Showing papers on "Thermal contact conductance published in 2000"
TL;DR: The observation of a quantized limiting value for the thermal conductance, Gth, in suspended insulating nanostructures at very low temperatures is reported, consistent with predictions for phonon transport in a ballistic, one-dimensional channel.
Abstract: The physics of mesoscopic electronic systems has been explored for more than 15 years. Mesoscopic phenomena in transport processes occur when the wavelength or the coherence length of the carriers becomes comparable to, or larger than, the sample dimensions. One striking result in this domain is the quantization of electrical conduction, observed in a quasi-one-dimensional constriction formed between reservoirs of two-dimensional electron gas. The conductance of this system is determined by the number of participating quantum states or 'channels' within the constriction; in the ideal case, each spin-degenerate channel contributes a quantized unit of 2e^2/h to the electrical conductance. It has been speculated that similar behaviour should be observable for thermal transport in mesoscopic phonon systems. But experiments attempted in this regime have so far yielded inconclusive results. Here we report the observation of a quantized limiting value for the thermal conductance, G_(th), in suspended insulating nanostructures at very low temperatures. The behaviour we observe is consistent with predictions for phonon transport in a ballistic, one-dimensional channel: at low temperatures, G_(th) approaches a maximum value of g_0 = π^2k^2BT/3h, the universal quantum of thermal conductance.
810 citations
TL;DR: In this article, a correlation for fin-and-tube heat exchanger having plain fin geometry is proposed, which can describe 88.6% of the database within ±15%.
417 citations
TL;DR: In this paper, the impact and solidification of molten tin droplets on a stainless steel surface was studied and a simple energy conservation model was used to predict the maximum spread of droplets during impact.
390 citations
TL;DR: The thermal conductivity of boron nitride and aluminum nitride particle epoxy-matrix composites was increased by surface treatment of the particles prior to composite fabrication as discussed by the authors.
Abstract: The thermal conductivity of boron nitride and aluminum nitride particle epoxy-matrix composites was increased by up to 97% by surface treatment of the particles prior to composite fabrication. The increase in thermal conductivity is due to decrease in the filler-matrix thermal contact resistance through the improvement of the interface between matrix and particles. Effective treatments for BN involved acetone, acids (nitric and sulfuric) and silane. The most effective treatment involved silane such that the coating resulted from the treatment amounted to 2.4% of the weight of the treated BN. The effectiveness of a treatment was higher for a larger BN volume fraction. At 57 vol.% BN, the thermal conductivity reached 10.3 W/ m·K. The treatments had little effect on the specific surface area of the BN particles. Silane treatments were also effective for AlN. At 60 vol.% AlN, the thermal conductivity reached 11.0 W/m·K.
256 citations
TL;DR: In this article, the authors measured the thermal conductivity in a bulk crystal of highly enriched (99.8588%) 28 Si for temperatures between 2 and 310 K. This is six times larger than in natural silicon and even exceeds the maximum in diamond with natural isotope abundance.
210 citations
164 citations
TL;DR: In this article, the authors used the transient heating of a plane double spiral sandwiched between two pieces of the investigated material to derive both the thermal conductivity and the thermal diffusivity from one single transient recording provided the total time of the measurement is chosen within a correct time window defined by the theory and the experimental situation.
Abstract: The objective of this work is to improve measurements of transport properties using the hot disk thermal constants analyzer. The principle of this method is based on the transient heating of a plane double spiral sandwiched between two pieces of the investigated material. From the temperature increase of the heat source, it is possible to derive both the thermal conductivity and the thermal diffusivity from one single transient recording, provided the total time of the measurement is chosen within a correct time window defined by the theory and the experimental situation. Based on a theory of sensitivity coefficients, it is demonstrated how the experimental time window should be selected under different experimental situations. In addition to the theoretical work, measurements on two different materials: poly(methylmethacrylate) and Stainless Steel A 310, with thermal conductivity of 0.2 and 14 W/mK, respectively, have been performed and analyzed based on the developed theory.
