Electronic device

Abstract

To provide an electronic device capable of naturally cooling an electronic component without providing a duct in a housing.SOLUTION: A PLC 1 comprises: an electronic substrate 15 including a substrate 40 and a radiator which is adhered to a CPU 18 mounted on a first face 40b of the substrate 40 and promotes heat radiations from the CPU 18; and a housing 2 in which the electronic substrate 15 is accommodated. A second face side heat radiation structure is included for promoting heat radiation from the electronic component 15 from the side of the second face 40c of the substrate 40. The second face side heat radiation structure includes at least a housing outside radiator 50, which is disposed outside of the housing 2, and a heat conductive rubber member 41 which promotes heat conduction to the housing outside radiator 50 while being adhered to a mounting rear side area A1 on the rear side of a mounting area of the CPU 18 on a first face 40b of the substrate 40 in all the areas of the second face 40c of the substrate 40. The housing outside radiator 50 includes an opening penetration part 50b which penetrates a penetration opening 6b provided in the housing 2 and holds the heat conductive rubber member 41 with the mounting rear side area A1.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] The present invention relates to electronic devices such as PLCs (Programmable Logic Controllers). [Background technology]

[0002] Conventionally, electronic devices have been known that include an electronic board having a substrate and a heat sink that is in close contact with a first electronic component mounted on a first surface of the substrate and promotes heat dissipation from the first electronic component, and a housing that houses the electronic board.

[0003] For example, Patent Document 1 discloses an electronic device comprising a housing and an electronic circuit board housed within the housing. The electronic circuit board is fixed within the housing with a heat sink (heat sink) heat sink plate extending in the vertical direction of the housing to promote heat dissipation from a first electronic component mounted on the board. The housing has a plurality of air intakes in the bottom wall and a plurality of air outlets in the top wall of the housing. The first electronic component and the heat sink are housed within a hollow duct within the housing. The duct is fixed within the housing with the hollow extending in the vertical direction. Air taken into the duct through the air intake in the bottom wall of the housing is heated by heat dissipation from the heat sink, and rises due to buoyancy. The air is then discharged outside the housing through an air outlet in the top wall of the housing. Patent Document 1 states that an electronic device with such a configuration can efficiently cool the first electronic component while using natural air cooling. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-232287 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the electronic device described in Patent Document 1 has a problem in that providing a duct inside the housing increases costs.

[0006] The present invention has been made in view of the above background, and its object is to provide an electronic device that can naturally cool electronic components without providing a duct inside the housing. [Means for solving the problem]

[0007] The present invention provides an electronic device comprising a substrate and an electronic board having a heat sink that is in close contact with electronic components mounted on a first surface of the substrate to promote heat dissipation from the electronic components, and a housing that houses the electronic board, the electronic device comprising a second surface side heat dissipation structure that promotes heat dissipation from the electronic components from the second surface side of the substrate, the second surface side heat dissipation structure comprising at least an external housing heat sink that is a heat sink arranged outside the housing, and a heat conductive rubber member made of insulating rubber that is in close contact with a mounting back side area that is an area of the entire second surface of the substrate that is located behind the mounting area of the electronic components on the first surface of the substrate to promote heat conduction from the mounting back side area to the external housing heat sink, the external housing heat sink having an opening through-hole that passes through a through-hole provided in the housing and sandwiches the heat conductive rubber member between the external housing heat sink and the mounting back side area. [Effects of the Invention]

