Method for manufacturing cooling unit comprising heat pipes and cooling unit

The present invention relates to a cooling unit for electronic devices wherein the manufacturing method comprises the steps of: (a) preparing a plate-type metal block for removing heat generated from an electronic component, the metal block having holes in the thickness part of the metal block and having convex portions formed on one main surface or both main surfaces of the metal block; (b) inserting heat pipes into the holes; and (c) applying a local and two-dimensional force from the surface of the metal block to the convex portions to make the surface flat bringing the outer surface of each heat pipe into close contact with the inner wall of each hole in the metal block.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for manufacturing a cooling unit 
and the cooling unit comprising heat pipes for diffusing heat generated 
from electronic components or the like which has a semiconductor device 
and others mounted thereon and generates heat. 
2. Description of the Related Art 
As a means for preventing electronic equipment from overheating, a 
forced-air cooling system employing an air-cooled fan has been adopted. 
However, in high-density packaging electronic equipment typified by recent 
computers, heat generated by the equipment tends to prominently increase 
because of the high density of heat generating components such as 
integrated circuits (IC) or large scale integration (LSI) mounted in the 
equipment, and the cooling system using the air-cooled fan has a limited 
cooling capability. 
Further, with the rapid advance of reducing the size of electronic 
equipment, a space for mounting the cooling unit becomes smaller within 
the equipment, which makes heat diffusion in the electronic equipment 
difficult. 
As a countermeasure for solving such problems, there has been proposed a 
mechanism by which heat generated by electronic components or electronic 
devices (referred to as electronic components hereinafter) is received by 
a heat conductor and that heat is then removed from the electronic 
components. Such a mechanism is partially put into practical use. 
According to this method, a heat conductive plate or the like is brought 
into contact with the electronic components which must be cooled down and 
heat of the electronic components is diffused to the plate or the like to 
suppress excessive increase in temperature of the electronic components. 
Moreover, the heat diffused to the plate or the like is further diffused 
in the electronic equipment or discharged outside the electronic equipment 
if necessary. 
When bringing the heat conductor into contact with a specific electronic 
component for the purpose of cooling, it is desired to increase the volume 
of the heat conductor to enlarge the heat capacity thereof and to increase 
the area of the heat conductor which is brought into contact with the 
electronic component to increase the speed of transferring heat from the 
electronic component. However, because minimization of electronic 
components have been advanced in recent days, the contact area of such 
components relative to the heat conductor is limited, and use of the 
cooling unit having a large volume is impossible. 
A method for enhancing heat diffusion by attaching heat pipes to the heat 
conductor has been, therefore, proposed. Working liquid that repeatedly 
evaporates and condenses is sealed inside the heat pipe, and heat 
generated from the electronic component is transferred to an evaporation 
part of the heat pipe. The evaporated working liquid is then moved to a 
condensation part to condense in order to discharge heat. Excellent heat 
dissipation can be realized because the speed of the working liquid is 
extremely high. 
FIGS. 14 through 16 show an example of a conventional cooling unit 
utilizing such heat pipes. FIG. 14 is a plan view showing a conventional 
cooling unit; FIG. 15 is a partially enlarged cross-sectional view taken 
along line A--A of FIG. 16; and FIG. 16 is a front view of the cooling 
unit. This cooling unit constitutes heat pipes 1 each of which has a flat 
cross section and has an outer diameter of approximately 2 mm in the 
vertical direction that transverses the length of the pipe and an outer 
diameter of approximately 4 mm in the horizontal direction that 
transverses the length of the pipe, a metal block 2 attached to an 
evaporation part 10 of each heat pipe 1, and radiation fins 3 disposed to 
a condensation part 11 of each heat pipe 1. As for the metal block 2, 
aluminum or aluminum alloy is generally used for reducing the weight and 
size of the cooling unit. Attachment of the heat pipe 1 to the metal block 
2 in the evaporation part 10 is achieved by forming a pipe insertion hole 
21 slightly larger than the flat heat pipe 1 in the metal block 2 in the 
direction of the thickness and inserting the flat heat pipe 1 into the 
pipe insertion hole 21 as shown in FIG. 15. Soldering metal 20 is 
subsequently poured into a gap between the surface of the heat pipe and an 
inner wall of the insertion hole 21 for integration. 
