Screen printing beautiful patterns and texts on the raw material, then the graphic overlay is finished. Usually, In general, the membrane switch manufacturer uses PET, PC or other colorless transparent sheets, which thickness is less than 0.25mm. As we all know, the main function of graphic overlay is to play the role of mark and button. It always acts as a touch screen not only in membrane switch keyboards but also membrane switch panels. And for keypads, their control panels are raised. Therefore, the material should have features of high transparency, high ink adhesion, high elasticity, and high toughness. Of course, according to the needs of customers and application scenarios, we HuaiSong Industrial can change the material to engineer and manufacture cost effective products. Usually, we also use silicone rubber keypad, commonly known as a rubber dome keyboard or rubber dome switches.
The main function of the graphic adhesive is to closely connect the membrane overlay with the upper circuit layer. So that it will achieve the sealing and connection effect. In general, this layer requires a thickness of between 0.05 and 0.15 MM. Also, it should have high strength and aging resistance. In the production, the switch manufacturer always uses a special membrane switch double-sided tape. However, some membrane switches are required to be waterproof and resistant to high temperatures. Therefore, we have to select materials of different properties according to the different needs of customers.
It is between the graphic adhesive layer and the adhesive separator. Generally, we use PET double-side tape. An upper circuit is formed by attaching the metal dome to a single layer of glue. Materials include flexible circuit layer, copper flex, and hard circuit board. As we all know, the metal dome can generate tactile feedback. While pressing membrane switches, the contacts of the upper circuit are deformed downward and are in contact with the plates of the lower circuit. After releasing the finger, you can get a tactile feel, and the upper circuit contact bounces back. Then, the circuit is broken, and the loop triggers a signal.
It is between the upper circuit and the lower circuit layer. And it functions as a seal and connection. In general, we use high quality PET double-sided tape, which thickness ranges from 0.05 MM to 0.2 MM. When selecting this layer material, we should fully consider the product features. Including the overall thickness, insulation, the hand feeling of circuit keys package and sealing.
This layer usually uses a good performance polyester film (PET) as a carrier for the switching circuit pattern. Membrane switch keypad suppliers use a special process to screen conductive silver paste and conductive inks. So, the custom membrane switch will have electrical conductivity. In general, its thickness is within 0.05MM–0.175MM, and the most common is 0.125MM PET. Because it has good insulation, heat resistance, high mechanical strength, transparency, and air tightness. Especially, it has flexural resistance and high elasticity is the ideal material of making a custom membrane keypad.
Of course, according to customer needs, we also use FPC or PCB board to design and manufacture this layer. In order to increase some display effects on user interfaces, we can add LED light and SMT components. Furthermore, the fiber optic can be used under the user interface to provide visual feedback. What’s more, sometimes, the lower circuit layer may have terminals to connect the machine interfaces.
The use of the rear adhesive layer is closely related to the material which pastes with the keypad. Commonly, membrane switch keypad suppliers use ordinary double sides tape, 3M glue, waterproof glue and so on.
Place the PET material on the grill and push it into the oven for baking. In general, the baking temperature is 160 degrees, and the baking time is 25 minutes. This process is to reduce the heat shrinkage of the PET.
A good performance polyester film (PET) is used as a carrier for the switching circuit pattern. Screen printing the conductive silver paste, conductive carbon paste and UV layer. Then the switch keypad will have conductive property. What’s more, the UV layer is used to protect the circuit effectively.
After screen printing the conductive inks and silver paste, we adopt hot air circulating tunnel furnace for baking. Furthermore, the baking temperature is 110 degrees, and the speed is 5 meters per minute. While, a UV curing oven is used for baking the screen printed UV layer, and the parameter is 500 joules.
During the screen printing process, we design positioning holes on the PET. While, in this process, we use a laser punch machine through the holes. As we all know, the role of positioning holes is to ensure the smooth going of later testing and lamination.
This is a process that we test the conductivity and insulation of the printed lower circuit layer. (Parameter: 300V/100M)After testing, we can make sure that the circuit characteristics of the lower circuit can meet customer requirements.
Place the screen printed product on the visual inspection station to check the circuit. As you can see, the surface of the station is transparent. Below are some lights, the light fell on the table. So it can help inspectors to check the circuit layer of membrane keyboards.
Laminate the graphic adhesive, upper circuit layer, and adhesive separator together. In order to avoid the deviation and speed up the production, we always make a jig.
Assembly the metal dome with the bonded graphic adhesive, upper circuit layer, and adhesive separator. It can’t be installed on the reverse, missing and multi domes loading.
Avoid the missing, reverse and multiple loading problems of metal domes by the double domes test.
After laminating the top adhesive layer, the upper circuit layer, the isolation layer, and the lower circuit layer, the semi-finished membrane keypad is out. Then we die cut it into the shape required by customers.
Assemble the membrane overlay with the die cut semi-finished product. During the assembly process, we must ensure that there is no misalignment between each layer.
Using a machine to press the assembled dome switch keyboard. The pressure is about 100kg, and the pressing time is about 5 seconds. As we all know, this process is to ensure a firm bond between each layer of the custom membrane keypad.
The finished product is tested for open circuit, short circuit, conductivity, and insulation. So that we can make sure that the product is functioning properly.
Check if there are any problems such as scratches, crushing, dirt, offset, unclear printed lines, and severe deviations. Make sure that there are no poor appearance products delivered to customers.
Put membrane keyboards in the PE bag and then pack PE bags into cartons.
The quality inspector carries on the sampling inspection to the packaged finished membrane keypads. And this is checking the appearance and functions of products to avoid defective products.
Put the qualified finished products after spot check into the warehouse.
a. Working voltage: ≤50V (DC)
b. Working electric current: ≤100mA
c. Contact resistance: 0.5~10Ω
d. Insulation resistance: ≥200MΩ (100V/DC)
e. Substrate withstand voltage: 2kV (DC)
f. Rebound time: ≤6ms
g. Loop resistance: three gears of 50Ω, 150Ω, 350Ω. It can be determined according to customer needs.
h. Insulation ink withstand voltage: 100V/DC
a. Button life: >200,000 times. Can be determined according to customer needs.
b. Closed displacement: 0.1~0.4mm (no tactile type) and 0.4~1.0mm (touch type)
c. Button elastic force: 15~750g
d. No oxidation on the silver paste line, no impurities.
e. Silver paste line width ≥ 0.3mm, minimum interval is 0.3mm, line burr < 1/3, line gap < 1/4 line width.
f. Pin pitch standard : 2.54 2.50 1.27 1.25 1.0 0.5mm
a. Working temperature: -20 ° C ~ +70 ° C
b. Storage temperature: -40 ° C ~ +85 ° C temperature 95% ± 5%
c. Large air pressure: 86~106KPa