GB2278676A

GB2278676A - Cooling electronic apparatus

Info

Publication number: GB2278676A
Application number: GB9409781A
Authority: GB
Inventors: Junji Sotani; Suemi Tanaka; Masaaki Yamamoto; Kenzo Kobayashi
Original assignee: Furukawa Electric Co Ltd
Current assignee: Furukawa Electric Co Ltd
Priority date: 1993-05-14
Filing date: 1994-05-16
Publication date: 1994-12-07
Anticipated expiration: 2014-05-16
Also published as: GB2278676B; GB9409781D0

Abstract

A coding radiator includes heat pipes (1) mounted on one piece heat conductive aluminum or aluminum alloy plates (2). A part of each heat pipe (1) having a flat or elliptical cross section is inserted into a pipe insertion hole (20) having a flat or elliptical cross section with a major axis of the pipe insertion hole parallel to one surface of the heat conductive plate. Both the major-axial surfaces of the inserted heat pipe portion are attached to the major-axial inside wall surface of the pipe insertion hole (20) by heating the heat pipe (1). <IMAGE>

Description

HEAT PIPE TYPE RADIATOR AND METHOD FOR MANUFACTURING SAME BACKGROUND OF THE INVENTION Field of the Invention: This invention relates to a heat pipe type radiator for cooling heat-generating components such as LSI mounted on an electronic apparatus and a method for manufacturing such a heat pipe type radiator.

Description of the Prior Art: Conventionally, a forced-air cooling type radiator by means of an air cooling fan has been adopted in most cases as means for preventing the inside of an electronic apparatus from being overheated. However, in recent electronic apparatuses, heat-generating components such as LSI (Large Scale Integrated Circuit) are mounted in high density, and the heat generating rate within each electronic apparatus tends to remarkably increase. Thus, the forced-air cooling type radiator by means of the air cooling fan has been limited in cooling capability. In addition, the mounting space for a radiator within the electronic apparatus has been becoming narrower with the miniaturization of the electronic apparatus, so that the heat radiation within the electronic apparatus has been getting into an extremely difficult situation.

In view of the circumstances described above, the present inventors have already proposed a small-sized radiator utilizing a small-diameter heat pipe so as to obtain high cooling capability (See Japanese Patent Application No. 4-105382).

Figs. 10 and 11 are respectively a perspective view and a side view showing a heat pipe type radiator proposed by the present inventors.

The radiator shown in Figs. 10 and 11 is composed of two pieces of heat pipes 1 each having a flat cross section to have an outer diameter of approximately 1.5 mm in the minor axis direction, heat conductive plates 8, 9 respectively mounted on an evaporative section 10 and a condensive section 11 of each heat pipe 1, and radiation fins 30 mounted on both surfaces of the heat conductive plate 9.

The heat conductive plate 8 on the side of the evaporative section is composed of a planar main body 80 and a cover body 81. As shown in Fig. 12, the evaporative section 10 of the heat pipe 1 is inserted into a groove 82 formed on the surface of the main body 80, and molten solder 83 is poured into a gap between the inside wall of the groove 82 and the evaporative section 10 of the heat pipe 1. Then, the cover body 81 is covered on the main body 80 and fixed thereto with the solder 83.

The heat conductive plate 9 on the side of the condensive section is constituted by a flat plate having a thickness of approximately 3.5 mm and composed of two sheets of aluminum plates bonded to each other with solder. The condensive section 11 of the heat pipe 1 is inserted into a groove formed on one or both plates, and fixed thereto with solder.

Each of the radiation fins 30, 30 fixedly attached to both surfaces of the heat conductive plate 9 by means of soldering is constituted such that a flat fin member and two pieces of fin members of the same shape respectively pressed into a rectangular wave shape are alternately laminated and fixed together by means of brazing or the like.

As shown in Fig. 11, the heat pipe type radiator constituted as described above is used by installing the heat conductive plate 8 to a printed circuit board 7 in such a state that heat-generating components 5 such as LSI mounted on the printed circuit board 7 are brought into contact with the back surface of the main body 80 through a highly heat conductive rubber 6.

In the state of installation as shown in Figs. 10 and 11, a heating section is constituted by the main body 80 of the heat conductive plate 8 and the highly heat conductive rubber 6, while a cooling section is constituted by the heat conductive plate 9 and the radiation fins 30.

In addition, in the state of installation as shown in Figs. 10 and 11, the heat generated in the heat-generating components 5 such as LSI conducts to the heat conductive plate 8 through the highly heat conductive rubber 6, and heats the evaporative section 10 of the heat pipe 1 to evaporate working fluid sealed in the heat pipe. The vapor pressure in the evaporative section 10 of the heat pipe 1 is raised due to the evaporation of the working fluid, and a vapor stream is produced toward the condensive section 11 having a lower pressure. The heat of the vapor transported to the condensive section 11 conducts to the radiation fins 30 through the heat conductive plate 9, and is radiated to ambient air through the entire surface of the radiation fins 30 exposed to air.

