Abstract
Whiskers are small crystalline growths, which can grow from certain metals or alloys. Reaching up to several millimeters long, whiskers have the potential to cause device failures due to short circuits and contamination by debris. Tin (Sn) is one such metal that is particularly prone to whisker development. Until the 2006 RoHS Initiative, lead (Pb) was added to tin in small amounts (up to 2%) to greatly reduce the growth of whiskers. Since then, however, industry has switched to lead-free tin solders and coatings, and the issue of whisker growth on tin has attracted new interest. A reactive-sputtering-deposited nickel oxide sublayer was shown recently to strongly suppress the growth of whiskers from an overlaying tin layer. This paper reports on using nickel oxide films, obtained by a sol–gel dip coating method, as whisker suppressing sublayers. The proposed method is simple, low-cost, and can easily be scaled up for manufacturing purposes. The properties of the sol–gel deposited nickel oxide film were examined using SEM, EDS, and Raman spectroscopy. Samples containing the nickel oxide sublayer were observed through SEM periodically over several months to examine the surfaces for whisker development, and the results show that such layers can be very effective in suppressing whisker growth.
Highlights
Metal whiskers are long, thin, hair-like structures, which grow on the surfaces of thin films of certain metals and alloys
The thickness of the NiO films deposited by dip coating was measured by crosssectional SEM
Assuming an equal thickness deposited during each dip coating cycle, the thickness of the single-cycle dip coating cycle was taken to be 60 nm
Summary
Thin, hair-like structures, which grow on the surfaces of thin films of certain metals and alloys. There are several ways in which whiskers can lead to device failures [3,8,18] These include both permanent and transient short circuits [2], contamination by debris, and metal vapor arcing. Such failures have been documented in the telecom, military, aerospace [19], energy, and medical industries since the 1940s [3,18]. Small amounts of lead were added to tin to suppress the growth of whiskers [18] This was the standard preventative measure until the passage of the RoHS Directive [15,20]. Effective 1 July 2006, this directive prevents the sale of products containing lead within the European Union (which represents a market large enough to influence industry practices around the globe)
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