I. Background

With the rapid growth of the 5G era and new energy vehicles, electronic devices are evolving towards higher performance and higher density. Consequently, the high heat flux generated during operation poses significant challenges to the thermal management of electronic equipment. To ensure continuous and stable operation of electronic components, thermally conductive and electrically insulating materials with high heat dissipation performance have become essential in the thermal design of electronic devices.

Due to the inherently low thermal conductivity of polymer materials, the thermal conductivity of composites is primarily determined by the filler. The key focus is how thermally conductive fillers achieve high thermal conductivity. Four main approaches are employed: filler selection, particle size grading of fillers with different diameters, improving the intrinsic thermal conductivity of the filler, and surface modification of the filler. Each is analysed below.

II. Approach 1: Filler Selection

Commonly used thermally conductive materials include metals, ceramics and carbon-based fillers. For electrical insulation purposes, metals are unsuitable. Carbon-based fillers present dispersion challenges within the matrix. Ceramic fillers offer a favourable combination of properties. Among these, spherical alumina is widely regarded as a cost-effective thermally conductive and electrically insulating material due to its high thermal conductivity, low filling viscosity and moderate price.

While the principle of increasing thermal conductivity appears straightforward, achieving optimal thermal performance through appropriate filler formulation is complex. This requires the three approaches described below.

III. Approach 2: Particle Size Grading of Fillers with Different Diameters

The packing effect of mixed fillers with different particle sizes is superior to that of single-size fillers. Under different particle size ratios, the viscosity and thermal conductivity of the composite vary with the relative content of the two fillers. Mixing particles of different sizes increases the packing fraction. Small particles fill the voids between large particles, creating close packing of particles with different sizes and forming a more effective thermally conductive pathway.

Bestry's BAK series spherical alumina offers particle sizes from 1 μm to 120 μm with controlled particle size distribution. This enables contact between alumina particles of different sizes and effective filling of interstitial spaces, thereby improving thermal conductivity and reducing filling viscosity.

IV. Approach 3: Improving Intrinsic Thermal Conductivity of the Filler

Structure determines performance. To enhance the intrinsic thermal conductivity of alumina, the alumina filler must have a high α-phase content. Bestry's NSM series near-spherical alumina exhibits high α-phase content, good stability, high crystallinity and uniform particle size. Under the same filling ratio, the thermal conductivity of NSM-1S high-thermal-conductivity alumina filler is 15% higher than that of BAK-1 spherical alumina.

V. Approach 4: Surface Modification of Fillers

Alumina has high surface polarity, resulting in poor interfacial compatibility with organic resin matrices. Improving the compatibility between alumina powder and polymer matrices is therefore an important issue in the application of alumina-filled materials. Surface modification of alumina enhances its compatibility with the matrix.

The following data compares the filling viscosity of modified and unmodified spherical alumina in a silicone system. Surface-modified spherical alumina effectively reduces filling viscosity in the silicone system.

*BAK-5, BAK-10: Unmodified spherical alumina*

*BAK-5H4, BAK-10H4: Modified spherical alumina*

Oil phase: Silicone oil

VI. Results: High Loading and High Thermal Conductivity

By integrating the three approaches of particle size grading, improving intrinsic thermal conductivity and surface modification, Bestry has achieved the following performance for alumina under high-loading, high-thermal-conductivity conditions.

Under pure alumina filling conditions, Bestry's spherical alumina products achieve a thermal conductivity exceeding 6 W/(m·K). Compared with nitrides, this offers both high thermal conductivity and excellent cost-effectiveness.

Through in-house process development and proprietary core equipment, Bestry delivers a comprehensive portfolio of stable-quality products. The company provides full coverage of thermally conductive fillers across the entire ultra-wide particle size range of spherical alumina, meeting customer requirements for diverse application scenarios.