A comprehensive introduction to Membrane Keypad Panel

1. What is Membrane Keypad Panel?

To put it simply, Membrane Keypad Panel is a simple human-computer interaction page referred to as HMI. It can also be called an electronic Metal Dome circuit printed with silver foil. The membrane Keypad Panel is an interactive product between the operator and the device. A Membrane Keypad Panel with excellent design and high aesthetics is beneficial to reduce operating errors, improve product durability and make an impressive effect.

For customers and designers looking for an excellent and powerful HMI, Membrane Keypad Panel is an extremely good choice. Here, Niceone-Keypad hopes to assist customers in designing and improving customers’ only reserves. Membrane switches and mechanical switches belong to switch type electronic accessories, but Membrane Keypad Panel is more suitable as HMI in most of the time.

The market of Membrane Keypad Panel is mainly distributed in medical, marine, agricultural, industrial, military, and food equipment.

What are the extended products of the Membrane Keypad Panel? How is it named?

Extended products are LGF Membrane Keypad Panel, FPC Membrane Keypad Panel, PCB Membrane Keypad Panel, Lens Membrane Keypad Panel, OCA Membrane Keypad Panel, Resin Dome Membrane Keypad Panel, Non-Tactile Membrane Keypad Panel, Tactile Membrane Keypad Panel, etc.

The naming method is mainly based on: technical parameters to name, line selection to name and additional functions to name, etc.

2. What are the advantages of Membrane Keypad Panel?

It has been 50 years since the Membrane Keypad Panel came out. Even in the past few years due to the emergence of touch screens, etc., the market share of Membrane Keypad Panel has not been reduced. On the contrary, it still has a place in the HMI market as in the past. The main reasons are:

• Simple operation of Membrane Keypad Panel:

The simple operation of the Membrane Keypad Panel is impressive, and it also provides various types of operation techniques and aesthetic possibilities. Although the touch screen offers greater possibilities than the Membrane Keypad Panel, compared to some products that do not require too much operation, such as microwave ovens and weighing machines, the cost is greatly increased. Touch screens are not a good choice. However, the Membrane Keypad Panel is simple and clear, easy to operate but suitable for many electronic control products, and also reduces the purchase cost.

• Diversity of Membrane Keypad Panel:

Whether Membrane Keypad Panel is used in food, medical, marine, or military industries, the reason why it can perform well is because Membrane Keypad Panel only needs proper adjustment of materials and structure to meet the needs of various industries, even if the products look similar, but Inside, there are great things. For example: Anti-ultraviolet material and waterproof frame structure can make Membrane Keypad Panel use for a long time without problems. The choice of conventional materials can meet most of the needs of the food industry but the cost is relatively low. So Membrane Kypad Panel has diversity.

• Durability of Membrane Keypad Panel:

Membrane Keypad Panel through reasonable design and good material selection such as 3M, Kotutai, Nicomatic LEDs and shrapnel and berg connector, etc. can make the product easily through hundreds of thousands of touches and up to 20,000H of use. Membrane Keypad Panel can maintain the same performance even in humid, high pressure, and strong ultraviolet environment. This benefited from the advancement of materials science and the 50-year accumulation of technology of Membrane Keypad Panel.

• Brand benefits brought by Membrane Keypad Panel:

Since the Membrane Keypad Panel often prints the user’s logo on the surface, a good Membrane Keypad Panel will impress people and at the same time will play a role in publicity. This will help users seize market share.

3. What is the development history of Membrane Keypad Panel?

Passed 1 month of research and industry experience in Niceone-Keypad. We sorted out the history of Membrane Keypad Panel to help everyone better understand this kind of products.

In 1969, the function of Membrane Keypad Panel was not as it is now. The existing LGF, LEDs can even resist ultraviolet rays. The original idea was to protect the mechanical keyboard and make the mechanical keyboard more beautiful. At that time, it was not called Membrane Keypad Panel, it was called Graphic Overlay of screen printing type. However, the quality of this kind of Graphic Overlay was not good, it was very easy to peel off and unstable, so the response in the market was not good.

