JP2010251466A - Heat dissipation substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for dissipation heat at a heat generating body and its periphery, in the substrate of a semiconductor device, with high thermal conductivity. <P>SOLUTION: The heat-dissipation substrate 10 is formed by arranging many graphite sheets which are rectangular in plan view such that one side of each of the graphite sheets forms a part of a surface to be mounted with a semiconductor device 1 of the substrate 10 and another side sharing a vertex with the one side is in the thickness direction of the substrate, and then charging metal material 22 between the many graphite sheets. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a substrate on which a heating element typified by a semiconductor light emitting device is mounted, and more particularly to a substrate having heat dissipation properties.

  In recent years, the power consumption of various semiconductor devices has increased at an accelerated pace due to higher performance, and the amount of heat generated has increased accordingly.

  As an example of measures for heat dissipation of the semiconductor device as described above, it is conceivable to employ a mounting substrate having excellent thermal conductivity and thermal diffusivity. As an example of the substrate, a metal core substrate or a ceramic substrate has been put into practical use.

  Recently, carbon materials have attracted attention as substrate materials having higher thermal conductivity than metals. In particular, graphite is known to have a thermal conductivity 2 to 3 times that of copper, although it has anisotropy in thermal conductivity due to the characteristics of the crystal structure.

  As an effort to apply this carbon material to a heat dissipation board, a structure in which a graphite sheet is insert-molded on one surface of a resin chassis with which a solder surface of a circuit board is in contact (for example, see Patent Document 1), carbon fibers are arranged in the thickness direction. In addition, a carbon composite plate integrated using a liquid curable material (see, for example, Patent Document 2) or a composite material in which long-chain carbon nanotubes are integrated with aluminum powder is disclosed (for example, And Patent Document 3).

JP 2006-319134 A JP-A-11-054677 WO2005 / 040067 publication

  Incidentally, even in a light-emitting diode device (hereinafter also referred to as an LED) which is a kind of semiconductor light-emitting device, power consumption increases as brightness (performance) increases.

  As a problem due to the performance improvement in LED (the increase in power consumption associated therewith), since most of the power input at the time of light emission becomes heat, there is an event that brightness (performance) is reduced by the heat. From the above factors, in order to obtain the desired performance of the LED, it is required to use the LED in an appropriate temperature environment.

  In particular, in the case of an LED light source for illumination, the area per chip is very small and the power consumption is high (emits a high heat of several [W] per chip). There are many arrangements. For this reason, in the case of an LED light source for illumination, the heat generation density (heat generation amount per area) is particularly high, and measures to diffuse this heat amount over a wide area are urgently needed.

  That is, in order to efficiently cool a high heat generation density device represented by an LED light source for illumination, it is important to improve the heat conductivity in the surface direction of the heat sink and lower the heat generation density by thermal diffusion. . Furthermore, if the thermal conductivity in the thickness direction can be increased at the same time, a further heat radiation effect can be expected.

However, the conventional technique has the following problems.
In the invention disclosed in Patent Document 1, although the thermal diffusion in the surface direction is enhanced by the graphite sheet insert-molded on one surface of the resin chassis, the thermal diffusion in the thickness direction is affected by the metal inserted into the graphite sheet and the heat conduction. It depends on the thermal conductivity of the resin material having a low rate. For this reason, in the patent document invention, it is considered that efficient heat dissipation in the thickness direction cannot be obtained.

  In the inventions disclosed in Patent Document 2 and Patent Document 3, although the thermal conductivity in the thickness direction is increased by the arranged carbon fibers and carbon nanotubes, these materials having high thermal conductivity are integrated with a base material. Therefore, the thermal diffusion in the plane direction depends on the thermal conductivity of the base material (resin or aluminum having low thermal conductivity). Therefore, in the inventions disclosed in Patent Document 2 and Patent Document 3, it is considered that efficient heat dissipation in the plane direction cannot be obtained because the thermal diffusion in the plane direction depends on the thermal conductivity of the base material. .

  As described above, a carbon material or a composite material containing a carbon material has anisotropy in thermal conductivity due to the crystal structure of the carbon material constituting the material.

