JP2011204749A - Sheet-like structure, electronic apparatus, and method for manufacturing electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet-like structure of very high heat conductivity and electrical conductivity that uses a linear structure of carbon element, and an electronic apparatus that uses the sheet-like structure, and also to provide a method for manufacturing the same.SOLUTION: The sheet-like structure has: a plurality of linear structures 12 of carbon element, and a packing layer 14 of thermoplastic resin that is arranged among the plurality of linear structures 12. At least one end part of the plurality of linear structures 12 is exposed from the packing layer 14, and a part of linear structure 12 that is exposed from the packing layer 14 is bent in the direction parallel to the surface of the packing layer 14.

Description

  The present invention relates to a sheet-like structure having a linear structure of carbon elements, an electronic device having the sheet-like structure, and a method for manufacturing the same.

  Electronic components used in CPUs (Central Processing Units) of servers and personal computers are required to efficiently dissipate heat generated from semiconductor elements. For this reason, these electronic components have a structure in which a heat spreader made of a material having high thermal conductivity, such as copper, provided immediately above the semiconductor element is disposed.

  At this time, since the surface of the heat generation source and the heat spreader has fine irregularities, a sufficient contact area cannot be obtained even if they are brought into direct contact with each other, and the contact interface has a large thermal resistance, thereby efficiently dissipating heat. Can not do. For this reason, for the purpose of reducing the contact thermal resistance, a heat source and a heat spreader are connected via a thermal interface material (TIM).

  For this purpose, in addition to being a material with high thermal conductivity, the thermal interface material itself is required to have characteristics that allow it to contact a large area against minute irregularities on the surface of the heat source and heat spreader. ing.

  Conventionally, as the thermal interface material, heat dissipating grease, phase change material (PCM), indium or the like is used. One of the major characteristics that these materials are used as heat dissipation materials is that they have fluidity below the heat-resistant temperature of electronic equipment, so that a large contact area can be obtained with respect to fine irregularities. .

  However, thermal grease and phase change material have a low thermal conductivity of 1 W / m · K to 5 W / m · K. In addition, indium is a rare metal, and the price is soaring due to a significant increase in demand related to ITO, and a cheaper alternative material is expected.

  From such a background, a linear structure made of a carbon element typified by carbon nanotube has attracted attention as a heat dissipation material. Carbon nanotubes not only have very high thermal conductivity (1500 W / m · K to 3000 W / m · K) in the axial direction, but also are excellent in flexibility and heat resistance, and have a high potential as a heat dissipation material. have.

  As a heat conductive sheet using carbon nanotubes, a heat conductive sheet in which carbon nanotubes are dispersed in a resin, or a heat conductive sheet in which a bundle of carbon nanotubes oriented and grown on a substrate is embedded with a resin or the like has been proposed.

JP 2006-295120 A JP 2007-294554 A Special table 2007-532335 gazette JP 2009-164552 A

  However, the conventional thermal conductive sheet using carbon nanotubes cannot fully utilize the high thermal conductivity of carbon nanotubes.

  An object of the present invention is to provide a sheet-like structure having a very high thermal conductivity and electrical conductivity using a linear structure of a carbon element, an electronic device using the sheet-like structure, and a method for manufacturing the same. It is in.

  According to one aspect of the embodiment, a plurality of linear structures having a plurality of carbon element linear structures and a thermoplastic resin filling layer disposed between the plurality of linear structures. Is a sheet-like structure in which at least one end is exposed from the filling layer, and the portion of the linear structure exposed from the filling layer is bent in a direction parallel to the surface of the filling layer. Provided.

  Further, according to another aspect of the embodiment, the heating element, the radiator, the linear structure of the plurality of carbon elements disposed between the heating element and the radiator, and the plurality of the linear structures A thermoplastic resin filling layer disposed between the bodies, at least one end of the plurality of linear structures is exposed from the filling layer, and the portion of the linear structure exposed from the filling layer There is provided an electronic apparatus having a sheet-like structure in which the structure is bent in a direction parallel to the surface of the filling layer.

  Further, according to still another aspect of the embodiment, a plurality of carbon element linear structures and a thermoplastic resin disposed between the plurality of linear structures are disposed between the heating element and the heat radiating body. And at least one end of the plurality of linear structures is exposed from the filler layer, and the portions of the linear structures exposed from the filler layer are parallel to the surface of the filler layer. A step of arranging a sheet-like structure bent in any direction, a step of heating the heat dissipation material to melt the thermoplastic resin, and a step of cooling the heat dissipation material to solidify the thermoplastic resin. A method for manufacturing an electronic device is provided.

  According to the disclosed sheet-like structure, the contact area of the linear structure of the carbon element with the adherend can be increased, and the contact thermal resistance and contact resistance with respect to the adherend can be greatly reduced.

  In addition, by disposing such a sheet-like structure between the heat generating body and the heat radiating body, the thermal conductivity between the heat generating body and the heat radiating body can be greatly improved. Thereby, the thermal radiation efficiency of the heat | fever emitted from a thermal radiation body can be improved, and the reliability of an electronic device can be improved.

