JP2018129482A - Heat dissipation sheet, heat dissipation sheet manufacturing method, and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat dissipation sheet whose thermal conductivity does not easily deteriorate even when reused, a method for manufacturing the heat dissipation sheet, and an electronic device. SOLUTION: A first carbon nanotube sheet 31 having a plurality of carbon nanotubes 25, a peripheral edge portion 32a having a plurality of carbon nanotubes 25 adhered to an upper surface 31p of the first carbon nanotube sheet 31, and a peripheral edge portion 32a A second carbon nanotube sheet 32 having a flexible central portion 32b, and a third carbon nanotube sheet 33 having a plurality of carbon nanotubes 25 adhered to an upper surface 32p of the second carbon nanotube sheet 32. According to the heat dissipation sheet 34. [Selection diagram] Fig. 5

Description

  The present invention relates to a heat dissipation sheet, a method for manufacturing a heat dissipation sheet, and an electronic device.

  In a server or a personal computer, a heat spreader is fixed to an electronic component in order to dissipate heat generated by an electronic component such as a CPU (Central Processing Unit) to the outside.

  If the heat resistance between the heat spreader and the electronic component is high, the heat of the electronic component cannot be quickly transmitted to the heat spreader. For this reason, a heat radiating sheet having excellent thermal conductivity may be interposed between the electronic component and the heat spreader.

  There are various types of heat dissipation sheets. An indium sheet is an example of a heat radiating sheet. However, since expensive indium is used, it is difficult to reduce the cost of the heat radiating sheet. Moreover, the thermal conductivity of indium is 80 W / m · K, and it is difficult to efficiently dissipate heat from the electronic component with this thermal conductivity.

  Although there is a method of using a heat conductive polymer as a heat dissipation sheet, it cannot be said that the heat conductivity of the heat conductive polymer is sufficiently high.

  Therefore, a heat radiating sheet using carbon nanotubes has been studied as a heat radiating sheet instead of an indium sheet or a heat conductive polymer.

  Carbon nanotubes have a thermal conductivity of about 1500 W / m · K to 3000 W / m · K, which is very high compared to the thermal conductivity of indium (50 W / m · K). It is suitable for.

JP 2009-124110 A International Publication No. 2011/111112 JP 2005-150362 A JP 2006-147801 A JP 2006-303240 A

  By the way, in the electronic device in which the heat dissipation sheet is interposed between the electronic component and the heat spreader as described above, a defect may be found in the manufacturing process. If the cause of the problem is not in the heat dissipation sheet, it is advantageous in terms of cost to reuse the heat dissipation sheet for another electronic device.

  However, if the thermal conductivity of the heat-dissipating sheet deteriorates due to reuse, the original purpose of using carbon nanotubes having excellent thermal conductivity for the heat-dissipating sheet is lost.

  In one aspect, an object of the present invention is to provide a heat radiating sheet, a method for manufacturing the heat radiating sheet, and an electronic device that hardly deteriorate in thermal conductivity even when reused.

  In one aspect, a first carbon nanotube sheet having a plurality of carbon nanotubes, a peripheral portion having a plurality of carbon nanotubes in close contact with an upper surface of the first carbon nanotube sheet, and a central portion that is more flexible than the peripheral portion And a third carbon nanotube sheet provided with a plurality of carbon nanotubes in close contact with the upper surface of the second carbon nanotube sheet.

  According to one aspect, since the central part of the second carbon nanotube sheet is made more flexible than the peripheral part, the pressure acting on the central part during the manufacture of the electronic device is relieved. For this reason, the end of the carbon nanotube in the central portion is not easily destroyed, and deterioration of the thermal conductivity can be suppressed even if the heat dissipation sheet is reused.

FIG. 1A and FIG. 1B are cross-sectional views (part 1) in the middle of manufacturing an electronic device including the heat dissipation sheet according to the first embodiment. 2A and 2B are cross-sectional views (part 2) of the electronic device including the heat dissipation sheet according to the first embodiment during manufacture. 3A and 3B are cross-sectional views (part 3) of the electronic device including the heat dissipation sheet according to the first embodiment during manufacture. FIG. 4: is sectional drawing (the 4) in the middle of manufacture of the electronic device provided with the heat radiating sheet which concerns on 1st Embodiment. FIG. 5: is sectional drawing (the 5) in the middle of manufacture of the electronic device provided with the heat radiating sheet which concerns on 1st Embodiment. FIG. 6 is a graph showing an example of a heating profile of the heat treatment according to the first embodiment. FIGS. 7A to 7C are plan views of the first to third carbon nanotube sheets according to the first embodiment. FIG. 8 is a cross-sectional view of an electronic device according to a comparative example. FIG. 9 is a cross-sectional view of the electronic device when the electronic component is warped in the first embodiment. FIG. 10 is a graph obtained by investigating how the thermal conductivity of the heat dissipation sheet according to the comparative example changes before and after reuse. FIG. 11 is a graph obtained by investigating how the thermal conductivity of the thermal sheet according to the first embodiment changes before and after reuse. FIG. 12 is a diagram obtained by examining the Raman spectrum of the carbon nanotube in the first embodiment. FIG. 13 is a diagram obtained by investigating the thermal conductivity of carbon nanotubes in the first embodiment. FIG. 14 is a plan view of a second carbon nanotube sheet provided in the heat dissipation sheet according to the first example of the first embodiment. FIG. 15 is a cross-sectional view of an electronic device including a heat dissipation sheet according to a first example of the first embodiment. FIG. 16 is a plan view of a second carbon nanotube sheet provided in the heat dissipation sheet according to the second example of the first embodiment. FIG. 17 is a cross-sectional view of an electronic device including a heat dissipation sheet according to a second example of the first embodiment. FIG. 18 is a cross-sectional view (part 1) of the electronic device including the heat dissipation sheet according to the third example of the first embodiment during manufacture. FIG. 19 is a cross-sectional view (part 2) of the electronic device including the heat dissipation sheet according to the third example of the first embodiment during manufacture. 20A to 20C are plan views of first to third carbon nanotube sheets according to a third example of the first embodiment. FIG. 21 is a cross-sectional view (part 1) of the electronic device including the heat dissipation sheet according to the fourth example of the first embodiment during manufacture. FIG. 22 is a cross-sectional view (part 2) of the electronic device including the heat dissipation sheet according to the fourth example of the first embodiment during manufacture. FIG. 23 is a cross-sectional view of an electronic device including a heat dissipation sheet according to a fifth example of the first embodiment. FIG. 24: is sectional drawing (the 1) in the middle of manufacture of the electronic device provided with the heat radiating sheet which concerns on 2nd Embodiment. FIG. 25: is sectional drawing (the 2) in the middle of manufacture of the electronic device provided with the heat radiating sheet which concerns on 2nd Embodiment.