Until around 1979, the Graphic Overlay and Membrane Keypad Panel used polycarbonate materials, which also had the ability to resist moisture and chemicals. As the material properties of Polycarbonate are better than that of paper and conventional sheets, it is not easy to peel off and is stable, so that the feedback of this kind of products in the market gradually gains a place. Unfortunately, users have encountered another problem, the material is very brittle. At the same time, some users asked whether Graphic Overlay or Membrane Keypad Panel can be embossed so as to give the product more possibilities. Polycarbonate did not meet these requirements in the early stage, which is also due to the limitations of material properties. Suppliers of Membrane Keypad Panel are also looking for other types of sheets to replace, so as to win a larger share in the market.

By the end of 1980, structural optimization and material replacement (Polyester replaced the use of polycarbonate and metal dome) solved the needs and problems of Membrane Keypad Panel in 1979. Not only did the product have a longer lifespan, but the first Membrane Keypad Panel with Metal Dome appeared on the market.

Around 1985, the manufacturer of Membrane Keypad Panel encountered a new idea. Can Leds or indicator lights be assembled on Membrane Keypad Panel? Fortunately, this problem was quickly solved and gradually matured into LEDs Membrane Keypad Panels. The reason is that the biggest problem is how to fix the LEDs. The Membrane Keypad Panels manufacturer at that time used glue to fix the LEDs and solder solutions to easily solve this type of problem. If FPC is used as the line, then this problem is easier to solve.

In 2012, a customer in European countries asked Niceone-Keypad whether it could attach the glue process of Silicone Rubber Keypad to Membrane Keypad Panel? The Resin Dome process used on Membrane Keypad Panel will have the most serious problem. It cannot be shaped or the glue leaks before molding. Fortunately, Niceone-Keypad solves such problems through silk screen printing, and Resin Dome Membrane Keypad Panel has also become a star product.

In 2016, a medical user in the United States asked how Niceone-Keypad emits light in a large area and the cost is lower than that of Optical fiber, and the lifespan is longer than that of EL type Membrane Switch? And given the light-emitting area of ​​the following picture. Although the traditional LEDs Membrane Keypad Panel has a relatively long life, the area that illuminates the keys is uneven and the brightness is insufficient to meet the needs of users. Niceone-Tech’s parent company uses LEDs with higher LGF and MCD to solve the problem and perfectly meet the needs of users.

4. What is the structure of Membrane Keypad Panel?

The structure of the Membrane Keypad Panel is roughly divided into 4, 6 , 8

The 4-layer structure is usually LEDs Membrane Keypad Panel without Metal Dome, Capacity Membrane Keypad Panel or Membrane Keypad Panel without Metal Dome Silver Dome Membrane Keypad Panel. The cost of 4-layer Membrane Keypad Panel is generally more competitive, and the thickness is smaller. Tactile Feedback will be worse if there is no Embossing. The specific structure is as follows:

6-layer structure usually Membrane Keypad Panel comes with Metal Dome, LEDs and other components. The 6-layer Membrane Keypad Panel comes with Embossing most of the time. Tactile Feedback is relatively better and is the most common type of Membrane Keypad Panel structure. The choice of circuit is more diversified, including Polyester silver oil circuit, Flex copper circuit and Printing circuit board. At the same time, the choice is more diversified. If the Membrane Keypad Panel attached to the back panel becomes a 7-layer structure. The most conventional design is shown below:

The 8-layer structure is often used in the Polyester circuit Membrane Keypad Panel. Because the Polyester Circuit Membrane Keypad Panel cannot fully implement the circuit function on the first layer, the 8-layer structure is used to complete its function. The cost is lower than Flex copper circuit and printing circuit board, but the stability is not as good as both. However, this type of design can be selected when cost-effectiveness is prioritized. If the backplane is attached, it becomes a nine-layer structure. The most conventional structure is as follows:

5. How does Membrane Keypad Panel work?

The working principle of Membrane Keypad Panel has different driving methods according to different types. According to the definition of the market, Niceone-Keypad sorts out the operating methods of these commonly used Membrane Keypad Panels.