Since the heat conductive plate 9 can radiate and transport the heat through the condensive section 11 of the heat pipe 1 to the remote portion located far from the heat pipe 1, the heat conductive plate 9 as a whole comes closer to an almost uniform temperature distribution.

The radiation fin 30 mounted on the heat conductive plate 9 has the extremely large surface area per unit volume. Further, the distance from the surface of the heat conductive plate 9 to each of the upper surface of the upper radiation fin 30 and the lower surface of the lower radiation fin 30 in Fig. 11 is small. Therefore, any large temperature drop is not produced even at the remotest portion of the radiation fin 30 located far from the heat conductive plate 9, and the radiation fins 30 as a whole come closer to an almost uniform temperature distribution, so that the radiation capability can be enhanced by the increment of the surface area of the radiation fins.

According to the reasons described above, the heat pipe type radiator proposed by the present inventors as shown in Figs. 10 and 11 has had the effect of making it possible to remarkably enhance the radiation capability even though this heat pipe type radiator is relatively small in size.

Incidentally, the evaporative section of the heat pipe 1 and both the main body 80 and the cover body 81 of the heat conductive plate 8 in the above-mentioned heat pipe type radiator are fixed together with the solder 83 as described above.

However, the method of fixing the heat conductive plate to the heat pipe by means of soldering involves such problems that since the solder is heavy, the weight of the radiator is increased when a solder layer is thick, or that the solder 83 between the main body 80 and the cover body 81 is protruded to damage the external appearance of the radiator. On the other hand, when the solder layer is thinned in order to make the radiator lightweight, voids 84 are easily produced in various parts of the layer of the solder 83 in case of manufacturing the radiator. These voids 84 bring about the reduction of radiation capability since the thermal resistance of a soldered portion between the heat conductive plate and the heat pipe 1 becomes large due to the voids, while the thermal resistance is dispersed.

Further, as has been already described, there have been demands that the radiator of this kind should be made more lightweight and miniaturized with the tendency to make the electronic apparatus lightweight and miniaturized. However, when the heat conductive plate 8 having a two-piece structure composed of the main body 80 and the cover body 81 as shown in Fig. 12 is manufactured by aluminum or aluminum alloy in order to make the radiator lightweight and miniaturized, the heat conductive plate 8 could not be made small (thinned) to a certain degree or below for the following reasons.

According to one of the reasons, when the main body 80 and the cover body 81 are thinned in excess, the heat conductive plate 8 is deformed with the lapse of time, or the bond portion between the heat pipe 1 and the heat conductive plate 8 is easily separated with the lapse of time.

According to another reason, the surface of the main body 80 to be brought into contact with the heatgenerating component 5 should be worked into a smooth surface by means of cutting after the main body 80, the cover body 81 and the heat pipe 1 are soldered in order to enhance the close contact state between the heat conductive plate 8 and the heat-generating component 5 so as to prevent the reduction of thermal conduction therebetween. However, when the main body 80 and the cover body 81 are thinned in excess, the cutting of the surface of the main body 80 becomes impossible or difficult.

Namely, when the heat conductive plate 8 is fixed by a tool (not shown) and then cut as described above, the cover body 81 is deformed or the main body 80 is separated from the cover body 81.

On the other hand, when the heat conductive plate is molded into a solid one piece by aluminum or aluminum alloy, instead of two pieces as shown in Figs. 10 to 12, the strength of the heat conductive plate can be enhanced to make the heat conductive plate thinner.

However, this case involves other problems.

Namely, in a prior art technique, the heat pipe and the heat conductive plate molded into a solid one piece are fixed together according to a method including the steps of forming a pipe insertion hole in a thickness portion of the heat conductive plate, then inserting the heat pipe into the pipe insertion hole, and pouring the solder into a gap between the surface of the heat pipe and the inside wall of the pipe insertion hole. However, since an oxidizing layer formed on the surface of aluminum hinders the adhesion of solder, a large number of voids are produced between the heat pipe surface and the inside wall of the pipe insertion hole.

The voids reduce the radiation capability of the radiator, since the thermal resistance becomes large due to the voids.

Further, in order to fix the heat pipe into the pipe insertion hole without producing any void, the pipe insertion hole should be enlarged to further increased a quantity of solder to be poured. However, in this case, the weight of the radiator is increased due to the increment of solder. In addition, the heat conductive plate should be necessarily thickened according as the pipe insertion hole is enlarged. Thus, it becomes impossible to make the heat conductive plate thinner.

For instance, in a radiator for cooling LSI mounted on a note type personal computer, it is necessary to make the heat conductive plate thin (i.e., not more than 3 mm) for miniaturization. However, when a small-diameter heat pipe is to insert into and fix by soldering to the pipe insertion hole formed in the thickness portion of the thin type heat conductive plate so as to reduce the number of voids described above while preventing the thermal resistance from increasing, the heat pipe should be worked into a flat shape such that the minor axis thereof becomes further shorter.

