Microstructure and defect analysis of tin coating of hot-dip tin-plated electronic copper strip during reflow soldering
Hot-dip tin-plated electronic copper strip is a key conductor material for high-end connectors and PCB(Printed circuit board),and the defects generated during reflow soldering seriously affect its service performance.Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)were used to characterize the types and distribution morphology of defects in the hot-dip tin-plated copper strip during reflow soldering.The surface morphology of reflow soldering solder bead samples,abnormal reflow soldering samples and normal reflow soldering samples was compared.The results show that during the reflow soldering,there are varying degrees of hole defects in the sample coating,with the hole sizes ranging from 0.2 to 36 μm.There is no obvious correlation between the formation of holes and the type of substrate alloy,the thickness of substrate alloy and the thickness of coating.The morphology of the holes is not consistent,and it is found that the edges of the holes exhibit a three-dimensional network structure,with uneven edges and the presence of small particles in the holes.During the reflow soldering,Cu and Sn elements in the tin plating layer are redistributed,and the distribution of elements caused by different defects is not the same.In the coating structure,there is no significant correlation between the height fluctuations of the compound layer and multiphase interface and the surface height fluctuations of the coating.
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