Thermal Performance of Natural Graphite Heat Spreaders

2005 ◽  
Author(s):  
Martin Smalc ◽  
Gary Shives ◽  
Gary Chen ◽  
Shrishail Guggari ◽  
Julian Norley ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Numerical Models ◽  
Laptop Computer ◽  
Natural Graphite ◽  
Heat Spreader ◽  
Graphite Sheet ◽  
Cooling Fan ◽  
Heat Spreaders ◽  
Graphite Heat

Heat spreaders can be made from natural graphite sheet materials. These spreaders take advantage of the anisotropic thermal properties of natural graphite. Natural graphite exhibits a high thermal conductivity in the plane of the sheet combined with a much lower thermal conductivity through the thickness of the sheet. As a result, a natural graphite sheet can function as both a heat spreader and an insulator and can be used to eliminate localized hot spots in electronic components. In some cases, a natural graphite heat spreader can replace a conventional thermal management system consisting of a heat sink and cooling fan. This paper examines the properties of natural graphite heat spreaders and the application of these spreaders to thermal management problems in laptop computers. The thermal and mechanical properties of natural graphite heat spreaders are presented along with a discussion of how those properties are measured. The use of a natural graphite heat spreader to reduce the touch temperature in a laptop computer is presented. Both experimental techniques and numerical models are used to examine performance of the heat spreader in this application.

Thermal Performance of Natural Graphite Heat Spreaders With Embedded Thermal Vias

2007 ◽  
Author(s):  
Martin Smalc ◽  
Prathib Skandakumaran ◽  
Julian Norley
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Performance ◽  
Numerical Models ◽  
Accelerated Aging ◽  
High Heat ◽  
High Heat Flux ◽  
Natural Graphite ◽  
Heat Spreaders ◽  
Graphite Heat

Natural graphite heat spreaders are in use in electronic cooling applications where heat flux density is low. Natural graphite is an anisotropic material, with a high thermal conductivity in the plane of the spreader combined with a much lower thermal conductivity through its thickness. This low through-thickness thermal conductivity poses a problem when attempting to cool heat sources with relatively high heat flux densities. This problem can be overcome by embedding a thermal via in the graphite material. This via is made from an isotropic material with a thermal conductivity significantly higher than the through-thickness graphite conductivity. This paper examines the thermal performance of a natural graphite heat spreader with an embedded thermal via. The work is primarily experimental although numerical models were used to guide the experiments. The thermal performance of these spreaders is compared to that of spreaders made from conventional isotropic materials. The effect of accelerated aging tests on the performance of these graphite spreaders is reviewed. Finally, two applications are examined; first cooling an ASIC module and second, cooling an FB-DIMM memory card.

Design of Thermal Ground Planes for Cooling of Foldable Smartphones

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Ali Nematollahisarvestani ◽  
Ryan J. Lewis ◽  
Yung-Cheng Lee
Keyword(s):  
Thermal Management ◽  
Temperature Difference ◽  
Ground Plane ◽  
Heat Sources ◽  
Heat Spreader ◽  
Fem Model ◽  
Graphite Sheet ◽  
Promising Solution ◽  
Graphite Heat ◽  
Near Future

Foldable smartphones are expected to be widely commercialized in the near future. Thermal ground plane (TGP), known as vapor chamber or two-dimensional flat heat pipe, is a promising solution for the thermal management of foldable smartphones. There are two approaches to designing a TGP for foldable smartphones. One approach uses two TGPs connected by a graphite bridge and the other approach uses a single, large, and foldable TGP. In this study, different thermal management solutions are simulated for a representative foldable smartphone with screen dimensions of 144 × 138.3 mm2 (twice the screen of iPhone 6 s with a 10 mm gap). In addition, the simulation includes two heat sources representing a main processor with dimensions of 14.45 × 14.41 mm2 and power of 3.3 W (A9 processor in iPhone 6S) and a broadband processor with dimensions of 8.26 × 9.02 mm2 and power of 2.5 W (Qualcomm broadband processor). For the simulation, a finite element method (FEM) model is calibrated and verified by steady-state experiments of two different TGPs. The calibrated model is then used to study three different cases: a graphite heat spreader, two TGPs with a graphite hinge, and a single, large, and foldable TGP. In the fully unfolded configuration, using a graphite heat spreader, the temperature difference across the spreader's surface is about 17 °C. For the design using two TGPs connected by a graphite bridge, the temperature difference is about 7.2 °C. Finally, for the design using a single large TGP with a joint region, the temperature difference is only 1–2 °C. These results suggest that a single foldable TGP or a configuration with two TGPs outperform the graphite sheet solution for the thermal management of foldable smartphones.

