Date of Award
Master of Science in Industrial Engineering (MSIE)
Systems Science and Industrial Engineering
Conformal coatings protect printed circuit board assemblies, including the electronic components that the assemblies are populated with. A variety of materials and application methods can be used to conformally coat assemblies. The process setup is crucial to repeatable process reliability. The manual spray based conformal coating is widely used. This method of application was selected due to its compatibility, affordability, and efficiency with the required application. Polyurethanes, one of the families of conformal coatings, provide resistance against abrasion, heat, and chemicals while reducing the risk of tin whiskers. In order to minimize the need for rework and create an efficient, repeatable and reproducible process, an option is to automate the process of conformal coating application. This research addressed the research and development of a process specific to SODIMM type memory modules using a two-component polyurethane based conformal coating material. The yield was improved by systematically working on quality by analyzing yield improvements while preventing observed defects. A ‘DoE” based approach was used. Upon validating ‘optimal’ input configurations, the overall process qualification was executed for controlled lots which were then analyzed for visual defects and thickness establishing process effectiveness. The sub-processes for the conformal coating process include board wash, ionograph test, masking, plasma cleaning, conformal coating spray, and cure. The board wash sub-process was qualified using three different temperature and time durations as inputs.
When examined under a microscope, white residue was observed for lower temperature configurations. Next, ionograph tests were conducted to verify ionic contamination levels on the surface of the SODIMM products and it was observed that all samples passed. It was observed that an oxygen-based plasma cleaning process provided the minimum contact angles of 8° or below. Argon, by itself, performed equally well but the mixture of the two gases resulted in an angle greater than 8°; hence oxygen was selected. It was seen that the metalized surfaces of the components exhibited thinner deposits of coating than the other areas on board. The final program was modified to accommodate for cross-directional passes and an air tack time of an hour to resolve the observed issue, which turned out to be a successful solution. Controlled lots were processed and inspected for coating thickness. No additional defects were observed. This research has also helped in identifying potential opportunities for improvement.
Dhiman, Rajat, "DESIGN AND QUALIFICATION OF A ROBUST POLYURETHANE BASED CONFORMAL COATING PROCESS FOR SODIMMs" (2018). Graduate Dissertations and Theses. 92.
Available for download on Monday, August 02, 2021