Preventing whiskers in electrodeposited tin for semiconductor lead frame applications

Abstract

A new pure tin process is described which produces a deposit with a crystal orientation combination that minimises whisker growth, particularly when used with a specific pre‐treatment process. A recommended etch depth of minimum 2.5 μm has been shown to reduce whisker growth, particularly with thin (3 μm) tin coatings. Crystal orientation is determined by X‐ray diffraction and the angles between adjacent crystal planes are calculated from the pattern produced. A minimum proportion of small angles is required for lowest whisker risk. Angles smaller than 22° have been shown to be critical. The predominant orientations of the deposits from new tin process are 101, 211, 112, and 312. This combination of orientations has 8 percent of angles in the critical range. A typical pure tin process with a high tendency for whiskering may have a texture of 431, 321, and 211 orientations, and this combination produces 65 percent of angles smaller than 22°.

Citation

Whitlaw, K., Egli, A. and Toben, M. (2004), "Preventing whiskers in electrodeposited tin for semiconductor lead frame applications", Circuit World, Vol. 30 No. 2, pp. 20-24. https://doi.org/10.1108/03056120410512118