Composite Thermal Interface Materials Research Articles

Synergistic effect of amino and hydroxyl bifunctional modified h-BN on interfacial thermal conductivity in polydimethylsiloxane matrix: Simulations and experiments

As a widely used thermal conductive matrix material, the interface problem between polydimethylsiloxane (PDMS) and thermal conductive fillers needs to be solved urgently. The interfacial heat transfer mechanism between PDMS and hexagonal boron nitride (h-BN) modified by different groups was studied by combining density functional theory (DFT) simulation and molecular dynamics (MD) simulation. The bi-functionalization of h-BN was achieved by the environmentally friendly 6-aminocaproic acid (ACA) additive-assisted water ball milling process. The h-BN/PDMS composite thermal interface materials were prepared using a simple rolling method. The thermal conductivity of the obtained sample reached 1.256 W m−1 K−1 at a filler loading of 15 wt%. The proposed bifunctional synergistic heat transfer mechanism is expected to provide theoretical guidance for the preparation of high thermal conductivity and insulating PDMS used in electronic communications.

Regulatable Orthotropic 3D Hybrid Continuous Carbon Networks for Efficient Bi-Directional Thermal Conduction

HighlightsA composite thermal interface material with three-dimensional hybrid carbon network-reinforced polydimethylsiloxane was proposed.The cooperative regulation of thermal conductivity and mechanical properties was achieved by controlling the assembly process of micro-nano scale unit carbon materials.The orthotropic continuous carbon structure endowed the composites with in-plane and out-of-plane thermal conductivities of up to 113.61 and 24.37 W m−1 K−1, respectively.The excellent compressibility and adhesion properties cooperatively improved the effective thermal conductivity by more than an order of magnitude.

Effect of submicron pore sized waste coffee emesis biochar on glass–epoxy composite thermal interface material

Effect of submicron pore sized waste coffee emesis biochar on glass–epoxy composite thermal interface material

Production of AlN/CNT reinforced PVA nanofibers as a thermal conductive net for thermal interface applications

The amount of heat generated by electronic components is increasing daily, in line with their growing power and performance. Consequently, there is a heightened demand for thermal interface materials for enhanced cooling of electronics. This study employs a novel approach to fabricate a nano composite thermal interface material on copper substrates to address this challenge. The thermal interface coatings, consisting of carbon nanotubes (CNT) and aluminum nitride (AlN)-reinforced polyvinyl alcohol (PVA) nanofibers with and without an epoxy resin matrix, are fabricated using the electrospinning technique. The findings demonstrate the successful fabrication of a 2.5 µm-thick CNT/AlN-PVA nanocomposite fiber mat coating with an average fiber diameter of 318 nm onto copper substrates. Scanning electron microscope (SEM) images revealed that the AlN particles and CNTs penetrated the fibers. The successful incorporation of AlN particles into PVA fibers was also verified by the Fourier-transform infrared spectroscopy (FT-IR) spectrum of CNT/AlN-PVA nanofibers. No major weight loss was observed in the thermogravimetric (TG) analysis curves up to 200 °C, indicating the thermal stability of coatings. The thermal diffusivity of the copper substrate coated with the CNT/AlN-PVA nanocomposite fiber mat was measured at 36.6 mm2/s. Moreover, the developed CNT/AlN-PVA nanocomposite fiber mat was also applied on top of the fire-retardant epoxy resin-coated copper substrate, which is conventionally used in electronic devices to provide electrical insulation. SEM images revealed that the existence of an epoxy layer on top of copper substrates did not alter the fiber formation during the electrospinning process, and an approximately 2.5 µm-thick CNT/AlN-PVA nanofiber mat was effectively embedded in the epoxy layer after a 1-hour electrospinning process. The thermal diffusivity of the resulting epoxy matrix CNT/AlN-PVA nanofiber reinforced nanocomposite coating is determined to be 7.792 mm2/s, which is 30-fold higher compared to the thermal diffusivity of neat epoxy resin coatings (0.254 mm2/s).

