JP4256463B1 - Heat dissipation structure - Google Patents

Abstract

The heat generated by an exothermic device can be efficiently dissipated, and there is no generation of dust such as carbon powder and metal fiber projections that adversely affect the electrical characteristics of the exothermic device.
A heat dissipation structure includes a glass epoxy substrate having a heat generating device mounted on a main surface and a heat dissipating sheet including a polypyrrole infiltrating sheet. . A front surface circuit pattern layer 62 made of a conductive material is formed on the main surface of the substrate, and a back surface circuit pattern layer 66 made of a conductive material is formed on the back surface 50b. The front surface circuit pattern layer 62 and the back surface circuit pattern layer 66 are electrically connected through the through hole 64. The exothermic device is mounted so as to be in close contact with the surface circuit pattern layer with the insulating layer 68 interposed therebetween. The heat dissipation sheet is in close contact with the back surface of the substrate, and the heat sink 56 is in close contact with the heat dissipation sheet.
[Selection] Figure 6

Description

  The present invention relates to a heat dissipation structure that efficiently dissipates heat generated from a power device or a light emitting device to the outside.

  Heat-generating electronic components such as power devices and light-emitting devices (hereinafter also referred to as heat-generating devices) are overheated by the heat generated by themselves and their own temperature rises, resulting in deterioration of electrical characteristics or optical properties. Degradation of performance such as deterioration of characteristics occurs. Therefore, in order to maintain the performance of the exothermic device, it is necessary to efficiently dissipate heat generated from the exothermic device to suppress the temperature rise of the exothermic device.

  In view of this, for the exothermic devices, a configuration is adopted in which heat generated from these exothermic devices is dissipated outside the exothermic devices by attaching a heat dissipation mechanism. Here, the heat dissipation mechanism refers to a mechanism in which a heat dissipation structure including a printed wiring board on which a heat generating device is mounted and a heat dissipation plate or a heatsink (heat sink) are closely attached.

  In order to dissipate heat outside the exothermic device, it is effective to improve the function as a heat dissipation mechanism for the printed wiring board itself on which the exothermic device is mounted, and various attempts have been made for that purpose. For example, there is disclosed a structure in which a heat-generating device is provided with a component mounting conductor pattern, connected to a back conductor pattern through a through-hole provided in a printed wiring board immediately below, and a heat sink attached to the back conductor pattern ( For example, see Patent Documents 1 to 3). Furthermore, an internal circuit pattern layer made of a conductive material is interposed inside the printed wiring board, and this internal circuit pattern layer includes a surface circuit pattern layer formed on the main surface of the printed wiring board via a through hole. Attempts to enhance the function as a heat dissipation mechanism for the printed wiring board itself have been disclosed as a configuration for conducting the back circuit pattern layer formed on the back surface of the printed wiring board (see, for example, Patent Documents 4 and 5).

  Further, in order to reduce the contact thermal resistance between the printed wiring board on which the exothermic device is mounted and the heat sink, means for interposing a heat radiation sheet between the printed wiring board and the heat sink has been taken.

  It is conceivable to use a single metal plate as the heat dissipation sheet, but if the heat dissipation sheet is a single metal plate, the weight increases. Therefore, the use of a single metal plate as a heat radiating sheet is not applied to mobile electronic devices and the like that are required to reduce the weight as much as possible. Therefore, recently, it has been proposed to use a graphite sheet that is lightweight and has a high heat dissipation effect instead of a single metal plate as a material of the heat dissipation sheet (see, for example, Patent Documents 6 and 7).

  However, it has been pointed out that the graphite sheet is prone to delamination. In view of this, an example is disclosed in which a graphite sheet is integrated by being sandwiched by a net-like body made of a metal wire and processed as a heat radiation sheet in order to make it difficult for delamination of the graphite sheet (see Patent Document 8).

In addition, a heat dissipation sheet formed by using a graphite film obtained by sheeting graphite powder such as natural graphite and forming an inorganic material layer on the surface of the graphite film is disclosed (see Patent Document 9). Here, the inorganic material layer formed on the surface of the graphite film is a metal film formed by plating or the like, or an inorganic material film formed by directly applying a liquid material for forming an inorganic material on the graphite film. Etc. This heat radiating sheet is characterized by having a flexibility that it can be easily attached to a curved portion of an electronic device or the like.
Japanese Patent Laid-Open No. 6-268341 Japanese Patent Laid-Open No. 11-54883 Japanese Patent Laid-Open No. 10-93249 Japanese National Patent Publication No. 8-505013 JP 2001-267473 A Japanese Patent Laid-Open No. 11-240706 JP2003-168882 JP 2005-229100 A JP 2008-78380 A

  However, in a heat dissipation structure including a heat dissipation sheet configured using a graphite material as the heat conductive layer, dust such as carbon powder is generated from the cut surface of the heat dissipation sheet. The dust such as carbon powder adheres to the printed wiring portion of the printed wiring board constituting the heat dissipation structure or the exothermic device attached to the main surface of the printed wiring board, resulting in inconvenience such as an electrical short circuit. there is a possibility.

  Further, according to the heat dissipation structure provided with the heat dissipation sheet disclosed in Patent Document 8 described above, a very excellent heat dissipation characteristic can be obtained, but metal fibers protrude from the cut surface of the heat dissipation sheet, and handling for the metal fibers is performed. Is troublesome. This metal fiber may cause inconveniences such as an electrical short circuit in the printed wiring portion of the printed wiring board or the heat generating device, like the above-described carbon powder.

