Membrane Keyboard

Chapter 1: What is a Membrane Keyboard? How Does It Work?

A membrane keyboard is a type of keyboard technology found in many electronic gadgets and appliances. A keyboard, as we all know, is essential hardware that allows us to input data, information, and command to an electronic device or a computer. Computer keyboards are mainly used for typing and gaming applications. But how does a membrane keyboard exactly work?

A membrane keyboard is made up of a few layers. The topmost layer of the keyboard contains all the keys. This is where the users touch and press the keyboard and are exposed to the environment. It can be made of various materials such as plastic or rubber. Below the keys are pressure pads – these pressure pads are made of thin, flexible rubber or plastic membrane with printed conductive traces on its backside. The next layer is called the hole layer; this layer separates the pressure pad next to a key to the bottommost layer such that there will be no mechanical contact when the key is not pressed. Finally, the bottommost layer also contains printed conductive traces connected to the keyboard’s circuit.

When a certain key or button is pressed, the conductive trace underneath the key touches the conductive trace attached to the circuit inside the keyboard. The circuit has an array of switches, and each switch is assigned to a key. This mechanical contact causes the assigned switch to close and allow electrical current to flow. This action registers the pressed alphanumeric character or command by sending the corresponding signal to the processing system of the device. All of the switches in the keyboard circuit are normally open when the key is not in use.

Membrane keyboards are found in a number of applications such as industrial control systems, medical equipment, telephone systems, computers, electrical appliances, retail store machines, and a lot more. The design of these keyboards is not limited to the conventional QWERTY format. Depending on the application, it can be customized flexibly to provide a better user experience. They are lightweight and more portable than mechanical keyboards, the other type, which use a spring-loaded switch. We will be comparing both types and discussing the advantages of membrane keyboards in the succeeding chapters.

Chapter 2: Types of Membrane Keyboard

There are several types of membrane keyboards:

Flat-Panel Membrane Keyboards

Flat-panel membrane keyboards are the simplest keyboards, and they are the ones found in the keypads of household appliances (e.g., washing machines, air conditioners, refrigerators, microwave ovens), vending machines, printers, and photocopying machines. However, they are barely found in computers. They are composed of several layers:

• The top layer is a strong, thin film wherein the character or the icon of the command to be inputted to the machine is printed. The design of the icon can be customized depending on the preference of the customer. This layer also has a conductive metal strip printed on its backside.
• The spacer layer is filled with air or sometimes with an inert gas. Its purpose is to separate the top and bottom layers.
• The bottom layer also has a conductive metal strip connected to an electric circuit of the device. When the button on the top layer is pressed, the metal strip on its backside will touch the metal strip of the bottom layer, registering a character or a command to the system.

Due to their design, flat-panel membrane keyboards require only a light finger pressure when activating a button, which increases the ergonomics of the device. However, they have low physical tactile feedback. To increase the physical tactile feedback of flat-panel membrane keyboards, the device or appliance can be designed such that lights, vibration, or sounds are produced when a certain button is pressed; this is to communicate to the user that the command has registered to the system. An example of this feature is found in microwave ovens; as the buttons are pressed, the beeping sound is created.

Full Travel Membrane Keyboards

Full travel membrane keyboards are the type of membrane keyboard more frequently seen in computers. Their keys are directly integrated into the keypad and are made of a single piece of plastic or rubber material. Their flexible membrane is placed over a matrix of electrical switches. The keys act as a plunger: as a certain key is pressed down, the key pushes the membrane to the bottom layer of the keyboard which causes the assigned switch to close. The elasticity of the membrane will cause the key to move upward when the finger pressure is released. Most full travel membrane keyboards have a spring underneath each key.

Full travel membrane keyboards are an economical option for computer keyboards. However, their physical tactile feedback is lower than mechanical keyboards.

Dome Switch Membrane Keyboards

Dome switch membrane keyboards, or direct-switch keyboards, combine the features of flat-panel membrane and mechanical switch keyboards. Their keypad is made of rubber or silicone, and a metal or rubber dome is found underneath each key. The domes contain a conductive trace in each key that closes the corresponding switch when pressed down.

Metal domes are very reliable and provide crisp and positive tactile feedback for every keystroke. Stainless steel is the commonly used material for metal domes. It can be plated in gold, silver, or nickel. Rubber domes, on the other hand, are cheaper and quieter during operation than metal domes. However, some find rubber domes very soft or “mushy” as they do not give positive feedback as much as metal domes when pressed. Rubber domes are typically made from polyurethane, and their inside bubble is coated with graphite.

Dome switch membrane keyboards are commonly found in handheld controllers, consumer electronics, mobile phones, and medical devices. They are also found in personal computers.

Scissor-Switch Keyboards

Scissor-switch keyboards are a special type of dome switch keyboard. They feature a scissor-like mechanism in their keystroke. The “legs of the scissors” connect each keycap to the keyboard. At the bottom of every keycap is a plunger or rubber dome which actuates the membrane down into the bottom layer, causing the switch to close. The legs of the scissors shorten the travel of the key, the rubber dome, and the membrane during a keystroke. Hence, the service life of the membrane is prolonged as it is less stretched when actuated.

