Circuit World, Vol. 35, No. 1, pp. 3-8, 2009

Evaluation of Pure Tin Plated Copper Alloy Substrates for Tin Whiskers

Sony Mathew
Michael Osterman
Michael Pecht
Center for Advanced Life Cycle Engineering (CALCE)
University of Maryland
College Park, Maryland, USA

Frank Dunlevey
Brush Wellman Inc.
Cleveland, Ohio, USA

Purpose – The purpose of this paper is to present the results from work on a project aimed at evaluating six different copper alloy substrates coated with pure tin for tin whisker growth. The influence of intermetallic growth between the copper alloy substrate and the tin-plating on the growth of tin whiskers has been investigated.
Design/methodology/approach – The experiment consisted of six substrates of different alloys of copper, plated with bright tin including copper beryllium, cartridge brass, phosphor bronze, Cu-Ni-Si “7025” and Cu-Ni-Sn “spinodal”. The samples were mechanically stressed and then subjected to temperature humidity storage conditions for 1,000 h. These samples were then evaluated for tin whisker growth and intermetallic layer thickness.
Findings – Of the six samples five showed tin whisker growth. For these samples the intermetallic layer thickness has little effect on tin whisker growth. Sample with Cu-Ni-Sn “spinodal” alloy substrate showed very low whisker density and comparatively lower maximum whisker length than the other tested substrate material.
Research limitations/implications – More samples per condition should be evaluated to bolster the conclusions. For the sample without tin whisker growth, holes on the surface of the plating were observed. The holes in the plating provide an opportunity for stress relaxation after the plating process. Since stress in the plating layer is low, tin whiskers are not formed on the sample surface.
Originality/value – The paper details the tin whisker growth on six tin plated copper substrate samples. The intermetallic layer thickness for each copper alloy substrate is calculated. The relationship between the intermetallic layer thickness and tin whisker growth for the six substrates are discussed.

Keywords: Copper, Alloys, Substrates, Compressive strength, Crystallization

Complete article is available to CALCE Consortium Members.

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