Ion Track Enabled High Aspect Ratio Flexible PCB Via Technology
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Ion Track Enabled High Aspect Ratio Flexible PCB Via Technology Mikael Lindeberg, Hanna Yousef, Erik Öjefors, Anders Rydberg and Klas Hjort* Dept. of Engineering Sciences, The Ångström Laboratory, Uppsala University Box 534, SE-751 21 Uppsala, Sweden ABSTRACT By combining ion track technology with ordinary low-resolution printed circuitboard lithography it is possible at low cost to create high aspect ratios via connectors, as solid plugs or consisting of bundles of sub-micron connector wires at a small total cross-section. Ion track enabled microwave circuits in flexible printed circuit boards are suggested to be used in applications like inductors, ferromagnetic resonance microwave filters, circulators and magnetoresistive sensors. In this paper we demonstrate this technology with integrated printed circuitboard devices in two different flexible polyimide-based foils (Espandex and Kapton HN), using the ultra-high-density vias and the sub-micron wires.
INTRODUCTION The general trend of diminishing dimensions of the silicon integrated circuits is currently pursued by the packaging and interconnection technology in e.g. flexible printed circuitboards (PCBs). Flexible PCB is used in diverse consumer electronics such as flat panel displays, harddisks, cameras, mobile phones, and inkjet printers because of the extensive wiring capabilities, lightness and flexibility. As the packing density and number of I/Os between the active components increases in these applications, demands for higher interconnection densities in combination with more complex wiring designs is growing. In the future, it has been argued that new highly sophisticated carriers will incorporate opto-electronic and radio frequency circuits, e.g. resistors, inductors, capacitors and photodiodes. New multilevel packages must be developed containing microvias, high aspect ratio through holes and ultra high-density interconnections to enhance design freedom for embedded components, e.g. multichip modules [1] and PCBs. These laminates can also be used with ordinary rigid PCBs, either as all-polymer dielectrics laminates, or in rigid-flex technology where the flexible laminate provides integrated connections between rigid boards [2]. Flexible PCB laminates are composed of one or several metallic layers (multilayer flex) with intermediate dielectric layers. The through-hole microvias allow more complex and higher interconnection densities by reducing the minimum pitch distances and allowing multilayer laminate structures. A surprisingly large number of fabrication techniques for microvias exist [3], and are still used by industry for different reasons: mechanical drilling, punching, laser drilling, plasma etching, chemical etching [4], and photo-polymer processing. All of these have their specific drawbacks and advantages considering attainable via dimensions, volume production, and cost-effectiveness. Chemical etching and photo-polymer processing are suitable for highvolume production. Laser drilling is, although very small via dimensions are possible
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