Heat Sink Applications Research Articles

Thermal Management Materials for Advanced Heat Sinks used in Modern Microelectronics

Heat sinks are used for dispensing the heat from a system in many modern microelectronic components. It helps in systematically absorbing the heat from the system and dissipating it to the atmosphere, thereby ensuring system performance, extended life and reliability. The material used for the heat transfer device is one of the utmost significant parameter, which decides the size of the heat transfer device and its heat transfer efficiency. Lower values of density, overall cost, and coefficient of thermal expansion along with higher thermal conductivity, are considered as the essential properties required for any heat sink material. Though, the Copper and Aluminium materials are generally observed to be the best materials for a heat sink applications, some of their alloys are also found to be suitable. The manufacturing difficulty, the higher cost involved, comparatively poor thermo-physical properties and insufficient investigation are some of the factors that have limited the use of advanced composites in heat sink applications. A comparative numerical analysis for different thermal management materials like Copper, Aluminium, Al2O3, AlN, and Si3N4, is presented in this paper. COMSOL MULTIPHYSICS software is used for the present analysis to check the suitability of these materials for construction of heat sink. Moreover, the study of the cost-effectiveness of the material selected is important before the actual application of that material for heat sinks.

Ultra-low temperature fabrication of copper carbon fibre composites by hydrothermal sintering for heat sinks with enhanced thermal efficiency

Fabrication of dense Cu/40CF metal matrix composites for heat sink applications by hydrothermal sintering at low temperature (P = 250 MPa; T = 265 °C, tsinter = 60 min; water quantity = 5 wt%) is reported. Study of various sintering parameters and their influence on densification are investigated. Comparative thermal and microstructural properties of hydrothermally sintered samples with the conventionally used uniaxial hot-pressing samples on Cu/40CF material show considerable improvements, namely increase of thermal conductivity (TC) and decrease of coefficient of thermal expansion (CTE). Hydrothermal sintering yields, through a dissolution/precipitation mechanism, quasi-isotropic thermal properties (TC = 300 W/mK and CTE = 8 10−6/K).

Numerical Analysis of Fluid Flow and Heat Transfer in Micro-Channel Heat Sinks with Double-Layered Complex Structure.

Micro-channel heat sink (MCHS) has been extensively used in various electronic cooling fields. Double-layered MCHS, or DL-MCHS, is regarded as one effective technique for high-heat-flux transfer and is expected to meet the ever-increasing heat load requirement of future electronic device generations. In order to improve the cooling capacity, two new types of the MCHS, with a double-layered matrix structure (DL-M) and double-layered interlinked matrix structure (DL-IM) are proposed and investigated numerically. The two designs are compared with the traditional double-layered rectangular structure (DL-R) and the double-layered triangular structure (DL-T). Different properties of the heat sink are investigated to assess the overall heat transfer performance, for which coolant flow and heat transfer are both evaluated. The numerical results reveal that the periodical slot subchannel in the matrix has a significant effect on fluid flow for heat transfer. In comparison to the DL-R and the DL-T, the DL-M and DL-IM realize a much lower pressure drop and temperature rise at the base surface and also have higher Nusselt number and secondary flow intensity, therefore, manifesting better overall thermal performance. In the DL-M and DL-IM, the coolant flows along the periodical subchannel in one layer and is redirected into the second layer with vortices being induced. The vortices promote the coolant mixing and enhance the mass and heat transfer. These geometric design strategies can provide references for wide heat sink applications.

