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July 2014 • SMT Magazine 47 used in the testing. The application thickness of the coatings was 1.0, 2.0 or 3.0 mils for the acrylic and polyurethane coating and 0.5 mils for the parylene coating. Prior to the coating process, the samples were cleaned using the existing in-line cleaner and then baked at 85°C for two hours. The ap- propriate areas of the coupons were masked using tape. The acrylic and polyurethane coatings were applied using a spray coat process and the parylene coating was applied using a vapor deposition process. All test coupons were coated by the com- pany. The samples were labeled ac- cording to Table 2. Following the conformal coating of the test coupons, and a visual in- spection to insure continuity of the coating as well as a measurement of the coating thickness on approxi- mately ten samples to insure that the proper coating thicknesses were applied, the samples were placed in an environmental chamber. The en- vironmental chamber was capable of maintaining a temperature of 50° ± 10°C and a relative humidity of 50% ± 15%. The oven was equipped with a fail-safe device to ensure against overheating. The internal working envelope of the environ- mental chamber was 16in x 16in x Table 1: Properties of confomal coatings used in testing. (note: Properties from material technical data sheets.) Table 2: Test coupon matrix. TIN WHISKER RISK MANAGEMENT By CoNFoRMAl CoATING continues fEATURE