Scissor-switch keyboards are quiet during operation, despite the inclusion of the scissor-like components. They are found in laptop keyboards and built-in keyboards. However, they are slightly more expensive than the previous types. They are harder to clean because of the limited movement of the keys and their multiple attachments, but debris is less likely to get trapped as gaps between the keys are often smaller.

Chiclet Keyboards

Chiclet keyboards, or island-style keyboards, are one of the most popular types of modern keyboard technology found in the latest laptops and desktops. They are known for their distinct sleek and minimalist style, characterized by their square or rectangular keys with rounded corners and relatively short height. The individual keys are separated from each other by a perforated plastic plate that runs across the entire keyboard area.

Chiclet keyboards first appeared in the late 1970s to the mid-1980s in the personal computers TRS-80 Color Computer, TRS-80 MC-10, and Timex Sinclair 2068. These keyboards are named after the chewing gum brand “Chiclet”, as the keys resemble their manufactured gum. Chiclet keyboards had a lot of negative reviews after the first few releases due to the poor quality experienced by the users. However, in the 1990s, the design of the chiclet keyboards was reinvented and gained the approval of millions of users worldwide. Up to this time, chiclet remains one of the widely used keyboard designs adapted by many PC manufacturers.

Chiclet keyboards have the same operating mechanism as the conventional membrane keyboards but with minor differences. To close a specific key switch and record the keystroke, the mechanical contact of the top and bottom conductive traces can be accomplished by either of the two methods:

• The keys are connected to an underlying molded rubber. As the key is pressed down, the thin sides of the molded rubber collapse, allowing the center of the rubber to move downwards. This forces the top membrane layer against the bottom layer. The collapse of the keys in this type feels sudden, which produces more tactile feedback.
• The other type eliminates the use of an upper membrane. Instead, the keys have a conductive coating on their backside. As the keys are pressed down, the coating underneath it touches the bottom layer.

Chiclet keyboards operate more silently than mechanical keyboards and provide a good typing experience. They are considered “business keyboards”. Yet, the feedback of the users regarding these keyboards is split. Since the gap between each key is larger, the occurrences of typographical errors are minimized. Due to their short height, the keystroke during each click is also shorter and flatter, which some typists perceive as comfortable. However, the wider spaces can be a problem to some as they need to overextend their fingers when typing. The tactile feedback is not comparable to mechanical keyboards. Chiclet keyboards are also not the best for hardcore gaming, as they are prone to “ghosting.” Hence, manufacturers innovate the design of their chiclet keyboard in order to accommodate more extensive gaming applications.

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Chapter 3: Terms Used in Describing Keyboards

The following are the terms used in describing the properties of keyboards. Though subjective, they can be great criteria in selecting and assessing keyboards. We may be subconsciously aware of these properties, though they significantly affect our overall typing experience.

Key Travel and Actuation Point

The key travel refers to the distance traveled by the key from rest until it reaches the actuation point, the point at which the input through the keyboard is registered. Key travel is typically measured in millimeters. A shorter key travel may provide a lighter touch or feeling while typing.

Actuation Force

The actuation force refers to the force required to reach the actuation point of the keys. This tells how hard a user must press the keys for the input to be recorded by the keyboard. It is usually measured in centi-Newton (cN) or gram-force (gf).

Tactility in Keyboards

Do you feel a bump on your fingers as you press a key on your keyboard? The feeling we get as we type on our keyboards is attributed to a property called tactility. Tactility refers to the sensory feedback that a user receives when pressing the keys of a keyboard. This feedback “tells” the user that his/her input has been recorded by the keyboard. It is associated with the position of the key travel.

Tactility can affect the finger pressure exerted by the user on keys. The finger pressure of the user on the keys can exceed the actuation force if the device gives little feedback which signals him/her that his/her input is recorded.

As introduced in the previous chapter, the forms of tactile feedback are audible, tactile, and visual feedback. A combination of those forms exists in most keyboards.

• Audible feedback is the sound that a key makes during a keystroke. A clicking sound is oftentimes naturally caused by the key itself. In electronic devices such as cell phones and telephones, an artificial keypad tone may be activated. When the keypad tone is activated, a tone will be heard as the user types or dials a number on the keypad.

Another property that arises from audible feedback is the noise level, which is determined by the switching mechanism. As the audible feedback produced by a keyboard increases, the noise level also increases.

• Tactile or haptic feedback is the physical sensation felt by the user when a key is pressed. It provides a physical “texture” during typing. Bumps and increase in resistance during key travel are the common forms of tactile feedback caused by the key. Vibrations are produced as the keys are pressed in some devices to increase tactile feedback.
• Visual feedback is the visual cue generated during a keystroke. It can be as simple as seeing your keys move downward while typing. Another example of this feedback is when you press a button of a device (e.g., power button, caps lock or num lock key), a bright flash of light will be displayed on the keyboard or screen.

