Hotspot Heat Flux Research Articles

CFD simulation of novel adaptive pin-fins microchannel heat sink to improve thermal management of electronic chips

Frequent hotspots pose a significant challenge for chip thermal management. Conventional microchannel with fixed structure cannot deal with random hotspots, which appear in irregular time and space. To address random hotspots and reduce microchannel energy consumption, a novel adaptive pin-fins microchannel (A-MCHS) is proposed in this paper to intelligently tackle with the hotspot region, which consists of a number of pin-fins with property of phase transition and volume shrinkage when the temperature is raised to 313.15 K. A CFD method is applied to study its thermal performance and user defined function (UDF) is used to realize the adaptive thermal response of pin-fins. It’s found that the adaptive pin-fins of the hotspot undergo volume reduction and enlarged local coolant flow under higher hotspot heat flux, illustrating the automatic and adaptive flow regulation effect. Compared with the fixed pin–fin microchannel, the local heat transfer performance of A-MCHS in the hotspot region is enhanced by 37.9 %, average Nu of the microchannel is advanced by 7.4 %, and the maximum chip surface temperature is reduced by up to 3.12 K. Moreover, it also shows a significant reduction of 10.7 % in pressure drop, suggesting a great energy saving in pumping cooling fluid. It’s indicated that the adaptive pin-fins microchannel provides efficient cooling and intelligently enhanced thermal management and energy saving for high heat flux electronic chips.

A novel microchannel-twisted pinfin hybrid heat sink for hotspot mitigation

Thermal hotspots cause excessive localized temperature rise, leading to significant temperature gradients across the microprocessor, which is the primary reason for its inadequate performance and early failure. This study proposes microchannel-pinfin hybrid heat sinks incorporating twisted and non-twisted pinfins of various cross-sectional shapes (hexagonal, pentagonal, square, and triangular) to demonstrate energy-efficient hotspot mitigation in a microprocessor with highly non-uniform power distribution. Microchannels and pinfins are positioned at low- and high-heat-flux zones, respectively, to reduce the temperature variations utilizing their unequal heat transfer capabilities. Here, high- and low-heat-flux zones represent the microprocessor-core area (hotspot) and remaining chip area (background zone), characterized by heat fluxes of 300 W/cm2 and 50 W/cm2, respectively. The pinfin twisting angle varies from 0° to 360° at a step of 45°. Conjugate heat transfer analyses are conducted through numerical solutions of the continuity, Navier-Stokes, and energy equations. The performance of the proposed hybrid heat sinks is compared with the non-hybrid (NH) and hybrid circular pinfins (HCP) heat sinks at Re = 120–440. The hybrid heat sink featuring triangular pinfins twisted at 225° angle (HTP-225) exhibits a remarkable reduction of 48.2 % in the total thermal resistance (Rth) and 58.4 % in the temperature non-uniformity (δT,bs) as compared to the NH heat sinks at Re = 440. Compared to the HCP design, the HTP-225 design shows 26.9 % and 35.8 % lower Rth and δT,bs, respectively. Moreover, the HTP-225 heat sink outperforms the NH heat sink with 46.0 % and 57.0 % lower Rth and δT,bs, respectively, at an equal pumping power of 18.6 mW. Furthermore, the HTP-225 heat sink demonstrates a 96.4 % and 38.5 % higher critical hotspot heat flux dissipating capacity than the NH and HCP heat sinks, respectively, making it a viable and effective solution for alleviating hotspots in high-power-density devices.

