SMTA International Conference Proceedings


Authors: B. Rickett and P. Elmgren et al.
Company: Molex, Inc.
Date Published: 9/26/2004   Conference: SMTA International

Abstract: In response to the legislative initiatives presently underway to remove lead from electronic components, an experimental study was undertaken to determine the susceptibility of lead-free electrodeposited connector finishes to metallic whisker formation, the reliability failure mode presently of greatest concern to the electronics industry.

The first phase of the study included exposure of mechanically stressed electroplated finishes to thermal aging, elevated temperature / humidity, and thermal cycling conditions. The samples examined during this phase included various pure Sn, SnCu, and SnBi plating configurations. Based upon the results of these initial environmental aging studies, some of which lasted as long as 16 months, it was determined that a finish of pure Sn over Ni would be the most suitable for minimizing the likelihood of whisker formation.

The second phase of the study focused on comparing the whisker susceptibility of matte Sn to bright Sn (both over a nickel barrier layer) during exposure to either thermal aging, elevated temperature / humidity, or room temperature aging conditions. The second phase samples were pre-conditioned via temperature cycling rather than mechanically induced stressing of the electrodeposit.

The susceptibility of each plated finish to whisker formation has been extensively documented via a scanning electron microscopy (SEM) evaluation. The implications with respect to whisker mitigation strategies and whisker testing methodologies are also discussed.

Key Words: lead-free, tin whisker, tin electrodeposit, tincopper electrodeposit, tin-bismuth electrodeposit

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