Conductivity Of Thermal Interface Materials Research Articles

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.

Comparison between CNT Thermal Interface Materials with Graphene Thermal Interface Material in Term of Thermal Conductivity

Thermal interface material (TIM) had been well conducted and developed by using several material as based material. A lot of combination and mixed material were used to increase thermal properties of TIM. Combination between materials for examples carbon nanotubes (CNT) and epoxy had had been used before but the significant of the studied are not exactly like predicted. In this studied, thermal interface material using graphene and CNT as main material were used to increase thermal conductivity and thermal contact resistance. These two types of TIM had been compare to each other in order to find wich material were able to increase the thermal conductivity better. The sample that contain 20 wt. %, 40 wt. % and 60 wt. % of graphene and CNT were used in this studied. The thermal conductivity of thermal interface material is both measured and it was found that TIM made of graphene had better thermal conductivity than CNT. The highest thermal conductivity is 23.2 W/ (mK) with 60 w. % graphene meanwhile at 60 w. % of CNT only produce 12.2 W/ (mK thermal conductivity).

Strategies for enhancing thermal conductivity of polymer-based thermal interface materials: a review

Thermal management has been considered as a key issue for high-power electronics. Thermal interface materials (TIMs) play an extremely important role in the field of thermal management. Owing to their excellent insulation, mechanical properties and low processing costs, functional polymers have become the popular candidate for preparing TIMs. In order to develop high thermally conductive TIMs, the inorganic fillers with high thermal conductivity are generally composited with polymers. For this purpose, some key technologies are needed to improve the dispersibility of fillers to reduce interfacial thermal resistance and increase thermal conduction channels. This paper reviews recent progresses on effective methods for improving thermal conductivity, which mainly include filler functionalization and processing, filler hybridization and coating, filler orientation and network. After implementing these strategies, the interfacial interaction between fillers and polymers, the synergy effect of different fillers and the thermal conduction pathway inside the matrix can be highly improved, hence enhancing the thermal conductivity of TIMs.

Ultrahigh Thermal Conductivity of Interface Materials by Good Wettability of Indium and Diamond

Ultrahigh Thermal Conductivity of Interface Materials by Good Wettability of Indium and Diamond

Enhanced thermal conductivity of polydimethylsiloxane composites with carbon fiber

Abstract Highly thermal conductive thermal interface materials are playing an irreplaceable role in modern highly integrated microelectronic devices. A facile method was used to fabricate a highly thermal conductive composite combined with highly thermal conductivity and excellent flexibility. The carbon fiber/polydimethylsiloxane (CF/PDMS) composites were prepared by solution blending with PDMS as matrix and different contents CF as thermal conductive fillers. Thermal conductivity of the PDMS composite is up to 2.73 W/mK with 20 wt% CF filler loading. Otherwise, we have characterized the heat transport performance of composites under various conditions. The results indicate that it has very stable and efficient thermal conductivity, which can meet the heat dissipation requirements under various conditions. Therefore, the CF/PDMS composite is a promising thermal management material that can be used to the heat dissipation of electronic devices in the near future.

Effects of selective distribution of alumina micro-particles on rheological, mechanical and thermal conductive properties of asphalt/SBS/alumina composites

Constructing thermal conductive pathways is an effective route to increase the thermal conductivity of thermal interface materials (TIMs). Asphalt/styrene-butadiene-styrene tri-block copolymer (SBS)/alumina composites with alumina micro-particles selectively distributed in SBS (denoted as asphalt/SBS/sd-Al2O3) were fabricated through pre-dispersion of alumina micro-particles in SBS, followed by compounding with asphalt. The effects of alumina distribution on the rheological, mechanical and thermal conductive properties of the asphalt-based composites were systematically studied. Compared with the composites with randomly distributed alumina, i.e., asphalt/SBS/rd-Al2O3, those with selectively and homogeneously distributed alumina micro-particles in SBS formed a continuous thermal conductive SBS/alumina network. Therefore, the asphalt/SBS/sd-Al2O3 composites displayed maximum thermal conductivity enhancement of ~35% at 30 vol% alumina. At 50 vol% alumina, the thermal conductivity of the asphalt/SBS/sd-Al2O3 composites reached ~0.99 W/mK, which is 400% higher than that of the asphalt/SBS blend (0.20 W/mK). Also, the asphalt/SBS/sd-Al2O3 composites possessed higher values of storage modulus, tensile strength and softening point. This work has provided a promising approach to fabricate high-performance and low-cost TIMs.