Microfluidic silicon interposer for thermal management of GaN device integration

With the popularity of the third generation semiconductor applications, silicon-based hetero-integration is driven to be applied massively by the miniaturization of microsystems and modules. The system-level power has a sharp increase in recent years, and consequently, hotspot thermal management is being increasingly concerned. A high-power GaN device with chip heat fluxes > 500 W/cm2 and hotspot heat fluxes > 30 kW/cm2 is implemented in this work to study extremely uneven hotspot cooling for silicon-based hetero-integration. A customized microjet silicon interposer (SI) is designed and fabricated based on the on-chip hotspot distribution, and another common microchannel SI in similar sizes is prepared for comparison. The GaN device is integrated on SI and micro-assembled in a test cube. The measurement results demonstrate that the maximum junction temperature of the GaN device on microjet SI is down to 150.3 ℃ at 70 ℃ ambient temperature with a pressure drop of 231.9 kPa. The overall thermal resistance (TR) of the test vehicle with microjet cooling has a 7.11 ∼ 7.72 % reduction and its heat transfer coefficient (HTC) increases by 12.3 ∼ 28.3 % compared to that with microchannel cooling with the pumping power of 0.5 ∼ 1.5 W. The material properties of the GaN chip and SI are extracted from the measurement results and then used in the analysis of the thermal and hydraulic properties of both microfluidic SIs numerically. Their cooling performance and efficiency are evaluated and compared based on the performance evaluation criteria (PEC), field synergy number and entropy generation rate. According to the evaluation results, while the PEC of microjet and microchannel SIs increases with the pumping power, the microjet SI can contribute to the enhancement of the synergetic relationship between the flow and temperature fields and reduction of total irreversibility in the heat transfer process compared to the microchannel SI in pursuit of low overall TR. The field synergy number improves by 90.40 % and the argument entropy generation rate is 0.376 when the overall TR is 1.35 K/W. The findings can provide valuable references for hotspot thermal management in silicon-based hetero-integration.

Numerical investigation of heat transfer and pressure drop characteristics of flow boiling in manifold microchannels with a simple multiphase model

The Manifold Microchannel (MMC) heat sink is an emerging micro-scale electronic cooling technology with high heat dissipation potential and application prospects. This paper numerically studied the subcooled flow boiling in MMC heat sinks. The feasibility of using the Mixture multiphase flow model to simulate the subcooled flow boiling in the MMC heat sink is validated. As the vapor-liquid interfaces are not reconstructed in this model, less computational resources are needed compared with other multiphase models. The results show that at constant channel width, the maximum and average temperatures of the MMC decrease with the increase of the microchannel aspect ratio. For cases with an inlet velocity of 0.35 m/s, the average wall temperature decreases from 388.53 K to 374.26 K when the aspect ratio increases from 6.67 to 16.67. The difference between the maximum and the minimum temperature on the heated surface increases with the increase of channel aspect ratio, resulting in an uneven temperature distribution. The thickness of temperature boundary layer near the divider is thicker than that near the heated base at low aspect ratio. Low pressure drops are obtained for cases with high aspect ratios due to the increase in cross-sectional area. The pressure drop of MMC with aspect ratio of 6.67 is nearly twice of the case with aspect ratio of 16.67. Although the Mixture model could not characterize the bubble shapes, the numerical results are similar to those obtained by the VOF model and the experimental visual results. A complex case of subcooled flow boiling in Z-type MMC with a hotspot heat flux of 800 W/cm2 is also conducted using the whole computational domain. Mal-distributions of mass flux, wall temperature and vapor void fraction are observed for this complicated problem. The difference between the maximum and the minimum temperatures is about 12 K. The Mixture model is more suitable to obtain reasonable numerical results of flow boiling in complex MMC with much less computational resource.

Experimental investigation on heat transfer and pressure drop characteristics of confined jet impingement boiling on hybrid-structured surface

In this study, confined jet impingement boiling experiments are carried out using ammonia for the heat dissipation of high-heat-flux hotspot. A hybrid-structured surface with triangular prism-convex structure in the stagnation zone and microchannel structure in the wall jet zone is designed for heat transfer enhancement. Utilizing the advantages of jet impingement and microchannel flow boiling, the temperature of the heating surface is maintained below 86.5 °C when subjected to a hotspot heat flux of 1367 W/cm2, verifying the promising cooling performance of jet boiling on hybrid-structured surface. Effects of jet velocity (0.34–7.07 m/s), heat flux (752, 1064, and 1367 W/cm2), saturation temperature (22, 26, and 30 °C), and inlet condition (subcooled, near-saturated, and two-phase state) are also investigated. Increasing jet velocity and saturation temperature are beneficial to the heat transfer of jet boiling in the central stagnation zone. For high jet velocity flow (V > 2.3 m/s), the junction-to-fluid thermal resistance is the lowest at heat flux of 753 W/cm2; while for low jet velocity flow (V < 2.3 m/s), the best cooling performance is obtained at heat flux of 1367 W/cm2. The pressure drop increases with jet velocity and inlet vapor quality, and shows no significant dependence on heat flux and saturation temperature.