However, when the small-diameter heat pipe is worked into a flat shape such that the minor axis thereof becomes short in excess, the heat transportation rate in the flat portion of the heat pipe is remarkably reduced.

The problems in the case of fixing the heat conductive plate 8 to the heat pipe 1 as described above are pertinent also to the case of fixing the other heat conductive plate 9 to the heat pipe 1 as they are.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat pipe type radiator which enables to make the radiator as a whole lightweight and miniaturized by further thinning a heat conductive plate.

Another object of the present invention is to provide a heat pipe type radiator which has smaller thermal resistance between a thin heat conductive plate and a heat pipe.

A further object of the present invention is to provide a heat pipe type radiator manufacturing method which can fix a heat conductive plate and a heat pipe together without increasing the thermal resistance and is suitable to a mass production when a thinner heat conductive plate molded into a solid one piece is used.

In order to achieve the objects described above, according to the present invention, a heat pipe type radiator including one or a plurality of heat pipes mounted on a heat conductive plate to carry out the heat exchange between heat-generating components of an electronic apparatus and the heat pipes through the heat conductive plate comprises the heat conductive plate molded into a solid one piece by aluminum or aluminum alloy, and a pipe insertion hole having an approximately flat or elliptical cross section and formed in a thickness portion of the heat conductive plate such that a major axis of the pipe insertion hole extends parallel to one surface of the heat conductive plate, wherein the heat pipe is inserted partially or wholly into the pipe insertion hole, the partially or wholly inserted portion of the heat pipe into the pipe insertion hole is formed to have an approximately flat or elliptical cross section and has both the major-axial surfaces pressedly attached in an almost close contact state to the majoraxial inside wall surface of the pipe insertion hole.

The partially or wholly inserted portion of the heat pipe into the pipe insertion hole is preferably constituted such that the ratio of a minor axis to a major axis is not more than 0.6 and the minor axis is not less than 1.5 mm.

Further, the heat conductive plate is preferably constituted by an extruded material having a thickness of not less than 2.5 mm.

One or both the major-axial surfaces of the partially or wholly inserted portion of the heat pipe into the pipe insertion hole may be fixedly attached to the inside wall surface of the pipe insertion hole through a thin solder layer.

In the radiator described above, when the heat pipe is inserted partially into the pipe insertion hole of the heat conductive plate, radiation fins are mounted on the other portion of the heat pipe partially or wholly.

In the radiator described above, when the heat pipe is inserted wholly into the pipe insertion hole of the heat conductive plate, the radiation fins are preferably mounted on a part of the heat conductive plate.

As described above, according to the heat pipe type radiator of the present invention, both the majoraxial surfaces of the partially or wholly inserted portion of the heat pipe into the pipe insertion hole of the heat conductive plate are pressedly attached to the major-axial inside wall surface of the pipe insertion hole of the heat conductive plate. Therefore, the heat conducted from the heat-generating components to the heat conductive plate further conducts to the heat pipe mainly through the contact surface between the heat pipe and the major-axial inside wall surface of the pipe insertion hole of the heat conductive plate.

Since both the major-axial surfaces of the partially or wholly inserted portion of the heat pipe are pressedly attached in an almost close contact state to the major-axial inside wall surface of the pipe insertion hole of the heat conductive plate, the sufficient heat conduction is carried out with small thermal resistance.

Since the heat conductive plate is molded into a solid one piece by aluminum or aluminum alloy, the heat conductive plate is light in weight and can maintain sufficient strength even though the heat conductive plate is made thinner. Therefore, the radiator as a whole can be made thinner and lighter in weight.

In order to achieve the objects described above, according to the present invention, a method for manufacturing a heat pipe type radiator including one or a plurality of heat pipes mounted on a heat conductive plate molded into a solid one piece by aluminum or aluminum alloy to carry out the heat exchange between heat-generating components of an electronic apparatus and the heat pipes through the heat conductive plate, comprises a step of inserting a partially or wholly heat pipe portion to be inserted having a flat or elliptical cross section into a pipe insertion hole having a flat or elliptical cross section and formed in a thickness portion of the heat conductive plate such that a major axis of the pipe insertion hole extends approximately parallel to one surface of the heat conductive plate, in such a state that a major axis of the inserted heat pipe portion extends approximately parallel to the major axis of the pipe insertion hole, and a step of pressedly attaching both the major-axial surfaces of the inserted heat pipe portion to the major-axial inside wall surface of the pipe insertion hole by heating the heat pipe to expand the inserted heat pipe portion toward a minor axis of the heat pipe.

The partially or wholly heat pipe portion to be inserted is preliminarily worked into a flat or elliptical shape in cross section such as to be slightly smaller in size than the pipe insertion hole of the heat conductive plate, before or after working fluid is sealed into the heat pipe.

