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Conformal Coatings - New Solutions to Existing Problems
This paper describes work carried out by Humiseal to investigate root causes of these problems, and to introduce materials with improved performance.
Technical Paper
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Authored By:
Chris Brightwell
Humiseal Europe – A Chase Corporation Company
Berkshire, United Kingdom
Summary
Conformal Coatings are used to protect Printed Circuit Boards (PCBs) against the effects of moisture and corrosive environments. The performance of the conformal coating often is limited by certain common failure modes, including entrapped bubbles in cured coating, lack of protection of component edges, and defects developing during thermal excursions. Humiseal, along with other conformal coating manufacturers have worked to develop materials that overcome these shortcomings. This paper describes Research and Development work carried out by Humiseal to investigate root causes of these problems, and to introduce materials with improved performance.
Conclusions
Progress has been made developing improved products in all three problem categories.
Coatings with reduced bubble entrapment have been developed which will allow faster processing in a wider range of products to marketed in multiple product categories, including acrylic and polyurethane. The reduction in bubble entrapment will allow faster processing with less bubble entrapment more readily on a wide range of board types.
UVA LED curable conformal coatings show performance equalling or exceeding the current UV curable conformal coatings products cured exclusively by mercury discharge lamps. They show great potential for delivering high protection of PCBs. The increased protection is very pronounced in tests of Thermal Shock resistance, which rely on physical stability of the coatings. The increased deep penetration of UVA light into organic polymers produces a uniform cure profile, leading to polymers with consistent properties. This improvement in cure is evidenced by less weight loss during post UV-cure heating tests. These results will form the basis of new UV coating designs, which will also exploit the other processing advantages of LED cure, such as reduced heat, increased equipment reliability and no ozone generation.
Coatings with improved sharp edge coverage continue to be developed, and show great promise to provide easy to apply coatings with significantly increased protection against moisture ingress and corrosion.
Initially Published in the SMTA Proceedings
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