Abstract
To provide a mounting board and an electric apparatus equipped with the mounting board. The mounting board includes an electronic component, a printed circuit board, a heat spreader, and a heat dissipation component. A first insulating member and a second insulating member each being an insulator are arranged between the electronic component and the heat spreader and between the heat spreader and the heat dissipation component, respectively, and a hardness of the first insulating member and a hardness of the second insulating member are lower than a hardness of the heat spreader.
Claims
1. A mounting board, comprising: an electronic component including an electronic element, a package surrounding the electronic element, and a heat dissipation pad having heat dissipation ability; a printed circuit board, the electronic component being mounted on the printed circuit board via a terminal connected to an external circuit; a heat spreader including a metal as a main component, heat generated in the electronic component being transferred to the heat spreader; and a heat dissipation component including a metal as a main component, heat from the heat spreader being further transferred to the heat dissipation component to be dissipated into air, wherein a first insulating member and a second insulating member each being an insulator are arranged between the electronic component and the heat spreader and between the heat spreader and the heat dissipation component, respectively, and a hardness of the first insulating member and a hardness of the second insulating member are lower than a hardness of the heat spreader.
2. The mounting board according to claim 1, wherein the hardness of the first insulating member according to Asker C hardness standard is in a range from Asker C 5 to Asker C 50.
3. The mounting board according to claim 1, wherein the first insulating member has a thickness in a range from 0.2 mm to 0.8 mm.
4. The mounting board according to claim 1, wherein an area of the heat spreader is 2 times or more and 7 times or less an area of the heat dissipation pad.
5. The mounting board according to claim 1, wherein a thermal conductivity of the first insulating member is higher than a thermal conductivity of the second insulating member.
6. The mounting board according to claim 1, wherein the first insulating member has a thermal conductivity in a range from 3 W/mK to 20 W/mK.
7. The mounting board according to claim 1, wherein the heat spreader has a thickness in a range from 0.3 mm to 1.0 mm.
8. The mounting board according to claim 1, wherein the first insulating member is connected to the heat dissipation pad of each of a plurality of the electronic components.
9. An electric apparatus that performs power conversion of power supplied from a power supply device, wherein the electric apparatus is equipped with the mounting board according to claim 1.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1 is a schematic cross-sectional view of an example of a mounting board according to a first embodiment of the present invention.
[0021] FIG. 2 is a schematic cross-sectional view of the mounting board according to the first embodiment of the present invention, illustrating how a printed circuit board with an electronic component mounted thereon is screwed to a heat sink.
[0022] FIG. 3A and FIG. 3B are tables showing results of a comparative evaluation, in terms of thermal resistance, of the mounting boards according to the first embodiment of the present invention, which have different characteristic values of the first insulating member and the heat spreader.
[0023] FIG. 4A and FIG. 4B are tables showing results of a comparative evaluation, in terms of strain in the printed circuit board, of the mounting boards according to the first embodiment of the present invention, which have different characteristic values of the first insulating member and the heat spreader.
[0024] FIG. 5 is a schematic cross-sectional view of an example of a power conditioner equipped with the mounting board according to the first embodiment of the present invention.
[0025] FIG. 6 is a schematic cross-sectional view of a mounting board according to a second embodiment of the present invention, illustrating how a printed circuit board with an electronic component mounted thereon is screwed to a heat sink.
DESCRIPTION OF EMBODIMENTS
Application Example
[0026] Hereinafter, an application example of the present invention will be generally described with reference to some of the drawings. The present invention can be applied to a mounting board 1 as illustrated in FIG. 1. Further, the present invention can also be applied to a power conditioner 8 (corresponding to an electric apparatus in the present invention) as illustrated in FIG. 5 by providing the mounting board 1, as illustrated in FIG. 1, in the power conditioner 8.
