High Through-plane Thermal Conductivity Research Articles

A binder-free ice template method for vertically aligned 3D boron nitride polymer composites towards thermal management

Hexagonal boron nitride (BN) is an attractive filler candidate for thermal interface materials, but the thermal conductivity enhancement is limited by the anisotropic thermal conductivity of BN and disordered thermal pathways in the polymer matrix. Herein, a facile and economic ice template method is proposed, wherein BN modified by tannic acid (BN-TA) directly self-assemble to form vertically aligned nacre-mimetic scaffold without additional binders and post-treatment. The effects of the BN slurry concentration and the ratio of BN/TA on three-dimensional (3D) skeleton morphology are fully investigated. The corresponding polydimethylsiloxane (PDMS) composite via vacuum-impregnation achieves a high through-plane thermal conductivity of 3.8 W/mK at a low filler loading of 18.7 vol%, which is 2433% and 100% higher than that of pristine PDMS and the PDMS composite with randomly distributed BN-TA, respectively. The finite element analysis results theoretically demonstrate the superiority of the highly longitudinally ordered 3D BN-TA skeleton in axial heat transfer. Additionally, 3D BN-TA/PDMS exhibits excellent practical heat dissipation capability, lower thermal expansion coefficient, and enhanced mechanical properties. This strategy offers an anticipated perspective for developing high-performance thermal interface materials to address the thermal challenges of modern electronics.

SiC Nanowires Bridged Graphene Aerogels with a Vertically Aligned Structure for Highly Thermal Conductive Epoxy Resin Composites and Their Mechanism

Thermal conductive composites have a wide application in the electronic packaging field, and fabricating three-dimensional (3D) graphene aerogels by the self-assembly method is a facile way to construct thermal conductive networks in polymer composites. But those self-assembled graphene aerogels can only endow composites with a limited thermal conductivity because (1) abundant defects on RGO sheets reduce their intrinsic thermal conductivity and (2) massive edges and gaps in aerogels cause severe phonon scattering. Many works before have been done to heal the defects by high-temperature annealing, but the works of filling gaps and decreasing phonon scattering are rare. Herein, we designed a facile route to synthesize SiC nanowires on the edges of RGO sheets for connecting adjacent RGO sheets, decreasing phonon scattering, and enhancing thermal conduction efficiency in graphene aerogels. Before that, RGO/Si aerogels with vertically aligned structures were obtained by the chemical reduction method and the freeze-drying method to enhance their through-plane thermal conduction efficiency. When the initial mass ratio of GO solute/silicon powder was 5:1, HGA-5 endowed the EP composite with a high through-plane thermal conductivity of 3.59 W m–1 K–1 at a relatively low filler loading of 2.87 wt %. Finite element analysis was applied to illustrate the thermal conductive mechanism of the hybrid aerogels-filled EP composites. The EMI shielding performance of the composites was also discussed in this work.

A Hierarchically Structured Graphene/Ag Nanowires Paper as Thermal Interface Material

With the increase in heat power density in modern integrating electronics, thermal interface materials (TIM) that can efficiently fill the gaps between the heat source and heat sinks and enhance heat dissipation are urgently needed owing to their high thermal conductivity and excellent mechanical durability. Among all the emerged TIMs, graphene-based TIMs have attracted increasing attention because of the ultrahigh intrinsic thermal conductivity of graphene nanosheets. Despite extensive efforts, developing high-performance graphene-based papers with high through-plane thermal conductivity remains challenging despite their high in-plane thermal conductivity. In this study, a novel strategy for enhancing the through-plane thermal conductivity of graphene papers by in situ depositing AgNWs on graphene sheets (IGAP) was proposed, which could boost the through-plane thermal conductivity of the graphene paper up to 7.48 W m-1 K-1 under packaging conditions. In the TIM performance test under actual and simulated operating conditions, our IGAP exhibits strongly enhanced heat dissipation performance compared to the commercial thermal pads. We envision that our IGAP as a TIM has great potential for boosting the development of next-generation integrating circuit electronics.

