Purpose
This paper aims to analyze the morphology transformation on the Cu3Sn grains during the formation of full Cu3Sn solder joints in electronic packaging.
Design/methodology/approach
Because of the infeasibility of analyzing the morphology transformation intuitively, a novel equivalent method is used. The morphology transformation on the Cu3Sn grains, during the formation of full Cu3Sn solder joints, is regarded as equivalent to the morphology transformation on the Cu3Sn grains derived from the Cu/Sn structures with different Sn thickness.
Findings
During soldering, the Cu3Sn grains first grew in the fine equiaxial shape in a ripening process until the critical size. Under the critical size, the Cu3Sn grains were changed from the equiaxial shape to the columnar shape. Moreover, the columnar Cu3Sn grains could be divided into different clusters with different growth directions. With the proceeding of soldering, the columnar Cu3Sn grains continued to grow in a feather of the width growing at a greater extent than the length. With the growth of the columnar Cu3Sn grains, adjacent Cu3Sn grains, within each cluster, merged with each other. Next, the merged columnar Cu3Sn grains, within each cluster, continued to merge with each other. Finally, the columnar Cu3Sn grains, within each cluster, merged into one coarse columnar Cu3Sn grain with the formation of full Cu3Sn solder joints. The detailed mechanism, for the very interesting morphology transformation, has been proposed.
Originality/value
Few researchers focused on the morphology transformation of interfacial phases during the formation of full intermetallic compounds joints. To bridge the research gap, the morphology transformation on the Cu3Sn grains during the formation of full Cu3Sn solder joints has been studied for the first time.
Two copper substrates electroplated with Sn, both consisted of Cu/Sn + Sn/Cu structures, but they were bonded over different times in order to investigate the interfacial reaction. The growth morphologies of Cu6Sn5 and Cu3Sn were analysed, respectively. The growth mechanisms for Cu6Sn5 and Cu3Sn were investigated. The results show that the growth of Cu6Sn5 is primarily controlled by grain boundary-diffusion. However, the growth Cu3Sn is controlled by the reaction of Cu-Cu6Sn5 at the beginning of the reaction, and then controlled by volume-diffusion as the thickness of the Cu3Sn layer increases.
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