Conductivity Of Thermal Interface Materials Research Articles

Reinforcement of microwave absorption and thermal conductivity of polydimethylsiloxane achieved by metal-organic framework-derived carbon nanotube/boron nitride flake heterogeneous structure

Due to the rapid advancement of electronic devices towards miniaturization, high-integration, multi-functionality, high-power, and high-frequency, it is necessary to design thermal interface materials (TIMs) that possess exceptional thermal conductivity as well as good capabilities for absorbing electromagnetic waves. In this report, carbon nanotubes (CNTs) containing cobalt (Co) nanoparticles have been in-situ grown on the surfaces of boron nitride flakes (BNFs) using the Co nanoparticles as catalysts which formed by the high-temperature pyrolysis and reduction of zeolite-imidazolate skeleton. Then, a multifunctional heterogeneous structure of Co@CNT/BNFs has been developed with tunable microwave absorption (MA) property and high thermal conductivity, which can be applied to enhance the MA performance and thermal conductivity of polymers simultaneously. The minimum reflection loss can reach −46.6 dB and a broad absorption bandwidth of 5.92 GHz can be obtained when adjusting the content of Co@CNT/BNFs in the absorbers. Furthermore, the thermal conductivity of the polydimethylsiloxane measured using the transient hot-wire apparatus is 0.72 W/(m·K) when the content of Co@CNT/BNFs is 30 wt%, exhibiting excellent heat dissipation performance in thermal management. This work is significant for investigating MA packaging and high thermally conductive TIMs for the electronic devices.

Soft and Damping Thermal Interface Materials with Honeycomb-Board-Mimetic Filler Network for Electronic Heat Dissipation.

High-power-density electronic devices under vibrations call for soft and damping thermal interface materials (TIMs) for efficient heat dissipation. However, integrating low hardness, high damping, and superior heat transfer capability into one TIM is highly challenging. Herein, soft, damping, and thermally conductive TIMs are designed and prepared by constructing a honeycomb-board-mimetic boron nitride nanosheet (BNNS) network in a dynamic polyimine via one-step horizontal centrifugal casting. The unique filler network makes the TIMs perform a high through-plane thermal conductivity (> 7.69W m-1 K-1) and a uniform heat transfer process. Meanwhile, the hierarchical dynamic bonding of the polyimine endows the TIMs with low compressive strength (2.16MPa at 20% strain) and excellent damping performance (tan δ > ≈0.3 at 10-2-102Hz). The resulting TIMs also exhibit electrical insulation and remarkable recycling ability. Compared with the commercial ones, the TIMs provide better heat dissipation (4.1°C) for a high-power 5G base station and less temperature fluctuation (1.8°C) for an automotive insulated gate bipolar transistor (IGBT) under vibrations. This rational design offers a viable approach to prepare soft and damping TIMs for effective heat dissipation of high-power-density electronic devices under vibrations.

Enhancing Thermal Conductivity of Thermal Interface Materials through Aligned Liquid Metal Pillars: A Promising Strategy

Enhancing Thermal Conductivity of Thermal Interface Materials through Aligned Liquid Metal Pillars: A Promising Strategy

Stable self-crosslinking phase change composites with vertically aligned boron nitride for high thermal conductivity thermal interface materials

Thermal interface materials (TIMs) must have a high through-plane thermal conductivity in order to efficiently transfer the heat generated by electronic components to heat sinks. Nevertheless, the achievement of high through-plane thermal conductivity is still a great challenge due to the inadequate thermal conductivity network as well as the lack of thermal response from the polymer matrix. Herein, we have developed a solid-solid phase change polymer matrix achieved through self-crosslinking polyethylene glycol (SCPEG). Subsequently, high-performance TIMs based on the SCPEG matrix and vertically aligned boron nitride (BN) nanosheets are obtained by bidirectional freezing, hot pressing, and longitudinal slicing. The prepared BN/SCPEG composites (BN content of 80 vol%) with a vertically oriented network achieved a through-plane thermal conductivity of 23.03 W m-1 K-1. More importantly, the vertically aligned BN nanosheets improve the thermal conductivity of composites, while the SCPEG matrix can reduce the hardness of composites by absorbing the heat, thus decreasing the contact thermal resistance.

