Issue link: https://iconnect007.uberflip.com/i/455818
February 2015 • SMT Magazine 75 probability of straight whisker emanating from a point on one surface and making contact with an adjacent surface. The configuration of the leads used in that model is shown in Figure 13. This model requires inputs, typically based on experimental data, for the density of whiskers in various regions of the component lead and some estimate for the length distribution. The model from reference [11] has been im- plemented in a spreadsheet tool that allows the user to estimate the number of shorts between leads for a given set of conditions. While this model was developed for leaded components such as a quad flat pack, it does allow the user to input lead geometry to define extremely short portions of the lead to effectively set them as zero length. To assess the tin whisker risk for the connector, the lead parameters for the model were set to values to produce straight leads that were either the full length of the lead (~1.1 mm) or the worst-case unsoldered length of the lead (0.3 mm). The testing in this study observed ~7 whis- kers occurring on two leads out of 14,580 total Feature TIN WHISKer rISK aSSeSSMeNT OF a TIN SurFaCe FINISHed CONNeCTOr continues Figure 10: cross-sectional view of connector after reflow soldering. Figure 12: SeM assessment illustrating complete solder wetting and coverage for region b. Figure 13: bridging by tin whiskers between component leads [11] . Figure 11: SeM cross-sectional view of connector after reflow soldering illustrating specific regions of interest: a = whisker risk region, b = lead frame breakoff tab region, c = solder coverage region.