Without dimple Metal dome as keypad contact

Recently we phased in the meal metal dome as rubber keypad contact solution. The same solution implement to many cell phone keypad solution also. The good is that metal dome can sustain 2,000,000 times of finger press lifetime verse 300,000 times for polydome.

We removed the dimple from the metal dome in order to reach higher lifetime. Because of the dimple will damage the gold plating on the PCB and obtain verdigris from the copper layer base of PCB. The verdigris will finally disconnect the metal dome and contact pad on PCB result in keypad malfunction.

After several times trial run, we found we didn’t get the profit of long lifetime but met the keypad insensitive pressing issue. The keypad press feeling is good but no function while press it slightly. We must give more force to press the keypad then active the key. The worst is that sometimes the insensitive keypad happens after a period of usage.

We did investigation on the insensitive keypad and found some tiny dust or fiber under metal dome or on the PCB contact area will bring this kind of defect. the foreign partials will stop the metal dome contact to the PCB while slightly press. The metal dome will contact to PCB while give more force press down the keypad and squelch the partials.

So, how can we do? add the dimple back to metal dome? Sealing the metal dome on PCB under clear room environmental?

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