In this-configured cooling unit comprising heat pipes, the main back 
surface of the metal block 2 is brought into contact with each heat 
generation component 5 such as an LSI on a printed board 7 through a high 
heat conductive rubber 6 having a good heat conductivity, and the metal 
block 2 is attached to the printed board 7 in this state. Heat generated 
in the heat generation components 5 heats the evaporation part 10 of each 
heat pipe 1 to evaporate the working liquid sealed inside the pipe 1. This 
increases the vapor pressure in the evaporation part 10 of the heat pipe 1 
so that a vapor flows toward the condensation part 11 where the pressure 
is low. Heat from the vapor moves to the condensation part 11 and is 
transferred to the radiation fins 3 and diffused in the air. Accordingly, 
it is possible to obtain a relatively-small cooling unit having an 
extremely-high radiation performance. 
The metal block 2 and the evaporation part 10 of each heat pipe 1 in the 
above-described cooling unit are provided with heat pipes that are fixed 
by means of the solder alloy 20 as mentioned above. However, when the 
material of the metal block is aluminum or aluminum alloy, an oxide film 
forms on the surface of the metal block preventing the soldering metal 
from being attached thereon and a void or bubble is generated between the 
surface of the heat pipe and the inner wall of the insertion hole, and the 
heat resistance between the heat pipe and the metal block becomes large, 
thereby lowering the cooling characteristic of the unit. Furthermore, the 
pipe insertion hole must be made large to increase the amount of the 
solder to be poured therein in order to suppress generation of the void 
and fix the heat pipe in the pipe insertion hole. In this case, because 
the large specific gravity of the solder metal increases the weight of the 
cooling unit and enlarges the insertion pipe, the thickness of the metal 
block must also be increased, and reduction in the thickness of the 
cooling unit can not be achieved. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a method 
for manufacturing a cooling unit comprising heat pipes which reduces the 
thickness of the metal block resulting in lighter weight of the entire 
unit and decreased heat resistance when connecting the metal block with 
the heat pipes to achieve excellent heat dissipation or heat removal 
performance and to provide a cooling unit. 
According to a first embodiment of the present invention, there is provided 
a cooling unit manufacturing method comprising the steps of: 
(a) preparing a substantially-plate-type metal block for removing heat 
generated from an electronic component, the metal block having holes in 
the thickness .of the metal block into which heat pipes are inserted and 
having convex portions formed on one main surface or both main surfaces of 
the plate-type body corresponding with the holes; 
(b) inserting the heat pipes into the holes for removing heat of the metal 
block; and 
(c) applying local and two-dimensional force from the surface of the metal 
block to the convex portions to make the surface substantially flat after 
inserting the heat pipes into the holes and bringing the outer surface of 
each heat pipe into close contact with the inner wall of each hole in the 
metal block. 
According to a second embodiment of the present invention, there is 
provided the cooling unit manufacturing method, wherein each hole into 
which the heat pipe is inserted has a substantially circular cross section 
and the heat pipe has a substantially circular cross section. 
According to a third embodiment of the present invention, there is provided 
the cooling unit manufacturing method, wherein each of the convex portions 
has a substantially rectangular or trapezoidal cross section. 
According to a fourth embodiment of the present invention, there is 
provided the cooling unit manufacturing method, wherein each of the convex 
portions has a substantially triangular cross section. 
According to a fifth embodiment of the present invention, there is provided 
the cooling unit manufacturing method, wherein each of the convex portions 
has a cross section substantially shaped corresponds to a combination of a 
trapezoid and a triangle. 
