EVALUATION OF CONFORMAL COATINGS AS A TIN WHISKER MITIGATION STRATEGY, PART II
Authors: Thomas A. Woodrow, Ph.D. and Eugene A. Ledbury Company: The Boeing Company Date Published: 9/24/2006
Abstract: The objective of this ongoing study is to evaluate the ability of conformal coatings to mitigate the formation and growth of tin whiskers. Conformal coatings were chosen as a mitigation strategy because they are one of the few processes that are actually under the control of OEMs that manufacture high reliability electronics. Brass coupons were plated with bright tin and then conformal coatings were applied. The coupons were aged in a 25°C/97%RH (relative humidity) environment and observed for whisker formation and penetration of the coatings by whiskers. The results of this test suggest that conformal coatings can suppress the formation of whiskers and OSE’s (odd shaped eruptions). With time, however, all of the coupons in this test began to grow whiskers under the coatings and once whisker growth began, all of the coatings were penetrated regardless of the coating thickness. These observations differ from a prior study in which the coupons were aged in a 50°C/50%RH environment. In that study, only the thinner (less than 1.5 mil) coatings were penetrated by whiskers or OSE’s during the test. In this current study, unusual eruptions of tin were observed that were capped with a thick crust of material. Auger analysis suggested that the crust was a mixture of tin, tin oxide and zinc oxide.
Key Words: tin whiskers, conformal coatings, mitigation