Conformal Coating Questions & Answers
Conformal coatings are used to protect electronic components and circuitry on printed circuit boards from damaging environmental factors. There are many different types of materials on the market from epoxy to parylene, but users of light-cure coatings frequently ask similar questions about the technology.
A few of the more common Q&As are summarized below:
Question: Does liquid resin that flows under a component (into a shadowed area) cure over time?
Answer: It depends on the formulation and its secondary cure mechanism. UV/moisture-cure coatings will cure over time without light exposure. Time alone does not cure UV/heat-cure conformal coatings.
Question: If a small amount of conformal coating material goes into a shadowed area and a secondary heat cure is not used, what impact does the uncured conformal coating have on my board and components?
Answer: It depends on many variables including the amount of coating, board topography, and presence of contaminants on the board. Small quantities of uncured conformal coating alone have not been known to impact the long-term performance of boards. Dymax always recommends that measures be taken to eliminate the presence of uncured conformal coating through controlled dispensing methods, and, when necessary, multiple-cure mechanisms.
Question: Why does the conformal coating feel tacky or sticky on the surface minutes after curing?
Answer: The coating was likely not exposed to enough UV light. A high-intensity lamp utilizing a bulb with maximum wavelength output at 365 nm (nanometers) is recommended. Dymax coatings should be tack free almost immediately after cooling.
Question: How do you know if the conformal coating is cured?
A Printed Circuit Board Coated with Conformal Coating Cures Inside a Light-Curing Conveyor System
Answer: When the coating is tack free and the coating in contact with the board is solidified. All light-cure coatings feel tacky immediately after they are cured and still warm from the lamps. Tackiness should be judged after the coating has cooled, which is often seconds after leaving the light source. Very soft coatings have a slightly tacky feel, like soft rubber. To judge whether the coating flush to the board is cured, run a test specimen and try to pick the coating away from the specimen using a sharp tool.
Question: How do you know if the material is cured in a shadowed area after a secondary cure?
Answer: For UV/Visible light-cure coatings, this work may include destructive and performance testing of parts made with minimum and maximum amounts of coating, UV/Visible light intensity, and exposure time allowable by the process.
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