Guidelines
to Designing Membrane Switches
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.
General Considerations
Environmental
• What temperatures and humidity range will this
product experience?
• What type of contaminants or solvents will come
into contact with this product?
• Will this product be used indoors or outdoors,
exposed to the elements?
Mechanical
• Will tactile response be required?
• To what material will the switch be laminated?
• What number of actuation’s will the product
receive?
• Will actuation force be a factor?
Electrical
• 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?
Appearance
• 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.
Tooling
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.
• 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
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