According to a sixth embodiment of the present invention, there is provided 
the cooling unit manufacturing method, wherein the metal block is made of 
aluminum or aluminum alloy. 
According to a seventh embodiment of the present invention, there is 
provided a cooling unit comprising the metal block and heat pipes produced 
by the above manufacturing method. 
According to an eighth embodiment of the present invention, there is 
provided a cooling unit manufacturing method comprising the steps of: 
(a) preparing a substantially-plate-type metal block for removing heat 
generated from an electronic component, the metal block having holes in 
the thickness of the metal block into which heat pipes are inserted and 
having U-shaped grooves each provided with protruding portions on at least 
one main surface or both main surfaces of the plate-type body 
corresponding with the holes; 
(b) providing heat pipes in the U-shaped grooves for removing heat of the 
metal block; and 
(c) applying local and two-dimensional force from the surface of the metal 
block to the protruding convex portions to make the surface substantially 
flat after mounting the heat pipes on the U-shaped grooves and to bring 
the outer surface of each heat pipes into close contact with the inner 
wall of each hole in the metal block. 
According to a ninth embodiment of the present invention, there is provided 
the cooling unit manufacturing method, wherein each of the holes in which 
the heat pipes are inserted has a substantially circular cross section and 
each of the heat pipes has a substantially circular cross section. 
According to a tenth embodiment of the present invention, there is provided 
the cooling unit manufacturing method, wherein convex portions are further 
formed on the other surface with which the U-shaped grooves having the 
protruding portions from the main surface correspond. 
According to an eleventh embodiment of the present invention, wherein each 
of the further-formed convex portions has a substantially trapezoidal 
shape. 
According to a twelfth embodiment of the present invention, there is 
provided the cooling unit manufacturing method, wherein the metal block is 
made of aluminum or aluminum alloy. 
According to a thirteenth embodiment of the present invention, there is 
provided a cooling unit comprising the metal block and the heat pipes 
which are produced by the above manufacturing method. 
According to a fourteenth embodiment of the present invention, there is 
provided a cooling unit manufacturing method comprising the steps of: 
(a) preparing a substantially-plate-type metal block for removing heat 
generated from an electronic component, the metal block having holes in 
the thickness part of the metal block into which the heat pipes are 
inserted and having convex portions formed on one main surface of the 
metal block corresponding to the holes; 
(b) inserting the heat pipes into the holes for removing heat from the 
metal block; and 
(c) applying local and two-dimensional force to the surface of the metal 
block to the convex portions to make the surface substantially flat after 
inserting the heat pipes into the holes and to bring the outer surface of 
each heat pipe into close contact with the inner wall of each hole in the 
metal block. 
According to a fifteenth embodiment of the present invention, there is 
provided the cooling unit manufacturing method, wherein each of the holes 
into which the heat pipes are inserted has a substantially circular shape 
and each of the heat pipes has a substantially circular shape. 
According to a sixteenth embodiment of the present invention, there is 
provided the cooling unit manufacturing method, wherein each of the convex 
portions has a substantially trapezoidal or rectangular shape. 
According to a seventeenth embodiment of the present invention, there is 
provided the cooling unit manufacturing method, wherein the metal block is 
made of aluminum or aluminum alloy. 
According to an eighteenth embodiment of the present invention, there is 
provided a cooling unit comprising the metal block and the heat pipes 
which is produced by the manufacturing method comprising the steps of: 
(a) preparing a substantially plate-type metal block for removing heat 
generated from an electronic component, the metal block having a hole in 
the thickness of the metal bock and having a convex portion formed on one 
main surface of the metal block corresponding to the hole; 
(b) inserting a heat pipe into the hole for removing heat from the metal 
block; and 
(c) applying local and two-dimensional force from the surface of the metal 
block to the convex portion to make the surface substantially flat and to 
bring the outer surface of each heat pipe into close contact with the 
inner wall of each hole in the metal block.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT OF THE INVENTION 
The present invention will now be described in detail with reference to the 
accompanying drawings. In the following description, a heat pipe has a 
circular cross section with a diameter that ranges from 2 to 5 mm and a 
rod type heat pipe having a length of approximately 50 to 200 mm and being 
made of copper or aluminum. Further, a metal block is usually made of 
aluminum or aluminum alloy to reduce weight. 
