GRAPHITE HEAT SINK AND METHOD OF MANUFACTURING THE SAME

Info

Publication number: 20190120568
Type: Application
Filed: Oct 2, 2018
Publication Date: Apr 25, 2019
Inventors: RYOU KUWABARA (Osaka), NAOMI NISHIKI (Kyoto), MASATO MORI (Hyogo), TAKESHI NISHIKAWA (Osaka)
Application Number: 16/149,359

Abstract

A graphite heat sink with light weight and high mechanical strength includes graphite fins and a metal press-fitted and fixed to a part of a surface of the graphite fin.

Description

Description

TECHNICAL FIELD

The technical field relates to a graphite heat sink and a method of manufacturing the same capable of managing heat radiated from a heat source of an electronic device, etc.

BACKGROUND

As small-sized electronic devices with an ability to operate at high processing speed and high frequencies having more complicated power conditions, there are a microprocessor, electronic and electric components, integrated circuits of devices, and high-output optical devices, etc. The development of these electronic devices is highly advancing, and an extremely high temperature can be generated. However, in general, the microprocessor, the integrated circuits or other high-performance electronic components operate efficiently only under threshold temperatures within a specific range. Excessive heat generated during operation of the electric component is not only harmful to an intrinsic performance of the component but also the performance and reliability of the entire system may be impaired due to the heat, which may cause a system failure. As a range of ambient conditions including the excessive temperature expected by operation of an electronic system becomes wider and wider, adverse effects due to excessive heat may be promoted.

As the necessity of dissipating heat from the small-sized electronic devices is increased, management in design of electronic devices is becoming a more important element. Both the performance reliability and the expected lifetime of the electronic device are in inverse proportion to a component temperature of the electronic device. For example, when an operation temperature of a device such as a typical silicon semiconductor is decreased, processing speed, reliability and the expected lifetime of the device can be increased. Therefore, the most important thing for obtaining the maximum component lifetime and reliability is to control the operation temperature of the device within a limit set by designers.

Materials attracting attention as materials excellent in the above-described heat management are carbon materials typified by graphite. Graphite has a thermal conductivity equivalent to aluminum and copper which are common materials having high thermal conductivities and also has more excellent heat transfer properties than that of copper, therefore, graphite attracts attention as the material for heat dissipation fins used for a heat spreader of an LSI chip, a heat sink of a semiconductor power module, etc.

In a related-art heat sink using the carbon material, for example, as shown in JP-T-2009-505850 (Patent Literature 1, the contents of which are incorporated herein by reference), a metal film is coated on compressed and solidified brittle carbon particles to thereby prevent peeling of graphite and improve mechanical strength.

However, the heat sink of Patent Literature 1 is made of material obtained by compressing and solidifying graphite particles that does not form a graphite structure that is dense in a planar direction, therefore, heat transfer performance is low. The graphite particles have to be fixed by an adhesive and have low mechanical strength. Furthermore, a coating agent to be used is made of metal, therefore, the entire heat sink becomes heavy in weight. Additionally, processes including metal coating, adhesive bonding, etc. are complicated, which increases manufacturing costs.

SUMMARY

The present disclosure has been made in view of the above problems and an object thereof is to provide a graphite heat sink with light weight and high mechanical strength.

In order to achieve the above object, the graphite heat sink according to the present disclosure includes graphite fins and a metal press-fitted and fixed to parts of surfaces of the graphite fins.

A method of manufacturing a graphite heat sink according to the present disclosure includes the steps of forming a graphite plate by applying pressure to a plurality of laminated polymer films and by heating the films to be graphitized to obtain a graphite fin and press-fitting and fixing a metal to apart of a surface of the obtained graphite fin.

When adopting the graphite heat sink according to the present disclosure, it is possible to provide the graphite heat sink with light weight and high mechanical strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a structure of a graphite heat sink according to Embodiment 1;

FIG. 2A is a schematic view showing a bonding structure between a graphite fin and a fin base in FIG. 1;

FIG. 2B is an enlarged view showing the details of the bonding structure of FIG. 2A;

FIG. 3 is a schematic view of thermal conductivity evaluation test TEG according to Embodiment 1 and comparative examples;

FIG. 4A is an enlarged schematic view showing a state obtained before press fitting in the bonding structure between the graphite fin and the fin base in the case where a gap is provided at least one of both sides of the graphite fin;

FIG. 4B is an enlarged schematic view showing a bonding structure obtained after the graphite fin of FIG. 4A is press-fitted to the fin base;

FIG. 5A is an enlarged schematic view obtained before press fitting in a bonding structure between the graphite fin and the fin base in a case where a side surface shape of a groove for the fin is a wedge shape; and

FIG. 5B is an enlarged schematic view showing a bonding structure obtained after the graphite fin of FIG. 5A is press-fitted to the fin base.