137 citations
TL;DR: In this paper, the authors used the 3ω method to measure the thermal conductivity of thin films and multilayers of amorphous and microcrystalline oxides.
Abstract: Accurate and simple measurements of the thermal conductivity of thin films deposited on high thermal conductivity substrates have been recently enabled by the development of an AC hot-wire method, the 3ω method. Recent progress in the measurement and understanding of heat transport in ultra-thin films (1 μm thick) and multilayers is reviewed, and the possibility of using solid-solid interfaces on nanometer length scales to control heat transport in thin film materials is explored. The finite thermal conductance of solid-solid interfaces becomes important when considering heat transport in single layer films < 100 nm thick. Through the use of multilayer films-for example, epitaxial superlattices of crystalline semiconductors or nanometer-thick layers of amorphous and microcrystalline oxides-we can study materials with an extremely high and controllable density of internal interfaces, and evaluate the effect of these interfaces on heat transport. For the case of Si-Ge superlattices, the relatively large mismatch of the vibrational properties of silicon and germanium creates a larger reduction in thermal conductivity than for GaAs-AlAs superlattices. Surprisingly, heat conduction in multilayers of disordered oxides is essentially unchanged by a high interface density.
93 citations
TL;DR: In this article, an experimental plate mold has been designed to evaluate the nature of the thermal contact between the polymer and the mold during the holding and cooling phase, and an inverse method is used to determine the heat flux density crossing the polymer mold interface.
Abstract: In injection molding, the pressure in the cavity usually reaches the atmospheric pressure before the ejection, therefore the thermal contact between polymer and mold is modified. This paper aims to evaluate the nature of the thermal contact between the polymer and the mold during the holding and cooling phase. An experimental plate mold has been designed to study this phenomenon. Thermal sensors facing each other and pressure sensors have been set in the mold. An inverse method is used to determine the heat flux density crossing the polymer mold interface, and the mold surface temperature. Then, a second inverse algorithm allows to determine the temperature profile at the end of the filling and the time evolution of the thermal contact resistance (TCR). Finally, the polymer temperature distribution in the thickness is determined between the thermal sensors. The results of this study show that the TCR between the polymer and the mold is not negligible and not constant with time. The polymer temperature at the surface can be 20°C higher than the mold surface temperature. Moreover, asymmetric air gaps have been observed when cavity pressure becomes equal to atmospheric pressure, therefore asymmetric temperature profile in the thickness are generated.
90 citations
23 May 2000
TL;DR: In this article, a simulation program based on the matrix method was used to study the effect of considering 2-D and 3-D cases, matrix thickness, volume percentage of particles, and base material and particles of different conductivities.
Abstract: A very important aspect in chip design in flip chip technology is the heat dissipation. As the surfaces of the heat sink, the heat spreader and the chip are rough there are imperfect contacts leading to higher thermal resistance due to the contact resistance. A method to decrease this contact resistance is by the use of thermal interface material. These thermal interface materials can be of various types, but most of them are polymers. Percolation theory holds a key to understanding the behavior of these polymers. Percolation, used widely in electrical engineering, is a phenomenon in which the highly conducting particles distributed randomly in the matrix form at least one continuous chain connecting the opposite faces of the matrix. This phenomenon was simulated and analytical results drawn from the program, to study the effect of considering 2-D and 3-D cases, matrix thickness, volume percentage of particles, and base material and particles of different conductivity. The simulation program was based on the matrix method, which not only simplifies the method of calculation but also increases the accuracy of the result thus obtained as compared to the calculations based on Kirchoffs Law or systematic node elimination, to obtain resultant thermal conductivity of the mixture. The analysis showed a sudden increase in thermal conductivity as soon as the percentage of particles reached the percolation threshold, which varied with all the parameters listed above. Comparison with the existing experimental results and the other existing models showed that the results from the percolation model were more accurate than other models, especially at high filler concentration.
