Title: Heat discharger suitable for application to heat pipes
Abstract: One object of the present invention is to realize a heat discharger having a high precision and in which heat conduction efficiency is maintained at the bonding between the heat pipe and heat sink. A heat discharger comprises a heat pipe and a heat sink formed separately from the heat pipe and bonded to the heat pipe via solder. The contact surface portion between the heat pipe and the solder and the contact surface portion between the heat sink and the solder are made of a wettable material having a wettablility such that the contacting angle with respect to the solder is 90 degrees or less.
Patent Number: 6,994,153 Issued on 02/07/2006 to Nomura
| Inventors:
|
Nomura; Takehide (Tokyo, JP)
|
| Assignee:
|
Mitsubishi Denki Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
231240 |
| Filed:
|
August 30, 2002 |
Foreign Application Priority Data
| Dec 28, 2001[JP] | 2001-399650 |
| Current U.S. Class: |
165/133; 165/104.21; 165/104.33; 165/185; 165/906; 228/111.5 |
| Current Intern'l Class: |
F28F 13/18 (20060101) |
| Field of Search: |
165/41,104.33,104.21,104.26,47,185,133,906
428/552
228/111.5
|
References Cited [Referenced By]
U.S. Patent Documents
| 5759707 | Jun., 1998 | Belt et al.
| |
| Foreign Patent Documents |
| 60-49862 | Mar., 1985 | JP.
| |
| 7106479 | Apr., 1995 | JP.
| |
| 9-42870 | Feb., 1997 | JP.
| |
| 10-098142 | Apr., 1998 | JP.
| |
Other References
Richards, B. P., et al., "An Analysis of the Current Status of Lead-Free Soldering",
Jan. 1999.
Fusion Incorporated, "Paste Brazing & Soldering Alloys", 1996, pp. 1-18 (Document 1).
"Fusion No. 450" (Document 2).
Mitsubishi Electric Corporation, "Satellite-Borne Equipments" (Document 3).
|
Primary Examiner: Ciric; Ljiljana
Attorney, Agent or Firm: Buchanan Ingersoll PC
Claims
What is claimed is:
1. A heat discharger comprising:
a heat pipe; and
a heat sink formed separately from the heat pipe and bonded to the heat pipe
via a solder, wherein
a contact surface portion between the heat pipe and the solder and a contact
surface portion between the heat sink and the solder each being made of a wettable
material having a wettability such that the contacting angle between each of the
contact surface portions and the solder is 90 degrees or less.
2. A heat discharger according to claim 1, wherein the contact surface portions
between the heat pipe and the solder and between the heat sink and the solder are
formed by a coating which is made of the wettable material.
3. A heat discharger according to claim 1, wherein
in the heat pipe, only the contact surface portion is made of the wettable material; and
the heat sink is made entirely of the wettable material.
4. A heat discharger according to claim 1, wherein the wettable material includes
at least one of copper, tin, and nickel.
5. A heat discharger according to claim 1, wherein penetrating holes are provided
in the heat sink in a direction perpendicular to the contact surface portion.
6. A heat discharger according to claim 1, wherein the ratio between the thickness
of the heat sink and the wall thickness of the heat pipe is 2.5 or greater.
7. A heat discharger according to claim 1, wherein the solder is a low temperature solder.
8. A heat discharger according to claim 1, wherein the solder melts at a temperature
of approximately 200° C.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat discharger, and, in particular, to a
heat discharger suitable for application in heat pipes intended for artificial
space satellites.
2. Description of the Related Art
Most space satellites in earth orbit are provided with a network of heat pipes
for conducting heat. Such a network of heat pipes is provided so that the heat
locally generated or accumulated, such as absorbed radiant heat from the sun, in
one section of the satellite can be conducted through the heat pipes to sections
in which heat is not accumulated. Heat sinks for discharging heat are provided
for the heat pipes so that the heat conducted via the heat pipes can be radiated
away via the heat sinks. The heat pipe and heat sink are integrally formed by extrusion
so that the heat from the heat pipe is efficiently conducted to the heat sink.