  The inventor of the present invention has conducted a number of trials, and as a result, heat is efficiently generated by a heat dissipation sheet formed by closely adhering a polypyrrole infiltrated sheet infiltrated with a polypyrrole polymer into a cellulose sheet and a metal layer. I found it to be dissipated. Moreover, it has been found that heat can be efficiently dissipated by a heat dissipating sheet formed by adhering a metal sheet to the main surface and / or the back surface of the polypyrrole infiltrating sheet via an adhesive member. . Moreover, it was confirmed that no dust such as carbon powder was generated from these heat radiation sheets.

  Furthermore, the inventor of the present invention can form a heat dissipation structure including a printed wiring board configured to be connected to the back surface conductor pattern through a through hole, and a heat dissipation sheet including the above-described polypyrrole infiltrating sheet as a component. Based on the excellent heat dissipation characteristics of the heat dissipation sheet, the inventors have come to realize that a heat dissipation structure capable of efficiently dissipating the heat generated by the exothermic device is realized.

  Therefore, the present invention has the thermal characteristics that the heat generated by the exothermic device can be efficiently dissipated, and the generation of dust such as carbon powder that adversely affects the electrical characteristics of the exothermic device and An object of the present invention is to provide a heat dissipation structure having no metal fiber protrusion.

  According to the gist of the present invention, the heat dissipation structure has the following structural features.

  The first heat dissipating structure of the present invention dissipates the heat of the exothermic device configured to include a substrate on which the exothermic device is mounted on the main surface and a heat dissipating sheet closely attached to the back surface of the substrate. This is a heat dissipation structure. The heat radiating sheet is configured such that a metal layer is in close contact with either or both of the main surface and the back surface of a polypyrrole infiltrated sheet in which a polypyrrole polymer is infiltrated into a cellulose sheet.

  The second heat dissipation structure of the present invention is similar in configuration to the first heat dissipation structure, but the configuration of the heat dissipation sheet is different. That is, the heat radiating sheet provided in the second heat radiating structure has a metal sheet via an adhesive member on both or either one of the main surface and the back surface of the polypyrrole infiltrated sheet in which the polypyrrole polymer is infiltrated into the cellulose sheet. It is composed by bonding.

  The above-mentioned substrate has a front surface circuit pattern layer made of a conductive material formed on the main surface thereof, and a back surface circuit pattern layer made of a conductive material formed on the back surface. It is preferable that the layer is electrically connected through a through hole.

  In addition, an internal circuit pattern layer made of a conductive material is interposed inside the substrate, and the internal circuit pattern layer is a surface circuit pattern layer formed on the main surface of the substrate through a through hole. And, it is preferable that the back surface circuit pattern layer formed on the back surface of the substrate is electrically connected. The internal circuit pattern layer may be provided in a plurality of layers separated in the thickness direction of the substrate.

  The heat dissipation sheet provided with the first and second heat dissipation structures of the present invention includes a polypyrrole infiltrated sheet infiltrated with a polypyrrole polymer, and the polypyrrole infiltrated sheet has a metal layer directly adhered thereto, or a metal sheet Are bonded via an adhesive member.

  The thermal conductivity of the polypyrrole infiltrated sheet is smaller than the thermal conductivity of the metal sheet or metal layer. However, since this heat dissipation sheet is configured such that the polypyrrole infiltrated sheet is in close contact with the metal sheet or the metal layer, the heat diffusivity αp parallel to the surface of the heat dissipation sheet is greater than the heat diffusivity αt in the vertical direction, That is, αp / αt> 1.

  For this reason, the isothermal surface when this heat radiating sheet is closely attached to the substrate spreads at a higher speed in a direction parallel to the direction perpendicular to the surface of the heat radiating sheet.

  Here, the thermal conductivity is a physical quantity indicating the propagation characteristic of thermal energy, whereas the thermal diffusivity is a physical quantity indicating the propagation characteristic of temperature. That is, the temperature diffusivity is a value proportional to the thermal conductivity of the material and inversely proportional to the heat capacity.

  In order to efficiently cool the exothermic device, it is necessary that the temperature of the place where the exothermic device and the heat dissipation structure are in contact with each other is always kept lower than that of the exothermic device. In addition, the lower the temperature at which the exothermic device and the heat dissipation structure are in contact, the higher the cooling efficiency of the exothermic device, and the lower the thermal resistance between the exothermic device and the heat sink, the more exothermic The device is cooled efficiently.

  Thermal resistance means the amount of temperature rise with respect to the amount of heat generated per unit time, and approximately the reciprocal of the heat transfer coefficient between the heat generating device (high temperature part) and the heat sink (low temperature part). It is calculated by dividing by the contact area. The heat transfer coefficient is obtained by dividing the thermal energy passing through the unit area in a short time between the exothermic device and the heat sink by the temperature difference between the exothermic device and the heat sink. That is, the thermal resistance is a numerical value indicating difficulty in transmitting temperature, and the larger the numerical value, the harder it is to transmit temperature.

  Here, even when the low temperature part corresponding to the heat sink is an ambient space atmosphere surrounding the high temperature part such as a heat-generating device, the thermal resistance can be defined. As will be described later, it is also possible to calculate the thermal resistance value between the exothermic device and the space in contact with the exothermic device. The greater the thermal resistance between the exothermic device and the space in contact with the exothermic device, the less heat that is generated from the exothermic device is dissipated, and the temperature of the exothermic device itself is more likely to rise. It means that there is.

  The first and second heat dissipating structures of the present invention are parallel to the surface of the heat dissipating sheet that is in close contact with the heat dissipating sheet provided in the heat dissipating structure through the printed wiring board. It has a thermal characteristic that a high temperature region is formed in a short time over a wide range of the heat sink surface that diffuses quickly along the direction and is in contact with the heat dissipation sheet. The total amount of heat absorbed by the heat sink per unit time is larger as the temperature of the heat sink surface in contact with the heat radiating sheet is higher over a wide range.

