High Thermal Contact Resistance Research Articles

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.

Remarkable reduction in thermal contact resistance between target and heat exchanger using TIMs in isotope neutron source accelerator

The high thermal contact resistance (TCR) between the target and the heat exchanger in the Isotope Neutron Source Accelerator will cause the high-energy charged particle beam to stay in the target, resulting in a remarkable increase of temperature which affects the production of stable isotopes. At present, the usage of thermal interface materials (TIMs) can fill the gap at the contact surface and thus reduces the TCR. In this paper, aiming at the actual working condition of neutron source, the steady-state TCR measurement experiment is designed under vacuum and high temperature environment. The TCR at the contact surface was reduced after adding graphite films, thermal greases, liquid metals and preloads. The improvement of TCR of the contact surface between palladium (Pd), copper (Cu) and graphite (Gr) were measured respectively. The results show that the TCR between palladium and graphite is reduced by 95 % by adding liquid metal (Gallium alloy). The TCR between copper and graphite was reduced by 91 % by brazing method. Compared with other TIMs, graphite film has the advantages of high thermal conductivity, high temperature resistance and no fluidity. Adding 0.08 mm thick graphite film between Pd/Gr and Cu/Gr contact surface can reduce the TCR by 50 % and 70 %, respectively. The improvement effect between the two contact surfaces was not obvious when 15.9–318.3 kPa preload was applied.

Phase change mediated graphene hydrogel-based thermal interface material with low thermal contact resistance for thermal management

Thermal interface materials (TIMs) are the key to solving heat dissipation problems in high-power electrical equipment. TIMs with high thermal conductivity and low thermal contact resistance (TCR) will enhance interfacial heat transfer. In this work, a phase-change mediated graphene composite hydrogel with low TCR and high thermal conductivity is designed. In addition, by introducing the hydrogel cross-linked network into the phase change material, the phase change material leakage problem is effectively solved. The thermal conductivity of the phase change hydrogel is enhanced by 324% from 0.3 Wm−1K−1 to 1.23 Wm−1K−1 at a filling rate of 7 wt% of graphene. The effects of temperature and pressure on phase change composite hydrogels are investigated. When the temperature is increased from 50 °C to 80 °C, TCR decreases rapidly from 90 K∙cm2/W to 0.2–0.5 K∙cm2/W, which is attributed to the improved interfacial wettability mediated by the phase change. When the pressure is increased from 10 Psi to 50 Psi with 80 °C, TCR decrease from 20 K∙cm2/W to 0.5 K∙cm2/W, improving interfacial contact and enhancing interfacial heat transfer. Combining a hydrogel with a cross-linked structure with the phase change material resulted in an excellent encapsulation of the phase change material. The thermal management performance of the phase change hydrogel is evaluated using infrared thermography and shows good thermal response behavior as the temperature rose to 68.7 °C after 120 s of heating. The strategy of combining phase change materials with hydrogels will provide new ideas for the design of TIMs.

Enhanced Thermal Transport across Self‐Interfacing van der Waals Contacts in Flexible Thermal Devices

AbstractMinimizing the thermal contact resistance (TCR) at the boundary between two bodies in contact is critical in diverse thermal transport devices. Conventional thermal contact methods have several limitations, such as high TCR, low interfacial adhesion, a requirement for high external pressure, and low optical transparency. Here, a self‐interfacing flexible thermal device (STD) that can form robust van der Waals mechanical contact and low‐resistant thermal contact to planar and non‐planar substrates without the need for external pressure or surface modification is presented. The device is based on a distinctive integration of a bioinspired adhesive architecture and a thermal transport layer formed from percolating silver nanowire (AgNW) networks. The proposed device exhibits a strong attachment (maximum 538.9 kPa) to target substrates while facilitating thermal transport across the contact interface with low TCR (0.012 m2 K kW−1) without the use of external pressure, thermal interfacial materials, or surface chemistries.