  The present invention has been made in view of the above points. That is, an object of the present invention is to provide a technique for diffusing the surrounding heat including a heating element in a substrate of a semiconductor device with high thermal conductivity.

In order to solve the above problems, the present invention has the following means.
That is, the present invention is such that one side of the graphite sheet having a rectangular shape in a plan view whose thermal conductivity in the sheet plane direction is higher than the thermal conductivity in the sheet thickness direction forms part of the semiconductor device mounting surface of the substrate. A large number are arranged so that the other side sharing the apex with one side is the thickness direction of the substrate (so that the sheet surface of the graphite sheet faces the thickness direction of the substrate), and a metal material is filled between the many graphite sheets This is a heat dissipating substrate.

  By comprising as mentioned above, this invention has high thermal conductivity in the thickness direction of a board | substrate by arrange | positioning the sheet | seat surface of a graphite sheet in the said direction. And this invention can be utilized as a single board | plate material by filling a metal material between many graphite sheets.

  Therefore, according to the present invention, the surrounding heat including the heating element can be efficiently diffused with high thermal conductivity in the substrate of the semiconductor device.

  Further, according to the present invention, the graphite sheet is arranged so that one of the apexes on one side is disposed in the vicinity thereof including the heating element mounting position, and the other apex is positioned radially outward in a plan view of the heating element mounting surface. It may be.

  In the present invention, a rectangular graphite sheet is formed such that one side forms a part of the semiconductor device mounting surface of the substrate with the semiconductor device mounting position as the center, and the other side sharing the vertex with the one side is the thickness of the substrate. A large number of them are arranged so that they are in the same direction (so that the sheet surface of the graphite sheet is in the thickness direction of the substrate). That is, in the present invention, a large number of graphite sheets are arranged as spokes with the semiconductor device mounting position as the wheel hub. And in this invention, it is set as one composite material by filling a metal material between these many graphite sheets.

By configuring as described above, the present invention has a high thermal conductivity on the semiconductor device mounting surface by arranging a large number of long sides of the graphite sheet radially around the mounting position. Moreover, this invention has high heat conductivity in the thickness direction of a board | substrate by arrange | positioning the sheet | seat surface of a graphite sheet in the said direction. And this invention can be utilized as a single board | plate material by filling a metal material between many graphite sheets.
Therefore, according to the present invention, the surrounding heat including the heating element can be diffused in both the surface direction and the thickness direction of the substrate of the semiconductor device.

  In the present invention, the metal material may be aluminum or an aluminum alloy. Furthermore, although it is a non-metallic material, alumina may be used as a suitable alternative material for the metallic material.

  As described above, according to the present invention, it is possible to provide a technique for diffusing heat around a substrate including a heating element in the substrate of the semiconductor device with high thermal conductivity.

1 is a top perspective view of a substrate according to an embodiment of the present invention. It is an upper surface see-through perspective view of the substrate concerning this embodiment. It is an upper surface perspective view which shows the structure of the graphite sheet contained in the inside of the board | substrate concerning this Embodiment, and the structure of the thermal-diffusion part comprised by this graphite sheet. It is a top view of the temperature distribution of the board | substrate of this Embodiment. It is sectional drawing in the board | substrate center part of the temperature distribution of a board | substrate. 6 is a top view of a temperature distribution in Comparative Example 1. FIG. 5 is a cross-sectional view of the center of a substrate in Comparative Example 1. FIG. It is a top see-through perspective view showing the structure of the substrate of the second embodiment. It is a top view of the mounting surface which shows the result of having mounted LED in the center of the mounting surface of the board | substrate of 2nd Embodiment, and having performed the thermal analysis on the same conditions. It is bb sectional drawing of FIG. It is cc sectional drawing of FIG.

First, an outline of the present invention will be described.
In the present invention, attention is paid to a graphite sheet which is one of materials having high thermal diffusion in constructing a substrate having high heat dissipation (having a high thermal diffusivity). In the present invention, this graphite sheet is used upright with respect to the semiconductor device mounting surface (so that the sheet surface of the graphite sheet faces the thickness direction of the substrate). That is, the first gist of the present invention is to improve the thermal conductivity in the thickness direction of the substrate.

