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Practical Application of the World’s Lowest-Profiled Heatsink

1.

INTRODUCTION

As computers improve in speed and performance inrecent years, MPU (Micro Processing Unit) that constitutes the core component increases in heat generation,
rendering thermal countermeasures indispensable. Thus
it can be said that heat-dissipation has become a key
technology particularly for electronic equipment withlimited case volumes such as notebook PCs, DVD players, digital cameras, mobile phones, game machinesof the next generation and digital home appliances.
Accordingly, Furukawa Electric has been offering to themarket comprehensive heat-dissipating technologies thatmake efficient use of heatpipes.
More specifically, from the standpoint of heat generation, whereas high-end MPUs continue to increase in
the heat generated, power-saving MPUs are also being
developed, whereby the generated heat tends to be suppressed while the performance carries on to improve.
Recently electronic equipment with these MPUs withsmall heat generation onboard acquire a good reputationfrom the marketplace.
Meanwhile, these electronic equipment with powersaving MPUs onboard are required to have such features
as portability, space saving, lightweight and low noise
as well as small power consumption. In order to satisfy
all these requirements, we have developed the world’s
lowest-profiled heatsink (as of March 1, 2005; to the bestof our knowledge) that employs an improved version of
the 1-mm thick heatpipe we have already developed.

2.

STRUCTURE

Heatpipes designed for room temperature operation normally consist of a copper container and a working fluid ofwater, and the inside is depressurized virtually to a vacuum. When heat is applied to the one end (evaporator section) of the heatpipe, the working fluid nearby vaporizes
to deprive the region of a vaporization heat while simultaneously raising the pressure rapidly, and subsequently
the vaporized working fluid moves to the other end (condenser section) that is low in pressure. Upon reaching thecondenser section, the vapor condenses and liquefies
to release as a latent heat the thermal energy it has carried, and then the liquefied working fluid is refluxed to theevaporator section through a wick which is provided withcapillary mechanism. That is to say, because the working
fluid circulates within the heatpipe taking advantage ofphase change, a large quantity of heat can be transferred
between the points of quite a small temperature difference.
Figure 1 shows the structure of the 1-mm thick heatpipe. The mesh is arranged at the center or the end of thecross section of the flat copper container, thereby separating the passage for the refluxing working fluid and thatfor the vapor, which constitutes the central feature of thisheatpipe. Using such a structure, the vapor passage is
obtained to result in sufficient circulation of the water andvapor even when the heatpipe is flattened to have a total
thickness of 1 mm, making it possible to have an ample
heatpipe function.
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Figure 1

Structure of 1-mm heatpipe.

Recently, we have reviewed the design and material of such heatpipes for optimization, and succeeded
in improving the maximum heat transfer rate and reducing the thermal resistance —both parameters are themost important performance indices for heatpipe— while
maintaining conventional production costs. Due to these
improvements it became possible to apply the upgradedheatpipes to the heatsinks for MPUs where heatpipes
were not applicable before, so that the world’s lowestprofiled heatpipe-based heatsink —including heatpipe, finand fan— has been successfully developed. See Figure 2
for comparison of the heatsinks.

Furukawa Review, No. 27200586

Practical Application of the World’s Lowest-Profiled Heatsink

Figure 23.

Comparison of the profiles of heatsinks withequivalent thermal performance. Above: Developedheatsink, 1.7 mm and 9 mm for the heat-absorbing
section and fins, respectively. Below: Conventionalheatsink, 4.5 mm and 13 mm, respectively. The
widths of the fin assemblies are the same.

PERFORMANCE

Figure 3 and Figure 4 compare the maximum heat transfer rate and thermal resistance of the conventional anddeveloped 1-mm thick heatpipes, respectively. As can beseen from these Figures, the new heatpipe has achieved
substantial improvements over the conventional one—about 70 % in the maximum heat transfer rate andabout 60 % in the thermal resistance. The improvements
made it possible to provide more latitude to the heatsink designs where greater multifunctionality is always
required in a limited space. Below will be described someexamples.
First, the use of 1-mm thick heatpipe allows reduction of the thickness of heatsinks. To provide thermal
performance equivalent to that of a heatsink using the1-mm thick heatpipe developed here, heatsinks using
conventional heatpipes would have to be 2.5 to 4 times
thicker than their counterpart. Specifically, while the heatabsorbing section of the developed heatsink is 1.7 mm
thick —heat receiving plate: 0.5 mm, heatpipe: 1.0 mm,and heatpipe cover: 0.2 mm, that of the conventional one
is approximately 4.5 mm.
Secondly, given a certain cubic measure, heatsinks
using the 1-mm thick heatpipe are superior to those using
conventional heatpipes in terms of thermal performance.
In one example, the use of the heatsink developed here
has achieved experimentally a temperature reduction of10°C in an MPU with an input heat of 27 W. This is dueto the fact that the surface area of the heat-dissipating
fin assembly —a key factor component for heat dissipation— has been increased by as much as the heatpipe
thickness has been reduced, because basically the heatdissipating performance improves by increasing the heatdissipating surface areas, although it is also subject tothe influence of such factors as the pressure loss due toairflow and the airflow behavior. In addition, the improvement in the thermal performance has made it possible, even with a suppressed rotation speed of the fan, toobtain the thermal performance equivalent to that of conventional heatsinks. This eventually leads to the reductionof wind noise and fan motor noise.
To summarize, the significant improvements in the heat-��������� �������
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Figure 3

Comparison of maximum heat transfer rate of 1-mm
thick heatpipes.

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Figure 4

Figure 5Comparison of thermal resistance of 1-mm thickheatpipes.

Appearance of the world’s lowest-profiled heatsink.

pipe has resulted in the performance upgrading of heatsinks overall, thereby succeeding in the development of alow-profiled, high-performance heatsink that is capable ofsolving various problems related with conventional heatsinks.
Figure 5 shows the appearance of the heatsink developed here.

Furukawa Review, No. 27

200587

Practical Application of the World’s Lowest-Profiled Heatsink

For more information, please contact:
Thermal and Antenna Solutions Dept., ElectronicComponents Div., Electronics and Automotive Systems
Co.
TEL: +81-463-24-9784
FAX: +81-463-24-9786

Furukawa Review, No. 27

200588