Light or Soft Touch

Light or soft touch is the desirable feature that both ergonomists and users sought. It is affected by both actuation force and key travel, and it is achieved when the finger pressure exerted in pressing the keyboard is little. Lighter and easy-to-press keys reduce stress on the finger joints while typing; however, these keys reduce the accuracy during typing, as some keys can be inadvertently pressed since they are easily actuated.

Chapter 4: Comparison of Membrane and Mechanical Keyboards

What Are Mechanical Keyboards?

Mechanical keyboards are one of the main categories of keyboards based on mechanism. Mechanical keyboards have a key switch, consisting of a spring, a plunger, and a pair of metal contacts, underneath each key. When a certain key is pressed, the plunger moves down to push the spring, forcing the pair of metal contacts together. This closes the switch and records the input on the keyboard. When the finger pressure is released, the spring and the plunger will return to their original position which gives a bumping sensation while typing. The different types of key switches are linear, tactile, and clicky switches, characterized by their tactility, actuation force, and noise level.

Linear switches produce the least noise and give a smooth keystroke. The keys move up and down with little resistance. Hence, they can be actuated rapidly, but they do not provide tactile feedback. Tactile and clicky switches give a bumping sensation near or at the actuation point. Tactile switches produce moderate noise, while clicky switches are the loudest among the key switches.

The following are the comparison of both types of keyboards, based on different criteria:

Noise Level

Membrane keyboards produce little noise during typing because the membrane absorbs the audible feedback naturally created during a keypress. These keyboards are generally quieter than mechanical keyboards. Mechanical keyboards, on the other hand, produce a loud click sound at the actuation point. Membrane keyboards are ideal if you intend to work in a public space or wish not to disturb anyone nearby.

Cost Advantage

Membrane keyboards are much cheaper compared to mechanical keyboards. You can get a high-quality membrane keyboard at an affordable price.

Construction and Weight

Membrane keyboards are more lightweight, portable, and compact compared to mechanical keyboards. They have a relatively simple design. Hence, they are suitable for individuals who travel often with their computers. This is because there are fewer moving parts, and the switching mechanism is primarily composed of silicone, rubber, or plastic membrane. Membrane keyboards have a more minimalistic and classic appearance.

Wide Application Range

Membrane keyboards have a wider range of applications compared to mechanical keyboards. The application of membrane keyboards extends outside the computer realm; membrane keyboards are found in household appliances, telephones, and industrial, laboratory, and medical equipment.

Key Travel

All membrane keyboards and mechanical keyboards utilizing linear key switches require the keys to “bottom out” (i.e., the lowest position of the keys) to reach the actuation point and record the input. In tactile and clicky switches, the actuation point is reached before bottoming out, allowing the user to release his/her fingers in the middle of the key travel and still register a keystroke.

Anti-Ghosting Feature

Anti-ghosting is a keyboard feature that allows the user to press several keys simultaneously. This feature is critical in hardcore and competitive gaming and high-speed typing applications. N-key rollover (NKRO) is a rating of keyboards that tells how many keys can be pressed simultaneously without missing any keystroke, denoted by the letter N in the acronym. For instance, a 6-KRO keyboard means that a user can make six registered keystrokes simultaneously. In full NKRO keyboards, a user can press all the keys and register all the keystrokes at the same time. Full NKRO is more common in mechanical keyboards, as their construction is insusceptible to ghosting.

Due to the singular construction of their membrane, membrane keyboards generally have low NKRO. Full NKRO is found in high-end membrane keyboards.

Tactility Feeling

Membrane keyboards give a lighter touch but with a “mushy” feeling while typing. These keyboards provide less feedback during a keypress, but high-end membrane keyboards nowadays incorporate an improvised tactile speed bump and audible feedback to increase responsiveness. On the other hand, mechanical keyboards naturally give more solid and tactile feedback due to the presence of mechanical switches.

Cleanability and Serviceability

Membrane keyboards are harder to clean and replace keycaps. If one key or component fails, you will have to replace the entire keyboard. In mechanical keyboards, the keycaps can be easily dismantled for cleaning and replacement.

Service Life

Mechanical keyboards last for 20 million to 100 million keypresses, while membrane keyboards only serve 5 million to 10 million keypresses during their lifetime. Nonetheless, membrane keyboards are a cost-effective option for low to medium-duty applications.

Summary

• The membrane keyboard is a type of keyboard technology that utilizes a pressure pad to force two metal contacts together, thereby closing a switch connected to the circuitry of the keyboard and registering an input character or command.
• The types of membrane keyboards are flat-panel membrane keyboards, full travel membrane keyboards, dome switch keyboards, scissors-switch keyboards, and chiclet keyboards.
• The terms used in describing keyboards are key travel, actuation point, actuation force, tactility, noise level and, light or soft touch.
• Mechanical keyboards have a physical switch or key switch underneath each key. The types of key switches in mechanical keyboards are linear, tactile, and clicky switches.
• Membrane keyboards are lightweight, portable, and compact. They produce little noise and give a light but mushy feeling while typing. These keyboards are affordable and cost-effective for low to medium-duty applications. However, they provide less tactile feedback and NKRO and are harder to clean and service.

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