FIG. 1 is a schematic cross-sectional view showing the structure of the carbon nanotube sheet according to the first embodiment. FIG. 2 is a process cross-sectional view (part 1) illustrating the method of manufacturing the carbon nanotube sheet according to the first embodiment. FIG. 3 is a process cross-sectional view (part 2) illustrating the method of manufacturing the carbon nanotube sheet according to the first embodiment. FIG. 3 is a process cross-sectional view (part 3) illustrating the method of manufacturing the carbon nanotube sheet according to the first embodiment. FIG. 5 is a schematic cross-sectional view showing the structure of the carbon nanotube sheet according to the second embodiment. FIG. 6 is a schematic cross-sectional view illustrating a method of manufacturing a carbon nanotube sheet according to the second embodiment. FIG. 7 is a process cross-sectional view illustrating the method of manufacturing the carbon nanotube sheet according to the second embodiment. FIG. 8 is a perspective view (No. 1) showing the carbon nanotube sheet manufacturing method according to the second embodiment. FIG. 9 is a perspective view (No. 2) showing the carbon nanotube sheet manufacturing method according to the second embodiment. FIG. 10 is a perspective view (No. 3) showing the method of manufacturing the carbon nanotube sheet according to the second embodiment. FIG. 11 is a schematic cross-sectional view showing the structure of an electronic device according to the third embodiment. FIG. 12 is a process cross-sectional view illustrating the method for manufacturing the electronic apparatus according to the third embodiment. FIG. 13 is a graph showing the relationship between the film thickness of the carbon nanotube sheet and the thermal resistance.

[First Embodiment]
The carbon nanotube sheet and the manufacturing method thereof according to the first embodiment will be described with reference to FIGS.

  FIG. 1 is a schematic cross-sectional view showing the structure of the carbon nanotube sheet according to the present embodiment. 2 to 4 are process cross-sectional views illustrating the method of manufacturing the carbon nanotube sheet according to the present embodiment.

  First, the structure of the carbon nanotube sheet according to the present embodiment will be described with reference to FIG.

  The carbon nanotube sheet 10 according to the present embodiment is a sheet-like structure having a plurality of carbon nanotubes 12 and a thermoplastic resin filling layer 14 filled in the gaps between the carbon nanotubes 12, as shown in FIG. .

  At least one end of the plurality of carbon nanotubes 12 is exposed from the filling layer 14. In the example of the carbon nanotube sheet 10 shown in FIG. 1, one end portion of the carbon nanotube 12 is covered with the filling layer 14, and the other end portion is exposed from the filling layer 14. Both ends of the carbon nanotube 12 may be exposed from the filling layer 14.

  The portion of the carbon nanotubes 12 embedded in the filling layer 14 is oriented in the thickness direction of the sheet, that is, in the direction intersecting the surface of the sheet. The ends of the carbon nanotubes 12 exposed from the filling layer 14 are bent in a direction parallel to the surface of the sheet.

The carbon nanotube 12 may be either a single-walled carbon nanotube or a multi-walled carbon nanotube. The surface density of the carbon nanotubes 12 is not particularly limited, but is preferably 1 × 10 ¹⁰ pieces / cm ² or more from the viewpoint of heat dissipation and electrical conductivity.

  The length of the carbon nanotube 12 is determined by the application of the carbon nanotube sheet 10 and is not particularly limited, but can be preferably set to a value of about 5 μm to 500 μm. When the carbon nanotube sheet 10 is used as a thermal interface material formed between a heat generation source (for example, a semiconductor element) and a heat dissipation component (for example, a heat spreader), the carbon nanotube sheet 10 is at least longer than the length that fills the irregularities on the surface of the heat generation source and the heat dissipation component. It is desirable to be.

  As described above, in the carbon nanotube sheet 10 according to the present embodiment, at least one end of the carbon nanotube 12 is exposed from the filling layer 14. Thereby, when the carbon nanotube sheet 10 is brought into contact with the heat radiating body or the heat generating body, the carbon nanotubes 12 are in direct contact with the heat radiating body or the heat generating body without going through the filling layer 14, thereby greatly increasing the heat conduction efficiency. Can do. Further, since the carbon nanotubes 12 have conductivity, the carbon nanotubes 12 can be used as a wiring body that penetrates the sheet by exposing both ends of the carbon nanotubes 12. That is, the carbon nanotube sheet 10 according to the present embodiment can be used not only as a heat conductive sheet but also as a vertical wiring sheet.

  In addition, since the carbon nanotubes 12 embedded in the filling layer are oriented in the film thickness direction of the sheet, the characteristics of the carbon nanotubes 12 that have extremely high thermal conductivity and conductivity in the axial direction are not observed. Demonstrating high thermal conductivity and electrical conductivity.

  Further, the end portion of the carbon nanotube 12 exposed from the filling layer 14 is bent in a direction parallel to the surface of the sheet, and contacts the heat radiating body or the heating element not only at the end portion of the carbon nanotube 12 but also at the side surface portion. Can do. Further, when the bent carbon nanotubes 12 are in contact with each other, heat conduction and electric conduction in a direction parallel to the surface of the sheet can be performed. Thereby, the contact area between the carbon nanotube 12 and the heat radiating body or the heat generating body can be increased, and the heat conduction efficiency and the electrical conductivity can be further increased.

  The filling layer 14 is formed of a thermoplastic resin. The thermoplastic resin that forms the packed layer 14 reversibly changes between a liquid and a solid depending on the temperature, is a solid at room temperature, changes to a liquid state when heated, and exhibits adhesive properties when cooled. There is no particular limitation as long as it returns to a solid while developing.