Graphene double cross-linked thermally conductive hydrogel with low thermal contact resistance, flexibility and self-healing performance

With the booming development of electronic devices usually used in a dynamic working environment, there is an urgent need for thermal interface materials with low thermal contact resistance, high thermal conductivity, excellent elasticity, and self-healing properties. A novel thermal interface material is obtained by incorporating graphene into a polyacrylate-based double cross-linked hydrogel. The introduction of graphene into the hydrogel can improve the thermal conductivity of the thermal interface material and enhance the tensile properties of the hydrogel. The composite thermally conductive hydrogel has self-healing properties, precisely meeting the thermal interface material's dynamic working environment. Besides, the effects of pressure and temperature on the thermal contact resistance are investigated. When the pressure increases from 10 Psi to 50 Psi at 35 °C, the thermal contact resistance is reduced to 0.069 K ∙ cm2/W. Under certain pressure, the effect of temperature on the thermal contact resistance is minor. Overall, the thermal contact resistance remains low (0.5–0.9 K ∙ cm2/W). The composite hydrogel is demonstrated excellent thermal management performance under the combined effect of high thermal conductivity and low thermal contact resistance by steady-state thermal analysis simulations and infrared thermography. Highly elastic, self-healing, low thermal resistance composites will present ideas for further construction of new thermal interface materials.

Numerical prediction of high temperature thermal contact resistance of HTA–C/ZrB2-SiC with radiation effects

High temperature thermal contact resistance is the research focus of many applications involving thermo-mechanical issues including spacecraft thermal protection, nuclear reactor cooling and heat treatment process. In this paper, a finite element contact model was developed with the rough surfaces, which were generated from the optically measured surface topography of HTA and C/ZrB2-SiC. The mechanical deformation was conducted account for the elastic-plastic mechanics, then the thermal analysis was completed in terms of the interface heat transfer condition with the solid spots conduction, far-field and near-field radiation. The results show that thermal contact resistance decreases from 1611 to 488 mm2K/W when the interface pressure increases from 0.1 to 0.6 MPa, as the solid spots conduction is sensitive to pressure. Also, thermal contact resistance decreases from 1611 to 340 mm2K/W when the interface temperature increases from 630 to 1100 K, due to the enhancement of heat transfer by radiation. And the thermal contact resistance account for solid conduction and radiation is reduced to 1/25 of that only considering solid conduction. Additionally, the accuracy of present method was effectively validated by comparing the numerical results with experimental data.

Thermal Properties Enhancement of Vertically Aligned Carbon Nanotubes-Based Metal Nanocomposites as Thermal Interface Materials

Increasing power densities in high-power electronic packages require advanced heat dissipation from their respective thermal interface materials (TIMs). Modern TIMs does not accommodate both factors of thermal performance and mechanical compliance with increasing device power density. Vertically aligned carbon nanotubes (VACNT) are advantageous in that their intrinsic properties promote both high thermal conductivity while maintaining a mechanically flexible/compliant interface. Therefore, it is a promises approach to use of carbon nanotubes (CNTs), specialty VACNTs, to make a novel interface heat transfer material. However, the high thermal contact resistance between VACNTs and substrate(s) has been a big issue to limit its application. In this study, the effect of post-processing techniques such as plasma treatment and surface metallization of VACNT layer (directly grown on Cu substrate) on interfacial properties of CNTs with mating substrate were explored and the thermal properties were evaluated via Laser Flash testing system. Thermal test results demonstrated that modifying the surface of the VACNT layer is effective method to improve interfacial attachment between CNTs and mating substrate. Results indicated that, among different VACNT surface modification methods, the plasma treated VACNT layer surface promote the best thermal properties of VACNT-based metal nanocomposite (MNC) as TIM. Compared to the unmodified VACNT layer, in this study, the interphase thermal resistance of the Cu/VACNT/matched substrate sample made from the plasma treated VACNT layer was reduced approximately 80%.

