High throughput R2R printing, testing and assembly processing of flexible RGB LED displays

Abstract

This paper introduces high throughput processing of hybrid flexible RGB LED displays. Processing consists of conductive tracks printing on PET substrate, verification of printed substrate quality by specific characterization equipment and assembly of individually addressable RGB LEDs on substrate using adhesive bonding process. High throughput in manufacturing of flexible displays is achieved utilizing roll-to-roll processes in all steps of the manufacturing process. Utilization of seamless printing tool doubled printing process throughput compared to traditional printing process requiring two printing tools and steps. Implemented roll-to-roll automated electrical test equipment enabled high throughput testing and verification of printed substrate web functionality. Testing was a very important step to verify that printed wiring on the web fulfilled quality requirements for the assembly process. Required SMD components electrically bonded on substrate with R2R assembly machine by utilizing Isotropic Conductive Adhesive (ICA). In addition, Non-Conductive Adhesive (NCA) utilized to provide mechanical support of component, when flexible system bended to smaller than 20 mm radius. Dispensing process noticed to be the most time consuming process in flexible LED display manufacturing, when numerous adhesive dots applied on the substrate. In order to increase throughput in manufacturing, decrease of time used in dispensing process needed. Throughput increase by a factor of ten was possible to achieve by utilizing high speed dispensing process. Increase of more dispenser units in the dispensing process furthermore increase achievable throughput in the manufacturing process. Two meter long flexible display system demonstrator was designed, manufactured and tested based on processed flexible display element.