Fundamental and innovative approaches for filler design of thermal interface materials based on epoxy resin for high power density electronics application: a retrospective

The journey in the packaging of microelectronics with intense heat transfer rate and miniaturization are continuing. To satisfy the above criteria, the thermal interface materials (TIMs) classified into two categories. One should have high thermal conductivity, high dielectric constant or low electrical conductivity, and high mechanical strength inclusive of processability. Other is high thermal conductivity along with electrical conductivity properties. In this review, we have reported the idea and concept behind TIMs including varieties of TIMs and their significance. We also referred to a few progressive techniques of thermally conductive filler synthesis and preparation of epoxy-based thermal conductive TIMs. Some basic thermal conductivity models have been adopted to conceptualize the thermal conductivity mechanism along with various types of thermal conductivity measurement principle. We also explore how the morphological characteristics of different filler system affect the thermal conductivity of the epoxy matrix. In addition to thermal performance and efficiency, the reliability testing of TIM during package development stage is analyzed in which the design iteration has been considered for long-term packages and feasibility study. The specified utility of TIMs in different electronics application has been described according to properties of fabricated composite with the high-performance interface. The future perspectives of electronics packaging in advanced and miniaturized application for epoxy-based TIMs are briefly elaborated.

Flexible thermal interfacial materials with covalent bond connections for improving high thermal conductivity

Owing to the rapid development of modern electronic devices, high through-plane thermal conductive thermal interface materials (TIMs) with satisfied electrical insulation property have become increasingly important in affecting the lifetime and reliability of electronics. Meanwhile, how to maximize the performance comprehensively over all aspects undoubtedly inspired the research interests. Here, BN/CNTs/NR composites were synthesized by the vacuum-assisted method and the highest thermal conductivity could reach 1.34 W m−1 K−1. The covalently bonded connections of BN/CNTs hybrids had a significant contribution for the thermal conductivity by reducing the filler/filler interfacial thermal resistance and phonon scatterings. In addition, the sensitive response ability of thermal and satisfactory electrical insulation further demonstrated its strong potential practicality in TIMs. More importantly, this approach opened up a novel way to design TIMs and showed promising applications in the modern electronic devices.

Oxide-Mediated Formation of Chemically Stable Tungsten-Liquid Metal Mixtures for Enhanced Thermal Interfaces.

Modern microelectronics and emerging technologies such as wearable devices and soft robotics require conformable and thermally conductive thermal interface materials to improve their performance and longevity. Gallium-based liquid metals (LMs) are promising candidates for these applications yet are limited by their moderate thermal conductivity, difficulty in surface-spreading, and pump-out issues. Incorporation of metallic particles into the LM can address these problems, but observed alloying processes shift the LM melting point and lead to undesirable formation of additional surface roughness. Here, these problems are addressed by introducing a mixture of tungsten microparticles dispersed within a LM matrix (LM-W) that exhibits two- to threefold enhanced thermal conductivity (62 ± 2.28 W m-1 K-1 for gallium and 57 ± 2.08 W m-1 K-1 for EGaInSn at a 40% filler volume mixing ratio) and liquid-to-paste transition for better surface application. It is shown that the formation of a nanometer-scale LM oxide in oxygen-rich environments allows highly nonwetting tungsten particles to mix into LMs. Using in situ imaging and particle dipping experimentation within a focused ion beam and scanning electron microscopy system, the oxide-assisted mechanism behind this wetting process is revealed. Furthermore, since tungsten does not undergo room-temperature alloying with gallium, it is shown that LM-W remains a chemically stable mixture.

