TouchPad has the ability to take on any of your membrane switch design projects. We have extensive experience with a wide variety of materials, stack-ups, and layer configurations. We specialize in membrane hybrid circuit technologies, and are experts at designing in Duraswitch patented technologies such as PushGate, Peel and Place, thiNcoder RT, and MagnaMouse PIC controller and joystick. TouchPad is a Duraswitch authorized design organization.
Since membrane switches are custom designed to meet specific applications, each product will have its own criteria to meet. There are, however, certain parameters which could be of value in enhancing appearance, improving reliability and reducing cost.
Ideally, the membrane switch will be designed simultaneously with the product on which it will be used. Too often, keyboards are the last component designed and must dovetail into a case in size and contents are already fixed and critical. Such constraints may inhibit the optimum design which other wise might have been available.
Since it is our goal to produce the best possible product for the lowest cost, we offer the following suggestions for your design considerations.
• What temperature and humidity ranges will this product experience?
• What types of contaminants or solvents will come into contact with this product?
• Will this product be used indoors or outdoors & exposed to the elements?
• How many switches will there be?
• What type of pinout will be used? (common bus, X-Y matrix, or other)
• What closed loop resistance will be acceptable?
• Will electrostatics or EMI shielding be necessary?
• Will edges be exposed, recessed, or covered by a bezel?
• Will embossing be required?
• Will there be different parts to the same product? (sets)
Basic Layout and Tolerances
• Edge clearance – Keypads should be a minimum of 0.500” from the edge of the switch panel.
• Allow at least 0.125” spacing between keypads or printed circuitry to the edge of a window or cutout.
• Avoid too many keypads in too small an area. Keypads smaller than 0.375” diameter will be awkward to operate, as well as requiring a higher actuation force.
• Steel rule dies normally achieve a tolerance of ± 0.010” when cutting material up to 0.025” in thickness. When cutting material over 0.030”, steel rule dies will lose their accuracy and sharpness, making close registration die cutting more difficult.
• Hard tooling (male/female punch dies) can achieve a tolerance of ± 0.002”. However, cost is significantly greater than steel rule dies. On short runs, laser cutting can save money.
Electrical Layout and Specifications
• A pinout and/or schematic for a common bus, X-Y matrix, or combinatorial matrix can be supplied, or TouchPad can design it for you.
• Closed loop resistance is normally between 20 and 100 ohms.
• Switches are usually rated to carry no more than 50mA. The power rating (current * voltage) should be kept below 1.5 watts. Materials – Graphic Overlay Types of material:
Polycarbonate (Lexan)……..005” – .030” thick
Polyester (Mylar)…………….005” – .010” thick