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.
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.
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, visit http://info.hotims.com/45604-401.