Researches on silane coupling agent treated AlN ceramic powder and fabrication of AlN/PTFE composites for microwave substrate applications

A study on water-resistant treatment of aluminum nitride (AlN) ceramic powder and the fabrication of AlN/PTFE(Polytetrafluoroethylene) composites for microwave substrate applications were described. AlN ceramic powder were modified by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (F8261). The dosage of F8261 ranged from 0.8 to 1.6 wt%. FTIR and XPS were employed to characterize surface elements of aluminum nitride powder before and after modification. We soaked different AlN powder with deionized water, tested the pH of soaking liquid and observed changes of surface appearance via SEM. Among these modified AlN ceramic powder, 1.2 wt% F8261 modified AlN ceramic powder performed best. This powder not only had the maximum contact Angle (θ = 150.8^o) and minimum surface energy (0.92 J/m²), but also had characteristic absorption peak of coupling agent (2922 cm⁻¹, 2856 cm⁻¹). Test results suggested that 1.2 wt% F8261 can make AlN powder obtain strong hydrophobicity, and greatly enhance the stability of AlN in wet environment. In another part, the optimal modified AlN powder and PTFE were combined, and the mass percentage of ceramics ranged from 15 to 45 wt%. Performance evaluation of above samples on the dielectric properties and thermal conductivity was accomplished by measuring their microstructure, moisture absorption and density. With 40 wt% filler, composites displayed satisfactory thermal conductivity (0.80 W/m K), reliable dielectric constant (ε_r = 3.23), admissible dielectric loss (tan δ = 0.0059) and low water absorption (0.02%).