According to the present invention, FIG. 1(b) shows one embodiment of a 
cooling unit provided with heat pipes. A metal block 2 is a plate which is 
made of aluminum or aluminum alloy and has outer dimensions of 
100.times.200 mm and a thickness of 3 mm. Each copper heat pipe 1 has an 
outer diameter of 3 mm. As shown in FIG. 1, the part of the heat pipe 1 
that is inserted into the metal block 2 is flat while the part of the heat 
pipe 1 which is outside the metal block 2 being circular. As shown in FIG. 
16, fins 3 are provided at one end of each heat pipe 1 by burring for the 
purpose of heat dissipation and are attached to the heat pipe 1 by 
caulking. 
A description will now be given as to a method for fixing the heat pipes 1 
to the metal block 2. The shape of the metal block 2 made of aluminum has 
a thickness t.sub.1 equal to 3 mm at a portion where no heat pipe 1 is 
inserted, and substantially trapezoidal or rectangular convex portions 15 
each of which has a width of t.sub.2 equal to 4 mm and a height t.sub.3 
equal to 0.4 mm provided on the metal block 2 portions where the heat 
pipes 1 are inserted in such a manner that the convex portions 15 are on 
opposing surfaces of the aluminum metal block 2. The metal block 2 having 
such a shape can be manufactured by hot-pressing or abrading aluminum. A 
circular insertion hole having a diameter of 3.2 mm is formed in one cross 
section of the metal block and each copper heat pipe having an outer 
diameter of 3 mm is inserted into the insertion hole. At this point in 
time, the heat pipe 1 has a circular cross section at the portion inserted 
into the hole. 
In this state, the pressure of 40 kg/cm.sup.2 is applied in both the upward 
and downward directions, as shown by arrows in FIG. 1(a). Such a 
mechanical pressure is preferably applied to the convex portions 15 and 
the inserted heat pipe is deformed to have a substantially flat shape as 
shown in FIG. 1(b). The type of deformation depends on values of the width 
t.sub.2 or the height t.sub.3 of the convex portion 15 or how the 
mechanical pressure is applied. Although this shape is preferably flat 
such that both main surfaces are completely flat as shown in FIG. 2(a), no 
problem occurs in the practical use even if the central part slightly 
projects as shown in FIG. 2(b) or the central part is slightly concave as 
shown in FIG. 2(c). Further, if the main surface of the metal block 2 (the 
surface wider than the side surface) is previously machined to have a 
shape conforming with that of the electronic component to be mounted, 
contact made between the metal block 2 and the electronic component can be 
improved, thereby increasing the heat removal efficiency. FIG. 2(b) shows 
an embodiment in which the surface of the metal block that is thermally 
connected with at least the electronic component is desired to be 
sufficiently smooth, and the main surface of the metal block 2 is smoothed 
by pressure application using a press or the like or abrasion or other 
methods if necessary. This maintains good contact with the electronic 
component which should be cooled down, thus realizing high performance. It 
is to be noted that FIG. 1 shows a case where the number of heat pipes 
used is three wherein the number and the interval between the respective 
pipes can be appropriately determined by taking the number of electronic 
components to be cooled down and the quantity of generated heat into 
account. 
As mentioned above, the cross section of the heat pipe 1 inserted into the 
metal block 2 is deformed to have a substantially-flat shape by 
application of mechanical pressure, the flat plane of the 
substantially-flat shape is pressed against the inner wall of the metal 
block 2 with very strong force to realize sufficient thermal contact, and 
the mean distance from the surface of the metal block 2 to the heat pipe 1 
is shortened, thereby reducing the heat resistance in the heat conduction. 
