Electroluminescent (EL) Panels Explained​

Electroluminescent (EL) Panels Explained

EL or Electroluminescence is one of many technologies used to uniformly backlight overlays or membrane keypads. EL is applied on a very thin layer between the graphic overlay and the circuit. EL uses a printable ink deposit to illuminate the switch and provide a uniformed illumination.

EL panels are the big brother to EL wires – it has the same glow effect but with a flat shape instead of a round shape. The panel is a large sheet of flexible plastic coated with EL material so it’s like one large glowing square. The EL panel emits an even and uniformed glow over the entire shape. 

You can attach the panel by adhered it to the back of a flat surface. It is flexible but will crease and damage if folded. You can cut the panel up as long as the shape you cut out is continuous and has the cable attached. This panel is a blue-green/aqua color when lit and is the brightest of the panels as it is the natural color of EL panel.

Like all EL products, an inverter is required to operate the panel. Because EL tape has more surface area than wire, it requires a more powerful inverter. We suggest you use our 4 x AAA inverter which is strong enough to power a single panel at once. For more permanent installations, the 12V EL inverter can also power a single panel and run off 8 x AA batteries or a wall adapter.

Advantages of Using Light Guide Film for Backlighting Membrane Switches​

Advantages of Using Light Guide Film for Backlighting Membrane Switches

Light Guide Film is designed to evenly distribute light from top or side firing LEDs, providing bright, uniformed illumination. It also reduces the amount of LEDs needed, saving power consumption. More on light guide film technology below. The design and utilization of light guide film (LGF) technology has become one of the most common methods of interface backlighting. CSI Keyboards uses proprietary techniques to design the light guide film so it is optimized for light redirection and reflection giving the customer the brightest possible backlighting solution. Light guide film dots are also designed and implemented which allow for the optimization of light distribution to obtain maximum brightness and uniformity. Common problems that many of our competitors face are light leakage and hot spots. CSI’s backlighting designs prevent any light leakage and hot spots from occurring, and also result in much brighter light guide film and interface.

The design typically consists of 1-4 side-firing LEDs as the light source. Hot pressing optical patterns or micro lens on the surface of the PC film to refract lights guided by the PC film. It can be easily assembled with dome switch or molded in keypad. 

The Features and Advantages of Light Guide Film are as follows:

Slim & Sleek Design

1. PC/PU/TPU film with optical pattern design (.125 – .30 mm thick)

2. Surface light source

3. High uniformed brightness

Cost

1. 50% cheaper than EL panels

2. 40% cheaper than using standalone LEDs

Energy Consumption

1. 6 LEDs light: 90mA. (LED: 15mA/pcs)

2 . LEDs + LGF: 40mA. (LED: 20mA/pcs)

Durability

1. LED light source offers 50,000 hours of life.

2. PC film is extremely durable and can function in bothhigh or low temperatures.

Use the Light Guide Film (LGF) for Keypads or LCD backlighting allows for backlighting only where needed. The CSI solution allows for uniform distribution of light regardless of the distance from LEDs. It also allows for segmentation of areas to avoid light leakage between areas or colors.

What Are Discrete LEDs and How Are They Utilized?

What Are Discrete LEDs and How Are They Utilized?

Discrete LEDs are surface mounted LEDs that are typically either lit individually or together to illuminate a small area. They are ideal for lighting small icons and indicators. They are popular in many user interface designs due to their low cost and thin construction.

However, there are situations when discrete LEDs are not suitable for an application or design. The biggest issue is that they can create hotspots (bright areas) over or near the LED. As a result, they aren’t ideal when lighting larger areas because the backlighting is often inconsistent with some areas brighter than others. 

There are a couple of ways to avoid hotspots in your design. The first way is through the use of an elastomeric or silicone rubber faceplate overlay (versus polyester/polycarbonate). Elastomer is a great conductor of light and therefore allow for excellent light dispersion across a large area using discrete LEDs. 

If you prefer to use a polyester or polycarbonate overlay, CSI could also utilize side firing LEDs and light guide film to backlight a larger area. Other options are fiber optic technologies, or EL panels.

Laser Etching and How it’s Used to Backlight Rubber Keypads

Laser Etching and How it's Used to Backlight Rubber Keypads

When a rubber keypad or rubber membrane switch calls for backlighting, you may often hear the term “laser etching” being used. Laser etching refers to a process in which a high powered laser is utilized to remove a layer or layers of paint on a keypad. 