  Examples of such thermoplastic resins include hot melt resins shown below. Examples of the polyamide-based hot melt resin include “Micromelt 6239” (softening point temperature: 140 ° C.) manufactured by Henkel Japan K.K. Examples of the polyester hot melt resin include “DH598B” (softening point temperature: 133 ° C.) manufactured by Nogawa Chemical Co., Ltd. Examples of the polyurethane hot melt resin include “DH722B” manufactured by Nogawa Chemical Co., Ltd. Examples of the polyolefin-based hot melt resin include “EP-90” (softening point temperature: 148 ° C.) manufactured by Matsumura Oil Co., Ltd. Examples of the ethylene copolymer hot melt resin include “DA574B” (softening point temperature: 105 ° C.) manufactured by Nogawa Chemical Co., Ltd. Examples of the SBR hot melt resin include “M-6250” (softening point temperature: 125 ° C.) manufactured by Yokohama Rubber Co., Ltd. Examples of the EVA hot melt resin include “3747” (softening point temperature: 104 ° C.) manufactured by Sumitomo 3M Limited. Examples of the butyl rubber hot melt resin include “M-6158” manufactured by Yokohama Rubber Co., Ltd.

  The thermoplastic resin forming the filling layer 14 can be selected based on the melting temperature of the thermoplastic resin according to the intended use of the carbon nanotube sheet 10. The lower limit of the melting temperature of the thermoplastic resin is desirably higher than the upper limit of the heat generation temperature during operation. This is because if the thermoplastic resin is dissolved during operation, the carbon nanotube sheet 10 may be deformed and the carbon nanotubes 12 may lose the orientation. The upper limit value of the melting temperature of the thermoplastic resin is preferably lower than the lower limit value of the heat resistance temperature of the heating element and the heat dissipation element. The carbon nanotube sheet 10 according to the present embodiment is desirably reflowed after being brought into contact with the heat radiating body and the heat generating body. However, if the melting temperature of the thermoplastic resin is higher than the heat resistant temperature, the heat generating body and / or the heat radiating body is damaged. This is because it becomes difficult to perform reflow without giving any. The reflow of the carbon nanotube sheet 10 will be described later.

  For example, when the carbon nanotube sheet 10 is used for heat dissipation of an electronic device such as a CPU, the upper limit of the heat generation temperature when the CPU is operating is about 125 ° C., and the heat resistance temperature of the CPU electronic component is about 250 ° C., A thermoplastic resin having a melting temperature of about 125 ° C. to 250 ° C. is suitable. For example, when used for an application such as an exhaust system of an automobile engine, a thermoplastic resin having a melting temperature of about 600 ° C. to 900 ° C. is preferable in view of the fact that the heat generation temperature is about 500 ° C. to 800 ° C. depending on the part.

  Moreover, you may disperse and mix an additive with the filled layer 14 as needed. As the additive, for example, a substance having high thermal conductivity or a substance having high conductivity can be considered. By dispersing and mixing an additive having high thermal conductivity in the filled layer 14 portion, the thermal conductivity of the filled layer 14 portion can be improved, and the overall thermal conductivity of the carbon nanotube sheet 10 can be improved. it can. Further, when the carbon nanotube sheet is used as the conductive sheet, an additive having high conductivity is dispersed and mixed in the filling layer 14 portion. Thereby, the electrical conductivity of the filling layer 14 part can be improved, and the electrical conductivity of the carbon nanotube sheet 10 as a whole can be improved. As the material having high thermal conductivity, carbon nanotube, metal material, aluminum nitride, silica, alumina, graphite, fullerene, or the like can be used. As the highly conductive material, carbon nanotubes, metal materials, and the like can be applied.

  Next, the method for manufacturing the carbon nanotube sheet according to the present embodiment will be explained with reference to FIGS.

  First, a substrate 30 used as a base for forming the carbon nanotube sheet 10 is prepared (FIG. 2A). As the substrate 30, a semiconductor substrate such as a silicon substrate, an insulating substrate such as an alumina (sapphire) substrate, an MgO substrate, or a glass substrate, a metal substrate, or the like can be used. In addition, a thin film may be formed on these substrates. For example, a silicon substrate having a silicon oxide film with a thickness of about 300 nm can be used.

  The substrate 30 is peeled off after the growth of the carbon nanotubes 12. For this purpose, it is desirable that the substrate 30 does not deteriorate at the growth temperature of the carbon nanotubes 12. Further, it is desirable that at least the surface in contact with the carbon nanotube 12 is formed of a material that can be easily peeled off from the carbon nanotube 12. Further, it is desirable that the carbon nanotube 12 be formed of a material that can be selectively etched.

  Next, an Fe (iron) film having a film thickness of, for example, 2.5 nm is formed on the substrate 30 by, eg, sputtering, and an Fe catalytic metal film 32 is formed (FIG. 2B). The catalytic metal film 32 is not necessarily formed on the entire surface of the substrate 30, and may be selectively formed on a predetermined region of the substrate 30 using, for example, a lift-off method.

  As the catalyst metal, in addition to Fe, Co (cobalt), Ni (nickel), Au (gold), Ag (silver), Pt (platinum), or an alloy containing at least one of these materials may be used. In addition to the metal film, metal fine particles prepared by controlling the size in advance using a differential mobility analyzer (DMA) or the like may be used as the catalyst. In this case, the metal species may be the same as in the case of the thin film.