Process-dependent anisotropic thermal conductivity of laser powder bed fusion AlSi10Mg: impact of microstructure and aluminum-silicon interfaces

PurposeAlSi10Mg alloy is commonly used in laser powder bed fusion due to its printability, relatively high thermal conductivity, low density and good mechanical properties. However, the thermal conductivity of as-built materials as a function of processing (energy density, laser power, laser scanning speed, support structure) and build orientation, are not well explored in the literature. This study aims to elucidate the relationship between processing, microstructure, and thermal conductivity.Design/methodology/approachThe thermal conductivity of laser powder bed fusion (L-PBF) AlSi10Mg samples are investigated by the flash diffusivity and frequency domain thermoreflectance (FDTR) techniques. Thermal conductivities are linked to the microstructure of L-PBF AlSi10Mg, which changes with processing conditions. The through-plane exceeded the in-plane thermal conductivity for all energy densities. A co-located thermal conductivity map by frequency domain thermoreflectance (FDTR) and crystallographic grain orientation map by electron backscattered diffraction (EBSD) was used to investigate the effect of microstructure on thermal conductivity.FindingsThe highest through-plane thermal conductivity (136 ± 2 W/m-K) was achieved at 59 J/mm3 and exceeded the values reported previously. The in-plane thermal conductivity peaked at 117 ± 2 W/m-K at 50 J/mm3. The trend of thermal conductivity reducing with energy density at similar porosity was primarily due to the reduced grain size producing more Al-Si interfaces that pose thermal resistance. At these interfaces, thermal energy must convert from electrons in the aluminum to phonons in the silicon. The co-located thermal conductivity and crystallographic grain orientation maps confirmed that larger colonies of columnar grains have higher thermal conductivity compared to smaller columnar grains.Practical implicationsThe thermal properties of AlSi10Mg are crucial to heat transfer applications including additively manufactured heatsinks, cold plates, vapor chambers, heat pipes, enclosures and heat exchangers. Additionally, thermal-based nondestructive testing methods require these properties for applications such as defect detection and simulation of L-PBF processes. Industrial standards for L-PBF processes and components can use the data for thermal applications.Originality/valueTo the best of the authors’ knowledge, this paper is the first to make coupled thermal conductivity maps that were matched to microstructure for L-PBF AlSi10Mg aluminum alloy. This was achieved by a unique in-house thermal conductivity mapping setup and relating the data to local SEM EBSD maps. This provides the first conclusive proof that larger grain sizes can achieve higher thermal conductivity for this processing method and material system. This study also shows that control of the solidification can result in higher thermal conductivity. It was also the first to find that the build substrate (with or without support) has a large effect on thermal conductivity.

Fabrication of Biobased Advanced Phase Change Material and Multifunctional Composites for Efficient Thermal Management

In this study, an advanced phase change material (PCM) was fabricated to combine the properties of a biobased thermoplastic polymer and the heat storage of PCM to overcome the limitations of the existing PCM composites. The novel PCM of erythritol (ET)-grafted polylactic acid (PLA) (ETPLA) was prepared by the in situ polymerization of ET and PLA. The thermally conductive ETPLA composites were fabricated by injection molding using a hybrid filler system of oxidized carbon fiber (CF-OH) and aluminum nitride (AlN), which showed a high through-plane thermal conductivity of 4.25 W/mK, a tensile strength of 16.4 MPa (1953% enhancement comparing pure ET), an elongation at break of 4.4% (189% enhancement comparing pure ET), and latent heat of 170.7 J/g. Thus, the ETPLA/CF-OH/AlN composites facilitate efficient thermal management to combine heat saving and heat dissipation through the large latent heat and high thermal conductivity. Thus, the fabricated PCM composites have potential applications in thermal management systems of next-generation electronic devices.

Improving the thermal conductivity of natural rubber by constructing three-dimensional thermal conductivity networks and chemically bonded filler-matrix interaction

It has become the mainstream way to take advantage of the new carbon materials to modify polymer matrix to prepare thermal interface materials (TIMs) with excellent comprehensive properties for the modern electronic packaging materials. Yet, how to make full use of the properties of new carbon materials is still facing the severe challenges. Herein, thiol-functionalized carbon nanotubes/natural rubber (CNTs-SH/NR) TIMs with three-dimensional networks (3D) and covalently bonded filler/matrix interactions were fabricated through the surface chemical treatment as well as ice-templated approach. The results proved that CNTs-SH/NR TIMs could achieve a high through-plane thermal conductivity of 1.22 W m −1 K −1 with CNTs-SH content was 25 wt%. Simultaneously, it showed sensitive heat response capacity. The improvement of filler/matrix interface and 3D networks were of great importance in abating the total thermal resistance. Moreover, the method provide a novel route to design high-performance thermal conductive TIMs and apply for the thermal management of electronics. • CNTs fillers with dual functions of thermal conductivity and enhancement are prepared by chemical etching and surface modification. • The covalent bonding between CNTs and NR is helpful to further improve the thermal conductivity of NR TIMs. • A thermal conductivity of 1.22 W m -1 K -1 is achieved for NR based TIMs.