After the heat conductive plate is molded into a solid one piece, the pipe insertion hole may be formed by mechanical means in molded the heat conductive plate.

However, an elongate plate extruded in such a state that the pipe insertion hole is formed in the length direction is preferably used as the heat conductive plate by cutting at an appropriate length.

Further, in case of heating the heat pipe, when the heat conductive plate and the heat pipe are small in size, the heat pipe is inserted into the pipe insertion hole of the heat conductive plate, and the heat conductive plate in this state is clamped by an appropriate holder and then heated.

Incidentally, in case of heating the heat pipe, only the heat pipe may be heated, or the heat pipe may be heated together with the heat conductive plate.

The method for manufacturing the heat pipe type radiator according to the present invention comprises the steps as described above. Thus, both the majoraxial surfaces of the inserted heat pipe portion are pressedly attached in an almost uniformly close contact state to the major-axial inside wall surface of the pipe insertion hole formed in the heat conductive plate due to the force exerting outwardly to the minor axis of the heat pipe.

Accordingly, the thermal resistance of the contact portions between both the major-axial surfaces of the inserted heat pipe portion and the major-axial inside wall surface of the pipe insertion hole of the heat conductive plate is small, and becomes approximately uniform without any dispersion. As a result, even though the contact area between the heat pipe and the heat conductive plate is small, the heat conduction capability is further enhanced. Therefore, a small-sized and lightweight heat pipe type radiator having more enhanced heat conduction capability can be manufactured by using a thinner heat conductive plate molded into a solid one piece.

Furthermore, since the sectional area of the inserted heat pipe portion is enlarged due to the expansion and enlargement of the heat pipe, the heat transportation rate can be increased, in comparison with that prior to the enlargement of the heat pipe.

A heat pipe type radiator having high efficiency and almost uniform radiation capability can be massproduced at lower cost by mass-producing the heat conductive plate as described above by means of extrusion, then inserting the heat pipe portion to be inserted having the flat or elliptical cross section into each pipe insertion hole of the heat conductive plate, and heating both the heat pipe and the heat conductive plate for a predetermined period of time in a heating furnace controlled at a sufficient temperature to expand the inserted heat pipe portion, for instance.

Both the surfaces of a flat or elliptical portion of the heat pipe can be pressedly attached to the inside wall of the pipe insertion hole of the heat conductive plate by means of pressing the heat conductive plate so as to pressedly attach the heat conductive plate to the heat pipe after inserting the heat pipe into the pipe insertion hole of the heat conductive plate, in addition to the method of the present invention.

However, according to the means as described above, the inserted heat pipe portion into the pipe insertion hole is elastically deformed due to the pressing action, and then pressedly attached to the inside wall of the pipe insertion hole due to the reaction against the elastic deformation. Thus, the contact portion between the heat pipe surface and the inside wall of the pipe insertion hole cannot get neither the sufficient strength nor the uniformly close contact state.

On the other hand, according to the method of the present invention, both the surfaces of the flat or elliptical portion of the heat pipe are forcibly brought into contact with the inside wall of the pipe insertion hole of the heat conductive plate due to the expansion force from the inside of the heat pipe as described above. Thus, even though the heat pipe has a small diameter and the heat conductive plate is of a thin type, the contact portion between the heat pipe surface and the inside wall of the pipe insertion hole can get both the sufficient strength and the almost uniformly close contact state.

According to the method of manufacturing the heat pipe type radiator of the present invention, the gap is formed between the surface of the inserted heat pipe portion and one or both the major-axial ends of the pipe insertion hole only by heating the heat pipe to pressedly attach both the major-axial surfaces of the heat pipe to the major-axial inside wall surface of the pipe insertion hole of the heat conductive plate. This gap may be filled with molten solder by means of pouring in the subsequent step. On the other hand, even though the gap is not filled with any solder, the method of the present invention can be carried out without reducing the radiation capability of the radiator.

However, when the heat pipe has a small diameter (i.e., the minor axis of the evaporative section of the heat pipe after the manufacture of the radiator is in the range of 1.5 to 3 mm), and the gap described above is not filled with any solder, the radiator is preferably manufactured such that the ratio of the minor axis to the major axis of the evaporative section becomes not less than 0.6.