[0027] FIG. 1 is a schematic cross-sectional view of an example of the mounting board 1 to which the present invention is applied. The mounting board 1 according to this application example includes an electronic component 2, a printed circuit board 3, a heat spreader 4, a heat sink 5, and the like. Examples of the electronic component 2 include a semiconductor component such as an application specific integrated circuit (ASIC) and a power semiconductor such as a metal oxide semiconductor field effect transistor (MOSFET). The electronic component 2 includes an electronic element (not illustrated), a package 21 formed so as to surround the electronic element, and a heat dissipation pad 22 having heat dissipation ability. The heat dissipation pad 22 is formed integrally with a lead 23 on which a semiconductor chip using, for example, gallium nitride (GaN) is mounted. When a current flows through the electronic element, the electronic component 2 generates heat. Although the mounting board 1 includes other electronic components (e.g., a capacitor) in addition to the electronic component 2, the electronic component 2 generates a larger amount of heat than the other electronic components.
[0028] The lead 23 serving as a terminal connected to an external circuit extends from the inside to the outside of the package 21 of the electronic component 2, and a part of the lead 23 is formed in a gull-wing shape. One end of the lead 23 is electrically connected to the printed circuit board 3 (specifically, an electrode or the like formed on a surface of the printed circuit board 3) via, for example, solder paste (not illustrated). In the case illustrated in FIG. 1, the electronic component 2 is mounted so as to be in contact with the printed circuit board 3. The printed circuit board 3 may be, for example, a build-up printed wiring board having a multilayer structure and including a thermosetting epoxy resin as a base material.
[0029] The heat spreader 4 includes, as a main component, a metal such as aluminum and has a thermal conductivity of about 190 W/mK. The heat generated in the electronic component 2, as described above, is transferred to the heat spreader 4 via the heat dissipation pad 22 and a first insulating member 6 described below. The area of the heat spreader 4 is larger than the area of the heat dissipation pad 22. The heat sink 5 also includes a metal such as aluminum as a main component. The heat absorbed by the heat spreader 4 is further transferred, via a second insulating member 61 described below, to the heat sink 5, at which the transferred heat diffuses to the surroundings, for example, the outside air. The thermal conductivity of the heat spreader 4 is much higher than those of the first insulating member 6 and the second insulating member 61. This facilitates heat transfer from the first insulating member 6 to the second insulating member 61. Here, the heat sink 5 corresponds to a heat dissipation component in the present invention.
[0030] The first insulating member 6 and the second insulating member 61 are, for example, sheet-like insulators made of silicone or the like. The first insulating member 6 is disposed between the electronic component 2 and the heat spreader 4, and the second insulating member 61 is disposed between the heat spreader 4 and the heat sink 5. To achieve closer bonding between the electronic component 2, the heat spreader 4, and the heat sink 5, adhesive members may be employed as the first insulating member 6 and the second insulating member 61.
[0031] In this application example, the characteristic values of the first insulating member 6 and the second insulating member 61 are as follows. The first insulating member 6 has a thickness of 0.3 mm, a thermal conductivity of 8 W/mK, and a hardness of Asker C 20. Asker C is a type of standard for expressing hardness. The second insulating member 61 has a thickness of 1.0 mm, a thermal conductivity of 1 W/mK, and a hardness of Asker C 20. The hardness of the first insulating member 6 and the second insulating member 61 is lower than the hardness of the heat spreader 4. The thermal conductivity of the first insulating member 6 is higher than the thermal conductivity of the second insulating member 61. Note that the above-described characteristic values are examples, and the present invention is not limited to the characteristic values as long as these conditions are satisfied.
First Embodiment
[0032] Hereinafter, the mounting board 1 according to a first embodiment of the present invention and the power conditioner 8 as an example of the electric apparatus will be described in more detail with reference to the drawings. Note that the mounting board 1 and the power conditioner 8 according to the present invention are not limited to the following configurations.
