JP6541766B1 - Electronic device - Google Patents

Abstract

The present invention provides an inexpensive electronic device capable of suppressing the occurrence of condensation on the surface of a printed circuit board without using an air blocking structure. An electronic device includes a housing (1), a printed circuit board (3) held in the housing (1) with one surface facing up, an electronic component (2) mounted on the printed circuit board (3), and the housing (1). And a fin 5 disposed in the upper area of the electronic component 2 and in contact with the air warmed by the heat generated by the electronic component 2 to form dew. [Selected figure] Figure 1

Description

  The present invention relates to an electronic device in which a printed circuit board on which an electronic component is mounted is housed in a housing.

  In the electronic device in which the printed circuit board is housed in the housing with the mounting surface of the heat generating component facing upward, the air temperature on the upper surface side of the printed circuit board in the housing is higher than the air temperature outside the housing due to heat generation of the heat generating component. Will also be high. Since there is no heat source on the lower surface side of the printed circuit board, the air temperature on the lower surface side of the printed circuit board in the housing is lower than the air temperature on the upper surface side of the printed circuit board. In addition, the air temperature inside the case is also affected by the air temperature outside the case.

  When the air temperature outside the housing is lowered, the air temperature on the lower surface side of the printed circuit board in the housing is reduced following the air temperature outside the housing. Thereby, the printed circuit board is cooled from the lower surface side, and dew condensation occurs on the upper surface of the printed circuit board.

  A circuit pattern having an anode and a cathode is formed on the printed circuit board. Therefore, when dew condensation water is present in the circuit pattern, so-called migration occurs in which the electrode material grows in a dendritic shape while repeating dissolution and precipitation. As migration continues to grow, the circuit patterns will short and the circuit will not function properly.

  In view of such a situation, various means for preventing the occurrence of condensation on the printed circuit board have been proposed.

  For example, in the prior art, the printed circuit board and the case material are assembled with an air blocking member interposed therebetween to prevent the flow of moist air into the space between the printed circuit board and the case material. A condensation prevention structure for a printed circuit board has been proposed (see, for example, Patent Document 1).

  In addition, a condensation prevention plate is provided at a position to block the flow path of air blown to the electronic component of the printed circuit board from the inner ceiling surface of the electronic unit case containing the printed circuit board to the upper surface of the printed circuit board Was suspended. As a result, water vapor contained in the air is condensed on the anti-condensation plate to lower the humidity of the air, and other conventional anti-condensing structures for printed circuit boards have been proposed to reduce the occurrence of condensation on electronic components and leads. (See, for example, Patent Document 2).

JP 2012-89767 A JP-A-9-102679

  However, with the conventional condensation prevention structure for a printed circuit board described in Patent Document 1, an air blocking member is required, and cost reduction can not be achieved.

  In another conventional printed circuit board condensation prevention structure described in Patent Document 2, a condensation prevention plate is provided at a position that blocks the flow path of air sprayed onto the printed circuit board electronic components. Therefore, air hits the dew condensation prevention plate without being warmed by the heat generated by the electronic component. As a result, the temperature difference between the air and the anti-condensing plate decreases, and the water vapor contained in the air can not be effectively condensed on the anti-condensing plate. As a result, the removal of water vapor contained in the air becomes insufficient, and the occurrence of condensation on the surface of the printed circuit board can not be suppressed.

  An object of the present invention is to solve such problems, and to obtain an inexpensive electronic device capable of suppressing the occurrence of dew condensation on the surface of a printed circuit board without using an air blocking structure. With the goal.

An electronic device according to the present invention includes a housing, a printed circuit board held in the housing with the one surface facing up, a heat generating component mounted on the printed circuit board, and an inner wall surface of a ceiling of the housing. And the condensation fin which is installed in the area above the heat-generating component and in which the air warmed by the heat generation of the heat-generating component contacts and condenses the dew condensation fins is installed on the inner wall surface of the ceiling The base portion and the tip portion provided to project downward from the base portion, the heat capacity of the base portion is larger than the heat capacity of the tip portion, and the base portion has a constant plate thickness The tip portion has a tapered shape in which the plate thickness gradually decreases from the base downward, and the plurality of condensation fins are separated from each other and arranged in parallel, and the plurality of condensations are formed. The fins are for the surface tension of water Ri between adjacent said base that is arranged capable of holding intervals condensed water.