Integration of Silver Heat Spreaders in LTCC utilizing Thick Silver Tape in the Co-fire Process

2015 ◽  
Vol 2015 (CICMT) ◽  
pp. 000062-000066 ◽  
Author(s):  
T. Welker ◽  
S. Günschmann ◽  
N. Gutzeit ◽  
J. Müller
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Heat Sink ◽  
Junction Temperature ◽  
Large Area ◽  
Heat Spreader ◽  
Integration Density ◽  
Heat Spreaders ◽  
Cte Mismatch ◽  
Pattern Resolution

The integration density in semiconductor devices is significantly increased in the last years. This trend is already described by Moore's law what forecasts a doubling of the integration density every two years. This evolution makes greater demands on the substrate technology which is used for the first level interconnect between the semiconductor and the device package. Higher pattern resolution is required to connect more functions on a smaller chip. Also the thermal performance of the substrate is a crucial issue. The increased integration density leads to an increased power density, what means that more heat has to dissipate on a smaller area. Thus, substrates with a high thermal conductivity (e. g. direct bonded copper (DBC)) are utilized which spread the heat over a large area. However, the reduced pattern resolution caused by thick metal layers is disadvantageous for this substrate technology. Alternatively, low temperature co-fired ceramic (LTCC) can be used. This multilayer technology provides a high pattern resolution in combination with a high integration grade. The poor thermal conductivity of LTCC (3 … 5 W*m−1*K−1) requires thermal vias made of silver paste which are placed between the power chip and the heat sink and reduce the thermal resistance of the substrate. The via-pitch and diameter is limited by the LTCC technology, what allows a maximum filling grade of approx. 20 to 25 %. Alternatively, an opening in the ceramic is created, to bond the chip directly to the heat sink. This leads to technological challenges like the CTE mismatch between the chip and the heat sink material. Expensive materials like copper molybdenum composites with matched CTE have to be used. In the presented investigation, a thick silver tape is used to form a thick silver heat spreader through the LTCC substrate. An opening is structured by laser cutting in the LTCC tape and filled with a laser cut silver tape. After lamination, the substrate is fired using a constraint sintering process. The bond strength of the silver to LTCC interface is approx. 5.6 MPa. The thermal resistance of the silver structure is measured by a thermal test chip (Delphi PST1, 2.5 mm × 2.5 mm) glued with a high thermal conducting epoxy to the silver structure. The chip contains a resistor and diodes to generate heat and to determine the junction temperature respectively. The backside of the test structure is temperature stabilized by a temperature controlled heat sink. The resulting thermal resistance is in the range of 1.1 K/W to 1.5 K/W depending on the length of silver structure (5 mm to 7 mm). Advantages of the presented heat spreader are the low thermal resistance and the good embedding capability in the co-fire LTCC process.

