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Printed Circuit Board Assembly & PCB Design Forum

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Conformal Coating over No Clean Flux



Conformal Coating over No Clean Flux | 29 January, 2001

Hi all, Here's the deal. I have a customer for whom I assemble a lot of product. All of their product mix goes through a water soluble process. Much of it gets conformal coated. They are in the high power arena but some products are simply control boards and motor starters. I'd like to shift over to a No Clean process on some of these products as it's more economical for us as well as my customer but I don't know if I can conformal coat boards with No Clean flux still on them. Does anyone know if there are any limitations or reasons why I can't do this??? I'm currently using Alpha UP-78 PT1 as my No Clean Flavor of the Month and the Humiseal 1C51 (Silicon) conformal coat. I look forward to any responses..

Thanks, Justin

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Conformal Coating over No Clean Flux | 29 January, 2001

We have been using a VOC-free, no-clean flux on our boards that we conformally coat with no problems. We're using both a UV cured and a heat cured Silicone conformal coating. One thing to beware of is inhibition in the silicone. We found that out the hard way with a peroxide cured EPDM material coming in contact with our platinum catalyzed, addition cured silicone potting compound.

If the Humiseal is an addition cure silicone, there might be some problems with the no-clean residues. Additon cure silicones are susecptable to inhibition by some fluxes. You need to run a compatibility study with the flux candidates and your conformal coating to find out if there may be inhibition. Many of the silicone manufacturers list the possible silicone inhibitors on their web pages.

Like I said though, no-clean fluxes and silicone conformal coatings can work.

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Conformal Coating over No Clean Flux | 29 January, 2001

BL is correct. The two issues are:

1 How thick are you putting the NC residues on your boards.

2 Some NC flux residues work with some conformal coats. Contact Graham Naisbatt [Concoat Ltd +44 (0) 1276 691100 Fax:+44 (0) 1276 69122 Alsasan House, Albany Park Camberley GU15 2PL UK]. He can give your specific suggestions about the combination you propose.

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Conformal Coating over No Clean Flux | 29 January, 2001

I know you're talking Humiseal, but this may help

Conformal Coatings (PDF Documents)

"Conformal Coating Overview" (Lester D. Bennington, Senior Development Chemist and David Crossan, Manager, Electronics Product Development, Loctite Corporation) "Process Requirements for Solvent-Free UV Conformal Coatings" (Barry Ritchie, Loctite Corporation USA) "Conformal Coating Over Existing Process Residues" (Barry Ritchie, Loctite Corporation USA)

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