A phase-change material with high through-plane thermal conductivity comprising a palmitic acid–cellulose nanofiber matrix with via acylation an expanded graphite@cellulose nanofiber@carbon nanotube hybrid filler

Although phase-change materials (PCMs) are promising candidates for thermal storage applications due to their high latent heat during phase transition, challenges such as the leakage problem during phase transition and low thermal conductivity must be overcome. We fabricated a palmitic acid (PA)–cellulose nanofiber (CNF) matrix via acylation and a hybrid expanded graphite (EG)@CNF@carbon nanotube (CNT) filler via grafting of CNFs onto the surface of the EG. The matrix and hybrid filler mixture were then hot-pressed to provide an efficient heat pathway. The fabricated composite with 7 wt% hybrid filler reached through-plane thermal conductivity of 1.98 W/mK and latent heat of 102.04 J/g. Especially, the fabricated composite showed 3.4 times higher thermal conductivity enhancement compared to raw PA-CNF. Furthermore, the composite is lightweight and flexible. Based on these findings, the manufactured composite possesses the potential as a PCM for thermal energy storage and thermal management applications.

Fabrication of wear-resistant PA6 composites with superior thermal conductivity and mechanical properties via constructing highly oriented hybrid network of SiC-packed BN platelets

Herein, a strong extensional and shearing field was introduced to construct highly oriented hybrid networks of silicon carbide (SiC)-packed boron nitride (BN) platelets to fabricate high-performance wear-resistant PA6 composites. Results show that in-plane and through-plane thermal conductivity (TC) of the prepared PA6 composites with a total filler loading of 20 wt.% reached 1.31 and 0.35 W/(m K), 352% and 25% higher than those of pure PA6, respectively. It is attributed to the highly oriented hybrid network that facilitates the formation of efficient thermal conductivity pathways. Temperature monitoring results during friction confirm that high TC favors the friction heat dissipation performance. Meanwhile, the yield strength of PA6 composites increased by 39.1% and they still have excellent ductility with an elongation at break of 207.1%. Finally, the wear rate of PA6 composites decreased sharply by 92.5%. This method can be used to manufacture advanced linear bearing and guideway parts, etc.

Leakage-Proof Flexible Phase Change Gels with Salient Thermal Conductivity for Efficient Thermal Management.

Phase change materials (PCMs) as one of the most potential latent heat storage techniques have been widely used for thermal management and energy storage. However, simultaneously imparting flexibility, high thermal conductivity, and considerable energy storage density to organic PCMs remains challenging. In this work, a coupling strategy combining substance exchange and magnetic orientation has been proposed to fabricate phase change gels (PCGs) with thermally induced flexibility and high through-plane thermal conductivity. In the PCGs, synthesized boron nitride/ferroferric oxide (BN@Fe3O4) particles and polyacrylic acid (PAA) precursor liquid are introduced to polyethylene glycol (PEG) aqueous solution, and a magnetic field is applied in the process of PAA network construction to promote ordered arrangement of BN@Fe3O4 along the direction of the magnetic field. Consequently, PEG is wrapped by the cross-linked PAA supporting network, forming PCGs with excellent shape stability and thermally induced flexibility. The vertical orientation structure of BN@Fe3O4 endows the PCGs with an enhanced through-plane thermal conductivity of up to 1.07 W m-1 K-1 at a BN@Fe3O4 loading of 25.6 wt % with an additional enhancement of 215% compared to the composite without BN. The thermally conductive leakage-proof PCGs present great application potential in heat storage and management.

