JPH07283567A - Cooling structure of printed board - Google Patents

Abstract

PURPOSE:To prevent inflow of air warmed by a heat sink cooling a hot element and thereby to obtain a cooling structure of a printed board having a high cooling efficiency, by a construction wherein an air passage to an inlet of a cooling fan mounted on the heat sink is isolated from a surrounding space by an air intake duct. CONSTITUTION:A heat sink 1 whereon a small-sized cooling fan 2 is mounted is fixed on each hot element 4 mounted on a printed board 6. Above the cooling fan 2, an air intake duct 5 is so disposed as to form an air channel for intake of air. The an intake duct 5 is a hollow tube body having a rectangular section and it is formed of synthetic resin or the like of which the heat conductivity is low, in order to make it hardly receive a heat from the surroundings. The air intake duct 5 is disposed in a state of being stretched over the full length of a line of mounting of the high heat generating elements 4, and the bottom wall thereof is brought into contact with the ceiling wall of the cooling fan 2 so as to prevent leakage of cooling air. Besides, a fan intake opening 15 corresponding to the heat sink 1 is provided in the bottom wall of the air intake duct 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board cooling structure. In recent years, as the degree of integration of semiconductor elements has improved, the amount of heat generated by semiconductor elements has tended to increase, and there is a demand for an efficient cooling structure for the semiconductor. And
In order to meet such a demand, attention is focused on a cooling method in which a small cooling fan 2 is mounted on a heat sink and spot-cooling a high heat generating element.

[0002]

20 and 21 show a cooling structure for a printed circuit board as described above. In the figure, 1 is a heat sink having a plurality of pin-shaped heat radiation fins 1a, 1a, ...
It is fixed to the heat sink surface of the high heat generating element 4 by appropriate means,
The cooling fan 2 is fixed to the upper surface of the heat sink 1.

[0003]

However, in the above-described conventional example, the cooling air heated by the heat sink 1 is forcibly introduced again to the heat sink 1 side by the cooling fan 2 as shown by the arrows in FIGS. Or
Alternatively, it is sucked into the cooling fan 2 on another high heat generating element 4 adjacent to the downstream side. Therefore, the temperature difference between the cooling air blown by the cooling fan 2 on the heat sink 1 and the junction temperature of the element is reduced, and the heat transfer coefficient is reduced, or the life of the fan bearing portion is shortened due to an increase in ambient temperature. There are drawbacks such as

The present invention has been made to solve the above drawbacks, and an object of the present invention is to provide a cooling structure for a printed circuit board having a high cooling efficiency. Furthermore, another object of the present invention is to lower the bearing temperature of the cooling fan 2 by lowering the intake air temperature of the cooling fan 2.
To prolong the life of.

[0005]

According to the present invention, the above object corresponds to an embodiment, as shown in FIG.
A cooling structure for a printed circuit board that cools a high heat generating element 4 with a heat sink 1 having a heat sink 1, wherein the air path to the suction port of the cooling fan 2 is isolated from the surrounding space by an intake duct 5. It is achieved by

[0006]

The intake duct 5 separates the cooling air passage supplied to the cooling fan 2 from the surrounding space, and prevents the warm air heated by the heat sink 1 from flowing in.

According to the second aspect of the present invention, the cooling fan 2 is fixed to the intake duct 5, so that the labor of fixing the cooling fan 2 for each heat sink 1 is omitted. In the invention described in claim 3, an effective modification is provided when the high heat generating element 4 is an element which is weak against vibration such as BGA (ball grid array). That is, the vibration isolating member 3 is interposed at the contact portion between the cooling fan 2 and the heat sink 1 to absorb the vibration and the like of the cooling fan 2.

In the invention described in claim 4, the intake duct 5 is arranged so as to connect the intake ports of the plurality of cooling fans 2, 2, ..., And the cooling air is supplied from each of the common intake ducts 5. Supplied to the radiator.

By making the air intake duct 5 common, not only the occupied area of the air intake duct 5 on the printed circuit board 6 can be reduced, but also the number of assembling and mounting steps can be reduced.

