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50 SMT Magazine • July 2014 ing thickness at the line of demarcation for the flat samples tended to be slightly less than that for the remainder of the sample but not signifi- cantly. Figure 4 includes scanning electron micro- graphs of the tin plating on a Copper C110 base metal coupon at the location of the bend pri- or to conformal coating. There are observable stress cracks in the tin plating caused by the bending process. The tin plating on the Alloy 42 base metal appeared similar. Inspection Results for Coupons without Conformal Coating Table 3 includes whisker density values for the uncoated samples for both the Copper C110 base metal and the Alloy 42 base metal on the control samples and on the bent samples for both regions in tension and compression. As of the fourth quarter of 2013 sampling, the whis- ker density on the Alloy 42 base metal control sample (62 whiskers/mm 2 ) was greater than that of the whisker density on the Copper C110 base metal control sample (39 whiskers/mm 2 ). The largest tin whiskers and odd-shaped eruptions observable on the control samples approached 5.0 mils, indicating that whiskers were present with minimum lengths dimensionally capable of extending through the conformal coating thicknesses applied to the test coupons. The ef- fect of the light scratches applied to the surface of the control samples was negligible with no observable pattern of whiskers accumulating along the scratches. fEATURE TIN WHISKER RISK MANAGEMENT By CoNFoRMAl CoATING continues figure 4: Scanning electron micrographs of the tin plating following the bending process on the Copper C110 base metal. Table 3: Average tin whisker densities on uncoated regions throughout environmental exposure.