When the radiation fins are mounted on the condensive section of the heat pipe, the radiation fins may be mounted directly on the heat pipe. Otherwise, after the condensive section of the heat pipe is preliminarily worked into a flat or elliptical shape in cross section, the radiation fins may be mounted on the heat conductive plate fixed to the condensive section according to the similar method to that of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and features of the invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which: Fig. 1 is a plan view, partly omitted, showing a heat pipe type radiator as an embodiment manufactured by a manufacture method according to the present invention; Fig. 2 is a fragmentary enlarged-scale sectional view taken along a line A-A in Fig. 1; Fig. 3 is a fragmentary enlarged-scale sectional view showing the state of an evaporative section of a heat pipe in the radiator as the embodiment shown in Fig. 1 prior to the expansion by heating; Fig. 4 is a fragmentary enlarged-scale sectional view showing a heat pipe type radiator as another embodiment according to the present invention; Fig. 5 is a front view showing the inclined state of the heat pipe type radiator as the embodiment shown in Fig. 1; Fig. 6 is a graph showing the relation between the inclination angle of the heat pipe of the radiator as the embodiment shown in Fig. 1 and the limit of a heat transportation rate of the radiator; Fig. 7 is a graph showing the relation between the ratio of a minor axis to a major axis of the evaporative section of the heat pipe of the radiator as the embodiment shown in Fig. 1 and the radiation capability; Fig. 8 is a front view showing a heat pipe type radiator as a further embodiment according to the present invention; Fig. 9 is an enlarged-scale sectional view taken along a line B-B in Fig. 8; Fig. 10 is a perspective view showing a prior art heat pipe type radiator which has been already proposed by the present inventors; Fig. 11 is a front view showing the radiator shown in Fig. 10; and Fig. 12 is a fragmentary enlarged-scale sectional view showing the radiator shown in Fig. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radiator shown in Fig. 1 comprises heat pipes 1, a heat conductive plate 2 fixed to an evaporative section 10 constituted as a part of each heat pipe 1, and a large number of radiation fins 3 mounted on a condensive section 11 constituted as the other part of the heat pipe 1.

The heat conductive plate 2 is constituted by an aluminum alloy (A6063) plate having a length L2 of 38 mm, a width W of 37 mm and a thickness T of 3.0 mm and has six pieces of pipe insertion holes 20 formed at approximately uniform intervals in the longitudinal direction such that a major axis of each pipe insertion hole extends parallel to one surface of the heat conductive plate. Each pipe insertion hole 20 has a flat (or elliptical) cross section having a major axis R1 of 4.2 mm and a minor axis R2 of 1.9 mm.

An extruded elongate plate having six pieces of pipe insertion holes 20 each having the sectional shape as described above is cut at a length of 38 mm to form the heat conductive plate 2.

The heat pipe 1 having the evaporative section 10 fixedly inserted into each pipe insertion hole 20 is a copper micro heat pipe having an outer diameter of 3 mm, the whole length L1 of 128 mm and a thickness of 0.3 mm and containing water as working fluid. A fine groove (not shown) is formed on the inside of the heat pipe 1 in the longitudinal direction.

The evaporative section 10 of the heat pipe 1 has a flat (or elliptical) cross section having a major axis rl of 3.6 mm and a minor axis r2 of 1.9 mm. Both surfaces (upper and lower surfaces in Fig. 2) of the evaporative section 10 along the major axis rl are pressedly attached in an almost close contact state to the upper and lower inside wall surfaces of the pipe insertion hole 20 along the major axis R1.

The condensive section 11 having a circular cross section and constituted as the other part of the heat pipe 1 is mounted with 40 pieces of radiation fins 30 at a pitch of 2 mm. Each radiation fin 30 has a size of 40 mm x 8 mm and a thickness of 0.2 mm.

The radiator is used in such a state that heatgenerating components (not shown) such as LSI are brought into contact with the underside of the heat conductive plate 2. In use of the radiator, the heat of the heat-generating components conducts to the evaporative section 10 of the heat pipe 1 through the heat conductive plate 2, evaporates the working fluid contained in the evaporative section 10, and is transported to the low-temperature condensive section 11 having a low internal pressure due to the vapor of the working fluid to be radiated to ambient air through the radiation fins 3.

The heat pipe type radiator as the embodiment shown in Figs. 1 and 2 is manufactured according to a manufacture method as will be described in the following.

At first, the heat conductive plate 2 is manufactured by cutting the extruded elongate plate as described above, and a part of each heat pipe 1 having a circular cross section is formed into an evaporative section 10 having a flat (or elliptical) cross section by means of pressing in advance such that the evaporative section 10 has a major axis r3 of 4 mm and a minor axis r4 of 1.2 mm.

Subsequently, the evaporative section 10 of the heat pipe 1 is inserted into each pipe insertion hole 20 of the heat conductive plate 2 in such a state that the major axis of the evaporative section extends approximately parallel to the major axis of each pipe insertion hole 20.

Then, the heat conductive plate 2 is mounted on a holder (not shown) and clamped. Both the heat conductive plate and the holder are heated for approximately 30 minutes in a heating furnace (not shown) held at 280"C, then carried out of the heating furnace and cooled down at room temperature.

Then, 40 pieces of radiation fins 3 having the size as described above are mounted at a pitch of 2 mm on the condensive section 11 of the heat pipe 1 to manufacture the radiator.