FIG. 3(a) shows a variation of the first embodiment according to the 
present invention, which is similar to the above example in that each 
convex portion 15 is provided on both surfaces of the metal block 2 at the 
portion where the heat pipe is inserted into the metal block but different 
from the example shown in FIG. 1 in that the thickness of the metal block 
2 into which the heat pipe 1 is inserted is larger than the outer diameter 
of the heat pipe 1. That is, in the embodiment shown in FIG. 3, an outer 
diameter of the heat pipe 1 is 3 mm; the metal block 2 has a thickness 
t.sub.1 equal to 4 mm; the convex portion 15 has a width t.sub.2 equal to 
4 mm and a height t.sub.3 equal to 0.2 mm; and the insertion hole has an 
outer diameter of 3.2 mm. If the thickness of the metal block 2 is larger 
than the outer diameter of the heat pipe 1, as it is in this embodiment, 
it is desirable that the height of the convex portion 15 is larger than 
the gap between the insertion hole formed in the base metal block and the 
outer diameter of the heat pipe 1 and that an area of the cross section of 
the convex portion 15 is larger than that of the gap. With the heat pipe 1 
being inserted into the insertion hole as shown in FIG. 3(a), press 
working is performed to obtain a shape illustrated in FIG. 3(b). In this 
method, because the quantity of deformation caused by pressure application 
is small as compared with the example shown in FIG. 1, pressing can be 
done at an ordinary temperature, and the time for applying pressure can be 
advantageously shortened. 
Although FIG. 3(a) shows an example where each convex portion 15 has a 
substantially trapezoidal or rectangular cross section, the cross section 
is not restricted to a substantially trapezoidal or rectangular shape. It 
may have, for example, a substantially triangular shape having a width of 
2 mm and a height of 0.5 mm as shown in FIG. 4(a). Also, the convex 
portion on both surfaces of the metal block may have a cross section which 
is a combination of a substantially trapezoidal or rectangular shape and a 
substantially triangular shape as shown in FIG. 4(b). In addition, the 
convex portions 15 may be provided on both surfaces of the metal block 2 
in such a manner that they are opposed to each other as shown in FIG. 
4(c), or the convex portions 15 may be alternately provided on both 
surfaces with respect to one heat pipe. In this case, because the quantity 
of deformation of the heat pipe is small, such an arrangement is effective 
especially when the diameter of the pipe is small and often is adopted 
when securing the passage of the heat pipe working liquid. 
FIG. 5 shows another embodiment according to the present invention. As 
shown in FIG. 5(a), U-shaped grooves 17 for mounting the heat pipe 1 are 
formed on one surface of the metal block 2, and convex portions 15 are 
provided on side parts of the grooves 17 while convex portions 16 each 
having a substantially-trapezoidal or rectangular cross section are 
provided on the other surface of the metal block 2. In this case, two 
convex portions 15 are formed on side portions of each groove which 
preferably have a cross sectional area larger than the difference between 
the cross-sectional area of the U-shaped groove and that of the heat pipe, 
i.e., the cross-sectional area A shown by notched lines in FIG. 5(c). In 
FIG. 5, an aluminum plate having a thickness of 5 mm is used as the metal 
block 2, an U-shaped groove 17 having a width of 3.2 mm and a depth of 4 
mm is formed on one surface of the plate, a convex portion 15 having a 
cross section of 1 mm.times.1 mm is provided on each of the side portions 
of the groove, and a convex portion 16 having a height of 0.2 mm and a 
width of 2 mm is provided on the back surface of the metal block 2. The 
heat pipe 1 having an outer diameter of 3 mm is mounted in the U-shaped 
groove 17 of the metal block 2, and mechanical force is applied to the 
surface of the metal block 2 by using a press machine. As a result, the 
heat pipe 1 is deformed to have a substantially flat shape and the heat 
pipe 1 and the metal block 2 are thermally and closely connected as shown 
in FIG. 5(b). 
