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While performing CPR on a MacBook Pro exposed to water, I accidentally removed a piece of glue/epoxy from the logic board. It is a strip of glue covering two components with blank metal surfaces.

It is visible here near the ethernet port:

It is visible here near the ethernet port

I found similar applications on the back-side of the logic board, more easily visible.

Do you have any idea what its purpose is? If removal may have caused damage and if it needs reapplication?

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I don't know what the glue is for, but it unlikely serves any electrical function. It may have something to do with the manufacturing process. Electrically the glue should be a insulator, so replacing it with air should do no harm at these voltages.

In any case, you've got little to loose by trying to power up the board again. If it works, great. If it doesn't, you are no worse off than if it is already broken.

There are two things to consider when dealing with wet electronics:

  1. Washing with ordinary tapwater is usually OK, but it is a good idea to do a final rinse with distilled or de-ionized water to make sure no residue is left over.

  2. Make sure the board is absolutely dry before powering it up again. This includes places you might not be able to see water, like under some surface mount chips. After the distilled water rinse, shake off as much water as you can, then let the board sit on something warm for a day, for example, to make sure it is really dry. Don't bake it or heat it warmer than you can touch, but elevated temperature compared to the surrouding air plus time will cause the remaining water to evaporate out of the nooks and cracks where you can't see it. Sitting on a radiator for a day should be good enough.

    A hair dryer far enough away to keep the board at touchable temperature will get the obvious surface water off quickly, but it takes time for the water to get out of all the little cracks. It can look and feel dry, but the water in the cracks where you can't see or feel it can still cause trouble. 24 hours of warmth in relatively dry air should be good enough.

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  • \$\begingroup\$ I've always rinsed wet components with 90% (or higher) rubbing alcohol. It displaces the water, and then evaporates very quickly. Is there some reason not to do this? Thanks! \$\endgroup\$
    – bitsmack
    Commented Apr 11, 2014 at 16:20
  • \$\begingroup\$ @bits: Isopropyl alchohol is generally safe on electronic components, but you should check first. It can be useful in dissolving some additional crud that water can't, but I wouldn't be lulled into complacency by the fact that it evaporates quickly. Water can still be stuck in cracks that the alchohol might not have replaced. \$\endgroup\$
    – Olin Lathrop
    Commented Apr 11, 2014 at 16:22
  • \$\begingroup\$ Cleaned it by submerging in Isopropyl and leaving to dry for two days. Powered up and working. Thanks Olin. \$\endgroup\$
    – chknapp
    Commented Apr 12, 2014 at 14:13
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This type of insulation is often used in High Voltage nodes, to avoid direct touching with other circuitry and human contact. So probably that is just a HV node.

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