When the heat pipe 1 is heated in the heating furnace, the internal pressure of the heat pipe is increased, and the evaporative section 10 having the flat cross section is expanded and enlarged so as to be further rounded, namely, toward the minor axis as shown in Fig. 2. Then, the upper and lower surfaces of the heat pipe are pressedly attached in an almost close contact state to the upper and lower surfaces of the pipe insertion hole 20.

When the heat pipe 1 is heated as described above, the condensive section 11 having the circular cross section and constituted as the other part of the heat pipe 1 is not expanded, since the strength of the condensive section 11 is larger than that of the evaporative section 11 having the flat cross section.

As described above, both the major-axial surfaces of the evaporative section 10 of the heat pipe 1 are pressedly attached in an almost uniformly close contact state to the upper and lower inside wall surfaces of the pipe insertion hole 20 of the heat conductive plate 2 due to the expansive force exerting outwardly to the minor axis of the heat pipe. Thus, the thermal resistance of the contact portion between the evaporative section 10 of the heat pipe 1 and the inside wall surface of the pipe insertion hole 20 of the heat conductive plate 2 is small and becomes approximately uniform without any dispersion. As a result, even though the contact area between the heat pipe 1 and the pipe insertion hole 20 of the heat conductive plate 2 is small, the heat conduction capability can be further enhanced.

In addition, a small-sized and lightweight heat pipe type radiator having more enhanced heat conduction capability can be manufactured by using a thinner heat conductive plate molded into a solid one piece.

Since the evaporative section of the heat pipe 1 and the inner wall of the pipe insertion hole 20 can be pressedly attached to each other by heating the heat pipe 1, a soldering step in the conventional manufacture method can be omitted, and therefore, the heat pipe type radiator can be mass-produced at lower cost.

As shown in Fig. 2, in the heat pipe type radiator manufactured according to the method described above, gaps 22 are formed between both the major-axial ends of the pipe insertion hole 20 of the heat conductive plate 2 and both the major-axial ends of the evaporative section 10. However, these gaps 22 have no possibility of reducing the radiation capability in the radiator as the embodiment described above.

On the other hand, these gaps 22 may be filled with solder 21 by means of pouring as shown in Fig. 4, for example. Other constituents and the size of various parts of the radiator shown in Fig. 4 are similar to those of the radiator shown in Figs. 1 and 2.

A sample 1 of the radiator shown in Figs. 1 and 2 and a sample 2 of the radiator shown in Fig. 4 were manufactured, while four kinds of samples of the radiators different from one another in the ratio of the minor axis r2 to the major axis rl of the evaporative section 10 of the heat pipe shown in Fig. 2 were manufactured, and the radiation capability of the sample of each radiator was measured.

On the basis of the result of the measurement, the ratio of the radiation capability a of the radiator as the sample 1 to the radiation capability b of the radiator as the sample 2 is expressed in the axis of ordinate, while the radiation capability of each of the radiators as four kinds of samples described above is expressed in the axis of abscissa, as shown in Fig. 7.

According to the result of the measurement, it is found that the radiation capability is not reduced even though the gaps 22 as shown in Fig. 2 remain between both the major-axial ends of the evaporative section 10 and both the major-axial ends of the pipe insertion hole 20 of the heat conductive plate 2, when the ratio of the minor axis r2 to the major axis rl of the evaporative section 10 of the heat pipe in the radiator is not more than 0.6, and the minor axis r2 is not less than 1.5 mm.

Then, a sample 3 of the radiator was manufactured by filling the gaps 23 between the evaporative section 10 of each heat pipe 1 and each pipe insertion hole 20 of the heat conductive plate 2 with molten solder (not shown) in the state shown in Fig. 3, and then mounting radiation fins similar to the radiation fins 30 shown in Fig. 1 on the condensive section of the heat pipe 1.

With respect to the radiator as the sample 3 and each of the radiators as the samples 1 and 2, the limit of the heat transportation rate of each sample was measured by bringing a heat-generating body 50 into contact with the heat conductive plate 2 as shown in Fig. 5, and then varying the inclination angle &commat; e of of the heat pipe 1, while sending air to the portion of the radiation fins. The results thus obtained are shown in Fig. 6.

According to the result of the measurement, the radiation capability of the radiator as each of the samples 1 and 2 according to the embodiment of the present invention was more than twice as much as the radiation capability of the radiator as the sample 3 according to the comparative embodiment, when the inclination angle G of the heat pipe 1 is 0 . On the other hand, the former radiation capability was approximately five times as much as the latter radiation capability, when the inclination angle &commat; e was was 90 .

When the overall thermal resistance was measured with respect to the radiator as each of the samples described above, the thermal resistance of the radiator as each of the samples 1 and 2 according to the embodiment of the present invention showed a value lower by approximately 5 % than the thermal resistance of the radiator as the sample 3 according to the comparative embodiment. This is because the conduction rate of condensive heat in the expanded heat pipe particularly has a value higher by 50 % or above than that in the heat pipe which is not expanded.

