Investigation On Mechanics Behavior And Microstructure Evolution Of Tin-Lead-silver Solders And Joints At Extremely Low Temperature

Deep space exploration is of great significance for the development of science,technology and human civilization.The electronic device is an important part of the deep space detector.The solder joints provide mechanical support,electrical connection and signal channel in the electronic system.Therefore,the performance and reliability of solder joints is crucial for the overall functioning of the electronic devices.Electronic devices in deep space exploration missions are subject to extreme temperature conditions,which may influence the microstructure and performance of solder joints of electronic devices.In this study,the mechanical behavior and fracture mechanisms of Sn62Pb36Ag2 and Pb88Sn10Ag2 solder and solder joints at extremely low temperatures were studied,and the microstructure evolution was also investigated.The mechanical properties of Sn62Pb36Ag2 and Pb88Sn10Ag2 solder and solder joints were evaluated by tensile test in the temperature range 20 °C to-196 °C were studied.As the temperature decreased,the ultimate tensile strength(UTS)of Sn62Pb36Ag2 solder and solder joints first increased and then decreased,reaching its maximum at-150 °C.While the UTS of Pb88Sn10Ag2 solder and solder joints gradually increased.With decreasing temperature,the ductility of the solder alloy was reduced,the fracture mode of Sn62Pb36Ag2 solder changed from ductile fracture to mixed ductilebrittle fracture,while the fracture mode of Pb88Sn10Ag2 solder was always ductile fracture.As the temperature decreased,the fracture mode of Sn62Pb36Ag2 joint changed from mixed ductile-brittle fracture to brittle fracture;and the fracture mode of Pb88Sn10Ag2 joint was always mixed ductile-brittle fracture.The impact toughness of Sn62Pb36Ag2 and Pb88Sn10Ag2 solder was evaluated by the Charpy impact test.It was found that as the temperature decreased from 20 °C to-80 °C,the impact toughness of the Sn62Pb36Ag2 solder gradually decreased.The fractographic analysis showed that the ductile-to-brittle transition temperature of Sn62Pb36Ag2 was about-30 °C.With the temperature decreasing from 20 °C to-180 °C,the impact toughness of Pb88Sn10Ag2 solder increased first and then decreased,but the fracture mode is always ductile fracture.The microstructure evolution of Sn62Pb36Ag2 and Pb88Sn10Ag2 joints and the effects on tensile properties of joints during storage at low temperatures(-100 °C and-196 °C)were investigated.For the Sn62Pb36Ag2 solder joints stored at-100 °C and-196 °C for 36 days,it was found that many Pb-rich phases near the interface were stripped off from the solder martrix.For the Pb88Sn10Ag2 solder joints,cracks occurred at the solder/IMC layer interface after storing at-100 °C and-196 °C for 9 days and 4 days,respectively,and the cracks continued to extend along the interface in the subsequent storage process.For the Sn62Pb36Ag2 and Pb88Sn10Ag2 solder joints stored at-100 °C and-196 °C,the UTS decreased with the prolonging of storage time,the fracture location of Sn62Pb36Ag2 solder joint gradually transferred to the solder matrix,while the fracture location of Pb88Sn10Ag2 solder joint gradually transferred to the interface IMC layer.