Conventional Membrane Keypad Panel, the main internal electronic accessories of this type of product are attached with Metal Dome. Through the operator’s touch on the button part, the Metal Dome is bent under force and contacts the silver oil circuit or copper foil at the bottom to form a conduction to realize the function.

The silver oil circuit Membrane Keypad Panel without metal dome uses conductive ink printed on the two-layer PET circuit below the top layer. Usually the thickness of both of them is between 0.1-0.125mm. When the user presses the button, the two will be turned on immediately after contact to realize the function. For Tactile Feedback, the mold of the Membrane Keypad Panel with silver oil circuit without shrapnel usually chooses stainless steel. The main reason is that the stainless steel mold will make the convex more linear and conform to the mechanics principle. At the same time, in order to avoid short circuits, the distance between the line and the line should be at least 0.125mm to avoid direct conduction. This kind of problem can also be solved by printing UV dots.

Capacitive Membrane Keypad Panel: Use IC to identify the capacitance change above the Capacitive Membrane Keypad Panel to realize the function. Once the human body is close to a capacitive product, the Capacitive Membrane Keypad Panel will change the amount of charge and capacitance. This is also the working principle of this type of switch. But Capacitive Membrane Keypad Panel has a very outstanding occasion, the life span can be as high as millions of times. Due to the flat design and the durability of the material, this is one of the reasons why Capacitive Membrane Keypad Panel is popular all over the world.

Silicone Rubber Keypad Membrane Keypad Panel:

A. Silicone Rubber Keypad comes with Carbon Dot, which realizes the function through the deformation of the Flexing web to make the carbon dot contact with the silver oil or gold-plated copper foil above the circuit.

B. Silicone Rubber Keypad without metal dome, by changing the composite wall (Web) to lightly touch the Metal Dome or Key and then change its stroke so that the electrical performance can be turned on.

6. What are the performance parameters and additional functions of Membrane Keypad Panel?

Additional functions of Membrane Keypad Panel are:

ESD/RFI/EMI: Membrane Keypad Panel electrostatic shielding commonly used technology to prevent electronic accessories from electromagnetic interference caused by static electricity, causing electronic accessories and Membrane Keypad Panel to malfunction. What’s more, the silver oil circuit is broken or appears due to static electricity. Silver migration phenomenon. Fortunately, ESD/RFI/EMI has certain resistance to electrostatic problems. The need for better antistatic effect needs to consider the waterproof frame design, FPC circuit or PCB circuit composite Membrane Keypad Panel. At the same time, in the process of inspecting the product, you need to wear an electrostatic ring to avoid damage to the product.

High Embossing: Use High Embossing to make the Membrane Keypad Panel Key more three-dimensional, making the product more aesthetic. In terms of feel, embossing that is too high requires a tactile dot under the Key to improve Tactile Feedback. Since Embossing needs to stretch the material after heating, the panel needs to choose a material with higher tensile strength. Embossing with a conventional thickness of 0.3-0.7mm has a greater effect on the feel of the Membrane Keypad Panel.

Waterproof: Make the waterproof grade of Membrane Keypad Panel reach IP65 and above. The conventional method is to make the layers below the surface glue of the Membrane Keypad Panel into a composite structure to surround the circuit of the Membrane Keypad Panel to protect the electrical function of the Membrane Keypad Panel. Sometimes it can also act on ESD/RFI/EMI.

Additional Back Panel: Membrane Keypad Panel additional Back Panel options are AL, FR4, the main two purposes: to reduce the end user mounting time and reduce the problem that users will not mount.

Resin Dome: Membrane Keypad Panel with 3D stereo Key. It makes the product more beautiful and comes with aesthetics. At the same time, AB glue is used to form the Resin Dome. The shape usually has an R angle.

