Massive Parallel Assembly and Interconnection for Micro-LEDs – a Technical Feasibility Study

This paper does not only present the RGB handling but also the electrical bonding of Micro-LED arranged onto a display. Micro-LEDs are getting more and more attractive for micro-screen applications since allowing energy saving for mobile applications. The present paper showcases a soldering based assembly technology to bond several thousand small size LED chips to a larger area substrate. The assembly of “RGB” micro-chips on a host substrate are presented using the developed assembly technology suitable for display applications using three individual “LED wafers”. The process combines handling of small size chips (ca. 20×20 µm) by a conveyor from a donor wafer (a flipped source wafer) to the soldering onto target substrate for reliable electrical connection. The component soldering is performed by a three steps sequential assembly to achieve the placement and final bonding inclusive electrical interconnects by AuSn soldering of three different chips of same size arranged in a 150×150 matrix array. A yield of 99.5 % of correctly connected die could be achieved within this demonstrative study of massive parallel assembly.