There has, however, been a tendency for the amount of heat generated by installed
electronic equipment to increase as a result of increases in size and complexity
of satellites, creating a need to increase the size of the heat sink as a countermeasure
against the increased amount of generated heat.
However, when the heat sink and heat pipe are integrally formed through
extrusion of aluminum, as shown in FIG. 20, if the thickness T
1 of the heat
sink is equal to or greater than 2.5 times the wall thickness T
2 of the
heat pipe, the material flows towards the heat sink (shown by an arrow a in FIG.
20) because of the degree of flow of aluminum. Therefore, there had been a problem
in that sections corresponding to the heat pipe could not be formed.
To this end, separately forming the heat sink and heat pipe and then welding
them
together has been proposed in consideration of the heat conduction efficiency.
However, because, in order to reduce weight, heat pipe is primarily made of aluminum,
application of heat generates strain, making welded aluminum pipe unsuitable for
equipment for use in outer space, which requires extremely high precision in assembly.
SUMMARY OF THE INVENTION
The present invention was conceived to solve the problems in the related art
and one object of the present invention is to realize a heat discharger having
high precision while maintaining heat conduction efficiency in the bonding between
a heat pipe and a heat sink.
In order to achieve at least this object, according to the present invention,
there is provided a heat discharger comprising a heat pipe and a heat sink formed
separately from the heat pipe and bonded to the heat pipe via solder, wherein the
contact surface portion between the heat pipe and the solder and the contact surface
portion between the heat sink and the solder are made of a wettable material having
a wettablility such that the contacting angle with respect to the solder is 90
degrees or less.
According to another aspect of the present invention, it is preferable
that, in the heat discharger, the contact surface portions between the heat pipe
and the solder and between the heat sink and the solder are formed by a coating
which is made of the wettable material.
According to yet another aspect of the present invention, it is preferable
that, in the heat discharger, only the contact surface portion is made of the wettable
material in the heat pipe, while the heat sink is made entirely of the wettable material.
According to a further aspect of the present invention, it is preferable
that, in the heat discharger, the wettable material includes at least one of copper,
tin, and nickel.
According to still another aspect of the present invention, it is preferable
that, in the heat discharger, penetrating holes are provided in a direction perpendicular
to the contact surface portion.
According to another aspect of the present invention, it is preferable
that, in the heat discharger, the ratio between the thickness of the heat sink
and the wall thickness of the heat pipe is 2.5 or greater.
According to another aspect of the present invention, it is preferable
that, in the heat discharger, the contact surface portions between the heat pipe
and the solder and between the heat sink and the solder have shapes that engage
each other.
According to another aspect of the present invention, there is further
provided a heat discharger comprising a heat pipe and a heat sink formed separately
from the heat pipe and brazed to the heat pipe, wherein the heat pipe is thermally treated.
According to the present invention, the heat conduction efficiency and
bonding strength can be simultaneously improved at the bonding between a heat sink
and a heat pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing a satellite to which the present invention
is applied.
FIG. 2 is a schematic view showing a structure of a heat pipe.
FIG. 3 is a schematic view for explaining a heat pipe.
FIG. 4 is a schematic view showing an application example of the present invention.
FIG. 5 is a schematic view enlarging the section for which the present invention
is applied.
FIG. 6 is a first cross sectional diagram showing a first embodiment of the
present invention.
FIG. 7 is a second cross sectional diagram showing the first embodiment of the
present invention.
FIG. 8 is a schematic view showing a second example in which the present invention
is applied.
FIG. 9 is a schematic view for explaining the wettability of solder.
FIG. 10 is a schematic view showing a structure of a heat sink.
FIG. 11 is a schematic view showing a first image of the soldered portion captured
through X ray imaging.
FIG. 12 is a schematic view showing a second image of the soldered portion captured
through X ray imaging.
FIG. 13 is a graph showing the separation strength.
FIG. 14 is a graph showing the thermal resistance for cases where bonding is
effected by a solder and by an adhesive.
FIG. 15 is a graph showing the shearing strength for cases where bonding is
effected by a solder and by an adhesive.
FIG. 16 is a cross sectional diagram showing a second embodiment according to
the present invention.
