The effects of Zn addition to Sn-0.7Cu are investigated, focusing on their interfacial reactions, microstructure and mechanical properties, when reacted with Ni-P under bump metallurgies (UBMs). The Zn content in Sn-0.7Cu-xZn varies as 0.2, 0.4 and 0.8 (in wt %). In the reaction with Ni-P UBMs, (Cu,Ni)6Sn5 intermetallic compounds (IMCs) are formed at the interface of the Sn-0.7Cu solder, while (Cu,Ni,Zn)6Sn5 IMCs in the Zn-doped solders. As the Zn content increases, the interfacial IMC growth is gradually reduced, yielding a reduction of 40-50% for 0.8% Zn. The same IMC particles are also observed in the matrix of each solder. In Sn-0.7Cu, (Cu,Ni)6Sn5 particles coarsen largely during aging, while (Cu,Ni,Zn)6Sn5 particles in the Zn-added solders are less coarsened and remain much smaller than (Cu,Ni)6Sn5. The growth of (Cu,Ni)6Sn5 during thermal aging is significantly suppressed by Zn addition. In addition, such a microstructure in the Zn-doped solders with Ni-P produces the stable mechanical properties, such as hardness and shear strength, during thermal aging.
By: Moon Gi Cho; Sung K. Kang; Sun-Kyoung Seo; Da-Yuan Shih; Hyuck Mo Lee
Published in: RC24849 in 2009
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