The formation and fixing structure of the intake duct 5 which is effective when the printed circuit board 6 is mounted in the shelf is provided in the invention described in claims 5 to 10, and in the invention described in claim 5, the intake duct 5 is provided. Is formed by using the back surface of another adjacent printed circuit board 6'as one side wall surface. By forming the intake air tunnel using the adjacent printed circuit boards 6 ', the entire structure can be simplified.

In the invention of claim 6, the intake duct 5 is formed over the entire upper surface of the printed circuit board 6, and the front plate 6a and the back panel 7 are used as the side wall surface of the intake duct 5. In the invention described in Item 7, a closing plate 5a that can be laid down is provided at a side edge of the intake duct 5 that is orthogonal to the front plate 6a to prevent interference with an adjacent printed circuit board 6'when mounted on a shelf. To be done.

Further, in the invention according to claim 8, a partition plate 5b is provided between the heat sinks 1 and 1 for preventing exhaust gas from flowing from the heat sink 1 on the upstream side to the heat sink 1 on the downstream side, and is heated. It is possible to prevent the temperature from rising to the downstream element due to exhaust.

In the invention according to claim 9, the intake duct 5 is fixed to the front plate 6a mounted on the printed circuit board 6, and the cooling air is introduced from the intake small holes formed in the front plate 6a.

According to the tenth aspect of the invention, the cooling air is forcedly introduced into the intake duct 5 by the auxiliary intake fan 5c to increase the amount of the cooling air from the cooling fan 2.
In the invention of claim 11, the exhaust gas from the heat sink 1 is introduced into the exhaust duct 8 which is separated from the surrounding space, and is prevented from being discharged into the surrounding space.

According to the twelfth aspect of the invention, there is provided a method of arranging the exhaust duct 8 which is particularly effective when the high heat generating elements 4 are arranged on a straight line. That is, the exhaust duct 8
Are shared by being arranged so as to connect the exhaust air outlets of the plurality of radiators, and the occupied area is reduced.

In the thirteenth aspect of the present invention, the exhaust gas introduced into the exhaust duct 8 is forcibly exhausted by the auxiliary exhaust fan 8a, and hot air is prevented from staying in the exhaust duct 8.

In the fourteenth aspect of the present invention, there is provided a structure for forced exhaust in the exhaust duct 8 without using the exhaust auxiliary fan 8a.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 1 to 3 show a first embodiment of the present invention. Reference numeral 4 in the drawing denotes a high heat generating element mounted on the printed circuit board 6, and a heat sink 1 having a small cooling fan 2 mounted thereon is fixed on each of the high heat generating elements 4, 4 ,. The heat sink 1 is formed of a material having good thermal conductivity such as aluminum, and has a plurality of pin-shaped heat radiation fins 1a, 1a, ...

Further, an appropriate number of high heat generating elements 4 are arranged in rows, and if necessary, elements 11 having a relatively small heat generation amount are mounted in the rows. The cooling fan 2 has a built-in small motor for rotating the rotary blades 2a, and the cooling air forcedly sucked from the suction opening formed on the upper surface is exhausted to the heat sink 1 side to generate the high heat generating element 4.
The cooling air that has been cooled and warmed is discharged from between the radiation fins 1a, 1a, ... Of the heat sink 1.

Further, an intake duct 5 is arranged above the cooling fan 2 to form an intake wind tunnel. The intake duct 5 is a tubular body having a hollow rectangular shape in cross section, and it is desirable that the intake duct 5 is made of synthetic resin or the like having low thermal conductivity in order to make it difficult to receive heat from the surroundings. It is also possible to use high thermal conductivity materials such as metals, except where it is significantly higher.

Incidentally, in order to prevent the cooling air introduced into the intake duct 5 from being discharged to the outside as it is, the final end thereof is closed by the closing wall 5d. The air intake duct 5 formed as described above is arranged so as to be bridged over the entire length of the mounting row of the high heat generating elements 4, and in order to prevent the leakage of the cooling air from the cooling wind tunnel, The wall is brought into contact with the ceiling wall of the cooling fan 2. Further, in order to guide the cooling air introduced into the cooling wind tunnel to the heat sink 1,
A fan intake opening 15 corresponding to the heat sink 1 is opened in the bottom wall of the intake duct 5.