Although FIG. 5 shows the example in which the U-shaped groove 17 is formed 
on one surface of the metal block 2 while the convex portion 16 is 
provided on the other surface of the metal block 2, the U-shaped groove 17 
and the convex portion 16 may be alternately arranged as shown in FIG. 
6(a). Alternatively, only the convex portions 15 formed on the side 
portions of the U-shaped groove 17 may be employed without using the 
convex portions 16 formed on the other surface, as shown in FIG. 6(b). 
FIG. 7 illustrates yet another embodiment of the present invention. In this 
embodiment, substantially trapezoidal or rectangular convex portions are 
provided on one main surface of the metal block, and holes in which the 
circular heat pipes are inserted are formed in the corresponding thick 
parts of the convex portions. After inserting the heat pipes into these 
holes, the metal block is pressed by, for example, a press so that a part 
of the circumferential portion of each heat pipe becomes flat. In this 
case, the cross section of each heat pipe is deformed as shown in FIG. 8 
depending on the degrees of the pressure or pressing employed by the 
method. The thermal contact achieved between the metal block and the heat 
pipes is superior to that attained by the solder alloy. 
FIGS. 9 and 10 show another method for pressing the metal block such that 
the cross section of each heat pipe has a substantially semicircular 
shape. In this case, the circular insertion hole is previously formed in 
the plate-type metal block. A spacer is set at a position where the heat 
pipe is inserted after inserting the heat pipe having a circular cross 
section in order to give pressure using a pressing machine. The circular 
heat pipe is then pressed to have a semicircular cross section as shown in 
the drawings, and the thermal contact between the metal block and the heat 
pipe is improved. 
The following describes the specific effect of the thermal contact between 
the metal block and the heat pipe in the embodiments according to the 
present invention. 
FIG. 11 is a schematic view showing a cooling unit according to the present 
invention. The block 20 is made of aluminum (A1100, a Japanese Standard 
for an aluminum alloy) and is a plate type having dimensions of 50 
mm.times.30 mm. This cooling unit was manufactured as follows. The block 
having a hole with a diameter equal to 3.1 mm was formed. The block has a 
thickness of 4 mm at a portion where the hole is formed and a thickness of 
2 mm at any other part. The copper heat pipe having a diameter of 3 mm, an 
overall length equal to 200 mm, a thickness equal to 0.3 mm, water was 
used as the working liquid, and a small groove formed inside (not shown) 
was inserted into the hole. The part of the block having a thickness of 4 
mm was subsequently subjected to press working along the thickness 
direction so that the part of the block to which the heat pipe was 
inserted had a thickness of 3 mm. As a result, the inserted heat pipe 1 
was deformed to have a substantially semicircular shape, and the hole was 
also deformed to have a substantially semicircular shape, as shown in FIG. 
11. In this way, a sample of the block 20 which is shown in FIG. 11 and 
attached to both ends of the heat pipe 1 having a length equal to 200 mm 
was manufactured. 
As shown in FIG. 13, one sample block 20a was soaked in hot water 24 having 
a temperature of 60 degrees Celsius. Here, the heat pipe 1 was maintained 
so as to be substantially vertical for five minutes in such a manner that 
approximately 15 mm of the block 20a was soaked in the hot water. After 
five minutes, the block 20a was taken out from the hot water 24, and 
temperatures of the block 20a and the metal block 20b at their central 
parts were rapidly measured and compared. The result showed that a 
difference between the temperatures of the block 20a and the block 20bwas 
6 degrees Celsius. 
COMATIVE EXAMPLE 1 
As a comparative example, the plate-type aluminum block (A1100) having no 
convex portion on the main surface and having the dimensions of 50 
mm.times.30 mm and the thickness of 4 mm was prepared. A hole was formed 
in the block at a position similar to that of the example shown in FIG. 