79 citations
TL;DR: An experimental method based on the 3ω technique has been developed to measure thermal conductivity of porous Xerogel films as a function of porosity as mentioned in this paper, which suggests that the tradeoff between thermal and electrical performance is an important consideration when implementing porous dielectric materials as interlevel dielectrics for on-chip interconnects.
Abstract: An experimental method based on the 3ω technique has been developed to measure thermal conductivity of porous Xerogel films as a function of porosity. The results show that the thermal conductivity of these porous dielectric films can be an order of magnitude smaller than that of SiO2. To account for the porosity dependence of thermal conductivity, two porosity weighted semiempirical models are introduced. These models suggest the scaling rule expressing the thermal conductivity as a function of porosity. The decrease observed in thermal conductivity of porous films suggests that the tradeoff between thermal and electrical performance is an important consideration when implementing porous dielectric materials as interlevel dielectrics for on-chip interconnects.
TL;DR: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability.
Abstract: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability. Addition of hexagonal boron nitride particles up to 16.0 vol. percent further increases the conductance of sodium silicate, due to the higher thermal conductivity of BN. However, addition beyond 16.0 vol. percent BN causes the conductance to decrease, due to the decrease in fluidity. At 16.0 vol. percent BN, the conductance is up to 63 percent higher than those given by silicone based pastes and is almost as high as that given by solder. Water is almost as effective as sodium silicate without filler, but the thermal contact conductance decreases with time due to the evaporation of water. Mineral oil and silicone without filler are much less effective than water or sodium silicate without filler. @S1043-7398~00!00402-3#
Journal Article•
TL;DR: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability as mentioned in this paper.
Abstract: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability Addition of hexagonal boron nitride particles up to 160 vol percent further increases the conductance of sodium silicate, due to the higher thermal conductivity of BN However, addition beyond 160 vol percent BN causes the conductance to decrease, due to the decrease in fluidity At 160 vol percent BN, the conductance is up to 63 percent higher than those given by silicone based pastes and is almost as high as that given by solder Water is almost as effective as sodium silicate without filler, but the thermal contact conductance decreases with time due to the evaporation of water Mineral oil and silicone without filler are much less effective than water or sodium silicate without filler @S1043-7398~00!00402-3#
DOI•
05 Nov 2000TL;DR: In this paper, the TES composite is a plate-like structure that consists of a central core of foamed aluminum that is packed with a phase change material (PCM).
Abstract: A Thermal Energy Storage (TES) system uses a Phase Change Material (PCM) to store heat during peak power operation of variable power dissipating devices via the latent heat effect. The TES composite developed is a plate-like structure that consists of a central core of foamed aluminum that is packed with a PCM. By considering the elements of the composite to be thermal resistors and constructing a flat -plate thermal conductivity apparatus, the plate-to-plate effective thermal conductivity is determined. The composite effective thermal conductivity is primarily composed of the thermal conductivity of the aluminum foam which is reduced by the effect of the aluminum foam-to-plate bond resistance. Heat flow through the PCM slightly augments the effective thermal conductivity. An increase in aluminum foam metal fraction results in an increase in the effective thermal conductivity of the composite because only about 2% of the heat flow is through the PCM, and the interfacial bond resistance decreases due to increased contact area. The trade-off is that as there is an increase in aluminum foam metal fraction, the volumetric latent heat decreases; thus, the storage time is reduced.
Patent•
02 Nov 2000TL;DR: A thermal pad for use in facilitating heat flow between a heat source surface and a heat sink surface includes a carbon fiber fabric that is impregnated with a thermal substance.
Abstract: A thermal pad for use in facilitating heat flow between a heat source surface and a heat sink surface includes a carbon fiber fabric that is impregnated with a thermal substance.
TL;DR: In this paper, a simple relation exists between the mean separation distance and surface roughness for all the gases and gas mixtures, which satisfies 85% of data points to within ± 4%.
TL;DR: In this paper, a theoretical model describing specific mechanisms of heat transport in as-prepared and oxidized nano-porous silicon (nano-PS) layers is described and the theoretical estimations are in a good agreement with experimental data obtained earlier.