<Configuration of Mounting Board>
[0033] FIG. 2 is a schematic cross-sectional view of the mounting board 1 according to the first embodiment of the present invention, illustrating how the printed circuit board 3 with the electronic component 2 mounted thereon is screwed to the heat sink 5. The printed circuit board 3 has a plurality of screw holes 31. The printed circuit board 3 can be fixed to the heat sink 5 by inserting screws 7 through the screw holes 31 and tightening the screws 7. The lead 23 is spaced from the first insulating member 6 by a distance D in the vertical direction and a distance D in the horizontal direction in FIG. 2 (hereinafter, the distance D and the distance D are collectively referred to as insulation distance). Here, although the insulation distance is for ensuring that the lead 23 and the first insulating member 6 are at a certain distance from each other, there is a possibility that the lead 23 or the first insulating member 6 is deformed by a force generated due to screwing and thus the lead 23 and the first insulating member 6 come into contact with each other. Therefore, if a non-insulating heat dissipation member is used instead of the first insulating member 6, a short circuit between the lead 23 and the heat dissipation member may occur. In addition, if the heat spreader 4 made of metal is bonded to the heat dissipation pad 22 via a non-insulating heat dissipation member, the heat spreader 4 will have the same potential as the heat dissipation pad 22, the insulation distance between the lead 23 and the first insulating member 6 will become short, and thus a short circuit may occur due to creeping discharge, space discharge, or the like.
[0034] In contrast, the first insulating member 6 is an insulator in the present embodiment, as described in the above-described application example, and thus, even if a force generated due to screwing brings the lead 23 into contact with the first insulating member 6, it is possible to prevent occurrence of a short circuit. In addition, the hardness of the first insulating member 6 and the second insulating member 61 is lower than the hardness of the heat spreader 4. Therefore, the second insulating member 61 is highly deformable and easily absorbs the force generated due to screwing (arrows illustrated in FIG. 2 indicate the force) including a force generated from the heat spreader 4 having a relatively high hardness. As a result of deformation of the second insulating member 61, deformation of the first insulating member 6 and the printed circuit board 3 is suppressed, and thus reduction of the insulation distance is also suppressed. As a result, it is possible to prevent the lead 23 and the first insulating member 6 from coming into contact with each other due to screw tightening. The relatively large thickness of the second insulating member 61 also contributes to absorption of the force generated due to screwing.
[0035] The second insulating member 61 can largely deform in response to application of a force, compared to the heat sink 5 that is less deformable. Thus, by pressing the heat spreader 4 against the second insulating member 61, intimate contact of the heat spreader 4 can be easily achieved compared with a case where the heat spreader 4 is directly pressed against the heat sink 5. Such close contact facilitates heat transfer from the heat spreader 4. As a result, the amount of heat which diffuses from the heat sink 5 to the surroundings also increases. Further, since the first insulating member 6 arranged in contact with the heat dissipation pad 22 is relatively thin and has a relatively high thermal conductivity, the heat generated by the electronic component 2 is easily transferred to the heat spreader 4.
Examples of Verification of Effect
[0036] FIG. 3A and FIG. 3B are tables showing results of a comparative evaluation, in terms of thermal resistance, of the mounting boards 1 according to the first embodiment of the present invention, which have different characteristic values of the first insulating member 6 and the heat spreader 4. FIG. 4A and FIG. 4B are tables showing results of a comparative evaluation, in terms of strain in the printed circuit board 3, of the mounting boards 1 according to the first embodiment of the present invention, which have different characteristic values of the first insulating member 6 and the heat spreader 4. Here, in the evaluation of thermal resistance, a good value is defined as a thermal resistance in a range from 5.0 K/W to 10.6 K/W (effective in FIG. 3A and FIG. 4A), a better value is defined as a thermal resistance of less than 5.0 K/W (significantly effective in FIG. 3A and FIG. 4A), and a value at which no significant effect is achieved is defined as a thermal resistance of more than 10.6 K/W (no effect in FIG. 3A and FIG. 4A). Similarly, in the evaluation of the strain in the printed circuit board 3 (hereinafter simply referred to as strain), a good value is defined as a strain in a range from 939 ST to 1101 ST, a better value is defined as a strain of less than 939 ST, and a value at which no significant effect is achieved is defined as a strain of 1101 ST.