Fundamental Study on Thermal Characteristics of Heat Spreaders

2011 ◽  
Author(s):  
Yasushi Koito ◽  
Yusaku Nonaka ◽  
Toshio Tomimura
Keyword(s):  
Thermal Management ◽  
Theoretical Study ◽  
Thermal Characteristics ◽  
Thermal Design ◽  
Design Parameters ◽  
Heat Spreader ◽  
Fundamental Study ◽  
Discharge Characteristics ◽  
Heat Spreaders ◽  
Large Heat

A heat spreader is one of the solutions for thermal management of electronic and photonic systems. By placing the heat spreader between a small heat source and a large heat sink, the heat flux is spread from the former to the latter, resulting in a lower thermal spreading resistance between them. There are many types of heat spreaders known today having different heat transfer modes, shapes and sizes. This paper describes the theoretical study to present the fundamental data for the rational use and thermal design of heat spreaders. Two-dimensional disk-shaped mathematical model of the heat spreader is constructed, and the dimensionless numerical analysis is performed to investigate the thermal spreading characteristics of the heat spreaders. From the numerical results, the temperature distribution and the heat flow inside the heat spreaders are visualized, and then the effects of design parameters are clarified. The discussion is also made on the discharge characteristics of the heat spreaders. Moreover, a simple equation is proposed to evaluate the heat spreaders.

Study of Miniaturization of a Silicon Vapor Chamber for Compact 3D Microelectronics, via a Hybrid Analytical and Finite Element Method

2019 ◽  
Vol 6 (5) ◽  
pp. 01-18
Author(s):  
Ma Yue ◽  
Shirazy Mahmoud ◽  
Coudrain Perceval ◽  
Colonna Jean-Phulippe ◽  
Souifi Abdelkader ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Numerical Models ◽  
Computational Cost ◽  
Vapor Chamber ◽  
Cooling Systems ◽  
Heat Spreaders ◽  
Operating Limits ◽  
Silicon Vapor ◽  
Core Height ◽  
Low Computational Cost

The interest in silicon vapor chambers (SVCs) has increased in the recent years as they have been identified as efficient cooling systems for microelectronics. They present the advantage of higher thermal conductivity and smaller form factor compared to conventional heat spreaders. This work aims to investigate the potential miniaturization of these devices, preliminary to integration on the backside of mobile device chips, located as close as possible to hotspots. While detailed numerical models of vapor chamber operation are developed, an easy modeling with low computational cost is needed for an effective parametric study.  Based on the study of the operating limits, this paper shows the thinning potential of a water filled micropillar for a device operating below 10 W and identify the corresponding vapour core height, and wick thickness.

Thermal Enhancement of an LED Light Engine for Automotive Exterior Lighting With Advanced Heat Spreader Technology

2016 ◽  
Author(s):  
Umut Zeynep Uras ◽  
Enes Tamdoğan ◽  
Mehmet Arık
Keyword(s):  
Thermal Conductivity ◽  
Numerical Models ◽  
Maximum Temperature ◽  
Vapor Chamber ◽  
Metal Core ◽  
Heat Spreader ◽  
Printed Circuit ◽  
Thermal Enhancement ◽  
Wide Range ◽  
Light Engine

In recent years, light emitting diodes (LEDs) have become an attractive technology for general and automotive illumination systems. LEDs have been preferable for automobile lighting due to its numerous advantages such as long life, low power consumption, optical control and light quality as well as robustness for high vibration. Thermal management is one of the main issues due to severe ambient conditions and compact volume. Conventionally, tightly packaged double sided FR4 based printed circuit boards are utilized for both driver electronics components and LEDs. In fact, this approach will be a leading trend for advanced Internet of Things (IOT) applications in near future. A series of numerical models are developed to determine the local temperature distribution on both sides of a light engine. Results showed that FR4 PCB has a temperature gradient of over 63°C while the maximum temperature is 105°C. This causes a significant degradation of lifetime and lumen extraction as many LEDs are recommended to be operated below 100°C. In addition to FR4, Aluminum metal core and vapor chamber based advanced heat spreader substrates are developed to obtain thermal impact on the substrate due to a wide range of thermal conductivity of three boards. To mimic real application, two special flex circuits are developed for LEDs and driver circuit. 10 red and 6 amber LEDs at one flex-PCB, and driver components are populated on the other flex-PCB are mounted. Both flex circuits are attached each side of the substrate. Experimental results showed that the local hotspots occurred at FR4 PCB due to low thermal conductivity. Later, a metal core printed circuit board is investigated to minimalize local hot spots. High conductivity metal core PCB showed a 19.9% improvement over FR4 based board. A further study has been performed with an advanced heat spreader based on vapor chamber technology. Results showed that a thermal enhancement of 7.4% and 25.8% over Al metal core and FR4 based boards with an advanced vapor chamber substrate.