(First embodiment)
In the present embodiment, a heat radiating sheet will be described in which the thermal conductivity is increased by the carbon nanotubes and the thermal conductivity is not easily deteriorated even when reused.

  1-5 is sectional drawing in the middle of manufacture of the electronic device provided with the thermal radiation sheet | seat which concerns on this embodiment.

  First, as shown in FIG. 1A, a silicon substrate is prepared as the substrate 20, and the surface of the substrate 20 is thermally oxidized to form a silicon oxide film having a thickness of about 300 nm as the base film 21.

  The substrate 20 is not limited to a silicon substrate, and any of an alumina (sapphire) substrate, a magnesium oxide substrate, and a glass substrate may be used as the substrate 20.

  Further, the base film 21 is not limited to the silicon oxide film. For example, an aluminum oxide film or a silicon nitride film can be formed as the base film 21.

  Next, as shown in FIG. 1B, an aluminum film is formed to a thickness of about 10 nm on the base film 21 by sputtering, and the aluminum film is used as the base metal film 22.

  As the material of the base metal film 22, in addition to aluminum, molybdenum, titanium, hafnium, zirconium, niobium, vanadium, tantalum, tungsten, copper, gold, platinum, palladium, titanium silicide, aluminum oxide, titanium oxide, and titanium nitride There is. Further, an alloy film containing any of these materials may be formed as the base metal film 22.

  Next, an iron film having a thickness of about 2.5 nm is formed on the base metal film 22 by sputtering, and the iron film is used as the catalyst metal film 23.

  The material of the catalytic metal film 23 is not limited to iron. The catalytic metal film 23 can be formed of cobalt, nickel, gold, silver, platinum, or an alloy thereof.

  Further, instead of the catalyst metal film 23, metal fine particles containing the same material as the catalyst metal film 23 may be attached on the base metal film 22. In this case, only fine metal particles having a diameter of about 3.8 nm are collected in advance by a differential electrostatic classifier or the like and supplied onto the underlying metal film 22.

  Subsequently, as shown in FIG. 2A, a plurality of carbon nanotubes 25 are grown by hot filament CVD (Chemical Vapor Deposition) using the catalytic action of the catalytic metal film 23.

  The growth conditions of the carbon nanotube 25 are not particularly limited. In this example, acetylene gas is used as a carbon source gas, and a mixed gas of the acetylene gas and argon gas is supplied to a growth chamber (not shown).

  The pressure of the mixed gas in the growth chamber is 1 kPa, and the partial pressure ratio between the acetylene gas and the argon gas is, for example, about 1: 9. The temperature of the hot filament is about 1000 ° C., and the growth time is about 20 minutes.

  The base metal film 22 and the catalyst metal film 23 are condensed into the granular metal particles 24 when the source gas is introduced into the growth chamber. Then, with the one end 25 a of the carbon nanotube 25 fixed to the metal particle 24, the other end 25 b grows along the normal direction of the substrate 20 by the action of the base film 21.

According to this growth condition, the surface density of the carbon nanotubes 25 is about 1 × 10 ¹¹ pieces / cm ² , the diameter of each carbon nanotube 25 is 4 nm to 8 nm, and the average diameter is about 6 nm. The growth rate of each carbon nanotube 25 is 4 μm / min.

  In each carbon nanotube 25, the single-layer graphene sheets are stacked from about 3 to 6 layers from the central axis to the outside, and the average value of the number of layers is about 4. Carbon nanotubes formed by stacking multilayer graphene sheets in this way are also called multilayer carbon nanotubes.

  Further, the film formation method of the carbon nanotube 25 is not limited to the above hot filament CVD method, and may be a thermal CVD method or a remote plasma CVD method. Further, instead of acetylene, hydrocarbons such as methane or ethylene, or alcohols such as ethanol or methanol may be used as the carbon source gas.

  Next, as shown in FIG. 2 (b), one end 25 a of the carbon nanotube 25 is mechanically peeled from the substrate 20 to obtain a sheet 29 in which the plurality of carbon nanotubes 25 extend in the thickness direction D.

  The thickness of the sheet 29 can be controlled by the growth time of the carbon nanotubes 25 in the process of FIG.

  Next, as shown in FIG. 3A, the sheet 29 is sandwiched from above and below by a jig (not shown), the jig is placed in an ultra high temperature graphite furnace, and each carbon nanotube 25 is heat-treated by a heater. Thereby, the crystallinity of each carbon nanotube 25 is improved. A carbon sheet may be disposed between the sheet 29 and the jig.

  The atmosphere of the heat treatment is not particularly limited, but in this example, after exhausting the residual gas in the ultra high temperature graphite furnace in advance by a vacuum pump, the argon gas is filled in the ultra high temperature graphite furnace, and the atmosphere in the argon gas And heat treatment.

  Thereby, the carbon nanotube 25 is heated not only by the radiant heat from the heater in the furnace but also by a high-temperature argon gas, and the carbon nanotube 25 can be efficiently heated.

  Further, the heating profile of this heat treatment is not particularly limited.

  FIG. 6 is a graph showing an example of a heating profile.

  As shown in FIG. 6, in the present embodiment, the temperature of the carbon nanotube 25 is raised from room temperature to a temperature of about 2400 ° C. at a temperature rise rate of 2 ° C./min in the first period T1 having a length of about 9 hours.

