SMTA International Conference Proceedings


ENHANCING THE TARNISH PERFORMANCE OF IMMERSION SILVER FINISHES

Authors: Elizabeth Norwood and John Swanson
Company: MacDermid, Inc.
Date Published: 9/25/2005   Conference: SMTA International


Abstract: In recent years, a variety of lead-free finishes for PWB "final finish" applications have emerged. Among these options is Immersion Silver. Significant commercial implementation of immersion silver began approximately 3-4 years ago, and it is now clear that this finish is gaining noteworthy popularity. Immersion silver is emerging as a preferred Pb-free finish due to the breadth of its appeal and its suitability for evolving PWB technologies.

A welldesigned and controlled immersion silver process presents minimal operational and implementation drawbacks; it compares favorably to other Pb-free surface finish alternatives such as OSP, ENIG, and Immersion Tin. One potential drawback that is often discussed is classic silver tarnish. Tarnishes naturally form on silver surface exposed to sulfur/sulfide bearing environments. This paper examines the functionality of PWB surfaces with progressing degrees of tarnish.

Further, this paper presents the benefits of a newly developed treatment process which significantly enhances the tarnish resistance of an immersion silver finish. Results will be presented which focus on tarnish, solderability, and ionic cleanliness performance following treatment and exposure to tarnish inducing environments. The practicality of this treatment for commercial PWB finishing and subsequent assembly is also discussed.



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