Figs. 8 and 9 show a radiator as another embodiment according to the present invention, respectively.

The radiator in this embodiment comprises heat pipes 1 each having a flat cross section as a whole, a heat conductive plate 2 fixed to an evaporative section 10 of the heat pipe 1, a heat conductive plate 4 fixed to a condensive section 11 of the heat pipe 1, and radiation fins 30 mounted on the heat conductive plate 4.

Each radiation fin 30 is constituted similarly to the radiation fin 30 in the radiator shown in Fig. 11.

The radiator in this embodiment is used in such a state that the heat-generating components 5 mounted on a printed circuit board 7 are brought into contact with the underside of the heat conductive plate 2 through a highly heat conductive rubber 6.

The heat conductive plate 2 is extruded by an aluminum alloy into a solid one piece, and has a thickness of 3 mm, a width of 100 mm and a length of 180 mm. Two pieces of flat pipe insertion holes 20 each having a major axis of 6.0 mm and a minor axis of 2.0 mm are formed in the center of a thickness portion of the heat conductive plate 2. The major axis of each pipe insertion hole 20 extends approximately parallel to one surface of the heat conductive plate 2.

Incidentally, the other heat conductive plate 4 has the pipe insertion holes (not shown) similar in size to those of the heat conductive plate 2.

The heat pipe 1 is constituted by working a copper pipe having a circular cross section into a flat shape. The heat pipe 1 prior to the manufacture of the radiator has a minor axis of 1.8 mm, a major axis of 5.8 mm and a length of 300 mm.

Each end of the heat pipe 1 is inserted into each pipe insertion hole 20 of each of the heat conductive plates 2, 4 such that the major axis of the heat pipe extends parallel to the major axis of the pipe insertion hole 20.

Then, the heat conductive plate 2 is mounted on a holder (not shown) and then clamped. Both the heat conductive plate 2 and the holder are heated for approximately 30 minutes in a heating furnace (not shown) held at 1800C, then carried out of the heating furnace and cooled down at room temperature.

When the heat pipe 1 having the flat cross section is heated in the heating furnace, the internal pressure of the heat pipe 1 is increased, and the heat pipe 1 is expanded and enlarged so as to be rounded, namely, toward the minor axis. Thus, as shown in Fig.

2, the upper and lower major-axial surfaces of the heat pipe 1 are pressedly attached in an almost close contact state to the upper and lower major-axial inside wall surfaces of the pipe insertion hole 2. In this manner, the heat conductive plate 2 is fixed to the evaporative section 10 of the heat pipe 1, while the heat conductive plate 4 is fixed to the condensive section 11 thereof.

The section of each of the evaporative section 10 and the condensive section 11 in the fixed state has a minor axis of 2.0 mm and a major axis of 5.68 mm.

As described above, after the heat conductive plates 2, 4 are respectively fixed to the evaporative section 10 and the condensive section 11 of the heat pipe 1, the radiation fins 30 are mounted on both surfaces of the heat conductive plate 4 to manufacture the heat pipe type radiator.

According to the radiator as the embodiment shown in Figs. 8 and 9, since other basic constitution and operation are approximately similar to those of the embodiment shown in Fig. 1, except that the radiation fins 30 each having a larger surface area are mounted on the heat conductive plate 4 fixed to the condensive section 11 of the heat pipe 1, the detailed description thereof will be omitted.

In each of the embodiments described above, after the inside wall surface of each pipe insertion hole 20 of each of the heat conductive plates 2, 4 is treated with solder and plating or the like, the heat pipe 1 may be pressedly attached to the pipe insertion hole 20 by partially inserting the heat pipe 1 into the pipe insertion hole 20 and then expanding the heat pipe 1 by heating.

Otherwise, after the partial or whole surface of the heat pipe 1 is treated with solder and plating or the like, the heat pipe 1 may be pressedly attached to the pipe insertion hole 20 by partially inserting the heat pipe 1 into the pipe insertion hole 20 and then expanding the heat pipe 1 by heating.

In these cases, a solder layer is interposed on the contact surface between the heat pipe 1 and each of the upper and lower inside wall surfaces of the pipe insertion hole 20.

While each of the embodiments has been described only in connection with a case of mounting the heat conductive plate 2 or those 2 and 4 on the evaporative section 10 or both the evaporative section 10 and the condensive section 11 of the heat pipe 1, the present invention includes also a case of integrating the heat conductive plate 2 and the other heat conductive plate 4 shown in Fig. 8 into a solid one piece, for example, and then fixing the heat pipe 1 and the heat conductive plate 2 together in such a state that the heat pipe 1 is wholly embedded in the heat conductive plate 2. In the radiator having the structure as described above, the appropriate radiation fins 30 are preferably mounted on a part of the heat conductive plate 2.