Eco-friendly and scalable strategy to design electrically insulating boron nitride/polymer composites with high through-plane thermal conductivity

Hexagonal boron nitride (h-BN)/epoxy composites with high through-plane thermal conductivity were successfully fabricated using core-shell h-BN/epoxy (e-BN) microspheres which were synthesized using a simple one-pot emulsion polymerization process in an eco-friendly aqueous medium. e-BN microspheres covered with self-assembled h-BN flakes (1 μm lateral size) on the surface of the epoxy microspheres facilitated the effective alignment and distribution of the flakes in the epoxy matrix. The e-BN/BN/epoxy composites fabricated by mixing the e-BN microspheres with the h-BN flakes (17 μm lateral size) exhibited far higher through-plane thermal conductivity than the BN/epoxy composites (without e-BN microspheres) with the same h-BN flake content. In particular, the e-BN/BN/epoxy composite with 50 wt% (33 vol%) h-BN flakes exhibited excellent through-plane thermal conductivity of 4.27 W/mK, which was approximately 3.7 times that of the BN/epoxy composite (1.17 W/mK), owing to a more random or isotropic orientation of the h-BN flakes in the e-BN/BN/epoxy composite. The experimentally measured thermal conductivities were well matched to those obtained from micromechanical estimations using the modified Mori-Tanaka method. We expect that this eco-friendly and scalable fabrication process of e-BN microspheres and e-BN/BN/epoxy composites could provide an innovative strategy for manufacturing electrically insulating polymer composites with high through-plane thermal conductivity.

A fundamental study of improving thermal interface connection by using silane modified, in-situ formed silver-graphene fillers in epoxy polymers for future semiconductor device packaging

Over the past half-century, the increase of on-chip power and on-chip integration density has created new thermal management challenges for 2.5D/3D semiconductor packaging. High-performance thermal management materials in electronic encapsulation are very important to ensure the performance and reliability of the electronic devices. Graphene-based polymer composites have attracted much attention due to the ultrahigh thermal conductivity and large surface area of graphene. However, graphene nanosheets easily aggregate and lack functional groups on their surfaces, leading to phonon scattering within the interfaces. In this work, silver nanoparticles are in-situ formed on the graphene surface by a facile method, then the graphene-silver nanofillers are modified by (3-Mercaptopropyl)trimethoxysilane (MPTS). MPTS reacts with silver nanoparticles to connect them with epoxy. Also, silver nanoparticles on the surface of graphene can fuse together to form metallurgical joints that connect graphene nanosheets.With the fundamental understanding of sintering mechanisms and reducing two types of thermal interfacial resistances (filler-filler and filler-epoxy interface resistances) simultaneously, the resultant epoxy nanocomposites achieve a high through-plane thermal conductivity of 0.99 W/mK at 8 wt% loading. This corresponds to a 465.7% increase in thermal conductivity as compared to that of neat epoxy. Also, the nanocomposites present a low CTE and high thermal stability. They show strong cooling capability and heat dissipation as thermal interface materials (TIMs) through both experimentation and simulation, providing a promising new insight into thermal management materials to meet the demands of next generation high-power and high-density semiconductor packaging.

Crumpled graphene epoxy nanocomposites modified with polydopamine for advanced semiconductor packaging applications

Graphene-based epoxy nanocomposites are effective TIMs due to the unique properties of graphene – extraordinarily high thermal conductivity and large specific surface area. However, graphene easily aggregates due to strong van der Waals interactions and has poor interfacial connections due to a smooth surface. In this work, a facile method fabricates highly crumpled graphene nanosheets. The crumpled architecture prevents graphene nanosheets from restacking and maintaining the high specific surface area. Polydopamine (PDA) is used to promote uniform dispersion of graphene through π−π bonds, reducing the thermal interface resistance. Additionally, it enhances the thermal transport between as a TIM as proved by experimentation and modeling. The resultant 2.5 wt% filler loading epoxy nanocomposites present a high through-plane thermal conductivity of 1.02 W/mK. They also have a low CTE, low viscosity, low moisture absorption, high electric resistivity, and high adhesion strength. These results provide insights into the design of graphene-based epoxy nanocomposites to meet TIMs requirements in high density 3D electronic packaging.