Study of the Mechanism of Liquid‐Metal‐Assisted Thermal Interface Materials

With the increase in power consumption of integrated circuits, thermal interface materials (TIMs) attract significant attention. Liquid metal (LM) is an emerging high thermal conductive TIM, because of its excellent rheological properties which are helpful to fill micro gaps existing in a thermal interface. However, due to the apparent leakage hazard of pure LM, they are usually mixed with other materials for applications. In this work, the thermal resistance of silicone oil mixed with LM is about five times lower than that of it mixed with AlN powder of the same volume. This is a counterintuitive fact as the intrinsic thermal conductivity of LM is ≈20 Wm−1 K−1, which is more than ten times lower than AlN's thermal conductivity of 260–320 Wm−1 K−1. In this study, it is suggested that the reason can be attributed to deformed LM and their wetting process on the interface. Moreover, when introducing high load (83 vol%) LM or simultaneously introducing LM and AlN (sum‐load 83 vol%) in silicone oil, these composites achieve high thermal conductivity, low thermal resistance, and good compressibility. In practical application, the SO + LM + AlN composites also show much better heat‐dissipation ability than commercial thermal grease.

Nano-capsuled thermal interface materials filler using defective multilayered graphene-coated silver nanoparticles

To increase the thermal conductivity of thermal interface materials (TIM), the selection of thermally conductive filler is crucial. In this study, defective graphene-coated silver nanoparticles (Ag NPs) were selected as TIM fillers with low electrical resistivity. Poly-vinylpyrrolidone (PVP) coated Ag NPs were fabricated by polyol process to be used as a precursor, while a multi-layer graphene (MLG) coated layer about 3–4 nm in thickness was formed on the surface of Ag NPs which is 95 nm through a chemical vapor deposition (CVD) process. For application as a metal TIM filler for MLG-coated Ag NPs, the thermal properties of MLG-coated Ag NPs with varying ratios of PVP solution added to the PVP-coated Ag NPs during CVD, were evaluated. Moreover, the peak for crystalline carbon was confirmed through XRD analysis at 26.207°, while the d-spacing was measured to be 3.40 Å. Through Raman analysis, the presence of D peak (1350 cm−1), G peak (1590 cm−1), and 2D peak (2850 cm−1) proved the successful formation of defective MLG on the surface of Ag NPs. Finally, high thermal conductivity of 71 W/(m∙K) with electrical resistivity of 6.0 × 10−8 Ω∙m was obtained when adding 60 wt% PVP solution to PVP-coated Ag NPs during CVD, showing complete isolation among MLG-coated Ag NPs while PVP solution added less than 60 wt% did not prevent Ag NPs from coarsening, increasing its electrical resistivity. Therefore, nano-capsuled TIM fillers composed of defective MLG-coated Ag NPs with high thermal conductivities were obtained to demonstrate their potential for high-performance computing devices in thermal management.

Enhanced interface heat transfer based on gallium-based liquid metal infiltrated into vertically aligned copper nanowire arrays

Owing to the high aspect ratio and thermal conductivity, copper nanowires have great potential as novel thermal conductivity fillers. However, the thermal conductivity of thermal interface materials (TIMs) prepared by copper nanowires with polymer matrices is low. In contrast, gallium-based liquid metal has a higher thermal conductivity than polymer, while it is difficult to wet copper nanowires with liquid metal to prepare the TIMs. In this study, TIMs with a thickness of 53 µm were prepared by forming a galvanic cell between gallium-based liquid metal and vertically aligned copper nanowire arrays to improve wettability, and the heat transfer performance of the TIMs was experimentally investigated. The results show that the total thermal contact resistance of the composite thermal interface material is as low as 3.20 ± 0.24 mm2K/W. Compared with commercial thermal grease, the total thermal contact resistance is reduced by 86.30 %. The total thermal contact resistance increases with the surface roughness as the actual contact area decreases. In HCl/CuSO4 solution, the wettability of gallium-based liquid metal on the surface of vertically aligned copper nanowire arrays was improved, and the contact angle was 10.1 ± 0.9°. Furthermore, after 360 h of ageing, the total thermal contact resistance of the sample increased by 0.57 mm2K/W. This study provides new directions for designing high-performance TIMs with excellent overall heat transfer properties for the thermal management of electronic equipment.