A standard rubber keypad is simply printed to add graphics or nomenclature. This method will suffice as long as the keypad is not backlit. It’s a cheap and easy way to create letters, numbers, and special characters on keys, making it the preferred choice among many companies. But in order to backlight molded rubber, the rubber must be laser etched: which is a newer, more advanced method for producing backlit nomenclature, graphics, indicators, etc.

The molded rubber typically starts off as a translucent, milky-like color and is then painted with opaque colors designed into the part. The rubber is then laser etched down to the translucent layer(s) of the keypad that will eventually be backlit with LEDs. The laser is carefully guided across the surface of the key, burning away paint in select areas. After the paint has been removed, it reveals the translucent layer below. The result is a contrasting translucent and opaque color, making the backlit areas pop with a higher level of crispness, brightness and visibility.

Laser etched keypads are extremely rugged and durable. The combination of molded light blocks inside the part and the laser etched nomenclature on the faceplate make for an unmatched backlit keypad.

What is Embossing in Membrane Switches?

Embossing in Membrane Switches

To provide tactile feel to a membrane switch or graphic overlay, the polyester or polycarbonate material can be embossed to raise the key area. Embossing is achieved by raising the key area using magnesium membrane switch overlay embossing dies. Embossing has really become standard in membrane switch designs. Not only does it give it a better look and feel, but it also allows the user of the end product to find the key with ease and provide tactile confirmation that the button is present even before it’s pressed. 

There are essentially three options when it comes to embossing membrane switches:

1. Pillow emboss

2. Rim or perimeter emboss

3. LED or Braille emboss

How to Prevent Hot Spots in Membrane Switches

How to Prevent Hot Spots in Membrane Switches

A common issue that many membrane switch manufacturers have when backlighting keypads are hot spots. A hot spot occurs when the light source used for backlighting doesn’t evenly distribute the light causing some areas to appear brighter (hot spot), while other areas are dimly lit. 

CSI Keyboards is a global leader in membrane switch backlighting and interface backlighting technology. Whether backlighting a logo, individual keys, or the entire interface surface, CSI will design and manufacture a backlit membrane keypad switches or backlit interface that will stand out both visually and aesthetically. Backlighting on a membrane switch can be a simple and cost effective solution to enhance the user experience.  

Evenly lighting a large area with a small light source like an LED can be challenging. The main challenges are the size of the backlit area, the amount of LED’s that can fit in the area, and the proximity of the LED’s to the backlit feature. Backlighting a small icon can be relatively easy, but the larger the backlit area, the more difficult it will be to evenly light the graphic without the appearance of hot spots. This is especially true if there is not enough room to place multiple LED’s surrounding the backlit feature.

How to Avoid Hot Spots

CSI Keyboards is an expert and integrating Light Guide Film (LGF) into our backlit solutions to prevent hot spots from occurring. Light Guide Film is designed to evenly distribute light from top or side firing LEDs, providing bright, uniformed illumination. It also reduces the amount of LEDs needed, saving power consumption. More on light guide film technology below. The design and utilization of light guide film technology has become one of the most common methods of interface backlighting. CSI Keyboards uses proprietary techniques to design the light guide film so it is optimized for light redirection and reflection giving the customer the brightest possible backlighting solution. Light guide film dots are also designed and implemented which allow for the optimization of light distribution to obtain maximum brightness and uniformity. Common problems that many of our competitors face are light leakage and hot spots. CSI’s backlighting designs prevent any light leakage and hot spots from occurring, and also result in much brighter light guide film and interface.

It’s always important to remember that the earlier CSI is involved in the design process the better. It’s a lot more difficult completely redesigning the backlighting layout, versus ensuring it is right from the onset of the design process!

What is a Dome Switch Keypad?

What is a Dome Switch Keypad?

CSI Keyboards designs domes into the majority of our membrane switches. Dome switch keypads use two circuit board traces in conjunction with a metal dome. Metal domes, which are typically made of stainless steel, are momentary switch contacts that provide tactility or “snap” when pressed. The domes become normally-open tactile switches when actuated on the circuit. 

The main advantage of dome switch keyboards is the tactile snap or feedback when actuated. When pressing the key, the user realizes they have actually actuated or successfully pressed the switch due to the feel and sound feedback received from the dome.

Another major benefit of the dome switches are the the long lifespan and reliability. Standard dome switch keypads are now rated from one million to even five million cycles. They are still the most reliable type of switch available in the membrane switch space. 

