Trends in State-of-the-Art Heatsinks andTheir Patent Technologyby Takeshi Hirasawa * and Yoshikatsu Inagaki *In recent years, the performance of electronic equipment improves year by year,
while the equipment continues downsizing. As a result, there is a need for more
efficient dissipation of heat generated by the electronic devices incorporated in the equipment.
Heatsink plays an important role for such performance improvements, making it indispensable
to use high-performance heatsinks suitable for each equipment so as to realize the designand performance required by customers. Accordingly, every heatsink manufacturer earnestly
develops various heatsink technologies, thereby improving heatsinks through application ofthese technologies.
This paper presents technologies for heatsink performance upgrading placing emphasis on
the patents owned by Furukawa Electric, together with explanatory description of the trends instate-of-the-art heatsink technologies.

ABSTRACTINTRODUCTION

In recent years personal computers rapidly improvein performance. While this performance improvementowes much to the development of microprocessor unit(MPU) and graphics processor unit (GPU), it is known
that such development provoked a rapid increase in heatgeneration density. As can be seen from Figure 1, theheat generation density of MPU and GPU has alreadysurpassed that of electric hot plate, and is gradually
approaching that of nuclear fusion reactor. Since therapid increase in heat generation density accompanied
by temperature rises begins to pose limitations on theperformance of not only MPU and GPU but also thatof electronic equipment itself, there is an urgent needfor developing a new cooling technology that does not
impede downsizing and performance upgrading of theseequipment.
In the past decade, development of cooling devices
and systems has made a rapid progress, centering onsuch areas as fan, various fins, graphite sheet, micro
heatpipe (hereafter called µHP), vapor chamber andwater-cooled system 1)~3). Cooling methods may beroughly classified into two types: passive methods using
fan-less heatsinks; and active methods using fan-basedheatsinks and power-driven cooling devices.
The passive devices include graphite sheet, µHP-basedheatsink, and peraflex ® —an advanced vapor chamber; and they have the advantage of maintaining silentoperation of the equipment since no fans are used.
These devices are mainly used in portable PCs having a* Thermal and Antenna Solutions Dept., ElectronicComponents Div., Electronics and Automotive Systems Co.

heat generation rate of not more than 30 W, and in suchapplications, they are required to perform a function ofefficiently diffusing heat over the entire equipment as wellas to be low-profiled and lightweight. Whereas graphite
sheet is superior in terms of lightweight, its thermal conductivity is at most twice that of copper, so that in casewhere a heat dissipation rate in excess of 5 W is required,a hybrid device gains superiority whereby the 1-mm thickheatpipe having an equivalent thermal conductivity of asmuch as some tens to some hundreds times that of copper is combined with a metal sheet. It is expected thatperaflex, an advanced vapor chamber with a thickness ofabout 0.6 mm, will be widely used in future when the heatrate continues to increase while the thickness is strictly
restricted.
The active heatsink system refers to a combination of
fan and heatsink mentioned above, and fins to be mounted behind the fan play an important role since the system���� ���������� ������� �������1.

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Trends in State-of-the-Art Heatsinks and Their Patent Technology

is based on forced air cooling. Most of the heatsinks currently in use can be classified into this category. Since
it is anticipated that the heat generation rate of personal
computers continues to increase while the equipment
are still required to be low in height, light in weight, smallin size as well as low in noise, efforts must be made forthese active heatsinks that constitute the mainstream
to improve themselves to meet these requirements. In
this context, design optimization of active heatsinks has
become a differentiation technology in the sphere of personal computers.
Water-cooled system for notebook PCs is based ona concept of using a pump to circulate working fluid allover the equipment thereby dissipating heat, and its heatdissipating rate (i.e. typically around 30 W) is higher thanthat of the above-mentioned fan-less heatsinks that dissipate heat solely from the keyboard. But it is disadvantageous in terms of long-term reliability —such that it has amoving part like fan, its piping is rather long, and the fluid
decreases due to permeation through the piping— andcost, so that it is anticipated that the system has limited
applications in the immediate future.
Optimally designed heatsinks obviously incorporate
a variety of technologies and patents. Accordingly, thispaper predicts technology development of the heatsink of
the next generation in accordance with the segmentationof height reduction, weight reduction and size reduction.