BN green gel thermal interface material with high thermal conductivity and low thermal contact resistance for efficiently thermal management

As an important component of electronic devices, thermal interface materials (TIMs) provide a fast heat dissipation channel, which will significantly improve the reliability and long-term stability of electronic devices. Gel TIMs with good flexibility is a development direction for thermal management in the future. However, the green and environmental issues in the preparation of gel TIMs with good stability are also important problems that must be considered. Here, combining the advantages of green deep eutectics solvents and high thermal conductivity boron nitride, a boron nitride polymerizable deep eutectics solvents gel composite TIMs with high thermal conductivity, good stability and low thermal contact resistance (TCR) has been developed. The thermal conductivity of composite TIMs achieved 1.18 W/m·K at a boron nitride loading of 20 wt%. Under pressure gradient testing (10 Psi-50 Psi), the TCR of composite TIMs decreased to 0.76 K·cm2/W. In the temperature gradient test (30 °C-70 °C), the TCR of the composite TIMs dropped to 0.143 K·cm2/W. Furthermore, in the TCR cycling test, the composites showed better cycling stability. In addition, composite TIMs also show better thermal performance in practical applications. This work provides a green way for the fabrication of gel TIMs with high thermal conductivity, good stability and low TCR.

Covalent-assisted construction of “scale-like” boron nitride/polyimide thermal interface materials with high thermal conductivity

Polyimide (PI) is a special engineering plastic with high strength, high modulus, high temperature resistance and corrosion resistance, but its poor thermal conductivity limits its application in high-power miniaturized electric and electronic equipment. In this study, surface-activated and modified boron nitride (m-BN) is polymerized in situ and coated to form a “scale-like” composite thermal interface material (m-BN/PI) with PI. Moreover, the m-BN@PI composite films obtained by a simple co-blending process of m-BN and PI are used as a comparison. The in-plane thermal conductivity of m-BN/PI composite reached 4.43 W m−1 K−1, when the filler content is 30 wt %, which is about 12 times higher than that of the pure PI film (0.37 W m−1 K−1). At this load, the in-plane thermal conductivity of m-BN@PI is only 3.94 W m−1 K−1. In addition, the covalent bonding between m-BN and PI molecular chains in m-BN/PI effectively reduces the interfacial thermal resistance by fitting the EMT and Foygel models. Finally, using the m-BN/PI composite film as a thermal interface material placed at the CPU location, its role in the heat dissipation process of electronic devices is demonstrated.

Investigation on Thermal Conductivity Silver-coated Copper/GaInSn Composite Thermal Interface Materials

To enhance the heat transfer performance of GaInSn liquid metal, a new type of composite thermal interface material with GaInSn as thermal conductive matrix and silver-coated copper particles as thermal conductive fillers was prepared in this article. The morphology of the composites were characterized by scanning electron microscopy. The thermal conductivity of silver-coated copper/GaInSn composites with different silver-coated copper particle contents were measured by laser flash method. The interfacial bonding of the composites were investigated by X-ray diffraction. The results show that when the volume ratio of silver-coated copper particles is 15%, thermal conductivity of the silver-coated copper/GaInSn composite reaches the largest value of 25.01 W·m−1·K−1. The silver-coated copper/GaInSn composite material and commercially available thermal grease were put into the chip and copper plate to simulate the actual application scenarios for comparison. The heat dissipation capacity of silver-coated copper/GaInSn composite material is obviously better than that of the two commercially available thermal grease, and the chip temperature can be reduced by about 5°C.

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.

Enhanced thermal properties of epoxy composites by constructing thermal conduction networks with low content of three-dimensional graphene

Micro/nano electronic devices heat dissipation depends heavily on the thermal interface materials (TIMs). Despite notable progress, it is hard to efficaciously enhance the thermal properties of the hybrid TIMs with high-load additives due to an absence of effective heat transfer routes. Herein, the low content of three-dimensional (3D) graphene with interconnected networks is adopted as the additive to improve the thermal properties of epoxy composite TIMs. The thermal diffusivity and thermal conductivity of the as-prepared hybrids were dramatically improved by constructing thermal conduction networks after adding 3D graphene as fillers. The 3D graphene/epoxy hybrid’s optimal thermal characteristics were observed at 1.5 wt% of 3D graphene content, corresponding to a maximum enhancement of 683%. Besides, heat transfer experiments were further performed to determine the superb heat dissipation potential of the 3D graphene/epoxy hybrids. Moreover, the 3D graphene/epoxy composite TIM was also applied to high-power LED to improve heat dissipation. It effectively reduced the maximum temperature from 79.8 °C to 74.3 °C. These results are beneficial for the better cooling performance of electronic devices and provide useful guidelines for advancing the next-generation TIMs.

