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Membrane switches are ubiquitous. Anytime one interfaces with the world of electronics, the odds are that he is doing so through a membrane switch of some type. As common as they are, membrane switches are also perhaps one of the more unsung and least visible members of the flex circuit family. As switches are fundamental elements of the electronic interconnection hierarchy, it is worthwhile to look more deeply into this important flex circuit family member.
Basically, a membrane switch is as its name implies an electrical switch created on a thin film or membrane. They are typically low power with maximum current ratings of around 1/10 of an amp. The circuitry for these devices is often somewhat elaborate since they frequently provide connections for a host of different input functions. Perhaps the most common application for membrane switches is in a keyboard of some type. While not all keyboards are made of flexible materials, a great many are. The most common layouts are matrix type (i.e., rows and columns) and common line connections (i.e., a common trace plus some number of switches). Other structures are possible depending on the needs of the user including integration of electronic ciruits, including passives devices, such as resistors, and land patterns for component mounting.
The conductor material used for membrane switches varies by application. Copper and polymer thick film (PTF) inks are the most common choices. Cost is normally a...