  That is, if the heat generating device and the heat sink are indirectly contacted via the heat dissipation structure of the present invention, the heat generated from the heat generating device can be efficiently dissipated.

  In addition, the heat dissipation sheet constituting the heat dissipation structure of the present invention does not generate carbon powder or the like during work processing such as cutting processing. Therefore, according to the heat dissipation structure of the present invention, there is no inconvenience that carbon powder or the like adheres to the electronic module attached to the heat dissipation structure or the like and an electrical short circuit occurs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments of the present invention are not limited to these drawings. These drawings only schematically show the shape, size, and arrangement of the components to the extent that the present invention can be understood, and the numerical and other conditions described below are merely preferred examples. The present invention is not limited to only the embodiments of the present invention.

  In describing the first and second heat dissipation structures of the embodiment of the present invention, first, the configuration of the heat dissipation sheet that is a component of the heat dissipation structure, the manufacturing method thereof, and the verification experiment on the thermal properties thereof The result of will be described.

<Heat dissipation sheet>
With reference to FIGS. 1 (A) and (B), the structure of the heat-dissipating sheet, which is a component of the heat-dissipating structure, and the method for manufacturing the same will be described. FIGS. 1A and 1B are schematic cross-sectional structure diagrams cut in a direction perpendicular to a main surface and a back surface of a heat dissipation sheet, which is a component of the first and second heat dissipation structures, respectively. In the following description, a heat radiating sheet that is a component of the first heat generating structure is referred to as a first heat radiating sheet, and a heat radiating sheet that is a component of the second heat generating structure is referred to as a second heat radiating sheet.

  The first heat dissipating sheet shown in FIG. 1 (A) is configured by adhering a metal layer to at least one of the main surface 18a and the back surface 18b of the polypyrrole infiltrating sheet 18 in which a cellulose sheet is infiltrated with a polypyrrole polymer. The FIG. 1 (A) shows an example in which the metal layer 16 and the metal layer 20 are formed on the main surface 18a and the back surface 18b of the polypyrrole infiltrating sheet 18, respectively. It is sufficient that one of them is formed.

  The first heat radiation sheet shown in FIG. 1 (A) can be formed by three manufacturing methods, and these methods are as follows.

  The first method is a step of producing a polypyrrole infiltrated sheet in which a polypyrrole polymer is infiltrated into a cellulose sheet (hereinafter also referred to as step (2-1-1)) and at least one of the polypyrrole infiltrated sheet. This is a method including a step of forming a metal layer on one surface by a vacuum deposition method (hereinafter also referred to as a (2-1-2) step).

  The second method is a step of making a polypyrrole polymer infiltrated into a cellulose sheet to produce a polypyrrole infiltrated sheet (hereinafter also referred to as the (2-2-1) step) and at least one of the polypyrrole infiltrated sheet. This method includes a step of forming a metal layer by printing and fixing metal fine particles on one surface (hereinafter also referred to as a (2-2-2) step).

  The third method is a step of infiltrating a polypyrrole polymer into a cellulose sheet to produce a polypyrrole infiltrated sheet (hereinafter also referred to as the (2-3-1) step) and at least one of the polypyrrole infiltrated sheet. This method includes a step of forming a metal layer on one surface by a plating method (hereinafter also referred to as a (2-3-2) step).

  The (2-1-1) step, the (2-2-1) step and the (2-3-1) step are common to produce a polypyrrole infiltrated sheet in which a polypyrrole polymer is infiltrated into a cellulose sheet. Since these are steps, these steps will be described collectively below. The step of producing the polypyrrole infiltrating sheet includes (3-1) and (3-2) steps.

  The step (3-1) is a step of impregnating the cellulose sheet with cupric chloride, and is performed as follows. For example, a filter paper having a thickness of 0.1 mm for a filtering operation is immersed in an aqueous solution of cupric chloride having a concentration of 2 mol / liter so that the cupric chloride is sufficiently infiltrated into the filter paper. Thereby, the (3-1) step is executed.

  Evaluation of thermal characteristics to be described later was performed on the first heat radiating sheet composed of a polypyrrole infiltrated sheet prototyped using the filter paper having a thickness of 0.1 mm for the filtering operation described here as a component. However, the polypyrrole infiltrated sheet is not limited to the formation of a filter paper having a thickness of 0.1 mm for filtration work, and is a commercially available filter paper made from cotton fibers whose main component is a cellulose sheet. Alternatively, it can be formed using Japanese paper or the like as appropriate.

  The third (3-2) step is a step of bringing pyrrole in a gaseous state into contact with the cellulose sheet impregnated with cupric chloride, and is performed as follows. For example, pyrrole is heated to 80 ° C. to vaporize, and a filter paper infiltrated with polypyrrole polymer is formed by passing the vaporized pyrrole vapor through a filter paper soaked with cupric chloride for 10 minutes.

  The (2-1-2) step in the first method is a step of forming a metal layer on at least one surface of the polypyrrole infiltrated sheet by a vacuum deposition method. For the metal layer, copper, gold, silver, aluminum or the like is appropriately selected, and these metals are vaporized in vacuum by resistance heating or electron beam overheating, and vacuum deposition is performed on at least one surface of the polypyrrole infiltrated sheet. Just do it. At this time, it is not necessary to make the vapor deposition range the entire main surface or back surface of the polypyrrole infiltrated sheet. The vapor deposition range can be set as appropriate according to the form of use of the first heat dissipation sheet.

  The step (2-2-2) in the second method is realized by printing and fixing metal fine particles on at least one surface of the polypyrrole infiltrated sheet using a printing technique. At this time, as in the above-described step (2-1-2), the printing range need not be the entire main surface or back surface of the polypyrrole infiltrated sheet. It is possible to set the printing range as appropriate according to the use form of the first heat dissipation sheet.

