Non-Tactile Bottom Circuit Layer
Membrane Switch Circuitry
Diagram of a non-tactile membrane switch circuit
The bottom circuit layer, or static layer of the membrane switch contains the main circuitry necessary for the switch to function. The circuitry consists of printed conductive ink traces, the flex cable, support connectors and any optional components. While this layer may be flexible, it does not flex during switch activation. For this reason it requires a rigid surface behind it to stabilize the switch.
Membrane Switch Traces
The circuitry traces are printed using specially formulated inks containing conductive materials; typically silver, copper, or carbon. The width of the traces directly affects the reliability of the switch. Thicker traces, while more costly, increase the speed of electrical current flow and ensure easy passage.
Membrane Switch Flex Cable
The flex cable, often called the tail, connects the switch to the PCB that controls the electronic device. The tail also allows interconnection to the power source and other components. The tail must not be curved or folded beyond a .100" radius therefore it must be of sufficient length and positioned properly in relation to the PCB it will connect to. The tail cannot be extended post production without incurring tremendous cost. A layer of shielding, typically polyester, is often laminated over the tail traces to prevent abrasion or electrostatic discharges which may result in circuit failure.
Membrane Switch Components
Components such as LED's are soldered to the static layer because it does not flex ensuring the reliability of the joints. Other components include hard switches and displays.
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