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Cleaning before Conformal Coating

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Amol

#36590

Cleaning before Conformal Coating | 9 September, 2005

Hi, I am running a circuit board that needs a part to be put on it after cleaning and before conformal coating. the only problem is that after cleaning and hand assembly of the part, there is a thin whitish residue in the ckt board that one can see when seen at an angle under light. brushing with xylene will clean it. After conformal coating, the ckt boards that were left uncleaned of this white residue show good conformal coat coverage, but the ckt boards scrubbed clean with xylene shoe dewetting on the coat. I am using Humiseal UR coat. does anyone have an idea of what this whitish layer is??

Thanks, Amol

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URL

#36591

Cleaning before Conformal Coating | 9 September, 2005

The hand assembled part is soldered in? If so, the white residue may be from the operator using some added wave solder flux to get better wetting when hand soldering.

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patrickbruneel

#36592

Cleaning before Conformal Coating | 9 September, 2005

If the white residue is from a no-clean flux or no- clean solder flux core you can leave it on the board. (Consult with the flux or cored solder manufacturer) Because after being encapsulated with conformal coating the residue is sealed from humidity. I believe the reason for the dewetting after cleaning with xylene is that xylene is water repellent (not soluble in water) and if you use water-borne polyurethane coating the xylene residue will cause dewetting.

Why are you using xylene to clean the board? Xylene is a solvent used in epoxy based coatings.

Hope this helps Patrick

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GS

#36595

Cleaning before Conformal Coating | 9 September, 2005

You can find some input on IPC-HDBK-830 Guidelines for Design, Selection and Apllication of Conf Coating.

Also look at IPC-CH-65A, Guidelines for Cleaning of Printed Board Assemblies.

Regards...........GS

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Amol

#36612

Cleaning before Conformal Coating | 12 September, 2005

The fluxes used in the board manufacture are RMA fluxes. The board is cleaned according to the IPC standards and tested to ensure quality.

I am thinking of designing a DOE to isolate the problem

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#36615

Cleaning before Conformal Coating | 12 September, 2005

Amol,

Your problem is already very isolated only one part has the problem (the part that is hand soldered) Manual cleaning is very difficult. Why are you not considering a no-clean cored solder to solder the one part and skip the manual cleaning. Don't forget to check what URL said in his response this happens a lot.

Good luck and it would be nice if you let us know the outcome

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Amol

#36842

Cleaning before Conformal Coating | 26 September, 2005

hi, sorry for the late reply. We solved the problem by rinsing the boards in deionized water after alcohol scrub

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