In addition, as a base film for these catalytic metals, Mo (molybdenum), Ti (titanium), Hf (hafnium), Zr (zirconium), Nb (niobium), V (vanadium), TaN (tantalum nitride), TiSi _x (titanium) Silicide), Al (aluminum), Al ₂ O ₃ (aluminum oxide), TiO _x (titanium oxide), Ta (tantalum), W (tungsten), Cu (copper), Au (gold), Pt (platinum), Pd A film made of (palladium), TiN (titanium nitride), or an alloy containing at least one of these materials may be formed. For example, a stacked structure of Fe (2.5 nm) / Al (10 nm), a stacked structure of Co (2.6 nm) / TiN (5 nm), and the like can be applied. When metal fine particles are used, for example, a laminated structure such as Co (average diameter: 3.8 nm) / TiN (5 nm) can be applied.

  Next, the carbon nanotubes 12 are grown on the substrate 30 by, for example, hot filament CVD using the catalytic metal film 32 as a catalyst. The growth conditions of the carbon nanotube 12 include, for example, a mixed gas of acetylene and argon (partial pressure ratio 1: 9) as a source gas, a total gas pressure in the film forming chamber of 1 kPa, a hot filament temperature of 1000 ° C., and a growth time of 25. Minutes. As a result, it is possible to grow multi-walled carbon nanotubes having 3 to 6 layers (average of about 4 layers), a diameter of 4 nm to 8 nm (average of 6 nm), and a length of 100 μm (growth rate: 4 μm / min). . The carbon nanotubes may be formed by other film forming methods such as a thermal CVD method and a remote plasma CVD method. The growing carbon nanotube may be a single-walled carbon nanotube. Moreover, as a carbon raw material, you may use hydrocarbons, such as methane and ethylene other than acetylene, alcohols, such as ethanol and methanol.

  The length of the carbon nanotube 12 is determined by the application of the carbon nanotube sheet 10 and is not particularly limited, but can be preferably set to a value of about 5 μm to 500 μm. When the carbon nanotube sheet 10 is used as a thermal interface material formed between a heat generation source (for example, a semiconductor element) and a heat dissipation component (for example, a heat spreader), the carbon nanotube sheet 10 is at least longer than the length that fills the irregularities on the surface of the heat generation source and the heat dissipation component. It is desirable to be.

Thus, a plurality of carbon nanotubes 12 oriented in the normal direction of the substrate 30 (vertical orientation) are formed on the substrate 30 (FIG. 2C). In the carbon nanotubes 12 formed under the above growth conditions, the surface density of the carbon nanotubes 12 was about 1 × 10 ¹¹ pieces / cm ² . This corresponds to the carbon nanotubes 12 being formed on a region of approximately 10% of the surface area of the substrate 30.

  Next, a thermoplastic resin processed into a film (thermoplastic resin film 34) is placed on the carbon nanotubes 12 grown on the substrate 30 (FIG. 3A). The film thickness of the thermoplastic resin film 34 is desirably set as appropriate according to the length of the carbon nanotubes 12. For example, when forming the carbon nanotube sheet 10 in which only one end of the carbon nanotube 12 is exposed as shown in FIG. 1, the length of the carbon nanotube 12 is preferably about the same, for example, about 5 μm to 500 μm. Moreover, when forming the carbon nanotube sheet | seat 10 which the both ends of the carbon nanotube 12 exposed, a grade slightly thinner than the length of the carbon nanotube 12, for example, about 4 micrometers-about 400 micrometers is suitable.

  As the thermoplastic resin of the thermoplastic resin film 34, for example, the following hot melt resin can be applied. Examples of the polyamide-based hot melt resin include “Micromelt 6239” manufactured by Henkel Japan Co., Ltd. Examples of the polyester hot melt resin include “DH598B” manufactured by Nogawa Chemical Co., Ltd. Examples of the polyurethane hot melt resin include “DH722B” manufactured by Nogawa Chemical Co., Ltd. Examples of the polyolefin-based hot melt resin include “EP-90” manufactured by Matsumura Oil Co., Ltd. Examples of the ethylene copolymer hot melt resin include “DA574B” manufactured by Nogawa Chemical Co., Ltd. Examples of the SBR hot melt resin include “M-6250” manufactured by Yokohama Rubber Co., Ltd. Examples of the EVA hot melt resin include “3747” manufactured by Sumitomo 3M Limited. Examples of the butyl rubber hot melt resin include “M-6158” manufactured by Yokohama Rubber Co., Ltd.

  Here, as an example, a case where a thermosetting resin film 34 obtained by processing “Micromelt 6239” manufactured by Henkel Japan Co., Ltd. into a film having a thickness of 100 μm will be described. “Micromelt 6239” has a melting temperature of 135 ° C. to 145 ° C. and a viscosity at the time of melting of 5.5 Pa.s. s to 8.5 Pa. s (225 ° C.) hot melt resin.

  Next, the substrate 30 on which the thermoplastic resin film 34 is placed is heated at a temperature of 195 ° C., for example. As a result, the thermoplastic resin of the thermoplastic resin film 34 is dissolved and gradually penetrates into the gaps of the carbon nanotubes 12. In this way, the thermoplastic resin film 34 is permeated to such an extent that it does not reach the surface of the substrate 30 (FIG. 3B).

  By processing the thermoplastic resin into a sheet in advance, the amount of filler can be controlled by the sheet thickness. Thereby, it can control so that a filler may not penetrate | invade to the board | substrate 30 by control of heating temperature and a heating time.

  The thickness of the thermoplastic resin film 34 penetrating into the gaps between the carbon nanotubes 12 can be controlled by the heat treatment time. For example, the carbon nanotubes 12 having a length of 100 μm grown under the above conditions can be permeated to such an extent that the thermoplastic resin film 34 does not reach the substrate 30 by performing a heat treatment at 195 ° C. for 1 minute.