  In the second period T2, the carbon nanotubes 25 are maintained at a constant temperature of about 2400 ° C. for about 1 to 3 hours. Hereinafter, this constant temperature is also referred to as a heat treatment temperature.

  Thereafter, the temperature of the carbon nanotube 25 is lowered to room temperature at a temperature drop rate of 2 ° C./min in the third period T3 having a length of about 9 hours.

  Next, as shown in FIG. 3B, the sheet 29 is put between the two press plates 30, and the sheet 29 is pressed by these press plates 30 from above and below with a pressure of about 1 MPa.

  Thereby, the waviness of the sheet 29 generated by the heat treatment in FIG. 3A is flattened, and the flatness of the sheet 29 is improved.

  Next, as shown in FIG. 4, first to third carbon nanotube sheets 31 to 33 are cut out from the sheet 29.

  FIGS. 7A to 7C are plan views of the first to third carbon nanotube sheets 31 to 33, and the sectional views of the carbon nanotube sheets 31 to 33 in FIG. This corresponds to a cross-sectional view taken along line II of a) to (c).

  As shown in FIGS. 7A and 7C, the first carbon nanotube sheet 31 and the third carbon nanotube sheet 33 have a substantially square shape with a side length of about 10 mm to 40 mm in plan view.

  On the other hand, as shown in FIG. 7B, the second carbon nanotube sheet 32 has two rectangular peripheral portions 32a and a central portion 32b.

  An opening 32x is formed in the central portion 32b. Since the carbon nanotube 25 does not exist in the opening 32x, the central portion 32b is more flexible than the peripheral portion 32a.

  The carbon nanotube sheets 31 to 33 may be cut out from one sheet 29, or the sheet 29 is prepared for each carbon nanotube sheet 31 to 33, and the carbon nanotube sheets 31 to 33 are formed from the sheets 29. It may be cut out.

  Next, the process shown in FIG. 5 will be described.

  First, the circuit board 35 on which the electronic component 36 is mounted is prepared. The electronic component 36 is a CPU, for example, and is connected to the circuit board 35 via the solder bumps 37.

  Further, in order to prevent heat from being generated inside the electronic component 36, the electronic component 36 is not resin-sealed, and a semiconductor substrate such as a silicon substrate is exposed on the upper surface 36 x of the electronic component 36. In the case where heat is not a problem, an electronic component 36 formed by resin-sealing a semiconductor substrate may be used.

  Then, the aforementioned first to third carbon nanotube sheets 31 to 33 are stacked in this order on the electronic component 36, and these carbon nanotube sheets 31 to 33 are used as the heat dissipation sheet 34.

  The heat dissipating sheet 34 has a first main surface 34 a and a second main surface 34 b that are opposed to each other, and the first main surface 34 a is in close contact with the electronic component 36.

  The other end 25 b of the carbon nanotube 25 of the second carbon nanotube sheet 32 is in close contact with the upper surface 31 p of the first carbon nanotube sheet 31. Further, the other end 25 b of the carbon nanotube sheet 25 of the third carbon nanotube sheet 33 is in close contact with the upper surface 32 p of the second carbon nanotube sheet 32.

  Thereafter, a metal heat spreader is placed as the heat radiating member 38 on the second main surface 34 b of the heat radiating sheet 34.

  Then, by pressing the heat radiating member 38 against the circuit board 35, the end of the heat radiating member 38 is bonded to the circuit board 35 with the sealant 39 while the heat radiating sheet 34 is brought into close contact with each of the electronic component 36 and the heat radiating member 38.

  As described above, the basic structure of the electronic device 40 according to the present embodiment is completed.

  In the electronic device 40, a heat radiating sheet 34 including the carbon nanotubes 25 having excellent thermal conductivity is interposed between the electronic component 36 and the heat radiating member 38. Therefore, the heat of the electronic component 36 is quickly transmitted to the heat radiating member 38 through the carbon nanotubes 25 of the heat radiating sheet 34, and the electronic component 36 can be efficiently cooled.

  In the present embodiment, the carbon nanotube sheets 31 to 33 are not fixed to the electronic component 36 or the heat dissipation member 38 with an adhesive or the like, and the heat dissipation sheet 34 can be peeled off from each of the electronic component 36 and the heat dissipation member 38. It has become. Similarly, the carbon nanotube sheets 31 to 33 are not bonded to each other, and the carbon nanotube sheets 31 to 33 can be separated from each other.

  Therefore, when a defect is found in the electronic component 36 or the heat dissipation component 38 after the electronic device 40 is manufactured, the carbon nanotube sheets 31 to 33 are easily taken out from the electronic device 40 and the heat dissipation sheet 34 is replaced with another electronic device 40. Can be easily reused.

  In particular, in this example, the central portion 32b of the second carbon nanotube sheet 32 is made more flexible than the peripheral portion 32a. Therefore, even if the heat radiation sheet 34 is reused as described below, its thermal conductivity is unlikely to deteriorate.

  FIG. 8 is a cross-sectional view of an electronic device 40 according to a comparative example in which an opening is not provided in the central portion 32b of the second carbon nanotube sheet 32 and the central portion 32b is not flexible. In FIG. 8, the same elements as those in FIG. 5 are denoted by the same reference numerals as those in FIG.

  In the comparative example, since the opening 32x is not provided in the second carbon nanotube sheet 32, the planar shape of the second carbon nanotube sheet 32 is substantially the same as the first and third carbon nanotube sheets 31, 33. It becomes.

  In addition, the electronic component 36 may warp with the top convex due to the difference in thermal expansion coefficient with the circuit board 35. Such warping occurs, for example, when the circuit board 35 and the electronic component 36 are heated to melt the solder bumps 37 and then contract with different contraction amounts when they return to room temperature.

  When the electronic component 36 is warped in this way, when the heat dissipation member 38 is pressed against the circuit board 35 in the process of FIG. Is done. Therefore, a strong pressure is applied to the interfaces A and B of the carbon nanotube sheets 31 to 33 in the central portion 32b, and the ends of the carbon nanotubes 25 at these interfaces A and B are destroyed.