Hotspot thermal management of silicon-based high power hetero-integration

Extremely uneven thermal distribution due to the hotspots generating at the transistor channel regions on GaN power chip is one of the major obstacles to high power hetero-integration on silicon. In this work, a 12 mm × 18 mm × 0.7 mm embedded converging-diverging microchannel (CDMC) cooler silicon interposer (SI) is put forward to address the hotspot cooling. A 5.3 mm × 3.5 mm × 0.08 mm GaN monolithic microwave integrated circuit (MMIC) 3-stage power amplifier (PA) chip with DC heating power of ∼ 101 W was integrated on the SI to evaluate the on-chip hotspot cooling performance. The average hotspot heat flux was up to 306.8 ∼ 307.1 W/mm2, and the average chip heat flux achieved 545.4 ∼ 546.3 W/cm2. The maximum junction temperature of the GaN chip on CDMC SI was 137.2 ∼ 147.4 °C with the pressure drop of 122.8 ∼ 394.3 kPa and pumping power of 0.41 ∼ 3.29 W at 70 °C ambient temperature. The thermal and hydraulic characteristics of the CDMC SI are analyzed based on field synergy principle and thermodynamic properties using finite element method (FEM). The heat transfer coefficient (HTC) of the CDMC SI has 22.4 ∼ 35.4% increase compared with that of a typical microjet array (MJA) SI. The cooling performance and efficiency of the CDMC SI have been validated theoretically and practically to be prior to those of the MJA SI, and it is a promising solution for high power hetero-integration on silicon with brilliant hotspot thermal management capability.

Local hotspot thermal management using metal foam integrated heat sink

Single phase liquid-cooled parallel micro/mini-channel heat sinks are commonly used for electronic cooling because of their superior thermal–hydraulic performance. However, heterogeneous integration of electronic chips, especially in 2.5D and 3D integrated circuits (ICs), results in highly non-uniform heat flux distribution and consequently generates localized hotspots. Conventional micro/mini-channel heat sinks often fail to suffice concentrated local hot spots due to the insufficient heat transfer area and local heat transfer coefficient. Therefore, in this paper, three novel water-cooled aluminum (Al) metal foam (MF) integrated compound heat sink layouts, namely solid fin-MF, rectangular fin-MF, and MF heat sink, have been proposed to mitigate local hotspot resulting from non-uniform heat generation. The main concept of the proposed compound heat sinks is to deploy MF in the hotspot region to take advantage of the superior thermal performance of metal foam with minimal pumping power. 3D computational fluid dynamics/heat transfer (CFD/HT) simulations have been performed to quantify and compare the effectiveness of the proposed compound heat sinks with conventional plate-fin heat sink over a wide coolant flow rates/pressure difference ΔP range within the laminar flow regime. Numerical results showed that the solid fin-MF layout provides the best thermal–hydraulic performance compared to all other layouts and offers the highest temperature uniformity, especially at a higher coolant flow rate. Moreover, for the solid fin-MF layout, an optimal porosity and pore density of MF has been identified as 0.9 and 5 PPI (pores per inch), respectively. Finally, at ΔP of 250 Pa and 400 Pa, the optimized solid fin-MF heat sink layout successfully dissipated ∼22.6% and ∼33.4% higher hotspot heat flux compared to the conventional solid fin layout with ∼21% and ∼18.3% lower pumping power penalty while maintaining the peak junction temperature below 85°C.

