Surface modified and gradation-mixed Al₂O₃ as an effective filler for the polyphenylene oxide (PPO) insulative layer in copper clad laminates

Although filling ceramic powders into the insulative polymer layer has long been realized as an effective strategy to elevate the heat dissipation capability and service life of copper clad laminates (CCLs), the weak interfacial bonding between inorganic filler and organic matrix and the discontinuous thermal conductive network have hindered such beneficial effects. Herein, the silane coupling agent (KH-560) modified and gradation mixed Al₂O₃ served as an effective filler for CCLs. After optimization of the filling scheme through tremendous efforts, the maximum thermal conductivity of corresponding CCLs with surface modified and gradation-filled Al₂O₃ achieved to 0.646 W/m·K, apparently higher than that of pure resin CCLs (0.291 W/m·K) and single-size Al₂O₃ filled CCLs (Al₂O₃-20 μm-50%, 0.573 W/m·K). Simultaneously, the peel strength and bending strength of the CCLs with the surface modified and graded-mixed Al₂O₃ kept at a satisfactory level (0.903 N/mm and 306 MPa, respectively), surpassing those of CCLs with pristine Al₂O₃ fillers. In addition, the dielectric loss reduced to 4.67 × 10^–3 and the water absorption was as low as 0.364%. Such a comprehensive performance could be ascribed to the improved interfacial bonding brought by KH-560 and a more contiguous heat conduction network formed by the gradation-filled Al₂O₃. This study offers a new strategy promising for high speed and high frequency applications of CCLs with so many alternative ceramic fillers.