Interactions between Sn and Cu substrate with various surface finishes

Lai Wei-Han,Wang Chao-Hong,Shen Han-Ting

doi:10.1109/impact.2010.5699619

Abstract

In this paper, the reaction couples were prepared to investigate the interaction between Sn and Cu substrate with various surface finishes. The studied interfacial systems contain Sn/Ni/Ag/Cu, Sn/Ag/Cu and Sn/Cu/Ag/Cu. The corresponding surface finish, Ag or Ni layer, is about 1~2μM. In the Sn/Ni/Ag/Cu reaction, the formed phase was Ni 3 Sn 4 at first, indicating that Sn reacted with Ni at the Sn/Ni interface. Sequentially, as the limited Ni layer was consumed completely, Sn kept diffusing across the Ni 3 Sn 4 and reacted with Ag layer to form Ag 3 Sn. Further, Sn diffused into Cu substrate and produced Cu 6 Sn 5 and Cu 3 Sn. Meanwhile, Cu also diffused toward the opposite direction and then caused the prior Ni 3 Sn 4 layer to gradually transform to (Cu, Ni) 6 Sn 5 . The (Cu, Ni) 6 Sn 5 layer growth thickness depends on the initial Ni layer. Notably, the original continuous Ag 3 Sn layer became the discontinuous particulates and intercalated in-between (Cu, Ni) 6 Sn 5 and Cu 6 Sn 5 . For comparison, the result in the Sn/Ag/Cu specimen revealed the Ag 3 Sn layer remained continuous and no Cu 6 Sn 5 was accumulated at the Sn/Ag 3 Sn interface. Moreover, the total thickness of Cu 6 Sn 5 and Cu 3 Sn layers in Sn/Ni/Ag/Cu is much smaller than that of the Sn/Cu. The initial reaction rate at the interface with the Ni/Ag surface finish is relatively slow. Nevertheless, after the Ag layer is consumed to form Ag 3 Sn, Cu would be induced by the Ni 3 Sn 4 to rapidly form the thicker (Cu, Ni) 6 Sn 5 layer.

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