Vitrimer-Assisted Construction of Boron Nitride Vertically Aligned Nacre-mimetic Composites for Highly Thermally Conductive Thermal Interface Materials

Modern electronic equipment with high integration and power consumption levels urges for more effective thermal interface materials (TIMs) to tackle its increasingly severe cooling issues. To effectively transfer the heat generated by electronic components to the radiator, the TIM is supposed to have a high through-plane thermal conductivity (λ⊥); however, achieving that proved devilishly challenging. Herein, inspired by the structure of the natural shell nacre and based on the construction of a cis-polybutadiene (BR) vitrimer network with reversible B–O bonds, the nacre-mimetic microstructure with vertically aligned hexagonal boron nitride (BN) was rationally designed and fabricated. Combining the hot-pressed orientation with the stacking-welding method, the vertically aligned BN/BR composite (VAC) was obtained by longitudinal slicing, and the designed microstructure with intense orientation was verified by scanning electron microscopy and small-angle X-ray scattering. As a result, the VAC reached an unprecedented λ⊥ of 14.1 W·m–1·K–1 as the BN content was 52 vol %, and the running chip temperature was greatly reduced compared with that of commercial TIM. Besides the superior thermal conductivity, the BN/BR composite has excellent electrical insulation and flame resistance. It is believed that the simple fabrication and extendibility of the biomimetic composites pave a new way for the design and preparation of high-performance TIMs.

Offset supper-cell model of polymer composites with oriented anisotropic fillers for thermal conductivity prediction considering shape factor

Thermal conductivity of polymer composites with oriented anisotropic fillers is commonly predicted based on the simplified cuboid unit-cell models. However, the models are too simple to reveal the real thermal conductivity of composites without absolutely aligned fillers. Here, a super-cell model with offset fillers based on a hexagonal prism primitive-cell after considering shape factor [Chem. Eng. J. 2022, 441, 136104.] is established to predict thermal conductivity as close to reality as possible for polymer composites with oriented fibrous, wirelike, and flake fillers. The impact of shape factor, fillers’ intrinsic thermal conductivity, size and loading, polymer's intrinsic thermal conductivity, and thermal interface resistance between polymer and fillers, on the anisotropic thermal conductivity of polymer composites are systematically evaluated by performing finite element numerical simulation. The model is applied to predict the anisotropic thermal conductivity of polymer based highly through-plane thermally conductive thermal interface materials, and highly in-plane thermally conductive thermal diffusion materials, which are in excellent agreement with the experimental ones. This work not only provides a practical means to predict the thermal conductivity of the oriented anisotropic fillers /polymer composites, but also has the guiding significance for designing thermal management materials.

Highly thermally conductive flexible insulated PI/BNNS@rGO nanocomposite paper with a three-dimensional network bridge structure

The sharp increases in power consumption and heating capacity caused by the emergence of intelligent electronic devices necessitate the development of highly thermally conductive thermal interface materials (TIMs) with good heat dissipation properties. Boron nitride nanosheets (BNNS) are ideal materials with high thermal conductivity. Hence, it should be possible to produce flexible high thermal conductivity nanocomposites with a three-dimensional network containing ultrathin, large, and uniformly thick BNNS. In this study, large-scale (1–1.5 µm) fewer-layered (2 nm) BNNS with a high yield of 80% were prepared through the separation of a NaOH–LiCl aqueous solution by a hydrothermal method and in ball milling. Highly thermally conductive insulating nanocomposite paper with a three-dimensional bridging structure of two-component nanosheets filled with nanofibers was fabricated by a simple electrospinning–electrospraying technique. The mechanical properties of the polyimide (PI)/BNNS@reduced graphene oxide nancomposite paper were improved by 168% as compared with those of the PI/BNNS composite. With an increase in the BNNS content, a layered microstructure similar to that of natural nacre was produced, which resulted in a large in-plane thermal conductivity of 16.92 W/m·K. The described method can facilitate the design of TIMs with good electrical insulation properties, thermal stability, and flexibility.