DESCRIPTION OF EMBODIMENTS

A graphite heat sink according to an aspect includes graphite fins and a metal press-fitted and fixed to parts of surfaces of the graphite fins.

According to the above structure, contact performance between the graphite fin and the metal can be increased as well as a graphite heat sink with light weight and high strength can be obtained.

In the graphite heat sink according to another aspect, a press-fitting amount of the metal may be 15% or more to 35% or less of a thickness of the graphite fin extending along a press-fitting direction.

The graphite heat sink according to further another aspect may further include a metal fin base continued from the metal.

A method of manufacturing a graphite heat sink according to an aspect includes the steps of forming a graphite plate by applying pressure to a plurality of laminated polymer films and by heating the films to be graphitized to obtain a graphite fin and press-fitting and fixing a metal to a part of a surface of the obtained graphite fin.

In the method of manufacturing the graphite heat sink according to another aspect, the polymer film may be at least one kind selected from a group including polyoxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, polypyromellitimide, aromatic polyamide, polyphenylene benzimidazole, polyphenylene benzobisimidazole, polythiazole and polyparaphenylene vinylene.

In the method of manufacturing the graphite heat sink according to further another aspect, a press-fitting amount of the metal may be 15% or more to 35% or less of a thickness of the graphite fin extending along a press-fitting direction.

In the method of manufacturing the graphite heat sink according to further another aspect, the step of press-fitting and fixing the metal to a part of the surface of the graphite fin may include the steps of providing a groove for the fin in the fin base continued from the metal and setting up the graphite fin in the groove for the fin to press-fit the graphite fin to the fin base.

In the method of manufacturing the graphite heat sink according to further another aspect, a gap between the graphite fin and the groove for the fin may be within a range from 1% to 5% when a width of the groove for fin is 100% in the step of setting up the graphite fin in the groove for the fin to press-fit the graphite fin to the fin base.

Hereinafter, a graphite heat sink and a method of manufacturing the same according to embodiments will be explained with reference to the attached drawings. In the drawings, the same reference numerals are given to substantially the same members.

Embodiment 1 <Graphite Heat Sink>

Hereinafter, a graphite heat sink 101 according to Embodiment 1 will be explained with reference to the drawings.

FIG. 1 is a schematic view showing a structure of the graphite heat sink 101 according to Embodiment 1. FIG. 2A is a view schematically showing a bonding structure 100 between a graphite fin 102 and a fin base 103 in FIG. 1. FIG. 2B is an enlarged view showing the details of the bonding structure 100 of FIG. 2A. In the drawings, a press-fitting direction of the graphite fin 102 to the fin base 103 is shown as a “−z axis direction” for convenience. An extending direction of the fin base 103 is shown as an “x axis direction”.

The graphite heat sink 101 includes the graphite fins 102 and the metal 103 press-fitted and fixed to parts of surfaces of graphite fins 102.

Component members forming the graphite heat sink 101 will be explained below.

<Graphite Fin>

As the graphite fin 102, for example, a pressure laminate product of highly-oriented graphite can be used. The graphite fin 102 may be, for example, a columnar shape, a plate shape, a foil state, etc.

<Fin Base: Metal>

As the metal 103 press-fitted and fixed to parts of surfaces of graphite fins 102, for example, a single element and an alloy such as copper, aluminum, stainless steel, die cast, etc. can be used. A metal press-fitting portion 104 to be press-fitted and fixed in the metal 103 may have a shape protruding into the graphite fin 102 as shown by an enlarged view of FIG. 2B. The shape may be any of, for example, a protrusion shape, a claw shape, a columnar shape, a plate shape, etc.