2.

HEIGHT REDUCTION TECHNOLOGY

In notebook PCs, performance upgrading and height
reduction are progressing in parallel.
While at first fans were mounted in the shape of a box
independently on the heat-diffusion plate and the like,gradually the casing for small fans was integrated in its
lower portion with the heat-diffusion plate. Moreover,there have been many changes including: the material
for fan casing has been changed from resin to metal toimprove thermal performance; the air intake of the fanfrom single-sided to double-sided to increase the airflow
rate, together with the shape from a box to a half cylinder
with a lower flow resistance; and the air exhaust hole fromsingle-sided to double-sided.
Heat-diffusion plates initially used aluminum in the formof die-casts and the like for its advantages in cost andweight, but recently, copper begins to be used for performance improvement.
Fins were integrally formed by die-casting at the beginning, but afterward manufacturing technologies suchas the caterpillar fin technology whereby combined finsare continuously fabricated were developed to enable
narrow-pitched fabrication together with the stacked fintechnology, and currently products using these technologies are emerging as the mainstream.
µHPs that were primarily φ 3 mm in size have grown to
φ 6 mm as the heat rate and the heat density increased,
and they are mostly flattened to approximately 3 mm forapplication. Recently, a heatsink using 1-mm thick heatpipe has reached the level of practical application along

Figure 2

Appearance of vapor chamber.

with a vapor chamber shown in Figure 2 that incorporates
heat-diffusion plate and µHP. The heatsink based on
1-mm thick µHP has achieved a thermal resistance of 1
K/W or less with a thickness of 10 mm including the fins.
Whereas bonding of µHP with fin and heat-diffusion
plate has been carried out by using adhesives or additional covering materials in the beginning, recently manyheatsinks are either directly soldered so as to reduce
thermal resistance or mechanically bonded by caulking.
The company-owned patents that contribute to theheight reduction technology will be described below.
2.1 µHP(1) Japanese Patent 3408033
This patent features prescribing the thickness of theoxide layer inside a µHP, which is essential for assuringlong-term reliability. Referring to the recent trends in thetechnologies of other companies in the same business, it
is inferred that this patent would be extensively used.
(2) Japanese Patents 1942645, 3045491 and 3035772
These patents become necessary for practical application of thin heatpipes having a thickness of less than
2 mm, describing a structure in which wire and the likeis gathered to a part of the pipe cross-section, securing
passages for the working fluid and the vapor separately.
(3) Japanese Patent 3403307
It is crucial for vapor chambers, since they directly cool
MPUs and the like in close contact, to maintain flatnessof the contact surface as well as to prevent dryout evenin case of high heat density. These problems have been
overcome by a supporting post shown in Figure 3 connecting the top and bottom sides of the device, and thistechnology has been incorporated in realizing a vapor
chamber by Furukawa Electric for the world's first practical application.
2.2

Bonding Method and Relative Position ofComponents(1) Japanese Patent 3454761To realize an ideal low-profiled heatsink, it is essentialthat the heatsink has a structure such that a free space isprovided above the air intake of the fan, fins are mounted
in the way of the fan exhaust, and µHPs are bonded —using soldering and the like to effect low thermal resistance bonding— on the upper part of the fins at a loca-

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Trends in State-of-the-Art Heatsinks and Their Patent Technology

Figure 3

Figure 5

Schematic of internal structure of vapor chamber,with a supporting post numbered 15.

Example of mechanical fitting of µHP into fin.

tion higher than the air intake. The patent discloses, as
shown in Figure 4, bonding position of the µHP relative
to each constituting components aiming at obtaining anideal structure for heatsinks. While this patent discloses
an ideal position of the µHP relative to the heat-diffusion
plate, another patent has been filed that features a structure in which a part of the heat-dissipating section is
located higher than the air inlet of the fan.

Figure 6

Schematic of heat-diffusion plate with heatpipe
and fin.

As described above, a variety of technologies areincorporated into low-profiled heatsinks, and they are disclosed in the form of patents.

3.