  The (2-3-2) step in the third method is realized by plating a metal layer on at least one surface of the polypyrrole infiltrated sheet using a plating solution. The plating solution can be prepared, for example, by adding 150 g of cupric sulfate and 20 ml of sulfuric acid to 500 ml (milliliter) of distilled water and stirring to completely dissolve the cupric sulfate. This plating solution was set to 35 ° C., and the main surface and the back surface of the polypyrrole infiltrated sheet were plated. In performing the plating, a polypyrrole infiltrated sheet was connected to the cathode to form a 0.02 mm thick copper layer.

  When producing a first heat dissipation sheet in which a metal layer is formed only on one of the main surface and the back surface of the polypyrrole infiltrated sheet, the surface on which the metal layer is not formed is an insulator film such as a polymer film. The (2-1-2) step, the (2-2-2) step, and the (2-3-2) step may be executed after covering.

  Similarly, after covering the region where the metal layer is not formed on the main surface and the back surface of the polypyrrole infiltrated sheet with an insulating film such as a polymer film so as to expose only the region where the metal layer is formed (2-1 -2) If the steps (2-2-2) and (2-3-2) are executed, the first heat-dissipating sheet in which the metal layer is formed only in the required area is produced. Is possible. That is, the range in which the metal layer is formed by the (2-1-2) step, the (2-2-2) step, and the (2-3-2) step as appropriate according to the use form of the first heat dissipation sheet Can be set.

  The second heat dissipation sheet shown in FIG. 1 (B) is a metal sheet via an adhesive member on at least one of the main surface 26a and the back surface 26b of the polypyrrole infiltrated sheet 26 in which the polypyrrole polymer is infiltrated into the cellulose sheet. It is composed by bonding. In FIG. 1 (B), a metal sheet 22 is bonded to the main surface 26a of the polypyrrole infiltrating sheet 26 via an adhesive member 24, and a metal sheet 30 is bonded to the back surface 26b via an adhesive member 28. Although the second heat radiation sheet is shown, any one of the metal sheet 22 and the metal sheet 30 may be formed.

  As the adhesive members 24 and 28, a double-sided adhesive tape (product number NW-50) manufactured by Nichiban Co., Ltd. or cemedine (product number SX720W) which is an acrylic modified silicone resin manufactured by Cemedine Co., Ltd. is appropriately selected and used. It is possible.

<Verification of thermal properties of heat dissipation sheet>
With reference to FIG. 2 to FIG. 5, the result of the verification experiment on the thermal properties of the heat dissipating sheet according to the embodiment of the present invention will be described.

  FIG. 2 is a diagram for explaining the verification experiment about the thermal properties of the heat dissipation sheet according to the embodiment of the present invention, and schematically shows the arrangement relationship of the exothermic device 40, the electrical wiring board 42, the heat dissipation sheet 44, and the heat sink 46. FIG.

  A 1 W light emitting diode was used as the exothermic device 40. As the electrical wiring board 42, a well-known universal printed circuit board was used. This universal printed circuit board is a universal printed circuit board (model number: ICB-93SHG) manufactured by Sanhayato Co., Ltd., formed using a glass epoxy material. As the heat sink 46, an aluminum plate heat sink made of aluminum and having a thickness of 0.5 mm was used.

  The electrical wiring board 42, the heat radiation sheet 44, and the heat sink 46 are cut into 60 mm squares and overlapped as shown in FIG. The center position of the exothermic device 40 is 5 mm away from one side of a 60 mm square, and is arranged at an equal distance from two sides perpendicular to the one side.

  As the heat radiating sheet 44, a heat radiating sheet composed of the heat radiating sheet shown in FIG. 1A and a graphite material for comparison was used to verify the thermal characteristics. For comparison, the thermal characteristics in the case where the electric wiring board 42 and the heat sink 46 are in direct contact with each other without using these heat radiating sheets were also verified. Note that the heat dissipation sheet shown in FIG. 1B is the same as the thermal characteristics of the heat dissipation sheet shown in FIG.

  Evaluation of the thermal characteristics of the heat-dissipating sheet was performed by observing changes in temperature with time from the start of energization to the exothermic device 40 at a total of eight locations CH1 to CH8 shown in FIG. CH1, CH3, CH5, and CH7 indicate temperature measurement points on the surface of the electrical wiring board 42 on the side where the exothermic device 40 is installed. Further, CH2, CH4, CH6, and CH8 indicate temperature measurement points on the surface of the heat sink 46 opposite to the side where the electric wiring board 42 is installed.

  As shown in Figure 2, CH1 is a temperature measurement point set directly under the exothermic device 40, and CH3, CH5, and CH7 are located 15 mm, 30 mm, and 45 mm away from the exothermic device 40, respectively. This is the set temperature measurement point. CH2 is a temperature measurement point set directly under the exothermic device 40, and CH4, CH6, and CH8 are temperature measurement set at positions 15 mm, 30 mm, and 45 mm away from the exothermic device 40, respectively. It is a point.

  Table 1 summarizes the thermal resistance values obtained in the evaluation of the thermal characteristics of the heat dissipation sheet in a list. The vertical columns labeled I and II show the magnitude of thermal resistance when using a heat radiating sheet composed of the first heat radiating sheet and the graphite material shown in FIG. It is shown. The vertical column shown as III shows the magnitude of the thermal resistance when no heat dissipation sheet 44 is installed.

