Thin film flexible circuits: Technology, characteristics and applications

In parallel to the increasing complexity of electronic circuits and systems, the requirements on the interconnections (interface) between components, and also the “circuit carrier substrate” (PCB) itself have increased strongly over the last years. The interconnecting parts and the PCBs have to fulfill a very important task within an effective electronic system: they have to provide the right electrical resistivity, RF parameters, mechanical and thermal properties, etc., to match the inputs and outputs of the different parts of a system. Conventional circuit carriers use the printed circuit technology (i.e. copper metallization with subtractive patterning), which is limited in regards to minimum feature sizes and usable substrate materials. In contrary to this, thin film type substrates, due to the application of semiconductor-like manufacturing processes for the pattern generation, are able to provide features with much higher resolution and tighter tolerances, combined with a wide variety of substrate materials to pick from. This paper will highlight general aspects of the fabrication of thin film flexible circuits, realized using different substrate materials. Fundamental properties and results from reliability measurements will be presented and discussed, also in view of practical use in different applications.