Comparison between experimental and theoretical thermal conductivity on epoxy based aluminium hydroxide and silica aerogel composite materials

The aerogels are having nanoparticles that are connected to form a freely connected 3D network, leaving a high fraction of space in between nanoparticles. In between a high fraction of space is called porosity, and due to this high porosity, aerogel material has an exceptional property such as low dielectric constant, low density, and very low thermal conductivity. Thermal conductivity plays a vital role in the thermal property of polymer composite materials and also plays an essential role in calculating the heat conduction as an insulation application. The silica aerogels have limited use as thermal insulation material because of its high cost. The present research work aims to study the thermal conductivity of reinforcing materials as aluminium hydroxide and silica aerogels mixed with epoxy resin as matrix material. Aluminium hydroxide/ silica aerogels of different compositions in the epoxy resin are used for the preparation of composite specimens. Finally, the heat flow guarded meter test method was used to evaluate the thermal conductivity of different composition of polymer composites. Related theoretical models were deduced based on the equal law of the specific thermal conductivity and law of minimal thermal resistance. The experiment measured values of thermal conductivity compared with the value of theoretical models thermal conductivity are relatively close. This study has shown that the aluminium hydroxide mixed with epoxy matrix results in significant increases in heat conductivity to use in heat sink application and silica aerogels mixed with epoxy effect in decreases heat conductivity thereby improving its thermal insulation ability to use insulation application.

Significant effects of temperature on biological properties of ZnO

Zinc oxide (ZnO) is an inorganic compound and it usually appears as a white powder. The powder is widely used as an additive into numerous materials. Inorganic nanoparticles are made by combining organic materials with inorganic materials which forms hybrids and has unique properties. The biological properties of zinc oxide nanoparticles like absorption coefficient, refractive index, concentration, conductivity, pH-values and temperatures were investigated. The diffusion techniques facilitate the measurement of the biological properties of liquids. The results show that absorption coefficient decreases with increasing the thickness of the zinc oxide pellet. The resistivity of the ZnO decreases with increasing the temperature was observed. The concentration of the sample increases conductivity also decreases. Zinc oxide refractive index changes with wavelength. The pH depends on temperature and biological effects were observed at lower concentration and which are playing a vital role in the metabolism of human beings and plant systems. The pH-profiles were measured after 24 h. One-way ANOVA showed significant differences of all tested materials. Variant refractive index can generate resonant cavity that can enhance phase shift of output light and fabricate a variety of optoelectronic device. Materials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulation. The biological properties like absorption coefficient, refractive index, concentration, conductivity, pHvalues and temperature were used in many advanced biological, medical and engineering applications such as heat exchangers.

Numerical Simulation of Heat Transfer in GraduallyVarying Microchannel Heat Sink

Microchannel heat sink has broad relevance in microelectronics and optical devices. Study in this paper focuses on enhancing the cooling characteristics of microchannel heat sink used in such devices. Instead of conventional, rectangular or circular cross-section channel designs, this study uses microchannels with gradually varying cross-section along the length. Three channels geometries employing entirely diverging or converging designs as well as combined diverging-diverging design are studied. The cooling performance is ascertained by using nanofluid and DI water as coolants flowing at different Reynolds numbers by analysing thermal characteristics such as temperature variation and Nusselt number using commercial software ANSYS® Fluent. Study demonstrates that the nanofluid is more efficient for the heat sink application irrespective of the channel geometry.

Synthesis of W-AG Nanoalloys and Computer Aided Thermal Analysis of W-AG Nanoalloys Based Heat Sink

W-Ag finds applications in many frontier areas such as heat sinks and microwave absorbers for microelectronics devices, arcing tips, resistance welding electrodes, electrical contacts and heavy duty electronic contacts. These nanoalloys prepared by mechanical milling process result in highly dense product. Chemical approaches have significant advantages in terms of better stoichiometric control, purity and controllable particle size. The variation in chemical composition of these composites allows the match of thermal expansion coefficient with ceramic substrates used in semiconductor devices. In the present study, Ag nanoalloys with average sizes below 200 nm were prepared using tungsten powder and silver nitrate as precursors. Compositional characterization of W-Ag nanoalloys was carried out using portable XRF.The developed material i.e. W-Ag is used as heat sink application in which the heat sink is modeled and thermally analyzed for evaluation of heat flux. The heat flux obtained was compared with aluminum heat sink. It was perceived that W-Ag heat sink exhibited superiority in withstanding higher temperature. Whereas, heat sink designed from aluminum was limited with their parameter which is thermal conductivity.

