Process Simulation And Characterisation Of Solder Joint Organisation For CGA Friction Welding Column

Column Grid Array(CGA)is the preferred form of large size package,which is widely used in aerospace and military industry due to its good heat dissipation,excellent electrothermal performance,higher interconnection density and reliability.The traditional grid array requires the mold to position the column,and realizes the column connection through reflow welding.Our research group proposes a new column connection process based on friction welding principle,which can effectively simplify the packaging process and save costs.In the welding process,the solder joint size is small,and the temperature change near the interface is difficult to measure by test.In this paper,ABAQUS finite element analysis software was used to simulate the process of forming Sn37Pb/Cu,SAC305/Cu,SAC305/Fe-Cr-Ni alloy solder joints at the speed of 5000 r/min,and the friction stud technology was studied by combining numerical simulation and experiment.At the same time,the SAC305/Fe-Cr-Ni solder joint was subjected to 120?isothermal aging treatment to analyze the solder joint reliability.Simulation results show that the temperature fields of solder joints of different materials are basically symmetric along the center of the solder column,and the highest temperature of solder joints is located below the center of the bottom surface of the solder column and the middle position of the edge of the solder column.The peak temperatures of Sn37Pb/Cu,SAC305/Cu and SAC305/Fe-Cr-Ni alloys are 122.9?(87.04%of the melting point of 456.15 K),145.5?(85.61%of the melting point of490.15 K)and 114.3?(79.02%of the melting point of 490.15 K).The results of local thermocouple temperature measurement test are similar to the temperature trend obtained by simulation,and whose error is within 9%.The inner area far from the surface of the welding column and close to the lower part of the welding ball is the stress concentration area,and the stress value is the highest.The maximum equivalent stress of Sn37Pb/Cu,SAC305/Cu,SAC305/Fe-Cr-Ni alloy welding spot is 34.95 MPa,45.67 MPa,45.21 MPa,respectively.With the increasing of the overall temperature of the solder joint,the stress is released and the stress gradient is smaller,and the maximum equivalent stress in the solder joint gradually decreases to 23.8 MPa,33.47MPa and 37.46 MPa at the end of welding.According to the microstructure characteristics of Sn37Pb/Cu solder joints obtained from the test results,the solder joints are divided into four regions under the action of thermodynamic coupling.The mixing zone is about 0-50?m away from the interface,where the microstructure of the solder is fine and the grain size is small,resulting in plastic flow.Combined with the simulation results,it can be seen that this region is in a state of high temperature and large strain,and the maximum temperature exceeds the critical point of recrystallization,which has the conditions for recrystallization.The distance from the interface is about 50-110?m heat engine influence zone;About 110-250?m from the interface is the stretch zone;The base metal area is about 250?m away from the interface.The IMC layer at the solder joint interface of SAC305/Fe-Cr-Ni alloy is not obvious and the solder joint strength is 30.3 N.After isothermal aging at 120?for4/9/16/25/36 days,the average thickness of IMC layer was 2.11?m,3.04?m,3.62?m,3.92?m and 4.15?m,respectively,which was intermetallic compound Fe Sn₂.After aging,the solder joint strength is significantly improved,which is 56.1 N,61.1N,65.9 N,63.6 N,62.5 N,respectively.After 25 days of aging,the solder joint strength increased by 117.5%compared with the strength of unaging.The growth rate of IMC layer of SAC305/Fe-Cr-Ni solder joint is lower than that of SAC305/Cu solder joint,which effectively reduces the solder joint failure risk caused by the growth of too thick interface layer,and is also in line with the practical application of electronic components in high temperature conditions for a long time.