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research-article

Gold-Tin Solder Wetting Behavior for Package Lid Seals

[+] Author and Article Information
Paul Vianco

Sandia National Laboratories, P.O. Box 5800 MS0889, Albuquerque, NM 87185-0889
ptvianc@sandia.gov

Alice C Kilgo

Sandia National Laboratories, P.O. Box 5800 MS0889, Albuquerque, NM 87185-0889
ackilgo@sandia.gov

Bonnie B McKenzie

Sandia National Laboratories, P.O. Box 5800 MS0889, Albuquerque, NM 87185-0889
bbmcken@sandia.gov

1Corresponding author.

ASME doi:10.1115/1.4039749 History: Received October 24, 2017; Revised March 20, 2018

Abstract

This study examined the cause of non-wetted regions of the gold (Au) finish on iron-nickel (Fe-Ni) alloy lids that seal ceramic packages using the 80Au-20Sn solder (wt.%, abbreviated Au-Sn) and their impact on the final lid-to-ceramic frame solder joint. The Auger Electron Spectroscopy (AES) surface and depth profile techniques identified surface and through-thickness contaminants in the Au metallization layer. In one case, the AES analysis identified background levels of carbon (C) contamination on the surface; however, the depth profile detected Fe and Ni contaminants that originated from the plating process. The Fe and Ni could impede the completion of wetting and spreading to the edge of the Au metallization. The Au layer of lids not exposed to a Au-Sn solder reflow step had significant surface and through-thickness C contamination. Inorganic contaminants were absent. Subsequent simulated reflow processes removed the C contamination from the Au layer without driving Ni diffusion from the underlying solderable layer. A Au metallization having negligible C contamination developed elevated C levels after exposure to a simulated reflow process due to C contamination diffusing into it from the underlying Ni layer. However, the second reflow step removed that contamination from the Au layer, thereby allowing the metallization to support the formation of lid-to-ceramic frame Au-Sn joints without risk to their mechanical strength or hermeticity.

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