The intake duct 5 can be fixed by using a fastener such as a screw on the ceiling surface of the cooling fan 2 or by fitting it to the frame 2b of the cooling fan 2. The frame 2 of one of the cooling fans 2
It is also possible to integrally mold the cooling fan 2 with each other, and it is also possible to connect the ones integrally molded with the frame 2b of each cooling fan 2 to each other to form the intake duct 5 as a whole.

FIG. 4 shows a modification of the heat sink 1. In this modification, the cooling fan 2 is incorporated in the central portion of the heat sink 1, and a lid having a fan intake opening (not shown) corresponding to the suction port of the cooling fan 2 is provided on the upper surface of the heat sink 1. The body 1b is fixed. The lid 1b is made of a highly heat-conductive material such as aluminum and is fixed to the bottom wall of the metal intake duct 5. This modification is an effective modification for improving the cooling efficiency as a whole by positively forming a heat radiation path that passes through the lid 1b to the air intake duct 5, but the air intake duct 5 is replaced by one of the heat radiation plates. The structure shown in FIG. In the modification shown in FIG. 5, a concave portion 5j corresponding to the location of the heat sink 1 is formed in the metal intake duct 5, and the cooling fan 2 is placed on the heat sink 1 so as to sandwich the bottom wall of the concave portion 5j. Fixed.

Therefore, in this embodiment, when each cooling fan 2 is driven, a flow of air flowing from the suction port of the cooling fan 2 to the heat sink 1 side is formed. As a result, as shown by the broken line arrow in FIG. The warm air whose temperature has risen due to the heat exchange by the heat sink 1 is forcedly introduced into the inside 5 and is not sucked into the intake duct 5 again, as shown by the white arrow in FIGS. And is discharged to the outside of the casing from the most downstream part.

In the above, the case where a plurality of high heat generating elements 4 and 4 are arranged on the printed circuit board 6 and the intake duct 5 is provided for each row has been shown, but the present invention is not limited to this. When a single high heat generating element 4 is mounted on the printed circuit board 6 or the high heat generating elements 4 are arranged in a scattered manner, the intake ducts 5 are individually provided to the cooling fans 2 on each high heat generating element 4. It is also possible to dispose, and when the high heat generating elements 4 are mounted adjacent to each other over a plurality of rows, it is possible to provide one intake duct 5 for the plurality of rows. .

FIG. 6 shows a second embodiment of the present invention. In the following description of the embodiments, the same components as those in the above-mentioned embodiments are designated by the same reference numerals in the drawings, and the description thereof will be omitted. In this embodiment, the cooling fan 2 is fixed to the bottom wall of the intake duct 5 in advance, and is fixed to a predetermined position of the heat sink 1 by mounting the intake duct 5.

The fixing of the cooling fan 2 to the intake duct 5 is as follows.
This is performed by screwing the bottom wall of the intake duct 5 or the like, but as shown in FIG. 6, if the bottom wall of the intake duct 5 is made of the high thermal conductive material 5e, the heat radiation area is increased and cooling is performed. The efficiency is improved.

Further, as shown in FIG. 7, it is also possible to form a fixing flange 2c on the cooling fan 2 side and to fix it by engaging with an engaging portion 5f formed on the intake duct 5 side. 6 and 7, the case where the cooling fan 2 mounted while being housed in the heat sink 1 is fixed to the intake duct 5 is shown in FIG. 1 and FIG. It is of course possible to fix the cooling fan 2 mounted above to the intake duct 5.

If the high heat generating element 4 is vulnerable to vibration such as BGA (ball grid array), FIG.
As shown in FIG. 3, it is desirable to interpose the vibration isolating member 3 when fixing the cooling fan 2 to the heat sink 1 to prevent the vibration of the cooling fan 2 from being transmitted to the high heat generating element 4. A grommet or the like can be used as the vibration isolating member 3.

The third embodiment of the present invention is shown in FIG. This embodiment shows a modification effective in mounting the printed circuit board 6 on which the high heat generating element 4 is mounted together with another printed circuit board 6 ′ in the shelf. The starting end opening of the intake duct 5 is the printed circuit board 6 ′. Is fixed to the front plate 6a which is fixed to. The front plate 6a is perforated with small holes that do not impair the electromagnetic shield performance, and the outside air is introduced into the intake duct 5 through the small holes.

