Fabrication of Oxidation-Resistant Cu@glass Paste and Laser Patterning Technology for Si₃N₄ Thermal Management Substrate Metallization

The rapid development of high-power electronic devices has fueled demand for Si₃N₄ substrates, which combine high thermal conductivity (~80-90 W/m·K), excellent flexural strength (>800 MPa), and low thermal expansion (~3.2×10/K). However, conventional active metal brazing (AMB) faces challenges such as limited solder choices, stringent processing, and high temperatures, restricting further performance improvements. To overcome these limitations, this study proposes an oxidation-resistant Cu@glass thick-film metallization approach combined with laser sintering, enabling free-form, high-reliability circuits on Si₃N₄ substrates. Cu@glass composite powders were synthesized via a sol-gel route to form Bi₂O₃-B₂O₃-ZnO glass shells. After mixing with organic vehicles, the pastes were screen-printed and selectively sintered using laser scanning to define customized conductor patterns. The glass coating significantly improved oxidation resistance: while uncoated Cu powders began oxidizing at 121 °C and suffered rapid oxidation above 300°C, coated powders with 10 % and 20 % glass content delayed oxidation onset to 294 °C and 361 °C, respectively. Additionally, The glass coating on copper significantly enhanced the absorption of 1064 nm laser radiation. The uncoated pure copper powder exhibited a low absorption rate of only 0.96 %, whereas Cu@glass powders with 5 %, 10 % and 15 % glass content demonstrated markedly increased absorption rates of 54.96 %, 61.84 % and 67.12 %, respectively. This substantial improvement in laser absorption contributed to more efficient localized sintering during laser processing. Under processing parameters of 15 W laser power, 1 MHz frequency, 10 mm/s scanning speed, and 15 μm adjacent line spacing, the fabricated sample achieved a sheet resistance of 89.5 mΩ/□.