Effects of electrodeposited matte tin crystal orientation and grain structure on tin whisker growth propensity using stress-inducing test methods

Tin whiskers are thin, crystalline, conductive filaments that can emanate from electrodeposited tin coatings, which pose electrical reliability concerns. Several driving forces for tin whisker growth related to deposit stress have been identified and accelerated test methods have been developed to simulate these. Preferred crystal orientation (texture) and grain size of electrodeposited matte tin have been found to be correlated with whisker growth propensity. This paper examines tin whisker growth properties of electroplated matte tin deposits with specific crystal orientations <;220> and <;321> and grain sizes (5-8 μm diameter vs. 1-4μm diameter), using tin whisker tests designed to simulate stress formation due to ambient storage (30°C/60%) RH, 4000 hrs), high temperature and humidity storage (55°C/85% RH, 4000 hrs), thermal coefficient of expansion mismatch (TC +85°C/-55°C, 1500 cycles), externally applied forces (2000g load size / 1 mm diameter, 48 hrs), and corrosion (85°C/85% RH, 1000 hrs). In addition, these whisker results are compared to a tin deposit with <;112> and <;101> crystal orientations. The data and observations of the experiments are discussed in this paper.