Mechanism of Interfacial Reaction for the Sn-Pb Solder Bump with Ni/Cu Under-Bump Metallization in Flip-Chip Technology

Authors: Jang, Guh-Yaw; Huang, Chien-Sheng; Hsiao, Li-Yin; Duh, Jenq-Gong; Takahashi, Hideyuki

Source: Journal of Electronic Materials, Volume 33, Number 10, 1 October 2004 , pp. 1118-1129(12)

Publisher: Springer

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Abstract:

Nickel-based under-bump metallization (UBM) has been widely used in flip-chip technology (FCT) because of its slow reaction rate with Sn. In this study, solder joints after reflows were employed to investigate the mechanism of interfacial reaction between the Ni/Cu UBM and eutectic Sn-Pb solder. After deliberate quantitative analysis with an electron probe microanalyzer (EPMA), the effect of Cu content in solders near the interface of the solder/intermetallic compound (IMC) on the interfacial reaction could be probed. After one reflow, only one layered (Ni1–x, Cux)3Sn4 with homogeneous composition was found between the solder bump and UBM. However, after multiple reflows, another type of IMC, (Cu1–y, Niy)6Sn5, formed between the solder and (Ni1–x, Cux)3Sn4. It was observed that if the concentration of Cu in the solders near the solder/IMC interface was higher than 0.6 wt.%, the (Ni1–x, Cux)3Sn4 IMC would transform into the (Cu1–y, Niy)6Sn5 IMC. The Cu contents in (Ni1–x, Cux)3Sn4 were altered and not uniformly distributed anymore. With the aid of microstructure evolution, quantitative analysis, elemental distribution by x-ray color mapping, and related phase equilibrium of Sn-Ni-Cu, the reaction mechanism of interfacial phase transformation between the Sn-Pb solder and Ni/Cu UBM was proposed.

Keywords: DIFFUSION; FLIP CHIP; INTERMETALLIC COMPOUND; PHASE TRANSFORMATION; UNDER-BUMP METALLIZATION

Document Type: Research Article

Publication date: October 1, 2004

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