What is the specific internal structure of the membrane switch?

Membrane Switch is a new type of electronic key operation system that integrates the functions of buttons, indicator elements and instrument panels. Its internal structure is very precise, usually being assembled by layering multiple layers of flexible film materials (such as PET or PC) through pressure-sensitive glue or heat-sealing processes.

From bottom to top, its core structure usually consists of the following five to six key components:

1. Lower circuit layer (lower base layer)
This is the design layer of the bottom circuit of the membrane switch, usually made of PET material. The surface of this layer is printed with corresponding circuit graphics using conductive materials (such as silver paste, carbon paste or copper foil alloy), forming the lower conductive part (fixed piece) of the switch circuit.

2. Isolation layer (interlayer / partition layer)
It is located between the upper and lower circuit layers. Usually, it is made of extremely thin PET double-sided adhesive (with a thickness generally ranging from 0.05 to 0.2mm). Its main function is to isolate the upper and lower layers of circuits, preventing accidental triggering. At the positions corresponding to the key contact points, the isolation layer will have breathable holes (keyhole), which is the space for the switch action and the contact between the upper and lower contacts.

3. Upper circuit layer (conductive path layer)
It is located above the isolation layer and is also printed with conductive silver paste or carbon paste traces on the flexible polyester film, forming the upper conductor (moving piece) of the switch. Each key corresponds to one conductive piece, and the moving piece is usually designed in a dome shape or with a special geometric shape such as a serpentine bend, giving it good elasticity and reset ability.

4. Panel layer (graphic covering layer)
This is the topmost layer of the membrane switch and the interface that users directly touch. It usually uses colorless transparent sheet materials such as PET or PC with a thickness of less than 1mm. The surface is printed with exquisite patterns, text labels, trademarks, or transparent windows through screen printing technology. It not only provides visual guidance but also serves to protect the internal circuits and prevent dust and water damage.

5. Backing Layer (Backside Adhesive Layer)
This layer is located at the bottommost part of the entire membrane switch and is used to firmly attach the assembled membrane switch to the casing or panel of the instrument or equipment. Common backing materials include the 3M series adhesives, which are required to maintain high strength and anti-aging properties in different temperature environments.

6. Additional Function Layer
According to specific application requirements, other functional layers can be added inside the membrane switch. For example, to provide a clear "click" tactile feedback, metal spring clips or raised structures can be added to the upper circuit layer; to make it visible in low light conditions, an LED backlighting layer can be added; to shield against electromagnetic interference, an electromagnetic shielding layer printed with conductive ink can be added.

Brief description of the working principle: When the finger is not pressing the panel, the contacts on the upper and lower circuit layers are in an open state due to the effect of the isolation layer; when the finger is pressed, the contact on the upper circuit layer deforms downward and passes through the through-hole of the isolation layer to come into contact and conduct with the lower circuit layer, thereby sending a trigger signal to the external device; after the finger is released, relying on the elasticity of the material, the contact on the upper circuit layer rebounds and resets, and the circuit is again disconnected.