Claims

Claims:

1. A heat pipe type radiator including one or a plurality of heat pipes (1) mounted on a heat conductive plate (2) to carry out the heat exchange between heatgenerating components (5) of an electronic apparatus and said heat pipes through said heat conductive plate (2), characterized in that: said heat conductive plate (2) is molded by aluminum or aluminum alloy into a solid one piece; a pipe insertion hole (20) having an approximately flat or elliptical cross section is formed in the thickness portion of said heat conductive plate (2) such that a major axis of said pipe insertion hole extends approximately parallel to one surface of said heat conductive plate; said heat pipe (1) is partially inserted into said pipe insertion hole (20); and the partially inserted portion of said heat pipe into said pipe insertion hole (20) is formed to have an approximately flat or elliptical cross section and has the surfaces approximately parallel to the major axis of the inserted portion, and said surfaces being pressedly attached in an almost close contact state to the inside wall surface approximately parallel to the major axis of said pipe inserted hole (20).

2. A heat pipe type radiator according to claim 1, wherein the inserted portion of said heat pipe (1) is constituted such that the ratio of a minor axis (r2) to a major axis (rl) is not more than 0.6, and the minor axis (r2) is not less than 1.5 mm.

3. A heat pipe type radiator according to claim 1 or 2, wherein said heat conductive plate (2) is constituted by an extruded material having a thickness of not less than 2.5 mm.

4, A heat pipe type radiator according to any one of claims 1 to 3, wherein the inserted portion of said heat pipe (1) has one or both surfaces approximately parallel to the major axis (rl) thereof and fixedly attached to said inside wall surface of said pipe insertion hole (20) through a thin solder layer.

5. A heat pipe type radiator according to any one of claims 1 to 4, wherein radiation fins (3) are mounted on at least a part of a portion of the heat pipe (1) other than said inserted portion.

6. A heat pipe type radiator including one or a plurality of heat pipes (1) mounted on heat conductive plates (2,4) to carry out the heat exchange between heat-generating components (5) of an electronic apparatus and said heat pipes (1) through said heat conductive plates (2,4), characterized in that: each of said heat conductive plates (2,4) is molded by aluminum or aluminum alloy into a solid one piece; a pipe insertion hole (20) having an approximately flat or elliptical cross section is formed in the thickness portion of each of said heat conductive plates (2,4) such that a major axis of said pipe insertion hole extends approximately parallel to one surface of each of said heat conductive plates (2,4); said heat pipe (1) is inserted into said pipe insertion hole (20); and said heat pipe is formed to have an approximately flat or elliptical cross section and has the surfaces approximately parallel to the major axis of an inserted portion, and said surfaces being pressedly attached in an almost close contact state to the inside wall surface approximately parallel to the major axis of said pipe insertion hole (20).

7. A heat pipe type radiator according to claim 6, wherein said heat pipe (1) is constituted such that the ratio of a minor axis (r2) to a major axis (rl) is not more than 0.6, and the minor axis (r2) is not less than 1.5 mm.

8. A heat pipe type radiator according to claim 6 or 7, wherein each of said heat conductive plates (2,4) is constituted by an extruded material having a thickness of not less than 2.5 mm.

9. A heat pipe type radiator according to any one of claims 6 to 8, wherein said heat pipe (1) has one or both surfaces parallel to the major axis (rl) thereof and fixedly attached to said inside wall surface of said pipe insertion hole through a thin solder layer.

10. A heat pipe type radiator according to any one of claims 6 to 9, wherein radiation fins (30) are mounted on a part of said heat conductive plate (4).

11. A method for manufacturing a heat pipe type radiator including one or a plurality of heat pipes (1) mounted on heat conductive plates (2,4) molded by aluminum or aluminum alloy into a solid one piece to carry out the heat exchange between heat-generating components (5) of an electronic apparatus and said heat pipes through said heat conductive plates (2,4), characterized in that: the partial or whole heat pipe portion to be inserted having a flat or elliptical cross section is inserted into a pipe insertion hole (20) having a flat or elliptical cross section and formed in the thickness portion of each of said heat conductive plates (2,4) such that a major axis of said pipe insertion hole extends approximately parallel to one surface of said heat conductive plate, in such a state that a major axis of the inserted heat pipe portion extends approximately parallel to the major axis of said pipe insertion hole (20); and the surfaces approximately parallel to the major axis of said inserted portion are pressedly attached to the inside wall surface approximately parallel to the major axis of said pipe insertion hole (20) by heating said heat pipe (1) to expand said inserted heat pipe portion toward the minor axis of said heat pipe.

12. A heat pipe radiator substantially as described with reference to, and as shown in, Figures 1 and 2, Figure 4, or Figures 8 and 9 of the accompanying drawings.

13. A method for manufacturing a heat pipe radiator, substantially as described with reference to Figures 1 to 9 of the accompanying drawings.