Flex-foil substrates

This article describes the development of a reel-to-reel system that handles the first stage in the process —placing the metal domes onto a flex-foil substrate. 

The use of flex-foil instead of standard SMD substrates, such as PCBs, lends itself to automated production of metal-dome switch contacts. The process requires a solution for placing the domes, which can be less than 60-pm thick, onto the sticky foils. 

A flying-lead structure is composed of a single layer of high-density-pitch copper conductors accessed from both sides of the substrate. Generally, the substrate side of a conductor on a circuit board is not electrically accessible because the conductive foil is typically laminated to the substrate board in sheet form. In the case of a flex circuit, however, the substrate can be... 

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