11, and the block was flattened by mechanical pressing after inserting the 
heat pipe into the hole, thereby producing the primary component of the 
cooling unit according to the present invention. The thickness of the 
block, including the part into which the heat pipe is inserted, before 
applying the mechanical press was uniformly 4 mm, but application of the 
press changed the thickness to 3 mm. As a result, the heat pipe was 
deformed to have a substantially-elliptical shape at the part inserted 
into the block. 
The performance of this comparative example was similarly measured as that 
of the first embodiment. The measurement showed that the difference in 
temperature between the metal blocks at both ends of the heat pipe was 
approximately 7 degrees Celsius. Compared with the first embodiment, 
although the heat capacity of the metal block is different to some extent, 
it can be noticed that the first embodiment realizes heat conduction 
property superior to that of comparative example 1. 
EMBODIMENT 2 
In this embodiment, a sample such as shown in FIG. 11 was produced by the 
manufacturing method illustrated in FIG. 1. The specific dimensions are 
the same as those described in connection with FIG. 1. It is to be noted 
that the block 21 is made of aluminum A1100 and is of a plate type having 
the dimensions of 50 mm .times.30 mm. One heat pipe was inserted into a 
hole having a diameter of 3.1 mm which was formed in the metal block 
having a thickness of 4 mm and press working was applied. The performance 
evaluation of the cooling unit was similarly carried out as that of the 
first embodiment and showed that a difference in temperature of the blocks 
21 provided on both ends of the heat pipe 1 was 7 degrees Celsius. 
FIG. 12 is a perspective view schematically showing a primary component of 
a conventional cooling unit. The block 22 is made of aluminum (A1100) and 
is of a plate type having the dimensions of 50 mm .times.30 mm. The 
thickness of the block 22 is 4 mm. A heat pipe 1 and block 22 are 
connected to each other by means of soldering. As to the manufacturing 
method, the melted solder alloy (composition: Sn/Pb=6/4) is filled in a 
hole having a diameter of 3.3 mm into which the heat pipe 1 is inserted 
with the block 22 being set on edge. In this state, the heat pipe 1 is 
slowly inserted and the solder alloy is then set. As a result of the 
performance evaluation similar to that effected in the first embodiment, 
it was found that a difference in temperature between the blocks 21 
provided at both ends of the heat pipe 1 was 8 degrees Celsius. 
As is apparent from the results of the above-mentioned performance 
evaluation of the primary component in the cooling unit, a difference in 
temperature between the blocks provided on both ends of the heat pipe is 
small and the good thermal contact between the heat pipe and the block is 
realized in the embodiments of the present invention. Therefore, use of 
the cooling unit according to the present invention as such a cooling unit 
shown in FIG. 1 enables the efficient heat removal or heat radiation from 
the electronic components. As compared with the above-described prior art, 
the cooling unit according to the present invention can be readily 
manufactured and is advantageous in terms of cost. 
As explained above in detail, according to the present invention, the holes 
or U-shaped grooves for mounting the heat pipes are formed in the metal 
block for attaching a heat generation part of the electronic component, 
the convex portions are provided in the metal block at positions where the 
heat pipes are mounted, and the mechanical force is applied using a 
pressing machine or the like after inserting the heat pipes in order to 
connect the heat pipes with the metal block. Thus, the cross section of 
each heat pipe is deformed to have a flat shape, and the outer surface of 
each heat pipe is closely brought into contact with the inner wall of each 
hole or each groove of the metal block to cause heat resistance to be 
prominently decreased at the contact part, thereby resulting in a cooling 
unit provided with heat pipes which has an extremely-high efficiency of 
heat radiation or cooling. 
Further, because the metal block and the heat pipes do not have to be 
connected by means of the solder alloy, the thickness of the metal block 
can be decreased, resulting in reduction in size and weight of the cooling 
unit. Furthermore, when at least one surface of the metal block is made 
flat and smooth by machining, the heat generation part and the metal block 
are closely connected with each other, which enables improvement of the 
heat radiation or cooling characteristic.