Highly integrated flexible electronic Circuits and Modules

Within the electronic circuit board industry flexible circuit still cover a small the market share, however, with the fastest growth rate. The technology is increasingly used in automotives and aerospace, in handheld mobile appliances and many medical devices like pace makers or hearing aids [1,2]. Over past years a European consortium of research institutes and industry has explored the future technological potential of flexible printed circuits in the framework of the project SHIFT. One aspect was to investigate the frontiers of flexible circuit fabrication with respect to minimum feasible line width and pitch using different manufacturing methods. Still further beyond today mainstream flex fabrication technologies were the developments to integrate active and passive components into the buildup layers of flex circuits. In this way extremely high integration of electronic systems and highest functional densities can potentially be realized. Techniques and results of these developments will be presented in this paper. Embedded components in order to comply with the thin buildups of flexible circuits should be very thin as well. To this aim components were be mechanically thinned to 20 ptm. A dicing by grinding technique was applied using etched separation grooves on the wafer. Two technologies for embedding of ultra thin components were developed. The first one is thin flip chip assembly on inner layers of the flex and embedding by subsequent lamination of build up layers. The gap between chip and substrate was in the order of a few microns using either low profile solder or anisotropic adhesive.