Novel TIM Evaluation Method With in Situ Electrical Monitoring

Thermal interface materials (TIMs) transfer heat between two surfaces in electronic assemblies. Specifically, a TIM 2 is a TIM used to transfer heat from a component’s lid to a heat sink. During use, TIM 2s experience thermal aging and mechanical stress (caused by board/component/heat sink expansion mismatches and warpage during heating/cooling). Understanding the response of TIMs to these stresses is critical for understanding TIM and product reliability. However, the responses of TIMs are complex and difficult to predict or model. TIMs are often polymeric materials heavily loaded with thermally conductive fillers and have time, temperature, and rate-dependent properties. Therefore, experimental studies are needed to address TIM reliability. However, monitoring TIM stability or performance while in situ is difficult. Electrical capacitance has been used to monitor the stability of dielectric TIM in situ, allowing for monitoring TIM stability and, indirectly, the TIM thermal performance, but electrically conductive TIMs cannot be used with capacitance measurements, so a new technique is needed. Monitoring a conductive TIM’s electrical resistance could give insight into a TIM’s stability, as both thermal and electrical resistances are affected by a TIM’s contact with surfaces, thickness, and area. This study examines four electrically conductive graphite pad TIMs on a test board, representing a large printed circuit board with a large shared heat sink, in an accelerated thermal cycle from 0 °C to 100 °C. The electrical resistance of the TIMs was monitored in situ, and after testing, postmortem failure analysis of the TIMs was done. The efficacy of electrical resistance monitoring for evaluating TIM stability was examined, and correlations with failure analysis results were made. Electrical resistance monitoring provided insight into the TIMs’ stability, failure time, and extent of failure.

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.

Dual-Aligned carbon nanofiber scaffolds as heat conduction path to enhance thermal conductivity of polymer composites

To improve the thermal conductivity of thermal interface materials (TIM), we constructed a dual-aligned scaffold, i.e., both aligned carbon nanofiber (CNFs) in the microscopic structures and directional microporous channels, serving as the heat conduction paths of TIMs. The dual-aligned scaffold was firstly fabricated by combining magnetic alignment and conventional freeze-casting, and the composites of the dual-aligned scaffold and silicone rubber (D-AS/SR) were then obtained by immersing the dual-aligned scaffold into the silicone rubber with vacuum assistance. Through this method, not only the high axial thermal conductivity of CNFs can be fully utilized, but also a long-range continuous and parallel structure can be fabricated as the heat conduction paths of TIMs. The results show that the thermal conductivity of the D-AS/SR composites reached 4.66 W/(m·K) at 7.73 vol% CNFs, which is 1.5 times higher than that of the composites constructed by conventional freezing casting and 25 times higher than that of pure silicone rubber. Additionally, the compressive strength of the D-AS/SR composites was greatly improved, whereas the electrical insulation of the composites was significantly reduced, which limited the use of D-AS/SR composites in conditions requiring good electrical insulation.