FIG. 17 is a cross sectional diagram showing a third embodiment according to
the present invention.
FIG. 18 is a cross sectional diagram showing a fourth embodiment according to
the present invention.
FIG. 19 is a schematic view showing another embodiment.
FIG. 20 is a schematic view for explaining integral formation of a heat sink
and a heat pipe by extrusion.
DESCRIPTION OF PREFERRED EMBODIMENTS
Embodiment 1
FIG. 1 shows a space satellite which comprises a container
16 in which
electronic equipment for controlling the satellite are provided, a solar panel
17 for obtaining power by photoelectrically converting the sunlight, and
an antenna
18 for transmitting electric waves to the earth.
Because the satellite must be lightweight and have high durability, a lightweight
member is used which comprises a honeycomb structure in which a plurality of aluminum
plates are formed with a predetermined gap to form a beehive-like structure. For
the container
16, approximately 60 heat pipes are provided for heat conduction.
As shown in FIG. 2, the heat pipe
1 is made of a hollow aluminum member
with a cross section having a quadrilateral outer periphery and a circular inner
periphery. In the heat pipe
1, a plurality of channels or "wicks"
20
are provided on the inner surface along the longitudinal direction of the heat
pipe
1 in a predetermined space in between. Also, a heat sink
2 for
discharging heat is provided on the outer side surface of and at one end of the
heat pipe
1. In consideration of use in outer space, ammonia is sealed inside
the heat pipe
1 in the present embodiment. This may not be the case in devices
intended for use in other environments.
As shown in FIG. 3, ammonia sealed in the heat pipe
1 is vaporized to
absorb
heat at one end of the heat pipe
1 which is heated. This ammonia flows to
the other end which has a lower temperature and is liquefied on the inner surface
of the other end, so that heat is discharged via the heat sink
2. The liquefied
ammonia then flows towards the one end through the capillary action of the wicks
20 formed on the inner surface of the heat pipe
1. Therefore, the
heat pipe is configured to conduct heat from one end to the other by ammonia circulating
inside the heat pipe while absorbing and discharging heat.
FIG. 4 shows an example of the actual use of the heat pipe
1. As shown
in FIG. 4, in some cases, a heat pipe
7 (hereinafter referred to as "connective
heat pipe") may be mounted on panels
5a and
5b onto
which solar panels
17 are mounted. The present embodiment will be described
using this example.
FIG. 5 shows the connection between the connective heat pipe
7 and the
panel
5a. In order to facilitate understanding, the cross sections
for the connection between the connective heat pipe
7 and the panel
5a
are shown in FIGS. 6 and 7, which respectively show the cross section along
lines A—A and B—B in FIG. 5.
The panel
5a is a plate-like member in which aluminum plates are
assembled in a honeycomb construction, and this plate-like member will hereinafter
be referred to simply as the "honeycomb structure". Heat pipes
1 (
1a˜
1d)
and heat sinks
2 (
2a˜
2d) are embedded
in panel
5a, and face sheets
6a and
6d made
of aluminum are provided on the honeycomb structure.
On the heat pipe
1a, heat sinks
2 (
2a˜
2d)
and heat pipes
1 (
1b˜
1d) are provided
in contact with the heat pipe
1a with the heat sink and heat pipe
alternating as heat sink, heat pipe, heat sink, etc. The heat pipes
1b˜
1d
are adhered to the heat pipe
1a perpendicular to the longitudinal
direction of the heat pipe
1a using an adhesive
10 (
10a,
10b, and
10c). As the adhesive
10, an adhesive
material having a heat conductivity of, for example, approximately 1 [W/mK] can
be preferably used.
The heat sink
2 is an aluminum member having a cross section of an approximately
T-shape, and comprises a planer section having a widened portion and a main body
section for supporting the planer section. The heat sink
2 is formed so
that the length (y axis direction) and width (X axis direction) of the main body
section have the same size as the length and width of the surface actually opposing
the heat pipe
1a to which the heat sink
2 is adjacent within
the honeycomb structure. At the ends of the planar section, fasteners
9
(
9a and
9b) are provided at positions which are at
a predetermined distance away from the central axis (y axis direction) of the planer
section. The planer section is hereinafter referred to as "attachment support"
2s.
