Designing a filler material to reduce dielectric loss in epoxy-based substrates for high-frequency applications

In response to the demand for epoxy-based dielectric substrates with low dielectric loss in high-frequency and high-speed signal transmission applications, this study presents a surface-engineered filler material. Utilizing ball-milling, surface-modified aluminum flakes containing organic (stearic acid) and inorganic (aluminum oxide) coatings are developed. Incorporation of the filler into the epoxy matrix results in a significant increase in dielectric permittivity, <i>ε</i> _r, by nearly 5 times (from 4.3 to 21.2) and nearly an order of magnitude reduction in dielectric loss, tan <i>δ</i>, (from 0.037 to 0.005) across the 1 to 10 GHz frequency range. Extension of this method to glass fabric-reinforced epoxy-based substrates, resembling widely used FR4 in printed circuit boards, exhibits minimal permittivity variation (4.5-5.4) and considerable reductions in dielectric loss (from 0.04 to 0.01) within the same frequency range. These enhancements are attributed to improved filler dispersion and suppression of electron transport facilitated by double-layer coatings on the flake surface under varying electric fields. The findings highlight the potential of surface-modified aluminum flakes as a promising filler material for high-frequency and high-speed substrate applications requiring low-loss.