Research On Process Simulation Of Friction Welding Pillar Planting Of CuCGA Devices And Post-weld Heat Treatment

CuCGA has the advantages of high packaging density,good heat dissipation,and thermal fatigue resistance.It is widely used in high-end electronic packaging fields such as military,aviation and aerospace.At present,the method of planting Cu pillars is mainly to locate the Cu pillars in an array with the help of a mold device,and then realize the connection of the planting pillars by reflow soldering.Due to the high cost of the mold device,this research group proposed a method to realize the Cu pillars and the Cu pillars using a micro drilling machine.The method of centering and positioning of the solder ball,using the friction heat engine between the Cu column and the solder ball under high-speed rotation to realize the connection of the planting column.Due to the small size of the solder joints,it is difficult to monitor the temperature change of the solder joints during the process of Cu column friction planting through experimental methods.This paper uses ANSYS simulation software to simulate the pure Cu column with Sn37 Pb solder ball and SAC305 solder at 2400r/min.The friction planting process of the ball,and the temperature field simulation results are corrected in combination with the experiment;considering that the Cu post friction planting time is short,which may not be conducive to element diffusion,the effect of post-weld heating treatment on the interconnection strength of Cu column solder joints is studied influences.Research indicates:1.The highest temperature of Sn37 Pb connector and SAC305 connector is distributed in the edge area of the bottom surface of the copper column.The solder temperature near the copper column is higher,and the temperature gradient is larger.The temperature cloud pattern is cup-shaped,and the highest temperature of the Sn37 Pb connector reaches 402.14 K,which is 88.16% of the melting point(456.15 K)of Sn37 Pb solder;the highest temperature of SAC305 joint reaches 419.71 K,which is 85.63% of the melting point(490.15 K)of SAC305 solder.The error between the experimental temperature measurement result and the temperature field simulation result is within 2%.2.The maximum strain level of Sn37 Pb joint and SAC305 joint is located at the position where the bottom edge of the copper column is in contact with the solder,followed by the solder area in contact with the side of the copper column.The strain range of Sn37 Pb joint is 3.1915e-4?0.08301;the strain range of SAC305 joint is3.1125e-4?0.12485,and the strain gradient varies greatly.3.In the process of friction welding column planting,the solder flow rate of Sn37 Pb joint and SAC305 joint near the edge of the copper column side and bottom surface is relatively high,and the solder flow velocity decreases rapidly with the increase of the distance from the copper column.The distribution trend is similar.The solder flow rate of Sn37 Pb joints varies from 0 to 33.17 mm/s,and the solder flow rate of SAC305 joints varies from 0 to 30.15 mm/s..4.Combining the above simulation results of the temperature field and strain field with the microstructure and morphology characteristics of the solder joints,it is judged that the solder area near the copper column has undergone plastic flow and recrystallization softening during the friction welding column planting process,and the joint strength is not high.5.In the process of friction welding column planting,the maximum equivalent stress of Sn37 Pb joint and SAC305 joint is located in the area where the bottom edge of the copper column is in contact with the solder.Secondly,the stress values of the middle local area on the surface of the solder ball and the middle local area at the bottom of the solder ball are also relatively high.After welding,the maximum residual stress of the two joints is located in the area where the bottom edge of the copper column is in contact with the solder.Secondly,the residual stress in the area where the side of the copper column is in contact with the solder is also larger.The maximum residual stress of the Sn37 Pb joint is 36.95 MPa,and the SAC305 joint The maximum residual stress is 53.256 MPa.6.After the copper pillar solder joints were heated at 120 ? for 30 min,the average pull-off load of the Sn37 Pb joint and SAC305 joint increased from 28.9 N and 32.5 N to 71.9 N and 78.4 N,respectively,and the average thickness of the interface layer increased from 0.32 ?m and 0.36 ?m to 2.35 ?m and 2.51 ?m;indicating that sufficient atom diffusion can significantly increase the joint strength of the joint;with the increase of heating temperature and heating time,the strength of the two joints shows a trend of increasing first and then decreasing.