A metal micro-dot array-based alignment-free flip-chip bonding technique for Micro-LED display fabrication

Because of their remarkable performance, Micro-LEDs have attracted a lot of attention in the display sector in recent years. This has driven the development of devices towards smaller sizes and higher pixel densities, but it has also introduced difficult fabrication problems. Standard flip-chip bonding technology poses very strict requirement the precise alignment of ultra-high pixel density Micro-LEDs to their driver substrates during the bonding, whereas typical wafer bonding techniques need high temperatures and pressures. In order to overcome these obstacles, we propose a novel method that uses a high-density metal micro-dot array with a spot size of 2 μm and a pitch of 4 μm to achieve alignment-free bonding under low-temperature and low-pressure conditions. This method enables the fabrication of Micro-LED devices with a pixel size of 6 μm and a pitch of 9 μm. According to experimental results, a 100 % bonding yield was achieved at 225 °C and 75 N, which are much lower than those reported by literature, respectively. The viability of low-temperature, low-pressure alignment-free bonding for the fabrication of ultra-high pixel-density Micro-LED devices has been effectively confirmed by this study.