A press-fitting amount 106 of the metal 103 is preferably 15% or more to 35% or less of a thickness of the graphite fin 102 extending along the press-fitting direction (−z axis direction), and particularly preferably 20% or more to 30% or less. When the press-fitting amount 106 is less than 15%, it is difficult to hold the graphite fin 102 as the surface of graphite is slippery. The graphite fin 102 slips out due to impact at a drop test, a vibration test and so on, therefore, it is difficult to secure the contact and heat dissipation performance is reduced. On the other hand, when the press-fitting amount 106 exceeds 35%, the graphite structure of the graphite fin 102 is broken and it is difficult to keep the strength in the planar direction (x axis direction). Accordingly, an appropriate range of the press-fitting amount 106 is 15% or more to 35% or less of the thickness of the graphite fin 102 extending along the press-fitting direction (−z axis direction).

The metal 103 may further configure the fin base 103 supporting the graphite fins 102. Heat can be dissipated through the metal and the fin base 103. The fin base 103 may be provided with grooves for fins sandwiching the graphite fins 102. At that time, caulking grooves 105 may be formed in the vicinity of the grooves for fins in the fin base 103.

<Method of Manufacturing Graphite Heat Sink>

Next, a method of manufacturing the graphite heat sink 101 will be explained.

(1) First, a plurality of polymer films of at least one kind selected from a group including polyoxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, polypyromellitimide, aromatic polyamide, polyphenylene benzimidazole, polyphenylene benzobisimidazole, polythiazole and polyparaphenylene vinylene are laminated, which are heated and fired while controlling an applied pressure to be graphitized, thereby forming a graphite plate and fabricating the graphite fins 102.
(2) Second, the graphite fins 102 are set up on the metal fin base 103 with grooves and part of the fin base 103 is press-fitted and fixed to parts of surfaces of the graphite fins 102, thereby forming the graphite heat sink 101. As metal used for the fin base 103, for example, a single element or an alloy such as copper, aluminum, stainless steel, die cast and so on can be used.

According to the above, the graphite heat sink 101 shown in FIG. 1 can be obtained.

Furthermore, the step of setting up the graphite fin 102 of (2) described above on the metal fin base 103 and press-fitting and fixing a part of the fin base 103 to part of the surface of the graphite fin 102 will be explained.

FIG. 2A is a schematic view showing the bonding structure 100 between the graphite fin 102 and the fin base 103. FIG. 2B is an enlarged view showing the details of the bonding structure 100 of FIG. 2A, schematically showing the metal press-fitting portions 104 press-fitting and fixing a part of the fin base 103 to a part of the surface of the graphite fin 102. As one of methods of forming the bonding structure 100 of the metal press-fitting portions 104, there is a method in which the metal of the fin base 103 is heaped up around the graphite fin 102 by pressurizing a portion near the grooved fin base 103 at an angle of 45 degrees, and in that state, a part of metal of the fin base 103 is press-fitted into the graphite fin 102 to be fixed. At that time, the caulking grooves 105 are formed in the vicinity of the groove for the fin in the fin base 103.

As another method of forming the bonding structure 100 of the metal press-fitting portions 104, there is a method in which the graphite fin 102 is inserted into a portion where the groove of the fin base 103 is expanded in a high-temperature environment and the graphite fin 102 can be fixed due to contraction of the metal at the time of returning to room temperature by using extremely small variation in thermal expansion coefficient of graphite and a difference in thermal expansion between graphite and metal. It is not necessary to form the caulking grooves 105 in this method. However, the method depends on the thermal expansion coefficient of the fin base 103, and for example, an aluminum base using aluminum as the metal expands only several μm even at 500° C. Accordingly, high-temperature environment exceeding 500° C. and the process of setting up the graphite fin 102 in that environment are necessary. Therefore, the former method is preferable for the process for forming the bonding structure of the metal press-fitting structure.

Furthermore, as a result of considering positional relationship between the groove for the fin of the fin base 103 and the graphite fin 102, it is found that it is preferable that there is a gap 112 on at least one side between a groove for the fin 114 and both sides of the graphite fin 102.

FIGS. 4A and 4B are enlarged views showing states obtained before press fitting and after press fitting in the bonding structure between the graphite fin 102 and the fin base 103 in the case where the gap 112 is provided on at least one of both sides of the graphite fin 102. FIG. 4A shows the state obtained before press fitting and FIG. 4B shows the state obtained after press fitting. When the graphite fin 102 is set up so as to correspond to the groove for the fin 114, the gap 112 is formed between the groove for the fin 114 and the graphite fin 102 (FIG. 4A). After that, the fin base 103 is locally pressurized to form the caulking grooves 105, thereby forming the metal press-fitting portions 104 so as to bite into the graphite fin 102 (FIG. 4B). Considering structural symmetry, it is particularly preferable to provide equal gaps 112 on both sides of the graphite fin 102.