  The heating time of the thermoplastic resin film 34 is such that the length of the carbon nanotubes 12, the viscosity at the time of melting of the thermoplastic resin, the thermoplastic resin film so that the thermoplastic resin film 34 penetrates to the extent that it does not reach the surface of the substrate 30. It is desirable to set appropriately according to the film thickness of 34.

  In the case of producing the carbon nanotube sheet 10 in which both ends of the carbon nanotube 12 are exposed, a thermoplastic resin film 34 that is thinner than the length of the carbon nanotube 12 is used, and the thermoplastic is used until the upper end of the carbon nanotube 12 is exposed. The resin film 34 may be permeated.

  The shape of the thermoplastic resin is preferably processed in advance into a film shape, but may be a pellet shape or a rod shape.

  Next, after allowing the thermoplastic resin film 34 to penetrate to a predetermined position, the thermoplastic resin film 34 is cooled to room temperature, and the thermoplastic resin film 34 is solidified. In this way, the filling layer 14 formed of the thermoplastic resin of the thermoplastic resin film 34 and filled in the gaps of the carbon nanotubes 12 is formed.

  Next, the carbon nanotubes 12 and the filling layer 14 are peeled from the substrate 30 (FIG. 3C). At this time, since the bonding between the carbon nanotubes 12 and the substrate 30 is weak, the carbon nanotubes 12 and the filling layer 14 can be easily separated from the substrate 30.

  Next, the surface of the filling layer 14 where the carbon nanotubes 12 are exposed is pressed against a member having a flat surface (for example, the substrate 40), and the portion exposed from the filling layer 14 of the carbon nanotubes 12 is pushed down (FIG. 4A). . Since the carbon nanotubes 12 are a material having a high flexibility, the carbon nanotubes 12 that are not embedded in the filling layer 14 can be selectively pushed down by being pressed against the substrate 40.

  4A shows a state in which the ends of the plurality of carbon nanotubes 12 are pushed down in a random direction, it is not necessarily required to be pushed down in a random direction. The nanotubes 12 may be pushed down in the same direction.

  In this manner, the end portion of the carbon nanotube 12 exposed from the filling layer 14 is bent in a direction parallel to the surface of the sheet to complete the carbon nanotube sheet 10 according to the present embodiment (FIG. 4B).

  Thus, according to this embodiment, the carbon nanotubes exposed from the filling layer are bent in a direction parallel to the surface of the sheet, so that the contact area of the carbon nanotubes with the adherend can be greatly increased. Thereby, the contact thermal resistance and contact resistance of the carbon nanotube sheet with respect to the adherend can be greatly reduced.

[Second Embodiment]
The carbon nanotube sheet and the manufacturing method thereof according to the second embodiment will be described with reference to FIGS. The same components as those of the carbon nanotube sheet and the manufacturing method thereof according to the first embodiment shown in FIGS. 1 to 4 are denoted by the same reference numerals, and description thereof is omitted or simplified.

  FIG. 5 is a schematic cross-sectional view showing the structure of the carbon nanotube sheet according to the present embodiment. 6 and 7 are schematic cross-sectional views illustrating the method of manufacturing the carbon nanotube sheet according to the present embodiment. 8 to 10 are perspective views illustrating the method of manufacturing the carbon nanotube sheet according to the present embodiment.

  First, the structure of the carbon nanotube sheet according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 5, the carbon nanotube sheet 10 according to the present embodiment is the first embodiment shown in FIG. 1 except that a coating film 16 is formed on one end of the carbon nanotube 12 covered with the filling layer 14. It is the same as the carbon nanotube sheet 10 according to the form.

  The material for forming the coating film 16 is not particularly limited as long as it has a higher thermal conductivity than the constituent material of the filling layer 14. When the carbon nanotube sheet 10 is also used for electric conduction, a conductive material such as a metal or an alloy can be applied. As a constituent material of the coating 16, for example, copper (Cu), nickel (Ni), gold (Au), or the like can be used. Moreover, the coating film 16 does not need to have a single layer structure, and may have a laminated structure of two layers or three or more layers such as a laminated structure of titanium (Ti) and gold (Au).

  The film thickness of the coating film 16 is not particularly limited as long as it does not inhibit the penetration of the thermoplastic resin film 34 in the manufacturing process. The film thickness of the coating film 16 is desirably set as appropriate according to the permeability of the thermoplastic resin film 34, the characteristics required for the carbon nanotube sheet 10, the constituent material of the coating film 16, and the like.

  By providing the coating film 16 having high thermal conductivity, the contact area of the carbon nanotube sheet 10 with respect to the adherend (heat radiating body, heating element) can be increased as compared with the case where the coating film 16 is not provided. Thereby, the contact thermal resistance between the carbon nanotube 12 and the adherend is reduced, and the thermal conductivity of the carbon nanotube sheet 10 can be increased. When the carbon nanotube sheet 10 is also used as a conductive sheet, the conductivity can be increased.

  FIG. 5 shows the case where the coating 16 is formed on one end of the carbon nanotube 12 covered with the filling layer 14, but the other end of the carbon nanotube 12 exposed from the filling layer 14 is shown. Alternatively, a film may be formed. The coating film 16 may be formed only on the other end of the carbon nanotube 12.

  Next, the method for manufacturing the carbon nanotube sheet according to the present embodiment will be explained with reference to FIGS.

  First, for example, the carbon nanotubes 12 are grown on the substrate 30 in the same manner as the carbon nanotube sheet manufacturing method according to the first embodiment shown in FIGS. 2 (a) to 2 (c).