Chloroform-Assisted Rapid Growth of Vertical Graphene Array and Its Application in Thermal Interface Materials.

With the continuous progress in electronic devices, thermal interface materials (TIMs) are urgently needed for the fabrication of integrated circuits with high reliability and performance. Graphene as a wonderful additive is often added into polymer to build composite TIMs. However, owing to the lack of a specific design of the graphene skeleton, thermal conductivity of graphene‐based composite TIMs is not significantly improved. Here a chloroform‐assisted method for rapid growth of vertical graphene (VG) arrays in electric field‐assisted plasma enhanced chemical vapor deposition (PECVD) system is reported. Under the optimum intensity and direction of electric field and by introducing the highly electronegative chlorine into the reactor, the record growth rate of 11.5 µm h−1 is achieved and VG with a height of 100 µm is successfully synthesized. The theoretical study for the first time reveals that the introduction of chlorine accelerates the decomposition of methanol and thus promotes the VG growth in PECVD. Finally, as an excellent filler framework in polymer matrix, VG arrays are used to construct a free‐standing composite TIM, which yields a high vertical thermal conductivity of 34.2 W m−1 K−1 at the graphene loading of 8.6 wt% and shows excellent cooling effect in interfacial thermal dissipation of light emitting diode.

Research progress of thermal transport in graphene-based thermal interfacial composite materials

With the rapid increase of the thermal power density of microelectronic devices and circuits, controlling its temperature has become an urgent need for the development and application of the electronic industry. By virtue of the ultrahigh thermal conductivity of graphene, developing high-performance graphene-based composite thermal interface materials has attracted much research attention and become one of hot research topics. The understanding of phonon transport mechanism in graphene-based composites at atomic scale can be helpful to enhance the heat conductive capability of composites systems. In this review, focused on graphene-based thermal interfaces materials, the heat conduction mechanism and the regulating strategy are introduced on both the internal thermal resistance and interfacial thermal resistance. Finally, the reseach progress and opportunities for future studies are also summarized.

Liquid cooling system for battery modules with boron nitride based thermal conductivity silicone grease.

Heat-conductive silicone grease (HCSG), one of the most common composite thermal interface materials (TIMs) used in many advanced applications, is limited by its low thermal conductivity (TC). Different surface modification agents are required to improve the dispersion of TC additives and the interfacial compatibility with the silicone matrix. In this study, MQ silicone resin (MQ) was used to modify two kinds of self-made spherical boron nitrides (SBNs), with different particle sizes, using the sedimentation method. The amount of filler content allowed within the SBNs increased owing to the similar polarity of the MQ and the silicone matrix, and a HCSG with a TC of 1.22 W (m−1 K−1) and a thermal resistance (TR) of 0.49 °C W−1 was obtained, respectively. In addition, the TC pathway was formed more easily with the 15 μm SBNs than with the 5 μm SBNs. In order to verify its potential application in battery thermal management, the HCSG was assembled on the surface of the liquid-cooling plate in the 18 650-battery module, and it was found that the maximum temperature of the battery module could be maintained below 42 °C, and the temperature difference could be controlled within 5 °C. Thus, with these excellent performances, the MQ silicone resin reported here, with respect to the assembly methods, will provide insights into the thermal management and energy storage fields.

금속 입자 기둥 고분자 복합소재 TIM의 열전도 특성

Special pariticle column and silicone composite thermal interface material were designed and proposed to assure reliability via CTE matching owing to the rise in the quantity of heat produced per unit area of electronic devices. Using nickel columns, a total of nine thermal interface materials (TIMs) were developed based on the mixing ratio and pattern of thermal TIMs. As a result, an experiment was carried out on thermal performance as a function of load variation. Thermal resistance reduced as load rose in all TIMs, heater power increased, and then thermal resistance was slightly raised or not altered after exhibiting the lowest value at 15W. The 10:7 mixing ratio of Silicon-Nickel produced the best thermal performance. The heat conduction performance of TP107 with a mixing ratio of 10:7 was 7 to 8% better than TP109 and 14 to 16 percent greater than TP105. Furthermore, as compared to pads with higher nickel hardness, pads with reduced nickel hardness enhanced heat transfer performance by 12-14 percent. It can be expected that there is an ideal mixing ratio for TIM via the metal pillar, and that by lowering metal hardness, contact thermal resistance between metal particles may be lowered.