  In the horizontal columns indicated as A to H in Table 1, the values of the thermal resistance between the two locations shown below are shown. Column A is the thermal resistance value between the exothermic device and the space in contact with this exothermic device, column B is the thermal resistance value between the space in contact with CH2 and CH2, and column C is in contact with CH3 and CH3 The thermal resistance value between the space, D column is the thermal resistance value between the space in contact with CH4 and CH4, E column is the thermal resistance value between the space in contact with CH5 and CH5, F column is CH6 The thermal resistance value between the space in contact with CH6, the G column indicates the thermal resistance value between the space in contact with CH7 and CH7, and the H column indicates the thermal resistance value between the space in contact with CH8 and CH8. ing.

  FIG. 3 is a diagram showing temporal changes in temperature in CH1 to CH8 when a heat dissipation sheet, which is a component of the first heat dissipation structure of the embodiment of the present invention, is used as the heat dissipation sheet 44. The horizontal axis shows time in units of minutes, and the vertical axis shows temperature in degrees Celsius.

  The heat-dissipating sheet, which is a component of the first heat-dissipating structure according to the embodiment of the present invention, has a 0.1 mm-thick copper plate with an adhesive on a polypyrrole infiltrated sheet formed using a filter paper having a thickness of 0.1 mm. It is a heat radiating sheet configured to be in direct contact without being used. Here, the universal printed circuit board as the electric wiring board 42 and the heat dissipation sheet 44 are in direct contact with each other, and the aluminum heat sink as the heat sink 46 and the heat dissipation sheet 44 are in close contact with each other.

  As shown in FIG. 3, the temperature change at the temperature measurement point CH1 set immediately below the exothermic device 40 reaches 45.4 ° C. 3 minutes after the start of energization of the light emitting diode as the exothermic device. Finally, the temperature reaches 52.7 ° C. and is in a thermal equilibrium state. The temperature measurement points CH2 to CH8 are approximately 15 ° C. lower than CH1.

  As shown in Table 1, when the heat dissipation sheet, which is a component of the first heat dissipation structure of the embodiment of the present invention, is used as the heat dissipation sheet 44, the thermal resistance value is approximately 21.2 ° C / W to 37.3 ° C / W.

  FIG. 4 shows a conventional heat dissipating sheet 44 disclosed in Patent Document 3 as a heat dissipating sheet 44 for comparison with the case where the heat dissipating sheet as a heat dissipating sheet 44 is a component of the first heat dissipating structure of the embodiment of the present invention. Temperature in CH1 to CH8 when using the same type of heat dissipation sheet (made by Japan Matex Co., Ltd., trade name `` Jits 3D Thermal Conduction Sheet '') composed of a graphite sheet sandwiched between nets made of metal wire It is a figure which shows the time change of. The thickness of this heat radiating sheet is 0.15 mm. The horizontal axis of FIG. 4 shows time in units of minutes, and the vertical axis shows temperature in units of degrees Celsius.

  As shown in FIG. 4, the temperature change at the temperature measurement point CH1 set immediately below the exothermic device 40 reaches 49.1 ° C. 3 minutes after the start of energization of the light emitting diode as the exothermic device. Finally, the temperature reaches 57.5 ° C. and is in a thermal equilibrium state. The temperature measurement points CH2 to CH8 are approximately 15 ° C to 18 ° C lower than CH1.

  As shown in Table 1, when the heat dissipation sheet is used as the heat dissipation sheet 44, which is formed by integrally sandwiching a graphite sheet with a net made of a metal wire, the thermal resistance value is approximately 19.0 ° C / W to 32.7 ° C / W.

  FIG. 5 is a diagram showing temporal changes in temperature in CH1 to CH8 when the electric wiring board 42 and the heat sink 46 are in direct contact without using the heat dissipation sheet 44. FIG. The horizontal axis shows time in units of minutes, and the vertical axis shows temperature in degrees Celsius.

  As shown in FIG. 5, the temperature change at the temperature measurement point CH1 set immediately below the exothermic device 40 reaches 93.6 ° C. 3 minutes after the start of energization of the light emitting diode as the exothermic device. Further, it can be seen that the temperature tends to increase with time. The temperature measurement points CH2 to CH8 are approximately 60 ° C. lower than CH1.

  Curves giving temperature changes at the temperature measurement points CH2 and CH4 to CH8 are very close to each other, and curves giving temperature changes at CH2 and CH4 to CH8 are gathered together as shown by two broken lines in FIG. Therefore, in FIG. 5, individual curves that give temperature changes in CH2 and CH4 to CH8 are omitted.

  The temperature change at the temperature measurement point CH1 set immediately below the exothermic device 40 when using the heat dissipation sheet shown in FIG. 3 and FIG. 4 described above remains in the range of 50 ° C. to 60 ° C. Thus, when the heat dissipation sheet shown in FIG. 5 is not used, the temperature at CH1 rises to 90 ° C. or more. From this, it can be seen that the temperature rise of the exothermic device can be effectively prevented by using the heat dissipation sheet.

  Further, as shown in Table 1, the thermal resistance value when the heat radiating sheet 44 is not used is approximately 14.5 ° C./W to 75.5 ° C./W. In particular, it can be seen that the thermal resistance value between the exothermic device shown in column A of Table 1 and the space in contact with the exothermic device is remarkably high. In other words, if the heat dissipation sheet 44 is not used, the heat generated from the exothermic device cannot be effectively dissipated, and the temperature rise of the exothermic device is large, resulting in performance such as deterioration of electrical characteristics or optical characteristics. This suggests the possibility of degradation.

  On the other hand, by using a heat dissipating sheet comprising a polypyrrole infiltrating sheet, heat dissipating is constructed by sandwiching a conventional graphite sheet, which is said to have excellent heat dissipation properties, with a net made of metal wire. It was confirmed that the heat dissipation effect equivalent to or higher than that of the sheet was realized. In addition, the heat dissipating sheet comprising the polypyrrole infiltrating sheet has an excellent characteristic that dust such as carbon powder that adversely affects the electronic module is not generated.