  According to the present invention, the condensation fins are installed in the region above the heat generating component on the inner wall surface of the ceiling of the housing. Thus, the water vapor in the air can be sufficiently removed without using an air shielding structure, and the humidity of the air can be reduced. As a result, it is possible to obtain an inexpensive electronic device capable of suppressing the occurrence of condensation on the surface of the printed circuit board.

FIG. 1 is a perspective view of an on-vehicle electronic control device according to a first embodiment of the present invention as viewed from a side of a case. FIG. 2 is a perspective view of the in-vehicle electronic control unit according to Embodiment 1 of the present invention as viewed from a case opening; It is a schematic diagram explaining the behavior of the air warmed by the electronic component in the fin periphery of the vehicle-mounted electronic control unit which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the generation | occurrence | production initial state of dew condensation on the fin surface of the vehicle-mounted electronic control unit which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the state in which the water droplet is growing on the fin surface of the vehicle-mounted electronic control apparatus which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the state in which the dew condensation water is drawn up between the base of a fin in the vehicle-mounted electronic control apparatus which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the state by which the dew condensation water in the vehicle-mounted electronic control apparatus which concerns on Embodiment 1 of this invention is hold | maintained between the base of a fin. It is the perspective view which looked at the vehicle-mounted electronic control apparatus which concerns on Embodiment 2 of this invention from the housing | casing opening part. It is the perspective view which looked at the vehicle-mounted electronic control apparatus which concerns on Embodiment 3 of this invention from the housing side surface. It is the perspective view which looked at the vehicle-mounted electronic control unit concerning Embodiment 3 of this invention from the housing | casing opening part.

  Hereinafter, although each embodiment of this invention is described based on figures, in each figure, the same code | symbol is attached | subjected and demonstrated about the same or equivalent member and site | part.

Embodiment 1
FIG. 1 is a perspective view of the in-vehicle electronic control device according to the first embodiment of the present invention as viewed from the side of the case, and FIG. 2 is a case opening of the in-vehicle electronic control device according to the first embodiment of the present invention It is the perspective view seen from the part.

  In FIG. 1 and FIG. 2, in the on-vehicle electronic control device 100 as an electronic device, a resin-made case 1 formed in a rectangular box shape having an opening 1a on the front surface and an electronic component 2 as a heat generating component A printed circuit board 3 mounted, a connector 4 mounted to one end of the printed circuit board 3, and a plurality of fins 5 as condensation fins provided on an inner wall surface of a ceiling of the housing 1 are provided. Here, for convenience, the left and right direction in FIG. 1 is the front and back direction of the housing 1, the left and right direction in the width direction of the housing 1 in FIG. 2, and the top and bottom direction in FIG. Do.

  The printed circuit board 3 is guided from the opening 1 a to the guide grooves 6 a of the guide members 6 provided on the inner wall surfaces of both side walls facing each other in the width direction of the housing 1 and inserted into the housing 1. Then, the connector 4 is fitted in the opening 1 a, and the printed circuit board 3 is accommodated and held in the housing 1 with the electronic component 2 facing upward. Although the opening 1a is closed by the connector 4, since the connector 4 is fitted in the opening 1a, the housing 1 does not have a sealed structure.