  In FIG. 1 to FIG. 5, the carbon nanotubes 12 are drawn in a simple cylindrical shape for simplification of the drawings. However, the carbon nanotubes 12 are not necessarily in a complete cylindrical shape due to growth variations in the initial stage of growth. The carbon nanotubes 12 are oriented in the film thickness direction of the sheet as a whole. For example, as shown in FIG. 8, the upper end portion of the carbon nanotubes 12 is inclined with respect to the normal direction of the substrate 30 and grows. The length of the carbon nanotube 12 may vary.

  Next, Au (gold) with a film thickness of about 300 nm is deposited on the carbon nanotubes 12 by, for example, vapor deposition to form a coating film 16 of Au (FIG. 6A). The coating film 16 may be formed using another film forming method (for example, a sputtering method or the like) as long as it does not damage the carbon nanotubes 12.

  The material for forming the coating film 16 is not particularly limited as long as it has a higher thermal conductivity than the constituent material of the filling layer 14. When the carbon nanotube sheet 10 is also used for electric conduction, a conductive material such as a metal or an alloy can be applied. As a constituent material of the coating 16, for example, copper (Cu), nickel (Ni), gold (Au), or the like can be used. Moreover, the coating film 16 does not need to have a single layer structure, and may have a laminated structure of two layers or three or more layers such as a laminated structure of titanium (Ti) and gold (Au).

  In the initial stage of growth, the coating 16 is formed so as to cover the tip portion of each carbon nanotube 12 as shown in FIG. 9, for example. As the grown film thickness increases, the coatings 16 formed on the tip portions of the adjacent carbon nanotubes 12 are connected to each other. Thereby, the coating film 16 is formed so as to bundle the tip portions of the plurality of carbon nanotubes 12, as shown in FIG. 10, for example. When the growth film thickness of the coating film 16 is further increased, the coating film 16 is completely connected in a two-dimensional direction parallel to the surface of the sheet, and becomes a complete film with no gap.

  The film thickness of the coating film 16 to be formed is preferably set as appropriate according to the diameter and surface density of the carbon nanotubes 12 in consideration of the permeability of the thermoplastic resin film 34 when forming the filling layer 14.

For example, when the diameter of the carbon nanotube 12 is 10 nm and the surface density is 1 × 10 ¹¹ cm ⁻² , the gap between the adjacent carbon nanotubes 12 is approximately 50 nm. In this case, in order for the adjacent carbon nanotubes 12 to be connected by the coating film 16, it is desirable to form the coating film 16 having a thickness of at least half of the gap, that is, a thickness of about 25 nm or more. Further, if the coating film 16 is too thick, the coating film 16 becomes a complete film without gaps, and the permeability of the thermoplastic resin film 34 is lowered. Therefore, the upper limit film thickness of the coating film 16 is the permeability surface of the thermoplastic resin film 34. It is desirable to set from From these viewpoints, it is desirable that the film thickness of the coating film 16 is set to about 25 nm to 1000 nm in the carbon nanotube 12 under the above conditions.

  Next, for example, in the same manner as in the method of manufacturing the carbon nanotube sheet according to the first embodiment shown in FIGS. Is formed (FIG. 6B).

  The coating 16 does not necessarily have to have a film thickness sufficient for adjacent carbon nanotubes 12 to be connected to each other, but this has the effect of bundling a plurality of carbon nanotubes 12 by the coating 16 (for example, FIG. 10). reference). Thereby, when the thermoplastic resin film 34 osmose | permeates between the carbon nanotubes 12, it can suppress that the carbon nanotubes 12 fall apart. Further, the adjacent carbon nanotubes 12 are connected to each other, whereby heat conduction and electric conduction in the lateral direction are possible.

  Next, the carbon nanotubes 12, the coating film 16, and the filling layer 14 are peeled from the substrate 30 (FIG. 6C).

  Next, for example, in the same manner as in the method of manufacturing the carbon nanotube sheet according to the first embodiment shown in FIGS. 4A and 4B, the end of the carbon nanotube 12 exposed from the filling layer 14 is pushed down, and the book The carbon nanotube sheet according to the embodiment is completed (FIG. 7A).

  Thereafter, if necessary, a film 18 similar to the film 16 is formed on the surface where the pushed carbon nanotubes 12 are exposed. The method for forming the film 18, the forming material, and the like are the same as those for the film 16.

  Thus, according to this embodiment, the carbon nanotubes exposed from the filling layer are bent in a direction parallel to the surface of the sheet, so that the contact area of the carbon nanotubes with the adherend can be greatly increased. Thereby, the contact thermal resistance and contact resistance of the carbon nanotube sheet with respect to the adherend can be greatly reduced. Further, by providing a coating on at least one end of the carbon nanotube, the contact thermal resistance and contact resistance of the carbon nanotube sheet with respect to the adherend can be further reduced.

[Third Embodiment]
An electronic device and a manufacturing method thereof according to the third embodiment will be described with reference to FIGS. Components similar to those of the carbon nanotube sheet and the manufacturing method thereof according to the first and second embodiments shown in FIGS. 1 to 10 are denoted by the same reference numerals, and description thereof is omitted or simplified.

  FIG. 11 is a schematic cross-sectional view showing the structure of the electronic apparatus according to the present embodiment. FIG. 12 is a process cross-sectional view illustrating the method for manufacturing the electronic apparatus according to the present embodiment. FIG. 13 is a graph showing the relationship between the film thickness of the carbon nanotube sheet and the thermal resistance.

