Mini LED array transferred onto a flexible substrate using Simultaneous Transfer and Bonding (SITRAB) process and Anisotropic Solder Film (ASF)

We transferred and bonded a Mini-LED array onto flexible substrates using the simultaneous transfer and bonding (SITRAB) technology. We also developed the bonding material called anisotropic solder film (ASF). ASF consisted of thermosetting resin as the base matrix and type-7 Sn/58Bi solder powder and reductant. We fabricated Mini-LED carriers and substrates to analyze the compatibility of the SITRAB process and ASF with the flexible substrates. The Mini-LED carrier was made of glass, and transparent PDMS was used as an adhesive considering the laser's wavelength in the SITRAB process. Mini LEDs are arranged in a 32 × 32 array by 450 μm pitch on the glass carrier. Substrates were made of a 20 μm-thick polyimide (PI) and a 75 μm-thick polyethylene terephthalate (PET), respectively. 32 × 32 Mini-LED arrays were successfully transferred and bonded onto those substrates using the SITRAB process and ASF. We measured the light output from the Mini-LED array on the flexible substrate and performed a bending test. All LED was worked without degradation with a bending radius of less than 3 mm. We also observed the bonding joint from the cross-sectional microscopic and SEM images of Mini-LED on the flexible substrate.