The face sheet
6a at the side on which the heat sink
2 is
provided has rectangular openings on the surface opposing the attachment support
2s, and the fasteners
9 are exposed through the openings.
As shown in FIGS. 4 through 6, the connective heat pipe
7 is bent into
a C-shaped structure along the wall surface constructed by sandwiching a panel
5c by panels
5a and
5b. On the surface
of the connective heat pipe
7 which is in contact with the panel
5a,
a plate-like member (hereinafter referred to as "attachment")
7s is
integrally formed. At the ends of the attachment
7s, penetrating
holes
7h are provided at positions which are at a predetermined distance
away from the central axis of the attachment (y axis direction). The fasteners
9 of the attachment support
2s and the penetrating holes
7h
of the attachment
7s are provided at corresponding positions.
The connective heat pipe
7 and the heat sink
2 are configured so
that they are joined to each other by screws
8 (
8a,
8b,
8c, and
8d) inserted through the penetrating holes
7h of the attachment
7s of the connective heat pipe
7, such that they join with the fasteners
9 of the attachment support
2s of the heat sink
2.
In addition, the connective heat pipe
7 is also directly joined to heat
pipes
1b˜
1d which are in contact with the heat
sinks
2a˜
2d. This structure allows heat to freely
be conducted between the connective heat pipe
7, heat sinks
2a˜
2d,
and heat pipes
1b˜
1d.
As described above, the heat sinks
2a˜
2d and
the heat pipes
1b˜
1d are also connected to the
heat pipe
1a. With such a structure, it is possible to allow heat
to be freely conducted between the heat sinks
2a˜
2d
and heat pipes
1b˜
1d and heat pipe
1a.
Therefore, the heat pipe
1a can receive heat which is conducted
from the connective heat pipe
7 via the heat sinks
2a˜
2d
and heat pipes
1b˜
1d or heat which is conducted
from the heat pipes
1b˜
1d, and discharge the
heat via the panel
5a. In this process, the heat sinks
2 also
discharge a portion of the received heat.
Because a plurality of heat pipes
1a reprovided in combination,
even if one of the heat pipes fails, heat can be conducted through the other heat
pipes, and thus, the structure is internally redundant and highly resistant to failure.
As described, in an satellite, heat generated within the satellite is conducted
between a plurality of heat pipes
1 (
1a,
1b˜
1d)
and heat sinks
2 which are joined, and is radiated into space. An example
procedure for discharging, into space, the heat generated within the satellite
will now be described.
A first example concerns a case in which one of the panels of the satellite is
heated and the generated heat is radiated from another panel.
More specifically, when sunlight is incident on the panel
5a of
the satellite, heat is accumulated in the panel
5a onto which the
sunlight is incident, and a temperature difference is created between the panel
5a and another panel
5b. Therefore, in the satellite,
the panel
5a becomes a high temperature portion and the panel
5b
becomes a low temperature portion. The heat of the panel
5a is
transmitted via the connective heat pipe
7 connected to both the heat pipes
embedded within the panels
5a and the heat pipes embedded within
the panel
5b, and then radiated into space from the panel
5b.
A second example concerns a case as shown in FIG. 8 in which heat generated by
electronic equipment
14 attached to a panel
5 is discharged from
another panel.
More specifically, when the temperature of the panel
5 is higher than
that of the connective heat pipe, the heat generated from the electronic equipment
14 is conducted through heat pipes embedded in the panel
5 (not shown)
directly below the mounted electronic equipment
14 to the heat pipe
1a.
A portion of the heat is further conducted to the connective heat pipe through
the heat pipe
1b or the like and another portion of the heat is further
conducted to the connective heat pipe through the heat sinks
2a,
2b, etc. Ultimately, the heat is discharged into the space from another
panel provided at the side opposite that of the panel
5.