In FIG. 9, reference numeral 12 indicates a shelf ceiling surface, and 10 indicates an entire cooling fan mounted on the shelf ceiling surface, and the air flow by the overall cooling fan 10 is indicated by a white arrow. Further, the cooling fan 2 can be fixed to the heat sink 1 side or the intake duct 5 side. However, in the configuration in which the cooling fan 2 is fixed to the intake duct 5 side, The vibration of the cooling fan 2 can be diffused to the front plate 6a, which is effective for reducing the mechanical load on the high heat generating element 4.

FIG. 10 shows a fourth embodiment of the present invention. In this embodiment, another printed circuit board 6 ′ mounted in parallel in the shelf is used as one side wall of the intake duct 5, and the intake duct 5 is opened to the adjacent other printed circuit board 6 ′ side. An opening is formed in the wall surface on the heat sink 1 side, that is, the bottom wall of the intake duct 5, corresponding to the suction port of the cooling fan 2.

Therefore, in this embodiment, when the printed circuit board 6 is mounted in the shelf, the upper opening edge of the intake duct 5 comes into contact with the back surface of another adjacent printed circuit board 6 ', and the other adjacent to the intake duct 5. The printed-circuit board 6 forms an intake air tunnel.

In the embodiment described above, the case where the upper opening edge of the intake duct 5 is mounted in close contact with the back surface of another adjacent printed circuit board 6'is shown, but it is adjacent to the intake duct 5. The gap between the back surface of the other printed board 6 and the back surface of the other printed board 6 is allowed as long as the wind tunnel is substantially formed by the other printed board 6 ′.

11 and 12 show a fifth embodiment of the present invention, in which the intake duct 5 is formed over the entire upper surface of the printed circuit board 6. The intake duct 5 can be formed by fixing a tubular member capable of forming a wind tunnel by itself, as shown in FIG. 1 or FIG. 8 shows a case where the printed circuit board 6 ', the front plate 6a, and the back panel 7 which are adjacent to each other are used for the formation.

That is, the bottom plate 13 having substantially the same outer shape as the printed circuit board 6 is fixed above the printed circuit board 6. The bottom plate 13 is fixed by screwing a fastener such as a screw onto the cooling fan 2 fixed to the heat sink 1, but the cooling fan 2 is fixed to the bottom plate 13 side in advance.
It is also possible to fix it above the printed circuit board 6 by appropriate means.

In FIG. 11, 14 is a connector mounted on the printed circuit board 6, 15 is a fan intake opening opened corresponding to the inlet of the cooling fan 2, and 16 is a screw hole for fixing the fan.

The bottom plate 13 is provided with a closing plate 5a. The closing plate 5a is arranged at one side edge orthogonal to the front plate 6a and is exposed to the front plate 6a side.
It is possible to change from a lying posture along the bottom plate 13 to a standing posture which stands upright at a right angle with respect to the bottom plate 13 by operating the. It is formed to have a size reaching the vicinity of the back surface of 6.

Therefore, in this embodiment, the closing plate 5
When the printed circuit board 6 is mounted on the back panel 7 in a state in which a is in the lying posture, and then the operating lever 17 is operated to erect the closing plate 5a, the bottom plate 13, the front plate 6a, the back panel 7, and the closing plate 5a are closed. An intake duct 5 is formed, the four surfaces of which are surrounded by the plate 5a. By configuring the closing plate 5a to fall down, it is possible to prevent interference with another adjacent printed circuit board 6 when the printed circuit board 6 is mounted.

FIG. 13 shows a modification of FIG. In this modification, a partition plate 5b is provided on the back surface of the bottom plate 13. The partition plate 5b is provided to prevent the warm air discharged from the heat sink 1 on the upstream side from flowing into the heat sink 1 on the downstream side as it is by appropriately partitioning the heat sinks 1 and 1. Is preferably determined so that an appropriate discharge path is formed so that the exhaust gas does not stay, and as shown in FIG. The relationship may be changeable.

In FIG. 13, arrows indicate the exhaust path of the warm air exhausted from between the radiation fins 1 and 1.
In 3 (b), 5h is a sliding piece that slides on the bottom plate 13, and 5i is a guide pin 13a protruding from the bottom plate 13.
Indicates a guide hole that is inserted to regulate the swing stroke of the partition plate 5b.

