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The Knowledge and Know-how Connection
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June 18, 2013
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Conformal Coating & Humidity
Can conformal coating protect a circuit board that will be operating in a humid environment? Is there a specific process?
Expert Panel contributors for this topic:
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Wayne Wagner, President, Krayden Inc. | |
Jade Bridges, European Technical Support Specialist, Electrolube Ltd | |
Dr. Brian Toleno, Application Engineering, Henkel Electronics | |
James Mahoney, Applications Project Manager, Quick Turn Flex Circuits LLC | |
Edward Zamborsky, Regional Sales Manager, OK International Inc. | |
Scott D. Szymanski, Global Marketing Manager, Nordson MARCH |
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Views: 3992
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What about inside the board, especially with multilayer PCBs? The conformal coating which adheres well to the surface of the PCB may, indeed, protect this surface from SIR degradation and related failure types. But the same materials, e.g., silicone, have very high water diffusion coefficient and moisture may start collecting at interfaces (glass-polymer) inside the board. Electrochemical migration may occur there leading to failure. A method to prevent this mode would be appreciated by those who design outdoor equipment.
Michal Tencer, MST Consulting, Canada
With regards to moisture resistance, yes this one of the benefits of using conformal coating. Beofre deciding on a type of conformal coating it needs to be determined what type of moisture resistance is needed. Depending on moisture resistance you can use Epoxy, Humi Seal 1B 31 Parylene.
When dipping or spraying conformal coatings you will find that they are not pin hole free which allows moisture to penetrate and also you have to apply the materials thicker because when curing they will shrink and you will also get over spraying. If you use Parylene, it is a vacuum deposited, pin hole free, thin coating that has exceptional moisture resistance. At the end of the day the choice of what conformal coating to use depends on the moisture resistance required and the costs needed.
Bill Yager, Para Tech Coating, Inc
Conformal coatings do protect circuit boards from humidity very well. The choice of materials and application methods will depend on your specific environmental requirement as well as what level of re-work you may want to have available. We currently have several customers that require an acrylic coating which provides excellent protection from moisture and is very easy to remove if any repairs are required, the application method is atomized spray using an HVLP (high volume low pressure) paint gun.
Coating thickness targeted at 3mils and is determined by methods described in IPC-CC-830 (thickness range is 1-5mils). One thing to keep in mind in wet environments is that interconnects must be chosen carefully as they will be the weak point on a properly coated assembly.
Bert Furr, Benchmark Electronics, USA