Membrane Switch Structure

Structure of membrane switch

1. Panel layer

The panel layer is generally made of fine patterns and characters on the colorless and transparent sheet wires such as PET and PC which are less than 0.25mm. The main function of the panel layer is  marking and pressing keys, so the selected materials must have the characteristics of high transparency, high ink adhesion, high elasticity and high toughness.

2. Surface adhesive layer

The main function of surface adhesive is to connect the panel layer and circuit layer closely to achieve the effect of sealing and connection. The thickness of this layer is generally required to be between 0.05-0.15mm with high stickiness and aging resistance; During the production, the special double-sided adhesive for membrane switch is generally selected. Some membrane switches are required to be waterproof and high temperature resistant, so the surface adhesive must also use different materials according to the needs.

3. Upper and lower layers of control circuit

This layer adopts PET membrane with good performance as the carrier of switch circuit diagram, and uses special process to screen conductive silver paste and conductive carbon paste on it, so that it has conductive performance. Its thickness is generally within 0.05-0.175mm, and the most common is 0.125mm PET.

4. Intercalation layer

It is between the upper and lower circuit layers and plays the role of sealing and connection. Generally, PET double-sided adhesive is used, with the thickness ranging from 0.05 to 0.2mm. When selecting the material of this layer, the overall thickness, insulation, the hand wrapping feel of circuit key and tightness shall be fully considered.

5. Back adhesive layer

The use of back adhesive is closely related to the material kind  which the membrane switch is pasted with. The commonly used material are double-sided adhesive, 3M adhesive, waterproof adhesive, etc.

Membrane switches are classified by structure:

1) Flat with no touch type:

Long service life and no touch;

2) Convex adhesive sheet with touch type:

Good touch feeling, but relatively short service life;

3) Convex frame with no touch type:

Beautiful appearance, strong three-dimensional perception and no touch;

4) Convex frame with touch type:

Beautiful appearance, strong three-dimensional perception and touch;

5) Convex panel with touch type:

(a)type: it is easy to have two-section phenomenon for the appropriate design, the electrical performance is still good though the panel is damaged;

(b)type: no two-section phenomenon, and less structural layers, more economical, but the electrical performance will be damaged if the panel is damaged,;

6) Metal shrapnel type:

(a) type: the most basic and commonly used structure. The shrapnel not only plays the role of touch but also acts as the upper circuit;

(b) type: complex structure, used for the occasions where there are more compact shrapnel and no jumper. The shrapnel is placed on the upper circuit, the conductive surfaces of the upper and lower circuits are upward, and the upper circuit needs to be punched. When this kind of structure is connected, the four legs of the shrapnel are not in the same plane as the center point, and there are two sections. At the same time, the shrapnel is often in the excessive concave state. After a long time, the shrapnel will not rebound, so the type is not recommended;

(c) type: the shrapnel is placed on the upper circuit and only plays the role of touch. When the upper circuit is conductive downward and the lower circuit is conductive upward, and there are "two sections", so the type is not recommended;

(d) type I: the shrapnel is placed on the lower circuit, and both the upper and lower wires are routing. The shrapnel not only plays the role of touch, but also connects the upper and lower circuits. It is used in the situation where there are more shrapnel which is more compact and no jumper, and its structure is simpler than type (b). During the design, attention should be paid to avoid the four legs of the shrapnel in case short circuit.

7) Luminescent body type: must open the base adhesive mold;

(a) type: The LED wire and the lower wire are on the same layer: the structure is simple, but if the selected LED light is high, the LED light will jack up the panel. At this time, the LED window on the panel should be convex, or the surface adhesive layer should be thickened to make it thicker than the LED light;

(b) type: LED wire and lower wire are on the different layers: the structure is complex, but the LED window does not have to be convex, but the upper area of the LED light must be hollowed out to prevent the light from passing through the hole of the LED light. Note: at this time, the LED light hole should be kept away from the wiring when routing the lower circuit.

8) fold type:

This type can avoid jumper and do not need to filling holes to make the conductive surface downward. The disadvantage is that the circuit is easy to break at the fold.

9) Waterproof type of inner and outer frame:

The outer frame is a closed frame without wire routing, which protects the inner frame and prevents moisture from entering the shell from the outlet groove.