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Potting/Conformal Coating

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#75385

Potting/Conformal Coating | 24 February, 2016

I have a customer who is rather inexperienced, and asking us for a solution for them.

They have a circuit board that's roughly two inches long by 1/2" wide or so, with component placements on one end of the board. The other end has a trace that I suspect is an antenna for RFID or some other type of application. They'd like to protect the component placements with a transparent material (as there are indicator LEDs contained in this section), akin to potting....though, they'd prefer to not use a pot. They're thinking of something along the lines of a thicker material that I could dip the board into to cover the components.

We've reviewed the inability of standard conformal coating to accomplish this. We've also suggested using a case enclosure, but, they also want to prevent end users from reworking the components.

Anyone have any thoughts as to a type of translucent material that is viscous enough to accomplish this type of encapsulation?

Thanks, ..rob

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#75389

Potting/Conformal Coating | 25 February, 2016

Have you looking into acrylic? We've had huge success with boards with stringent keep out areas while achieving proper thickness. Acrylic requires a thinner or cutting agent to perform repair/rework.

-TSS

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#75390

Potting/Conformal Coating | 25 February, 2016

I'm sure they'd be open to acrylic, as it'll provide a nicely hardened finish for them once cured.

The real question is would it be workable to do what they're asking. That is, thick enough to coat the board when we dip it in without all slopping off, but, still thin enough to actually dip the board into it.

I'm starting to think that this is a fools errand. The best method for this process seems to be a mold of some description to pour the material into, and allow to cure around the part. Problem is they're asking for quotes of 100, 1000, and 5000 pieces...I can't see that being a great process in those quantities.

Thanks! ..rob

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#75391

Potting/Conformal Coating | 25 February, 2016

How thick are their requirements? A barrier can be made using peelable latex. That would then require manual or automatic dispense of latex to create a dam. Then you should be able to use an automated dispense system with a large orifice and flood it. If it's a double sided board that would be two passes. I've never been involved in the potting process myself.

-TSS

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#75392

Potting/Conformal Coating | 25 February, 2016

They're open ended on the thickness (read that as, have no clue).

They've indicated that they would like the coating to protect the circuitry from ESD, and mechanical shock. They also would like to be able to see the LED's through the material. And, finally, give the user something to hold on to.

I think the tallest component is an SOIC...so, let's say somewhere in the 3-5mm range for thickness. And, yes, double sided.

About the only thing I can think of is a mold that the board can sit in during curing; but, they're interested in not having a mold (read, not spending the money).

Thanks, ..rob

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#75394

Potting/Conformal Coating | 26 February, 2016

Rob,

Have you considered doing multiple dips to build the coating thickness up to what your customer thinks is good? We've done this on a small handful of products for several years. Extends your lead time, but it doesn't need to fully cure between coats.

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#75407

Potting/Conformal Coating | 2 March, 2016

Sounds like over molding would be ideal, but if they don't want to spend for a mold I would look at silicone conformal coatings that can be used in a dip process. Silicones are thicker than other coating materials and multiple drippings may provide the desired thickness.

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#75415

Potting/Conformal Coating | 4 March, 2016

Try Humiseal 2A53. This is a very old 2-part epoxy coating that is still used by a number of companies as well as the military. Very hard to rework, transparent and may be what you are looking for

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