Through Plane Networked Graphene Oxide/Polyester Hybrid Thermal Interface Material for Heat Management Applications

ABSTRACT The role of electronic devices in our lives is increasing rapidly, with more research focusing on miniaturization, creating more demand for thermal interface materials (TIM). Grease-based TIM presently available have good thermal conductivity values, but issues such as contamination, pump-out, and an additional curing step are observed. Fibrous textile substrates are soft and flexible, making them suitable for occupying the asperities between the heat sink and heat-producing devices. However, they are insulating in nature and can be made conductive using conductive fillers such as graphene oxide (GO). In this article, a networked through-plane thermally conductive TIM using the cutting waste of polyester and GO was fabricated. The methodology involved functionalizing the PET substrate and studying its interaction with GO. A networked GO/PET, (N-GOPET) hybrid TIM was fabricated from waste PET with good through-plane heat conduction performance, softness, and cuttability as a promising replacement for grease-based TIM.

Printing Liquid Metal Elastomer Composites for High‐Performance Stretchable Thermoelectric Generators

AbstractContinuous powering of wearable electronics and personalized biomonitoring systems remains a great challenge. One promising solution is the use of thermoelectric generators (TEGs) that convert body heat to electricity. These energy harvesters must conform to curved surfaces and minimize thermal barriers to maintain efficiency while still exhibiting durability under large deformations. Here, highly efficient, stretchable thermoelectric generators made of inorganic semiconductors and printed multifunctional soft matter are introduced. Liquid metal elastomer composites with tailored microstructures are printed as highly conductive thermal interface materials and stretchable interconnects. Additionally, elastomer composites with hollow microspheres are formulated to print a deformable and lightweight thermal insulator within the device. These stretchable thermoelectric wearables show an excellent performance by generating an open‐circuit voltage of 392 mV and a power density of ≈650 µW cm−2 at ∆T = 60 °C and withstanding more than 15 000 stretching cycles at 30% strain. Furthermore, the additive manufacturing process is leveraged by direct writing of the TEGs on textiles to demonstrate their seamless integration and by 3D printing of stretchable heatsinks to maintain a large temperature gradient across the device and to study the effect of convective heat transfer on device performance.

Millefeuille-Inspired Thermal Interface Materials based on Double Self-Assembly Technique for Efficient Microelectronic Cooling and Electromagnetic Interference Shielding.

Owing to the increasing power density of miniaturized and high-frequency electronic devices, flexible thermal interface materials (TIMs) with the electromagnetic interference (EMI) shielding property are in urgent demand to maintain the system performance and reliability. Recently, carbon-based TIMs receive considerable attention due to the ultrahigh intrinsic thermal conductivity (TC). However, the large-scale production of such TIMs is restricted by some technical difficulties, such as production-induced defects of graphite sheets, poor microstructure architecture within the matrix, and nonnegligible interfacial thermal resistance result from the strong phono scattering. In this work, inspired by the structure and production process of millefeuille cakes, a unique double self-assembly strategy for fabricating ultrahigh thermal conductive TIMs with superior EMI shielding performance is demonstrated. The percolating and oriented multilayered microstructure enables the TIM to exhibit an ultrahigh in-plane TC of 233.67 W m-1 K-1 together with an outstanding EMI shielding effectiveness of 79.0dB (at 12.4GHz). In the TIM evaluation system, a nearly 45°C decrease is obtained by this TIM when compared to the commercial material. The obtained TIM achieves the desired balance between thermal conduction and EMI shielding performance, indicating broad prospects in the fields of military applications and next-generation thermal management systems.

Optimization of Effective Thermal Conductivity of Thermal Interface Materials Based on the Genetic Algorithm-Driven Random Thermal Network Model.

Polymer-based thermal interface materials (TIMs) are indispensable for reducing the thermal contact resistance of high-power electronic devices. Owing to the low thermal conductivity of polymers, adding multiscale dispersed particles with high thermal conductivity is a common approach to enhance the effective thermal conductivity. However, optimizing multiscale particle matching, including particle size distribution and volume fraction, for improving the effective thermal conductivity has not been achieved. In this study, three kinds of filler-loaded samples were prepared, and the effective thermal conductivity and average particle size of the samples were tested. The finite element model (FEM) and the random thermal network model (RTNM) were applied to predict the effective thermal conductivity of TIMs. Compared with the FEM, the RTNM achieves higher accuracy with an error less than 5% and higher computational efficiency in predicting the effective thermal conductivity of TIMs. Combining the abovementioned advantages, we designed a set of procedures for an RTNM driven by the genetic algorithm (GA). The procedure can find multiscale particle-matching ways to achieve the maximum effective thermal conductivity under a given filler load. The results show that the samples with 40 vol %, 50 vol %, and 60 vol % filler loading have similar particle size distribution and volume fractions when the effective thermal conductivity reaches the highest. It should be emphasized that the optimized effective thermal conductivity can be improved obviously with the increase in the volume fraction of the filler loading. The high efficiency and accuracy of the procedure show great potential for the future design of high-efficiency TIMs.

