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I have a well tested PCB which uses 12µA in sleep mode. I decided to apply conformal coating.

I must say I was a bit liberal with the spray (Plastik 70.)

pcb

I waited around 30 minutes before checking the PCB current in sleep mode. It turned out to have increased by over 100 times to ~1600 µA.

I want to know if there's something I did wrong. Did I apply too much coating, or I did I not wait long enough for it to dry?

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  • \$\begingroup\$ Data sheet page 1: For repair works PLASTIK 70 can be soldered through or be totally removed with acetone, THINNER FOR PLASTIK 70. \$\endgroup\$
    – Russell McMahon ♦
    Commented Sep 13, 2021 at 12:55
  • \$\begingroup\$ Try again in 48 hours. \$\endgroup\$
    – user16324
    Commented Sep 13, 2021 at 13:46
  • \$\begingroup\$ @user_1818839, I followed advice as given in answer. After drying (under hair blower for 30 mins), I used the pcb again, and it starts functioning perefectly, however, after an hour or two of operation, it starts to falter again. I again did the hair dryer thing, it again became functional, and then went back into bad state after couple of hours again. What exactly may be the reason for that? \$\endgroup\$
    – Ouroboros
    Commented Sep 14, 2021 at 10:06
  • \$\begingroup\$ Note that nail varnish remover is not pure acetone (and some is not acetone at all). impurities may allow moisture absorption or porous structures in the next concoat. For example, alcohols absorb water. Set this PCB aside, build and test another, follow proper procedure in coating. If that works, come back to cleaning this one properly. (If not, buy a better concoat) \$\endgroup\$
    – user16324
    Commented Sep 14, 2021 at 12:19

1 Answer 1

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Plastik 70 needs 24 hours of drying time to get to the dielectric specifications in the datasheet.

Also:
Contains “moisture warning”: To avoid involuntary encapsulations of moisture, Plastik 70 will warn you when applied on a humid surface, by showing a frosted, mat appearance.
And now look at your photo...

Rinse with acetone, dry the board in the oven, and try again. This time according to application instructions.

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  • \$\begingroup\$ Do you think waiting 24 hours will make the pcb current come back to normal? @Jerone3, please let me know. \$\endgroup\$
    – Ouroboros
    Commented Sep 13, 2021 at 7:39
  • \$\begingroup\$ And i have nail thinner. Can I use that to rinse? \$\endgroup\$
    – Ouroboros
    Commented Sep 13, 2021 at 7:41
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    \$\begingroup\$ @Ouroboros if you leave the coating with the moisture underneath it may even get worse. Why not follow the good advice given? \$\endgroup\$
    – Solar Mike
    Commented Sep 13, 2021 at 7:51
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    \$\begingroup\$ @Ouroboros Possibly. Try it on an old pcb first that it doesn't dissolve the green mask, text and parts bodies. Since nail remover isn't acetone anymore. No-clean flux remover also works, but less effective. Electrolube also sells coating remover, may work on this. \$\endgroup\$
    – Jeroen3
    Commented Sep 13, 2021 at 7:58
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    \$\begingroup\$ @Ouroboros Yes, remove it. Dry your board (in an oven 60 C for 30 mins). Then re-apply. \$\endgroup\$
    – Jeroen3
    Commented Sep 13, 2021 at 8:23

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