When, on the other hand, the temperature of the panel
5 is less than
that of the connective heat pipe, the process is reversed. In other words, a portion
of the heat transported by the connective heat pipe is transmitted to the heat
pipes
1b, etc., and the remaining heat is transmitted to the heat
pipe
1a via the heat sinks
2a,
2b, and
etc., so that the heat is diffused in the panel
5 and radiated into space.
In such a structure, the heat pipe
1a and the heat sinks
2a˜
2d
are bonded by a low temperature solder
4 (
4a˜
4d).
Moreover, copper coatings
3 (
3a˜
3h) as
a wettable material are formed on the contact surface between the heat pipe
1a
and the low temperature solder
4 and on the contact surface between
the heat sinks
2a˜
2d and the low temperature
solder
4.
The copper coating
3 has good wettability with respect to the low temperature
solder, and, as shown in FIG. 9, the contact angle with respect to the solder at
the contact surface with the low temperature solder is 90 degrees or less. The
copper coatings
3 are formed through a plating process.
Therefore, in the first embodiment, the heat pipe
1a and
the heat sinks
2 are bonded by forming copper coatings
3 on the surfaces
of the heat pipe
1a and of the heat sinks
2 that oppose each
other when bonded (hereinafter, these surfaces are referred to as a "bonding surface")
and uniformly distributing low temperature solder
4 on the bonding surfaces,
so that the bonding surfaces can be bonded over the entire surface and the bonding
strength (that is, the strength necessary to separate the bonded members) can be improved.
In the first embodiment, by forming copper coatings
3 on the bonding surface
between the heat pipe
1a and heat sinks
2 and the low temperature
solder
4, it is possible to prevent corrosion resulting from a potential
difference between the aluminum heat pipe
1a or heat sinks
2
and the low temperature solder
4.
Furthermore, because the low temperature solder
4 is a lead-free
solder (for example, having a composition of 96.5% tin and 3.5% silver) and melts
at a temperature of approximately 220° C., the solder has a characteristic
that it can be bonded at a temperature lower than a mid temperature solder or a
high temperature solder.
On the other hand, the heat pipe
1a and heat sinks
2 which
are made of aluminum and which are to be soldered by the low temperature solder
4 have a characteristic that when they are exposed to a high temperature
such as 400° C. or higher, the heat pipe
1a and heat sinks
2
are annealed, and the strength rapidly falls to a strength corresponding to O condition
(low strength material).
Therefore, in the first embodiment, by bonding the heat sinks
2
and the heat pipe
1a through low temperature solder
4, the
heat sinks
2 and the heat pipe
1a can be bonded while maintaining
the strength.
As a method for recovering the reduced strength of aluminum, for example, a method
known as thermal treatment is sometimes employed. In this method, aluminum is rapidly
heated to a temperature of approximately 520° C., rapidly cooled, and then
heated for a predetermined amount of time at a temperature of approximately 180°
C. However, when the strength between the heat pipe
1a and the heat
sinks
2, reduced by the effects of soldering, is recovered through this
method, there is a problem in that the soldered portions are damaged or destroyed
by the heating, and therefore this thermal treatment cannot be used in conjunction
with the present embodiment.
Also, the low temperature solder
4 has a thermal conductivity of 30˜50
[W/mK] and has a characteristic that it can be drawn to a thickness of several
tens of micrometers. Because of this, the thermal resistance at the bonding surface
between the heat sinks
2a˜
2d and the heat pipe
1a is very small compared to the thermal conductivity of the adhesive
as described above. The specific value for the thermal resistance is less than
0.03 [° C./W] per unit bonding area (1 cm
2), which is significantly small.
For example, even when an adhesive with good thermal conductivity (hereinafter
referred to as "thermally conductive adhesive") is used, the actually measured
value for the thermal conductivity of the thermally conductive adhesive is only
about 1 [W/mK]. In addition, because such a thermally conductive adhesive has a
high viscosity, it is difficult to draw the thermally conductive adhesive into
a thin film. In fact, the thickness can be reduced only to approximately 0.2 [mm].
Therefore, the thermal resistance of the thermally conductive adhesive can be reduced
only to approximately 2 [° C./W] per unit area (1 cm
2). If the
thickness of the thermally conductive adhesive is greatly reduced, the bonding
strength would be reduced.
