Development of fluxes for lead-free solders containing zinc
New lead-free solders based on the Sn-Zn eutectic (92 wt. pct Sn - 8 wt. pct Zn) are promising candidates to replace near-eutectic tin-lead solders because these solders are less expensive than alternatives such as Sn-Ag eutectic base solders and the melting point of the tin-zinc eutectic (198 C) is much closer to melting point of commonly used tin-lead eutectic (183 C) than the melting point of the Sn-Ag eutectic (221 C). Solders based on the Sn-Zn eutectic have been shown to have excellent mechanical properties. However, the Zn-bearing solders oxidize easily during soldering and for this and perhaps other reasons the contact angle on copper for Sn-Zn solders is rather high when utilized with fluxes used for Sn-Pb solders. Tin chloride containing fluxes give satisfactory wetting of Sn-Zn eutectic solders on Cu but tin chloride is corrosive and, therefore, unacceptable as a flux for electronic applications. Development of a non-corrosive flux that gives satisfactory wetting of copper surfaces by tin-zinc eutectic solders is thus needed. At the present time tin or tin-lead solders are used for pre-tinning. This procedure adds to the production cost. Also Sn-Pb coatings are unacceptable for a lead-free soldering system. As this paper demonstrates, a tin containing organic compound that decomposes at soldering temperatures to produce metallic tin on surfaces to be soldered can be added to the flux to improve wetting of Sn-Zn eutectic solder on Cu. It may also be used for general pretinning purposes done before soldering.
- Research Organization:
- Northwestern Univ., Evanston, IL (US)
- OSTI ID:
- 20006429
- Journal Information:
- Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 12 Vol. 41; ISSN 1359-6462; ISSN SCMAF7
- Country of Publication:
- United States
- Language:
- English
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