Development of Digital Signage Modules composed of Mini-LEDs using Laser-Assisted Bonding (LAB) Technology

Light-emitting diodes (LED) based displays are highlighted because of their interesting features compared with others. Especially, the LED display with active matrix (AM) has additional advantages such as low power consumption, elimination of current cross talk, and so on. However, AM- driving LED displays are fabricated on active substrates with transistors so that there are many problems like high-cost, difficulty in enhancing yield, and repair problem. As an alternative, an AM-driving LED display on a passive substrate has been developed in this study. One pixel is composed of RGB mini-LEDs and a control IC, fabricated using the CMOS technology. It can decrease the cost of a substrate compared with other AM LED displays, and keep constant the complexity of substrate regardless of the variations of the pitch of mini-LEDs. To mount mini-LEDs and control ICs at the same time needs the technical innovations because they have different surface finishes. Moreover, there is no solder resist layer on a substrate because of the fine-pitch of mini-LEDs and control ICs in a single pixel. The Solder-on-Pad (SoP), fluxing underfill, and Laser-Assisted Bonding (LAB) technologies are developed to implement digital signage modules, successfully.