In a case where there is no gap on both sides of the graphite fin 102, the graphite fin 102 is slightly lifted up at a moment of press fitting to the fin base 103, therefore, contact between a bottom surface of the groove 114 for the fin 102 and a cross section of the graphite fin 102 becomes insufficient and it may be difficult to obtain sufficient thermal conductivity. On the other hand, when there is the gap 112 on at least one of both sides of the graphite fin 102, the timing of press fitting of the graphite fin 102 is slightly shifted. Accordingly, the graphite fin 102 itself is not lifted up and the contact between the graphite fin 102 and the bottom surface of the groove for the fin 114 of the fin base 103 can be held.

The gap 112 is defined by (a width of the bottom surface of the groove for the fin 114−a thickness of the graphite fin 102) (FIG. 4A), and the gap 112 is preferably 1 to 5% with respect to the width of the bottom surface of the groove for the fin 114.

The shape of the groove for the fin 104 is not limited to a rectangular shape. Any shape may be adopted as far as the contact between the cross section of the graphite fin 102 and the bottom surface of the groove for the fin 114 is secured after the press fitting and reliability strength can be maintained. Therefore, it is further preferable that the position of the graphite fin 102 can be fixed before press fitting and a force applied to the graphite fin 102 at the moment of press fitting is in a direction of the fin base 103 (downward direction in the drawing: −z axis direction).

FIG. 5A is an enlarged schematic view showing the bonding structure between the graphite fin 102 and the fin base 103 obtained before the press fitting in a case where a side surface shape of the groove for the fin 114 is a wedge shape. FIG. 5B is an enlarged schematic view showing the bonding structure obtained after the graphite fin 102 of FIG. 5A is press-fitted into the fin base 103. For example, when the wedge shape as shown in FIG. 5A and FIG. 5B is adopted as the shape of the side surface of the groove for the fin 114, an effect of pushing the graphite fin 102 into the fin base 103 at a moment of press fitting can be obtained, which is very preferable. The side surface shape of the groove for the fin 114 as shown in FIG. 5A and FIG. 5B is cited as an example, and the shape is not limited to this. For example, a protrusion shape, a claw shape, a columnar shape, a plate shape, etc. may be adopted. However, it is common to use the rectangular shape because of high costs in processing.

As described above, the press-fitting amount 106 of the metal of a part of the fin base 103 is preferably 15% or more to 35% or less of the thickness of the graphite fin 102 extending along the press-fitting direction (−z axis direction), and particularly preferably 20% or more to 30% or less. When the press-fitting amount 106 is less than 15%, it is difficult to hold the graphite fin 102 as the surface of graphite is slippery. The graphite fin 102 slips out due to impact at the drop test, the vibration test and so on, therefore, it is difficult to secure the contact and heat dissipation performance is reduced. On the other hand, when the press-fitting amount 106 exceeds 35%, the graphite structure of the graphite fin 102 is broken and it is difficult to keep the strength in the planar direction (x axis direction). Accordingly, an appropriate range of the press-fitting amount 106 is 15% or more to 35% or less of the thickness of the graphite fin 102 extending along the press-fitting direction (−z axis direction).

According to the above structure, connection between the graphite fin 102 and the fin base 103 as the metal can be mechanically performed, which differs from chemical bond using an adhesive, therefore, higher strength can be realized than in the related-art heat sink using graphite. Moreover, structural materials such as a metal coating agent and the adhesive used in the above related-art literature are not necessary, therefore, a weight can be reduced to approximately ¾ of the related-art graphite heat sink. As the bonding is completed only by the caulking process, processes can be simplified and productivity is largely improved.

Example 1

The graphite heat sink 101 according to Embodiment 1 was fabricated as follows.

First, a pressure laminate product of highly-oriented graphite with 50 mm in height, 50 mm in width and 0.2 mm in thickness was used as the graphite fin 102. A graphite plate was used, which has been obtained by laminating a plurality of polymer films of polyoxadiazol as a starting material and firing while controlling the applied pressure to make graphite. As the fin base 103, an aluminum base with 50 mm square, 5 mm in thickness with eight grooves each having 2 mm in depth at intervals of 4 mm was used. At the time of caulking, aluminum was press-fitted into the graphite fin 102 at a pressing force of 15 t with a press-fitting amount of 0.06=(30%) to fabricate the graphite heat sink 101. Performance evaluation was performed to the fabricated graphite heat sink 101 by a thermal conductivity test before and after a drop test and a vibration test.