Synthesis of Mo-Cu Nanoalloys and Computer Aided Thermal Analysis of Mo-Cu Nanoalloys Based Heat Sink

Mo-Cu alloys are used as heat sinks, microwave absorbers in microelectronic devices and as electric contacts in circuit breakers. Mo-Cu nanoalloys with average sizes below 200 nm were prepared using molybdenum powder and copper nitrate. Compositional characterization of Mo-Cu alloys was carried out using portable XRF. The developed material i.e. Mo-Cu is used as heat sink application in which the heat sink is modeled and thermally analyzed for evaluation of heat flux. The heat flux obtained was compared with heat sink made of aluminum. It was observed that the Mo-Cu heat sink exhibited superiority in withstanding higher temperature whereas, heat sink designed from aluminum was limited with their parameter which is thermal conductivity.

Thermal expansion behavior of Al–B4C composites by powder metallurgy

In the present investigation, Al/B4C composite samples were prepared by hot press method. Thermal properties of the samples containing different reinforcement contents were evaluated. XRD characterization did not reveal the presence of any detrimental phase. Density and microhardness measurements confirmed proper compaction and high hardness of the samples, respectively. SEM observations showed no evidence of cracks at the matrix/reinforcement interface and it was seen that B4C particles had high wettability with Al matrix. Dilatometry tests demonstrated that by improving the reinforcement content, the coefficient of thermal expansion declined in a way that Al/25% B4C sample had the lowest thermal expansion coefficient (8 ppm/C), which makes it suitable for heat sink applications. Moreover, the experimental results were in good agreement with thermoelastic models in specific temperature ranges.

Heat transfer performance of a novel tubular oscillating heat pipe with sintered copper particles inside flat-plate evaporator and high-power LED heat sink application

Abstract A novel tubular oscillating heat pipe (OHP) with sintered copper particles (SCPs) inside a flat-plate evaporator for the thermal management of high-power LED chips was designed and fabricated. The thermal performance of designed OHP, temperature distribution and illumination profiles of LED array were experimentally tested and evaluated. Results showed that the addition of SCPs on the evaporator of OHP can facilitate the startup and make oscillating motions of liquid-plugs/vapor-bubbles inside copper tubes more easily. A lowest thermal resistance of 0.168 K/W was achieved by the OHP with SCPs when the input power to the LED array was 60 W, and the corresponding maximum LED temperature can be controlled below 70 °C. The temperature distribution of LED array at different inclination angles was almost coincident and achieved good uniformity if the designed OHP was operated at low filling ratios, indicating that the gravity action can be partially neglected. It was also found that the temperature of LED array was inversely proportional to the illumination intensity, and a high filling ratio can cause the degradation of illumination intensity of LED chips. A low filling ratio of 30% was preferred for the designed OHP applied in high-power LED cooling.

Thermal Characterization of Aluminium-Based Composite Structures Using Laser Flash Analysis

Al-2024-based alloy with Al2O3 reinforcement composite is suitable for heat dissipation components due to its enhanced thermal conductivity and higher heat flux distribution. Al-2024 composite has a wide range of applications in aerospace industry; specifically this utilization is observed in heat sinks which are made up of aluminium alloys. Stir casting method was used for the fabrication of the composite due to its effective cost and even particle distribution. In the present study, the effects of increase in reinforcement per cent that brings out the well-regarded changes in conductivity of composites are characterized. Tests such as thermal diffusivity, thermal conductivity and specific heat were conducted to evaluate the material characteristics using laser flash analysis method. This method adores the accurate values of conductivity for varied composition of particles and is highly accurate and precise. The composite consists of 93.5% of pure aluminium, and the rest can be reinforced. Due to high strength and fatigue resistance, this material can be used in aerospace structures under tension and susceptible to thermal shock. The composition at 10 wt% of Al2O3 illustrates the optimum values for thermal conductivity. The advancement of changes in composite attribute is detected with increase in temperatures of 30 °C, 100 °C and 200 °C. The optimum values of thermal conductivity, diffusivity and lower heat flux distribution can be substituted in the components for heat sink applications.

