Development of simultaneous transferring and bonding (SITRAB) process for µLED arrays using Anisotropic Solder Paste (ASP) and Laser-Assisted Bonding (LAB) Technology

We have transferred and bonded a μLED array to the patterned substrate using SITRAB (Simultaneous transferring and bonding) and ASP (Anisotropic Solder Paste). ASP contained epoxy as a base matrix, solder powder, and a small fraction of polymer balls and was applied to the substrate using screen printing. We have arrayed 20×20 of μLEDs on the interposer, which is PDMS laminated glass wafer. The interposer was picked-up by quartz bonder-head and aligned to the substrate. After aligning the interposer to the substrate, the bonder-head moved to the substrate and applying pressure. While applying the pressure, the homogenized laser with a wavelength of 980nm was irradiated through the quartz bonder-head for a few seconds. In this process, transferring and bonding the μLED array are performed simultaneously, so we named this process SITRAB. After the SITRAB process, the μLED array bonded substrate was cured at 120°C for 2 hours. Because the ASP contains no vaporizable substance, there is no fume during the SITRAB process, and the cleaning is unnecessary after the post-cure process. Using ASP material and the SITRAB process, a 20×20 μLED-array was successfully transferred and bonded to the substrate. We observed the light output from the μLED array bonded to the electrodes and measured a cross-sectional SEM image to analyze the bonding joint.