JP7135514B2 - Circuit board heat dissipation structure - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat dissipation structure for a circuit board in which a switching element and a capacitor connected between power supply terminals for supplying driving power to the element are surface-mounted on different sides.

For example, when configuring an inverter circuit for driving a motor using a MOSFET as a switching element, an aluminum electrolytic capacitor may be used to smooth the driving power supply. Then, when mounting each circuit element and the like on a double-sided substrate, for example, the following mounting structure is assumed. An FET is mounted on one side, and an aluminum electrolytic capacitor is mounted on the other side. At this time, if the impedance between the capacitor and the FET is reduced by matching the mounting areas on each surface of the FET and the aluminum electrolytic capacitor, the noise generated when the FET is switched can be efficiently absorbed by the capacitor.

JP 2005-191378 A

However, the amount of heat generated when switching the FET is large compared to the amount of heat generated by the aluminum electrolytic capacitor. Therefore, if the above-described mounting mode is adopted, the heat generated by the FET is likely to be transferred to the capacitor side, and there is concern that the temperature of the capacitor may rise.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to provide a heat dissipation structure for a circuit board that makes it easier for a capacitor to absorb noise generated by a switching element and reduces the influence of heat received by the capacitor. That's what it is.

According to the heat dissipation structure of the circuit board according to claim 1, the switching element for controlling the current flowing through the load by the switching operation and the capacitor connected between the terminals of the drive power supply correspond to each other on different surfaces of the circuit board. are surface-mounted in each mounting area. In the inner layer of the circuit board, the conductive pattern is arranged avoiding the portion corresponding to the mounting area.

With this configuration, there is no conductive pattern with high thermal conductivity in the inner layer of the circuit board at the portion corresponding to the mounting area of the switching element and the capacitor. Therefore, the heat generated by the switching element is less likely to be transmitted to the capacitor side via the inner layer, and the effect of heat on the capacitor can be reduced.
According to the circuit board heat dissipation structure of claim 1, the first heat dissipation path for transmitting heat generated by the switching element in a predetermined direction is formed on the mounting surface of the switching element by the same metal material as the conductive pattern. A second heat dissipation path for dissipating heat generated by the capacitor is formed on the mounting surface of the capacitor with a metal material such that the direction of heat transfer is opposite to that of the first heat dissipation path. there is

According to the circuit board heat dissipation structure of claim 2, the heat insulating layer is formed of a material having a lower thermal conductivity than the substrate material in the portion corresponding to the mounting area of the inner layer. With this configuration, the heat generated by the switching element is less likely to be transmitted to the capacitor side via the inner layer, and the effect of heat on the capacitor can be further reduced.

According to the circuit board heat dissipation structure of claim 3, as in claim 1, the switching element and the capacitor are surface-mounted in corresponding mounting regions on different surfaces of the circuit board. Then, a heat insulating layer made of a material having a lower thermal conductivity than the substrate material is formed inside the circuit board at a portion corresponding to the mounting area. With this configuration, heat generated by the switching element is less likely to be transmitted to the capacitor side because the heat insulating layer is formed inside the circuit board. Therefore, the influence of heat on the capacitor can be reduced.

According to the heat dissipation structure of the circuit board according to claim 4, the layer structure of the part related to the mounting area is made to be a conductive pattern, a heat insulating layer, and a conductive pattern from one surface to the other surface. With this configuration, the heat insulating layer is directly arranged between the conductive patterns on each surface, so that the thermal conductivity can be greatly reduced. The layer structure of the portion related to the mounting area is composed of a conductive pattern, a heat insulating layer, and a conductive pattern from one surface to the other surface.

FIG. 1 is a plan view of a multilayer substrate, which is a first embodiment, and shows a part of the substrate in perspective; Schematic cross-sectional view of a multilayer substrate A bottom view of a multilayer substrate partially transparent A diagram showing a configuration example of a heat insulating layer Circuit diagram showing a variable valve timing system FIG. 2 is a plan view of a multilayer substrate, which is a second embodiment, and shows a part of the substrate in perspective; Schematic cross-sectional view of a multilayer substrate It is a third embodiment, and is a schematic cross-sectional view of a double-sided board. This is the fourth embodiment, and shows an example of layout when three aluminum electrolytic capacitors are mounted on both sides of six FETs.