Dome Options:

  • Dome plating: can be plated in other metals such as nickel, silver or gold
  • Dome shapes: four legged, triangle, round, oblong
  • Dome sizes: standard sizes are 6mm, 7mm, 8.5mm, 10mm, 12mm, 14mm, 16mm
  • Dome forces: standard forces range from 85g to 700g
  • Other options: dimpled, hole in center (for backlighting key), double-contact closure domes. 
 
Understanding Dome Actuation Forces:

Actuation force is the amount of force required to make the dome snap. Or in other words, how much force is required to change the dome from the open position to the closed position. Dome actuation force is typically measured in grams. 
 
Internal Venting for Dome Switches:
 
A critical aspect to keep in mind when designing a dome switch keypad is internal venting. When the dome is actuated, air is trapped underneath the dome with nowhere to go. It is therefore recommended that venting is incorporated in the membrane switch design. Not properly venting the dome will result in poor tactile response, key failure and potential issues with air entrapment under the membrane surface.
 

How Do I Choose the Right Dome for my Membrane Switch?

The CSI engineers will work very closely with you in deciding which dome is best for your application. Typically the decision is based on the force of the dome (how soft or hard of a press it takes to actuate the dome) and is extremely subjective. CSI can mock up different sample keypads with different dome options so the customer can decide through a more “hands-on” approach.

Dome Arrays

When a Non-Tactile Membrane Switch Makes Sense

When a Non-Tactile Membrane Switch Makes Sense

A non-tactile membrane switch is a switch that lacks snap or tactility when pressed or actuated. Non-tactile membrane switches are constructed of copper flex circuity using polyimide Kapton as the base material. Copper flex keypad switches are manufactured by laminating a thin sheet of copper to a flexible film substrate. The copper is then chemically etched away, leaving the copper traces. An additional layer of polyimide is laminated to the circuit leaving the gold contacts exposed.

Non-tactile membrane switches are typically designed into a product due to one of the following reasons:

  1. The Need for Dense Traces to Create a Sensor or Slider Interface: typically in user interface designs where the customer is looking for a sensor or slider interface solution, where the user can run his/her finger along the surface and make contact/actuation. CSI can integrate added points, ribs, or sections providing tactile feedback. The advantage of this product is that it does not require any sensor electronics, and has no moving parts. The solution is extremely robust and cost effective. It’s a great alternative to more expensive and sophisticated capacitive touch solutions. 
  2. Size Constraints: when there simply just isn’t enough room for domes due to the small size of the design.
  3. Light Activation Force: the customer wants to simply be able to run their finger over the key with a very light press in order to make contact ie does not want any snap when pressing the key.

Advantages of Copper Flex Membrane Switches

  • Improved creasability – the ability to fold or crease without causing open circuits which you are susceptible to using silver ink
  • Ability to put solder components directly on flex, better adhesion than bonding to silver ink
  • Much more resistant to thermal shock
  • No potential problems with silver migration
  • Greater conductivity
  • Lowering the closed loop resistance and switch bounce will be reduced by gold plating the contacts. We will have a gold to gold contact with no bounce versus silver to gold dome
  • Applying stiffener to tail end using heat lamination versus cold lamination which provides better adhesion and better for pinning
  • Ability to have a 0.5mm pitch vs. the 1.0mm minimum with printed silver
  • Tighter trace routing capabilities

Backlighting Copper Flex Membrane Switches

LEDs: 

LEDs are the most popular and economical method for keyboard backlighting. LEDs are a great option for backlighting non-tactile membrane switches, as they can be easily integrated into the flexible circuit and act as indicator lights providing visual feedback for users, since they don’t feel the snap of a switch when they pressed. LEDs are most commonly used to backlight keys, icons and symbols. LEDs are also typically used as indicator lights. A combination of LEDs, Light Guide Film and proprietary CSI backlighting methods can be designed to backlight the entire surface of a user interface.

Light Guide Film (LGF): 

Light Guide Film is designed to evenly distribute light from top or side firing LEDs, providing bright, uniformed illumination. It also reduces the amount of LEDs needed, saving power consumption. More on light guide film technology below. The design and utilization of light guide film (LGF) technology has become one of the most common methods of interface backlighting. CSI Keyboards uses proprietary techniques to design the light guide film so it is optimized for light redirection and reflection giving the customer the brightest possible backlighting solution. Light guide film dots are also designed and implemented which allow for the optimization of light distribution to obtain maximum brightness and uniformity. Common problems that many of our competitors face are light leakage and hot spots. CSI’s backlighting designs prevent any light leakage and hot spots from occurring, and also result in much brighter light guide film and interface.