  The plurality of fins 5 respectively extend in the front-rear direction through the upper portion of the electronic component 2 and are arranged in a plurality at a constant pitch in the width direction. The fins 5 are provided on the inner wall surface of the ceiling of the housing 1, and the base 5a having a rectangular cross section orthogonal to the front and rear direction and the tip of the triangle having a triangular cross section extending downward from the lower end of the base 5a It is formed in a strip of pentagonal cross section consisting of 5b. The tip portion 5b has a tapered shape in which the plate thickness gradually decreases from the base 5a downward, and the heat capacity thereof is smaller than the heat capacity of the base 5a. The electronic component 2 is located in the installation area of the plurality of fins 5 in the width direction and the front-rear direction. That is, the electronic component 2 is located in the installation area of the plurality of fins 5 when viewed from above. The gap between the adjacent bases 5 a is set so as to be able to hold the condensed water 12 in consideration of the surface tension of water, the wettability of the water and the fins 5, and the like. Thereby, the distance between the bases 5 a changes depending on the material of the fins 5.

  Next, the behavior of the air in the housing 1 at the time of operation of the on-vehicle electronic control device 100 will be described.

  With the operation of the on-vehicle electronic control device 100, the electronic component 2 generates heat. As a result, the air in the vicinity of the electronic component 2 is warmed by the heat generated by the electronic component 2 and ascends as shown by the arrows in FIGS. 1 and 2 and enters between the adjacent fins 5. Next, the air entering between the adjacent fins 5 flows in the front-rear direction between the adjacent fins 5 as shown by the arrows in FIG. The air that has flowed forward between adjacent fins 5 descends along the connector 4 and returns along the upper surface of the printed circuit board 3 to the vicinity of the electronic component 2. On the other hand, the air which has flowed backward between adjacent fins 5 descends along the rear inner wall surface of the housing 1 and returns to the vicinity of the electronic component 2 along the upper surface of the printed circuit board 3. Thus, the air circulates in the upper space of the printed circuit board 3 in the housing 1.

  Here, dew condensation on the fins 5 will be described with reference to FIGS. 3 to 7. FIG. 3 is a schematic view for explaining the behavior of air warmed by electronic components around the fins of the on-vehicle electronic control device according to the first embodiment of the present invention, and FIG. 4 relates to the first embodiment of the present invention FIG. 5 is a schematic view showing an initial state of occurrence of condensation on the fin surface of the in-vehicle electronic control device, and FIG. 5 shows a state in which water droplets grow on the fin surface of the in-vehicle electronic control device FIG. 6 is a schematic view showing a state in which dew condensation water is drawn up between the bases of the fins in the on-vehicle electronic control device according to the first embodiment of the present invention, and FIG. 7 is a view showing the first embodiment of the present invention. It is a schematic diagram which shows the state by which the dew condensation water in the vehicle-mounted electronic control apparatus which concerns is hold | maintained between the base of a fin.

  The air warmed by the heat generation in the electronic component 2 rises, and is guided by the tapered wall surface of the tip 5 b of the fin 5 as shown by the arrow in FIG. To flow. At this time, the fins 5 are in contact with the outside air through the housing 1 and have a temperature equal to the outside air temperature. That is, the temperature of the warmed air is higher than the temperature of the fins 5. Then, when the warmed air comes in contact with the fins 5, dew condensation occurs on the surfaces of the fins 5. Thereby, small water droplets 10 adhere to the entire surface of the fins 5 as shown in FIG.

  Since the tip 5b of the fin 5 has a smaller heat capacity than the base 5a, the temperature of the surface of the tip 5b quickly becomes the same temperature as the warmed air. As a result, the water droplets 10 generated on the surface of the tip 5b become smaller or disappear. On the other hand, since the base 5a of the fin 5 is thick, the heat capacity is large compared to the tip 5b. Further, the base 5 a is in contact with the external air through the housing 1. Thereby, the temperature rise of base 5a resulting from contact with warmed air is suppressed, and the surface temperature of base 5a is kept lower than the temperature of the warmed air. As a result, as shown in FIG. 5, the water droplets 10 generated on the surface of the base 5 a grow and become large water droplets 11.

  Then, the water droplets 11 generated on the surface of the fins 5 come in contact with each other, are connected and enlarged by surface tension, and finally become condensed water 12. The condensed water 12 is sucked between the adjacent bases 5a by the surface tension of water as shown in FIG. That is, the condensed water 12 is drawn between the adjacent base portions 5a by capillary action. And the condensed water 12 drawn in between the adjacent base parts 5a is hold | maintained between the adjacent base parts 5a by surface tension of water, as FIG. 7 shows. As a result, the water vapor in the air is removed, and the humidity of the air returned to the electronic component 2 along the upper surface of the printed circuit board 3 is reduced.