Abstract: Recently discovered phenomenon of extremely low thermal conductivity of nano-porous silicon (nano-PS) is discussed in detail A theoretical model describing specific mechanisms of heat transport in as-prepared and oxidized nano-PS layers is described The theoretical estimations are in a good agreement with experimental data obtained earlier The low thermal conductivity values allow to use this promising material as thermal insulator in microsensors and microsystems To ensure an efficient thermal isolation, a nano-PS layer has to be as thick as possible and mechanically stable We describe here the procedures to form thick (up to 200 μm) and stable nano-PS layers Distribution of Si oxidized fraction along the layer thickness after thermal oxidation in dry O2 atmosphere at 300°C during 1 h is studied
TL;DR: In this paper, a theoretical model of the gap nucleation process during pure metal solidification on a deformable mold of finite thickness is presented, which leads to two coupled differential equations for the shell thickness and contact pressure perturbations which are solved with a numerical scheme.
Abstract: A theoretical model of the gap nucleation process during pure metal solidification on a deformable mold of finite thickness is presented. Both surfaces of the mold follow a sinusoidal lay for which the ratio of the amplitude to the wavelength, or aspect ratio, is much less than one. This makes the aspect ratio a convenient perturbation parameter for the thermal and mechanical problems since it is indicative of the spatial variation in the surfaces. The thermal and mechanical fields are coupled along the upper surface of the mold through a pressure-dependent thermal contact resistance. The main goal of the model is to develop a means for examining the contact pressure along the mold-shell interface and how variation of the mold surface wavelength affects the time and location of gap nucleation. Gaps, which result from irregular distortion of the shell due to the modest variation of the mold surface geometry, are assumed to nucleate when the contact pressure locally falls to zero. The model leads to two coupled differential equations for the shell thickness and contact pressure perturbations which are solved with a numerical scheme, Using a series solution methodology, it is shown that the contact pressure perturbation predicted by the present model reduces to that for a rigid, perfectly conducting mold (which was considered in another work) in the limit of zero mold thickness. In the companion paper, we specifically examine various combinations of pure materials acting either as the shell or the mold material. The concept of a critical wavelength, which separates those wavelengths that lead to gap nucleation at the crests, from those that lead to gap nucleation at the troughs, is introduced. The potential for development of design criteria for mold surface topographies using the present theoretical model as a limiting solution for finite element models of more complex casting processes is discussed.
TL;DR: In this article, the effective thermal conductivity and thermal diffusivity of a two-layer system were investigated from the theoretical point of view for application to photoacoustic experiments.
Abstract: The effective thermal conductivity and thermal diffusivity of a two-layer system are investigated from the theoretical point of view for application to photoacoustic experiments. The effective thermal parameters are obtained by comparing the temperature distribution on the left or right surface of the layered structure and some effective one-layer material. These effective thermal parameters are calculated for some special cases as for example, low and high chopper frequency. The influence of the interface thermal contact between the layers plays an important role on the effective thermal parameters. It is shown that the effective thermal conductivity and thermal diffusivity depend strongly upon the used photothermal technique.
Patent•
11 Jan 2000
TL;DR: In this article, a thermal joint for facilitating heat transfer between two components is described, which is formed from an alloy of at least two constituents, i.e., a liquid temperature and a solid temperature.
Abstract: A thermal joint for facilitating heat transfer between two components is described. The thermal joint is formed from an alloy of at least two constituents. The alloy has a liquid temperature and a solid temperature. When the operating temperature falls between the liquid temperature and the solid temperature, the alloy has at least one liquid phase which is in substantial equilibrium with at least one solid phase. The thermal joint is used between a heat-generating component, such as a semiconducting device, and a heat-dissipating component, such as a heat sink. Such thermal joint substantially reduces the thermal resistance between the two components.
TL;DR: In this paper, a detailed analysis of the resistance to heat transfer across the joint to the resistance of heat flow from the specimens to the surroundings is presented, and it is shown that the heat losses may be reduced by the provision of a shield.