Experimental investigation of high temperature thermal contact resistance of thin disk samples using infrared camera in vacuum condition

High temperature thermal contact resistance between materials has significant influence on thermal design of many engineering applications. In this paper, an experimental setup was established to measure thermal contact resistance at high temperature based on steady state method. A data processing technique was developed to determine the thermal contact resistance. Moreover, the employment of thin disk samples was proved to be effective to ensure 1D axial heat flow by numerical prediction. The analyzed uncertainty of the test method is less than 10% with the validation of repeating experiments of HTA–HTA (high temperature Inconel 718 alloy). Additionally, thermal contact resistance of HTA–HTA, ZrB2/SiC/C–ZrB2/SiC/C (carbon fiber reinforced zirconium diboride and silicon carbide based composite) and HTA–ZrB2/SiC/C were investigated varied with the temperature ranging from 630 to 1100 K and the pressure ranging from 0.1 to 0.6 MPa. The results show that thermal contact resistance decreases with increasing the interface temperature as the enhancement of radiative heat transfer. At the same time, thermal contact resistance decreases with increasing the interface pressure due to the increase of contact area, and the effects of pressure on thermal contact resistance is much lower at high temperature.

Identification and characterization of the dominant thermal resistance in lithium-ion batteries using operando 3-omega sensors

Poor thermal transport within lithium-ion batteries fundamentally limits their performance, safety, and lifetime, in spite of external thermal management systems. All prior efforts to understand the origin of batteries' mysteriously high thermal resistance have been confined to ex situ measurements without understanding the impact of battery operation. Here, we develop a frequency-domain technique that employs sensors capable of measuring spatially resolved intrinsic thermal transport properties within a live battery while it is undergoing cycling. Our results reveal that the poor battery thermal transport is due to high thermal contact resistance between the separator and both electrode layers and worsens as a result of formation cycling, degrading total battery thermal transport by up to 70%. We develop a thermal model of these contact resistances to explain their origin. These contacts account for up to 65% of the total thermal resistance inside the battery, leading to far-reaching consequences for the thermal design of batteries. Our technique unlocks new thermal measurement capabilities for future battery research.

Printed fabric heater based on Ag nanowire/carbon nanotube composites

The increasing demand for smart fabrics has inspired extensive research in the field of nanomaterial-based wearable heaters. However, existing stretchable heaters employ polymer substrates, and hence require additional substrate-fabric bonding that can result in high thermal contact resistance. Moreover, currently used stretchable fabric heaters suffer from high sheet resistance and require complex fabrication processes. In addition, conventional fabrication methods do not allow for patternability, thus hindering the fabrication of wearable heaters with diverse designs. Herein, we propose an improved spray coating method well suited for the preparation of patternable heaters on commercial fabrics, combining the structural stability of carbon nanotubes with the high electrical conductivity of Ag nanowires to fabricate a stretchable fabric heater with excellent mechanical (stretchability ≈ 50%) and electrical (sheet resistance ≈ 22 Ω sq−1) properties. The fabricated wearable heater reaches typical operating temperatures of 35 °C–55 °C at a low driving voltage of 3–5 V with a proper surface power density of 26.6–72.2 (heater area: ) and maintains a stable heating temperature for more than 30 h. This heater shows a stable performance even when folded or rolled, thus being well suited for the practical wearable applications.

Measurement method and instrument of thermal contact resistance at high temperature

The high temperature thermal contact resistance (TCR) is one of the vital parameters for system thermal management since the interfacial contact heat transfer process under high temperature conditions is widely existed in the fields of aerospace, energy, thermonuclear reaction, etc. The characterization method and experimental investigation of the TCR at a high temperature (~1200°C) are not systematically established so far and the pertinent researches are scarce. This paper carries out a research on high temperature TCR measuring system design and presents a steady-state bi-directional loading heat flow method with symmetrical test columns. A measurement instrument is developed and its performance (e.g., measuring accuracy, uncertainty and influence factors) is tested under high temperature condition. Furthermore, the high temperature TCR and conductivity experiments are conducted through the instrument. The results show that the high temperature TCR can be precisely measured and the measurement uncertainty is within 10%, which verifies the feasibility and reliability of the homemade instrument and the presented measuring method at high temperature.