Direct measurements of thermal transport in glass and ceramic microspheres embedded in an epoxy matrix

The time-domain thermoreflectance metrology is applied to evaluate the thermal conductivities of filler particles embedded in a composite matrix. Specifically, a system of glass and ceramic microspheres with a diameter of 100 to 150 μm embedded in an epoxy matrix was used as a representation of a typical composite thermal interface material (TIM) suitable for microelectronics applications. These measurements provide a direct characterization of the thermal properties of filler materials. The measured thermal conductivities of both borosilicate glass and yttria stabilized zirconia microspheres agree well with literature values for bulk materials, whereas the thermal conductivity of the alumina microspheres is nearly 50% lower than that of bulk crystals. The reduction in thermal conductivity of the alumina microspheres highlights how important this level of understanding is for TIM development and is attributed to enhanced phonon scattering due to structural heterogeneity, such as defects induced by phase mixing and microvoids. Combining sample preparation, structural characterization, and direct thermal measurements, our study reveals the structure–thermal property relationship for individual microspheres. The results of this work can facilitate the design and engineering of composite-based thermally conductive materials for thermal management applications.

Thermally conductive and stretchable thermal interface materials prepared via vertical orientation of flake graphite

With the increase of power density of electronic devices, there is a compromise between thermal conductivity and stretchability of thermal interface materials to reduce thermal contact resistance, enhance interfacial heat transfer, and relieve the warpage failure caused by stress concentration. Here, we report on the styrene-ethylene/butylene-styrene block copolymer (SEBS)/flake graphite composite thermal interface materials, fabricated via the vertical orientation of flake graphite. When the mass ratio of flake graphite to SEBS is 1:1, the thermal interface material exhibits a high out-of-plane thermal conductivity of 10.08 W/(m K) and maintains a considerable stretchability (elongation at break of 63%). The balance of thermal conductivity and stretchability keeps the thermal contact resistance of thermal interface material at a low value of 0.51×10-4 K ·m2/W. The thermal interface material consisted of SEBS/flake graphite builds a new way to address the challenge of thermal management in modern electronic products.

Thermal interface material with graphene enhanced sintered copper for high temperature power electronics

Sintered nano-copper is becoming a promising candidate as thermal interface material (TIM) for die attaching in high power electronics. It exhibits much higher thermal conductivity and operating temperature than conventional TIMs based on polymer and solder joints, and higher electromigration resistance and lower cost than sintered nano-silver TIM. However, the performance of existing sintered nano-copper is lower than expected because of high porosity resulted from poor sintering of copper particles with oxide shell. Here we demonstrate a method of improving the thermal conductivity of sintered copper by addition of graphene/Cu–Cu x O with controllable diameter of ∼163 nm. The measured thermal conductivity of the sintered composite TIM is enhanced by up to 123.5% compared with that of sintered pure copper. It can be understood as a result of the formation of graphene heat transfer network in sintered TIM. In addition, the C–O–Cu bonds formed at the interface between graphene and copper nanoparticles are critical for improving thermal performance as well as electrical and mechanical performance of the TIM. The developed TIM can be widely used in high power electronic packaging especially for high temperature applications, including IGBT, SiC and GaN power devices.

Simultaneous improvement of thermal conductivity and mechanical properties for mechanically mixed ABS/h‐BN composites by using small amounts of hyperbranched polymer additives

AbstractRecently, thermal interface materials (TIMs) are in great demands for modern electronics. For mechanically mixed polymer composite TIMs, the thermal conductivity and the mechanical properties are generally lower than expected values due to the sharply increased viscosity and poor filler dispersion. This work shows that addition of a small amount of polyester‐based hyperbranched polymer (HBP) avoided the trade‐off in mechanically mixed ABS/hexagonal boron nitride (h‐BN) composites. After adding 0.5 wt% HBP, the maximum h‐BN content in the composites increased from 50 to 60 wt%. The out‐of‐plane, in‐plane thermal conductivity, and tensile strength of ABS/h‐BN with 50 wt% h‐BN were 0.408, 0.517 W/mK, and 18 MPa, respectively, and were increased to 0.729, 0.847 W/mK, and 32 MPa by adding 0.5 wt% HBP, while 0.972, 1.12 W/mK, and 29.5 MPa were achieved for ABS/h‐BN/HBP with 60 wt% h‐BN. The morphological and rheological results proved that these enhancements are due to the improved h‐BN dispersion by decreasing viscosity of composites during mixing. Theoretical modeling based on the modified effective medium theory confirmed such results and showed that the interfacial thermal resistance also decreased slightly. Thus, this work demonstrates a facile and scalable method for simultaneously improving the thermal conductivity and mechanical properties of thermoplastic‐based TIMs.