<Heat dissipation structure>
The difference between the first heat dissipation structure and the second heat dissipation structure of the present invention lies in the structure of the heat dissipation sheet that is a component. Since the structure of the heat dissipating sheet used for the first and second heat dissipating structures of the present invention has already been described, the exothermic property commonly used for the first and second heat dissipating structures of the present invention is described below. The configuration of the substrate on which the electronic component is mounted will be described with reference to three examples. In the following description, since the contents are common to the first and second heat dissipation structures of the present invention, the first and second heat dissipation structures are not distinguished and may be simply referred to as a heat dissipation structure. In addition, the first and second heat radiating sheets may be simply referred to as heat radiating sheets unless it is particularly necessary to distinguish them.

  A heat radiating structure according to first to third embodiments of the present invention will be described with reference to FIGS.

  In the following description of the first to third embodiments, any of the first and second heat dissipation sheets described above can be used as the heat dissipation sheet.

  FIG. 6 is a diagram for explaining the heat dissipation structure of the first embodiment, and is a schematic cross-sectional configuration diagram including a heat dissipation sheet and a heat sink. The heat dissipation structure 54 of the first embodiment includes a glass epoxy substrate 50 having a heat generating device 60 mounted on the main surface 50a, and a heat dissipation sheet 52 in close contact with the back surface 50b of the substrate 50. ing. The substrate 50 is not limited to a glass epoxy substrate, and may be an aluminum substrate configured with an insulating layer for electrical insulation from the exothermic device 60 or the like.

  A surface circuit pattern layer 62 made of a conductive material is formed on the main surface 50a of the substrate 50, and a back circuit pattern layer 66 made of a conductive material is formed on the back surface 50b. The front surface circuit pattern layer 62 and the back surface circuit pattern layer 66 are electrically connected through the through hole 64.

  The front surface circuit pattern layer 62 and the back surface circuit pattern layer 66 mean, for example, a copper wiring layer formed on the main surface 50a and the back surface 50b of the glass epoxy substrate 50 on which the circuit pattern is formed.

  The exothermic device 60 is mounted so as to be in close contact with the surface circuit pattern layer 62 with the insulating layer 58 interposed therebetween. The heat dissipation sheet 52 is in close contact with the back surface 50b of the substrate 50, and the heat sink 56 is in close contact with the heat dissipation sheet 52. The heat sink 56 is a commonly used aluminum plate or an aluminum plate having a fin structure or the like. The exothermic device 60 refers to an active electronic element such as a light emitting diode (LED), a logic integrated circuit, and a power transistor.

  Heat generated in the exothermic device 60 is transmitted to the surface circuit pattern layer 62 through the insulating layer 58, and is propagated through the surface circuit pattern layer 62 and diffused. The heat diffused to the front surface circuit pattern layer 62 propagates through the through-holes to the back surface circuit pattern layer 66 and is diffused. The heat that reaches the back surface circuit pattern layer 66 and is diffused is transferred to the heat dissipation sheet 52.

  The heat transmitted to the heat radiating sheet 52 is transmitted to the heat sink 56 that is in close contact with the heat radiating sheet 52, and is radiated to the outside.

  As described above, the heat dissipation sheet 52 in close contact with the substrate 50 has a characteristic of spreading heat at a higher speed in a direction parallel to the direction perpendicular to the surface of the heat dissipation sheet 52. Therefore, when the heat generated from the exothermic device 60 is transferred to the heat radiating sheet 52 through the substrate 54, it quickly diffuses along the direction parallel to the surface of the heat radiating sheet 52 and is in contact with the heat radiating sheet 52. A high temperature region is formed in a short time over a wide range of the main surface 56a of 56.

  The total amount of heat absorbed by the heat sink 56 per unit time is larger as the temperature of the main surface 56a of the heat sink 56 in contact with the heat dissipation sheet 52 is higher over a wide range. That is, if the heat generating device 60 and the heat sink 56 are indirectly contacted via the heat dissipation structure 54, the heat generated from the heat generating device 60 can be efficiently dissipated.

  FIG. 7 is a diagram for explaining the heat dissipation structure of the second embodiment, and is a schematic cross-sectional configuration diagram including a heat dissipation sheet and a heat sink. The heat dissipation structure 74 of the second embodiment is different from the heat dissipation structure 54 of the first embodiment described above in that an internal circuit pattern layer 68 is provided inside the substrate 70. Since the other components are the same as those of the heat dissipation structure 54 of the first embodiment, a duplicate description is omitted.

  The internal circuit pattern layer 68 is, for example, a layered copper plate formed as a plane parallel to the main surface 70a and the back surface 70b inside a glass epoxy substrate 70, and a copper wiring layer on which a circuit pattern is formed Can be.

  Since the heat dissipation structure 74 of the second embodiment is provided with the internal circuit pattern layer 68 inside the substrate 70, the heat generated from the exothermic device 60 is once generated in the internal circuit pattern layer 68 by the internal circuit pattern layer 68. Since diffusion is performed along the horizontal direction, the thermal diffusion efficiency in the substrate 70 is increased. Therefore, the heat generated from the exothermic device 60 can be dissipated more efficiently than the heat dissipation structure of the first embodiment described above.

  FIG. 8 is a diagram for explaining the heat dissipation structure of the third embodiment, and is a schematic cross-sectional configuration diagram including a heat dissipation sheet and a heat sink. The heat dissipating structure 76 of the third embodiment is that the first internal circuit pattern layers 68-1 and 68-2 are provided in the substrate 72 so as to be separated from each other in the thickness direction of the substrate. And the heat dissipating structures 54 and 74 of the second embodiment are different. The other constituent elements are the same as those of the heat dissipation structures 54 and 74 of the first and second embodiments, and a duplicate description is omitted.