An improved interface temperature distribution in shallow hot mix asphalt patch repair using dynamic heating

ABSTRACT This study focuses on the issue of hot mix asphalt patch repairs, the performance of which is greatly reduced by repair edge disintegration. This is caused by low interface temperatures which result in poor repair bonding between fill material and host pavement. Twenty-four pothole repairs, 45 mm in depth, comprising 12 static and 12 dynamic repairs heated for 10 min 15 s and 21 min 49 s, respectively have been investigated. Dynamic heating has been completed using an experimental infrared heater. Temperatures were measured at 11 locations on the repair interfaces during the pouring and compaction of the fill mix. Volumetric of asphalt mixtures were also investigated. The results demonstrated that for static repairs, the lowest maximum temperatures were located at corners and on vertical repair boundaries. It was found that high thermal contact resistance in these interfaces dramatically affect the temperature levels. However, the figures improved in dynamically heated repairs. Comparing dynamically heated repairs of 10 min 15 s and 21 min 49 s with static repairs, showed average corner temperatures increase 10.85–24.45°C and 29.51–36.73°C, respectively, with accompanying increases in vertical interface temperatures 34.97°C and 46.41°C, respectively.

Effects of pressure on thermal contact resistance for rough mating surfaces

Thermal contact resistance has been studied experimentally to investigate the effect of pressure between two aluminium or two brass rough surfaces at three different heat flux levels. Three different rough surfaces are considered in the range of 2.63 to 40.69μm. It is demonstrated that the thermal contact resistance reduces significantly with pressure for both materials, the harder material gives higher thermal contact resistance as expected

Geometrical evaluation of T-shaped high conductive pathway with thermal contact resistance for cooling of heat-generating medium

The present work employs Constructal Design to numerically evaluate the geometrical configuration which facilitates the heat transfer through a T-shaped conductive pathway and heat-generating volumetric medium with low thermal conductivity. It is inserted a third material placed between the conductive pathway and the heat-generating medium which acts as thermal contact resistance. The objective function is to minimize the maximum excess of temperature over the entire system (materials with high and low thermal conductivity and thermal contact resistance), i.e., reduce the hot spots of a system with uniform heat generation. The total volume is fixed, however the volume of the high thermal conductivity material as well as the amount of the material that represents the thermal contact resistance can vary. Considering all possible geometries the configuration was optimized by varying the lengths and widths of the two branches forming the “T’’, keeping fixed the aspect ratio of the area of the conductive material with respect to the total area of the body. For the three times optimized geometry, the presence of thermal contact resistance changed the optimal length and width ratios in nearly 16% and 12% in comparison with optimal ratios achieved for the case with perfect thermal contact.

Contact resistances in spark plasma sintering: From in-situ and ex-situ determinations to an extended model for the scale up of the process

Heating in spark plasma sintering is a key point of this manufacturing process that requires advanced simulation to predict the thermal gradients present during the process and adjust them. Electric and thermal contact resistances have a prominent role in these gradients. Their determination is difficult as they vary with pressure and temperature. A calibration method is used to determine all of the contact resistances present within tools of different sizes. Ex situ measurements were also performed to validate the results of the in-situ calibrations. An extended predictive and scalable contacts model was developed and reveals the great importance and diversity of the contact resistances responsible for the general heating of the column and high thermal gradients between the parts. The ex/in situ comparison highlights a high lateral thermal contact resistance and the presence of a possible phenomenon of electric current facilitation across the lateral interface for the high temperatures.

Dog-bone copper specimens prepared by one-step spark plasma sintering

Copper dog-bone specimens are prepared by one-step spark plasma sintering (SPS). For the same SPS cycle, the influence of the nature of the die (graphite or WC–Co) on the microstructure, microhardness, and tensile strength is investigated. All samples exhibit a high Vickers microhardness and high ultimate tensile strength. A numerical electro-thermal model is developed, based on experimental data inputs such as simultaneous temperature and electrical measurements at several key locations in the SPS stack, to evaluate the temperature and current distributions for both dies. Microstructural characterizations show that samples prepared using the WC–Co die exhibit a larger grain size, pointing out that it reached a higher temperature during the SPS cycle. This is confirmed by numerical simulations demonstrating that with the WC–Co die, the experimental sample temperature at the beginning of the dwell is higher than the experimental control temperature measured at the outer surface of the die. This difference is mostly ascribed to a high vertical thermal contact resistance and a higher current density flowing through the WC–Co punch/die interface. Indeed, simulations show that current density is maximal just outside the copper sample when using the WC–Co die, whereas by contrast, with the graphite die, current density tends to flow through the copper sample. These results are guidelines for the direct, one-step, preparation of complex-shaped samples by SPS which avoids waste and minimizes machining.