  Next, the behavior of the air in the housing 1 when the on-vehicle electronic control device 100 is not in operation will be described.

  When the on-vehicle electronic control device 100 is not in operation, there is no circulation of air in the housing 1 due to the heat generation of the electronic component 2. However, when the vehicle moves from the low land to the high land, the air temperature inside the housing 1 becomes relatively high, for example, when the air temperature outside the housing 1 changes rapidly from high temperature to low temperature due to a weather phenomenon. As a result, water vapor contained in the air in the vicinity of the fins 5 condenses on the surface of the base 5 a of the fins 5 to form condensed water 12 and is held between the bases 5 a. As a result, dripping of the dew condensation water 12 to the printed circuit board 3 is suppressed.

  Here, the dew condensation water 12 held between the bases 5 a of the adjacent fins 5 becomes water vapor due to the rise of the air temperature inside the casing 1 accompanying the rise of the air temperature outside the casing 1. Accordingly, it is not necessary to provide a condensed water discharge mechanism such as a drain port for discharging the condensed water 12 to the outside of the housing 1.

  In the first embodiment, the plurality of fins 5 are installed on the inner wall surface of the ceiling of the housing 1 so as to include the installation area of the electronic component 2 as viewed from above. Thus, in the process of circulating air in the upper space of the printed circuit board 3 in the housing 1, water vapor in the air is condensed on the surface of the fin 5 and removed, and the electronic component 2 is formed along the upper surface of the printed circuit board 3. The humidity of the air returned to the

  Here, when the air temperature outside the housing 1 is lowered, the air temperature on the lower surface side of the printed circuit board 3 in the housing 1 is lowered following the air temperature outside the housing 1. As a result, the printed circuit board 3 is cooled from the lower surface side. However, since the humidity of air returning to the electronic component 2 is low along the upper surface of the printed circuit board 3, the occurrence of condensation on the upper surface of the printed circuit board 3 is suppressed. As a result, the occurrence of migration on the upper surface of the printed circuit board 3 is suppressed, and the occurrence of a short circuit accident of the circuit pattern and further an operation failure of the circuit is suppressed.

  Further, each of the plurality of fins 5 is formed in a band-like body including a base 5 a and a tapered tip 5 b extending downward from the lower end of the base 5 a. The plurality of fins 5 are arranged in parallel, spaced apart from each other by a distance capable of holding the dew condensation water 12 between the adjacent bases 5 a by the surface tension of water. Therefore, when the temperature of the inner wall surface of the ceiling of the housing 1 falls following the decrease in the temperature outside the housing 1, condensation on the fins 5 increases, and the amount of condensed water 12 increases. As described above, even if the amount of the condensed water 12 increases, the condensed water 12 is held between the bases 5 a of the adjacent fins 5, and the dripping to the upper surface of the printed circuit board 3 is suppressed. Furthermore, even if the posture of the housing 1 changes, the condensed water 12 is held between the bases 5 a of the adjacent fins 5, and dripping on the upper surface of the printed circuit board 3 is suppressed. As a result, the occurrence of migration on the upper surface of the printed circuit board 3 is suppressed, and the occurrence of a short circuit accident of the circuit pattern and further an operation failure of the circuit is suppressed.

  Further, the tip 5 b of the fin 5 is formed in a tapered shape. Then, the air warmed by the electronic component 2 flows in between the adjacent base parts 5a smoothly.

  In addition, a plurality of fins 5 are arranged in parallel, spaced apart from one another. Then, the air which flowed in between the adjacent fins 5 flows along the fins 5 in the front-rear direction. Thereby, the air in the upper space of the printed circuit board 3 of the housing 1 is rectified in a fixed direction, and the circulation of the air becomes smooth.

