Carbon Oil Board

A PCB with screen-printed carbon ink pads used as low-cost dome-key and rubber-keypad contacts. Carbon ink is deposited on top of finished copper pads after solder mask, then cured to form a wear-resistant conductive surface that mates with carbon pills or conductive elastomers under a silicone keypad. Compared with gold-plated contacts, carbon ink is far cheaper, doesn't tarnish, gives a controlled higher contact resistance that suppresses contact bounce, and survives millions of key presses in consumer products. Typical uses are remote controls, calculators, white-goods control panels, audio mixer keypads, electronic toys, and instrumentation front panels where cost per contact is the dominant constraint.