Effect of laser beam power on microstructure evolution and interface kinetics of laser-soldered mini-LEDs for MEMS packaging

Laser soldering offers localized heating and shorter processing times, reducing thermal damage and improving Mini-LED bonding reliability over reflow soldering in microelectromechanical systems packages. This study examines the microstructural, mechanical, and aging properties of Mini-LED joints formed using Type-8 (2–8 µm) Sn–3.0Ag–0.5Cu solder paste in a Laser-Assisted Bonding process. Effective bonding was achieved at laser beam power 47–57 W, with Cu₆Sn₅ intermetallic compound (IMC) thickness increasing from 2.2 ± 0.58 μm at 47 W to 2.6 ± 0.3 μm at 57 W. Isothermal aging at 125 °C further increased IMC thickness to 4.8 ± 0.15 μm after 400 h for 57 W soldered joints, alongside microstructural coarsening. Joints soldered at 52 W showed the highest initial shear strength (0.9 ± 0.5 N), but aging altered fracture modes, with coarsened Ag₃Sn and thicker Cu₆Sn₅ IMCs causing brittle failures at higher power levels. These results highlight the need to optimize laser beam power for balanced mechanical reliability and thermal stability in Mini-LED packaging.