  Next, according to the present invention, the graphite sheet, which is upright with respect to the semiconductor device mounting surface as described above, is arranged in a circular radial pattern around the semiconductor device mounting position. That is, the second gist of the present invention is to simultaneously improve the thermal diffusivity in the surface direction in addition to the thickness direction of the substrate.

  Furthermore, since the present invention has insufficient mechanical strength as a substrate on which a semiconductor device is mounted only with a carbon material (graphite sheet) as described above, the metal material is poured into the gap between the graphite sheets and integrated. That is, the third gist of the present invention is to satisfy the strength, moldability and handleability as well as the improvement of thermal diffusibility.

The outer shape of the substrate 10 will be described.
FIG. 1 is a top perspective view of a substrate 10 according to an embodiment of the present invention (with a semiconductor device mounting surface as an upper surface). FIG. 2 is a top perspective view of the substrate 10 according to the present embodiment. Referring to FIGS. 1 and 2, a substrate 10 includes a mounting surface 11 on which a light emitting diode 1 which is an example of a semiconductor device is mounted, four side surfaces 12 in the thickness direction sharing sides with the mounting surface 11, and a mounting surface. The mounting surface 11 and the back surface 13 have a substantially cubic shape having an area larger than that of the side surface 12.

  Examples of the light-emitting diode 1 that is a heat source include a light-emitting diode (hereinafter also referred to as an LED) for illumination. The light emitting diode 1 is bonded to the Ni / Au plated portion provided on the upper layer of the mounting surface 11 using AuSn eutectic solder.

Next, the configuration of the substrate 10 will be described with reference to FIG.
The substrate 10 includes a heat diffusing portion 20 composed of a number of rectangular graphite sheets as a central portion 21 centering on the mounting position of the semiconductor device on the mounting surface 11. In addition, the substrate 10 includes a metal material 22 that forms a substantially cubic outer shape of the substrate 10 by filling the periphery of the thermal diffusion unit 20.

  FIG. 3 is a top perspective view showing the configuration of the graphite sheet and the configuration of the thermal diffusion unit 20 configured by the graphite sheet included in the substrate 10 according to the present embodiment.

  The graphite sheet 100 is a rectangular sheet material having long sides 101a and 101b and short sides 102a and 102b (vertical (short side) 5 mm × horizontal (long side) 25 mm).

  Here, various graphite sheets in the present invention can be used as appropriate, but from the viewpoint of improving thermal diffusion, those having a thermal conductivity in the plane direction of 500 [W / m · K] or more are used. It is desirable. In addition, 10-50 [W / m * K] is a general value for the thermal conductivity in the thickness direction.

  In the present embodiment, a graphite sheet 100 having a thermal conductivity in the plane direction of 1000 [W / m · K], a thermal conductivity in the thickness direction of 50 [W / m · K], and a thickness of 200 [μm] is used. It was.

  As shown in FIG. 3, the heat diffusing unit 20 is arranged such that the long side 101a (corresponding to one side of the present invention) of the graphite sheet 100 is arranged radially in a plan view from the center part 21 (the mounting position of the light emitting diode 1 is set to a wheel A large number of short sides 102a and 102b (corresponding to the other sides of the present embodiment) sharing the apex with the long side 101a are arranged in the thickness direction of the substrate 10. Configured.

  By arranging a large number of graphite sheets 100 so that the sheet surfaces are arranged perpendicularly to the semiconductor device mounting surface to form the thermal diffusion section 20, the substrate 10 of the present embodiment has a high thermal conductivity that the sheet surface of the graphite sheet 100 has. Thus, it is possible to efficiently diffuse the heat from the mounting position of the light emitting diode 1 in the thickness direction (short side 102a, 102b direction).

  Further, the substrate 10 of the present embodiment is configured such that the thermal diffusion portion 20 is configured by arranging the graphite sheet 100 radially from the mounting position of the light emitting diode 1 on the mounting surface 11, so that high heat conduction is also achieved in the direction of the mounting surface 11. Can diffuse at a rate.