(First embodiment)
In this embodiment, the circuit board heat dissipation structure is applied to an EDU (Electronic Driver Unit) constituting a variable valve timing system mounted on a vehicle, as shown in FIG. 5, for example. 5, only the part related to the gist of the present invention will be explained. The EDU 1 drives the motor 3 based on a control command input from an engine ECU (Electronic Control Unit) 2 . A rotating shaft of the motor 3 is connected to an intake valve (not shown), and the motor 3 controls opening and closing of the intake valve. EDU1 corresponds to a motor drive device.

The EDU 1 has a control circuit 4 and an inverter circuit 5 . The inverter circuit 5 is configured by connecting six N-channel MOSFETs 6 in a three-phase bridge. Each phase output terminal of the inverter circuit 5 is connected to each phase winding terminal of the motor 3 . A power source VB is supplied to the EDU 1 from a vehicle battery 7 . A power supply VB is supplied to the inverter circuit 5 via a π-type filter consisting of two aluminum electrolytic capacitors 8 a and 8 b and a coil 9 .

As shown in FIGS. 1 to 3, the FET 6 and the aluminum electrolytic capacitor 8 are surface-mounted on one side and the other side of the multilayer substrate 11, respectively. The multilayer substrate 11 has a first resin substrate 12, a second resin substrate 13, and a third resin substrate 14 from the top to the bottom shown in FIG. A copper foil pattern 15 is arranged between the first resin substrate 12 and the second resin substrate 13 . A copper foil pattern 16 is arranged between the second resin substrate 12 and the third resin substrate 14 . The copper foil patterns 15 and 16 correspond to conductive patterns. Although FIG. 2 is a cross-sectional view, some hatching is omitted in order to show the transmission paths of heat and noise.

A thick copper pattern 17 is formed on the surface side of the first resin substrate 12 , and a thick copper pattern 18 is formed on the surface side of the third resin substrate 14 . That is, the multilayer board 11 is a four-layer board having four wiring layers. Here, the thickness dimension of the substrates 12-14 is about 0.2-0.6 mm, and the thickness dimension of the copper foil patterns 15 and 16 is about 30-40 μm. The thickness dimension of the thick copper patterns 17 and 18 is, for example, about 100 μm. In FIG. 2, the thick copper patterns 17 and 18 are formed in a state of being embedded in resin portions of the substrates 12 and 13, respectively. This is the result of applying pressure by pressing from above and below when the multilayer substrate 11 is integrally formed.

The capacitor 8 and the FET 6 are surface-mounted so that their respective positions overlap in the vertical direction in FIG. A heat insulating layer 19 made of a material having a lower thermal conductivity than resin is formed on the second resin substrate 13 in a portion corresponding to the mounting area of the capacitor 8 and the FET 6 . The heat insulating layer 19 may be a cavity made of air. The copper foil patterns 15 and 16 are not arranged on the upper and lower surfaces of the heat insulating layer 19, and the upper and lower surfaces of the heat insulating layer 19 are directly connected to the first resin substrate 12 and the third resin substrate 14, respectively. in contact with

Here, for example, if the substrates 12 and 13 are glass epoxy substrates (FR4) with a thermal conductivity of about 0.7 W/(m·K), the thermal insulation layer 19 has a thermal conductivity of about 0.3 W/(m·K). A PPS (polyphenylene sulfide) resin or the like having a lower (m·K) is used. Also, as shown in FIG. 4, a plurality of through holes 26 and air holes may be formed in the glass epoxy substrate. As a result, when the heat insulating layer 19 is formed using air as a material, the air is trapped in the multilayer substrate 11, so when the temperature rises, the internal pressure rises and the substrate 11 deforms. In order to prevent this, the deformation of the substrate can be prevented by suppressing the increase in the internal pressure of the air in the through holes 26 . In addition, since the thermal conductivity of the epoxy resin alone is about 0.2 W/(mK), the mixing ratio of the glass fiber and the epoxy resin can be adjusted to reduce the thermal conductivity from 0.7 W/(mK). A material for the thermal insulation layer 19 can also be formed.

Thick copper patterns 18 a , 18 b and 18 c are formed on the third resin substrate 14 . Among these, the thick copper pattern 18b is a wiring pattern connected to the lead extending from the package of the FET6. The thick copper pattern 18c is formed to dissipate heat generated by the FET 6 so as to extend rightward in the figure from directly below the package of the FET 6. As shown in FIG.