scholarly journals Study of Miniaturization of a Silicon Vapor Chamber for Compact 3D Microelectronics, via a Hybrid Analytical and Finite Element Method

2019 ◽  
Vol 7 (6) ◽  
pp. 1-16
Author(s):  
Yue MA ◽  
M. R. S. Shirazy ◽  
Q. Struss ◽  
P. Coudrain ◽  
J.P. Colonna ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Numerical Models ◽  
Computational Cost ◽  
Vapor Chamber ◽  
Cooling Systems ◽  
Heat Spreaders ◽  
Operating Limits ◽  
Silicon Vapor ◽  
Core Height ◽  
Low Computational Cost

The interest in silicon vapor chambers (SVCs) has increased in the recent years as they have been identified as efficient cooling systems for microelectronics. They present the advantage of higher thermal conductivity and smaller form factor compared to conventional heat spreaders. This work aims to investigate the potential miniaturization of these devices, preliminary to integration on the backside of mobile device chips, located as close as possible to hotspots. While detailed numerical models of vapor chamber operation are developed, an easy modeling with low computational cost is needed for an effective parametric study.  Based on the study of the operating limits, this paper shows the thinning potential of a water filled micropillar for a device operating below 10 W and identify the corresponding vapour core height, and wick thickness.

Numerical Analysis of Conduction in a Foam

2002 ◽  
Author(s):  
A. M. Druma ◽  
M. K. Alam ◽  
C. Druma
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Numerical Models ◽  
High Porosity ◽  
Material Microstructure ◽  
Element Analysis ◽  
Empirical Parameter ◽  
Bulk Properties ◽  
Heat Spreaders ◽  
Homogeneous Models

Porous organic materials are being developed for use as insulation, heat spreaders, and compact heat exchanger cores. The bulk properties of such a porous medium are difficult to determine analytically, particularly for the case of high porosity or when the porous material is not isotropic or homogeneous. Models that predict thermal conductivity of foams often use an empirical parameter to account for the effect of pore shape and material microstructure on the conduction process. A finite element analysis has been developed to calculate the thermal conductivity of a porous medium containing micropores. The effective thermal conductivity and the empirical conduction parameter are evaluated by comparing the results of the analytical and numerical models.

Multi-Objective Parameterization of Graphite Heat Spreader for Portable Systems Applications

2007 ◽  
Author(s):  
Arijit Banerjee ◽  
Nikhil Lakhkar ◽  
Shahi Riaz ◽  
Gamal Refai-Ahmed ◽  
Dereje Agonafer
Keyword(s):  
Heat Sinks ◽  
Published Data ◽  
Portable Devices ◽  
Electronic Systems ◽  
Heat Spreader ◽  
Suitable Alternative ◽  
Multi Objective ◽  
Heat Spreaders ◽  
Graphite Heat ◽  
The Cost

The advancement made in portable electronic systems has primarily been due to miniaturization of electronic systems. This in turn leads to an increase in power density which leads to higher temperatures and formation of hot spots. There is a temperature specification of system surfaces for human comfort (such as the surface close to a keyboard on laptops). Challenge in cooling portable devices is that there is not enough room to accommodate heat sinks. It is therefore important to have heat spreaders that can transfer the heat from critical devices to regions where cooling is available. Traditionally, copper has been the best heat spreader due to its high thermal conductivity. However, copper has a relatively high density and correspondingly high weight. Graphite is a suitable alternative. Recent advances in graphite technology have resulted in fairly high conductivity in the planar directions. In spite of these advances, the cost of graphite is an issue. In this paper, a multi-objective parameterization is utilized that considers weight and temperature distribution of the graphite heat spreader as objective parameters. The data is then compared to published data that utilizes graphite in a laptop.

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