  In addition, when the graphite sheets 100 are arranged radially in a plan view as described above, the intervals between the individual graphite sheets 100 increase in the outer circumferential direction. Therefore, in the thermal diffusion section 20 of the substrate 10 of the present embodiment, the graphite sheet is cut to a size smaller than the size of the graphite sheet 100 and inserted between the graphite sheets 100, so that the density of the graphite sheets (graphite sheets per unit area). May be increased).

  That is, in the present embodiment, the thermal diffusion unit 20 inserts the graphite sheet 200 between the graphite sheets 100, inserts the graphite sheet 300 between the graphite sheets 100, and the graphite sheet 100 and graphite. The graphite sheet 400 is inserted between the sheet 300 and the graphite sheet 500 is inserted between the graphite sheet 200 and the graphite sheet 300 so that the vertex position of the long side of the graphite sheet in plan view is a quadruple circle. .

  In creating the thermal diffusion portion 20, the joining portion including the central portion 21 with which the long side 101a of the graphite sheet 100 contacts is joined using, for example, an epoxy-based adhesive (not shown).

  The substrate 10 is filled with a metal material 22 around the thermal diffusion portion 20 configured as described above, thereby defining a substantially cubic external shape as described above. As the metal material 22, aluminum is used in the present embodiment.

  In the present invention, the filling method of the metal material 22 is not particularly limited as long as it can fill between a large number of graphite sheets and determine the outer shape of the heat diffusion portion 20. In this embodiment, the discharge plasma sintering method, which is optimal for sintering the mixed material as in the present invention, is used.

  In the present embodiment, the aluminum filled around the thermal diffusion section 20 is filled with a graphite sheet and sintered, so that aluminum powder is used. At this time, the average particle diameter of the aluminum powder is desirably about 50 [μm].

  The shape of the aluminum powder is not particularly limited, such as a sphere, a fiber, an indeterminate shape, or a tree shape, and various shapes can be used as appropriate.

[Verification of thermal diffusivity of substrate]
In order to visualize and compare the heat diffusing performance of the substrate 10 of the present embodiment created as described above with respect to the state of thermal diffusion with the conventional substrate, a heat conduction analysis was performed. Below, the verification result of the board | substrate 10 and a comparative example is demonstrated.

  In addition, as a comparison object with the substrate 10 of the present embodiment, a pure aluminum material plate material that does not include a graphite sheet therein (assuming a metal core substrate) is used as Comparative Example 1, and a pure copper material plate material is used as Comparative Example 2. Used as.

A common boundary condition between the substrate 10 and the comparative example will be described below.
The heat source was a 1 [mm] square light emitting diode (hereinafter also referred to as LED) for illumination, and the input power was 5 [W]. The LED was bonded to the Ni / Au plated portion provided on the surface of each substrate by AuSn eutectic solder.

  To the back surface (lower surface) of the LED mounting surface of each substrate, a heat sink having an approximately cubic shape with a side of about 10 [cm] having a capacity capable of sufficiently cooling the heat generated by the LED was connected.

  Note that the heat transfer coefficient on the lower surface of the substrate per heating element is the same value in all the examples and comparative examples in order to compare the heat dissipation performance of the substrate itself (the cooling performance of the heat sink connected to the lower surface of the substrate is the same). It was made to become.

  Table 1 shows a comparison result of the increase value with respect to the ambient air temperature of the heat generation source and the thermal resistance value under the common boundary conditions as described above.

  4 is a top view of the temperature distribution of the substrate 10 of the present embodiment, and FIG. 5 is a cross-sectional view of the temperature distribution of the substrate 10 at the center of the substrate.

  FIG. 6 is a top view of the temperature distribution in Comparative Example 1 shown as an example of the temperature distribution in Comparative Examples 1 and 2, and FIG. 4 to 7, the darker color portion has a higher temperature. In Comparative Example 2, the temperature value is shifted in the lower temperature direction as compared with Comparative Example 1, and the state of thermal diffusion is substantially the same as that of Comparative Example 1, and thus illustration is omitted.

