Flake-Shaped Boron Nitride (BN) Filler for High-Thermal-Conductivity Compounds

As power semiconductor devices continue to deliver higher output, heat generation within packages has increased significantly. This trend has intensified the need for advanced thermal management materials capable of efficiently transferring heat to external cooling systems (Fig. 1(a)). A similar challenge exists in LED devices. Higher luminance demands more effective thermal design, and the prepreg layer—serving as electrical insulation between the circuit layer and the base metal—must provide not only insulation but also high thermal conductivity (Fig. 1(b)).

To meet these requirements, insulating thermal sheets and printed circuit board materials commonly rely on compounds highly filled with thermally conductive fillers such as silica or aluminum hydroxide. While boron nitride (BN) is attractive due to its excellent thermal conductivity and electrical insulation, achieving high BN loading in resins remains difficult because of poor compatibility, which leads to excessive viscosity during processing.

Fig. 1(a) Thermal Management in Molded Power Semiconductor Packages

Fig. 1(b) Thermal Management in LED Devices

Solution

Enhanced Thermal Conductivity Through Higher Resin Loading

Boron nitride (BN) combines high thermal conductivity with electrical insulation, making it an ideal filler for thermal management applications. However, increasing BN content in resin systems typically causes a sharp rise in viscosity during mixing, limiting achievable filler loading. Although surface modification is a common approach to improve filler–resin compatibility, BN presents a unique challenge. Its flake-shaped particles contain reactive functional groups—such as hydroxyl and amino groups—only at their edges, making uniform surface treatment difficult. Plasma treatment has been explored as a solution, but scalability remains a concern for mass production. To overcome these limitations, Resonac has developed “ST-BN”, a flake-shaped boron nitride with a proprietary chemical surface treatment designed for large-scale processing (Fig. 2). This treatment enhances compatibility with resin systems, enabling higher filler loading without compromising processability.

When compounded with epoxy resins, surface-treated BN achieves higher loading levels than untreated BN, resulting in a substantial improvement in thermal conductivity (Fig. 3).

Fig. 2 Resonac’s Proprietary Surface-Treatment

 

 

Fig. 3 Relationship Between Filler Content and Thermal Conductivity ¹⁾

 

• 1) BN and a diluent solvent were mixed with epoxy resin to prepare a varnish. The varnish was coated, laminated by roll pressing and cured by hot pressing to obtain sheet-shaped compounds. Thermal conductivity was measured using the laser flash method.
• Note: The data shown are representative examples of measurement and calculation results and do not guarantee quality.

Features

Reduced Viscosity for Improved Processability

As shown in Fig. 4, varnishes prepared with ST-BN exhibit significantly lower viscosity at 50 vol% BN content compared with untreated BN. This reduction in viscosity improves varnish handling and supports stable, high-volume manufacturing of thermally conductive compounds.

(a) d50 = 1.5 µm

(b) d50 = 8.5 µm

• 2) After preparing a varnish by mixing BN and a diluent solvent with epoxy resin, viscosity was measured using a rheometer.
• Note: The data shown are representative examples of measurement and calculation results and do not guarantee quality.

Enhanced Adhesion Strength

Adhesion between the compound and copper foil was also evaluated. The results show that surface treatment approximately doubles adhesion strength compared with untreated BN-filled compounds (Fig. 5). This improvement is expected to enhance interfacial reliability in applications such as copper-clad laminates and prepregs.

Fig. 5 Adhesion Strength of Compounds to Copper Foil at 50 vol% BN Loading ³⁾

• 3) Test specimen: Varnish prepared from epoxy resin, BN, and a diluent solevent was coated onto copper foil (35µm), laminated, roll-pressed, and cured to form a 400 µm-thick copper-clad sheet. Spwciments were cut into 10mm-wide strips. Evalution method: A 90° peel test was conducted at 50mm/min, and adhesion strength was calculated from the peel force.
• Note: The data shown are representative examples of measurement and calculation results and do not guarantee quality.

Updated: April 23, 2026

Need More Information?

Click here for details on material properties and dielectric breakdown strength.

Datasheet Download

Contact Us

Please don't hesitate to contact us if you have any questions.

Contact Form