Ask the Experts
September 13, 2010
Conformal Coating and Moisture Absorption
Prior to conformal coating, how long can we keep circuit board assemblies in an open condition before they will be impacted by moisture absorption?
Expert Panel Responses
A protective layer of conformal coating will indeed expand the life expectancy of an electronic board that is then exposed to the working conditions, however a number of other parameters also play a role that needs to be considered.
For example an acrylic will have a reasonable performance however if outdoors the life expectancy maybe greatly by organic pollution that may affect the coating layer, while a urethane coating will resist most contaminants yet it will be very much affected by sunlight, oxidation and thermal cycling.
A silicone will resist most environmental attacks although direct abrasion will shorten the life expectancy. Only an integral approach in selecting the adequate conformal coating will provide the highest chance of electronic survival for each system (Otherwise only there would be one conformal coating in the market). This makes very important for you to work close with your CC provider to help you select the ideal conformal coatings for your application.
Most brands if not all, will offer tutorial and selection tools on their websites. The best solution again is to work closer to the experts to get the optimum selection.
Wayne Wagner has over 25 years in the conformal coating industry and is the president of Krayden Inc., a leading distributor of engineered materials.
It depends on the relative humidity of the environment,..drier is better. The board surface will absorb water relatively quickly (minutes to hours).
The extent of absorption is influenced by % RH and temperature. Cool and dry is the key, by all anecdotal sources I have talked with.
Jim Willimas is a PhD Chemist in Polymers and Materials Science. He specialize in printing, cleaning, inks, and coatings used in electronics manufacturng operations. Williams has more than 30 years experience.
Boards can be kept indefinitely in room temperature and humidity conditions as conformal coatings are breathable and will allow moisture pass from the board through the coating.
A coated board can for example be kept at elevated temperature for several hours and moisture will still be removed from the FR4.
Chris Palin is currently managing European sales and support for HumiSeal Conformal Coatings. His expertise is in test & reliability, solder technology, power die attach and conformal coating.