Last article I mentioned that my company applied the metal dome without dimple as keypad contact solution just like the cell phone but we met keypad press insensitive issue. Now we had solved the problem by adding the dimple back to the metal dome and still reach 1,000,000 times of finger press cycle lifetime.
We did some failure analysis and found the keypad insensitive defect was caused by two major issues. One is the foreign contamination, include dust and fiber, that I mentioned at last article. Another one is the oxidation show on the immersion gold finished on the ENIG board pads.
We found the oxidation particles look like the chemical of “P” exuded from base material of PCB. The “P” is one of the major element for the ENIG fabrication process. So we only can control less “P” but can’t remove it from the board.