The starting material of the pressure laminate product of highly-oriented graphite is not limited to the above polyoxadiazol as the polymer film. For example, at least one kind selected from a group including polyoxadiazole, polybenzothiazol, polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, polypyromellitimide, aromatic polyamide, polyphenylene benzimidazole, polyphenylene benzobisimidazole, polythiazole and polyparaphenylene vinylene may be used as the polymer film.

Example 2

In Example 2, a graphite heat sink was fabricated in substantially the same conditions as Example 1 except that the press-fitting amount of aluminum was 0.04 mm (20%).

Example 3

In Example 3, a graphite heat sink was fabricated in substantially the same conditions as Example 1 except that the press-fitting amount of aluminum was 0.03 mm (15%).

Example 4

In Example 4, a graphite heat sink was fabricated in substantially the same conditions as Example 1 except that the press-fitting amount of aluminum was 0.07 mm (35%).

Example 5

In Example 5, a graphite plate was coated with polyimide at a thickness of 5 μm, and a graphite heat sink was fabricated in the same conditions as Example 1 other than the above.

Comparative Example 1

As Comparative Example 1, a heat sink was fabricated in the same conditions as Example 1 except that a pressure laminate product fabricated by using a polyester film (other than those of Example 1) as a polymer film was used.

Comparative Example 2

As Comparative Example 2, the graphite plate and the fin base in Example 1 were used, and the graphite plate and the fin base were bonded by a conductive grease (manufactured by Shin-Etsu Chemical Co., Ltd.) to fabricate a heat sink.

Comparative Example 3

As Comparative Example 3, a graphite heat sink was fabricated in substantially the same conditions as Example 1 except that the press-fitting amount of aluminum was 0.02 mm (10%).

Comparative Example 4

As Comparative Example 4, a graphite heat sink was fabricated in substantially the same conditions as Example 1 except that the press-fitting amount of aluminum was 0.08 mm (40%).

<Evaluation Method> (Thermal Conductivity Evaluation Test)

Samples fabricated in Examples and Comparative Examples were subjected to the thermal conductivity evaluation test before and after the drop test and the vibration test. FIG. 3 is a schematic view of thermal conductivity evaluation TEG. In an evaluation in a forced cooling environment, a temperature measuring part 108 (10 mm square, t (thickness) 5 mm, made of copper) and a heater 110 (10 mm square, t (thickness) 1 mm, made of ceramic) were bonded by applying 0.3 mm grease layers 107 just under the center of the graphite heat sink described in the above examples and comparative examples, and a fan 109 with 50 mm square (model number: UDQF56C11CET (manufactured by Panasonic Corporation) is installed just above the heat sink, then, evaluation was performed by measuring temperatures at boundaries between the heater and the heat sink at the time of operating the heater and the fan at an input 11 V.

(Drop Test, Vibration Test)

Tests were performed to respective samples in conditions shown in Table 1 below.

TABLE 1 Drop test 100 G three directions (xyz) Vibration test Sinusoidal vibration test (conformance to Frequency range: 10 to 55 Hz three directions JIS C 60068-2-6) Sweep rate: 1 octave/min Displacement: 0.7 mm p-p Sweep cycle frequency: each axis 10 times

<Considerations>

Table 2 shows evaluation results of thermal conductivity according to Examples 1 to 5 and Comparative Examples 1 to 4.

TABLE 2 Starting material Coating Bonding method Caulking press fitting (%) Aluminum heat sink Example 1 polyoxadiazole not coated caulking 30 Example 2 polyoxadiazole not coated caulking 20 Example 3 polyoxadiazole not coated caulking 15 Example 4 polyoxadiazole not coated caulking 35 Example 5 polyoxadiazole Coated caulking 30 Comparative polyester film not coated caulking 30 Example 1 Comparative polyoxadiazole not coated adhesion — Example 2 Comparative polyoxadiazole not coated caulking 10 Example 3 Comparative polyoxadiazole not coated caulking 40 Example 4 Thermal conductivity evaluation [° C.] Temperature Temperature difference difference Strength Before After drop before and After vibration before and evaluation Overall test test after test test after test Determination Determination evaluation Aluminum 50.5 50.6 0.1 50.8 0.2 heat sink Example 1 43.6 43.8 0.2 43.5 −0.1 excellent good good Example 2 43.7 43.7 0.0 43.8 0.1 excellent good good Example 3 44.8 45.4 0.6 45.2 0.4 good good good Example 4 45.0 45.2 0.2 45.4 0.4 good good good Example 5 43.8 44.1 0.3 44.0 0.2 excellent good good Comparative 52.5 unmeasurable — unmeasurable — poor — poor Example 1 Comparative 44.0 48.3 4.3 47.1 3.1 poor good poor Example 2 Comparative 44.7 46.0 1.3 45.3 0.6 poor good poor Example 3 Comparative 44.9 46.1 1.2 45.7 0.8 poor poor poor Example 4

