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AR/UR Coating Application

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AR/UR Coating Application | 31 January, 2018

I'm working on bringing up a new conformal coat process/workcenter and have a few questions I'm hoping someone might have experience with.

Right now we're manually spraying both coating materials (1B31 and 1A33 from Humiseal) using HVLP guns. I run 10psi at the gun inlet and setup the gun per the manufacturers spec. This results in 2-3 coats per side with time between coats for flash off.

The problem with this approach is that we have to tape mask any connector and latex around the connector where the tape mask meets the PCB to avoid coating wicking into the connectors via exposed leads.

Has anyone found a way to avoid the extra labor of having to mask connectors so intensely and just avoid wicking altogether (and the subsequent labor of touching up the leads after manual spray)?

Thanks in advance for any insight! -Phil

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AR/UR Coating Application | 31 January, 2018

Hit wax dip of your edge connector. HVLP spray your conformal coating. hot alkaline wash to remove the wash. Followed by de-ionized water.

Other techniques using peallable latex.


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AR/UR Coating Application | 1 February, 2018

Interesting, never heard of using wax as a coating mask. Not sure how well the AR coating would hold up to a hot alkaline wash (unless you have experience with it), but that stuff usually starts to flake off/de-wet if you just look at it wrong.

I'm currently using tape to mask the body of the connector and liquid latex for where the leads meet the board, but it's a lot of labor and materials on both the front and back end.

I'm hoping I can find a way to spray the coating so that the solvents are almost evaporated by the time they hit the board, which will hopefully get rid of the wicking worry.

Experiment time I suppose.

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AR/UR Coating Application | 1 February, 2018

I'm not sure if your customer will allow it but consider sealing the perimeter of the connector where it meets the board with some kind of sealant or staking material. Cure it then apply tape on top of it. Then all you have to do is remove the tape and it also provides more mechanical stability to the connector as long as the sealant doesn't interfere with the mate. We used this approach on a couple of assemblies with success. Just be sure not to use any silicone, as it may affect the curing of the coating. To reduce time, consider using a boot instead of tape if you can obtain one that fits.

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AR/UR Coating Application | 1 February, 2018

We supply to defense primes, so there's not really any wiggle room on these sort of issues.

Thanks for the idea though.

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AR/UR Coating Application | 6 February, 2018

For anyone looking back on this post, I ended up figuring out something that will work for my process.

Jack up the atomization pressure on the guns, lower material flow, quicker-lighter coats, less time between coats, and more coats.

Smooth, even finish without worry of wicking into connectors due to the low amount of material deposited on each pass.

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AR/UR Coating Application | 9 February, 2018

Have you considered Teflon boots over your connectors? 1B31 cleans up quite nicely with IPA. It makes reusable fixture concepts pretty attractive.

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AR/UR Coating Application | 12 February, 2018

Yep, that's already in the works, but boots by themselves don't address the wicking issue.

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