  Comparing FIGS. 4 and 5 with FIGS. 6 and 7, the substrate 10 has higher thermal diffusion performance in both the thickness direction and the surface direction of the substrate compared to the comparative example 1 of the aluminum substrate. It can be seen that the temperature of the source and its vicinity is decreasing. As shown in Table 1, when the thermal resistances of the substrate 10 and Comparative Example 1 were compared, there was a reduction effect of 1.2 [° C./W].

  Table 1 also shows that the thermal diffusion performance of the substrate 10 is higher than that of the comparative example 2 of the copper substrate. Since the carbon / aluminum material is lighter than the copper material, it can be said that the present invention can exert a sufficient effect for reducing the weight of the product.

  In addition, the temperature rise value in the main part in the board | substrate 10 is +0.6 [degreeC] in the mounting surface 11 side center part 21 (directly under LED) of the board | substrate 10 on the basis of external air, and in the back surface 13 side center part 21. +0.5 [° C.], +0.5 [° C.] at the mounting surface 11 side end of the substrate 10, and +0.4 [° C.] at the back surface 13 side end of the substrate 10.

  Furthermore, in order to verify the effect of arranging the long side 101a of the graphite sheet in a circular shape in plan view from the semiconductor device mounting surface, the substrate 10 of the second embodiment has the same volume occupation ratio ( In the base material (metal material 22), the volume ratio of the thermal diffusion part 20 occupied by the graphite sheet to the aluminum (a metal material 22)) was arranged in parallel at equal intervals in the substrate.

  FIG. 8 is a top perspective view showing the structure of the substrate 30 according to the second embodiment. Similar to the substrate 10, the thermal diffusion section 40 of the substrate 30 has a predetermined interval (8 [in this embodiment], so that the short sides 102a and 102b are in the thickness direction so that the long side 101a forms part of the mounting surface. mm], a total of 60 sheets of graphite sheets 100 were arranged in parallel.

  9 to 11 are diagrams showing the results of thermal analysis under the same conditions in which an LED is mounted in the center of the mounting surface of the substrate 30 in the same manner as the substrate 10, FIG. 9 is a top view of the mounting surface, and FIG. 9 is a cross-sectional view taken along line bb in FIG. 9, and FIG. 11 is a cross-sectional view taken along line cc in FIG. Here, the orientation (direction of the sheet surface) of the graphite sheet 100 is the arrow direction (bb cross-sectional direction) in FIG.

  When comparing FIG. 10 and FIG. 11 of the substrate 30 of the second embodiment, the thermal diffusivity in the cc cross-sectional direction is lower than the bb cross-sectional direction which is the plane direction (orientation) of the graphite sheet 100. I can say that.

  The reason why the above results are obtained when the substrate 10 and the substrate 30 are compared is that, in the cc cross-sectional direction, the thermal conductivity of aluminum as a base material (aluminum is about 1/5 that of graphite). This is because the influence of (thermal conductivity) is large.

  Since the difference in thermal resistance between the substrate 10 of the first embodiment and the substrate 30 of the second embodiment is 0.5 [° C./W] from Table 1, the difference in the first embodiment is shown in FIG. It can be said that about half of the thermal resistance reduction effect of 1.2 [° C./W] compared to Comparative Example 1 of the substrate 10 is an effect of arranging the graphite sheets in a circular radial shape.

DESCRIPTION OF SYMBOLS 1 Light emitting diode 10 Board | substrate 11 Mounting surface 12 Side surface 13 Back surface 20 Thermal diffusion part 21 Center part 22 Metal material 100 Graphite sheet 101a, 101b Long side 102a, 102b Short side

Claims (3)

Arranged so that one side of the graphite sheet forming a rectangular shape in plan view forms part of the semiconductor device mounting surface of the substrate, the other side sharing the apex with the one side is in the thickness direction of the substrate,
A heat dissipating substrate formed by filling a metal material between the multiple graphite sheets. The graphite sheet is
2. The heat dissipating board according to claim 1, wherein one of the apexes of the one side is disposed in the vicinity thereof including the heating element mounting position, and the other apex is positioned radially outward in plan view of the heating element mounting surface. . The metal material is
The heat-radiating substrate according to claim 1 or 2, wherein the heat-radiating substrate is one of aluminum and an aluminum alloy.