A system level optimization of on-chip thermoelectric cooling via Taguchi-Grey method

In this paper, a framework for the system level optimization of the thin-film thermoelectric cooler (TFTEC) in 3D electronic packaging is developed based on Taguchi-Grey method. The influences of the size effect, the geometric effect, the parasitic effect and the localized hotspot are comprehensively considered. An L25 (56) orthogonal array is employed to assess the influences of the leg height, the fill-ratio, the electrode height, the gap distance, the hotspot size and the hotspot heat flux on the passive and active cooling effects of the TFTEC. The results show that the electrode height, acting as the primary factor, contributes 45.5% and 45.3% on the passive cooling and active cooling, respectively. The contribution ratios of hotspot size and hotspot heat flux to passive cooling reach 21.4% and 14.7%, respectively. The contribution ratios of leg height and gap distance to active cooling reach 25.7% and 18.8%, respectively. The optimum design factors for maximizing the cooling effects are also approached by the Grey relational analysis. A passive cooling of 16.82 °C and a maximum active cooling of 12.29 °C are achieved, leading to a total localized cooling of 29.11 °C for a chip hotspot.

Thermal-hydraulic performance analysis of a hybrid micro pin–fin, jet impingement heat sink with non-uniform heat flow

• We present a novel concept for hotspot-targeted, energy efficient HT-JIHS for electronic chips. • The optimized jet hole arrangement and target plate can efficiently alter the flow distribution. • The total pressure drop will be dramatically reduced by enlarging the inlet diameter. • Optimized design is suitable for highly non-uniform heat flux maps. • The pumping power consumption for optimized design is less than 0.1%. Jet impingement as a highly efficient cooling method has been broadly used in the field of heat dissipation for high heat flow electronics. Well-designed structures including jet hole and pin–fin arrangement can significantly alter flow fields to provide a favorable trade between increased heat transfer performance and total pressure loss. In order to solve the imbalance problem of temperature uniformity and power consumption caused by non-uniform heat flux distribution in multi-core integrated circuits, a novel jet impingement cooling concept, for hotspot-targeted, energy efficient cooling of non-uniform heat generation electronics, was proposed in this paper. A three-dimensional numerical simulation was carried out to investigate the effects of jet hole diameter and distribution, heat transfer plate type and inlet area on heat transfer and resistance performance. The heat transfer coefficient, total pressure drop, maximum temperature rise and temperature non-uniformity were selected as the performance parameters. Compared with the traditional jet impingement heat sink, the well-designed heat sink in this work achieves an improvement of 58% in temperature non-uniformity while the total pressure drop is reduced by 68.7% at the same mass flow rate. In addition, the pumping power consumption is only 0.093% and 0.061% of the total heating power for 150 W/cm 2 and 300 W/cm 2 hotspot heat flux respectively while ensuring the acceptable temperature non-uniformity.

Numerical study on hot spots thermal management in low pressure gradient distribution narrow microchannel embedded with pin fins

With the rapid development of high-performance electronic chips, chip hot spot management has become a prominent problem. Aimed at investigating the hot spots thermal management of gradient distribution narrow microchannel embedded with pin fins (MPFC), the effects of hot spot location, Reynolds number, hot spot area and heat flux on the chip surface were numerically studied. The maximum surface temperature on the chip does not change significantly with the change of hot spot location. However, with a Reynolds number of 281–844, the average temperature of MPFC-BP48, MPFC-BP2244, MPFC-BP264 at Hotspot 1 decreases by 4.6–10.8 K compared with that of MPFC-BP, but they show a significantly decrement of 7.7–19.6 K at Hotspot 2, indicating that the three improved gradient distribution microchannel embedded with pin fins exhibit better temperature uniformity and heat transfer capacity. In addition, an increase in hot spot area brings a temperature increment at hot spot, especially in MPFC-BP which has exceed the maximum temperature of 358 K, it is found that the embedded with pin fins is beneficial to enhanced the local heat transfer capacity. Furthermore, under different heat flux, MPFC-BP has exceeded the maximum temperature with the hot spot heat flux of 800 W/cm2, while MPFC-BP48, MPFC-BP2244, MPFC-BP264 can be kept below 358 K with the hot spot heat flux of 1000 W/cm2. This study optimizes the heat sink structure and has great significance for hot spot thermal management of chips.

The ICECool Fundamentals Effort on Evaporative Cooling of Microelectronics

The Intrachip Enhanced Cooling Fundamentals (ICECool Fun) effort was launched by the Defense Advanced Research Projects Agency (DARPA) under the leadership of Dr. Avram Bar-Cohen during 2012–2015 to target an order of magnitude improvement in chip level and hot spot heat fluxes, compared to the then state-of-the-art (SOA). Evaporative cooling technologies to achieve potential targets of 1 kW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the chip level and 5 kW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the hot spot level were targeted. A key goal was to improve fundamental understanding of the evaporative cooling physics at the relevant scales, and a numerical modeling capability to enable the co-design of such solutions in emerging computing and communications systems. A summary of the five projects pursued under this effort is provided, including the key accomplishments and developed capabilities.