Experimental investigation of high temperature thermal contact resistance between high thermal conductivity C/C material and Inconel 600

Abstract Thermal contact resistance at the assembly interface plays an important role in high temperature structure design and safety assessment. Thermal contact resistance between high thermal conductivity C/C material and superalloy Inconel 600 was experimentally investigated in the present paper. They are widely used in thermal protection structures of heat-pipe-cooled leading edges to enhance interface heat transfer. Results showed that thermal contact resistance between the two materials is about 5 × 10−5 m2 K/W, and it is necessary to take into account the effect of the thermal contact resistance in high thermal conductivity C/C material related thermal structure design.

접촉열전도재를 도포한 접촉열저항 특성연구

This paper describes the thermal contact resistance and its effect on the performance of thermal interface material. An ASTM D 5470 based apparatus is used to measure the thermal interface resistance. Bulk thermal conductivity of different interface material is measured and compared with manufacturers’ data. Also, the effect of grease void in the contact surface is investigated using the same apparatus. The flat type thermal interface tester is proposed and compared with conventional one to consider the effect of lateral heat flow. The results show that bulk thermal conductivity alone is not the basis to select the interface material because high bulk thermal conductivity interface material can have high thermal contact resistance, and that the center voiding affects the thermal interface resistance seriously. On the aspect of heat flow direction, thermal impedance of the lateral heat flow shows higher than that of the longitudinal heat flow by sixteen percent.

3D Compact Model of Packaged Thermoelectric Coolers

Hotspots on a microelectronic package can severely hurt the performance and long-term reliability of the chip. Thermoelectric coolers (TECs) can provide site-specific and on-demand cooling of hot spots in microprocessors. We develop a 3D compact model for fast and accurate modeling of a TEC device integrated inside an electronic package. A 1D compact model of a TEC is first built in SPICE and validated for steady-state and transient behavior against a finite-volume model. The 1D compact model of the TEC is then incorporated into a 3D compact model of a prototype electronic package. The results from the compact model for the packaged TEC are in good agreement with a finite-volume based model, which confirms the compact model's ability to accurately model the TEC's interaction with the package. Analysis of packaged TECs using this 3D compact model shows that (i) moving TECs closer to the chip results in faster response time and an increase in maximum cooling, (ii) high thermal contact resistance within the thermoelectric cooler significantly degrades performance of the device, and (iii) higher convective heat transfer coefficients (HTC) at the heat spreader surface increase steady-state cooling but decrease maximum transient cooling.

CMOS MEMS-based thermoelectric generator with an efficient heat dissipation path

This paper presents a CMOS MEMS-based thermoelectric energy generator (TEG) device with an efficient heat dissipation path. For present CMOS MEMS-based thermoelectric generator devices, the output performance is greatly limited by the high thermal-contact resistance in the system. For the device proposed in the work, the silicon substrate is etched into two comb-shaped blocks thermally isolated from each other, which form the hot and cold sides. Thin-film-based thermal legs are densely located between the two blocks along the winding split line. Low internal thermal-contact resistance is achieved with the symmetrical thermal structure. When the TEG device is embedded between the heat source and heat sink, the heat loss can be well controlled with flat thermal-contact pads of the device. For a full device with 900 n/p-polysilicon thermocouples, the measured open-circuit voltage reaches as high as 146 mV K−1, and the power factor reaches almost five times higher value compared to the previously reported results. A test system integrated with a single device presents an open-circuit voltage of 110 mV K−1 when forcibly cooled by a Peltier cooler, or 26 mV K−1 when cooled by ambient air.