N_Cook said:
Plasticizer or something leaching out of the flexible membrane, at the edge, dissolving the green pcb lacquer coating and etching lines into the pcbtraces. The one that failed was actually at this line through a test pad circle, rather than just the width of a trace
The plastic membrane seems to leave this oil slowly. I have so far not seenany secondary effect caused by this oil, it appears to be non conductive, non corrosive and it allows the contact of conductive pads without problems.. When I have to repair a remote I clean this oil but after some time of use it forms again near the most used buttons.
The conductive black rubber sooner or later wears out. Cleaning the surfacesometimes works but not for long. Time ago I used conductive paint but it does not last either. I found it difficult to paste conductive foil, it canfall easily and keep the button permanently pressed.
So for a lasting repair I use a needle to create a small hole across the rubber under the conductive surface, it is surprisingly easy to puncture. Then I run a very fine copper wire through this hole and bend the ends so theylay on the failing conductive pad. It lasts forever and works great.