[0008] According to the present invention, there is an excellent effect that electronic components can be cooled naturally without providing a duct inside the housing. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing a PLC according to a first embodiment, viewed obliquely from the front. [Figure 2] FIG. 2 is a front view showing the PLC with the front wall removed. [Figure 3] FIG. 2 is a plan view showing the top wall of the housing of the PLC from above. [Figure 4] FIG. 2 is a bottom view showing the bottom wall of the housing from below. [Figure 5]FIG. 2 is a front view showing the main components of the PLC with the front wall removed. [Figure 6] FIG. 2 is an enlarged cross-sectional view of the CPU and its surroundings of the PLC. [Figure 7] 2 is a partially enlarged cross-sectional view showing the CPU, the circuit board, the heat-conducting rubber member, and the left side wall of the PLC. FIG. [Figure 8] FIG. 10 is an enlarged cross-sectional view showing a CPU and its surroundings of a PLC according to a second embodiment. [Figure 9] 10 is a cross-sectional view showing the CPU, the circuit board, the heat-conducting rubber member, and the left side wall of the PLC, each divided into two parts. FIG. [Figure 10] FIG. 2 is a front view showing the main components of the PLC with the front wall removed. [Figure 11] FIG. 11 is an enlarged cross-sectional view showing a PHY of a PLC according to a third embodiment and its surroundings. [Figure 12] This is a view of the mounting surface of the copper inlay part as seen from the PHY side. [Figure 13] 10 is a cross-sectional view showing the PHY, substrate, copper inlay portion, heat-conducting rubber member, and left side wall of the PLC, each divided into two parts. [Figure 14] FIG. 10 is a front view showing a state in which the front wall is removed in the PLC according to the fourth embodiment. [Figure 15] FIG. 2 is an enlarged cross-sectional view of the CPU and its surroundings of the PLC. [Figure 16] FIG. 2 is a front view showing the main components of the PLC with the front wall removed. [Figure 17] FIG. 2 is an exploded perspective view showing the PLC according to the embodiment from the bottom wall side. [Figure 18] FIG. 2 is an exploded perspective view showing the PLC with some parts removed. [Figure 19] FIG. 2 is a perspective view showing a first electronic board of the PLC. [Figure 20] FIG. 2 is a perspective view showing the PLC from the bottom wall side with the main body cover removed. [Figure 21] FIG. 2 is a perspective view partially showing the first electronic board with some electronic components removed. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, various embodiments of a PLC will be described as an electronic device to which the present invention is applied. First, a PLC according to the first embodiment will be described. Fig. 1 is a perspective view of the PLC 1 according to the first embodiment, viewed obliquely from the front. In Fig. 1, arrow Z indicates the direction of gravity. The PLC 1 includes a housing 2, an RS-422A port 21, an RS-485 port 22, a LAN port unit 24, a USB port 26, a micro USB port 27, and the like. The housing 2 includes a front wall 7, a top wall 4, and a right side wall 5.

[0011] 2 is a front view showing the PLC 1 with the front wall (7) removed. In addition to the front wall (7), top wall 4, and right side wall 5, the housing 2 also has a bottom wall 3, a left side wall 6, and a rear wall 8. A first electronic board 15 is disposed within the housing 2. The first electronic board 15 includes a board 40, a CPU (Central Processing Unit) 18 as an electronic component, a power supply module (DC / DC converter) 90 as an electronic component, and a first heat sink 19 as a radiator. The CPU 18 is mounted on a first surface of the board 40. The power supply module 90 is mounted on a second surface of the board 40.

[0012] The first heat sink 19 is made of aluminum and is in close contact with the CPU 18 via a thermally conductive sheet or thermally conductive grease, functioning as a heat sink that promotes heat dissipation from the CPU 18. The first electronic board 15 is fixed inside the housing 2 in an orientation in which the second surface, on which the CPU 18 is not mounted, of the first and second surfaces of the board 40 faces the left side wall 6 of the housing 2.

[0013] FIG. 3 is a plan view showing the top wall 4 of the housing 2 from above. The top wall 4 is provided with a plurality of exhaust openings 4e. The exhaust openings 4e are regular hexagonal in shape. As shown in the figure, the top wall 4 has a honeycomb structure in which a plurality of regular hexagonal exhaust openings 4e are arranged in a staggered pattern like a honeycomb. With this configuration, the top wall 4 can exhibit the desired strength while maximizing the opening ratio of the plurality of exhaust openings 4e, thereby achieving excellent exhaust efficiency.

[0014] FIG. 4 is a bottom view showing the bottom wall 3 of the housing 2 from below. The bottom wall 3 is provided with a plurality of intake openings 3e. The intake openings 3e are regular hexagonal in shape. As shown in the figure, the bottom wall 3 has a honeycomb structure in which a plurality of regular hexagonal intake openings 3e are arranged in a staggered pattern like a honeycomb. With this configuration, the bottom wall 3 can exhibit the desired strength while maximizing the opening ratio of the plurality of intake openings 3e, thereby achieving excellent intake efficiency.

[0015] The larger the diameters of the regular hexagonal intake opening 3e and exhaust opening 4e, the greater the risk of foreign matter entering the housing 2 through the intake opening 3e and exhaust opening 4e. However, if the intake opening 3e and exhaust opening 4e are inscribed in a perfect circle with a diameter of 5 mm, even a common M3-sized machine screw can be prevented from entering the housing 2 through the intake opening 3e and exhaust opening 4e.