  Similarly to the internal circuit pattern layer 68, the internal circuit pattern layers 68-1 and 68-2 are formed in a plane parallel to the main surface 72a and the back surface 72b in the glass epoxy substrate 72, for example, in the thickness direction of the substrate. In some cases, the copper plates are layered copper plates that are spaced apart from each other, and may be copper wiring layers on which circuit patterns are formed.

  In the heat dissipation structure 76 of the third embodiment, since the internal circuit pattern layers 68-1 and 68-2 are provided inside the substrate 72, the heat generated from the exothermic device 60 is temporarily reduced to the internal circuit pattern layer. In 68-1 and 68-2, since diffusion is performed along the lateral direction of the substrate 72, the thermal diffusion efficiency in the substrate 72 is increased. Since the substrate 72 includes two internal circuit pattern layers, the lateral diffusion efficiency of the heat generated from the heat generating device 60 is higher than that of the substrate 70 of the second embodiment. Generally, the greater the number of internal circuit pattern layers provided in the substrate, the higher the lateral diffusion efficiency of heat in the substrate.

  Therefore, the heat dissipation structure 76 of the third embodiment can dissipate heat generated from the exothermic device 60 more efficiently than the heat dissipation structures of the first and second embodiments described above.

  An LED backlight module using the heat dissipation structure of the present invention will be described with reference to FIGS. 9 (A) is a front view of the LED backlight module, FIG. 9 (B) is a side view, FIG. 9 (C) is a back view, and FIG. 9 (D) is an enlarged side view. FIG.

  The LED backlight module using the heat dissipation structure of the present invention is configured by fixing a heat dissipation structure 82 on which the LED 80 is mounted to a heat sink 84 having a function as an attachment part. As the heat dissipation structure 82, the heat dissipation structure of the first embodiment of the present invention described above is used. As shown in FIG. 9 (D), the heat dissipation structure 82 is configured such that a heat dissipation sheet 82-2 is in close contact with a substrate 82-1 on which the LED 80 is attached. The heat radiation sheet 82-2 is attached so as to extend from a portion sandwiched between the substrate 82-1 and the heat sink 84 to a portion sandwiched between the aluminum back support panel 86 and the heat sink 84.

  LED light output from the LED 80 mounted on the heat dissipation structure 82 propagates through the acrylic light guide plate 90 while being irregularly reflected by the light reflector 88 supported by the aluminum back support panel 86, and the surface plate 92 is uniform. Designed to illuminate with brightness. The size of the surface plate 92 is A4 size (vertical 210 mm, horizontal 297 mm). That is, the dimension of the front view of the LED backlight module in FIG. 9A corresponds to the A4 size.

  On the other hand, heat is also generated from the LED 80, and this heat is transmitted to the heat sink 84 and the aluminum back support panel 86 via the heat dissipation structure 82 and diffused to the outside.

  Next, the result of the verification experiment on the thermal properties of the LED backlight module using the heat dissipation structure of the present invention will be described.

  When a forward current of 60 mA was applied to the LED 80 to emit light, the illuminance of the surface plate 92 was 6000 lux. The decrease in luminous efficiency due to the temperature rise of LED 80 was estimated to be within 2%, and the luminous efficiency of LED 80 was able to ensure 98% or more. Further, when the LED 80 was caused to emit light by flowing a forward current of 100 mA corresponding to 1.67 times the above condition, the illuminance of the surface plate 92 became 10,000 lux. At this time, the temperature of the LED backlight module rose to 54 ° C. at the center position on the back of the LED backlight module (point indicated by E in FIG. 9A), but the temperature of the LED 80 was 77 ° C. At this time, the decrease in luminous efficiency due to the temperature rise of the LED 80 was estimated to be within 9%, and the luminous efficiency of the LED 80 was able to ensure 91% or more.

  For comparison, an LED backlight module was constructed without using the heat dissipation structure of the present invention, and the same experiment was performed. In this comparative experiment, when a forward current of 60 mA was passed through the LED 80 to emit light, it was confirmed that the temperature of the LED 80 exceeded 100 ° C. and the luminous efficiency dropped to 70%.

  The evaluation of the thermal characteristics of the LED backlight module using the heat dissipation structure of the present invention is based on the change in temperature with time from the start of energization at a total of five points A to E shown in FIGS. 9 (A) to (D). Done by observing. A and B indicate measurement points in the vicinity of the LED 80, and C and D indicate measurement points of the heat sink 84. Although the temperature F of the frame of the LED backlight module is not shown in FIGS. 9A to 9D, it is the room temperature around the LED backlight module. G represents the center position of the front surface of the LED backlight module, and E represents the center position of the back surface of the LED backlight module.

  With reference to FIG. 10, the evaluation of the thermal characteristics of the LED backlight module using the heat dissipation structure of the present invention will be described. FIG. 10 is a diagram for explaining the evaluation of the thermal characteristics of the LED backlight module using the heat dissipation structure of the present invention. In FIG. 10, the horizontal axis indicates the time elapsed from the start of energization of the LED 80 in units of minutes. Further, the left vertical axis shows the temperature in A to F in units of ° C., and the right vertical axis shows the illuminance G of the surface plate 92 in units of Lux.

  The illuminance G of the surface plate 92 decreased immediately after the start of energization, but stabilized at 10000 lux. Further, the room temperature around the LED backlight module, which is the temperature F of the frame of the LED backlight module, is constant at approximately 30 ° C., and the temperatures in the vicinity A and B of the LED 80 do not rise above 77 ° C. Further, the measurement points C and D of the heat sink 84 close to the LED 80 are stable at about 55 ° C.