14 and 15 show a sixth embodiment of the present invention. This embodiment shows a modification effective for preventing the influence of the warm air discharged from the heat sink 1 on other elements, and the warm air discharge portion is covered with the exhaust duct 8 to form an exhaust air tunnel.

The exhaust duct 8 is a member having a hollow rectangular cross section, and it is desirable to use a low heat conductive material such as synthetic resin so that exhaust heat is not transmitted to the surroundings when the ambient temperature is low. When the ambient temperature is higher, it is desirable to use a material having a high thermal conductivity such as a metal in order to lower the ambient temperature.

The exhaust duct 8 is arranged so as to include at least the heat radiation fins 1a of each heat sink 1 in the exhaust wind tunnel, and the end portion of the exhaust duct 8 on the intake port side is closed by a closing wall so that the intake duct for the exhaust gas is exhausted. 5 is prevented from flowing.

It is desirable that the exhaust duct 8 be fixed by screwing or the like in consideration of replacement of the high heat generating element 4 and the like, but when the element replacement is not necessary, the exhaust duct 8 is fixed. It is also possible to project a fixed leg (not shown) from this and solder it to the printed circuit board 6.

Therefore, in this embodiment, the exhaust gas discharged from the intake duct 5 and cooled to warm the heat sink 1 is guided into the exhaust duct 8 and prevented from flowing out to the surrounding space. As a result, it is possible to prevent the other elements arranged around the high heat generating element 4 from being warmed by exhaust gas, or the heat transfer coefficient of the cooling air blown onto the printed circuit board 6 from being lowered to lower the cooling efficiency. To be done.

FIG. 16 shows a seventh embodiment of the present invention. In this embodiment, an intake auxiliary fan 5c is arranged at the start end of the intake duct 5 to forcibly introduce cooling air into the intake duct 5, and an exhaust auxiliary fan 8a is arranged at the end of the exhaust duct 8. The warm air in the exhaust duct 8 is forcibly discharged.

The forced introduction of cooling air into the intake duct 5
The cooling efficiency is improved by increasing the amount of cooling air blown from the cooling fan 2 to the heat sink 1, and the forced exhaust from the exhaust duct 8 prevents the warm air from staying in the exhaust duct 8 to prevent the exhaust duct 8 from being warmed up. Prevents internal temperature rise.

In the illustrated example, the intake auxiliary fan 5c and the exhaust auxiliary fan 8a are arranged in both the intake duct 5 and the exhaust duct 8, but they may be arranged in either one. It can be expected to improve the cooling efficiency. Further, the intake auxiliary fan 5c and the exhaust auxiliary fan 8a are not provided in pairs in the intake duct 5 or the exhaust duct 8, but when a plurality of intake ducts 5 and the like are arranged, appropriate numbers of these are provided. You may provide in the ratio of 1 per piece.

The structure of the forced exhaust of the exhaust gas in the exhaust duct 8 is, as described above, the exhaust auxiliary fan 8a.
17, the end opening of the exhaust duct 8 may be arranged so as to face the suction port of the overall cooling fan 10, as shown in FIG.

18 and 19 show an eighth embodiment of the present invention. In this embodiment, the intake duct 5 has a recess 5j formed at a position orthogonal to the windward direction or the wind direction of the heat sink 1, and the cooling fan 2 is fixed in the recess 5j. The side wall of the recess 5j has an opening for blowing air, and the wind blown on the bottom wall of the recess 5j hits the side surface of the heat sink 1 from the opening for blowing air as shown by the arrow in FIG. The heat sink 1 is cooled.

[0052]

As is apparent from the above description, according to the present invention, since warm air does not flow around the cooling fan in spot cooling using a heat sink having a cooling fan, the cooling efficiency is significantly improved. You can

Further, since the intake air temperature of the cooling fan is lowered, the temperature of the bearing portion of the cooling fan is lowered, so that the life of the bearing portion can be extended.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a side view of FIG.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a diagram showing a modification of FIG.

FIG. 5 is a diagram showing still another modified example of FIG. 1.

FIG. 6 is a diagram showing a second embodiment of the present invention.

FIG. 7 is a diagram showing a method of fixing a cooling fan.

8A and 8B are diagrams showing a fixed state of a cooling fan, FIG. 8A is a side view, and FIG. 8B is an enlarged view of a main part of FIG. 8A.

