Ask the Experts
October 6, 2017 - Updated
February 16, 2009 - Originally Posted

Conformal Coating and Connector Holes

How can we eliminate conformal coating from seeping into connector holes as the coating is applied? If we cannot completely eliminate the problem, how much coating residue is acceptable in the connector holes?

C. R.

Expert Panel Responses

If condensation due to high humidity is penetrating at only the interface(s) of your conformal coating and the board, you can increase the adhesion of the conformal coating to the board by using a suitable gas plasma treatment. The increased adhesion may be enough to keep the condensation out. This kind of plasma treatment is done to the entire surface of the board inside a low-pressure plasma system, just before your conformal coating step. Argon gas is a popular choice for this process, because it does not cause oxidation of the board material. The plasma treatment will activate the surface (increase the surface energy) of the board due to ion and free-radical interaction with the surface of the board, resulting in increased bondability to the conformal coating. However, if the condensation is actually penetrating the conformal coating itself, you may need to try a different type of conformal coating, one that is inherently less permeable to liquids. The problem with high-density conformal coatings is they're usually more difficult to bond to the board. As above, this kind of adhesion issue can be solved by using an appropriate gas plasma treatment. Gas plasma treatments are becoming increasingly popular for board manufacturing processes such as these. You can contact plasma system suppliers to see if they will run samples for you - most will do so at no charge in order to demonstrate the effectiveness of their gas plasma treatments.

Scott D. Szymanski
Global Marketing Manager
Nordson MARCH
Mr. Szymanski works to expand strategic alliances, strengthen partnerships with equipment suppliers, and develop future product offerings tailored to the semiconductor market.
NOTE: Mr. Szymanski is no longer working at Nordson MARCH

The approach to this problem is the correct application selection, and second the viscosity of the material selected. Selective coating systems are capable to coat a board without coating the connectors at all, leaving the edge of the wet coatings just a few dozens of mils away from the connector side thus preventing the risk of the capillary action to take place. Secondly, if the base of a connector has to be coated as well then the viscosity of the coating plays a key role. The higher the viscosity the less likely will be the seeping on the connector. An alternative approach would be to actually use a two product combination, to use a thyrotrophic material of the same nature as the coating, to surround the base of the connector: this eliminates the seeping completely while allows full coverage of the connector. It is important the material to be of the same nature than the coating to have same cure schedules and adhesion so they behave like a single block of material; silicone-silicone or acrylic-acrylic, etc.

Wayne Wagner
Krayden Inc.
Wayne Wagner has over 25 years in the conformal coating industry and is the president of Krayden Inc., a leading distributor of engineered materials.

This only generally happens with solvent based conformal coatings as 100% solids coatings tend to be higher in viscosity. Solvent based coatings can wick up into the connector body through capillary action. We solve this problem by producing a gel form of each conformal coating type. The gel can be applied around the connector base before coating with your standard viscosity conformal coating preventing entry into the connector. It is important that the coating gel used is compatible your conformal coating.

Chris Palin
European Manager
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.

Boards that are conformal coated have the areas that they don't want conformal coating on masked or taped off. There are several way to do this, people will use capton tape to tape off areas that they do not want the coating on. There are also solder mask materials that are room temp cure and also UV that are also used in this application.

Gary Bowman
Sales Manager
Krayden, Inc.
Gary Bowman has been in distribution sales for 33 years selling into Electronic, Aerospace, Medical and OEM market place. Bowman has been with Krayden for 18 years.

The easiest way to avoid conformal coating spreading into connectors is to use a masking agent. Liquid masking agents are easy to apply and can be room temperature or heat cured. For more information please follow the link to Electrolube.

Jade Bridges
European Technical Support Specialist
Electrolube Ltd
Jade Bridges is the European Technical Support Specialist for Electrolube. She is responsible for technical support within Europe, offering assistance to customers with product selection, implementation and after sales support across the range of Electrolube products. Her expertise is carried over from her position as R&D Manager for Electrolube, where she was responsible for the new product development and technical support across an array of chemical products for the electronics industry, including conformal coatings, encapsulation resins, thermal management products, contact lubrication and electronic cleaning solutions.

When we conformal coated our boards we used the spray method which prevented most material from getting into the holes and we were spraying 3 coats of UR. We also were using compliant pins from AMP which work very good from electrical properties as well as no masking and very good coverage between pads.

James Mahoney
Applications Project Manager
Quick Turn Flex Circuits LLC
James Mahoney is a Technical Operations Manager with a 20 year track record in managing new product introduction. He is a skilled leader, motivator and problem solver with a strong background in Product Knowledge and Engineering Management.

To avoid coating material to get inside the connectors, the masking is very important. For the base of the connectors, using liquid peal-able mask is a solution as well as a 2 step process - encapsulation of the areas around the connector base with a high viscosity material (dispensing) and then apply coating (spraying). Now from the acceptability criteria for coating inside connectors, definitely the connector pin mating surface has to be free of coating and should any coating material be on the connector surface, this will constitute a defect if it affecting the mechanical connect/disconnect process with the matting connector.

Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at

Reader Comment
Conformal coating materials are designed to "wick" under parts and in between pins to provide a complete coat. This also can create issues with wicking into holes and into connector pins which can create functional and solderability problems. Any coating residue in an area that requires soldering and or electrical contact can be problematic. I have found that with proper masking and using a spray application method I can control and eliminate the type of issue you are seeing by applying a light first coat. This will seal the area on a connector housing or in a masked area, subsequent coating can then be applied without the wicking into these areas.
Bert Furr, Benchmark Electronics

As part of our research into FC coatings we areinvestigating injecting a fluoropolymer coating into the connector around thebase. This quick drying coating seems to repel other conformal coatings verywell. This research is in a provisional trial stage and weshould have more results published on our Nexus site in the next few weeks. But the results look promising. It also has the added bonus of protecting the connectorinternally which the conformal coating cannot do.

Lee Hitchens
SCH Technologies
Lee has worked within the conformal coating and electronics industry for over 18 years. His work includes scientific research into long term reliability of electronics, technical sales of conformal coating materials and equipment, owner of SCH Technologies, a conformal coating service in the UK, a member of the Diamond Coating Solutions Group, a global liquid conformal coating and Parylene coating service solutions provider, a founding member of Nexus3c, Conformal Coating Centre and a partner of Thin Film Partners.

Reader Comment
We had a similar situation. The conformal coating was seeping through the leads of the low profile SMT connector by capillary action. We partly fixed the problem by using a viscous material of the same type around the connector leads and then sprayed the rest of the PCBA. This only reduced the number of returns, but did not eliminate the problem completely.
Sundaram, EIT LLC

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