Research On Interconnection Process And Microstructure Of CGA Welding Column Based On Friction Welding

In the area array package,the CGA device has higher reliability than the BGA device cause it has a higher package height,better heat dissipation and less shear strain in the solder interconnect caused by thermal mismatch.Conventional CGA device packages are mostly positioned by fixture mold,and then soldered to the welding columns and pads by reflow soldering.However,the mold blocks heat transfer,which results in poor solder joints and connection quality.Based on the process and principle of friction stir welding,this paper proposes a CGA welding column interconnection process based on friction welding.The friction welding test of 63Sn37Pb solder/brass column with the welding column speed of 1600 r/min and connection time of 13 s was carried out.The overall shape,partition structure and interface of the solder joint were studied.Friction welding process was simulated via the ANSYS software and the temperature simulation results were verified by a thermocouple temperature test.This study found:1.An interface layer of about 2?m thick is formed between the brass column and the solder ball,and there are no weld defects such as gaps or cracks at the interface.2.Under the thermo-mechanical effect,the solder zone forms different shapes and sizes of microstructure.Within a range of about 40?m from the interface of the brass column,the fine-grained?-Pb phase with a size of about 1?m to 3?m is dispersed in the?-Sn matrix,and a trace amount of Zn is diffused from the brass column to the near-interface region.A small block region containing a plurality of strip-shaped?-Pb phases of about 2?m to 3?m in length is formed.The size of the granular?-Pb phase in the?-Sn matrix increases from 2?m to 5?m from the interface of 40?m to 200?m.In the range of 200?m-260?m from the interface,the?-Pb phase is parallel and long stripe,and the stripes width and spacing are 0.5?m.In the region other than 260?m from the interface,the?-Pb phase is distributed in a short rod shape or an elliptical shape.3.The simulation results show that the temperature range of the solder joints is382.37K-388.98K at the end of the feeding of the brass column,which is 83.85%-85.30%of the melting point of the 63Sn37Pb solder?456K?.The temperature field simulation results are consistent with the thermocouple test results.The test temperature value is slightly higher than the simulation results,and the maximum error value is 8.83K.4.The simulation results show that the strain concentration zone is located in the solder zone adjacent to the bottom surface of the brass column and the adjacent side,and decrease along the parallel direction of the brass column/solder interface.The strain range of the solder zone is 9.1693e^-5 mm/mm-1.2056e^-2 mm/mm,and the strain gradient is large.5.The test and simulation results integrated of temperature field and stress field distribution show that the solder/brass column interface and the near-interface solder region have the temperature conditions of elemental diffusion and the stress conditions of grain fracture,thus forming a certain thickness.interfacial connection layer.The?-Pb phase in the?-Sn matrix of the solder region exhibits a finely divided granular dispersion under thermo-mechanical effect.The large-sized granular?-Pb phase and the striped?-Pb phase at the distal end may be the result of tissue deformation under recrystallization or stress.