How to design membrane switch

A. Analyze product requirements
A-1. Where is membrane switch used for?
The characteristics of the where membrane switch work on should be fully considered in the designing.For high-frequency devices (such as Musical Instruments and remote controls), the force button must be light, otherwise operator will feel tired on pressing.When membrane switch is used for some place who easy to stain like microwave oven, electronic scales, refueling machine, machine tools, medical equipment,the panel should be chosen gloss surface material which is easy to clean.Some membrane switch is used by old people should with big buttons and characters.
Braille need be added on panel if they are used for blind person.
All the above are design points are considered according to the application characteristics of the instrument.

A-2. What is the application feature?
We need consider the dimensions, thickness, connectors and mounting on structure .We can also consider whether the resistance, LED and other components can be designed in membrane switch.The normal membrane switch thickness is between 0.6 mm and 1.0mm.When designing the equipment enclosure, enough space for the membrane switch should be considered.

A-3. The using environment of membrane switch
We need consider material,structure,buttons,shielding function in different using environment.Panel should be PET material if they are used in long time sunlight environment.Panel should have waterproof sealing and glue if they are used in wet environment.The dome should be metal if they are used in high temperature environment.Because poly dome will lose elasticity in high temperature.

B.What we need prepare

	Art work drawing	Dimension drawing	Circuit Schematic	Specification	Requirement
Membrane panel	√	√	×	⃝	√
Membrane switch	√	√	√	√	√
Flexiable circuit	×	√	√	√	√
Capacitive Sensor	×	√	√	√	√
FSR	×	√	⃝	×	√
IMD	√	√	×	⃝	√
Rubber keys	√	√	×	⃝	√

√ Needed × Needless ⃝ Not essential

C.The available drawing files format
Membrane switch design drawing format ：*.ai; *.cdr; *.pdf; *.dwg
PCB drawing format：*.pcb; *.pcbdoc

D.The designing points of membrane switch
D-1. The minimum distance between button edge and the punching edge :a.Metal dome > 3mm; b.Poly dome>2mm.
If the button is too close to edge, it will lead to edge glue open , then water and air will enter the switch which make circuit oxidation failure.
D-2. The Poly dome button diameter range is 8~11mm.The normal size of Metal dome button is 8~16mm.
D-3. Do not put the tail root in the button area and the tail direction cannot coincide with the buttons (except for PCB membrane switch).
D-4. Since the screen printing color is printed layer by layer, two light-colored colors should not be directly combined which is prone to color overlap and edge discoloration.
D-5. The thinnest conductive silver-paste circuit shall not be less than 0.3mm, and the resistance of silver-paste circuit is much larger than that of copper foil circuit. Excessively fine silver-paste circuit will not only bring about high circuit resistance, but also lead to circuit burn out.
D-6. The safe distance between the silver slurry wiring shall be larger than 0.3mm.Because the edge of the silver-paste line will have very subtle saw tooth,and the silver-paste line will have subtle migration phenomenon under the power for a long time, the silver-paste line is too close to the risk of short circuit.
D-7. If LED and patch resistance need be placed on the same layer of circuit , it is better to control LED and patch resistance over than 3mm from the edge of the button .It will avoid crushing LED, resistance glue, who lead components poor contact when pressing the button.