Improved indium bumps bonding process using flexible composite structure temporary substrate for micro-LED display applications

Journal article, 2025

Micro-LEDs refer to light-emitting diodes with a size of less than 50 μm, which have superior performances compared to Liquid Crystal Displays (LCDs) and Organic Light-Emitting Diodes (OLEDs). Micro-LEDs are expected to constitute the mainstream electronic display technology in the future. Nevertheless, micro-LED technology is still facing some technical difficulties. Especially, in mass transfer technology, the non-parallel problem between the temporary substrate holding the micro-LED chips and the target substrate seriously affects the bonding quality of the micro-LED chips. To solve this problem, this paper proposes a Polydimethylsiloxane (PDMS)-based flexible composite structure temporary substrate (carrier) doped with dimethyl silicone oil, which is capable of generating a deformation of 6 μm under a pressure of 1 MPa and maintaining this property up to 250 °C. Utilizing this deformation property to cope with the non-parallel problem during the bonding process can significantly improve the bonding quality and yield of micro-LEDs. We placed 1600 (40 × 40) micro-LED chips of size 30 μm × 15 μm on the carrier with a chip pitch of 222 μm. The carrier was heat-treated at 250 °C for 2 min as an adhesion reduction method. Under a bonding temperature of 180 °C and a bonding pressure of 0.3 MPa, bonding of the micro-LEDs with a 1.98-inch thin film transistor (TFT) was implemented using the carriers. A micro-LED green display with a PPI of 114 was successfully fabricated, with a display yield of 95.18 % and a brightness of 18,710 cd/m2. The method developed in this paper can overcome the key challenges of micro-LEDs mass transfer technology and pave the way for the industrialization of micro-LEDs.