Synergistic enhancement of heat transfer between irregular shaped particles and boron nitride flakes at low loading

Thermal interface materials are the important development direction for solving heat transfer in microelectronics industry. Moreover, synergic effect is an important means to improve thermal conductivity of thermal interface materials. In this work, synergistic enhancement of heat transfer between irregular shaped particles and boron nitride flakes at low loading (5 wt%–30 wt%) are investigated, which includes irregular shaped MgO, Ag, Cu and CuO. The results show that the thermal conductivity of composites increase by filling with a small amount of boron nitride (1 wt% or 2 wt%). Furthermore, when the composite filled with 3 wt% Ag and 2 wt% BN, the thermal conductivity increased by 40%. In addition, besides the intrinsic thermal conductivity of additives, the geometrical characteristics of fillers and the thermal contact resistance between fillers and matrix are also key factors affecting the thermal transport properties of composites.

Through-plane assembly of carbon fibers into 3D skeleton achieving enhanced thermal conductivity of a thermal interface material

Thermal management has become one of the most important issues for electronic devices due to the continual increase in power density and consumption. Thermal interface materials (TIMs), applied between heat sources and heat sinks, are essential ingredients of thermal management. Carbon fibers are promising fillers because of its numerous advantages including high thermal conductivity, high strength-to-weight ratio, desired fatigue resistance, and corrosion resistance. However, they are rarely considered in preparing TIMs at present, because the one-dimensional structure of carbon fibers largely enhance the viscosity of the composites using conventional methods, and thus increase the complexity of processing. Herein, we report a thermally conductive TIM based on the construction of three dimensional and vertically aligned carbon fibers (3D-CFs) skeleton. The 3D-CFs skeleton is fabricated by vertical freezing the solution of CFs followed by freeze-dying to remove the ice and then infiltrating them with epoxy resin matrix. At a relatively low CFs loading of 13.0 vol%, the composites show an enhanced through-plane thermal conductivity (2.84 W m−1 K−1) compared to that of a neat epoxy resin (0.19 W m−1 K−1). Theoretical models qualitatively demonstrate that the interfacial thermal resistance is mainly originated from CFs–CFs interface not CFs–epoxy interface in oriented CFs/epoxy composites. In addition, the composites also possess a low thermal expansion coefficient (CTE) of 23.63 ppm K−1, and an increased glass transition temperature of 222.8 °C at a relatively small CFs loading (13.0 vol%) compared to that of pure epoxy resin. Our fabrication of through-plane assembly of carbon fibers skeleton has broad application prospects in TIMs.

Improvement in the heat dissipation of matrix LED headlamps for vehicles according to the thickness and thermal conductivity of thermal interface materials

This study examined the effects of thermal interface materials (TIMs) in light-emitting diode (LED) headlamps for vehicles based on thermally conductive plastics. Heat transfer is a very important issue in LED applications because the stability and performance of LEDs decrease considerably with increasing junction temperature. When two solid surfaces are placed in contact, a TIM is used to reduce the thermal interface resistance. This study examined the effects of the thickness (0.3, 0.5, and 1.0 mm) and thermal conductivity (1.8, 3.0, 5.0, and 11.0 W m−1 K−1) of a TIM on the soldering temperature (TS). TS increased with increasing TIM thickness. In addition, TS decreased with increasing thermal conductivity of the TIM. The junction temperature (TJ) was lower than the others when a TIM with a high thermal conductivity of 11 W m−1 K−1 was used. Overall, the TJ and TS can be reduced using a suitable high thermal conductivity TIM with an appropriate thickness.