Figure 4

Ideal positions of heatsink components relative toeach other.

(2) Japanese Patents 3413151 and 3413152
Depending on the location of MPU, it is occasionally impossible to secure a relative position with µHP as
described in the Clause (1). In such cases, as disclosed
in this patent, the µHP is mechanically fitted into the finsso as to enlarge fin area under the limitation of free spacethus achieving a low-profiled, high-performance heatsink.
See Figure 5.
(3) Japanese Patent 3273505
This patent features a heatsink structure whereby
fins and µHPs are mounted on a heat-diffusion plate as
shown in Figure 6.

WEIGHT REDUCTION TECHNOLOGY

Those heatsinks presented in Figures 4 through 6
are low-profiled heatsinks with excellent thermal performance. But since they are mainly made of copper,
problems arise about the cost and weight. To solve theseproblems, development of new heatsinks is under way,in which all the materials except for µHPs are changed toaluminum without degrading the thermal performance. It
has been confirmed, through various developmental studies, that the aluminum heatsink shown in Figure 7 canachieve weight reduction without sacrificing its thermal
performance.
The use of caulking can firmly fix the heat-receiving
block and the µHP, resulting in, although somewhat
depending on the caulking conditions and the structure, alower thermal resistance than soldering. However, despite
the fact that caulking itself is rather easy to carry out, caremust be taken to use right dimensions and structures forcaulking so as to avoid the possibilities of defective caulking such as buckling of µHP and gapping between theblock and the µHP. Aluminum heatsinks manufactured by

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fan for GPUs, so that noise caused by the fan is drawing
attention as a problem. This has resulted in a need forgreater heatsinks, but since simple size increase would
not improve thermal performance notwithstanding weightincrease, tower-type heatsink incorporating µHP has been
put into practical use. In this heatsink, technologies disclosed in Japanese patents 2685918 and 3106428 havebeen applied to realize a lightweight, compact heatsink.
See Figure 9.

Figure 7

Heatsink with aluminum fin and aluminumheat-receiving block.

good caulking can reduce the cost as well as weight by
20~40 % compared with the copper heatsinks describedin Chapter 2.
On the other hand, bonding of µHP and fins can yield,
by press fitting the µHP into each fin, a thermal resistanceequivalent to that of soldering. Since each fin is small insize, fin efficiency shows little difference notwithstanding whether copper or aluminum is used as the material,
resulting in no appreciable difference in thermal performance.
Japanese patents 3268734, 3010181 and 3438944
have supported the realization of this heatsink, disclosing
various caulking methods and structures that contributeto performance improvement.

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Figure 94.

SIZE REDUCTION TECHNOLOGY

Whereas in Chapters 2 and 3 the height and weight
reduction technologies for notebook PCs were described,
in this Chapter 4 downsizing technology incorporated
with weight reduction technology for desktop PCs will bepresented. Generally speaking desktop PCs afford ample
space, so that it is a normal practice to mount just above
the MPU a combination of fin array —e.g. extruded fin
with copper insertions, soldered copper fins and Crimped
fin® — and fan, as shown in Figure 8.
Recently, heat generation rate of GPUs has rapidly
increased as well as MPU necessitating heatsinks with5.

Schematic of tower-type heatsink.

CONCLUSION

This paper has presented state-of-the-art heatsinks andtheir technologies, which may be summarized as follows.
(1) Thin heatpipe to realize low-profiled heatsinks(2) Caulking techniques to reduce thermal resistance(3) Aluminum heatsink contributing to the weight
reduction of heatsinks(4) Tower-type heatsink to realize space-savingheatsinks
We intend to evolve these achievements further towardpractical application of high-performance heatsinks thatare lower-profiled, lighter and more compact.

REFERENCES
1) HAITAKKU, 2003-1, 13. (in Japanese)2) M.Oomi et al.: Furukawa Review 21 (2002), 69.
3) J.Niekawa et al.: Introduction to Micro-Heatpipe and Heat
Dissipation Technology, Nikkan Kogyo Shimbun Publishing. (inJapanese)
4) New Products, Furukawa Review, 25 (2004) 64.

Figure 8

Heatsink for desktop PC.

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