  When the electronic device 40 continues to use the heat radiating sheet 34, the carbon nanotube sheets 31 to 33 are in close contact with each other. Therefore, even if the end of the carbon nanotube 25 is broken in this way, Does not deteriorate greatly.

  However, when the carbon nanotube sheets 31 to 33 are taken out from the electronic device 40 for reuse and overlapped again, the end portions of the carbon nanotubes 25 are broken as described above. 33 does not adhere well.

  As a result, the thermal resistance of the heat radiating sheet 34 at the interfaces A and B increases as compared to before reuse, and the thermal conductivity of the heat radiating sheet 34 deteriorates.

  On the other hand, FIG. 9 is a cross-sectional view of the electronic device 40 when the electronic component 36 is warped in the present embodiment.

  In the present embodiment, since the central portion 32b of the second carbon nanotube sheet 32 is made flexible as described above, the pressure acting on the central portion 32b during the manufacture of the electronic device 40 is relieved, and the carbon nanotubes 25 above and below the central portion 32b are relaxed. It becomes difficult to destroy the end of the.

  As a result, even if the carbon nanotube sheets 31 to 33 are taken out from the electronic device 40 for reuse and stacked again, the carbon nanotube sheets 31 to 33 adhere to each other as well as before reuse. The heat conductivity of the heat dissipation sheet 34 is unlikely to deteriorate.

  In order to allow the heat dissipation sheet 34 to follow the warp of the electronic component 36, it is preferable that the heat dissipation sheet 34 be formed as thick as possible so that the heat dissipation sheet 34 has sufficient elasticity. For example, by setting the total thickness of the heat radiating sheet 34 to 100 μm or more, the heat radiating sheet 34 can have elasticity that does not cause a gap between the warped electronic component 36 and the heat radiating sheet 34. it can.

  However, if the heat dissipation sheet 34 is too thick, the overall heat resistance of the heat dissipation sheet 34 is increased. Is preferred.

  Further, if the second carbon nanotube sheet 32 is too thin, the flexibility of the second carbon nanotube sheet 32 is impaired, and there is a possibility that the ends of the carbon nanotubes 25 are broken at the interfaces A and B. In order to prevent this, it is preferable to form the second carbon nanotube sheet 32 with a thickness of 20 μm or more so that the second carbon nanotube sheet 32 has sufficient flexibility.

  However, if the second carbon nanotube sheet 32 is too thick, its thermal resistance increases. Therefore, by setting the thickness of the second carbon nanotube sheet 32 to 500 μm or less, the heat of the second carbon nanotube sheet 32 is reduced. It is preferable to suppress an increase in resistance.

  Furthermore, if the area of the central portion 32b when viewed in plan is too small, the flexibility is lowered, and therefore the central portion 32b is formed in an area of 30% or more of the entire area of the second carbon nanotube sheet 32. preferable.

  On the other hand, when the center portion 32b when viewed in plan is too wide, the area of the peripheral edge portion 32b is relatively narrow, and the heat resistance of the entire heat dissipation sheet 34 is increased. Therefore, it is preferable to suppress an increase in the thermal resistance of the heat dissipation sheet 34 by forming the central portion 32b in an area of 50% or less of the entire area of the second carbon nanotube sheet 32.

  The inventor of the present application investigated whether or not the thermal conductivity of the heat radiating sheet 34 actually deteriorates in the present embodiment.

  The results are shown in FIGS.

  FIG. 10 is a graph obtained by investigating how the thermal conductivity of the heat dissipation sheet 34 of the comparative example (see FIG. 8) changes before and after reuse.

  The vertical axis of the graph represents the temperature difference ΔT between the main surface 34a and the second main surface 34b when the heat dissipation sheet 34 is heated from the first main surface 34a (see FIG. 5). As the temperature difference ΔT is smaller, heat is quickly transmitted from the first main surface 34a to the second main surface 34b, and the heat conductivity of the heat radiation sheet 34 is better.

  In this investigation, the temperature difference ΔT was measured while pressure was applied to the heat dissipation sheet 34 from above and below to simulate the force applied to the heat dissipation sheet 34 when the electronic device 40 was manufactured. The horizontal axis of FIG. 10 shows the pressure applied to the heat dissipation sheet 34 in this way.

  The thicknesses of the carbon nanotube sheets 31 to 33 used in this investigation are 100 μm for the first carbon nanotube sheet 31, 100 μm for the second carbon nanotube sheet 32, and 100 μm for the third carbon nanotube sheet 33. .

  As shown in FIG. 10, in the comparative example, the temperature difference ΔT after reuse is increased at each pressure as compared to before reuse. This is presumably because the end of the carbon nanotube sheet 25 was destroyed as described above, and the thermal resistance at the interfaces A and B increased.

  On the other hand, FIG. 11 is a graph obtained by conducting the same investigation as FIG. 10 on the heat radiating sheet 34 according to this embodiment.

  Since the meanings of the horizontal axis and the vertical axis in FIG. 11 are the same as those in FIG. 10, the description thereof is omitted.

  In this investigation, the thickness of the first carbon nanotube sheet 31 was 100 μm, the thickness of the second carbon nanotube sheet 32 was 100 μm, and the thickness of the third carbon nanotube sheet 33 was 100 μm.

  As shown in FIG. 11, in this embodiment, the temperature difference ΔT before reuse and after reuse is substantially equal at each pressure, and the thermal conductivity of the heat dissipation sheet 34 is not deteriorated by reuse.

  From this result, making the central part 32b of the second carbon nanotube sheet 32 more flexible than the peripheral part 32a as in this embodiment suppresses deterioration of the thermal conductivity of the heat dissipation sheet 34 after reuse. It was confirmed that it was effective to do.

  In addition, in the present embodiment, heat treatment is performed on each carbon nanotube 25 as shown in FIG. It has been clarified that the heat treatment improves the crystallinity and thermal conductivity of the carbon nanotube 25 as follows.

  First, the results of investigation on crystallinity will be described.

