As a weekend project I am trying to fix my TV's remote and I noticed that the contacts of the remote's keyboard is covered by a thin blue film:
As you can see, the remote's PCB is covered by a blue layer of some sort of film. I wondered what is this film that the remote is covered with? Also can this film be affected somehow if the remote fails to indicate that a button has been pressed?
I have not seen this construction in the wild, but it looks to me like a printed dielectric layer and a printed carbon ink layer overtop of that. That allows a much cheaper punched single-layer paper-based phenolic PCB to be used- the carbon ink acts both as contacts for the silicone keyboard keys and as jumpers.
Lack of recognition of a button press could be because of a faulty connection between copper and carbon, a dirty contact on the silicone or PCB side, or a cracked PCB or lifted pad (remotes take a lot of abuse and come in intimate contact with greasy human paws and sometimes food and drink). They are also conveniently bone-shaped if you happen to have a large dog.
There is conductive traces in the top of the pcb to act like switch with upper membrane (keypad). This blue thing acts like some sort of insulator (solder mask or kapton) to protect the traces where supose not to contact.