The thermal conductivity evaluation was determined in comparison with evaluation results in the related-art aluminum heat sink.

As a structure of the aluminum heat sink, samples in which the base portion and the fin portion were integrally formed were used for valuation. As dimensions of the samples, the base portion having 50 mm square, 5 mm in thickness, and eight fin portions each having 48 mm in height, 200 μm in thickness at intervals of 4 mm were used. Evaluation criteria of thermal conductivity are as follows:

(1) Cases where the temperature difference before the drop/vibration test is 5° C. or more as well as the difference before and after the drop/vibration test is 0.3° C. or less are determined as “excellent”.
(2) Cases where the temperature difference before the drop/vibration test is 5° C. or more as well as the difference before and after the drop/vibration test is more than 0.4 to less than 1° C. are determined as “good”.
(3) Cases where the temperature difference before the drop/vibration test is 5° C. or more as well as the difference before and after the drop/vibration test is 1° C. or more are determined as “poor”.
(4) Cases where the temperature difference before the drop/vibration test is less than 5° C. are determined as “unacceptable”.

Concerning determination criteria of strength evaluation, observation of cross sections was performed after the evaluation of thermal conductivity after the drop and vibration tests. Cases where a crack caused by breaking of the graphite layer due to impact and vibration is not generated are determined as “good”. Cases where a crack is generated are determined as “poor”.

Lastly, as overall evaluation, only cases where both the thermal conductivity evaluation and the strength evaluation are “excellent” or “good” are determined as “good”, and cases where either or both of them are “poor” are determined as “poor”.

As can be seen from Examples 1 and 2, the graphite structure in the planar direction (x axis direction) of the graphite fin 102 is not broken as far as the press-fitting amount of the metal as the fin base 103 to a part of the surface of the graphite fin 102 is in the range from 20% or more to 30% or less of the thickness. Furthermore, the contact between the graphite fin 102 and the fin base 103 is secured without slipping, therefore, temperature variation after the drop and vibration tests is 0.2° C. or less. Moreover, as can be seen from Examples 3 and 4, temperature variation can be suppressed to 0.6° C. or less also when the press-fitting amount is within a range from 15% or more to 35% or less of the thickness of the graphite fin 102, which maintains sufficient heat dissipation performance. Concerning the strength evaluation, cases where the press-fitting amount is 35% or less of the thickness, the graphite structure on the plane of the graphite fin 102 is not cut though part of graphite is deformed by press fitting of aluminum. Accordingly, the graphite layer of the graphite fin 102 is not broken and a crack is not generated.

On the other hand, when a polymer film other than materials shown in Example 1 is used as shown in Comparative Example 1, graphitization of the polymer film is insufficient and bonding strength at the time of caulking is not sufficient either, therefore, it is unmeasurable after the drop and vibration tests, which makes the heat sink difficult to function. As can be seen from Comparative Example 2, in a graphite heat sink formed by adhesive bonding between the graphite fin and the fin base, thermal conductivity in the equivalent level is shown before the drop and vibration tests, however, the thermal conductivity is decreased as the adhesion is removed and part of the graphite fins 102 slips off after the test. As can be seen from Comparative Example 3, slipping occurs after the drop and vibration tests when the press-fitting amount of the metal at the time of caulking is small, which decreases thermal conductivity. However, slipping occurs because adhesiveness between the graphite fin 102 and an adhesive or the fin base is low in Comparative Examples 2 and 3, therefore, a crack is not generated in the graphite layer. Furthermore, as can be seen from Comparative Example 4, when the press-fitting amount of the metal at the time of caulking is too large, a crack is generated after the drop and vibration tests, which decreases thermal conductivity and strength.