The positive lead of the capacitor 8 is connected to the thick copper pattern 17(+) on the right side in the drawing, and the negative lead is connected to the thick copper pattern 17(-) on the left side in the drawing. The thick copper pattern 17(-) and the thick copper pattern 18a are thermally connected via the copper inlays 20 formed on the substrates 12, 13 and 14. FIG. Also, the thick copper pattern 17(-) and the thick copper pattern 18c are electrically connected through a plurality of vias 23 formed in the substrates 12-14. The via 23 passes through the heat insulating layer 19 at the second resin substrate 13 portion. The copper inlay 20 corresponds to a heat conducting portion.

The surface side of the third resin substrate 14 is covered with an aluminum housing 24, and a heat dissipating gel 25 is filled between the two. As a result, the heat generated by the FET 6 is transferred to the aluminum housing 24 via the heat-dissipating gel agent 25 and radiated. Note that FIG. 3 shows a state in which the heat dissipating gel agent 25 and the aluminum housing 24 are removed.

Next, the operation of this embodiment will be described. When the inverter circuit 5 drives the motor 3, the FET 6 performs a switching operation to control the current. At this time, in addition to heat generation due to the ON resistance of the FET 6, heat generation due to switching loss is generated. For example, when a large current of about 20 A is applied, heat of about 3 W is generated. Therefore, as described above, heat is dissipated through the heat path of FET 6→heat dissipating gel agent 25→aluminum housing 24→vehicle engine. In addition, heat is radiated through a heat path of FET 6→thick copper pattern 18c→heat releasing gel agent 25→aluminum housing 24→engine. These heat dissipation paths dissipate the self-heating of the FET 6 with low thermal resistance.

Further, switching noise is generated when the FET 6 is switched at a high frequency of about 100 kHz when the motor 3 is driven. In order to suppress this switching noise, it is necessary to suppress fluctuations in the power supply current that accompany the switching operation. Therefore, if an aluminum electrolytic capacitor 8 is placed near the FET 6, the capacitor 8 will discharge when the current supplied to the load is insufficient, and will be charged when the current becomes surplus, thereby reducing fluctuations in power supply current and voltage. is alleviated.

In order to enhance the noise absorption effect of the capacitor 8, it is desirable to reduce the impedance between the FET 6 and the capacitor 8 as much as possible. Therefore, as shown in FIG. 2, the FET 6 is mounted on one side of the multilayer substrate 11 and the capacitor 8 is mounted on the other side so that both mounting areas overlap. This reduces the impedance between the two.

However, mounting as described above causes a heat problem. The heat resistance temperature of the FET 6 is generally about 175.degree. C., while the aluminum electrolytic capacitor 8 is generally about 130.degree. Therefore, if the distance between the two is narrowed, when the heat generation temperature of the FET 6 rises, the heat may reach the capacitor 8 and exceed the heat resistance temperature, or the life of the element may be shortened.

Therefore, in this embodiment, a structure is adopted in the multilayer substrate 11 so that the capacitor 8 is not affected by the heat generated by the FET 6 as much as possible.
(1) A heat insulating layer 19 is positioned inside the multilayer substrate 11 between the FET 6 and the capacitor 8 to reduce the heat received from the FET 6 to the capacitor 8 . Also, the FET 6 and the capacitor 8 are electrically connected through a via 23, and the size of the via 23 is minimized so as not to lower the thermal resistance. i.e.
(Thermal resistance of FET 6→via 23→capacitor 8)
>> (FET 6 → thick copper pattern 18 → thermal gel 25 → thermal resistance of aluminum housing 24 )
Set to be

(2) The heat generated by the FET 6 is dissipated through a heat path extending rightward in the figure, which is FET 6→thick copper pattern 18c→heat releasing gel agent 25→aluminum housing 24. FIG. This heat path corresponds to the first heat dissipation path.

(3) When the inverter circuit 5 drives the motor 3, the capacitor 8 itself also generates heat. Therefore, the heat is dissipated through a heat path extending leftward in the figure, namely capacitor 8→thick copper pattern 17(-)→copper inlay 20→thick copper pattern 18a→heat releasing gel agent 25→aluminum housing 24. FIG. This heat path corresponds to the second heat dissipation path.

As described above, according to this embodiment, the FET 6 that controls the current flowing through the load by the switching operation and the aluminum electrolytic capacitor 8 that is connected between the terminals of the drive power supply correspond to each other on different surfaces of the multilayer substrate 11. are surface-mounted in each mounting area. In the inner layer of the multilayer substrate 11, the copper foil patterns 15 and 16 are arranged avoiding the portion corresponding to the mounting area. As a result, the heat generated by the FET 6 is less likely to be transmitted to the capacitor 8 side via the inner layer, and the effect of heat on the capacitor 8 can be reduced.

