Membrane switches are known for standing up to tough environmental conditions. Flexible and durable, the membrane switch can be customized with embossing, backlighting, sealing, and electrostatic discharge (ESD) shielding. Membrane switches can be made with either tactile or non-tactile feedback and they can be integrated with LEDs and other components. To get the switch that works for your application, follow these simple guidelines.

What Is A Membrane Switch And Why Use It?

Table 1. Membrane switch electrical rating
A membrane switch is a multi-layered momentary switch consisting of a graphic overlay, top circuit and bottom circuit. Pressing a key activates the electrical connection. Membrane switches are durable and have a low profile, which allows for space-saving designs and adaptability to each project. Table 1 shows the electrical rating for membrane switches.

Over the past decade, the membrane switch has grown in popularity as designers are seeking a more modernized look, avoiding the older, bulky switches, and looking for ways to fit switches into smaller footprints in today’s equipment. The membrane switch’s sleek, flat design with modern LED lights is appealing with a less industrial look. Figure 1 shows some of the many applications for membrane switches. Table 2 lists some of their design advantages.

Which Overlay Material Is Best For My Application?

Table 2. Advatages of membrane switches
The two most common materials used in making the graphic overlay for membrane switches are polycarbonate and polyester. All overlays begin as clear material, with the graphics printed on the reverse side. A variety of finishes can be placed to visually enhance the final membrane switch, including embossing, texturing or finish, varied colors, or backlighting. Table 3 is a guide for selecting the right material for an application.

A Word About Environmental Regulations

Most industries now require RoHS compliance. The RoHS (Restriction of Hazardous Substances) Directive, most well known as the lead-free requirement, also restricts the use of lead (Pb), mercury (Hg), Cadmium (Cd), Hexavalent chromium (Cr 6+), and polybrominated diphenyls (PBB and PBDE).

Ask The Right Questions

Figure 1. Membrane switch applications
Membrane switches are usually customized to fit each project and there is a virtually unlimited range of styles, colors and switch sizes. Please don’t be afraid to ask a professional; use experts who will advise you on your design. They can help you save money, create the most efficient membrane switch, and advise on graphic aesthetics. To find the right switch for your application, use your imagination, and ask yourself these questions. After establishing these answers, create a drawing and schematic for your membrane switch. This will give you a good starting point for requesting an accurate quote.

Overlay or membrane? Decide if you need an overlay (just the graphic) or a membrane switch (includes circuitry).

Table 3. Guide for selecting the right material
What size does the switch need to be? Determine the dimensions of the membrane switch and the total thickness that you can have. Remember, if you don’t adhere to the space you have available in your product, the membrane could be too high or too low. To save space, the circuit can be designed in a matrix layout (mapping of the traces using leads that run in both the “X” (rows) and “Y” (columns) directions, resulting in fewer leads with a greater number of connections.

Is a back plate or bezel involved? Is there a back plate or bezel to which the membrane will be applied? If so, ask the manufacturer to quote this. It makes your sub-assembly more complete and easier to install into your finished product.

Where will the switch be used? Consider the environment in which the membrane will be used so you can design your membrane switch for maximum reliability. For example, if it will be used outdoors, you will want a graphic material with UV protection. If it will be used in an environment where ESD is present, consider incorporating a shield into the design.

Figure 2. Tactile feedback from domes
Are there any industry-specific considerations that apply to your design? Some applications are simply harder on switches than others. A control panel for farm equipment may need to be designed to IP67 standards to prevent water ingress along with UV protected material to prevent fading. Industrial equipment used for manufacturing in a clean room may need a shield to prevent ESD from shorting out. Medical equipment may need to be protected with special antimicrobial material. For example, APEM supplies Autotex AM, a new hard-coated polyester film with Microban® protection incorporated into the textured hardcoat during the manufacturing process.

What is the mating connector? You can cut cost by using a standard 2.54mm pitch female connector.

Are there specific ergonomic concerns with the application? Consider embossing, which allows the user to locate keys easily. There are multiple types of embossing, including pillow, rim, logo, LED, and combination. Embossing can be beneficial for low lighting environments or for disabled users.

Is lighting required? Keypad can be backlit, with a thin film electroluminescent (EL) lamp, widely used for medical equipment and robotic controls, or light emitting diodes (LEDs), used in medical equipment, power supplies, generators, and hand-held devices, provides visual indicators to the user of actuation.

Figure 3. Labels and overlays
Do you need tactile feedback? In many applications, it is important what button is activated and when. From medical hand-held devices to control panels for industrial equipment, tactile feedback from metal or polyester domes is often required. Tactile feedback confirms through touch and sound that the switch was activated. If this is important to your application, consider a stainless steel dome, which can take high temperatures and are extremely durable. Polyester domes are rated to a maximum temperature of 60°C (122°F). Figure 2 shows a few possibilities for domes that give tactile feedback. Switches that do not require tactile feedback tend to be less expensive and have a simpler construction. They do not require a dome or dome retainer.

How do I get a graphic design that is aesthetically pleasing while not being too expensive? You can use embossing, multiple colors, graphic design, and material finish to convey your company’s message. To save on cost, minimizing the number of colors, using standard off-the-shelf connectors should be incorporated into your design. Avoid thin lines (less than 0.3mm) and serif fonts, which can be costly to print. Keep in mind that use of embossing and polycarbonate material will increase costs. Figure 3 provides some ideas on labels and overlays.

Following the basic guidelines in this article should simplify the job of selecting or designing a membrane switch for any application, and save you time and money in the process.

This article was written by Brian Tovtin, Product Management, Switch Product Line, APEM Components (Haverhill, MA). For more information, Click Here 

Embedded Technology Magazine

This article first appeared in the June, 2013 issue of Embedded Technology Magazine.

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