Effect of Ag Addition on the Ripening Growth of ${\rm Cu}_{6}{\rm Sn}_{5}$ Grains at the Interface of Sn-xAg-0.5Cu/Cu During a Reflow

Moon Gi Cho,Yong Sung Park,Hyuck Mo Lee,Sun-Kyoung Seo,Kyung-Wook Paik

doi:10.1109/tcpmt.2011.2160181

Abstract

The ripening growth (or lateral growth) of Cu 6 Sn 5 grains that form between molten Sn-rich solders and Cu under-bump metallurgies (UBMs) was investigated with Sn-0.5Cu, Sn-1.0Ag-0.5Cu, and Sn-3.0Ag-0.5Cu solders. After reactions with Cu UBMs, the size and morphologies of Cu 6 Sn 5 grains were compared with each other through the observation of the top views. The Cu 6 Sn 5 intermetallic compounds (IMCs) that form at the interface of Sn-3.0Ag-0.5Cu solders exhibit much smaller grains, though the thickness of the grains is similar to that of the grains that form in Sn-0.5Cu and Sn-1.0Ag-0.5Cu solders. In other words, the ripening growth of Cu 6 Sn 5 grains during a reflow is reduced in Sn-3.0Ag-0.5Cu solders. The effects of Ag on the ripening growth of Cu 6 Sn 5 grains were examined by comparing the angles of two neighboring Cu 6 Sn 5 grains that formed at the interface of each solder, in addition, the interfacial energies between the Cu 6 Sn 5 grains and the molten solders are discussed. The effect of Ag on the ripening growth of the Cu 6 Sn 5 grains depends on the solder volume: as the volume increases, the ripening growth of the Cu 6 Sn 5 IMCs at the interface is reduced more effectively, and small Cu 6 Sn 5 grains are produced during the reflow. The tendency of the way smaller Cu 6 Sn 5 grains to reduce the formation of Cu 3 Sn IMCs during thermal aging is also discussed.

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