High through-plane thermal conductivity and light-weight of UHMWPE fibers/PDMS composites by a large-scale preparation method

The high through-plane thermal conductivity of thermal interface materials (TIMs) is a major challenge in the thermal management of electronic devices. In this work, we have developed a large-scale fabrication process for high through-plane thermal conductivity of ultrahigh molecular weight polyethylene (UHMWPE) fibers/PDMS unidirectional (UD) composites using aligned UHMWPE fibers as filler and PDMS as the matrix. Due to the high orientation (0.93) and high crystallinity (90%), the UHMWPE fibers provided an effective thermal conductive pathway along with the fiber's axis. The results showed the thermal conductivity of UHMWPE fibers/PDMS UD composites was up to 4.03 W/m·K, which is increasing by ca. 2140% compared with that of pure PDMS (0.22 W/m·K). Moreover, the composites have versatile properties such as low density (ca. 1.0 g/cm3), good compressibility, and excellent thermostability. It has great potential in industry-scale applications for TIMs.

Highly conductive thermal interface materials with vertically aligned graphite-nanoplatelet filler towards: High power density electronic device cooling

Thermal interface materials (TIMs) play a crucial role in enhancing the reliability and sustainable utilization of next-generation electronics and thus can help meet the increasing demand for multifunctional devices with higher performance. Herein, we introduce a method for creating a TIM with high cross-plane thermal conductivity based on graphite nanoplatelet (GNP)/polyurethane (PU) films. The graphite nanoplatelets ensured the heat transfer properties of the TIM. Moreover, the hot-pressing procedure improved the thermal conductivity to 26.3 W (m K)−1 with the improved orientation of the GNPs in the PU matrix, as confirmed by microscopy investigation. Under a thermal dissipation power of 10–20 W, a drastic reduction in the chip temperature (17.5–42.3 °C) was achieved using our oriented GNP/PU TIM compared to a commercial silicone TIM (5.0 W (m K)−1). In addition, as-prepared pads can be mass produced at an acceptable cost, indicating that our work provides a promising new approach to fabricating TIMs for application in the next-generation thermal management of high power density electronics.

Effect of Micro-Scale and Nano-Scale Boron Nitride on Thermal Property of Silicone Rubber Via Experimental and Simulation Method

With the development of electronic integration, excellent insulation and high thermal conductivity thermal interface materials (TIMs) are needed to be used. Most of currently reported TIMs have high thermal conductivity, but their processing is complex and not suitable for industrial application. In this work, a simple method is provided to prepare thermally conductive silicone rubber (SR) composites. Effects of size and ratios of micro-scale boron nitride (BN) and nano- scale BN on mechanical properties, thermal conductivity and thermal stability of SR/BN composites are investigated. Results show that when the ratio of micro-scale BN loading to nano-scale BN loading is equal and the loading of BN are 60 phr, the thermal conductivity of SR/BN composites reaches to 2.632 W/(m·K), which is 18 times higher than that of SR. Meanwhile, when the loading of micro-scale BN is twice than that of nano-scale BN, the SR/BN composites maintain good mechanical properties (the tensile strength reaches to 6.2 MPa). In addition, the SR/BN composites exhibit excellent thermal stability and the heat loss of all samples are nearly 45%. This can provide a new idea for a simple and effective preparation of the SR/BN composites with a high thermal conductivity and insulating.