Electronic – Silicone Keypad Design Problems


My device uses a silicone keypad to detect a key press rather than a physical button.

After setting up, it works smoothly, even without applying much pressure to the keypad.

However, after a while ( say 2 months), you will need to apply much pressure on the key pad before a key is detected. It continues like this for a while, and then no keys can be detected again.

So we open, clean the PCB keypad traces with "methylated Spirit". And it works back as new. Sometime, we see black residue on the keypad PCB traces, which appears to come off the conductor of the silicone keypad. We wipe this off and everything is back to normal.

My question is how to avoid this problem.

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Best Answer

Electricity and water is the issue. The tin in the solder plating will grow a crystalline structure and form an oxide that doesn't conduct very well. Spent many months in the 1980s solving this problem and the bottom line is use gold plate. Don't be cheap on this. The company I worked for at the time sued the supplier a lot of money for their incompetence and they were big in the industry at that time.

If you can't seal it (and clearly you can't because you can clean the contacts) then water will get in. It's inevitable.