| CuCGA(Copper Column Grid Array),as a device packaging form evolved from CBGA(Ceramic Ball Grid Array),is often used in large-size packaging,aerospace and other fields because of its higher thermal reliability.The manufacturing of the device requires the positioning and connection of the copper pillars of the array.The traditional manufacturing method is achieved through the mold-assisted positioning-reflow soldering;this research group tried to use the friction welding method to locate and connect the copper pillars,which got rid of the traditional CuCGA device packaging form The reliance on molds reduces the packaging cost to a certain extent and simplifies the packaging process.In CuCGA,the process of connecting the Cu pillar to the pad is called pillar planting.In this study,a high-precision micro bench drill was used to frictionally implant a 0.8 mm Cu pillar into the Sn58 Bi solder ball above the 2.4 mm diameter Cu pad.Through the analysis of the interface structure of the post-planting and post-planting solder joints,and the pull-off strength test of the post-planting and post-planting solder joints,the following conclusions are drawn:1.After the Cu pillar is friction implanted,a 0.8 μm Cu-Sn diffusion layer is formed at the interface between the Cu pillar and the Sn58 Bi solder.In the simultaneous pull-off strength test of solder joints,the average pull-off strength of solder joints was 43.02 N.2.The solder is divided into four regions according to the difference of the structure and morphology under the thermal force of the rotational friction insertion of the Cu column.Among them,the stirring zone(SZ,Stirring zone)within about 50μm from the interface,the Bi-rich phase is in the form of fine pieces,The average size is 0.89μm;the dynamic recrystallization zone(DRZ)within about 50-90 μm from the interface,the DRZ has a similar morphology to the Bi-rich phase of SZ,and the average size is 2.50μm.In the Thermo-mechanically affected zone(TMAZ)within about 90-150 μm from the interface,the grain size is slightly increased and the Bi-rich phase is lath-like due to the action of the heat machine;and the distance from the interface is about 150 μm Other than(RSZ,Reflow soldering zone),its morphology is consistent with the morphology after reflow soldering,forming a network structure.3.The average indentation hardness of SZ,DRZ,TMAZ,RSZ zone is 223 MPa,240 MPa,440 MPa,460 MPa.Because the SZ and DRZ structures are recrystallized and softened under the action of the Cu column frictional heat machine,their hardness is low;the Bi-rich phase of TMAZ is lath-like,and the hardness of the Bi phase is increased due to the hard and brittle characteristics of the Bi phase.4.The creep resistance is judged by the m value of the creep rate sensitivity index of each zone.The m values of SZ,DRZ,TMAZ and RSZ zones are 0.454,0.462,0.258,0.039,respectively.It is introduced in the text that the creep strain rate sensitivity index n is usually used to analyze the creep mechanism of solder.The n values of SZ and DRZ are 2.001 and 2.039,respectively.The creep mechanism of RZ is grain boundary slip;the n value of TMAZ is 3.73.The dislocation creep mechanism dominates the creep deformation;the n value in the RSZ zone is 8.266,and the creep mechanism is dislocation slip.5.The pull-off loads for 4/9/16/25 days aging at 75℃ are 53.3 N,54.62 N,66.33 N,61.77 N,and the pull-off loads for 4/9/16/25 days aging at 90℃ are 55.41 N and 65.12,respectively.N,67.51 N,60.92 N.As the aging time increases,the pull-off load of the solder joints gradually increases and then decreases,reaching the maximum at 9 days of aging,and the pull-off strength of the solder joints increases slowly at 16 days of aging.When aging for 25 days,because the voids increase and become larger,at the same time,as the IMC grows too thick,the strength of the solder joint decreases.6.After aging at 75/90℃,the hardness of SZ and DRZ is higher than before aging due to aging strengthening.After aging at 75/90℃,both TMAZ and RSZ indentation hardness decreased.Among them,the RSZ indentation hardness decreased most obviously.The coarse structure reduced the ability of the solder to resist dislocation movement and grain boundary slippage.After aging,the strip-shaped Bi-rich phase is coarsened,and the TMAZ strip-shaped Bi-rich phase shrinks and breaks after aging,which increases the distribution density of the Bi block.At the same time,the coarsening degree of the Bi-rich phase is significantly lower than that of RSZ.Thereby slowing down the decrease of TMAZ indentation hardness. |
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