Thermal Conductivity of Thermal Interface Materials Evaluated By a Transient Plane Source Method

The thermal conductivity of thermal interface materials (TIMs) has been studied using a transient plane source (TPS) method. In thermoelectric generators designed for vehicle waste heat recovery, high thermal conductivity materials are needed for the cold-side interface between a polyamide flexible circuit and an aluminum plate heat exchanger. The conventional heat flow method described by ASTM D5470 is often used to determine thermal contact resistance of an interface with a thin layer of interface material. The apparent thermal conductivity values provided by materials manufacturers are used to calculate heat transfer through the interface. However, estimated parameters based on the thermal conductivity of a TIM often do not agree with the actual heat transfer through the interface. Thermal conductivity of a series of 10 commercial TIMs were evaluated by applying a small quantity to an embedded TPS sensor. The 2-mm radius sensor was able to operate under standard bulk material measurement mode and produced consistent thermal conductivity measurements of the interface materials. The TPS method is shown to be effective in ranking the available interface materials by thermal conductivity and to ensure that the material with consistent performance can be selected for the thermoelectric generator applications.

Fabrication of aligned carbon-fiber/polymer TIMs using electrostatic flocking method

Directional assembly of anisotropic appearance filler in the composite is an effective way to obtain higher thermal conductivity thermal interface materials (TIMs). In this study, vertically aligned carbon fiber (VACF) scaffold reinforced polymer TIMs were fabricated using electrostatic flocking method, in which the aligned carbon fibers formed efficient heat conduction paths through the polymer matrix. By using high thermal conductivity mesophase pitch-based carbon fibers (mPCF) as filler, the maximum through plane thermal conductivity of the TIM with 13.4 wt% mPCF could reach up to 15.3 W/(m K), 60.2 times higher than that of the matrix, and the TIM also performed excellent flexibility. The influence of electrostatic flocking parameters on flocking effect was investigated. It is found that the electric field strength and the conductivity of fibers were the major factors to affect the vertical ratio of the mPCFs, and proper panels distance and fiber length were needed to acquire better flocking effect. In addition, the charging regular and the motion mechanism of fibers in electrostatic field were also discussed.

Thermal Properties of the Graphene Composites: Application of Thermal Interface Materials

Epoxy mixed with others filler for thermal interface material (TIM) had been well conducted and developed. There are problem occurs when previous material were used as matrix material likes epoxy that has non-uniform thickness of thermal interface material produce, time taken for solidification and others. Thermal pad or thermal interface material using graphene as main material to overcome the existing problem and at the same time to increase thermal conductivity and thermal contact resistance. Three types of composite graphene were used for thermal interface material in this research. The sample that contain 10 wt. %, 20 wt. % and 30 wt. % of graphene was used with different contain of graphene oxide (GO). The thermal conductivity of thermal interface material is both measured and it was found that the increase of amount of graphene used will increase the thermal conductivity of thermal interface material. The highest thermal conductivity is 12.8 W/ (mK) with 30 w. % graphene. The comparison between the present thermal interface material and other thermal interface material show that this present graphene-epoxy is an excellent thermal interface material in increasing thermal conductivity.

Ball-milled dispersed network of graphene platelets as thermal interface materials for high-efficiency heat dissipation of electronic devices

