SMT007 Magazine

SMT-July2016

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52 SMT Magazine • July 2016 This paper presents a new technique for achiev- ing condensing conditions on circuit boards, and utilizes an approach of using a platen as an inde- pendent means of controlling the substrate tem- perature to induce condensation, which has been shown to be uniform. Hence complete control of the condensing conditions can be achieved in a wide range of temperature and relative humidity climatic conditions, and the level of condensation can be easily adjusted and maintained over long periods of time and readily cycled through those conditions. Since the whole test board is cooled on a platen the condensation film that forms will be uniform across the surface. This paper has shown that as the test becomes more severe the condensing conditions will find weaknesses in the coating quickly. While humid - ity SIR and a low profile condensing test, the test vehicle passed, as the geometry became more challenging weaknesses and failures were ob- served. The results confirmed the susceptibility of exposed edges under condensing conditions, and that complete coating coverage is crucial. The thicker polyurethane materials demon - strated much greater resistance to condensing environments, with polyurethane-1 in particular showing little change in SIR during the condensa- tion events. It was surprising how quickly the insulation resistance of the acrylic materials and polyure- thane-2 dropped with the onset of condensa- tion—the drop in SIR being almost instantaneous. Condensation conditions will find weaknesses in the coating quickly. Of particular surprise was the poor perfor- mance of the nano-coating. It showed no resis- tance to the condensing environments whatsoev- er, and corrosion was evident on the traces at both 1oz and 3oz copper track thickness. Although the coating contained a fluorescent trace it was im- possible to determine coverage by cross-section. Therefore, it is clear from both the SIR results, the cross-sections and the visual inspection that conformal coating coverage is crucial in provid- ing protection under condensing environments. There was a clear correlation between coating thickness and coverage and SIR under condens- ing environments. SMT References 1. BMW GS 95024-3-1 (Test K15). Note: This article was presented at the technical proceedings of the IPC APEX EXPO 2016. Chris Hunt leads the Electronics Inter- connection team at the National Physi- cal Laboratory (NPL). Ling Zou is the head of the Measure- ment Service for Industry in the area of Electronics Interconnection at NPL. Phil Kinner is the technical director of Electrolube's Coatings Division. A research group led by Profes- sor Mochida Tomoyuki of the Kobe University Graduate School of Sci- ence and Dr. Funasako Yusuke of the Tokyo University of Science has become the first in the world to de- velop an ionic liquid from a ruthe- nium complex with cyano groups that transforms into a solid when exposed to light and returns to liquid form when heated. If you apply ultraviolet light to the liquid for a few hours, it chang- es into an amorphous coordination polymer, and if you heat this solid for one minute at 130°, it returns to its original ionic liquid form. This research has led to the suc- cessful creation of a reusable photocurable liquid that can potentially be applied to printed circuit boards, 3D printing, and adhesives. New Compound Switches Between Liquid and Solid States when Exposed to Light or Heat CONDENSATION TESTING—A NEW APPROACH

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