[0037] In FIG. 3B, the mounting board 1 associated with a condition #1 has a standard configuration. Under a condition #2, a smaller strain and a higher thermal resistance are exhibited as compared with the condition #1. Under the condition #2, the thermal resistance is close to the upper limit (10.6 K/W) of the range of good values. Here, the mounting board 1 associated with the condition #2 can be regarded as a configuration having an effect of improving the heat dissipation ability. Under conditions #3 to #5, high thermal resistances are exhibited, which indicate that the conditions #3 to #5 are inferior to the condition #1 in terms of heat dissipation ability. In comparison with the other conditions, under the condition #3, the thermal conductivity (2 W/mK) of the first insulating member 6 is the lowest, under the condition #4, the area ratio (1.8 times) of the heat spreader 4 to the heat dissipation pad 22 is the smallest, and under the condition #5, the thickness (0.1 mm) of the heat spreader 4 is the thinnest. Note that under all conditions, better strain values are exhibited.
[0038] In FIG. 4B, the mounting board 1 associated with the condition #1 has a standard configuration. Under the condition #2, a lower thermal resistance and a large strain are exhibited as compared with the condition #1. Under the condition #2, the strain is close to the upper limit (939 ST) of the range of better values. Here, the mounting board 1 associated with the condition #2 can be regarded as a configuration having an improvement effect in terms of strain. Under the conditions #3 to #5, larger strains are exhibited than in the case of the condition #2, which are from better values to good values. As compared with the condition #2, under the condition #3, the hardness of the first insulating member 6 is higher, under the condition #4, the thickness of the first insulating member 6 is thinner, and under the condition #5, the area ratio of the heat spreader 4 to the heat dissipation pad 22 is larger. Under condition #6, the hardness of the first insulating member 6 is even higher than in the case of the condition #3, and a larger strain value is exhibited. Under condition #7, the hardness (Asker C 60) of the first insulating member 6 is the highest, as compared with the other conditions, and a strain value at which no significant effect is achieved.
[0039] The result of the comparative evaluation in terms of thermal resistance shown in FIG. 3A and FIG. 3B indicates that it is preferable that the first insulating member 6 of the mounting board 1 according to the first embodiment of the present invention have a thermal conductivity in a range from 3 W/mK to 8 W/mK. The first insulating member 6 may have a thermal conductivity in a range from 3 W/mK to 20 W/mK. It is preferable that the heat spreader 4 have a thickness in a range from 0.3 mm to 1.0 mm. The result of the comparative evaluation in terms of strain shown in FIG. 4A and FIG. 4B indicates that it is preferable that the first insulating member 6 of the mounting board 1 according to the first embodiment of the present invention have a hardness in a range from Asker C 20 to Asker C 50. It is more preferable that the first insulating member 6 have a hardness in a range from Asker C 5 to Asker C 20. It is preferable that the first insulating member 6 have a thickness in a range from 0.2 mm to 0.3 mm. The first insulating member 6 may have a thickness in a range from 0.2 mm to 0.8 mm. The result of the comparative evaluation of FIG. 3A and FIG. 3B indicates that the preferable area ratio of the heat spreader 4 to the heat dissipation pad 22 is 2 times or more and 4 times or less, whereas the result of the comparative evaluation of FIG. 4A and FIG. 4B indicates that a preferable area ratio of the heat spreader 4 to the heat dissipation pad 22 is 4 times or more and 7 times or less, and a more preferable area ratio is 4 times or more and 6 times or less.
<Configuration of Power Conditioner>
[0040] FIG. 5 is a schematic cross-sectional view of an example of the power conditioner 8 equipped with the mounting board 1 according to the first embodiment of the present invention. An electric apparatus may be equipped with the mounting board 1, and examples of the electric apparatus may include a power conversion device such as the power conditioner 8, a motor driving apparatus, and a power supply apparatus. The power conditioner 8 is connected to a power supply device (not illustrated) such as a photovoltaic cell, increases a voltage of power supplied from the power supply device, converts the power into alternating current power, removes noise to shape a waveform, and then supplies the alternating current power to a load (not illustrated) or an interconnected power system (not illustrated).
