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Interface reactions and phase equilibrium between Ni/Cu under-bump metallization and eutectic SnPb flip-chip solder bumps

Published online by Cambridge University Press:  06 January 2012

Chien-Sheng Huang
Affiliation:
Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China
Jenq-Gong Duh
Affiliation:
Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China
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Abstract

Ni-based under-bump metallization (UBM) for flip-chip application is widely used in today's electronics packaging. In this study, electroplated Ni UBM with different thickness was used to evaluate the interfacial reaction during multiple reflow between Ni/Cu UBM and eutectic Sn–Pb solders in the 63Sn–37Pb/Ni/Cu/Ti/Si3N4/Si multilayer structure. During the first cycle of reflow, Cu atoms diffused through electroplated Ni and formed the intermetallic compound (IMC) (Ni1−x, Cux)3Sn4. After more than three times of reflow, Cu atoms further diffused through the boundaries of (Ni1−x, Cux)3Sn4 IMC and reacted with Ni and Sn to form another IMC of (Cu1-y, Niy)6Sn5. After detailed quantitative analysis by electron probe microanalysis, the values of y were evaluated to remain around 0.4; however, the values of x varied from 0.02 to 0.35. The elemental distribution of IMC in the interface of the joint assembly could be correlated to the Ni–Cu–Sn ternary equilibrium. In addition, the mechanism of (Cu1−y, Niy)6Sn5 formation was also probed.

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Articles
Copyright
Copyright © Materials Research Society 2003

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