Conformal Coating Killing Circuits

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Hi, I have a PCB that works fine when tested before conforma... - Jul 29, 2020 by SMTA-64387706 SMTA

If the PCB is thin, is it possible that the board is warping... - Jul 30, 2020 by PhilC

Same line of thinking with Pete here. Why thin board and thi... - Jul 30, 2020 by Evtimov

Feel free to contact me via email as I can offer you help wi... - Aug 07, 2020 by Lou

We have found Acrylic CC under QFNs is a failure mechanism i... - Aug 10, 2020 by SMTA-64386637 SMTA

What your said looks like a acrylic coating thermal expansio... - Aug 20, 2020 by sssamw

SMTA-64387706

#85341

Conformal Coating Killing Circuits | 29 July, 2020

Hi, I have a PCB that works fine when tested before conformal coating with HumiSeal 1B73. It seems like the CC is causing electrical issues. We brush it on, so it is a bit thick. After curing we are getting QFNs that do not seem to connect well and a couple of pull up resistors that run into trouble. 0201 resistors, 6pin QFN, ENIG boards, boards are very thin .031"

1) Does anyone have any ideas?

2) Is there a service or company or consultant out there that can section / inspect the board for cracks or cracked solder or?

This message was posted via the Electronics Forum @ SMTA SMTA

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PhilC

#85344

Conformal Coating Killing Circuits | 30 July, 2020

If the PCB is thin, is it possible that the board is warping slightly during the curing process?

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Evtimov

#85346

Conformal Coating Killing Circuits | 30 July, 2020

Same line of thinking with Pete here. Why thin board and thick coating? Did you consider to use underfill instead?

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Lou

#85411

Conformal Coating Killing Circuits | 7 August, 2020

Feel free to contact me via email as I can offer you help with all aspects of the Conformal Coating process. Let's make sure that is right first.

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SMTA-64386637

#85428

Conformal Coating Killing Circuits | 10 August, 2020

We have found Acrylic CC under QFNs is a failure mechanism in thermal cycling. The coating acts as a wedge and causes solder joint cracks. We do not coat QFNs. To enhance reliability we have the vias plugged with solder mask. This eliminates some of the exposed metal. You could also try silicone coatings which can be more compliant.

This message was posted via the Electronics Forum @ SMTA SMTA

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sssamw

#85485

Conformal Coating Killing Circuits | 20 August, 2020

What your said looks like a acrylic coating thermal expansion causes small solder joint crack. Do you cure coating with heating, or heating after curing? Solder joint crack while you see resistor and QFN trouble? Clear and detail description of your problem can help to dig out the root cause.

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