  In the present embodiment, an electronic device to which the carbon nanotube sheet according to the first and second embodiments is applied as a heat conductive sheet and a manufacturing method thereof will be described.

  First, the structure of the electronic apparatus according to the present embodiment will be explained with reference to FIG.

  A semiconductor element 54 such as a CPU is mounted on a circuit board 50 such as a multilayer wiring board. The semiconductor element 54 is electrically connected to the circuit board 50 through protruding electrodes 52 such as solder bumps.

  A heat spreader 58 for diffusing heat from the semiconductor element 54 is formed on the semiconductor element 54 so as to cover the semiconductor element 54. The carbon nanotube sheet 56 of the first or second embodiment is formed between the semiconductor element 54 and the heat spreader 58. The heat spreader 58 is bonded to the circuit board 50 with an organic sealant 60, for example.

  As described above, in the electronic apparatus according to the present embodiment, the carbon nanotube sheet 56 according to the first or second embodiment is provided between the semiconductor element 54 and the heat spreader 58, that is, between the heat generating portion and the heat radiating portion. .

  As described above, in the carbon nanotube sheet according to the first and second embodiments, the carbon nanotubes 12 are oriented in the film thickness direction of the sheet, and the thermal conductivity in the perpendicular direction is extremely high. Further, the bent carbon nanotubes 12 are exposed on at least one surface side of the filling layer 14, and the contact area of the carbon nanotubes 12 with the adherend is very large. In the carbon nanotube sheet according to the second embodiment, the coatings 16 and 18 are formed on one end portion or both end portions of the carbon nanotube 12, and the contact thermal resistance can be greatly reduced.

  Therefore, by using the disclosed carbon nanotube sheet as a heat conductive sheet formed between the semiconductor element 54 and the heat spreader 58, the heat generated from the semiconductor element 54 can be efficiently transmitted to the heat spreader 58, and the heat dissipation efficiency Can be increased. Thereby, the reliability of an electronic device can be improved.

  In the carbon nanotube sheet 56, at least the surface layer of the filling layer 14 that supports the carbon nanotubes 12 is formed of a thermoplastic resin material. As a result, the adhesion of the carbon nanotube sheet 56 to the semiconductor element 54 and the heat spreader 58 can be enhanced, and the thermal conductivity of the carbon nanotube sheet 56 can also be enhanced.

  Next, the method for manufacturing the electronic apparatus according to the present embodiment will be explained with reference to FIG.

  First, the semiconductor element 54 is mounted on the circuit board 50 via the protruding electrodes 52. In the drawing of this embodiment, the concavities and convexities of the opposing surfaces of the semiconductor element 54 and the heat spreader 58 are emphasized in order to facilitate understanding of the effects of the electronic device according to the present embodiment.

  Next, the carbon nanotube sheet 56 described in the first or second embodiment is placed on the semiconductor element 54 mounted on the circuit board 50 (FIG. 12A). The drawing of this embodiment shows a case where the carbon nanotube sheet according to the first embodiment is used.

  Next, after applying an organic sealant 60 for fixing the heat spreader 58 on the circuit board 50, the heat spreader 58 is placed on the semiconductor element 54 on which the carbon nanotube sheet 56 is placed (FIG. 12B).

  Next, heat treatment is performed with a load applied to the heat spreader 58, and the carbon nanotube sheet 56 is reflowed. In the carbon nanotube sheet 56 using, for example, “Micromelt 6239” manufactured by Henkel Japan Co., Ltd. as the packed layer 14, for example, heat treatment is performed at 195 ° C. for 10 minutes, for example, with a load of 0.25 MPa.

  By this heat treatment, the thermoplastic resin forming the filling layer 14 of the carbon nanotube sheet 56 is melted in liquid form, and the carbon nanotube sheet 56 is deformed along the surface irregularities of the semiconductor element 54 and the heat spreader 58. Further, the carbon nanotubes 12 in the carbon nanotube sheet 54 are loosely restrained by the filling layer 14, and their end portions come into direct contact with the semiconductor element 54 and the heat spreader 58. At this time, since the carbon nanotube 12 is a flexible and flexible material, it can bend following the uneven shape of the semiconductor element 54 and the heat spreader 58. As a result, the carbon nanotubes 12 that are in direct contact with the semiconductor element 54 and the heat spreader 58 are increased, and the contact thermal resistance between the carbon nanotube sheet 56 and the semiconductor element 54 and the heat spreader 58 can be greatly reduced.

  The load at this time may be a load range in which the carbon nanotube sheet 56 is deformed along the irregularities present on the surfaces of the semiconductor element 54 and the heat spreader 58 to form a sufficient contact state. The temperature and time of the heat treatment are such that the thermoplastic resin present at the interface between the semiconductor element 54 and the heat spreader 58 is melted and moved, and the ends of the carbon nanotubes 12 are in direct contact with the semiconductor element 54 and the heat spreader 58. What is necessary is just to select the range which becomes a surface state.

  Next, it is cooled to room temperature, and the thermoplastic resin of the filling layer 14 is solidified, and the heat spreader 58 is fixed on the circuit board 50 with the organic sealant 60 (FIG. 12C). At this time, the thermoplastic resin of the filling layer 14 exhibits adhesiveness, and the semiconductor element 54 and the heat spreader 58 can be bonded and fixed by the carbon nanotube sheet 56. Thereby, even after cooling to room temperature, a low contact thermal resistance between the carbon nanotube sheet 56, the semiconductor element 54, and the heat spreader 58 can be maintained.