Single Phase Liquid Cooling of High Heat Flux Devices With Local Hotspot in a Microgap With Nonuniform Fin Array

Abstract Single-phase liquid cooling in microchannels and microgaps has been successfully demonstrated for heat fluxes of ∼1 kW/cm2 for silicon chips with maximum temperature below 100 °C. However, effectively managing localized hotspots in heterogeneous integration, which refers to the integration of various components that achieve multiple functionalities, entails further thermal challenges. To address these, we use a nonuniform pin-fin array. Single phase liquid-cooling performance of four silicon test chips, thermal design vehicles (TDVs), each with a nonuniform pin-fin array, are experimentally examined. We evaluate multiple combinations of hotspot and background heat fluxes using four background heaters aligned upstream to downstream, and one additional hotspot heater located in the center. We examine the thermal performance of cylindrical fin-enhanced TDVs and hydrofoil fin-enhanced TDVs, both with two designs: one with increased fin density around the hotspot only, and another with increased fin density spanning the entire width of the channel. The resulting heat flux ratio of the localized hotspot to background heaters varies from 1 to 5. TDVs with spanwise increased hydrofoil fin density (spanwise hydrofoil) exhibit the best thermal performance with 6% to 14% lower hotspot temperature than others. TDVs with spanwise increased cylindrical fin (cylindrical spanwise) maintain a balance between hotspot cooling performance and pressure drops. In general, as the temperature of the hotspot remains around 70 °C with a heat flux of 625 W/cm2, the nonuniform fin-enhanced microgaps appears to be a promising hotspot thermal management approach. The pressure drop of hydrofoil spanwise chip is highest among all the cases.

Thermal management of 3D chip with non-uniform hotspots by integrated gradient distribution annular-cavity micro-pin fins

Targeted at addressing practical thermal issues of 3D-IC chip, heat transfer characteristics and temperature uniformity of gradient distribution solid and annular-cavity micro-pin fins are experimentally and numerically investigated. At double side non-uniform heat flux condition (qb/qhs of 40/300 W/cm2), a significant deterioration of heat transfer is found with maximum temperature gradient of 44.6 K. With respect to uniform design, gradient distribution solid pin-fin chip provides considerable potentials to address a large hotspot heat flux (700 W/cm2) and improve temperature uniformity with a relatively small hotspot size (<200 * 200 μm). Further thermal-path analysis reveals that pin-fin surfaces act as a key role to transfer and redistribute the heat with transferring more than 64% of heat into the fluid. To address critical multiple heat flux condition, novel gradient distribution annular-cavity pin fins are designed to increase heat transfer area and eliminate flow dead zones. Applying two-side symmetrical inlet cavity, the coolant from micro-channel like rushes into the center cavity and forms local acceleration to impinge the next pin-fins. The combined effect of increasing heat transfer area and forming acceleration zones leads to a maximum reduction of the local hotspot temperature and total thermal resistance by 9 K and 34.5%, respectively.

Performance analysis of hotspot using geometrical and operational parameters of a microchannel pin-fin hybrid heat sink

In the present study, numerical investigation of hotspot heat transfer in a microchannel pin-fin hybrid heat sink is accomplished. The proposed heat sink consists of 20 microchannels at background zone and 143 pin-fins at hotspot zone. Therefore, the effect of parameters including geometrical properties (pin-fin shape, pin-fin angle and microchannel wall wave amplitude), Reynolds number and hotspot heat flux on different decisive parameters of heat sinks are investigated. Parameters such as average pressure drop, pumping power, mean absolute temperature difference (MATD) at background zone, MATD at hotspot zone and thermal resistance are considered as performance parameters. The results show that rectangular pin-fin with rounded edges have better thermal performance than NACA airfoil. Besides, increasing the NACA airfoil angle increases the heat transfer and consequently leads to decrease in hotspot temperature. Also, numerical results show that increasing the wall wave amplitude increases the heat transfer rate.

