Black Spherical Silica with Controlled Carbon Content for High-Frequency PPE-Based Copper-Clad Laminates: Dielectric Properties and GHz Communication Applications

Featured Application The black spherical silica developed in this study exhibits well-controlled particle size distribution (D50 ≈ 2.0 μm), low moisture content (<0.1%), high electrical insulation (volume resistivity ∼10 13 Ω·cm), and excellent dispersion stability. These properties make it suitable as a functional inorganic filler for high-frequency semiconductor packaging substrates, particularly for applications requiring both effective light-shielding capability (L* as low as 20.1) and low dielectric loss (D f ≤ 0.0017 at 1–10 GHz). The findings provide practical guidance for the design of black fillers used in copper-clad laminates for 5G/6G communication devices. This study utilized polysiloxane as the raw material to successfully prepare black spherical silica fillers with varying internal carbon content. Through different thermal treatment processes, a dense silica layer was formed on the particle surface, while the internal hydrocarbon groups were thermally decomposed into carbon. Four types of spherical silica with different carbon contents were systematically characterized in terms of particle size distribution (D50 ≈ 2.0 μm, D100 < 5 μm), scanning electron microscopy morphology, moisture content (<0.1%), specific surface area (~1.0–1.1 m 2 /g), true density (~1.90–1.97 g/cm 3 ), carbon content, blackness (L* values), and volume resistivity. The results indicate that the prepared black spherical silica exhibits a narrow particle size distribution, low moisture content, and high electrical insulation properties. Furthermore, the prepared black spherical silica was used as a filler in a polyphenylene oxide-based binder system to fabricate copper-clad laminates (CCLs), and their dielectric properties were systematically investigated. The study found that at electric field frequencies of 1 GHz and 10 GHz, the dielectric constant (D k ) and dielectric loss (D f ) of CCLs prepared with fillers containing less than 5% carbon remained largely consistent with those of carbon-free control samples. However, the D f of CCLs prepared with fillers containing 9.00% carbon increased nearly tenfold, indicating that when the internal carbon content of the filler exceeds a certain threshold, it adversely affects the high-frequency dielectric properties of the copper-clad laminate.