Although, among adhesive materials, an epoxy-based adhesive which has a
high bonding strength can be thinned to a thickness of approximately 0.1 [mm],
the thermal conductivity of such adhesive is only approximately 0.2 [W/mK], and,
thus, the thermal resistance is approximately 5° C./W per unit area (1 cm
2).
Therefore, in the first embodiment, by bonding the heat sinks
2
and the heat pipe
1a using the low temperature solder
4, it
is possible to increase the bonding strength between the heat sinks
2 and
the heat pipe
1a, and, at the same time, to decrease the thermal resistance.
In the first embodiment, because ammonia is used as an operational fluid for
conducting
heat in the heat pipes
1, the heat sinks
2 must be soldered to the
heat pipe
1a before ammonia is sealed in the heat pipes
1.
Next, the thermal resistance and the bonding strength between the connective
heat pipe
7 and the heat pipe
1a will be described.
As shown in FIG. 7, the thermal resistance between the connective heat pipe
7
and the heat pipe
1a comprises a first serially connected thermal
resistance of the low temperature solder
4 and the heat sink
2 and
second serially connected thermal resistance of heat pipe
1 and the adhesive
10, the first and second serially connected thermal resistances being connected
in parallel.
With respect to the first serially connected thermal resistance of the low temperature
solder
4 and the heat sink
2, because the heat sinks
2a˜
2d
are made of aluminum which has a good thermal conductivity, for example, when
the thickness is 15 [mm], the thermal resistance is 1 [° C./W] or less per
unit area (1 cm
2). As described above, the thermal resistance of the
low temperature solder
4 is less than 0.03 [ C./W]. On the other hand, with
respect to the second serially connected thermal resistance of the heat pipes
1b˜
1d
and the adhesive
10, the heat pipes
1 have a thermal resistance
of approximately 3 times that of the heat sinks
2. As described above, the
thermal resistance of the adhesive
10 is approximately 2 [° C./W].
In other words, although the first serially connected thermal resistance of the
low temperature solder
4 and the heat sinks
2 differs from the second
serially connected thermal resistance of the heat pipes
1b˜
1d
and the adhesive
10, the value of the first serially connected thermal
resistance of the low temperature solder
4 and the heat sinks
2 does
not create any problems in practice. Because of this, the low temperature solder
4 and the heat sinks
2 can efficiently conduct heat received from
the connective heat pipe
7 to the heat pipe
1a.
Moreover, because the heat sinks
2 and the heat pipes
1b˜
1d
are directly connected, the heat conducted from the connective heat pipe
7
to the heat pipes
1b˜
1d is conducted to the heat
sinks
2 which are connected to the heat pipes
1b˜
1d.
With such a structure, it is possible to conduct, through the heat sinks
2,
the portion of the heat which is not conducted through the heat pipe
1b˜
1d
to the heat pipe
1a. The conducted heat can be discharged at
the heat sinks
2.
Because the connective heat pipe
7 is only joined to the heat sinks
2, sufficient bonding strength is required between the connective heat pipe
7 and the heat pipe
1a. In other words, the configuration
of the first embodiment results in a relatively heavy load being applied to the
low temperature solder
4. Because of this, a thermally conductive adhesive
can be used as the adhesive
10 for the junction between the heat pipe
1a
and the heat pipes
1b˜
1d. With such a structure,
the bonding between the connective heat pipe
7 and the heat pipe
1a
has sufficient strength and sufficiently low thermal resistance.
In addition, as shown in FIG. 10, a plurality of penetrating holes are formed
as vent holes
30 in the heat sink
2 in a direction perpendicular
to the surface onto which the copper coating
3 is formed. These vent holes
30 allow discharge of gas generated when the low temperature solder
4
is applied. In this manner, the vent holes
30 of the heat sink
2
prevent decrease in the bonding area, that is, decrease in the bonding strength,
caused by accumulation of gas generated when the low temperature solder
4
is applied, around the bonding surface between the heat pipe
1a and
the heat sinks
2.