Electroluminescence (EL): 

EL is applied on a very thin layer between the graphic overlay and the circuit. EL uses a printable ink deposit to illuminate the switch and provide a uniformed illumination.

Fiber Optics: 

Fiber Optics provide a flexible back lighting layer that can be incorporated between the graphic overlay and the circuit layer allowing the entire surface area of the membrane switch to be evenly backlit.

Integrating Light Guide Film Backlighting

Integrating Light Guide Film Backlighting

CSI Keyboards is a global leader in membrane switch backlighting and interface backlighting technology. CSI has over 35 years of experiencing backlighting user interfaces, from as simple as backlighting a logo to backlighting individual keys to backlighting the entire interface surface. CSI’s backlit products include: backlit human machine interfaces, backlit membrane switches, backlit elastomeric keypads and backlit panels or signage.

Why Light Guide Film?

CSI integrates Light Guide Film (or LGF) into many of our backlit keypad interfaces and membrane switches. Light Guide Film is a thin film that will direct light produced by side-firing, or right-angle, LEDs across the area that needs to be backlit. The film is placed directly below the graphic overlay and above the circuit layer so that the light will not be obstructed by any circuit traces or tactile components. This film can be cut into any pattern or shape within your switch. Multiple LGF films can also be used within one application to provide discrete backlighting to different graphic features. Different colored LEDs can be used to achieve unique lighting effects or white LEDs can be used to light different printed graphics on the overlay.

It is critical that the LEDs are properly placed on the circuit in order to adequately light the intended area. CSI will carefully evaluate the placement of these LEDs to ensure adequate light distribution and to avoid any hot spots.  

There was a time when the only way to backlight interfaces was to use standalone LEDs or EL panels. The problem with using LEDs without LGF is the creation of hot spots and uneven dispersion of light. EL panels are not only expensive, but they are not as bright as today’s LEDs. LGF is extremely thin so it can be incorporated into membrane switches that can’t exceed a certain thickness.  It can provide even backlighting across large and small areas, and for applications where the light remains on while the switch is powered.

Backlighting Membrane Switches

Backlighting Membrane Switches

Membrane Switch Backlighting

CSI Keyboards has been backlighting membrane switches, HMIs and user interfaces for over thirty five years. We’ve used backlighting techniques from the simplest LED membrane switch using a single colored LED indicator with a transparent smoked LED window (to hide LED from surface), to the most complicated multi-colored membrane keypad switch assembly. We can bring your product to life and make it truly stand out from your competition. Typical backlit designs include: backlighting keys, nomenclature, logos, perimeters, indicators, or the entire keypad.

Rubber Switch Backlighting

When it comes to elastomeric rubber keypad backlighting, CSI has the expertise to utilize and take advantage of molded silicone rubber which is an excellent conductor of light. CSI Keyboards utilizes translucent rubber, laser etching, light piping technology as some of our many techniques.

Backlighting Solutions

LEDs: LEDs are the most popular and economical method for keyboard backlighting. LEDs are most commonly used to backlight keys, icons and symbols. LEDs are also typically used as indicator lights. A combination of LEDs, Light Guide Film and proprietary CSI backlighting methods can be designed to backlight the entire surface of a user interface.

Light Guide Film (LGF): LGF is designed to evenly distribute light from top or side firing LEDs, providing bright, uniformed illumination. It also reduces the amount of LEDs needed, saving power consumption. More on light guide film technology below. CSI Keyboards uses proprietary techniques to design the light guide film so it is optimized for light redirection and reflection giving the customer the brightest possible backlighting solution. Light guide film dots are also designed and implemented which allow for the optimization of light distribution to obtain maximum brightness and uniformity. Common problems that many of our competitors face are light leakage and hot spots. CSI’s backlighting designs prevent any light leakage and hot spots from occurring, and also result in much brighter light guide film and interface.

Electroluminescence (EL): EL is applied on a very thin layer between the graphic overlay and the circuit. EL uses a printable ink deposit to illuminate the switch and provide a uniformed illumination.

Fiber Optics: Fiber Optics provide a flexible back lighting layer that can be incorporated between the graphic overlay and the circuit layer allowing the entire surface area of the membrane switch to be evenly backlit.