Rupture time analyses of the Sn–3.5Ag solder alloys containing Cu or Bi
✍ Scribed by Jin Yu; D.K Joo; S.W Shin
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 460 KB
- Volume
- 50
- Category
- Article
- ISSN
- 1359-6454
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✦ Synopsis
The creep rupture properties of Sn-3.5Ag based ternary alloys with varying amounts of Cu or Bi were investigated using rolled and heat-treated bulk specimens. Nominal compositions of the third element were 0% (Base), 0.5, 0.75, 1.0 and 1.5% Cu and 2.5, 4.8, 7.5 and 10% wt% Bi, respectively. The alloys generally showed the secondary and tertiary creep characteristics only, and the minimum strain rates (e ˙min ) were lowest for the 0.75 Cu specimens, and highest for the 10 Bi specimens. The stress exponents (n) of e ˙min were usually around 4 ± 1, with the exception of the 0.5 Cu and 0.75 Cu alloys with n ϭ 6.0ෂ7.6, and the 10 Bi alloy which showed n ~2. Fractographic analyses revealed typical creep rupture by the nucleation and growth of cavities in the matrix for the Base and Cu-containing alloy except the 1.5 Cu specimens, which showed cavity nucleation by the cracking of brittle Cu 6 Sn 5 particles. On the other hand, all the Bi-containing alloys showed cavity nucleation on grain boundaries due to the segregation of Bi to the β-Sn grain boundaries. Subsequent rupture time analyses showed that creep rupture by necking could predict rupture times of the Base and the Cu-containing alloys reasonably, and that the model based on the continual nucleation of cavitating facets could explain the rupture times of the Bi-containing alloys reasonably well. The Kachanov equation made reasonable predictions of the rupture time for all cases.