Electrical Through-Hole and Planar Interconnect Generation in Roll-to-Roll LED Lighting Manufacturing using Industrial I
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Electrical Through-Hole and Planar Interconnect Generation in Roll-to-Roll LED Lighting Manufacturing using Industrial Inkjet Printheads Ingo Reinhold,1,2 Moritz Thielen,1 Wolfgang Voit,1,2 Werner Zapka,1,2 Reiner Götzen,3 Helge Bohlmann3 1 XaarJet AB, Elektronikhöjden 10, 17526 Järfälla, SE. 2 KTH Royal Institute of Technology, SE-100 44 Stockholm, SE. 3 microTEC Gesellschaft für Mikrotechnologie mbH, Bismarckstrasse 142, 47057 Duisburg, DE. ABSTRACT Despite the availability of many high-volume and low-cost manufacturing processes for LED-based lighting applications, relying mainly on fixed patterns such as LED-backlights and RGB-pixelated displays, novel applications, such as “mood lighting” or interior wall displays call for more complicated and shaped LED arrangements. The presented work is based of a novel roll-to-roll (R2R) process to adaptively and cost-efficiently generate LED arrangements on RMPD® substrates. Inkjet printing of planar and though-hole electrical interconnections is of high importance to the process, as it provides a fully digital way of interconnecting devices electrically, accounting for the actual position of the component and spatially provide different ink film thicknesses. Xaar’s industrial inkjet printheads are used to dispense defined volumes of 50 pL of a silver nanoparticle ink in order to provide high reliability and good positioning accuracy while maintaining low satellite drop densities. Specific printing strategies are investigated at a print speed of 0.1 m/s to allow for a reliable electrical connection in case of up to 50 µm deep via connections to the buried component. Due to the low glass-transition nature of the underlying substrates, low sintering temperatures are required to preserve the mechanical properties of the substrate. Low temperature oven sintering yielding sufficient conductivity to drive a current of 40 mA will be discussed. INTRODUCTION The European FP7 Light Rolls Project aims at a versatile manufacturing technology for inline production of LED packages in a R2R-process comprising a novel rotary RMPD® technology, self-alignment of bare LED dies as well as adaptive conductor path and through-hole conduction generation using inkjet technology [1]. While being drafted for this pilot application, the line would be adaptable to new products from various areas such as microfluidics, Lab-on-aChip systems as well as new micro-energy storage components. The present work focuses solely on the generation of conductor paths using inkjet printing of silver nanoparticle inks and evaluates one potential sintering technology with respect to the current specifications of the LED dies to be supplied with a current of 20 mA. The undertaken experiments were, therefore, designed to yield an insight into the capability of the tracks to conduct these currents as well as to assess the operational window of the produced electrical interconnects. While droplet formation, its reliability and consistency are of highest importance from the printer's point of view, the resulting functiona
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