Key Takeaways & Executive Findings
- •• A 3D heat conduction pathway is achieved by combining magnetic filler-modified BNNS (M@BNNS) and non-magnetic U-BNNS under a horizontal magnetic field, enabling superior thermal conductivity. • With only 5 wt% U-BNNS, the through-plane thermal conductivity (λ⊥) reaches 2.88 W m−1 K−1, a 194.2% improvement over single-oriented composites. • The 3D-bridging architecture also provides excellent flame retardancy, reducing peak heat release rate and total heat release by 58.9% and 36.9%, respectively, compared to pure WPU. • The composite demonstrates outstanding thermal management capability as a thermal interface material for LED and chip applications, offering broad potential in electronic packaging.
Abstract
The microstructure design for thermal conduction pathways in polymeric electrical encapsulation materials is essential to meet the stringent requirements for efficient thermal management and thermal runaway safety in modern electronic devices. Hence, a composite with three-dimensional network (Ho/U-BNNS/WPU) is developed by simultaneously incorporating magnetically modified boron nitride nanosheets (M@BNNS) and non-magnetic organo-grafted BNNS (U-BNNS) into waterborne polyurethane (WPU) to synchronous molding under a horizontal magnetic field. The results indicate that the continuous in-plane pathways formed by M@BNNS aligned along the magnetic field direction, combined with the bridging structure established by U-BNNS, enable Ho/U-BNNS/WPU to exhibit exceptional in-plane (λ//) and through-plane thermal conductivities (λ⊥). In particular, with the addition of 30 wt% M@BNNS and 5 wt% U-BNNS, the λ// and λ⊥ of composites reach 11.47 and 2.88 W m−1 K−1, respectively, which representing a 194.2% improvement in λ⊥ compared to the composites with a single orientation of M@BNNS. Meanwhile, Ho/U-BNNS/WPU exhibits distinguished thermal management capabilities as thermal interface materials for LED and chips. The composites also demonstrate excellent flame retardancy, with a peak heat release and total heat release reduced by 58.9% and 36.9%, respectively, compared to WPU. Thus, this work offers new insights into the thermally conductive structural design and efficient flame-retardant systems of polymer composites, presenting broad application potential in electronic packaging fields.
1. Introduction
The rapid development of miniaturized and integrated electronic devices has led to increasing power densities and heat generation, causing internal heat accumulation that poses significant threats to the reliability and safety of electronic systems. This challenge has heightened the demand for efficient thermal management and the mitigation of thermal runaway risks in electronic packaging materials. Polymers are widely employed in the encapsulation of electronic components due to their excellent insulation, ease of processing, and chemical stability. However, traditional polymers suffer from inherently low thermal conductivity, limited thermal stability, and flammability, restricting their application in advanced electronic devices.
To overcome these limitations, a widely adopted strategy is the incorporation of functional fillers, such as aluminum oxide, aluminum nitride, and boron nitride, into the polymer matrix, significantly advancing the development of polymer-based thermal management materials. Among these, two-dimensional (2D) materials like MXene and graphene have been extensively studied for their unique ability to enhance both the thermal conductivity and flame retardancy of polymer composites. However, the inclusion of large amounts of conductive fillers such as MXene and graphene would compromise the insulation properties of the polymer matrix, increasing the likelihood of electrical short circuits in precision electronic packaging and consequently reducing the overall reliability of electronic devices.
Boron nitride nanosheets (BNNS), derived from the exfoliation of hexagonal boron nitride (h-BN), are a graphene-like 2D material celebrated for their exceptional in-plane thermal conductivity, electrical insulation, and thermal stability. These properties make BNNS high...
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Hao Jiang, Yuhui Xie, Mukun He, Jindao Li, Feng Wu, Hua Guo, Yongqiang Guo, Delong Xie, Yi Mei, Junwei Gu (2025). Highly Thermally Conductive and Flame-Retardant Waterborne Polyurethane Composites with 3D BNNS Bridging Structures via Magnetic Field Assistance. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01651-1
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Frequently Asked Questions
What is the main innovation of this study?
The study introduces a novel approach to fabricate waterborne polyurethane composites with a three-dimensional (3D) thermally conductive network by combining magnetically modified boron nitride nanosheets (M@BNNS) and non-magnetic organo-grafted BNNS (U-BNNS) under a horizontal magnetic field. This 3D-bridging structure significantly enhances both in-plane and through-plane thermal conductivities while also improving flame retardancy.
How much improvement in thermal conductivity was achieved?
With the addition of 30 wt% M@BNNS and 5 wt% U-BNNS, the through-plane thermal conductivity (λ⊥) reached 2.88 W m−1 K−1, representing a 194.2% improvement compared to composites with only single-oriented M@BNNS. The in-plane thermal conductivity (λ//) reached 11.47 W m−1 K−1.
What are the flame retardancy benefits of the composite?
The 3D-bridging architecture composite exhibits excellent flame retardancy, with peak heat release rate and total heat release reduced by 58.9% and 36.9%, respectively, compared to pure waterborne polyurethane (WPU). This is attributed to synergistic condensed and gas phase mechanisms.
What are the potential applications of this composite?
The composite shows great potential as a thermal interface material for LED and chip cooling, as well as in electronic packaging fields where efficient thermal management and flame retardancy are critical.
How does the magnetic field assist in forming the 3D structure?
The magnetic field aligns the magnetically modified BNNS (M@BNNS) in the in-plane direction, creating continuous pathways. The non-magnetic U-BNNS then bridges these aligned sheets, forming a 3D network that enhances thermal conductivity in both in-plane and through-plane directions.
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