In addition, since the heat insulating layer 19 is formed of a material having a lower thermal conductivity than the substrate material at the portion corresponding to the mounting area of the inner layer, the heat generated by the FET 6 is more difficult to be transmitted to the capacitor 8 side. can further reduce the influence of heat received by

A first heat dissipation path is formed on the mounting surface of the FET 6 to transfer the heat generated by the FET 6 rightward in the drawing, and a second heat dissipation path is formed on the mounting surface of the capacitor 8 to dissipate the heat generated by the capacitor 8. was formed in a direction opposite to that of the first heat dissipation path. As a result, the heat can be dissipated without being affected by the heat generated by each other.

Further, the aluminum housing 24 is arranged on the mounting surface side of the FET 6, and the first heat radiation path is in contact with the aluminum housing 24 via the gel material 25 for heat radiation. Thereby, the heat radiation efficiency of FET6 can be improved. A copper inlay 20 for conducting heat to the mounting surface of the FET 6 is formed on the second heat dissipation path, and an extended heat dissipation path of the second heat dissipation path is formed on the mounting surface by a thick copper pattern 18a. Thereby, the heat radiation efficiency of the capacitor 8 can be improved. The thick copper pattern 18c of the first heat radiation path and the thick copper pattern 18a of the second heat radiation path are also thermally contacted with the aluminum housing 24 via the heat radiation gel agent 25, thereby further improving heat radiation efficiency. can be made

In addition, the FET 6 mounted on the multilayer substrate 11 constitutes the inverter circuit 5 , and the EDU 1 energizes each phase winding of the motor 3 . Therefore, the heat generated by the inverter circuit 5 can be efficiently dissipated when the motor 3 constituting the variable valve timing system is driven.

(Second embodiment)
Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted, and different parts will be described. The second embodiment differs from the first embodiment in the configuration of the heat insulating layer 31 . That is, as shown in FIGS. 6 and 7, a large number of through holes 32 are formed in the resin portion of the second resin substrate 13 where the heat insulating layer 19 was formed in the first embodiment. The inside of the through-hole 32 is filled with a heat insulating material 33 similar to that of the first embodiment. 6 shows only the through hole 32, and FIG. 7 shows the heat insulating material 33 by hatching.

As described above, according to the second embodiment, the heat insulating layer 31 is formed by forming the plurality of through holes 32 in the second resin substrate 13 and filling the through holes 32 with the heat insulating material 33 . With this configuration, the thermal conductivity of the heat insulating layer 31 can be adjusted by the number of through holes 32 formed and the material of the heat insulating material 33 .

(Third Embodiment)
As shown in FIG. 8, the third embodiment shows a case where a double-sided substrate 41 made of a single resin substrate is used instead of the multi-layer substrate used in the first embodiment. A thick copper pattern 17 is formed on the upper surface of the resin substrate 42 of the double-sided substrate 41, and a thick copper pattern 18 is formed on the lower surface thereof.

A heat insulating layer 43 is formed on the resin substrate 42 at a portion corresponding to the mounting area of the capacitor 8 and the FET 6 . The thick copper pattern 17(−) and the thick copper pattern 18a are thermally connected by a copper inlay 44 formed on the resin substrate 42. FIG. The thick copper pattern 17(+) and the thick copper pattern 18c are electrically connected by vias 45 formed in the resin substrate 42, as in the first embodiment.
As described above, according to the third embodiment, even when the double-sided substrate 41 is used, the same effect as in the first embodiment can be obtained.

(Fourth embodiment)
In the fourth embodiment, as shown in FIG. 5, an example of a layout in which three aluminum electrolytic capacitors 8a to 8c are connected to the power supply when the inverter circuit 5 is formed by six FETs 6 is shown. is shown. As shown in FIG. 9, six FETs 6a to 6f are arranged in a 2×3 matrix on the back surface of the substrate. In contrast, on the surface of the substrate, capacitor 8a is arranged between FETs 6a and 6d, capacitor 8b is arranged between FETs 6b and 6e, and capacitor 8c is arranged between FETs 6c and 6f. A heat insulating layer 51 indicated by a dashed line is formed inside the substrate corresponding to these mounting areas. A two-dot chain line indicates the aluminum housing 24 . Also, the thick copper pattern 17(-) and the thick copper pattern 18a are thermally connected by a plurality of vias.

As described above, according to the fourth embodiment, the effect similar to that of the first embodiment can be obtained with respect to the configuration in which the three capacitors 8a to 8c are connected to the six FETs 6a to 6f.

