Modification of Si3N4 ceramic powders and fabrication of Si3N4/PTFE composite substrate with high thermal conductivity

Si3N4 filled polytetrafluoroethylene (PTFE) composites were prepared for microwave composite substrates. The analyses of Si3N4 powder by XPS and FTIR confirmed the successful grafting of Si3N4 powder by F8261. The effects of Si3N4 content on the microstructure, density, moisture absorption, thermal conductivity and microwave dielectric properties (epsilon(r), tan delta) of Si3N4/PTFE composites were investigated. With an increase of Si3N4 content, the density, dielectric constant and moisture absorption increase. The composite filled with the modified ceramic powders have better dielectric properties, and the powders are more compatible with PTFE. Different models are used to predict the thermal conductivity of the composite substrate. When the content of Si3N4 ceramic filler is 62 vol% (70 wt%), the prepared Si3N4/PTFE composite exhibits excellent low dielectric loss (tan delta = 0.0014), low dielectric constant (epsilon(r) = 4.03), high thermal conductivity (lambda = 1.3 W/m.IG and relatively low water absorption (0.032%).