Basic structure and working principle of membrane switch

2020-07-16

　Basic structure and working principle of membrane switch
Membrane switch is a kind of multi-layer structure (planar) (non-locking) key switch composed of a certain elastic insulating material layer, which integrates the functions of keys, indicating elements, instrument panel and so on. The action of the membrane switch is only achieved by the vertical movement of the elastic membrane. Although the elastic membrane has undergone a million times of creeping, and the amplitude during creeping is very small, only 0.1-0.3MM, plus the rationality of the material selection, so the membrane material The ability to withstand a large life of more than one million times without deformation is what determines the durability of the membrane switch.
Membrane switches are beautiful in appearance, long in service life, simple in structure, easy to install, good in use feel, small in occupied area, etc., and are widely used in various industries, from household appliances to high-tech products, slowly replacing Some of the tact switch markets have a huge market share.
In general, the common membrane switch is mainly composed of 6 layers of materials, in order from the table to the inside are the panel, surface glue, upper circuit, isolation layer, lower circuit, bottom glue. Each layer structure is introduced below:
1) Graphic stacking: The panel is the "coat" of the entire membrane switch. On the basis of proper arrangement of the buttons, through different colors, patterns and button shapes, it plays a necessary decorative role for the entire membrane switch. The main function of the panel layer is to play the role of logo and key, so the selected material must have the characteristics of high transparency, high ink adhesion, high elasticity, and anti-folding.
2) Upper circuit and lower circuit: The upper and lower circuits are the electrical components of the membrane switch and the "off" and "key" of the switch. Their performance directly affects the performance of the switch electrical appliance, mainly by printing on the membrane Formed with a layer of conductive material. The upper and lower circuits are responsible for the two electric shock roles necessary for the switch to close. Its thickness is generally within 0.05--0.175MM, and the most common is 0.125MM PET.
3) Surface adhesive, isolation layer, and bottom adhesive: The materials of these three layers are double-sided adhesives, which have different names due to their different positions in the switch structure. The three-layer double-sided adhesive tapes have different thicknesses according to their respective levels. This is mainly determined by the thickness of the switch and the operating force of the buttons.

The basic working principle of the membrane switch is as follows: when the panel is not pressed, the membrane switch is in a normal state, and its upper and lower contacts are in a disconnected state, and the isolation layer isolates the upper and lower lines; when the panel is pressed, the upper The contact of the circuit is deformed downwards, and it merges with the lower circuit to make the circuit conductive. The connected circuit signals the external connection instrument (substrate) to achieve its corresponding function; when the finger is released, the upper circuit touches The point bounces back, the circuit is disconnected, and the loop triggers a signal.