FIG. 9 is a diagram showing a third embodiment of the present invention.

FIG. 10 is a diagram showing a fourth embodiment of the present invention.

FIG. 11 is a diagram showing a fifth embodiment of the present invention.

FIG. 12 is a view on arrow A in FIG. 11.

FIG. 13 is a diagram showing a modification of FIG. 11.

FIG. 14 is a diagram showing a sixth embodiment of the present invention.

15 is a cross-sectional view taken along the line AA of FIG.

FIG. 16 is a diagram showing a seventh embodiment of the present invention.

FIG. 17 is a diagram showing a modified example of FIG. 16.

FIG. 18 is a diagram showing an eighth embodiment of the present invention.

FIG. 19 is a plan view of FIG. 18.

FIG. 20 is a diagram showing a conventional example.

21 is a plan view of FIG. 20. FIG.

[Explanation of symbols]

 1 Heat Sink 2 Cooling Fan 3 Anti-Vibration Member 4 High Heating Element 5 Intake Duct 5a Blocking Plate 5b Partition Plate 5c Intake Auxiliary Fan 6 Printed Circuit Board 6a Front Plate 7 Back Panel 8 Exhaust Duct 8a Exhaust Auxiliary Fan 9 Heat Sink 9a Radiating Fin 10 Fan for overall cooling

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 23/467

Claims (14)

[Claims] 1. A cooling structure for a printed circuit board, wherein a high heat generating element (4) is cooled by a heat sink (1) having a cooling fan (2), wherein an air path to a suction port of the cooling fan (2) is provided. Cooling structure for the printed circuit board separated from the surrounding space by the intake duct (5). 2. The cooling fan (2) is an intake duct (5).
The cooling structure for a printed circuit board according to claim 1, which is fixed to the. 3. The cooling structure for a printed circuit board according to claim 1, wherein a vibration isolating member (3) is provided at a contact portion between the cooling fan (2) and the heat sink (1). 4. The intake duct (5) connects the suction ports of a plurality of cooling fans (2, 2, ...) And cools each of the cooling fans (2, 2, ...) From the intake duct (5). The cooling structure for a printed circuit board according to claim 1, 2 or 3, wherein air is supplied. 5. The printed circuit board according to claim 1, wherein the air intake duct (5) is formed by using a back surface of another adjacent printed circuit board (6 ′) as a side wall surface. Cooling structure. 6. The intake duct (5) is formed over the entire upper surface of the printed circuit board (6), and serves as a side wall surface of the intake duct (5). The front plate (6a) and the back panel (7). The cooling structure for a printed circuit board according to claim 5, wherein and are used. 7. A closing plate (5a) capable of standing up and down with respect to the front plate (6a) is provided at a side edge of the intake duct (5) orthogonal to the front plate (6a). The printed circuit board cooling structure described. 8. A partition plate (5b) is provided between the heat sinks (1, 1) to prevent exhaust gas from flowing from the heat sink (1) on the upstream side to the heat sink (1) on the downstream side. Alternatively, the printed circuit board cooling structure according to item 7. 9. The intake duct (5) is fixed to a front plate (6a) mounted on a printed circuit board (6), and cooling air is introduced from intake small holes formed in the front plate (6a). The cooling structure for a printed circuit board according to claim 1. 10. A printed circuit board cooling structure according to claim 1, wherein cooling air is forcibly introduced into said intake duct (5) by an auxiliary intake fan (5c). 11. The printed circuit board cooling structure according to claim 1, wherein exhaust gas from the heat sink (1) is introduced into an exhaust duct (8) separated from an ambient space. 12. The cooling structure for a printed circuit board according to claim 11, wherein the exhaust duct (8) connects the exhaust air outlets of the plurality of heat sinks (1, 1 ...). 13. A printed circuit board cooling structure according to claim 10, 11 or 12, wherein the exhaust gas introduced into said exhaust duct (8) is forcibly exhausted by an auxiliary exhaust fan (8a). 14. The exhaust air in the exhaust duct (8) is forcibly exhausted by causing the end opening of the exhaust duct (8) to face the suction port of the general cooling fan (10).
The printed circuit board cooling structure according to 0, 11 or 12.