In the first embodiment, in addition to the manufacturing conditions as described
above, the bonding strength and the heat conductivity can be improved by optimizing
other conditions such as, for example, the selection of an appropriate pasty solder,
the amount of applied pasty solder, flux to be combined, soldering temperature
and temperature raising rate when raising the temperature, heating method of the
solder, thickness of the solder layer, type and thickness of pre-processing coating,
fixing method during the soldering step of the heat pipe and heat sink, and gas
removal method for efficiently removing flux which is gasified.
Experimental results of application of the first embodiment will now
be described.
FIGS. 11 and 12 show states of soldering at the bonding section between the
heat sink
2 and heat pipe
1a obtained by an X-ray analysis.
FIG. 11 shows the state of soldering for a case wherein the heat sink
2
and the heat pipe
1a were bonded under the conditions described above.
FIG. 12 shows the state of soldering for a case wherein the heat sink
2
and the heat pipe
1a were bonded under conditions different from
those described above. In FIGS. 11 and 12, the white area represents the portion
where the heat sink and the heat pipe were soldered and the black area represents
the portion where the heat sink and the heat pipe were not soldered and a gap was
created (this portion is hereinafter referred to as a "void").
As is clear from FIGS. 11 and 12, when the soldering was effected under desirable
conditions, void generation at the bonding section between the heat sink
2
and the heat pipe
1a was inhibited, resulting in improvements in
the bonding area between the heat sink
2 and the heat pipe
1a,
in the bonding strength, and in the heat conduction.
FIG. 13 shows the difference, in terms of the force required to separate the
heat sink
2 and the heat pipe
1a, in the bonding strengths
for cases where the heat sink
2 and the heat pipe
1a were
bonded under desirable conditions and under other conditions. As shown in FIG.
13, when the heat sink
2 and the heat pipe
1a are bonded under
desirable conditions, the separation strength is as much as 4 times the separation
strength for the heat sink
2 and heat pipe
1a bonded under
conditions other than the desirable conditions.
FIG. 14 shows the thermal resistance for cases where the heat sink
2
and the heat pipe
1a were soldered based on the first embodiment
and where the heat sink
2 and the heat pipe
1a are bonded
using an adhesive, and FIG. 15 shows the searing strengths for these two cases.
In the experiments shown in FIG. 14, the overall thermal resistance from the heat
sink surface to the heat pipe was considered.
As shown in FIG. 14, when the heat sink and the heat pipe were bonded using solder,
the thermal resistance is reduced to approximately ⅔ of the thermal resistance
in the case where the heat sink and the heat pipe were joined by an adhesive. Also,
as shown in FIG. 15, when the heat sink and the heat pipe were bonded using solder,
the mechanical strength was approximately twice that of the case where the heat
sink and the heat pipe are joined by an adhesive.
The first embodiment is effective for cases where the thickness T
1 of
the heat sink is 2.5 times or greater than the wall thickness T
2 of the
heat pipe
1 (refer to FIG. 20), that is, when the wall thickness ratio between
the heat sink
2 and the heat pipe
1 is 2.5 or greater. However, the
first embodiment is not limited to such a case, and can be applied to cases where
the wall thickness ratio between the heat sink
2 and the heat pipe
1
is less than 2.5 as long as the heat sink
2 and the heat pipe
1 are
separately formed and then bonded together.
In the first embodiment, a plating process is described as an example in consideration
of the contact between the film and the aluminum heat sink
2 and the aluminum
heat pipe
1. However, other methods for forming a film can be used instead
of the plating such as, for example, metallization or evaporation.
Moreover, although in the first embodiment, a case where copper coatings
3 are formed at the bonding surface between the heat pipe
1 and the
heat sinks
2 before soldering is described, the coating can be made of other
metals such as tin or nickel. Furthermore, the coating can also be made of a mixture
of any two or more of copper, tin, and nickel.
In the example of the first embodiment, a lead-free solder is used in consideration
of the environment, but a tin-lead-based solder (for example, having a composition
of 50% tin and 50% lead) can also be used. The use of tin-lead-based solder (for
example, having a composition of 50% tin and 50% lead) is more advantageous with
respect to the thermal conductivity and the bonding strength between the heat pipe
1 and the heat sink
2, compared to the case where the lead-free solder
is used.
