Bonding of micro LEDs using wet reflow process of indium bumps based on SU-8 solder mask

Artikel i vetenskaplig tidskrift, 2026

This study proposes an innovative wet reflow process utilizing SU-8 photoresist as the solder mask for fabricating In bump arrays in Micro LED packaging. Conventional solder masks such as SiO2 or metal layers involve complex processes, elevated temperatures, and limited compatibility with flexible substrates. In contrast, SU-8 enables mask patterning via single-step UV lithography, greatly simplifying fabrication and effectively reducing manufacturing complexity and cost. The optimized process achieved a 480 × 640 In bump array with excellent morphology: surface roughness (Ra) reduced from 0.65 μm to 0.126 μm, height non-uniformity improved from 4.8 % to 0.28 %, and shear strength increased nearly tenfold to 1.106 N. Using glycerol as an eco-friendly wet reflow medium facilitated oxide mitigation and enhanced bump uniformity and bonding reliability. The results demonstrate that this low-temperature, efficient, and scalable approach offers clear advantages for high-yield Micro LED integration, particularly in flexible and high-resolution display applications.