The working principle of a membrane switch is based on the electrical conduction triggered by mechanical pressure, relying on the contact and separation of conductive layers within its layered structure to control the on/off state of a circuit. Here’s a detailed breakdown:
Core Components Involved
A typical membrane switch consists of several key layered components (from top to bottom):
Top Graphic Layer: A thin, flexible film (usually PET or PC) with printed labels, icons, or text for user identification. It protects internal layers and serves as the user interface.
Spacer Layer: A non-conductive, thin film (often PET) with precision-cut holes (or "windows") at switch positions. These holes separate the top and bottom conductive layers when the switch is not pressed, preventing unintended contact.
Upper Conductive Layer: A film (e.g., PET) coated with conductive ink (usually carbon or silver) at positions corresponding to the spacer’s holes. These are the "upper contacts."
Lower Conductive Layer: A base film (e.g., PET or PCB) with printed conductive traces (the "lower contacts") that connect to external circuits (e.g., a controller or microchip).
How It Works (Step-by-Step)
Rest State (Switch Off):
When no pressure is applied, the spacer layer keeps the upper and lower conductive layers physically separated. The circuit remains open, and no electrical current flows.
Activation (Switch On):
When a user presses the top graphic layer at a designated switch position, the pressure compresses the layers. The upper conductive layer (at the pressed position) bends downward through the spacer’s hole and comes into direct contact with the corresponding lower conductive layer.
This contact closes the circuit: electrical current flows from the lower conductive traces through the upper contact, creating a signal (e.g., to a microcontroller).
Deactivation (Switch Off):
When the user releases pressure, the flexibility of the top and upper conductive layers causes them to rebound. The upper conductive layer separates from the lower layer, breaking the electrical connection. The circuit opens again, and the signal stops.
Key Notes
Conductive Materials: The conductive layers use materials like carbon ink (cost-effective) or silver ink (higher conductivity, for low-resistance applications).
No Moving Parts: Unlike mechanical switches with metal levers or springs, membrane switches rely on the flexibility of thin films for operation, making them slim and durable.
Customization: The number and layout of switches (conductive contact pairs) can be tailored to specific needs, allowing for complex control panels (e.g., with multiple buttons or sliders).
In short, a membrane switch functions as a "pressure-sensitive conductor": mechanical pressure bridges the gap between separated conductive layers, completing the circuit and sending an electrical signal—all in a compact, low-profile design.