Thermal interface material (TIM) is a key component to dissipate the accumulated heat in the majority of power electronic systems. In this work, a facile and solid-state ball-milling method is adopted for the solvent-free reduction of exfoliated graphite nanoplatelets (EGNs) into high-quality ball-milled exfoliated graphite nanoplatelet (BMEGN) fillers. In addition, BMEGN fillers are embedded and uniformly dispersed with polydimethylsiloxane (PDMS) matrix to make a highly stretchable BMEGN-embedded PDMS-TIMs (BMEGN/PDMS) with strongly enhanced thermal conductivity. Furthermore, material characterizations were thoroughly investigated using scanning electron microscopy, transmission electron microscope, Raman spectroscopy, thermogravimetric analysis, and x-ray diffraction. Improvements in the thermal conductivity of TIMs by adding BMEGN were compared, the thermal conductivity was observed for BMEGN fillers with 0- to 48-h ball-milling time, and an enhanced in-plane thermal conductivity of 15.04 to 16.91 W/mK and through-plane thermal conductivity of 1.03 to 1.19 W/mK can be experimentally measured. A strong anisotropy was observed in the range of 14.60 (BMEGN12h/PDMS) to 14.21 (BMEGN48h/PDMS). The results reveal that the ball-milled graphene filler network with branched morphology can effectively provide the synergetic effect of a thermally conductive pathway via diffusion of phonon vibration in flexible composites. The combination of thermal conductivity and thermal stability may facilitate the applications in thermal management.

Thermal conductivity of Ni-coated MWCNT reinforced 70Sn-30Bi alloy

Abstract The high thermal conductivity of thermal interface material (TIM) is essential since the heat dissipation of electronic chips in an integrated circuit is solely achieved through TIM, which forms the bottleneck of the heat conduction. In the current study, the efficiency of utilizing multi-walled carbon nanotubes (MWCNTs) to increase the thermal conductivity of a typical TIM 70Sn-30Bi alloy has been investigated. Encapsulation of carbon nanotubes (CNTs) with nickel by electroless deposition was used to prevent aggregation of CNTs and to enhance the interfacial bonding between CNTs and the metal matrix. The nickel encapsulation also allows avoiding the separation of CNTs from the molten metal due to the buoyancy effect. The dispersion of Ni-encapsulated CNTs was assisted by sonication. The thermal conductivity of 3 wt % Ni/MWCNTs reinforced 70Sn-30Bi alloy was found to be more than 170% greater than that of the base alloy.

Technique for direct measurement of thermal conductivity of elastomers and a detailed uncertainty analysis

High thermal conductivity thermal interface materials (TIMs) are needed to extend the life and performance of electronic circuits. A stepped bar apparatus system has been shown to work well for thermal resistance measurements with rigid materials, but most TIMs are elastic. This work studies the uncertainty of using a stepped bar apparatus to measure the thermal resistance and a tensile/compression testing machine to estimate the compressed thickness of polydimethylsiloxane for a measurement on the thermal conductivity, keff. An a priori, zeroth order analysis is used to estimate the random uncertainty from the instrumentation; a first order analysis is used to estimate the statistical variation in samples; and an a posteriori, Nth order analysis is used to provide an overall uncertainty on keff for this measurement method. Bias uncertainty in the thermocouples is found to be the largest single source of uncertainty. The a posteriori uncertainty of the proposed method is 6.5% relative uncertainty (68% confidence), but could be reduced through calibration and correlated biases in the temperature measurements.

Preparation of tourmaline/graphene oxide and its application in thermal interface materials

Tourmaline/graphene oxide (TGOx, x = 5, 10, 15, and 20) compound with high thermal conductivity and high far infrared emissivity was prepared by a refluxing method. Transmission electron microscopy results confirmed that graphene oxide with a few layers was fabricated, and tourmaline nanoparticles were supported by graphene oxide layers. Thermal interface materials were prepared by adding tourmaline/graphene oxidex compound into epoxy resin. Far infrared emissivity of TGOx and thermal conductivity of thermal interface materials were increased with the weight ratio of graphene oxide in compound, but the corresponding electrical conductivity was slightly decreased. In particular, the tourmaline/graphene oxide15 (tourmaline/graphene oxide ratio of 85:15) showed an enhancement of 4% in far infrared emission than that of tourmaline. The thermal conductivity of thermal interface materials with 5 wt% tourmaline/graphene oxide15 was improved by 380% compared with that of pure epoxy resin, and the electrical conductivity of tourmaline/graphene oxide/epoxy was decreased slightly compared to that of graphene oxide/epoxy.