| CuCGA interconnection is usually used in high frequency,high power,high I/O large chip device packaging and high reliability requirements of aviation,aerospace,military electronic devices packaging.The existing methods of column planting are based on the vertical alignment of copper pillar and pad by means of different forms of hole molds,and the reflow welding between one end of copper pillar and pad is realized by heating the solder paste printed in advance on the melted pad.Its shortcomings are poor universality of the die,high cost,poor wetting of solder joints,blowhole and so on.It is of practical significance to study the problem of column planting in CuCGA devices.A new method of planting is presented in this paper.It uses micro drilling machine to clamp the copper stud to make it move to center,rotate and drill into a certain depth of solder ball obtained by reflow soldering on the pad,and realizes stud planting connection by means of thermal-mechanical action of friction feeding during the period.Purple copper column,Sn63Pb37 and SAC305 were used as research objects.The internal microstructures of solder joints under the new post-planting method were studied,and the internal microstructures of solder joints after reflow of the new post-planting method and the tensile strength of solder joints with different solders were further compared.The study found that:1.The microstructures of Sn63Pb37 solder joints have the same change rule in different sections.According to the different microstructures,the microstructures can be divided into four regions.With the increase of distance from the Cu column,the microstructures presented in turn as fine fragments,massive,fingerprint,circular or radial.In the range of solder joint size,the range of fine fragments is the smallest,and the range of blocks and fingerprints is relatively large.The changes of the side microstructures of Sn63Pb37 solder joints after refluxing with the new column planting method are different from those of the bottom of the Cu column.The morphology of the side microstructures of the Cu column does not change with the increase of distance from the Cu column,and the obtained microstructures are massive.2.The morphology and size of the interface obtained from different cross sections of Sn63Pb37 solder joints are identical.The thickness of the interface is about 1 μm,and the interface of Sn63Pb37 solder joints is scallop-like after refluxing with the new post-planting method.The thickness of is 2 μm.3.The average drawing load of Sn63Pb37 solder joints under the new column planting method is 17 N.The average drawing load of Sn63Pb37 solder joints after reflow under the new column planting method is 72 N.The average drawing load of solder joints after reflow is 55 N higher than that without reflow.4.The microstructures of different sections of SAC305 solder joint have the same regularity.According to the different microstructures,the microstructures of SAC305 solder joint can be divided into two regions.The microstructures change from fine grains to cell-like as the distance from the copper column increases.The microstructural changes of SAC305 solder joints after reflux of new column planting method are the same as those of SAC305 solder joints after reflux of new column planting method.However,the fine grain size formed after reflux is smaller than that without reflux,and the cell size formed after reflux is larger than that without reflux.5.The morphology and size of the interface obtained from different cross sections of SAC305 solder joint are identical.They are all gray thin layers with wavelet wavy shape and thickness of about 1 μm.The interface of SAC305 solder joint was scallop-like after refluxing with the new column implanting method,and the thickness of was 2 μm.6.The average drawing load of SAC305 solder joint is 19 N under the new column planting method,80 N after reflow under the new column planting method.The average drawing load of SAC305 solder joint after reflow is 61 N higher than that without reflow solder joint. |
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