  FIG. 12 is a diagram obtained by examining the Raman spectrum of the carbon nanotube 25. The horizontal axis of FIG. 12 shows the Raman shift defined by the difference between the wave numbers of the incident light and the Stokes light. The vertical axis in FIG. 12 indicates the intensity of Stokes light in an arbitrary unit.

There is a G / D ratio as an index for estimating the crystallinity of the carbon nanotube 25. The G / D ratio is a ratio (I _G / I) of the intensity I _{G of} a spectrum called G-Band near 1600 cm ^{−1 of} Stokes light and the intensity I _{D of} a spectrum called D-Band near 1350 cm ^−1. _D ) as defined.

  D-Band is known to increase in strength when defects occur in the carbon nanotube 25 and its crystallinity is disturbed. Therefore, the smaller the G / D ratio, the worse the crystallinity. The larger the / D ratio, the better the crystallinity.

  In this investigation, the Raman spectra of the carbon nanotube 25 that was not subjected to the heat treatment of FIG. 3A and the carbon nanotube 25 that was subjected to the heat treatment at a heat treatment temperature of 2700 ° C. were examined.

  In FIG. 12, the two graphs are shifted up and down so that the graphs with and without heat treatment do not overlap each other.

  According to the result of FIG. 12, the strength of D-Band is strong when heat treatment is not performed, whereas the strength of D-Band is weak when heat treatment is performed. When the heat treatment is performed, the G / D ratio is increased to about 8.8 times as compared with the case where the heat treatment is not performed.

  From this result, it has been clarified that the crystallinity of the carbon nanotube 25 is improved by setting the heat treatment temperature in FIG. 3A to about 2400 ° C.

  Next, the investigation result on the thermal conductivity of the carbon nanotube 25 will be described.

  FIG. 13 is a diagram obtained by investigating the thermal conductivity of the carbon nanotube 25, and the horizontal axis indicates the heat treatment temperature of the carbon nanotube 25 in the step of FIG.

  The vertical axis in FIG. 13 represents the temperature difference ΔT between the one end 25a and the other end 25b when the carbon nanotube 25 is heated from one end 25a (see FIG. 2B). Similar to FIGS. 10 and 11, the smaller the temperature difference ΔT, the better the thermal conductivity of the carbon nanotubes 25.

  In this investigation, a plurality of samples were used, and the temperature difference ΔT before and after the heat treatment was measured for each sample.

  As shown in FIG. 13, in almost all samples, the temperature difference ΔT is reduced after the heat treatment than before the heat treatment. In the sample with the largest decrease, the temperature difference ΔT after the heat treatment is reduced to 68% before the heat treatment.

  In particular, when the heat treatment temperature is 2200 ° C. or higher, the temperature difference ΔT after the heat treatment is reduced as compared with the sample heat-treated at a lower temperature.

  From this, it has been clarified that the heat conductivity of the carbon nanotube 25 is improved by setting the heat treatment temperature in the heat treatment of FIG. This is presumably because the crystallinity of the carbon nanotubes 25 was improved by the heat treatment as shown in FIG.

  In particular, since the carbon nanotubes 25 that have been heat-treated in this way are mechanically hardened, when the heat-dissipating sheet 34 is pressed as shown in FIG. The thermal conductivity of the heat radiation sheet 34 is likely to deteriorate due to reuse. Therefore, if the central portion 32b is made flexible as described above in the heat dissipating sheet 35 including the carbon nanotubes 25 subjected to the heat treatment in this way, it is effectively suppressed that the heat conductivity of the heat dissipating sheet 34 after reuse is deteriorated. can do.

  Next, various modifications of the heat dissipation sheet 34 according to the present embodiment will be described.

First Example FIG. 14 is a plan view of the second carbon nanotube sheet 32 provided in the heat dissipation sheet 34 according to the first example. FIG. 15 is a cross-sectional view of the electronic device 40 including the heat dissipation sheet 34 according to this example, and corresponds to a cross-sectional view taken along the line II-II in FIG.

  14 and 15, the same elements as those described in FIGS. 1 to 5 are denoted by the same reference numerals as those in FIGS.

  As shown in FIG. 14, in this example, the peripheral part 32a of the 2nd carbon nanotube sheet 32 is made into a ring shape, and the center part 32b is enclosed by the peripheral part 32a.

  By making the peripheral edge portion 32a into a ring shape in this way, heat generated at the peripheral edge portion of the electronic component 36 is evenly transmitted to the heat radiating member 38 via the second carbon nanotube sheet 32, and the electronic component 36 has insufficient cooling. Can be reduced.

  In addition, when it is difficult to process the peripheral portion 32a into a seamless ring shape, the peripheral portion 32a is cut along a cutting line C to be divided into two L-shaped parts, which are connected to form a ring shape. Also good.

  Further, the size of the central portion 32b is not particularly limited. For example, it is preferable to prevent the flexibility of the central portion 32b from decreasing by forming the central portion 32b in an area of 30% or more of the entire area of the second carbon nanotube sheet 32. Furthermore, it is preferable to suppress an increase in the thermal resistance of the second carbon nanotube sheet 32 by forming the central portion 32b in an area of 50% or less of the entire area of the second carbon nanotube sheet 32.

Second Example FIG. 16 is a plan view of the second carbon nanotube sheet 32 provided in the heat dissipation sheet 34 according to the second example. FIG. 17 is a cross-sectional view of the electronic device 40 including the heat dissipation sheet 34 according to this example, and corresponds to a cross-sectional view taken along line III-III in FIG.

  16 and 17, the same elements as those described in FIGS. 1 to 5 are denoted by the same reference numerals as those in FIGS. 1 to 5, and description thereof is omitted below.

  As shown in FIG. 16, in this example, an island 32 c including a plurality of carbon nanotubes 25 is provided at the center 32 y of the central portion 32 b of the second carbon nanotube sheet 32.

  The carbon nanotubes 25 in the island 32c extend from the first carbon nanotube sheet 31 to the third carbon nanotube sheet 33 as shown in FIG.

  As a result, heat generated at the center of the electronic component 36 is transmitted to the heat radiating member 38 via the island 32c, so that the center of the electronic component 36 can be prevented from being insufficiently cooled.