• Electrical performance
  • Working voltage: ≤50VDC
  • Working current: ≤100mA
  • Contact resistance: 5~10Ω
  • Insulation resistance: ≥100MΩ（100VDC）
  • Substrate withstand voltage: 2kDVC
  • Rebound time: ≤6ms
  • Loop resistance: 50 Ω, 150 Ω, 350 Ω three gears, or according to user needs
  • Insulating ink withstand voltage: 100VDC
• Mechanical properties
  • Reliability and service life: >1 million times
  • Closing displacement: 0.1~0.4mm (non-tactile type) 0.4~1.0mm
  • Healthy standard work force: 15~750g force
  • Silver paste migration: at 55℃, temperature 90%, after 56 hours, 10MΩ/50VDC between the second line
  • No oxidation and no impurities on the silver paste line
  • Silver paste line width ≥ 3mm, minimum interval 0.3mm, line burrs <1/3, line gap <1/4 line width
  • Lead pitch standard 54 2.50 1.27 1.25mm
  • Lead wire resistance to curvature, use d=10mm steel rod to roll the circuit 80 times continuously
• Environmental performance
  • Operating temperature: -20℃～+70℃
  • Storage temperature: -40℃～+85℃ temperature 95%±5%
  • Atmospheric pressure: 86～106kDa
• Printing index
  • The printing size deviation is ±15mm, and the outline edge is unclear. Knitting error ≤0.1mm
  • The color deviation is ±11mm/100mm, and the insulating ink covers all the silver paste circuits
  • No ink scattered, no incomplete handwriting
  • The color difference is not more than secondary
  • No creases, peeling paint
  • The transparent window is transparent and clean, with uniform color, free of scratches and impurities

7. What information is needed to design Membrane Keypad Panel?

When Niceone-Keypad gets detailed information, the fastest time for drawing out is within 12 hours. The usual time is 3 days. The samples are usually completed within 10-20 days after the customer confirms the drawings. So what information do we need to give customers drawings and samples as quickly as possible?

In terms of drawings: First of all, Niceone-Keypad needs to know the purpose of the product, the specific color number, the selection of the connector, the circuit principle and the editable document, etc.

• The purpose of the product includes: Use and medical, industrial, military, marine, fitness, and agricultural equipment, etc. The choice of materials is different. If you can inform in advance, then there will be a preliminary plan for the choice of materials. The medical industry pays attention to the stability and durability of the products, so Adhesive usually chooses 3M or Nitto, and the panel material often chooses AM series or antibacterial Silicone Rubber material. And marine equipment is more often considered waterproof and resistant. Ultraviolet rays. Waterproof structure is required for waterproofing, and UV-resistant materials such as XE series or HP92W should be considered for UV resistance. This information can confirm most material choices.
• Specific color number: Different color numbers are different. If there is no specific color number, the overlay cannot be completely designed unless the customer informs that the color can be customized. The commonly used color number is Pantone or RAL. If it is a special color, the customer can also send the color patch to let Niceone-Keypad match it.
• The choice of connector: ZIF, Male or Female is best shown in the drawing.

• Circuit principle: The position of PIN1, and the corresponding circuit principle drawing of each button.
• Editable document: Including size, color number, circuit principle, vector graphics is the best project document.
• The information contained in the figure below is very complete. This is also the information users most want to see. Including materials, circuit principle, color, size and structure settings.

• Master samples: If the customer cannot provide any documents, Master samples are also possible.

A good drawing requires the cooperation of customers and suppliers. Niceone-Keypad hopes to save users’ time and cost after providing Proof as soon as possible. This also requires the cooperation of customers.

How to get samples of Membrane Keypad Panel the fastest?

• It is better to choose more conventional materials.
• If the sample is particularly urgent, you can consider using laser cutting.
• Printing uses printing methods.
• If the product has Embossing, you can consider CNC etching abrasive tools.

In this way, the sample can be completed in about 5 days.

8. Common problems and solutions of Membrane Keypad Panel?

Newton’s ring: Newton’s ring appears in the window as shown in the figure. The main reason is that the panel window and the glass or PC air are automatically pasted together after being completely cleared.