[0041] A thermally conductive metal base 82 is provided on a side surface of a housing 81 of the power conditioner 8. The heat sink 5 connected with the printed circuit board 3 is screwed to the metal base 82 by using second screws 71. A part of the heat sink 5 is exposed to the outside of the housing 81, and thus heat generated in the electronic component 2 is easily transferred to the outside air.
[0042] The screws 7 are used to screw the printed circuit board 3 to the heat sink 5. In addition, a base 86 is screwed to the printed circuit board 3, the metal base 82, and the heat sink 5 via the spacers 83 to 85, and other functional components such as a terminal block 87 are fixed and attached to the base 86. Further, another circuit board such as a control board (not illustrated) may be attached to the printed circuit board 3 via a connector (not illustrated).
Second Embodiment
[0043] Next, a mounting board 10 according to a second embodiment of the present invention will be described with reference to FIG. 6. The mounting board 10 has many components in common with the mounting board 1 of the first embodiment, and such components are denoted by the same reference numerals and will not be described again. Further, the power conditioner 8 of the first embodiment can be equipped with the configuration of the mounting board 10.
<Configuration of Mounting Board>
[0044] FIG. 6 is a schematic cross-sectional view of the mounting board 10 according to the second embodiment of the present invention, illustrating how the printed circuit board 3 with the electronic component 2 mounted thereon is screwed to a heat sink 50. As compared with the lead 23 illustrated in FIG. 2, a lead 230 is longer in the thickness direction of the electronic component 2, and the electronic component 2 is mounted on the printed circuit board 3 such that a gap of a distance D2 is formed. Similarly to the mounting board 1 illustrated in FIG. 2, a force generated due to screwing the printed circuit board 3 (arrows illustrated in FIG. 6 indicate the force) is preferentially absorbed by the second insulating member 61, and thus deformation of the lead 230 is suppressed. Thus, reduction of the distance D2 due to deformation of the lead 230 is suppressed. As a result, it is possible to prevent the electronic component from being damaged by strain in the printed circuit board 3 and the lead 230 caused by contact between the printed circuit board 3 and the electronic component 2. Note that reduction of the insulation distance is suppressed as in the mounting board 1 illustrated in FIG. 2.
[0045] For the mounting board 10 according to the second embodiment of the present invention, results of comparative evaluations in terms of thermal resistance and strain in the printed circuit board 3 by using different characteristic values of the first insulating member 6 and the heat spreader 4 indicate tendencies similar to those shown in FIG. 3A, FIG. 3B and FIG. 4A, FIG. 4B.
<Supplement 1>
[0046] A mounting board (1, 10), including, [0047] an electronic component including an electronic element, a package (21) surrounding the electronic element, and a heat dissipation pad (22) having heat dissipation ability, [0048] a printed circuit board (3), the electronic component being mounted on the printed circuit board via a terminal (23, 230) connected to an external circuit, [0049] a heat spreader (4) including a metal as a main component, heat generated in the electronic component being transferred to the heat spreader, and [0050] a heat dissipation component (5, 50) including a metal as a main component, heat from the heat spreader being further transferred to the heat dissipation component to be dissipated into air, in which [0051] a first insulating member (6) and a second insulating member (61) each being an insulator are arranged between the electronic component and the heat spreader and between the heat spreader and the heat dissipation component, respectively, and [0052] a hardness of the first insulating member and a hardness of the second insulating member are lower than a hardness of the heat spreader.
REFERENCE SIGNS LIST
[0053] 1, 10: Mounting board [0054] 2: Electronic component [0055] 21: Package [0056] 22: Heat dissipation pad [0057] 23, 230: Lead [0058] 3: Printed circuit board [0059] 31: Screw hole [0060] 4: Heat spreader [0061] 5, 50: Heat sink [0062] 6: First insulating member [0063] 61: Second insulating member [0064] 7: Screw [0065] 71: Second screw [0066] 8: Power conditioner [0067] 81: Housing [0068] 82: Metal base [0069] 83 to 85: Spacer [0070] 86: Base [0071] 87: Terminal block
