[chbot] Plastic film on PCB for water-proofing

[Stephen Irons]

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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