• Solution 1: Use UV dot printing to form a gap between the panel window and the glass, PC or PMMA.
• Solution 2: Using OCA technology, using OCA tape, the glass is bonded to the Membrane Keypad Panel and then vacuumed again to eliminate bubbles. The cost of Membrane Keypad Panel is higher than that of conventional windows. But the aesthetics are better.

Silver migration: In a humid environment where the DC potential difference is too high, the PET circuit of the Membrane Keypad Panel often exhibits silver migration, which will cause loss of circuit functions.

• Solution 1: Choose Flex Copper circuit and Printing Circuit Board
• Solution 2: (a) Coating the bottom substrate with a silver composition and drying or curing the silver composition (b) Applying a carbon coating on the top of the silver composition and drying or curing the carbon Coating (c) coating the carbon with a dielectric composition and drying or curing the dielectric composition (d) applying a carbon paste composition to the dielectric and drying or curing the carbon paste composition ( e) Applying a silver paste composition to the carbon and drying or curing the silver paste composition to form a circuit.
• Solution 3: If it is the silver migration of the lead part of the circuit, you can consider stretching the line pitch to 2.54mm. At the same time, use a silk screen with a higher mesh to solve it. But if it still can’t be solved, FPC and PCB circuit are still a good choice.

Resistance is too high: It often appears in the PET Membrane Keypad Panel. There are 3 reasons for this problem:

• Metal Dome is stainless steel: Metal Dome is stainless steel, which will increase the overall resistance during use. The specific reason is still unclear.
• Limitations of the silver oil circuit: due to the poor conductivity of the silver oil lead-out circuit, the resistance of the lead-out wire is higher after it is larger than 200mm. At the same time, if the Membrane Keypad Panel is produced in the form of a bridge or a method of perforating, the resistance will be higher. If the line is too thin, the line resistance will be too high.
• Conductive ink: If you choose conductive ink with poor conductivity, this kind of problem will also exist.

In this case, how to solve the problem of high resistance of Membrane Keypad Panel?

• Try to choose Ni-plated or gold-plated Metal Dome for Metal Dome or Key. The performance is relatively stable and will not cause the product resistance to suddenly increase.
• If the Membrane Keypad Panel uses a combination of PET and silver oil as the line. The lead wire should be controlled within 200MM as far as possible. The thickness of the circuit needs to be controlled above 0.5mm. If you take a bridge or a hole-filling method, the better choice is Flex Copper Circuit or Printing Circuit Board.
• Conductive ink can be information Niceone-Keypad, it is best to choose the most suitable ink according to the actual situation. But in general, the higher the conduction rate, the better.

Dual Metal Dome: The Membrane Keypad Panel’s Key cannot be driven from time to time, and there is a dual Metal Dome phenomenon.

• Solution: QC inspection
• Solution: Use automated equipment to mount Metal Dome

LEDs offset: LEDs cannot be centered. It is very likely that manual welding was used instead of machine welding.

• Solution: Use machine welding.
• Solution: Rear of the LED can be encapsulated

Adhesive delamination: Adhesive in Membrane Keypad Panel will delamination due to the following reasons, which is also called peeling of adhesive tape.

• Reason 1: LEDs and Metal Dome are too close to the edge of Membrane Keypad Panel.
• Reason 2: Adhesive is not good enough.
• Reason 3: The structure of Membrane Keypad Panel is incorrect

In this case, how to solve the problem of adhesive delamination of Membrane Keypad Panel?

• Solution 1: LEDs or Metal Dome need to be far away from the edge of Membrane Keypad Panel. The best choice should be at least 3mm. If it is smaller than 3mm, it needs to be judged according to the actual use of Membrane Keypad Panel.
• Solution 2: Choose 3M or Nitto with good viscosity.
• Solution 3: Spacer chooses a thickness of 0.175mm, and if the Key is embossed, it can release the pressure of the Membrane Keypad Panel so as to prevent the Membrane Keypad Panel from opening.