Magnetic alignment of electrochemically exfoliated graphite in epoxy as a thermal interface material with high through-plane thermal conductivity

Magnetic alignment of electrochemically exfoliated graphite in epoxy as a thermal interface material with high through-plane thermal conductivity

Polydopamine-modified graphene with cellulose nanofibers to act as fillers in epoxy nanocomposites for application in the next generation of green electronic packaging materials

In this work, eco-friendly polydopamine (PDA) modifies graphene (PDA-G) through a π-π stacking interaction. Then, eco-friendly and biodegradable cellulose nanofiber (CNF) polymers are employed to combine with PDA-G to form a 3D thermal transport network. More significantly, their abundant functional groups, including hydroxyl groups and carboxyl groups, form interfacial hydrogen bonding with PDA-G to reduce the thermal interfacial resistance. With fundamental understanding of the interfacial engineering between CNF and PDA-G and with an effort to balance the effects of filler connection and thermal insulation of CNF, the resultant epoxy nanocomposites achieved a high through-plane thermal conductivity of 0.58 W/mK at only 3.05 wt% loading. In addition, the epoxy nanocomposites have a low CTE and high thermal stability. Meanwhile, the potential application of epoxy nanocomposites as thermal interface materials (TIMs) in semiconductor packaging has been demonstrated by both experimentations and simulation. These tests result in new pathways to design and modify fillers to meet the demands of next generation green polymer composites in 2.5D/3D semiconductor packaging.

Poly(dimethylsiloxane) grafting on palmitic acid and surface of expanded graphite for advanced phase change material composites

Phase change material (PCM) has attracted attention because of its heat-saving potential due to large latent heat, which can be applied in thermal energy storage and battery thermal management system. However, the intrinsic low mechanical and thermal properties of PCM are a hurdle in achieving a sufficient level for efficient thermal management. This study prepared the novel PCM of poly(dimethylsiloxane) (PDMS, (bis-hydroxyalkyl) terminated)-grafted palmitic acid (PA) and PDMS-grafted expanded graphite (EG) filler to fabricate novel, thermally conductive PCM composites. The proposed composites demonstrated a high through-plane thermal conductivity (2.06 W/mK), tensile stress improvement (230%), and latent heat (106.93 J/g). Therefore, the PA-PDMS/EG-PDMS composites can provide novel thermal management performance to combine high thermal conductivity and latent heat. Specifically, the fabricated PCM composites can contribute to developing PCM composites and the advanced electronic packaging fields.

Controlling anisotropic thermal properties of graphene aerogel by compressive strain

Materials with adjustable wide-ranging thermal conductivity are desired to tackle the problem of thermal management for electronic devices operating in an extended range of temperature. In this study, graphene aerogels (GAs) are fabricated and transformed from thermal insulators to thermal conductors by high-temperature annealing. The highest through-plane and in-plane thermal conductivity of annealed GA reaches 3.3 and 96 W/m·K, respectively, under 95% compressive strain. Using the annealed GA as thermal interface material leads to superior performance than commercially available products that have higher through-plane thermal conductivity in dissipating heat for high-power electronic devices (e.g., LED lamp). Furthermore, due to excellent elasticity, the thermal resistance of annealed GAs can be reversibly tuned about six-fold by compressive strain. This paves a novel venue in designing thermal management system for devices, which not only need excellent heat dissipation but also good thermal insulation at various operating environments.

Sepiolite Fiber Supports Tin Powder and Boron Nitride to Prepare Epoxy Composites with Insulation Properties and High Through-Plane Thermal Conductivity

Metal fillers are not suitable for direct mixing and casting with thermosetting resins to prepare thermally conductive and insulating materials due to their high density and electrical conductivity. Here, we obtain a filter cake by mixing sepiolite fiber, tin powder, and h-BN through vacuum filtration. Low melting point tin particles are melted and allowed to infiltrate to fill the void defects around them after the filter cake is heat-treated, and the added h-BN will coat the tin particles to prevent them from coming into contact with each other to conduct electricity but does not hinder heat conduction. The test results show that when the tin powder content is about 47.2 wt %, the thermal conductivity can reach 3.37 W/m·K and the volume resistance is still greater than 109 Ω·m. This method provides an idea for the preparation of high thermal conductivity metal-thermosetting resin composite materials.

