Membrane Switch Overview



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1. Features

 

As we all know, switches play a role in transmitting command information in electronic products. There are many varieties of switches, and their development is constantly updated with the progress of electronic products. In the 1950s, the toggle switch, toggle switch, and changeover switch of the Endeavour component were dominant; in the 1960s, a combination switch represented by the key switch appeared to complete simple function conversion; with the expansion and With the increase of the functions of the whole machine, conductive rubber keyboard switches appeared in the 1970s, and the membrane switch is a new type of electronic device researched and developed in the late 1970s and early 1980s. It conforms to the miniaturization and digitalization of electronic products. Intelligent, multifunctional development needs products.

 

Membrane switch is a switch made of conductive paste printed contact circuit on flexible polycarbonate or polyester film, which is a kind of contact switch.

 

The membrane switch is a flat, multi-layer combination and sealed structure. It is an assembly of an electronic control system integrating key switches, panel function marks, reading display transparent windows, indicator light windows and circuits.


 

It has the following characteristics:

 

(1) Durability

The life of membrane switches can generally reach more than one million times. The reason for such a long life is that the action of the switch is only realized by the vertical movement of the elastic membrane. Although the elastic film has undergone millions of creeps, the creep range is only 0.1~0.3mm (that is, the switching stroke), and the material selection is reasonable, and it is far from reaching the yield limit of the film. Therefore, the film material Can withstand more than one million times of life without deformation. On the other hand, the contacts of the switch are in vertical contact, and the wear is very small; while the screen printed contacts can form a sufficient thickness, and a layer of conductive carbon is printed on the silver paste contacts to achieve high The purpose of wear resistance and self-lubrication, so the life of the membrane switch is dozens of times longer than that of the mechanical contact switch.

 

(2) Good sealing performance.

 

Because the membrane switch is an integrally sealed structure, the contacts of the switch are not corroded by harmful gases and are not easily oxidized; it is waterproof and dustproof, so it is more suitable for use in various harsh environments.

 

(3) Small size, light weight and reliable structure.

 

Membrane switches can be arranged and combined into a membrane keyboard in design, with a high setting density, and it is a sealed sheet structure composed of multiple layers of membranes, and all switches are connected The wire and lead wire are completed by screen printing at one time, with a total thickness of 1~3mm, so the volume is reduced, the quality is reduced, and the reliability is improved.

 

(4) Rich colors and beautiful appearance

 

Membrane switches can be personalized in the design of color patterns according to the user's design ideas, and the comprehensive characteristics of beautiful materials, beautiful decorations and beautiful craftsmanship can be reflected in the decorative effect.

 

(5) Reduce the cost of supporting electromechanical products.

 

Traditional mechanical switches need to be welded during installation, and even have to be fitted with fixed brackets. The installation of the membrane switch is paste type, as long as the adhesive paper is removed, it can be firmly pasted on the surface of the whole machine, and its lead outlet is inserted into the socket of the rear circuit of the whole machine, and the circuit can be connected in an instant. It saves labor and materials, and reduces the cost of the complete machine.

 

2. Application

 

Membrane switch is a non-self-switching switch. It is suitable for working occasions where the switching power is less than 1W, the maximum working voltage is 42V (DC) or 25V (DC), and the maximum working current is less than 100 mA. It can be widely used in all microcomputers and numerical control. Many fields of intelligent instruments, meters and electronic circuits with distinguishing and memory functions.

 

3. Classification 

 

Membrane Switches can be classified according to the two major characteristics of use environment or circuit substrate. According to the environmental classification, it can be divided into two major categories: appreciation membrane switches and military membrane switches; if according to the circuit substrate, that is, according to the circuit formation method, it can be divided into two major categories of membrane switches: conductive printing printed circuits and copper-clad etching circuits.

 

(1) Commercial membrane switch

 

Promulgated on July 1, 1991, the evaluation criteria for high, low temperature, constant damp heat and temperature changes in the mechanical industry standard JB5045-91 "Technical Conditions of Membrane Keyboards" of the People’s Republic of China implemented in 1992 are:

high temperature: (55 +/-2) degrees (72h)

low temperature: (-40+/-3) degrees (16h)

constant humidity and heat: (40+/-2) degrees {relative humidity is 96%+/-(2~3)%, Lasting 96h}

Temperature change: -40~50°C (after 5 cycles of testing, it will recover for 2h under normal atmospheric conditions.

 

Any membrane switch that can pass this test condition and has the general function of membrane switch can usually be called commercial Membrane switches are the most common and characteristic products of membrane switches.

 

The panel layer of a commercial membrane switch is usually a PC or PET film as the substrate, and the circuit substrate is a conductive silver paste or a conductive silver-carbon paste mixed paste; the conductive printing material uses a PET film. For the consideration of application environment and reducing manufacturing cost, the isolation layer usually adopts cheap PVC film.

 

(2) Military membrane switch

 

The biggest difference between the two is that they are used in different environments, and the use environment of military membrane switches is quite harsh. As far as the ambient temperature is concerned, its working conditions not only need to meet -54~70 degrees, but it also needs to accept a temperature shock of -55 to 100 degrees, three cycles. Moreover, in foreign military standards, the high temperature test stipulates that the working temperature is 125 degrees, and the high temperature storage temperature is 150 degrees. It is obvious that commercial membrane switches are not suitable for working in such a harsh military environment.

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