  Generated from LED 80 because the temperature at measurement points C and D of heat sink 84 close to LED 80 is only 55 ° C and 22 ° C different from the temperature 77 ° C in the vicinity A and B of LED 80 It can be seen that the applied heat is efficiently transferred to the heat sink 84. This concludes that good results were obtained that the temperatures in the vicinity A and B of the LED 80 did not rise above 77 ° C.

FIG. 5 is a diagram for explaining the configuration of the heat dissipation sheet and the manufacturing method thereof, and (A) and (B) are perpendicular to the main surface and the back surface of the heat dissipation sheet, which are components of the first and second heat dissipation structures, respectively. FIG. 3 is a schematic cross-sectional structure diagram cut in various directions. FIG. 6 is a diagram for explaining a verification experiment on thermal properties of a heat dissipation sheet that is a component of the first and second heat dissipation structures of the embodiment of the present invention. FIG. 5 is a diagram showing a change in temperature over time in CH1 to CH8 when a heat dissipation sheet that is a component of the first heat dissipation structure of the embodiment of the present invention is used as the heat dissipation sheet 44. It is a figure which shows the time change of the temperature in CH1-CH8 at the time of using the heat-radiation sheet comprised by pinching | interposing the conventional graphite sheet | seat between the nets which consist of metal wires, and integrating. It is a figure which shows the time change of the temperature in CH1-CH8 at the time of setting it as the structure which contacts an electrical wiring board and a heat sink directly without using a heat radiating sheet. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a heat dissipation structure of a first embodiment of the present invention, and is a schematic cross-sectional configuration diagram including a heat dissipation sheet and a heat sink. FIG. 4 is a diagram for explaining a heat dissipation structure according to a second embodiment of the present invention, and is a schematic cross-sectional structure diagram including a heat dissipation sheet and a heat sink. FIG. 6 is a diagram for explaining a heat dissipation structure according to a third embodiment of the present invention, and is a schematic cross-sectional configuration diagram including a heat dissipation sheet and a heat sink. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining an LED backlight module using the heat dissipation structure of the present invention, (A) is a front view of the LED backlight module, (B) is a side view, and (C) is a back surface. It is a figure, (D) is a sectional structure figure expanding and showing a side view. It is a figure where it uses for description about evaluation of the thermal characteristic of the LED backlight module using the thermal radiation structure of this invention.

Explanation of symbols

16, 20: Metal layer
18, 26: Polypyrrole infiltrated sheet
22, 30: Metal sheet
24, 28: Adhesive member
40, 60: exothermic device
42: Electrical wiring board
44, 52, 82-2: Heat dissipation sheet
46, 56, 84: heat sink
50, 70, 72, 82-1: Board
54, 74, 76, 82: Heat dissipation structure
58: Insulating layer
62: Surface circuit pattern layer
64: Through hole
66: Back circuit pattern layer
68, 68-1, 68-2: Internal circuit pattern layer
80: LED
86: Aluminum back support panel
88: Light reflector
90: Acrylic light guide plate
92: Surface plate

Claims (8)

A heat dissipating structure that mounts heat-generating electronic components and dissipates heat from the heat-generating electronic components,
A substrate on which the heat-generating electronic component is mounted on the main surface;
Comprising a heat dissipation sheet in intimate contact with the back surface of the substrate;
The heat dissipation sheet is a heat dissipation structure characterized in that a metal layer is in close contact with either or both of the main surface and the back surface of a polypyrrole infiltrated sheet in which a cellulose sheet is infiltrated with a polypyrrole polymer. A front surface circuit pattern layer made of a conductive material is formed on the main surface of the substrate, and a back surface circuit pattern layer made of a conductive material is formed on the back surface of the substrate,
2. The heat dissipation structure according to claim 1, wherein the back surface circuit pattern layer and the front surface circuit pattern layer are electrically connected through a through hole. An internal circuit pattern layer made of a conductive material is interposed inside the substrate,
The internal circuit pattern layer is electrically connected to the surface circuit pattern layer formed on the main surface of the substrate and the back circuit pattern layer formed on the back surface of the substrate through the through holes. The heat dissipation structure according to claim 2.   3. The heat dissipation structure according to claim 2, wherein the internal circuit pattern layer is provided in a plurality of layers apart from each other in the thickness direction of the substrate. A heat dissipating structure that mounts heat-generating electronic components and dissipates heat from the heat-generating electronic components,
A substrate on which the heat-generating electronic component is mounted on the main surface;
Comprising a heat dissipation sheet in intimate contact with the back surface of the substrate;
The heat dissipating sheet is formed by adhering a metal sheet to the main surface and / or the back surface of a polypyrrole infiltrated sheet in which a polypyrrole polymer is infiltrated into a cellulose sheet via an adhesive member. Structure. A front surface circuit pattern layer made of a conductive material is formed on the main surface of the substrate, and a back surface circuit pattern layer made of a conductive material is formed on the back surface of the substrate,
6. The heat dissipation structure according to claim 5, wherein the back surface circuit pattern layer and the front surface circuit pattern layer are electrically connected through a through hole. An internal circuit pattern layer made of a conductive material is interposed inside the substrate,
The internal circuit pattern layer is electrically connected to the surface circuit pattern layer formed on the main surface of the substrate and the back circuit pattern layer formed on the back surface of the substrate through the through hole. The heat dissipation structure according to claim 6. 7. The heat dissipation structure according to claim 6, wherein the internal circuit pattern layer is provided in a plurality of layers apart from each other in the thickness direction of the substrate.

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