Flexible and quasi-isotropically thermoconductive polyimide films by guided assembly of boron nitride nanoplate/boron nitride flakes for microelectronic application

• A hierarchical “brick and plank” structure is fabricated by dopamine modified h -BN nanomaterials. • This special structure can be used to improve the performance of polyimide. • The modified PI films have quasi-isotropic thermal conductivity and high thermal stability. • The modified PI films have good flexibility and excellent electrical insulation. • The modified PI films show faster shape memory response time reducing 50 %. Currently, the application of polyimide (PI) based materials often demands mutual additional properties, such as high thermal conductivity, good flexibility, high thermal stability and low dielectric constant and loss, etc. . Herein, a well-aligned hierarchical “brick and plank” architecture by rational assembly of dopamine modified hexagonal boron nitride flakes and nanoparticles (PDA-BNF@BNNPs) which can effectively improve the thermal conductivity, thermal stability, electrical conductivity, dielectric properties and shape memory performance of pure PI. The alternating stacking of vertically arranged h -BNNPs and horizontally laid h -BNFs yield a quasi-isotropic thermal conductivity of PI films with a high through-plane thermal conductivity of 6.43 W/(mK) and an in-plane thermal conductivity of 11.85 W/(mK) because of the simultaneously vertical and horizontal phonon scattering enabled by the vertically arranged h -BNNPs and horizontally laid h -BNFs. Besides, this special structure also endues PI films high thermal stability of over 560 °C, prominent electrical resistance of over 1.40 × 10 -13 Ω•cm, and low dielectric loss of less than 0.02 in the high frequency. Moreover, the PDA-BNF@BNNP/PI films exhibit excellent flexibility and shape memory performance with faster recovery response time reduced over 50 % comparing with that of pure PI film. These outstanding properties combining with the facile and scalable fabrication process make PDA-BNF@BNNP/PI films are very promising in diverse electronic device applications, especially in flexible electronic devices or circuits requiring additionally high thermal conductivity and low dielectric loss.

Modulation of covalent bonded boron nitride/graphene and three-dimensional networks to achieve highly thermal conductivity for polymer-based thermal interfacial materials

Thermal interface materials (TIMs) with excellent comprehensive performance which own high thermal conductivity, good electrical insulation and mechanical properties have triggered considerable interests in addressing the interfacial transfer issue for the state-of-the-art electronic devices. Herein, a new method was developed to covalently bonded crosslink boron nitride (BN) and reduced graphene oxide (rGO) by the chemical surface modification technology and chemical reaction between the erent functional groups. Meanwhile, the integrated three-dimensional (3D) networks of BN-rGO filler and natural rubber (NR) matrix were fabricated by the ice-templated method. After vulcanization, the boron nitride- reduced graphene oxide/ natural rubber (BN-rGO/NR) TIMs owned good comprehensive performance. As a result, the highest through-plane thermal conductivity could reach 1.04 W m−1 K−1 and also possessed sensitive response ability of heat flux. Importantly, the approach provided a valuable guidance to design TIMs with excellent comprehensive properties and owned promising applications in the thermal management of electronics.

Nacre-mimetic elastomer composites with synergistic alignments of boron nitride/graphene oxide towards high through-plane thermal conductivity

Thermal-conductive yet electrical-insulating polymer composites are in urgent demand in modern microelectronics for efficient heat dissipation. However, the reported through-plane thermal conductivity of polymer composites under low filler loadings (<10 vol%) is dissatisfactory, due to undesirable heat transfer pathways and high interfacial thermal resistance. Herein, 3D lamellar‑structured fluorinated boron nitride nanosheets (F-BNNS)/graphene oxide (GO) skeleton prepared by bidirectional freezing assembly ensures the directional motion of heat flow, in which GO bridges adjacent F-BNNS for reducing thermal resistance via hydrogen bond of H-F and van der Waals interaction. After vacuum-infiltrating polydimethylsiloxane (PDMS), the 9.5 vol% F-BNNS/GO/PDMS presents fascinating characteristics: a high through-plane thermal conductivity of 3.28 W·m−1·K−1 and an excellent tensile strength of 3.19 MPa, with the enhancements of 1829% and 118% respectively compared to pure PDMS; besides, superior dimensional stability and electrical insulation were obtained, with thermal expansion coefficient of 79 ppm/K and volume resistivity of 2.45 × 1012 Ω·cm.