  Further, since the island 32c is provided only at the center of the central portion 32b, the flexibility of the entire central portion 32b is not greatly impaired by the island 32c, and the pressure acting on the central portion 32b during the manufacture of the electronic device 40 is relieved. The

  As a result, the end portion of the carbon nanotube 25 is not easily broken by pressure as described above, and deterioration of the thermal conductivity can be suppressed even when the heat dissipation sheet 34 is reused.

  In addition, if the ratio which the island 32c accounts in the center part 32b increases, the softness | flexibility of the center part 32b will be impaired by the island 32c. In order to prevent this, it is preferable to form the island 32c in an area of 15% or less of the area of the central portion 32b. Moreover, it is preferable to suppress an increase in the thermal resistance of the second carbon nanotube sheet 32 by forming the island 32c in an area of 10% or more of the area of the central portion 32b.

Third Example FIGS. 18 and 19 are cross-sectional views in the middle of manufacturing an electronic device including a heat dissipation sheet according to a third example.

  18 and 19, the same elements as those described in FIGS. 1 to 5 are denoted by the same reference numerals as those in FIGS. 1 to 5, and the description thereof is omitted below.

  In this example, as shown in FIG. 18, the 1st-3rd carbon nanotube sheets 31-33 are prepared similarly to the process of FIG.

  However, a plurality of carbon nanotubes 25 having a diameter smaller than that of the carbon nanotubes 25 in the peripheral portion 32a are provided in the opening 32x of the central portion 32b of the second carbon nanotube sheet 32.

  Thus, the central part 32b becomes softer than the peripheral part 32a by the soft carbon nanotube 25 with a small diameter.

  The manufacturing method of the center part 32b is not specifically limited. For example, apart from the sheet 29 for cutting out the peripheral edge portion 32a (see FIG. 3B), a sheet 29 having a carbon nanotube 25 with a smaller diameter than that in the peripheral edge portion 32a is produced, and the center of the sheet 29 is formed. What is necessary is just to cut out the part 32b. In this case, the center part 32b provided with the carbon nanotubes 25 having a diameter smaller than that of the peripheral part 32a is prepared by lowering the growth temperature of the carbon nanotubes 25 at the time of preparation of the sheet 29 by several tens of degrees C. obtain.

  Further, the carbon nanotubes 25 in the central portion 32b extend along the thickness direction D of the second carbon nanotube sheet 32 in the same manner as the carbon nanotubes 25 in the peripheral portion 32a.

  20A to 20C are plan views of the first to third carbon nanotube sheets 31 to 33 according to this example, and the cross-sectional views of the carbon nanotube sheets 31 to 33 in FIG. 20 corresponds to a cross-sectional view taken along line IV-IV in FIGS.

  As shown in FIGS. 20A to 20C, each of the carbon nanotube sheets 31 to 33 has a substantially square shape in plan view.

  Further, as shown in FIG. 20B, the central portion 32b of the second carbon nanotube sheet 32 has a strip shape in plan view.

  Next, as shown in FIG. 19, a circuit board 35 on which the electronic component 36 is mounted is prepared, and the first to third carbon nanotube sheets 31 to 33 are stacked on the electronic component 36 in this order, These carbon nanotube sheets 31 to 33 are referred to as a heat radiation sheet 34.

  Then, by pressing the heat radiating member 38 against the circuit board 35, the heat radiating sheet 34 is brought into close contact with each of the electronic component 36 and the heat radiating member 38. In this state, the end portion of the heat dissipation member 38 is bonded to the circuit board 35 with the sealant 39 to complete the basic structure of the electronic device 40 according to this example.

  According to this example, since the central portion 32b is more flexible than the peripheral portion 32a as described above, the pressure acting on the central portion 32b in the process of FIG. 19 is relieved. Therefore, the end portion of the carbon nanotube 25 in the central portion 32b is not easily destroyed, and deterioration of the thermal conductivity can be suppressed even when the heat radiating sheet 34 is reused.

  In addition, since the heat generated in the electronic component 36 is transmitted to the heat radiating member 38 via the carbon nanotubes 25 in the central portion 32b, the cooling of the electronic component 36 can be promoted by the central portion 32b.

  In particular, in this example, since the direction in which the carbon nanotubes 25 in the central portion 32b extend is the thickness direction D of the heat dissipation sheet 34, the heat of the electronic component 36 is quickly transmitted through the central portion 32b and reaches the heat dissipation member 38. The electronic component 36 can be quickly cooled.

-4th example FIG.21 and FIG.22 is sectional drawing in the middle of manufacture of the electronic device provided with the thermal radiation sheet | seat which concerns on a 4th example.

  Also in this example, as shown in FIG. 21, the 1st-3rd carbon nanotube sheets 31-33 are prepared similarly to the process of FIG.

  However, in this example, the direction of the carbon nanotube 25 in the central portion 32 b of the second carbon nanotube sheet 32 is a direction P perpendicular to the thickness direction D of the second carbon nanotube sheet 32.

  In addition, the diameter of the carbon nanotube 25 in the center part 32b is made thinner than the diameter of the carbon nanotube 25 in the peripheral part 32a as in the third example. Thereby, the center part 32b becomes softer than the peripheral part 32a similarly to the 3rd example.

  In this example, as in the third example, the growth temperature of the carbon nanotube 25 is lowered by about several tens of degrees C. compared to the time of manufacturing the sheet 29 (see FIG. 3B) for cutting out the peripheral edge portion 32a. A sheet 29 is prepared. And the center part 32b is produced by loosening each carbon nanotube 25 of the sheet | seat 29, and laying it in the opening 32x.

  Next, as shown in FIG. 22, the first to third carbon nanotube sheets 31 to 33 are stacked in this order on the electronic component 36 in the same manner as FIG. 19, and these carbon nanotube sheets 31 to 33 are stacked on the heat dissipation sheet. 34.

  The basic structure of the electronic device 40 according to this example is completed by adhering the end of the heat dissipation member 38 to the circuit board 35 with the sealant 39 while pressing the heat dissipation member 38 against the circuit board 35.

