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1. Silicone rubber keypad definition

As the name suggests, silicone rubber keypads are keypads made from silicone rubber. Silicone keypad is a kind of silicone product. It has many excellent features of heat, cold and environmental resistance, electrical insulation, fatigue resistance, and others. Also, there is a wide range of factors for the silicone keypad manufacturer to consider during design and manufacturing. For example, the diameter, length, width, and height of rubber keypad, keystroke distance, pressing force requirements, product hardness, color, and conductivity requirements.

2. Silicone keypad production process

2.1 Prepare the mold

HuaiSong Industrial can process the cost effective mold according to the keypad design or sample provided by customers. After making the silicone keypad mold, we will first test it. Only when we confirm the structure and producing process, they can be mass-produced. Then, in general, the rubber keypad manufacturer will make the mold’s surface treatment by sandblasting. If the appearance of custom silicone rubber keypads is required to be shiny, we spray glass sand. If keypad designed to be matte surface, spraying corundum or mixed sand. Or if there is no demand, spraying mixed sand is OK.
 

2.2 Prepare molded silicone material

According to the keypad design of the customer’s order, the silicone keypad manufacturer selects the hardness and bottom color of the material. Then, refining rubber on an open mill or internal mixer according to formula. After that, the rubber tablets are produced according to the specification formulated during the test and packing them with PE film. At the same time, prepare the external release agent, conductive rubber particles, and various tools.

 

2.3 Silicone vulcanization

In general, the rubber keypad manufacturer uses a flat vulcanizing machine to make compression molded silicone products. According to the function of the vulcanizing machine, it has manual, automatic, and vacuum models. The mold is composed of two layers of male and female molds. During production, lift up the female mold, put the conductive rubber black particles, and the silicone keypad material on the male mold. Also, we can insert the color key in the female mold if needed. When ready, close the mold for heating and compression molding.

The main control parameters of vulcanization are temperature, pressure, and time. The typical operating process conditions are controlling the temperature within 160 ℃ ± 10 ℃, the pressure within 15 ~ 20MPa, the time within 150 ~ 200s. And the time depends on the height of custom silicone rubber keypads. If the key button is low and small, only 30-40 seconds are enough. After finishing the compression molding, push the mold out of the machine. Carefully lift the female mold, use the air gun, and slowly remove the silicone rubber keypad from the mold.

2.4 Secondary vulcanization

The silicone rubber keypad manufacturer can decide whether to carry out the secondary vulcanization according to the custom designed drawing. It can remove the residual vulcanizing agent decomposition products in the molded silicone keypad and improve its performance. For the conventional secondary vulcanization of molded silicone rubber keypad, Huaisong Industrial adopts a vertical oven. We can complete it by baking at a temperature of 180 to 200 °C for 2 hours.

 

2.5 Keypad surface treatment

Custom designed keypad always has patterns on the key top. Suppliers use screen printing, laser etching, or other processes to make surface treatment according to customers’ requirements. Upon finished, send them for inspection.

Screen printing

Firstly, make a screen according to the pattern design. Pour the ink on the screen and permeate it. Apply a certain pressure to the ink on the screen with a squeegee. At the same time, move the other side. During moving, the ink will be pressed on the keypad through screen meshes.

Laser etching

It can show the laser etched graphics and texts by using a laser to burn off some of the material. Add light pipes at the bottom of laser etched keys. It will produce a strong light transmission effect. What color is the surface of the product, the light that it passes through the irradiation of the light pipes is what color.

 

2.6 Punching and deburring

According to the rubber keypad mold design, we can choose punching or manual deburring to remove and trim the excess burrs of keypads. This makes the surface of them be beautiful.

 

2.7 Process quality control

The first is process control during vulcanization. And the main inspection items are size, elasticity, hardness, stain, color difference, lack of materials, etc. Eliminate defective products and find major problems in time. Also, it’s important to give feedback and ask for improvement to reduce the production of defective products.

Next is quality control during screen printing. The focus of the inspection is ghosting, incomplete screen printing, unclear fonts, and poor abrasion resistance. We can use solvents to wipe off the screen printed keypads and reprint them after drying naturally.

Finally, silicone keypads designed and manufactured by HuaiSong Industrial will be sent to customers. Of course, if they function as graphic overlays in membrane keypads, we can also make switch assemblies.

3. Applications of silicone rubber keypad

3.1 Membrane keypads

Silicone rubber keypad switch is a kind of combination product of silicone keypad and membrane switch. The way of using a silicone keypad to fit the membrane switch can achieve the effect expected by customers. Also, it has perfect performance on properties and protection. In general, customers use the rubber keypad switch in outdoor or high-temperature operation areas.

The silicone rubber itself does not conduct electricity. But there are three main ways of keypad design to make it conductive.

The first is secondary molded carbon pills or black pills. During the compression molding process of silicone, put conductive carbon pills or black pills into the mold cavity together. After high-temperature vulcanization molding, the carbon pill or black pill will adhere to the contacts of the compression molded rubber keypad. Once pressing the rubber switch, it deforms to produce a tactile response. And the carbon pill or black pill contacts the circuit of the printed circuit board to form a function transfer. If the user looses the finger, the key top will go back to the position with positive feedback. And the circuit will disconnect.

 

Adopt screen printing or dot printing carbon oil or conductive ink on the surface. After the compression molding, add a process of printing conductive ink to make the conductive rubber switch.

Add a metal dome to the bottom of the key. This is attaching metal dome to the back of the rubber keypad.

 

Rubber keypad switch structure and switch assemblies

 

As we all know, the general membrane keypad has five layers. Graphic overlay, the adhesive layer, metal dome, circuit layer, and back adhesive. Assemble these layers together, membrane switches with tactile response are made. Benefit from the use of metal dome, you have the tactile feel when pressing the key top to function. And the service life of membrane keypads also depends on it. For the silicone keypad switch, the graphic overlay layer uses rubber material. And it always uses a printed circuit board as a circuit layer.

 

Using compression molding properties of custom silicone rubber material, the supplier creates gradient webbing around the button center. After pressing down the button, the web deforms to produce a tactile response. Remove the actuation force from the switch the webbing returns to its neutral position with positive feedback. For consumer and industrial electronic products, the carbon pill or metal dome is adopted to contact the printed circuit board when the web has been deformed to conduct electricity. Huaisong Industrial, which designs and manufactures cost effective silicone keypads since 2010, can also make membrane switch assembly.

 

3.2 Other applications

There is a wide range of actuation forces for keypads in different use. According to the difference, silicone keypads are also applied in the following areas.

 

The actuation force is about 50-80g, which is generally suitable for use in computer keyboards and calculator keys. The pressing force in this range is not high; it is easy to press and has a light tactile feel. It is suitable for rubber keypads that need to be clicked frequently.

 

The pressing pressure is about 80-120g, which is generally suitable for electrical buttons and remote controls. Its force is suitable, the hand feels comfortable, and the resilience is great.

If the actuation force is 120-180g, it is generally suitable for consumer and industrial electronic products. For example, keypad designed for sound equipment, industrial instruments, and mechanical remote controls. Its pressing force is much larger than that of the second type, and it is generally suitable for relatively large silicone keypads. Its resilience is also superior, but not suitable for products with frequent clicks.

 

The pressing pressure is more than 180g. In general, this type of pressing rubber keypad is relatively rare. It should be designed and manufactured for special industries, such as medical, aviation, and other industries. It needs frequent use of fingers for a short time, which makes it more acidic.

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