Thermal performance of micro-encapsulated PCM with LMA thermal percolation in TES based heat sink application

Paraffin is one of preferred entrant phase change material (PCM) for the thermal energy storage (TES) based heat sink application. Encapsulation is one of the preferred methods to address the inherent issue with paraffin such as volume expansion, spillage and low bulk thermal conductivity. In this study, describes the synthesis, characterization and heat transfer performance of micro-encapsulated (ME) paraffin of average size ∼64 µm by in-situ polymerization method. To conquer the adverse effect of reduced thermal diffusion in the bulk ME PCM, a thermal percolation by low melt alloy (LMA: Bi (32%), Sn (59%), Zn (4%) and In (5%)) of ∼16% volume was incorporated. The characterization results show the form-stability and thermal degradation of PCM. The experiment with heat sink was conducted with fin and without finned heat sink for power levels of 1.57, 2.45, 3.61, 4.49 and 5.51 kW/m2. The results reveal the promising role of ME PCM/LMA in keeping the heat sink without fin at a lower temperature for a prolonged duration. Obtained an enhancement ratio of 1.87–2.57 and 2.06–3.58 in time to reach set point temperatures of 55 and 65 °C with heat load of 1.57–5.51 kW/m2 LMA percolation. The complete melting and more uniform temperature distribution in the PCM occurred within the operating temperature. Moreover, the recovery time of heat sink also diminished radically. Based on the results, the ME PCM can conquer the adverse effect due to the above mentioned drawback of conventional paraffin and the LMA percolation layer gives a prompt thermal response compared with fins of same volume fraction in the heat sink.

Ab‐initio study of electronic, optical, thermal, and transport properties of Cr4AlB6

AbstractTheoretical investigation of different physical parameters of Cr4AlB6 have been done within the framework of density functional theory. Cr4AlB6 is a no band gap material. Its Cr‐3d states contributes the most at the Fermi level. Thermal properties are investigated using quasi‐harmonic Debye model as implemented in Gibbs code for different values of pressure and temperature. Study of transport property suggests that its electrical conductivity increases nonlinearly with increase in temperature but the relative change in its value is very low whereas its thermal conductivity increases linearly with the increase in temperature and relative increase in thermal conductivity is very high. The behavior of Cr4AlB6 is anisotropic and property is ceramic. It has potential applications in making ceramic capacitors. Its reflectivity is high in low energy region. It suggests that material can be used as coating material for far‐infrared radiation. Study of the transport property suggests that because of very high value of thermal conductivity, it can be used for heat sink applications.

Fabrication and Tailoring Interface Structure of Diamond/Al(and Al12Si) Composites for Heat Sink Applications by Vacuum Hot Pressing and Selective Laser Melting

Al and Al12Si matrix composites reinforced with synthetic diamond particles have been developed by using conventional powder metallurgy and emerging additive manufacturing techniques, i.e. vacuum hot pressing (VHP) and selective laser melting (SLM), respectively. Relative density and interface structure have been evaluated to relate to measured thermal conductivity (TC) of the composite. Despite very different physical and metallurgical mechanisms (VHP vs. SLM), the diamond/Al interface can be tailored allowing to form a ‘clean’ and tightly-adhered interface at the micrometer scale in both cases. This so-called diffusion-bonded interface is the most favorable for enhancing overall TC which demonstrates the potential of SLM for processing multifunctional Al matrix composites. However, how to realize full densification and simultaneously maintain such an interface structure during SLM remains a key technical problem to figure out.