Second Embodiment
FIG. 16 shows a heat pipe according to a second embodiment of the present invention.
The second embodiment differs from the first embodiment in that the heat sink
32
itself is made of copper. In the following, elements identical to those described
in the first embodiment are assigned the same reference numerals and will not be
described again. In the second embodiment, because the heat sink
32 is made
of copper, the process for forming the copper coatings
3 on the heat sink
2 as described in the first embodiment can be omitted. Moreover, there is
no possibility of the vent holes
30 of the heat sink
2 being filled
by the copper coatings
3.
Also, because copper has a thermal conductivity of 300 [W/mK] or greater, which
is greater than the thermal conductivity of aluminum, the thermal resistance can
be approximately halved by forming the heat sink
32 from copper rather than
from aluminum.
Because the heat pipe
1 is made of aluminum in the second embodiment
similar to the first embodiment, it is still preferable that a low temperature
solder
4 be employed.
With the second embodiment, advantages similar to those in the first embodiment
can be obtained.
Third Embodiment
FIG. 17 shows a heat pipe according to a third embodiment of the present invention.
The third embodiment differs from the first embodiment in that channels
12a
and
12b which constitute a first connection section and projections
13a and
13b which constitute a second connection section
are respectively provided at the bonding surface of the heat pipe
1a
and at the bonding surface of the heat sink
2. The channels
12a
and
12b and the projections
13a and
13b
are formed so that they can engage respectively. The elements identical to
those in the first embodiment are assigned the same reference numerals and will
not be described again.
In the third embodiment, heat pipe
1a and heat sink
2 can
be easily positioned for soldering because of the engagement between the channel
12a and the projection
13a and between the channel
12b and the projection
13b.
In the third embodiment, an example is described in which the channels
12a
and
12b are provided on the heat pipe
1a and projections
13a and
13b are provided on the heat sink
2.
However, the configuration can also be reversed, that is the projections
13a
and
13b can be provided on the heat pipe
1 and the channels
12a and
12b can be provided on the heat sink
2.
Moreover, although in the third embodiment, an example is described wherein
two channels
12 and two projections
13 are provided, the present
embodiment is not limited to such a case and the number of channels and corresponding
projections can be different, such as, for example one, three, etc.
Furthermore, in the third embodiment, channels
12 and projections
13 are provided on the heat sink
2 and the heat pipe
1 described
in the first embodiment. The channels
12 and projections
13 may also
be provided on the heat sink
32 and the heat pipe
1 described in
the second embodiment.
With the third embodiment, advantages similar to those in the first embodiment
can be obtained.
Fourth Embodiment
FIG. 18 shows a heat pipe according to a fourth embodiment of the present invention.
The fourth embodiment differs from the first embodiment in that a heat sink
42
and a heat pipe
41 are made of thermally treated aluminum and are brazed
together via an aluminum brazing sheet
11. Because the bonding between the
heat sink
42 and the heat pipe
41 are effected by brazing, no copper
coating is required.
That is, even when the heat sink
42 and the heat pipe
41 which
are made of thermally treated aluminum are brazed at a high temperature exceeding
600 [° C.], because the brazing temperature is higher than the temperature
for the solution treatment, the strength can be recovered through the solution
treatment and the age hardening treatment without the possibility of re-melting,
and thus, strength degradation of the heat pipe material can be avoided.
In the above embodiments, examples are described wherein the heat sinks
2
are provided between the heat pipe
1a and the heat pipes
1b˜
1d,
and the heat sinks
2 and the heat pipe
1a are bonded. In the
present embodiment, as shown in FIG. 19, it is also possible to provide and bond
a heat sink
52 at a branching point of heat pipes
51a and
51b, each having a portion bonded together.
In the above embodiments, examples are shown wherein the heat discharger is used
for heat pipes installed in a space satellite, but, and especially with the present
embodiment, the heat discharger can also be used for heat pipes used for computers
or machine tools used on earth. In particular, the present invention is effective
when used in machines, such as, for example, a large machine tool, in which significant
vibration generated during operation.
*