Poor Tactile Feedback: Membrane Keypad Panel sometimes has poor Tactile Feedback for Key. The specific reasons are as follows:

• Reason 1: Overlay material should be larger than 0.25mm. The thicker the material, the worse the Tactile Feedback.
• Reason 2: The exhaust structure is not done properly. The air in some Membrane Keypad Panel cannot be released, resulting in poor Tactile Feedback.
• Reason3: Metal Dome chooses too high load or too low load. Too high a load makes it difficult to drive the Membrane Keypad Panel, while a metal dome with too low a load will result in weak Tactile Feedback. If you choose a Metal Dome with a size of 6.0mm or less, the feel is even weaker.
• Reason 4: When the structure of Overlay adhesive, Spacer and Adhesive is incorrectly selected, and the panel does not have Embossing, the Metal Dome may not be able to drive, which makes Tactle Feedback worse.
• Reason 5: The storage temperature is incorrect, which causes the Embossing of the Membrane Keypad Panel to be deformed. This leads to embossing deformation.
• Reason 6: Mbossing is too high, too high can sometimes cause the Tactile Feedback of Membrane Keypad Panel to deteriorate.

In this case, how should we solve it?

Solution: If the Overlay has a bump, try to choose a material below 0.25mm. At the same time, the vent hole needs to be customized for the optimal solution according to the Membrane Keypad Panel. When Metal Dome chooses a size greater than or equal to 6.0mm, the load is controlled at 280-420G. Overlay Adhesive chooses a double-sided adhesive above 0.175mm, while Spacer considers between 0.05mm and 0.125mm. If it is not a special requirement, Key should try to increase Embossing. The best storage temperature of Membrane Keypad Panel is between 20-40 degrees Celsius. If Embossing is too high, consider adding Tactile Dot.

Loss of function during use of the line: Membrane Keypad Panel sometimes loses function during use. After inspection, some lines were worn out during use.

• Reason 1: Metal Dome wears out the silver oil circuit under the Key.
• Reason 2: Or the silver oil circuit of the lead-out part is worn out by external components.
• Reason 3: What’s more, it is because the voltage and humidity cause silver migration and lose the circuit function.
• Reason 4: The printed conductive ink has poor adhesion, and the ink will peel off as it is used.

Solution: The four corners of the Metal Dome and the lines with silver lines in and out need to be printed with carbon oil and UV ink to protect the silver oil lines under the KEY. At the same time, the silver oil circuit part of the lead wire needs to consider the transparent dragon protective film if the external components of the multiplexer are more. Conductive inks need to be tested before they can be used. Otherwise, serious electrical accidents will be caused to the product.

The panel window is scratched: If the panel window is scratched before using the Membrane Keypad Panel, it may be caused by the following situations.

• Reason 1: There is no protective film attached to the Overlay window of the Membrane Keypad Panel.
• Reason 2: The panel window is scratched during the mounting process.

If it is caused by scratches on the panel window during use, the main reason is: no hardening material is used.

Solution: If the Membrane Keypad Panel comes with a window, a protective film should be attached before use. The QC department should check the panel window during the placement process. At the same time, the Membrane Keypad Panel with window is best to use hardened and scratch-resistant materials such as EBG, single-sided hardened PC, hardened glass, etc.

Embossing misalignment: Customers sometimes find that the Embossing of the Membrane Keypad Panel is misaligned.

• Reason 1: Embossing mold is not calibrated.
• Reason 2: The silk-screen panel is not calibrated.

Solution: QC and engineering need to check molds and silk screen panels. This can solve this problem to a large extent。

Resin Dome is dirty: The raw material of Resin Dome is glue A and B. The situation of dirt and water streaks mainly depends on the environment and the way of standing.

Solution: It needs to be deployed and glued in a dust-free workshop. At the same time, use the grid board to stand the Resin Dome and make it solidify.

Backlight effect is not good: The effect of Backlight is mainly affected by the following aspects. You can click this article for details.