Analysis of the Effects of Joule Heating and Viscous Dissipation on Combined Pressure-Driven and Electrokinetic Flows in a Two-Parallel Plate Channel with Unequal Constant Temperatures

In this article, we perform an entropy generation analysis for the micro channel heat sink applications where the flow of fluid is actuated by combined influences of applied pressure gradient and electric field under electrical double layer phenomenon. The upper and lower walls of the channels are kept at different constant temperatures. The temperature-dependent viscosity of the fluid is considered and hence the momentum equation and energy equations are coupled in this study. Also, a hydrodynamic slip condition is employed on the viscous dissipation. For complete analysis of the entropy generation, we use a perturbation approach with lubrication approximation. In this study, we discuss the results depicting variations in the velocity and temperature distributions and their effect on local entropy generation rate and Bejan number in the system. It can be summarized from this analysis that the enhanced velocity gradients in the flow field due to combined effect of temperature-dependent viscosity and Joule heating and viscous dissipative effects, leads to an enhancement in the local entropy generation rate in the system.

Rapid Prototyping of Polymer-Based Rolled-Up Microfluidic Devices.

This work presents the simple and rapid fabrication of a polymer-based microfluidic prototype manufactured by rolling up thin films of polymer. The thin films were fabricated via a casting method and rolled up around a center core with the aid of plasma activation to create a three-dimensional (3D) spiral microchannel, hence reducing the time and cost of manufacture. In this work, rolled-up devices with single or dual fluidic networks fabricated from a single or two films were demonstrated for heat sink or heat exchanger applications, respectively. The experimental results show good heat transfer in the rolled-up system at various flow rates for both heat sink and heat exchanger devices, without any leakages. The rolled-up microfluidic system creates multiple curved channels, allowing for the generation of Dean vortices, which in turn lead to an enhancement of heat and mass transfer and prevention of fouling formation. These benefits enable the devices to be employed for many diverse applications, such as heat-transfer devices, micromixers, and sorters. To our knowledge, this work would be the first report on a microfluidic prototype of 3D spiral microchannel made from rolled-up polymeric thin film. This novel fabrication approach may represent the first step towards the development of a pioneering prototype for roll-to-roll processing, permitting the mass production of polymer-based microchannels from single or multiple thin films.

Experimental study on heat transfer performance of neopentyl glycol/CuO composite solid-solid PCM in TES based heat sink

In this study, the thermal/chemical property and heat transfer performance of a solid-solid nano-enhanced PCM (SSPCM) comprising of neopentyl glycol (NPG) and copper oxide (CuO) nanoparticles is assessed for its possible usage in thermal energy storage (TES) based heat sink application. The SSPCM samples were prepared by mixing NPG with CuO nanoparticle in 0.5, 1 and 3% weight proportions. The thermal and chemical compatibility of the prepared samples were tested and confirmed by TGA and FTIR characterization methods. The effect of using CuO nano additives on solid-solid transition enthalpy of NPG was studied with the aid of DSC analysis. The results showed a decrease of enthalpy from 3.1 to 9.6% for the corresponding CuO weight fractions ranging from 0.5 to 3%. The thermal conductivity of the composite SSPCMs measured through laser flash technique, showed a maximum relative enhancement of about 4.08 to the value for pure NPG with 3 wt% CuO nanoparticle additions. The results of heat storage and release performance test showed a reduction of 14.1–33.8% in the storage time corresponding to 0.5 to 3 wt% of CuO nanoparticles loading. The heat transfer performance of the NPG/CuO SSPCM was experimentally investigated using a heat sink. The results indicated that the time taken by the heat sink to attain a temperature of 60 °C during heating was increased by 2.36 times the time taken without using any PCM by the addition of 3% weight fraction of CuO nanoparticles. This made the heat sink to be maintained at a lower temperature for a longer period of time. Also, addition of CuO nanoparticles in the NPG reduced the recovery time of the heat sink during cooling.