  According to this example described above, since the carbon nanotube 25 having a diameter smaller than that of the peripheral part 32a is provided in the central part 32b, the central part 32b becomes flexible as in the third example, and the heat radiation sheet 34 can be reused. It can suppress that the thermal conductivity deteriorates.

  Further, since the direction of the carbon nanotube 25 in the central portion 32b is set to the direction P perpendicular to the thickness direction D, the carbon nanotube 25 in the central portion 32b is easily bent by a force acting along the thickness direction D. Thereby, the pressure which acts on the center part 32b in the process of FIG. 22 is eased further, and it becomes easy to prevent the edge part of the carbon nanotube 25 in the center part 32b from being destroyed.

Fifth Example FIG. 23 is a cross-sectional view of an electronic device 40 including a heat dissipation sheet according to a fifth example.

  As shown in FIG. 23, in this example, the opening 32x in the central portion 32b of the second carbon nanotube sheet 32 is filled with heat dissipating grease.

  The heat dissipation grease is not particularly limited, but in this example, silicon grease G-776 manufactured by Shin-Etsu Chemical Co., Ltd. is used as the heat dissipation grease.

  Since the heat dissipating grease has fluidity, the central portion 32b is more flexible than the peripheral portion 32a provided with the carbon nanotubes 25, and the pressure applied to the central portion 32b when the electronic device 40 is manufactured can be relaxed. As a result, when the electronic device 40 is manufactured, the ends of the carbon nanotubes 25 above and below the central portion 32b are not easily destroyed, and the thermal conductivity is prevented from deteriorating even when the heat radiating sheet 34 is reused. Can do.

(Second Embodiment)
In the first embodiment, as described with reference to FIG. 5, the carbon nanotube sheets 31 to 33 are not fixed to the electronic component 36 or the heat radiating member 38 with an adhesive or the like. Reusable.

  On the other hand, in the present embodiment, only the second carbon nanotube sheet 32 can be reused as follows.

  24 and 25 are cross-sectional views of the electronic device including the heat dissipating sheet according to the present embodiment during manufacture.

  24 and 25, the same elements as those described in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted below.

  First, as shown in FIG. 24, a heat radiation sheet 34 in which the first to third carbon nanotube sheets 31 to 33 described in the first embodiment are stacked in this order is disposed between the electronic component 36 and the heat radiation member 38. .

  In this example, the heat dissipation sheet 34 described in FIG. 5 of the first embodiment is used, but instead, it relates to the first to fourth examples (see FIGS. 14 to 23) of the first embodiment. A heat dissipation sheet 34 may be used.

  Further, the first metal paste 51 and the second metal paste 52 are previously applied to the surfaces of the electronic component 36 and the heat dissipation member 38. Each of the metal pastes 51 and 52 is formed by dispersing metal particles in an organic solvent, and in this state, is in an undried state. In addition, although the metal particle of each metal paste 51 and 52 is not specifically limited, It is preferable to use the metal paste 51 and 52 containing metal particles, such as gold | metal | money, silver, and copper excellent in thermal conductivity.

  Next, as shown in FIG. 25, the metal pastes 51 and 52 are heated to a temperature of about 140 ° C. while pressing the heat radiation member 38 against the circuit board 35.

  Thereby, the organic solvent of each metal paste 51 and 52 evaporates, the 1st main surface 34a of the thermal radiation sheet 34 is fixed to the electronic component 36 with the 1st metallic paste 51, and the 2nd main surface of the thermal radiation sheet 34 is obtained. The surface 34 b is fixed to the heat radiating member 38 by the second metal paste 52.

  Then, the basic structure of the electronic device 40 according to the present embodiment is completed by bonding the end of the heat dissipation member 38 to the circuit board 35 with the sealant 39.

  According to this embodiment described above, the heat radiating sheet 34 is fixed to the electronic component 36 and the heat radiating member 38 with the metal pastes 51 and 52 having excellent thermal conductivity. Therefore, the adhesion between the electronic component 36 and the heat dissipation sheet 34 and the adhesion between the heat dissipation member 38 and the heat dissipation sheet 34 are improved, and the heat generated in the electronic component 36 is quickly transferred to the heat dissipation member 38 via the heat dissipation sheet 34. It comes to be transmitted.

  In addition, since the second carbon nanotube sheet 32 is not fixed to the first and third carbon nanotube sheets 31 and 33, when a problem is found in the electronic device 40, the second carbon nanotube sheet 32 is not transferred from the electronic device 40 to the second carbon nanotube sheet 32. The nanotube sheet 32 can be taken out and reused.

  Moreover, since the central portion 32b of the second carbon nanotube sheet 32 is made more flexible than the peripheral portion 32a, even if pressure is applied to the heat dissipation sheet 34 in the process of FIG. 25, the central portion 32b of the second carbon nanotube sheet 32 has the same reason as in the first embodiment. The end of the carbon nanotube 25 is difficult to break. Therefore, even if the second carbon nanotube sheet 32 is reused as described above, the thermal conductivity of the second carbon nanotube sheet 32 is less likely to deteriorate after reuse.

  As mentioned above, although each embodiment was described in detail, the use application of the thermal radiation sheet 34 is not limited above. For example, a heat sink may be provided on the heat radiating member 38 (see FIG. 5) via another heat radiating sheet 34, and the heat of the heat radiating member 38 may be released to the heat sink via the heat radiating sheet 34. Further, the heat radiation sheet 34 may be applied to a high voltage module of an electric vehicle or an airplane.

  The following additional notes are disclosed for each embodiment described above.

(Appendix 1) a first carbon nanotube sheet comprising a plurality of carbon nanotubes;
A second carbon nanotube sheet comprising a peripheral portion having a plurality of carbon nanotubes closely attached to the upper surface of the first carbon nanotube sheet, and a central portion that is more flexible than the peripheral portion;
A third carbon nanotube sheet comprising a plurality of carbon nanotubes in close contact with the upper surface of the second carbon nanotube sheet;
A heat dissipating sheet characterized by comprising:

  (Additional remark 2) The heat dissipation sheet | seat of Additional remark 1 characterized by the above-mentioned.