Proposing a novel passive vascular self-cooling system

In this study, an innovative system is introduced to cool down the electronic components in the case of a malfunction of the equipment. A rectangular piece is considered in which heat is generated, while parallel channels are embedded into it to cool the element. In some of these channels (active channels), the cooling fluid flows, while in others (passive channels) fluid is stationary. The active and passive channels are placed alternately and separated by micro-thermostats. When malfunction happens, the heat flux is increased in an arbitrary spot of the piece, opening the closest thermostat and turning the adjacent passive channel into active channel. Therefore, the coolant flow at that portion is increased which dissipates the surcharge heat. The fluid flow is steady and laminar. The thermal entry length is considered, and the effect of local pressure loss is studied. The governing equations are resolved, analytically. Five different cases are studied. At three cases, one hot spot occurs at different locations; while at the other two cases, two hot spots happen simultaneously over the electronic board. Results show that invoking the recommended system at a malfunction situation can reduce the maximum temperature of the electronic piece up to 13.3, 15.2, 17.2, 19.3 and 17.0 °C for cases I–V, respectively; for hot spot heat flux 40 kW m−2.

Development and application of a solid-state fan for enhanced heat dissipation

The miniaturization and high integration of electronic devices require efficient heat transfer enhancement. The solid-state fan (SSF) based on corona discharge is a good candidate. The SSF shows advantages in energy consumption, size, cost, and operability et al. compared to traditional cooling systems. In this paper, a high performance SSF was proposed and developed for heat transfer enhancement. The generation of corona wind in SSF was explored theoretically, and a velocity correction method was proposed. The operating durability was improved under the action of carbon nanotube and manganese dioxide. The structure and electrical parameters of SSF can be optimized to obtain higher corona wind velocity. A 3.96 m/s corona wind velocity was obtained for the optimized SSF. The prototype of SSF shows better cooling performance for both uniform heat flux and hot spot heat flux. A temperature drop of 22.3 °C can be obtained for a light-emitting diode (LED) at the applied voltage of 6 kV, and the luminous flux decreased by only 1.5%, which is a satisfactory result. A coated SSF can increase the corona wind velocity at the same voltage and minimize the ozone generation to prolong the service life.

Experimental Study of a Single Microchannel Flow Under Nonuniform Heat Flux

Abstract Nonuniform heat fluxes are commonly observed in thermo-electronic devices that require distinct thermal management strategies for effective heat dissipation and robust performance. The limited research available on nonuniform heat fluxes focus mostly on microchannel heat sinks while the fundamental component, i.e., a single microchannel, has received restricted attention. In this work, an experimental setup for the analysis of variable axial heat flux is used to study the heat transfer in a single microchannel with fully developed flow under the effect of different heat flux profiles. Initially, a hot spot at different locations, with a uniform background heat flux, is studied at different Reynolds numbers, while varying the maximum heat fluxes in order to compute the heat transfer in relation to its dependent variables. Measurements of temperature, pressure, and flow rates at a different locations and magnitudes of hot spot heat fluxes are presented, followed by a detailed analysis of heat transfer characteristics of a single microchannel under nonuniform heating. Results showed that upstream hotspots have lower tube temperatures compared to downstream ones with equal amounts of heat fluxes. This finding can be of importance in enhancing microchannel heat sinks effectiveness in reducing maximum wall temperatures for the same amount of heat released, by redistributing spatially fluxes in a descending profile.

Numerical and experimental study of heat-transfer characteristics of needle-to-ring-type ionic wind generator for heated-plate cooling