  In addition, the plurality of fins 5 are installed so as to extend in the front-rear direction beyond the installation area of the electronic component 2 when viewed from above. As a result, the rectifying effect of the air in the upper space of the printed circuit board 3 of the housing 1 is increased, and the circulation of the air is further smoothed. Further, the surface area of the fins 5 is increased, and the amount of condensed water 12 generated between the adjacent fins 5 can be increased. Thereby, the humidity of the air returned to the electronic component 2 along the upper surface of the printed circuit board 3 can be reduced.

  In addition, the plurality of fins 5 are arrayed in the width direction of the housing 1 with the longitudinal direction of the strip as the front-rear direction of the housing 1. Therefore, the die cutting at the time of resin-molding the housing 1 becomes easy, the fins 5 can be integrally molded with the housing 1, and the processing cost can be reduced.

  Moreover, since the connector 4 is fitted in the opening part 1a, the housing | casing 1 is not sealed structure. As a result, the pressure inside and outside the housing 1 becomes the same, and the atmospheric pressure sensor IC can be installed in the on-vehicle electronic control device 100. In addition, since the air blocking member, which has been conventionally required, is not necessary, the cost can be reduced.

Second Embodiment
FIG. 8 is a perspective view of the in-vehicle electronic control unit according to the second embodiment of the present invention as seen from the case opening.

In FIG. 8, the heat capacity increasing member 7 is made of the same material as the housing 1 and formed into a rectangular solid, and the housing includes the mounting area of the electronic component 2 and the mounting area of the plurality of fins 5 when viewed from above. It is provided on the outer wall of 1 ceiling.
The other configuration is the same as that of the first embodiment.

  In the on-vehicle electronic control device 101 configured as described above, the heat capacity increasing member 7 includes an area where the installation area of the electronic component 2 and the installation area of the plurality of fins 5 overlap when viewed from above. It is provided on the outer wall surface of the ceiling of the housing 1. Therefore, the volume of the heat transfer path from the fins 5 to the air outside the housing 1 is increased, and the heat capacity of the heat transfer path is increased. Thereby, the temperature rise of the base 5a of the fin 5 by contact with the warmed air is suppressed. As a result, a large temperature difference is maintained between the warmed air and the fins 5, and the water vapor in the air can be effectively removed as the condensed water 12.

  In the second embodiment, the heat capacity increasing member 7 includes the area where the installation area of the electronic component 2 and the installation area of the plurality of fins 5 overlap when viewed from above. Although provided on the outer wall surface of the ceiling, the heat capacity increasing member 7 needs to necessarily include an area where the installation area of the electronic component 2 and the installation area of the plurality of fins 5 overlap when viewed from above Rather, it may be partially overlapped with the area where the installation area of the electronic component 2 and the installation area of the plurality of fins 5 overlap as viewed from above.

  In the second embodiment, although the heat capacity increasing member is made of the same material as the housing 1, the material of the heat capacity increasing member does not have to be the same material as the housing 1; Any material that can increase the heat capacity of the heat transfer path leading to the external air of 1 may be used.

Third Embodiment
FIG. 9 is a perspective view of the in-vehicle electronic control device according to the third embodiment of the present invention as viewed from the side of the case, and FIG. 10 is a case opening of the in-vehicle electronic control device according to the third embodiment of the present invention It is the perspective view seen from the part.

In FIG. 9 and FIG. 10, the printed circuit board 3 is accommodated in the housing 1 with the electronic component 2 facing downward.
The other configuration is the same as that of the first embodiment.

  In the third embodiment, with the operation of the on-vehicle electronic control device 102, the electronic component 2 generates heat. Thereby, the air in the vicinity of the electronic component 2 on the lower side of the printed circuit board 3 is warmed by the heat generation of the electronic component 2, and the housing is along the lower surface of the printed circuit board 3 as shown by the arrows in FIGS. It flows in the longitudinal direction and width direction of 1. Then, the warmed air descends along the inner wall surface, the rear inner wall surface, and the connector 4 opposite to each other in the width direction of the housing 1 and returns to the position just below the electronic component 2 along the bottom surface of the housing 1 . The air returned to the position immediately below the electronic component 2 rises and is warmed by the heat generated in the electronic component 2. Thus, air circulates in the lower space of the printed circuit board 3 in the housing 1. At this time, dew condensation occurs on the bottom of the housing 1 and no dew condensation occurs on the lower surface of the printed circuit board 3.

