The thermal properties of cordierite/diopside composites fabricated by glass–ceramics process for LED packages

Cordierite/diopside composites were manufactured by the heat-treatment of green compacts composed of diopside (CaO–MgO–2SiO2) and cordierite (2MgO–2Al2O3–5SiO2) glass frits. The thermal properties were analyzed as a function of the type and intensity of the crystalline phases generated and the microstructure. The composites contained 0–30 wt% diopside glass frits had α-cordierite as the major phase and the μ-cordierite as the minor phase (designated as α-series). In the composites containing 40–80 wt% of diopside frit, the μ-cordierite and diopside crystals were generated as the major and minor phase, respectively (designated as μ-series). Adding diopside glass frit decreased the thermal conductivity of the α-series specimens but increased that of the μ-series specimens. The density of the composites showed a linearly proportional relationship with the thermal conductivity. At an equal density, the α-series specimens had higher thermal conductivity than the μ-series specimens. 30–50 nm crystals were sparsely observed in the microstructures of the μ-series specimens and 30–100 nm crystals were formed compactly in the α-series specimens. The cordierite/diopside composites manufactured in this research can be applied as LED packaging materials due to their adequate thermal conductivity of 1–3 W/mK and their diffusivity of 0.5–1.3 mm2/s.