(Other embodiments)
The present invention is not limited to a four-layer board, and may be applied to a three-layer board or a board having five or more layers.
The configuration of the second embodiment may be applied to the third embodiment.
The switching elements are not limited to MOSFETs, and may be power transistors, IGBTs, or the like.
It may be applied to other than the EDU that constitutes the variable valve timing system.

Although the present disclosure has been described with reference to examples, it is understood that the present disclosure is not limited to such examples or structures. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and configurations, as well as other combinations and configurations, including single elements, more, or less, are within the scope and spirit of this disclosure.

In the drawings, 1 is an EDU, 3 is a motor, 5 is an inverter circuit, 6 is an N-channel MOSFET, 8 is an aluminum electrolytic capacitor, 11 is a multilayer substrate, 12 to 14 are first to third resin substrates, and 15 and 16 are copper. 17 and 18 are thick copper patterns; 19 is a heat insulating layer; 20 is a copper inlay; 24 is an aluminum housing;

Claims (12)

a switching element (6) for controlling current flowing through a load by switching operation;
a capacitor (8) connected between power supply terminals that supply drive power to the switching element;
a circuit board (11) on which the switching element and the capacitor are surface-mounted in corresponding mounting areas on one surface and the other surface;
The circuit board has one or more inner layers,
The conductive patterns (15, 16) of the inner layer are arranged avoiding the part corresponding to the mounting area ,
A first heat dissipation path (18c) for transmitting heat generated by the switching element in a predetermined direction is formed on the mounting surface of the switching element by the same metal material as the conductive pattern,
A second heat dissipation path (17(−), 20, 18a) for dissipating heat generated by the capacitor is formed on the mounting surface of the capacitor by the metal material, and the direction of heat transfer is different from that of the first heat dissipation path. A heat dissipation structure of a circuit board formed so as to be in the opposite direction . 2. A heat dissipation structure for a circuit board according to claim 1, wherein a heat insulating layer (19) is formed of a material having a lower thermal conductivity than the substrate material at a portion corresponding to the mounting area of the inner layer. 3. The circuit board according to claim 2, wherein substrates (12, 14) are respectively interposed between the conductive patterns (17, 18) formed on the one surface and the other surface and the heat insulation layer. heat dissipation structure. a switching element (6) for controlling current flowing through a load by switching operation;
a capacitor (8) connected between power supply terminals that supply drive power to the switching element;
a circuit board (41) on which the switching element and the capacitor are surface-mounted in corresponding mounting areas on one surface and the other surface;
a heat insulating layer (31) formed inside the circuit board at a portion corresponding to the mounting area and made of a substance having a lower thermal conductivity than the substrate material ,
The heat dissipation structure of the circuit board, wherein the layer structure of the portion related to the mounting area is composed of a conductive pattern (17), a heat insulating layer, and a conductive pattern (18) from one surface to the other surface . The heat insulating layer (31) includes a plurality of through holes (32) formed in the substrate,
5. The circuit board heat dissipation structure according to claim 4 , further comprising a heat insulating material (33) filled in the plurality of through holes. A metal housing (24) is arranged on the mounting surface side of the switching element,
The heat dissipation structure for a circuit board according to any one of claims 1 to 3, wherein the first heat dissipation path is in contact with the housing via a heat dissipation gel (25). A heat conducting part (20) reaching a mounting surface of the switching element is formed in the second heat dissipation path,
7. The circuit board heat dissipation structure according to claim 1 , wherein an extended heat dissipation path (18a) of the second heat dissipation path is formed by the metal material on the mounting surface of the switching element. . 8. The circuit board heat dissipation structure according to claim 7 , wherein the extended heat dissipation path is in contact with the housing through a heat dissipation gel. 9. The heat dissipation structure for a circuit board according to claim 8 , wherein the extended heat dissipation path is formed so that the thickness in the layer direction is thicker than the conductive pattern of the inner layer . The heat dissipation structure for a circuit board according to any one of claims 1 to 3 and 6 to 9, wherein the first heat dissipation path is formed so as to be thicker in the layer direction than the conductive pattern of the inner layer. 11. The heat dissipation structure for a circuit board according to claim 1, wherein the second heat dissipation path is formed to have a thickness in a layer direction larger than that of the conductive pattern of the inner layer. A motor driving device for energizing the windings of a motor (3), comprising one or more switching elements with the circuit board heat dissipation structure according to any one of claims 1 to 11.

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