Ionic wind generators have shown significant application potential in devices for cooling, air actuation, and flow control. In this study, a needle-to-ring electrode ionic wind generator with optimized parameters was employed to cool a heated copper plate. A three-dimensional numerical simulation was conducted to obtain the electric, flow, and temperature fields of the ionic wind generator. To verify the ionic wind generator's capacity to cool the heated plate, an ionic wind generator prototype was fabricated and experimentally tested. The temperature distribution of the plate heated by a uniform distributed heat flux and non-uniform heat flux with a local hot spot was analyzed. Results show that the applied voltage should be less than the threshold voltage of spark discharge to ensure effective and stable operation of the ionic wind generator. When the plate is heated by a uniform heat flux, the temperature distribution in most areas around the center of the plate is relatively uniform. If a hot spot exists, the temperature of the central plate is higher than that of the surrounding areas, and the radial temperature difference gradually increases with the increase of the hot-spot heat flux. Moreover, the high-temperature area in the center of the plate gradually expands with increasing hot-spot radius. Besides, the increase in the copper plate thickness has little influence on the final temperature distribution. The heated plate with a uniform heat flux below 2 kW/m2 could be cooled to below 80 °C by the ionic wind generator at an applied voltage of 11 kV. When the plate is heated by a non-uniform heat flux with a hot spot, compared with the experimental results of natural convection, ionic wind can effectively reduce the temperature of the plate (a temperature drop of at least 45 °C was observed). This study provides a potential solution for commercial chip cooling with needle-to-ring-type ionic wind generators.

Characterization of hierarchical manifold microchannel heat sink arrays under simultaneous background and hotspot heating conditions

A hierarchical manifold microchannel heat sink array is fabricated and experimentally characterized for uniform heat flux dissipation over a footprint area of 5 mm × 5 mm. A 3 × 3 array of heat sinks is fabricated into the silicon substrate containing the heaters for direct intrachip cooling, eliminating the thermal resistances typically associated with the attachment of a separate heat sink. The heat sinks are fed in parallel using a hierarchical manifold distributor that delivers flow to each of the heat sinks. Each heat sink contains a bank of high-aspect-ratio microchannels; five different channel geometries with nominal widths of 15 μm and 33 μm and nominal depths between 150 μm and 470 μm are tested. The thermal and hydraulic performance of each heat sink array geometry is evaluated using HFE-7100 as the working fluid, for mass fluxes ranging from 600 kg/m2 s to 2100 kg/m2 s at a constant inlet temperature of 59 °C. To simulate heat generation from electronics devices, a uniform background heat flux is generated with thin-film serpentine heaters fabricated on the silicon substrate opposite the channels; temperature sensors placed across the substrate provide spatially resolved surface temperature measurements. Experiments are also conducted with simultaneous background and hotspot heat generation; the hotspot heat flux is produced by a discrete 200 μm × 200 μm hotspot heater.Heat fluxes up to 1020 W/cm2 are dissipated under uniform heating conditions at chip temperatures less than 69 °C above the fluid inlet and at pressure drops less than 120 kPa. Heat sinks with wider channels yield higher wetted-area heat transfer coefficients, but not necessarily the lowest thermal resistance; for a fixed channel depth, samples with narrower channels have increased total wetted areas owing to the smaller fin pitches. During simultaneous background and hotspot heating conditions, background heat fluxes up to 900 W/cm2 and hotspot fluxes up to 2700 W/cm2 are dissipated. The hotspot temperature increases linearly with hotspot heat flux; at hotspot heat fluxes of 2700 W/cm2, the hotspot experiences a temperature rise of 16 °C above the average chip temperature.

Integrated Circuit Cooling Using Heterogeneous Micropin-Fin Arrays for Nonuniform Power Maps

As microelectronic system density continues to increase, cooling with conventional technologies continues to become more challenging and is often a limiter of performance and efficiency. The challenge arises due to both large heat fluxes generated across entire chips and packages, and localized hotspots with even higher heat flux. In this paper, nonuniform micropin-fin heat sinks are investigated for the cooling of integrated circuits with nonuniform power maps. Four heterogeneous micropin-fin samples were fabricated and tested in single-phase experiments with deionized water to investigate the effectiveness of local micropin-fin clustering for the cooling of hotspots. Cylindrical and hydrofoil micropin-fins were tested, as well as two types of heterogeneous arrays: those with pin-fins clustered directly over the hotspot and those with the high density cluster spanning the entire width of the channel to prevent flow bypass around the cluster. Samples were tested with a uniform nominal heat flux of 250 W/cm2 as well as a hotspot heat flux of 500 W/cm2. Local micropin-fin clustering was found to be an effective method of reducing local thermal resistance with a modest pressure drop penalty.