TL;DR: In this article, the thermal conductivity of two kinds of ZrO2 thin films (stabilized with Y2O3 or not) was analyzed and it was shown that a decrease in the dielectric thickness leads to a drastic drop in the thermal performance.
TL;DR: In this article, the thermal conductivity of glass has been measured by contacting the sample with a metal at a different uniform initial temperature, and the subsequent temperature response in the metal is measured by a tiny thermocouple just underneath the (contact) surface.
Abstract: The thermal (phonon) conductivity of glass has been measured by contacting the sample with a metal at a different uniform initial temperature. The subsequent temperature response in the metal is measured by a tiny thermocouple just underneath the (contact) surface. The coefficient of heat penetration λρcp follows directly from the fitted asymptotic temperature jump or drop for long times. Division by the separately measured heat capacity ρcp yields the thermal conductivity λ. The conductivity measurement reproducibility was σ = 3%. The standard deviation between validation measurements and round robin test results on Pyrex glass was σ = 5.8%, somewhat more than the accuracy σ = 5.2% of the round robin test results. The measurement method is insensible for slight imperfections of the thermal contact and infrared radiation diffusion (photon conductivity) in a hot glass. The method has been used with minor modifications for solid and molten samples at temperatures of 50–850°C and conductivities of 0.1–25 W/(m K). The thermal (phonon) conductivity of the investigated soda-lime silicate glasses increases slightly (∼27–30%) with temperature from ambient up to around the glass transition.
TL;DR: In this paper, the authors measured the thermal resistance and its temperature dependence for three industrial adhesives used for electronic packaging using the laser-flash method from room temperature to 300/spl deg/C.
Abstract: The thermal resistance and its temperature dependence was measured for three industrial adhesives used for electronic packaging. Measurements were made by the laser-flash method from room temperature to 300/spl deg/C. The samples were in the form of sandwiches consisting of two platelets of silicon carbide-reinforced aluminum (AlSiC) bonded together with the adhesives. The total thermal resistance of the bond (the sum of the bulk thermal resistance of the adhesive and the resistances at the two interfaces) was calculated from the thermal response of the sandwich subjected on one side to a single laser-flash. The total thermal resistance was found to decrease with increasing temperature. The bulk thermal resistance of the adhesive, calculated from its thickness and independently determined thermal conductivity, was found to be relatively independent of temperature. The interfacial resistance at the AlSiC interfaces, depending on the adhesive, ranged from about 60 to 80% of the total resistance decreasing to about 50% of the total interfacial resistance at 300/spl deg/C. For two of the adhesives considered in this study, the interfacial thermal resistances for the AlSiC/adhesive interfaces were found to be considerably higher than those found in an earlier study of Si/adhesive interfaces.
TL;DR: In this article, a three-dimensional thermal model for resistance spot welding in aluminum is presented, validated with experimental findings, considered phase change and the associated weld pool convection, and a parametric study was performed to determine the influence of welding features such as welding current, faying surface (workpiece contact surface) electrical contact resistance, and electrode-workpiece (E/W) thermal contact conductance.
Abstract: A three-dimensional thermal model for resistance spot welding in aluminum is presented. The numerical model, validated with experimental findings, considered phase change and the associated weld pool convection. A parametric study was performed to determine the influence of welding features such as welding current, faying surface (workpiece contact surface) electrical contact resistance, and electrode-workpiece (E/W) thermal contact conductance. These parameters have significant effects on the nugget and heat-affected-zone geometry. The phase change morphology, including melting and solidification rates and weld pool dynamics, was also significantly influenced by the parameters studied. The strongest convection was observed at the center of the molten pool in a vertical plane, aligned with gravity. Although two prominent convection cells developed, the phase change morphology was not significantly affected by convection due to the short welding time (less than 0.1 s) and low fluid velocity (smaller than 0.01 mm/s). The nugget grew nonlinearly with increasing current and faying surface electrical contact resistance, whereas it diminished with increasing E/W thermal contact conductance. The influence of electrical contact resistance at the faying surface on nugget size was less pronounced than that of the other parameters. The length of time that the weld pool existed was directly proportional to current and indirectly proportional to E/W thermal contact conductance.