Analysis of thermal flow around heat sink with ionic wind for high-power LED

This paper presents a new method of active cooling for a Light Emitting Diode (LED) application using the ionic wind which is a flow induced by a corona discharge at a tip of a curved electrode. Thermal flow around a heat sink for a high-power LED was analyzed and the ionic wind was investigated for the heat sink application in this study. Details of a numerical investigation of natural convection around the heat sink for the 200 W-LED were studied. The reliability of the computational fluid dynamics (CFD) was verified by experimental data of temperatures. A particle image velocimetry (PIV) test was performed to analyze the behavior of the ionic wind around the heat sink. The thermal flow around the heat sink fins was analyzed and it was concluded that the center pole of the cylindrical heat sink was unnecessary for the cooling performance. And, the ionic wind from a wire to cylinder electrode was applied to the heat sink to enhance the cooling performance. As a result, the optimum radius of the wire curvature and input voltage for the ionic wind were found to be 110 mm and 7.5 kV, respectively. The heat transfer coefficient of the heat sink increased by 37% from 96.7 to 133 W/m2 K by the ionic wind, which was confirmed experimentally. And, the cooling performance of the heat sink was enhanced by 148% in maximum by the ionic wind compared with that of the original heat sink for 0.6 W of the applied power. The result of this study can be used for the wide variety of the ionic wind application as a promising technology for the LED cooler.

Interfacial design of Mg/graphite flakes-MP (MP=Fe, Co or Ni) ferromagnetic composites with low density and high thermal conductivity

In the present work a new material based on the recently developed graphite flakes-SiC particles/metal composite, is described. The latter was processed by gas-pressure infiltration of the liquid metal into a preform obtained by packing a mixture of graphite flakes and SiC particles. Its microstructure consists of alternating layers of oriented graphite flakes and metal-particles composite, and, thus, it is highly anisotropic. Its highest thermal conductivity (>300 Wm−1K−1), attained in the plane parallel to the flakes plane, makes it suitable for heat sinking applications. Replacing SiC by particles of similar size and of ferromagnetic nature (Fe, Co and Ni), a material with moderate-to-high magnetic permeability and reasonably high thermal conductivity, has been produced. Mixtures of packed magnetic particles and graphite flakes were infiltrated with pure magnesium. In order to avoid chemical reaction, Co and Ni particles were carbon coated. Optimizing the combination of thermal conductivity and magnetic properties requires proper control of liquid metal infiltration variables, such as, temperature, pressure and contact time before metal solidification.

Evolution of mechanical performance with temperature of W/Cu and W/CuCrZr composites for fusion heat sink applications

Power exhaust and materials lifetime have been identified as key challenges for next-generation fusion devices. A water-cooled monoblock divertor, consisting of tungsten as the plasma facing material and copper-based composites as the heat sink, has been proposed as the baseline material. However, there is a large mismatch in the coefficient of thermal expansion and the elastic modulus between these metals, which requires the development of new materials.The goal of this study is the mechanical and microstructural characterization of two composites materials, W-30wt%Cu and W-30wt%CuCrZr, produced using liquid infiltration in an open porous tungsten preform. To reproduce the most adverse in-service conditions, materials were characterized under high vacuum atmosphere up to 800°C. From the measured mechanical properties, a remarkable temperature dependence can be assessed, since it is noticeable that for both materials, tensile and flexural strength equally decrease as the measurement temperature increases. However, the fracture behavior of W-30CuCrZr is on average 25% higher than that of W-30Cu (21MPam1/2 versus 17MPam1/2 at RT) although this gap is narrower at higher temperatures; at 800°C, the contribution of the Cu-based phase is quite low, thus fracture is primary controlled by the W initial skeleton. From these values, it can be inferred that the yield strength and fracture toughness of W-30CuCrZr composite are superior, whilst it presented lower elastic modulus and rupture strain values than the W-30Cu composite.As a result, the metal matrix composites presented in this article could effectively dissipate heat while overcoming the thermal stresses produced during operation, since a decent thermomechanical performance was observed at relevant reactor temperatures. This is of vital importance to enhance the performance, life cycle, and reliability of the component.