  In the above example, the carbon nanotube sheet 56 and the heat spreader 58 are separate electronic components. However, the carbon nanotube sheet 56 may be formed in advance on the inner surface of the heat spreader 58 to form one electronic component. In this case, the formation surface of the filling layer 14 of the carbon nanotube sheet 56 can be bonded to the inner surface of the heat spreader 58.

  FIG. 13 is a graph showing the relationship between the film thickness of the carbon nanotube sheet and the thermal resistance. The thermal resistance is the thermal resistance between the heat generating body and the heat radiating body joined via the carbon nanotube sheet, and corresponds to the thermal resistance between the semiconductor element 54 and the heat spreader 58 in the example of FIG. In the figure, the plots marked with ● are when the carbon nanotube sheet according to the first embodiment shown in FIG. 1 is used. The plots indicated by □ are the cases where a carbon nanotube sheet (corresponding to the structure shown in FIG. 3C) in which the ends of the carbon nanotubes 12 are not bent is used.

  As shown in FIG. 13, when any carbon nanotube sheet is used, the thermal resistance tends to increase as the thickness of the sheet increases. This is because the heat transfer path becomes longer as the thickness of the sheet increases.

  On the other hand, when the carbon nanotube sheet according to the first embodiment is used (● mark), the thermal resistance is lower than when the carbon nanotube sheet is not bent (□ mark). The value is about 20% lower. This is because the contact area of the carbon nanotube 12 with respect to the adherend is increased and the contact thermal resistance is reduced by bending the end of the carbon nanotube 12.

  From the above results, it was verified that the thermal resistance between the heat generator and the heat radiator can be significantly reduced by using the carbon nanotube sheets according to the first and second embodiments.

  Thus, according to this embodiment, since the carbon nanotube sheet according to the first or second embodiment is disposed between the semiconductor element and the heat spreader, the thermal conductivity between them can be greatly improved. it can. Thereby, the thermal radiation efficiency of the heat | fever emitted from a semiconductor element can be improved, and the reliability of an electronic device can be improved.

[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications are possible.

  The present invention is not limited to the above embodiment, and various modifications are possible.

  For example, in the above-described embodiment, the carbon nanotube sheet is shown as an example of the heat dissipation material using the carbon element linear structure, but the heat dissipation material using the carbon element linear structure is limited to this. is not. Examples of the carbon element linear structure include carbon nanowires, carbon rods, and carbon fibers in addition to carbon nanotubes. These linear structures are the same as the carbon nanotubes except that their sizes are different. The present invention can also be applied to a heat dissipation material using these linear structures.

  In addition, the constituent materials and manufacturing conditions described in the above embodiment are not limited to the descriptions, and can be appropriately changed according to the purpose and the like.

  Further, the purpose of using the carbon nanotube sheet is not limited to that described in the above embodiment. The disclosed carbon nanotube sheet is, for example, a CPU heat dissipation sheet, a radio communication base station high output amplifier, a radio communication terminal high output amplifier, an electric vehicle high output switch, a server, a personal computer, etc. Can be applied. Moreover, it is applicable to a vertical wiring sheet and various applications using the high allowable current density characteristic of carbon nanotubes.

DESCRIPTION OF SYMBOLS 10 ... Carbon nanotube sheet 12 ... Carbon nanotube 14 ... Filling layer 16,18 ... Coating 30 ... Substrate 32 ... Catalyst metal film 34 ... Thermoplastic resin film 50 ... Circuit board 52 ... Projection electrode 54 ... Semiconductor element 56 ... Carbon nanotube sheet 58 ... Heat spreader 60 ... Organic sealant

Claims (7)

A linear structure of a plurality of carbon elements;
A thermoplastic resin filling layer disposed between the plurality of linear structures,
At least one end of each of the plurality of linear structures is exposed from the filling layer, and the portion of the linear structure exposed from the filling layer is bent in a direction parallel to the surface of the filling layer. A sheet-like structure characterized by comprising: In the sheet-like structure according to claim 1,
A sheet-like structure formed on at least one end portion of the plurality of linear structures, and further having a film made of a material having a higher thermal conductivity than the thermoplastic resin. In the sheet-like structure according to claim 1 or 2,
The thermoplastic resin changes state between a liquid and a solid according to temperature. In the sheet-like structure according to claim 3,
The thermoplastic resin exhibits adhesiveness when the state changes from a liquid to a solid. In the sheet-like structure according to any one of claims 1 to 4,
A plurality of the linear structures in a portion where the filler layer is disposed are oriented in the film thickness direction of the filler layer. A heating element;
A radiator,
A plurality of carbon element linear structures disposed between the heating element and the heat dissipating body, and a thermoplastic resin filling layer disposed between the plurality of linear structures; A sheet-like structure in which at least one end of the structure is exposed from the filling layer, and the linear structure in the portion exposed from the filling layer is bent in a direction parallel to the surface of the filling layer And an electronic device. A plurality of linear structures including a plurality of carbon element linear structures and a thermoplastic resin filling layer disposed between the plurality of linear structures between the heating element and the heat radiator. A sheet-like structure is disposed in which at least one end of the linear structure is exposed from the filling layer, and the portion of the linear structure exposed from the filling layer is bent in a direction parallel to the surface of the filling layer. Process,
Heating the heat dissipating material to melt the thermoplastic resin;
And a step of cooling the heat-dissipating material to solidify the thermoplastic resin.

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