Table 3 shows results obtained by providing the groove for the fin in the fin base and measuring various gaps (No. 1 to No. 12) set between the graphite fin and the groove for the fin as well as performing thermal conductivity evaluation and strength evaluation in a condition of Example 1. The gap 112 is defined by (the width of the bottom surface of the groove for the fin 114−the thickness of the graphite fin 102).

TABLE 3 Thermal conductivity evaluation Gap Before After Temperature After Temperature Strength Overall [%] test drop difference vibration difference Determination Determination evaluation Aluminum 50.5 50.6 0.1 50.8 0.2 heat sink No. 1 1.2 44.3 44.3 0 44.4 0.1 good good good 2 1.6 43.6 43.7 0.1 43.8 0.2 good good good 3 2.2 43.7 44.1 0.4 44.0 0.3 good good good 4 2.2 43.6 43.8 0.2 43.9 0.3 good good good 5 2.5 43.4 43.3 −0.1 43.3 −0.1 excellent good good 6 2.7 43.6 43.8 0.2 43.5 −0.1 excellent good good 7 2.8 44.0 44.3 0.3 44.2 0.2 good good good 8 3 43.9 44.2 0.3 44.1 0.2 good good good 9 3.1 44.1 44.4 0.3 44.3 0.2 good good good 10 4.8 44.5 44.6 0.1 44.4 −0.1 good good good 11 0.5 48.2 48.1 −0.1 48.4 0.2 fair good fair 12 6.0 43.8 46.2 2.4 47.1 3.3 poor poor poor

As shown in Table 3, when a dimension of the gap is less than 1% of the width of the groove for the fin (No. 11), it is found that the contact with respect to the bottom surface becomes unstable and initial heat dissipation performance is reduced as described above. When the dimension of the gap is larger than 5% of the width of the groove for the fin (No. 12), it is found that the shape is unstable and heat dissipation performance is reduced after vibration and impact tests. Accordingly, it is preferable that the dimension of the gap is within a range of 1 to 5% of the width of the groove for the fin.

The present disclosure includes suitable combinations of arbitrary embodiments and/or examples in the above various embodiments and/or examples, whereby advantages possessed by respective embodiments and/or examples can be obtained.

The graphite heat sink according to the present disclosure can be used for heat dissipation in heat generation units in industrial equipment and the in-vehicle field.

Claims

1. A graphite heat sink comprising:

graphite fins; and

a metal press-fitted and fixed to parts of surfaces of the graphite fins.

2. The graphite heat sink according to claim 1,

wherein an amount of the metal press-fitted is 15% or more to 35% or less of a thickness of the graphite fin extending along a press-fitting direction.

3. The graphite heat sink according to claim 1, further comprising:

a metal fin base continued from the metal.

4. A method of manufacturing a graphite heat sink comprising:

forming a graphite plate by applying pressure to a plurality of laminated polymer films and by heating the films to be graphitized to obtain a graphite fin; and

press-fitting and fixing a metal to a part of a surface of the obtained graphite fin.

5. The method of manufacturing the graphite heat sink according to claim 4,

wherein the polymer film is at least one kind selected from a group including polyoxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, polypyromellitimide, aromatic polyamide, polyphenylene benzimidazole, polyphenylene benzobisimidazole, polythiazole and polyparaphenylene vinylene.

6. The method of manufacturing the graphite heat sink according to claim 4,

wherein a press-fitting amount of the metal is 15% or more to 35% or less of a thickness of the graphite fin extending along a press-fitting direction.

7. The method of manufacturing the graphite heat sink according to claim 4, wherein the press-fitting and fixing the metal to a part of the surface of the graphite fin further includes:

providing a groove for the fin in the fin base continued from the metal; and

setting up the graphite fin in the groove for the fin to press-fit the graphite fin to the fin base.

8. The method of manufacturing the graphite heat sink according to claim 7,

wherein, the setting up the graphite fin in the groove for the fin to press-fit the graphite fin to the fin base, further includes setting a gap between the graphite fin and the groove for the fin to be within a range from 1% to 5% when a width of the groove for the fin is 100%.

9. The method of manufacturing the graphite heat sink according to claim 7, wherein:

the providing of the groove includes expanding a width of the groove by heating the metal in a high-temperature environment; and

the setting up the graphite fin in the groove further includes contracting the width of the groove by returning the metal to room temperature so that the graphite fin is fixed due to contraction of the metal at the time of returning to room temperature.