Brief introduction of the printing process of membrane switch

I Characteristics, application and classification of membrane switches


1. features


As we all know, the switch plays a role in transmitting command information in the electronic machine products. There are many kinds of switches, and their development is constantly updated with the progress of electronic machine products. In the 1950s, the toggle switch, toggle switch and transfer switch of endeavor components were dominant; In the 1960s, the combination switch represented by the piano key switch appeared to complete the simple function conversion; With the expansion of the application field and the increase of the functions of the whole machine, the conductive rubber keyboard switch appeared in the 1970s. The membrane switch is a new type of electronic device researched and developed in the late 1970s and early 1980s. It is a product that meets the needs of the development of the whole electronic product to miniaturization, digitization, intelligence and multifunction.


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


The membrane switch is a plane type, multi-layer combination and sealed structure. It is an assembly of the electronic whole machine control system integrating key switch, panel function mark, reading display transparent window, indicator lamp window hole and circuit.


It has the following characteristics:


(1) Durability


The service life of the membrane switch can generally reach more than onemillion times. The reason for such a long service life is that the action of the switch is only realized by the vertical bouncing of the elastic membrane. Although the elastic film has undergone millions of times of creep, the creep range is very small, only 0.1~0.3mm (i.e. switching stroke), and the rationality of material selection is far from reaching the yield limit of the film. Therefore, the film material can withstand more than onemillion times of life without deformation. On the other hand, the contacts of the switch are vertical contacts with little wear; The screen printed contacts can form a sufficient thickness, and a layer of conductive carbon is printed on the silver paste contacts to achieve the purpose of high wear resistance and self lubrication. Therefore, the service life of the membrane switch is more than ten times that of the mechanical contact switch.


(2) Good sealing performance


As the membrane switch is an integral sealing structure, the contact of the switch is not eroded by harmful gas and is not easy to oxidize; With the characteristics of waterproof and dustproof, it is more suitable for various harsh environments.


(3) Small size, light weight and reliable structure


In design, membrane switches can be arranged and combined to form a membrane keyboard. Its setting density is large, and it is a sealed sheet structure composed of multi-layer membranes. The connecting lines and outgoing lines between all switches are completed at one time by screen printing, with a total thickness of 1~3mm. Therefore, the volume is reduced, the quality is reduced, and the reliability is improved.


(4) Rich colors and beautiful appearance


According to the user's design idea, the membrane switch can embody personalization in the design of color patterns and the comprehensive characteristics of material beauty, decorative beauty and process beauty in the decorative effect.


(5) Reduce the supporting cost of mechanical and electrical products


Traditional mechanical switches need to be welded or even matched with fixed supports during installation. The installation of membrane switch is adhesive type. As long as the adhesive paper is removed, it can be firmly pasted on the surface of the whole machine. Its lead outlet is inserted into the socket of the rear circuit of the whole machine, and the circuit can be connected instantly. Save labor and materials, and reduce the supporting cost of the whole machine.


2. application


Membrane switch is a kind of non self-contained 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 100mA. Can be widely used in all microcomputer, CNC. Intelligent instruments, meters, and electronic circuits with discrimination and memory functions.


3. classification of membrane switch


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


(1) Commercial membrane switch


In the mechanical industry standard of the people's Republic of China jb5045 － 91 technical conditions for membrane keyboard issued on July 1st, 1991 and implemented in 1992, the assessment criteria for high, low temperature, constant damp heat and temperature change of membrane switch are as follows:


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


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


Constant damp heat: (40+/-2) degrees {relative humidity 96%+/- (2~3)% for 96h}


Temperature change: -40~50 degrees (recover 2H under normal atmospheric conditions after 5 cycles of test


Any membrane switch that can pass this examination condition and has the general function of membrane switch can usually be called a commercial membrane switch. It is the most common and characteristic product of membrane switch.


The panel layer of the commercial film switch is usually PC or PET film as the substrate, and the circuit substrate is conductive silver paste or conductive silver carbon paste mixed paste; The carrier of conductive printing material adopts PET film. Considering the application environment and reducing the 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. The use environment of military membrane switches is very bad. As far as the ambient temperature is concerned, its working conditions not only need to meet -54~70 degrees, but also need to accept -55~100 degrees, three cycles of temperature shock. Moreover, in the foreign military standards, the high-temperature test stipulates that the working temperature is 125 ° C and the high-temperature storage temperature is 150 ° C. It is obvious that the commercial membrane switch is not suitable for working in such a harsh military environment.