What are the precautions for the design of backlit membrane switches backlit illuminated buttons?

2022-01-10

　

The precautions for the design of backlit membrane switches backlit illuminated buttons

membrrane switches provide electrical contacts closing when a front flexible membrane is compressed by a finger touch or the 
like against a rear surface,typically a second membrane, each of the membrane has electrical contacts printed on their opposing 
faces at button locations that are brought into electrical conduction when the membrane is flexed,and held apart by the natural 
elasticity of the membrane  and a spacer layer when the front membrane is released.

In some application,it may be desirable to illuminate the membrane switch keyboard,for example, by backlighting the individual buttons,while the membranes themselves may be transparent,the metallic conductors used to create the contacts block light producing shasdows on the button face.

The prior art has addressed the problem of shadowing in a number of ways,Most simply the conductive areas of the contacts are moved form alignment with the light conducting areas of the button ,In this approach,the light conductive areas munst be minimized so as to not unduly limit the aveilable conducting surface of  the contacts,and the graphics layer(which defines the light conducting areas ofr the button)and membrane keypad panel must be designed in tandem,making the design pricess more expensive and cumbersome.

An aletnative approach to eliminating the shadows caused by the membrane switch condutors employs a  diffuser or light pihe interposed between the membrane switch and the front graphic overlay layer,while this approach allows for some standardization of the membrane keypad switch and may undesirably increase the thickness of the switch and change its mechacical properties.

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