[chbot] Plastic film on PCB for water-proofing

[Tim Buchanan]

Hi Stephen,

It sounds like "conformal coating". You can get it in a spray can or as a
brush on goop. I've seen it used often in auto electronics. Some types are
a pain to get off, some peel off easily and some need a soak in IPA.

Hope this helps,
Tim

On Wed, Apr 3, 2024 at 9:53 AM Stephen Irons <stephen at irons.nz> wrote:

> Over the weekend, I repaired my e-book reader. The micro-USB connector was
> no longer working. It turned out that force from the USB cable had lifted
> the soldered connections from the PCB. I would have liked to have replaced
> the connector while the housing was open, but could not find a replacement
> that looked similar. However, touching up the solder joints with a fine
> soldering worked a treat.
>
> The e-book reader is sold as 'water-proof' to something like 2 m for 30
> minutes (IP-67?). It seemed that there were lots of places that water could
> get in: USB connector, power button, case-halves, screw holes, and the
> screen bezel, at the edges along the case and the edges along the screen.
>
> There was no real sealing around the USB connector. It was a close fit,
> but not tight by any means. I have opened many water-proof housings (pet
> trackers, trail cameras, etc) and was surprised by the lack of rubber
> seals, etc. I am sure water could get into the housing.
>
> The thing I found surprising was that the entire PCB was covered front and
> back with a thin plastic film. The film had obviously been applied after
> the connectors were fitted, as I had to break the film to remove the
> connectors.
>
> [There were 5 connectors on the PCB: the USB connector, 3 ZIF connectors
> for flex PCBs (for screen connection, magnetic cover sensor and one other),
> and a 2-pin battery connector. Also, a tiny power-button].
>
> The only breaks in the film were around the connectors, and the film was
> stuck very lightly to the PCB, around the USB connector (leaving the hole
> open), the flex-PCBs and the battery wires.
>
> So, water-proofing obviously comes from the plastic film. But what about
> the battery and screen?
>
> Has anyone seen something similar? What is this film or the process of
> applying it called?
>
> Stephen Irons
>
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