Conductive pills are frequently used in silicone keypads to short out the traces of a shorting pad on a printed circuit board. These pills, are usually made from a silicone conductive material that typically contains carbon. Conductive pills are attached to the plunger of a keypad for closing the circuit on a PCB trace. Before the silicone key is pressed, the trace located on the pad is in its open position. When the silicone key is pressed, the carbon makes contact with the traces located on the pad and creates a closed position allowing electricity to flow through the carbon to the traces.
Conductive pills are typically made the same way silicone keypads are made. The material makeup is composed of a mixture of silicone and conductive material. On a typical conductive pill, Carbon is used as a conductive material. When the silicone key is pressed, the conductive particles in the pill become squeezed together. This allows for a flow of electricity.
SiTech has the ability to create carbon pills in all shapes and sizes. We recommend a typical diameter shaped pill ranging in size from 0.100” – .325”, but if your design requires a custom shape we have the capability of providing these. Keeping your pill design similar throughout the keypad, will decrease costs compared to multiple sized and shaped conductive pills. Conductive pills contain silicone rubber within them, which allows for a permanent bond between the keypad and conductive. Each pill is molded into the parts by insert molding. The minimum pocket depth needed for a conductive pill is approximately 0.012”, and the maximum is typically 0.078”.
When backlighting is needed for your silicone keypad, but your PCB design dictates that conductive pills are needed a simple solution can be the use of a donut conductive pill. Donut conductive pills basically have a hole in the center of the pill, leaving an opening for an LED to backlight the keypad. Typically for the Donut pills, you would want a minimum thickness of approximately 0.090”.
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