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72 SMT007 MAGAZINE I JULY 2021 Article by Prabjit Singh and Larry Palmer, IBM CORPORATION; Chen Xu, Jason Keeping, Marko Pudas; Mei Ming Khaw, Kok Lieh Tan, KEYSIGHT; Mike Huang, Ruby Lin, WISTRON CORPORATION; Haley Fu, iNEMI Abstract e purpose of conformal coatings is to protect printed circuit boards and compo- nents mounted on them from the deleteri- ous effects of moisture, particu- late matter, and corrosive gases. The conventional method of testing the effectiveness of con- formal coatings is to e x p o s e t h e c o n - f o r m a l l y c o a t e d hardware to a cor- rosive environment for ex-tended peri- ods of time last- ing many months and determining the mean time to failure. A quicker method that takes less than a week is the subject of this paper. In this method the corrosion rates of conformally coated thin films of copper and silver, exposed to a sulfur gas environment, are used to characterize conformal coatings. is paper describes the test chamber design and setup and investigates how the tempera- ture and humidity impact the corrosion rates of conformally coated copper and silver thin films compared to uncoated films. Perfor- mances of acrylic, silicone, and atomic layer deposition (ALD) conformal coatings were studied as a function of temperature and rela- tive humidity. e test temperatures were 40°C and 50°C and the relative humidity levels were 15%, 31%, and 75%. Temperature affected the corrosion rates of conformally coated copper and silver thin films. Relative humid- ity had much less effect on cor- rosion rates. Signif- icant differences in corrosion protection provided by the three coatings will be reported along with a discussion on the optimum test conditions. Introduction e purpose of con- formal coatings is to pro- tect printed circuit boards and components mounted on them from the deleterious effects of corrosive environments that can have high concentrations of gases such as sulfur dioxide, hydrogen sulfide, free sulfur, chlorine, oxides of nitrogen, and ozone. Par- ticulate matter with low deliquescent relative humidity (DRH) can electrically short circuit features with potential differences across them Conformal Coating Evaluation Test Development

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