Interfacial Reactions and Joint Strengths of Sn-xZn Solders with Immersion Ag UBM

Authors: Jee, Y.¹; Yu, Jin²

Source: Journal of Electronic Materials, Volume 39, Number 10, October 2010 , pp. 2286-2291(6)

Publisher: Springer

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Abstract:

The solder joint microstructures of immersion Ag with Sn-xZn (x = 0 wt.%, 1 wt.%, 5 wt.%, and 9 wt.%) solders were analyzed and correlated with their drop impact reliability. Addition of 1 wt.% Zn to Sn did not change the interface microstructure and was only marginally effective. In comparison, the addition of 5 wt.% or 9 wt.% Zn formed layers of AgZn₃/Ag₅Zn₈ at the solder joint interface, which increased drop reliability significantly. Under extensive aging, Ag-Zn intermetallic compounds (IMCs) transformed into Cu₅Zn₈ and Ag₃Sn, and the drop impact resistance at the solder joints deteriorated up to a point. The beneficial role of Zn on immersion Ag pads was ascribed to the formation of Ag-Zn IMC layers, which were fairly resistant to the drop impact, and to the suppression of the brittle Cu₆Sn₅ phase at the joint interface.

Keywords: Solder joint microstructure; Zn; immersion Ag; drop impact reliability

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s11664-010-1308-z

Affiliations: 1: Department of Material Science and Engineering, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, Korea 2: Department of Material Science and Engineering, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, Korea, Email: jinyu@kaist.ac.kr

Publication date: 2010-10-01