Basic structure and working principle of membrane switch

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Basic structure and working principle of membrane switch

Membrane switch is a kind of multi-layer structure (plane) type (non-locking) key switch composed of a certain elastic insulating material layer, which integrates the functions of keys, indicating components, instrument panels, etc. The action of the membrane switch is only realized by the vertical movement of the elastic membrane. Although the elastic membrane has undergone millions of peristalsis, the amplitude of peristalsis is very small, only 0.1-0.3MM. In addition, the material selection is reasonable, so the membrane material can withstand a large life of more than one million times without deformation, which all determine the durability of the membrane switch.


Membrane switches have the characteristics of beautiful appearance, long service life, simple structure, convenient installation, good hand feeling, and small footprint. They are widely used in all walks of life, from household appliances to high-tech products, and slowly replace The market for some tact switches occupies a large share in the market.


Generally speaking, the common membrane switch is mainly composed of 6 layers of materials, which are panel, surface adhesive, upper circuit, isolation layer, lower circuit and bottom adhesive in the order from table to inside. The following describes the structure of each layer:


1) Panel: The panel is the "coat" of the entire membrane switch. On the basis of properly arranging the keys, through different colors, patterns, and key shapes, the entire membrane switch plays a necessary decorative role. The main function of the panel layer is to play the role of identification and keys, so the selection of materials must have high transparency, high ink adhesion, high elasticity, anti-folding and other characteristics.


2) Upper circuit and lower circuit: The upper and lower circuits are the electrical components of the membrane switch, and are also the "off" and "key" of the switch. Its performance directly affects the performance of the switch electrical appliance, mainly by printing on the membrane. Formed by a layer of conductive material. The upper and lower circuits play 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 primer: the materials of these three layers are all double-sided adhesive, which have different names due to the different positions in the switch structure. The three-layer double-sided tape has different thicknesses depending on the level of each, which is mainly determined by the thickness of the switch and the operating force of the key.


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, its upper and lower contacts are in an open state, and the isolation layer isolates the upper and lower circuits; When the panel is pressed, the contact of the upper circuit deforms downward, overlaps with the lower circuit and makes the circuit conductive. The conductive circuit signals the external connecting instrument (substrate), thus realizing its corresponding function; when the finger is released, the upper circuit contact bounces back, the circuit is disconnected, and the circuit triggers a signal.

Keywords: membrane switch, membrane panel, touch screen