Elastomeric Keypad Design Guidelines Elastomeric keypads can provide maximum tactile response due to their full travel flow when it comes to data entry Things to Consider when Designing interfaces. They consist of an elastomeric cover your Elastomeric Keypad: that is typically used as an actuator over 1. Environmental conditions another switching technology, most commonly (indoor/outdoor, harsh a membrane switch. They offer a lower unit environments, sunlight, etc.) cost than conventional switching products, and 2. Mechanical requirements are resistant to temperature, moisture, (material, actuations, tactile chemicals, and abrasion, providing them with a feedback, etc.) long operating life. 3. Electronics requirements Because every elastomeric keypad we create is (conductive pills) designed custom for your unique application, 4. Appearance (colors, key caps, certain specifications are required for each finishes, etc.) design. This set of design guidelines was created 5. Certifications (ISO, U.L., etc.) to assist you with the design and creation of your custom elastomeric keypad. Our highly skilled engineering team will carefully review your requirements to assist in designing the Materials: Elastomeric keypads are optimum keypad for your application. manufactured out of elastomers, which are described as a polymer that contains Elastomeric Keypad Construction: viscoelasticity. The most common material Elastomeric keypads are manufactured from used for graphic switches is silicone rubber; rubber, and are formed using molds. Most however EPDM is also a popular alternative. elastomeric keypads utilize the rubber as the Silicone rubber is resistant to extreme top circuit or actuator when pressed, making temperatures, moisture, chemicals, and contact with a lower switch circuit or PCB. abrasion. Fluorosilicone rubber is also available, Differing forces can be accomplished by using but primarily used for actuation and gaskets various key constructions as shown below in due to its superior characteristics and sealing Figure 1. capabilities. Additionally, fluorosilicone rubber is 3 to 5 times the cost of silicone rubber. Figure 1 311 Winton Street, Wausau, WI 54403-3235 • 800.950.5013 • [email protected] • www.wilsonhurd.com 1 Elastomeric Keypad Design Guidelines Colors: Wilson-Hurd most commonly uses the Molds: Elastomeric keypads are formed using Pantone Matching System or CMYK color either injection or compression molding. model to match custom colors. We can match Injection molding is ideal for manufacturing a to a specified or provided color. If you wish to product at high volumes, and the overall quality submit a sample, we prefer that it be 2 x 2” in of the parts produced is greater than when size. Elastomeric keypads are available with made using compression molding. Compression single or multi-colored surfaces. molding is a lower cost molding method, however it is possible that each part produced Artwork: Please visit the Resources section will not have a consistent level of quality. on Wilson-Hurd’s website to submit artwork, or Prototype molds can be completed in as little as simply visit the link below. 18 days. Hard molds can take up to 40 days and are more costly, however they are www.wilsonhurd.com/submit-artwork recommended for mass produced parts due to their increased operating life. Hard molds can We accept the following types of artwork be made out of hardened or pre-hardened (listed in order of preference): steel, while their more cost-effective • AutoCAD (2D)* counterparts are typically made of either • Solidworks (3D)* aluminum or a beryllium-copper alloy. • IGES (3D) Plastic and stainless steel key caps • STEP (3D) Key Caps: are available to incorporate into your • DXF (2D) elastomeric keypad design for added tactile • Gerber (PCB) – include dimensional of feedback. your part in one of the other formats • Adobe Illustrator (Graphics) – include Conductive Pills: Electronic capabilities can dimensions of your part be added to elastomeric keypads by including • PDF (Graphics or Dimensional Support) conductive pills on the base of the switch – with embedded fonts (Graphics) button. When the button is pressed, the • Postscript (Graphics) – with embedded conductive pills are then brought into contact fonts with the PCB below. *Most preferred forms of artwork Backlighting Options: We offer LEDs, Graphics: Graphics can be applied to electro-luminescence, fiber optics, and light elastomeric keypads using screen-printing, pad guide film for backlighting options. printing, and spraying and etching. Spraying and etching is capable of producing the finest Integration: The design options for detail out of the three different techniques. elastomeric keypads are incredibly flexible. They can easily be integrated into both flex and Over-coatings & Finishes: Over-coatings PCB-based membrane switch assemblies and finishes are recommended if you would like allowing for reduction in cost as well as to increase the durability and operating life of assembly time. With elastomeric keypads you your elastomeric keypad. Epoxy and also have the ability to use an entire polyurethane over-coatings are available to add elastomeric overlay, or incorporate elastomeric additional protection against chemicals and keys into other overlay material designs. abrasion, as well as increase the ink longevity of graphics. Fluorescent and anti-microbial finishes can also be applied. 