  On the other hand, in the upper space of the printed circuit board 3 in the housing 1, the air above the electronic component 2 of the printed circuit board 3 is warmed by the heat generated by the electronic component 2. The warmed air ascends as shown by arrows in FIGS. 9 and 10, enters between the adjacent fins 5, and flows in the front-rear direction between the adjacent fins 5. The air that has flowed forward between adjacent fins 5 descends along the connector 4 and returns to the position just above the electronic component 2 along the upper surface of the printed circuit board 3. On the other hand, the air that has flowed backward between adjacent fins 5 descends along the rear inner wall surface of the housing 1 and returns to the position just above the electronic component 2 along the upper surface of the printed circuit board 3. Thus, air circulates in the upper space of the printed circuit board 3 in the housing 1. At this time, the air flowing along the upper surface of the printed circuit board 3 is in a state where the moisture is removed and the humidity is reduced, and the occurrence of condensation on the upper surface of the printed circuit board 3 is suppressed. Further, the water vapor removed from the air becomes condensed water 12 and is held between the bases 5 a of the adjacent fins 5, and the dripping to the upper surface of the printed circuit board 3 is suppressed.

Therefore, also in the third embodiment, the same effect as that of the first embodiment can be obtained.
Also in the third embodiment, the heat capacity increasing member 7 includes the area where the installation area of the electronic component 2 and the installation area of the plurality of fins 5 overlap when viewed from above. It may be provided on the outer wall surface of the ceiling.

  In the above embodiments, the base 5a and the tip 5b are made of the same material, and the thickness of the base 5a and the tip 5b is changed to change the heat capacity of the base 5a and the tip 5b. There is. However, the heat capacity of the base 5a and the tip 5b may be changed by changing the material of the base 5a and the tip 5b.

  Further, in each of the above-described embodiments, a plurality of fins 5 are arranged on the inner wall surface of the ceiling of the housing 1, but the number of fins 5 is 1 if water vapor can be condensed from the warmed air to be effectively removed. It may be a sheet. In addition, as for the number of sheets of the fin 5 from a viewpoint of drip prevention of dew condensation water, it is desirable to set it as multiple sheets.

  Reference Signs List 1 housing, 2 electronic parts (heat generation parts), 3 printed circuit boards, 4 connectors, 5 fins (fins for condensation), 5a base, 5b tip, 7 heat capacity increasing member.

Claims (4)

And
A printed circuit board held in the housing with one side facing up;
A heat generating component mounted on the above printed circuit board,
It is an inner wall surface of a ceiling of the housing, and is provided in a region above the heat-generating component, and includes condensation fins which are brought into contact with air warmed by the heat generation of the heat-generating component .
The condensation fin is a band-like body including a base installed on the inner wall surface of the ceiling, and a tip provided to project downward from the base,
The heat capacity of the base is larger than the heat capacity of the tip,
The base has a constant thickness,
The tip portion has a tapered shape in which the plate thickness gradually decreases from the base downward,
The plurality of condensation fins are arranged in parallel, spaced apart from one another,
A plurality of the condensation fins, the electronic device that is arranged to capable of holding intervals condensed water between said base adjacent the surface tension of water. The condensation fins are on the inner wall surface of the ceiling, the strip is placed beyond the upper region of the heat generating component in the longitudinal direction according to claim 1 Symbol mounting electronic device of. The electronic device according to claim 1, wherein a connector attached to the printed circuit board is attached to an opening of the housing. Heat capacity increasing means is a outer wall surface of the ceiling, either above the region of the heat-generating component, and the claims 1 installed on the opposite side of the region of the installation region of the condensation fin according to claim 3 An electronic device according to any one of the preceding claims.

Images