, the exploration of outer space keeps pushing forward with the development of high reliability electronic devices. Due to deep space work, the electronic devices experience a complex external environment, mechanical environment, thermal environment, space radiation environment, where the temperature difference between day and night, and the fast rate of changing may result in devastating failure of solder electronic devices. And previous studies have focused on-55℃~+125℃ temperature range, less for the cryogenic temperature research. All of these demands and the factors have prompted a series of reliability research in cryogenic temperature solder.According to the above requirements, mechanical performance test was performed on 63Sn37Pb/Cu and Sn3.0Ag0.5Cu/Cu solder joint, and the temperatures were 20℃,-50℃,-100℃,-150℃ and-196℃, and the strain rates were 0.01/s and 0.001/s. Another test was tensile properties and microstructure evolution research of solder joints after ultra-low temperature(-196℃) storage. Finite element simulation of CBGA and CQFP were applied to get stress distribution and life expectancy under extreme low temperature thermal shock. Then get the mechanical properties at ultimate low temperature, microstructure and IMC evolution in internal solder joints and solder joint failure modes and failure mechanisms under extreme thermal shock temperature.The results showed that the tensile strength of the two solder joints increased fist then decreased with decreasing temperature. The tensile strength of solder joints were higher at higher strain rate, and tensile strength of solder joints at low temperature were higher then these at room temperature. At different temperatures and strain rates, corresponding to the two solder joints’ fracture SEM and EDX analysis,results showed that at room temperature solder joints fractured in bulk solders, with a mode of ductile fracture, while at low temperature fractured in IMC/solder interface and IMC layer, presenting brittle fracture mode. Description Both joints are brittle transition at a certain low temperature occurred. The lower the temperature was, the greater the strain rate was, the brittle fracture phenomenon was easier to happen.In ultra-low temperature(-196℃) storage for 25 days, the IMC didn’t change, no growth, no shrink, no fracture. Meanwhile, the solder matrix microstructure did not change, indicating-196 ℃ storage for 25 days Sn Pb/Cu and Sn Ag Cu/Cu solder joints unchanged. Moreover, cryogenic temperature storage rarely had effects on the tensile strength, the fracture location and the fracture mechanism of the two solder joints.Finite element simulation was applied on Sn63Pb37 and SAC305 solders, two types of electronic devices BGA and QFP at cryogenic temperature with large temperature difference. With the same type of device, SAC305 solder had higher life prediction. With the same solder, QFP device had higher lifetime. But life prediction of BGA and QFP were much low than the same device experiencing the temperature range of-55℃~125℃, the values were 1/7 and 1/3 of the latter respectively.