Authors: Zhang, Q.¹; Zou, H.²; Zhang, Z.²

Source: Journal of Electronic Materials, Volume 40, Number 11, November 2011 , pp. 2320-2328(9)

Publisher: Springer

Abstract:

In this study, the influences of substrate alloying and reflow temperature on the Bi segregation behaviors at the Sn-Bi/Cu interface were investigated. Cu and Cu-Ag alloys with different Ag contents were reflowed with Sn-Bi solder at 180°C, 200°C or 220°C, and then aged at 120°C for different times. The evolution of their interfacial morphologies during the aging process was observed, and tensile tests of some solder joints were conducted. The experimental results reveal that the Bi atoms that dissolved in the Cu₆Sn₅ during the reflow process are expelled when the Cu₆Sn₅ transforms into Cu₃Sn and then segregate around the Cu₃Sn/Cu interface, inducing interfacial embrittlement. Alloying the Cu substrate with Ag can alleviate the Bi segregation by suppressing Cu₃Sn formation and dissolving the Bi atoms in the Cu-Ag substrate; the critical Ag content to eliminate the Bi segregation is about 1 at.% for the interface reflowed at 200°C. For interfaces reflowed at 180°C, the Bi segregation is less serious because less Bi is dissolved in the Cu₆Sn₅, and 0.6 at.% Ag can eliminate it. Tensile tests demonstrate that the embrittlement will not occur at Sn-Bi/Cu-Ag joints once the Bi segregation is eliminated. Based on this understanding, aging embrittlement of Sn-Bi/Cu solder joints can be prevented by decreasing the reflow temperature and adding a small amount of Ag to the Cu substrate.

Keywords: Sn-Bi solder; Bi segregation; interfacial embrittlement; substrate alloying; reflow temperature; tensile strength

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s11664-011-1742-6

Affiliations: 1: Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110016, People's Republic of China, Email: zhfzhang@imr.ac.cn 2: Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110016, People's Republic of China

Publication date: 2011-11-01

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