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September 28, 2017

Alternative to Conformal Coating

Are there any reliable alternatives to the use of conformal coating to insulate solder joints and exposed conductors from condensing moisture?

Are you aware of any form of die cut sheet material that can be applied to serve the purpose?

B.W.

Experts Comments

Some manufacturers use epoxy to pot their products to protect them from any environmental exposure. By creating a cavity and placing the board in the cavity and filling it with epoxy is one way to accomplish this task.

After the potting process however there is no turning back, no rework, no nothing, if it works great and if it doesn't then it is scrapped. I'm mentioning this as this has to have some ROI analysis to compensate for yields and disposal cost.

Die cut sheet metal, would have to be soldered in place such as with microwave components. The sections on the board would have to be designed to have a soldered shield to prevent moisture entrapment and prevent leakage. This would also require the plugging of all via holes to prevent moisture from coming through those openings.

Best of luck

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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

There are many types of conformal coating and many ways to apply them. I am not aware of any die cut materials that would work in this application. Some solder companies claimed that some specific high residue pastes would act as a protective barrier around component legs but this never became popular.

If it is just local protection required on one specific part of a PCB then I suggest that you investigate selective application systems that can dispense, spray or jet the coatings onto specific parts of the PCB, or a paint brush!

One other alternative would be a hot melt conformal coating applied locally with a heat gun as this is VOC free and cures within seconds. It is also important to make sure that you select the correct conformal coating and one that is compatible with all other chemistries on your PCB.

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Chris Palin
European Manager
HumiSeal
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.

Not seen any precut sheet suited to this but a good chemical alternative is Rosin Lacquer as Rosin naturally repels water/moisture and is about the only material capable of locking away contaminants where as Conformal coatings generally only go over the top of them. Some liquid rosin fluxes offer this protection if left on the joint or PCB.

Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has twenty two years of service in Electronics industry. York has installed over 350 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
There are a number of UV/moisture dual cure and UV/heat dual cure materials that can be applied directly (jetted or needle) directly onto leads or the edges of connectors. There are also epoxy-based thermally cured materials. These all have the benefits of adding mechanical reinforcement as well as moisture and fluid barrier protection.  
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Dr. Brian Toleno
Application Engineering
Henkel Electronics
Dr. Brian Toleno is the Application Engineering Team leader for Henkel Technologies. He is responsible for the technical service and application engineering for Henkel's electronics assembly materials, including solder paste, underfills, PCB protection materials, and underfills.
Reader Comment
Would it be possible to have all electronic parts constructed where the pins & leads are under them? -i.e. similar to present BGAs & packs. If this is possible, then perhaps PWB boards can be designed to reciprocate this and no pins & pads are ever exposed. Then conformal coating operations maybe limited to few drops of a low viscous fluid that would seek these crevices and underfill them. Essentially no obvious exposed leads/pins.
Tomas Geronimo, Sanmina-SCI Corp., USA
Reader Comment
Yes, thin films of fluoropolymers have been used to provide an effective anti-moisture migration and anti-corrosion barrier on circuitry in several consumer electronics applications where traditional conformal coatings aren't practical. These fluoropolymers are delivered from non-flammable, non-VOC (US-EPA), low-GWP segregated hydrofluoroether solvents. The low viscosity and low surface tension of these fluids provide excellent wetting and can deliver the fluoropolymer into very tight spacings. Customer used application methods include dip, spray, precision-drop/line dispensing and brush.
Karl Manske, 3M Company
Reader Comment
I am not aware of any die cut material that would be able to provide the moisture resistance and the insulation of solder joints and exposed conductors. There are different types of conformal coatings from acrylic to silicone and parylene. Depending on the application and requirements and cost pinch points, parylene would be my choice.
William Yager
Reader Comment
In addition to conventional conformal coatings (usually based on acrylic, urethane or epoxy chemistries), another option has been used in some circumstances. Rather than a coating, it is a very thin layer of a fluoro-polymer, which acts as a surface modifier, rather than a barrier.

Condensed moisture does not wet to the surface, and so falls off or forms discrete beads which do not allow dendrite formation, for example. 
Peter Swanson, INTERTRONICS
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