311 Winton Street, Wausau, WI 54403-3235 • 800.950.5013 • [email protected] • www.wilsonhurd.com 2 Elastomeric Keypad Design Guidelines Technical Details: Current (A or I) Unit, Amp: The flow of electricity, i.e., the characteristic drift movement of carriers Type Specification such as ions, electrons, or holes. I=E/R Hardness Shore 20A-80A Elastomer: A polymer that displays viscoelastic Conductive Pill <100 ohms with 100gr traits. Contact Resistance loading Operating -25°C (-13°F) to 70°C Elastomeric Keypad: A keypad featuring an Temperature (158°F) elastomeric cover used as an actuator over another Storage Temperature -30°C (-22°F) to 85°C switching technology, typically a membrane switch. (185°F) Electrical Actuation: Switch actuation produced by various electrical phenomena. In most cases, the switching action involves a change in state rather GLOSSARY than a mechanical operation. Actuation: The process that causes a switch to Electro-luminescent Lighting (EL): Light produced by change position, i.e. to open or close. charged phosphorous. Actuation Force: The minimum force required to EPDM: Ethylene Propylene Diene Terpolymer electrically close a switch contact. Epoxy Coating: A durable coating made using epoxy Actuator: A formed or molded protrusion to make resins that increases a product’s durability and contact with the center of a switch location, resistance to moisture and extreme temperatures. improving tactile feedback. Feedback: The mechanism by which the operator Anti-Microbial Finish: An anti-bacterial coating that senses that a switch has been activated; audio, kills the biotic agents it comes into contact with. visual, or tactile. Backlighting: Illumination originating from within or Fiber Optic: Extruded materials, such as certain behind the switch panel which outlines or accents plastic filaments, which provide paths for light. specific areas. Typical lights are LEDs, fiber optics, electro-luminescence, and light guide film. Finishes: The application of a coating to a material that alters the surface appearance. CMYK Color Model: Also known as process color and four color, it is a color model used in color printing Flexible Membrane Switch: A membrane switch that utilizing the four inks cyan, magenta, yellow, and key contains a flexible printed circuit. (black). Flexible Printed Circuit (FPC): A printed circuit using Color Matching: The physical creation of a color in Kapton polyimide film as a substrate. the range of one-dimensional hues. Fluorescent Finish: A coating of the electromagnetic Compression Molding: A method of molding in spectrum. which pre-heated molding material is placed into a heated mold cavity. After the mold is sealed, Fluorosilicone Rubber: A rubber material pressure is then applied to force the material into occasionally used in elastomeric switches, comprised contact with the entire mold until it has been cured. of silicones and fluorocarbons. Conductive Pills: A small metal pill placed on the Injection Molding: A method of molding in which a base of a key in an elastomeric keypad, typically pre-heated molding material is injected into a mold made of either carbon or gold. Once the key is cavity where it cools and hardens, taking on the pressed, the conductive pill comes into contact with shape of the mold. a PCB below. 311 Winton Street, Wausau, WI 54403-3235 • 800.950.5013 • [email protected] • www.wilsonhurd.com 3 Elastomeric Keypad Design Guidelines Insulation Resistance: The alternating current Resistance Units – Ohms: The common unit of resistance between two electrical conductors, or two electrical resistance. One ohm is equal to one volt systems of conductors separated by an insulating per amp. material. Screen-Printing: Ink is forced through a Key Caps: Caps made out of plastic or stainless steel photographically created mesh stencil (screen) using that cover elastomeric keys. a rubber squeegee, allowing heavy ink deposits with a minimal number of passes. LED: Light-Emitting Diode Silicone Rubber: An elastomer composed of silicone Light Guide Film: A more recently developed containing silicon, carbon, hydrogen,