Development of Nanostructured-based Composites as Advanced Thermal Interface Materials

Thermal management is one of the most critical issues in electronics due to increasing power densities. This problem is getting even worse for small and sophisticated devices due to air gaps present between the heat source and heat sink. Thermal interface materials (TIM) are used to reduce the air gaps and significantly increase the heat transfer capability of the system. A high-thermal-performance, cost-effective and reliable TIM would be needed to dissipate the generated heat, which could enable significant reductions in weight, volume and cost of the thermal management system. In this study a number of different nanostructured materials are reviewed for potential use as a filler material in our effort to develop advanced TIM composite. Some of the candidate filler materials considered is Carbon Nanotubes, Graphene and Few Layer Graphene (FLG), Boron Nitride Nanotubes (BNNT) and Boron Nitride Nanomesh (BNNM) and Boron Arsenide (BAs). Objective is to identify composition of boron arsenide as filler in polymer-nanostructured material composite TIM for high heat flux applications. In order to design boron-arsenide-based TIM composite with enhanced effective thermal conductivity, a number of metallic and nonmetallic base-filler material composites are considered with varying filler fractions. Empirical mixture models based on effective medium theories (EMT) are evaluated for estimating effective conductivity of the two-component boron arsenide-filler composite TIM structure.

Effect of Fiber Concentration on Mechanical and Thermal Properties of a Solder Matrix Fiber Composite Thermal Interface Material

Increased demand on the mechanical and thermal properties on the thermal interface and die attach material creates a demand for materials with tailored material properties. Solder matrix fiber composites (SMFCs) have been shown to address these challenges, but have, so far, required complicated procedures and components. In this paper, we present the fabrication of a new type of SMFC based on commercially available fiber networks infiltrated with Sn–Ag–Cu alloy (SAC305) or indium using equipment for large-volume production. The composite material exhibits similar thermal properties compared to pure solder, and mechanical properties that can be tailored toward specific applications. We also show that the handling properties of the SMFC allows it to be used in process flows where multiple reflow cycles are required and can achieve a well-defined bond line thickness (BLT) and good bonding using fluxless reflow under pressure.

Thermal contact resistance of various carbon nanomaterial-based epoxy composites developed for thermal interface applications

Thermal interface materials (TIMs) are a vital component of electronic packaging as they facilitate heat removal from microchips by improving thermal contacts between the mating surfaces of chip and heat-sink. Filler-based polymer composite TIMs are utilized either as adhesives or pastes in electronic packaging. Carbon nanomaterials such as carbon nanotubes, graphite nanoplatelets (GNPs), few layered-graphene nanosheets (FLG) and carbon nanofibers have been extensively studied as fillers for the development of thermal interface adhesives or pastes due their high thermal conductivity. This work compares the thermal contact resistance (TCR) of epoxy composites incorporating FLG, GNPs or multiwalled carbon nanotubes (MWCNTs) under comparable conditions. GNPs and FLGs were produced by treating graphite flakes and graphite powder, respectively, via the Hummers’ process followed by thermal reduction. Commercial MWCNTs and GNPs as well as in house-synthesized FLG and GNPs were dispersed into rubbery epoxy at 4 wt% (2.1 vol%) by a combined sonication and solvent mixing technique. The morphology of the fillers and resulting composites was studied by electron microscopy. The TCR of these composite TIMs, as adhesive coatings, was studied according to the ASTM D5470 method. The results showed that the TCR of MWCNT-epoxy composites increased with increase of MWCNT loading from 1 to 8 wt%. The TCR of 1 wt% MWCNT/rubbery epoxy composite was found to be 1.05 × 10−4 m2 K/W at a bond line thickness of 15 µm, which was significantly higher than the value for corresponding FLG and GNP-based composites. The lowest TCR of 1.9 × 10−5 m2 K/W at bond line thickness of 18 µm was obtained from the in-house GNP-based composite, half that of the corresponding FLG-based composite, and this was attributed to the less defective structure of the in-house GNP compared to FLG. Thus, epoxy composites developed with in-house synthesized GNPs offer higher heat dissipating capability than commercial GNP-, MWCNT- or FLG-based epoxy composites.