TL;DR: In this paper, the authors investigated the effect of loading history on the thermal contact conductance and found that the number of load cycles and overloading pressure is a significant determinant of thermal contact resistance.
Abstract: A resistance to heat flow exists at the junction of two surfaces. It has long been recognized that there exists a hysteresis effect, that is, the value of thermal contact resistance in the unloading process is less than that in the loading process at the same load. However, little work has been done in utilizing this phenomenon to enhance the thermal contact conductance. The present experimental work investigated the effect of loading history; in particular the number of load cycles and overloading pressure, on the thermal contact conductance
23 May 2000
TL;DR: In this article, the results of characterization testing performed on three currently available phase-change thermal interface materials are discussed and an example of how to apply the test data to a specific application to predict the interface temperature difference when the interface mechanical specifications, mounting pressure and power density are defined.
Abstract: To aid in the understanding of phase-change thermal interface materials, the results of characterization testing performed on three currently available materials are discussed. These tests were performed using the methods of ASTM D 5470 modified to account for the properties of phase-change materials. These data reveal that while the materials tested show a variation in performance, they all achieve their minimum thermal impedance values by reducing their thickness and eliminating interfacial contact resistance after phase change. This paper also discusses an example of how to apply the test data to a specific application to predict the interface temperature difference when the interface mechanical specifications, mounting pressure and power density are defined.
TL;DR: In this paper, the authors used the Rainwater-Friend theory for the evaluation of the initial density dependence of the translational contribution of the thermal conductivity of polyatomic gases.
Abstract: The Rainwater–Friend theory is used for the evaluation of the initial density dependence of the thermal conductivity of the noble gases using accurate realistic potentials. This theory, which was originally developed for spherically symmetric potentials, is adapted for the calculation of the initial density dependence of the translational contribution of the thermal conductivity of polyatomic gases. The internal state contribution is evaluated using a combination of Mason–Monchick theory and hard-sphere Enskog theory. At high density, beyond the range of the Rainwater–Friend theory, a deviation thermal conductivity function has been presented. With the help of this function, an easily usable corresponding-states function for the calculation of the thermal conductivity of supercritical gases has been developed, which is valid over a wide temperature range and for pressures up to 400 MPa.
23 Mar 2000
TL;DR: In this paper, the authors present a fundamental and philosophical view of an ideal thermal conductivity measurement system and a measurement device and technique were developed that incorporated these ideals by modifying existing ASTM test methods.
Abstract: Principles and techniques of three ASTM test methods of measuring thermal conductivity and thermal impedance of thin thermal interfaces are discussed. Although some measurement limitations exist in these ASTM methods, they provide an excellent starting point for the development of thermal property test protocols. The key issue is to minimize the error associated with the assumptions related to the thermal contact resistance. This paper presents a fundamental and philosophical view of an ideal thermal conductivity measurement system. A measurement device and technique were developed that incorporates these ideals by modifying existing ASTM test methods. The developed technique provides a systematic means of minimizing measurement errors and increasing measurement sensitivity.
TL;DR: In this paper, the authors studied the phononic heat transfer through an atomic dielectric wire with both infinite and finite lengths by using a model Hamiltonian approach and found that the thermal conductance contributed by each phonon branch of a uniform and harmonic chain cannot exceed the well known value which depends linearly on temperature but is material independent.
Abstract: We studied the phononic heat transfer through an atomic dielectric wire with both infinite and finite lengths by using a model Hamiltonian approach. At low temperature under ballistic transport, the thermal conductance contributed by each phonon branch of a uniform and harmonic chain cannot exceed the well known value which depends linearly on temperature but is material independent. We predict that this ballistic thermal conductance will exhibit stepwise behaviour as a function of temperature. By performing numerical calculations on more realistic systems, where small atomic chains are placed between two reservoirs, we also found resonant modes, which should also lead to stepwise behaviour in the thermal conductance.