  (Supplementary note 3) The heat dissipation sheet according to supplementary note 1, wherein a plurality of carbon nanotubes having a diameter smaller than that of the carbon nanotube in the peripheral portion are provided in the central portion.

  (Additional remark 4) The said carbon nanotube of the said peripheral part and the said carbon nanotube of the said center part all extend along the thickness direction of a said 2nd carbon nanotube sheet | seat, The heat dissipation of Additional remark 3 characterized by the above-mentioned. Sheet.

(Additional remark 5) The said carbon nanotube of the said peripheral part is extended in the thickness direction of a said 2nd carbon nanotube sheet | seat,
The heat radiation sheet according to appendix 3, wherein the carbon nanotube in the central portion extends in a direction perpendicular to the thickness direction.

  (Supplementary note 6) The heat dissipation sheet according to supplementary note 1, wherein an opening is provided in the central portion, and the opening is filled with grease.

(Appendix 7) The peripheral edge is ring-shaped in plan view,
The heat radiation sheet according to appendix 1, wherein the central portion is surrounded by the peripheral edge in a plan view.

  (Supplementary note 8) The island according to supplementary note 7, wherein an island including a plurality of carbon nanotubes extending from the first carbon nanotube sheet to the third carbon nanotube sheet is provided at the center of the central portion. Heat dissipation sheet.

  (Additional remark 9) The said 2nd carbon nanotube sheet can peel from each of the said 1st carbon nanotube sheet and the said 3rd carbon nanotube sheet, The heat radiating sheet of Additional remark 1 characterized by the above-mentioned.

(Supplementary Note 10) A first carbon nanotube sheet having a plurality of carbon nanotubes, a second carbon nanotube sheet having a plurality of carbon nanotubes, and a third carbon nanotube sheet having a plurality of carbon nanotubes are sequentially stacked. Having a process of making a heat dissipation sheet,
The method of manufacturing a heat dissipation sheet, wherein the second carbon nanotube sheet includes a peripheral portion and a central portion that is more flexible than the peripheral portion.

(Additional remark 11) The heat-radiation sheet provided with the 1st main surface and 2nd main surface which mutually oppose,
An electronic component in close contact with the first main surface of the heat dissipation sheet;
A heat radiating member in close contact with the second main surface of the heat radiating sheet,
The heat dissipation sheet is
A first carbon nanotube sheet comprising a plurality of carbon nanotubes in close contact with the electronic component;
A second carbon nanotube sheet comprising a peripheral portion having a plurality of carbon nanotubes closely attached to the upper surface of the first carbon nanotube sheet, and a central portion that is more flexible than the peripheral portion;
An electronic device comprising: an upper surface of the second carbon nanotube sheet; and a third carbon nanotube sheet having a plurality of carbon nanotubes in close contact with each of the heat dissipation members.

  (Additional remark 12) The said heat-radiation sheet is peelable from each of the said electronic component and the said heat radiating member, The electronic device of Additional remark 11 characterized by the above-mentioned.

  (Supplementary Note 13) The first main surface of the heat dissipation sheet is fixed to the electronic component by a first metal paste, and the second main surface of the heat dissipation sheet is fixed to the heat dissipation member by a second metal paste. Item 14. The electronic device according to Appendix 10, wherein

DESCRIPTION OF SYMBOLS 20 ... Substrate, 21 ... Base film, 22 ... Base metal film, 23 ... Catalyst metal film, 24 ... Metal grain, 25 ... Carbon nanotube, 25a ... One end, 25b ... Other end, 29 ... Sheet, 30 ... Press plate, 31 ˜33: first to third carbon nanotube sheets, 31p: upper surface, 32a: peripheral portion, 32b: central portion, 32c ... island, 32p ... upper surface, 32x ... opening, 32y ... center, 34: heat dissipation sheet, 34a 1st main surface, 34b ... 2nd main surface, 35 ... Circuit board, 36 ... Electronic component, 36x ... Upper surface, 37 ... Solder bump, 38 ... Heat radiation member, 39 ... Sealant, 40 ... Electronic device, 51 ... 1st 1 metal paste, 52... Second metal paste.

Claims (6)

A first carbon nanotube sheet comprising a plurality of carbon nanotubes;
A second carbon nanotube sheet comprising a peripheral portion having a plurality of carbon nanotubes closely attached to the upper surface of the first carbon nanotube sheet, and a central portion that is more flexible than the peripheral portion;
A third carbon nanotube sheet comprising a plurality of carbon nanotubes in close contact with the upper surface of the second carbon nanotube sheet;
A heat dissipating sheet characterized by comprising:   The heat dissipation sheet according to claim 1, wherein an opening is provided in the central portion.   The heat radiation sheet according to claim 1, wherein a plurality of carbon nanotubes having a diameter smaller than that of the carbon nanotubes in the peripheral portion are provided in the central portion. The heat radiating sheet according to claim 1, wherein an opening is provided in the central portion, and the opening is filled with grease. A first carbon nanotube sheet having a plurality of carbon nanotubes, a second carbon nanotube sheet having a plurality of carbon nanotubes, and a third carbon nanotube sheet having a plurality of carbon nanotubes are sequentially stacked to form a heat dissipation sheet. Having a process,
The method of manufacturing a heat dissipation sheet, wherein the second carbon nanotube sheet includes a peripheral portion and a central portion that is more flexible than the peripheral portion. A heat dissipating sheet having a first main surface and a second main surface facing each other;
An electronic component in close contact with the first main surface of the heat dissipation sheet;
A heat radiating member in close contact with the second main surface of the heat radiating sheet,
The heat dissipation sheet is
A first carbon nanotube sheet comprising a plurality of carbon nanotubes in close contact with the electronic component;
A second carbon nanotube sheet comprising a peripheral portion having a plurality of carbon nanotubes closely attached to the upper surface of the first carbon nanotube sheet, and a central portion that is more flexible than the peripheral portion;
An electronic device comprising: an upper surface of the second carbon nanotube sheet; and a third carbon nanotube sheet having a plurality of carbon nanotubes in close contact with each of the heat dissipation members.

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