[0016] FIG. 5 is a front view showing the main components of the PLC 1 with the front wall (7) removed. The thick arrows in the figure indicate the direction of heat transfer. On the first surface side of the first electronic board 15, heat dissipation from the CPU 18 is promoted as follows: Heat from the CPU 18 is transferred to the first heat sink 19 via a thermally conductive sheet or thermally conductive grease, and then dissipated into the surrounding air from the heat sink 19a. The air, which has become lighter due to the heat dissipation, rises as an ascending air current and is exhausted outside the housing 2 through the exhaust opening 4e in the top wall 4. The ascending air current draws air present below the housing 2 and draws it into the housing 2 through the intake opening 3e in the bottom wall 3. The air then rises toward the heat sink 19a of the first heat sink 19, as indicated by the arrow Ud in the figure. In this way, on the first surface side of the first electronic board 15, an airflow is generated from the intake opening 3e of the bottom wall 3 toward the exhaust opening 4e of the top wall 4, and in the process, the CPU 18 is cooled via the first heat sink 19.

[0017] The housing 2 is made of a metal material such as aluminum, stainless steel, or iron. The PLC 1 has a second-surface-side heat dissipation structure that promotes heat dissipation from the CPU 18 from the second-surface side of the board 40. That is, the PLC 1 promotes heat dissipation from the CPU 18 on the first-surface side of the board 40 by the first heat sink 19, and also promotes heat dissipation from the CPU 18 on the second-surface side of the board 40 by the second-surface-side heat dissipation structure. With the PLC 1 according to the first embodiment having such a configuration, the CPU 18 can be cooled naturally without providing a duct inside the housing 2.

[0018] As the metal material for casing 2, it is particularly preferable to use aluminum from the viewpoint of weight reduction.

[0019] In the PLC 1 according to the first embodiment, the second surface heat dissipation structure described above is composed of a metal housing 2, a heat-conducting rubber member 41 as a heat-conducting member, through-hole vias (40a) described below, etc. The left side wall 6 of the housing 2 has an embossed portion 6a that is recessed toward the inside of the housing 2 on the outer surface of the left side wall 6 and protrudes toward the inside of the housing 2 on the inner surface of the left side wall 6.

[0020] 6 is an enlarged cross-sectional view of the CPU 18 and its surroundings. In the figure, the symbol A1 indicates a mounting back area, which is an area of the entire second surface 40c of the substrate 40 that is located on the back side of the mounting area of the CPU 18 on the first surface 40b of the substrate 40. As shown in the figure, the plate-shaped heat-conducting rubber member 41 that constitutes part of the second-surface-side heat dissipation structure described above is in close contact with the mounting back area A1 on the second surface 40c of the substrate 40, and promotes heat conduction from the mounting back area A1 to the metal housing 2.

[0021] The heat-conducting rubber member 41 is sandwiched between the mounting back area A1 on the second surface 40c of the substrate 40 and the boss 6a on the left side wall 6 of the housing 2. The second-surface heat dissipation structure transfers heat transferred from the CPU 18 to the substrate 40 (including the through-hole vias 40a, which will be described later) to the boss 6a on the left side wall 6 of the housing 2, while removing the heat from the mounting back area A1 on the second surface 40c of the substrate 40 via the heat-conducting rubber member 41. As shown in FIG. 5, a portion of the heat transferred to the boss 6a is released into the air from the boss 6a and rises. Another portion of the heat transferred to the boss 6a is released into the air while traveling in the planar direction of the left side wall 6.

[0022] The heat transferred to the embossed portion 6a is mainly released into the outside air from the left side wall 6, but if the amount of heat is large, it may be transferred from the left side wall 6 to other walls (front wall 7, rear wall 8, top wall 4, right side wall 5) and released into the outside air.

[0023] With the PLC 1 having such a configuration, the metal housing 2 can function as a heat sink. While the example has been described in which the second surface 40c of the substrate 40 faces the left wall 6 among the right wall 5, left wall 6, front wall (7), rear wall 8, bottom wall 3, and top wall 4, the second surface 40c of the substrate 40 may face the right wall 5, the front wall (7), the rear wall 8, or the bottom wall 3. In this case, an embossed portion may be provided on the wall facing the second surface 40c, and a heat-conducting rubber member 41 may be sandwiched between the embossed portion and the mounting backside area A1 of the second surface 40c.

[0024] In the PLC 1, to avoid interference between the various electronic components mounted on the second surface 40c of the circuit board 40 and the various components fixed to the inner surface of the left side wall 6 of the housing 2, the distance between the inner surface of the left side wall 6 and the second surface 40c of the circuit board 40 is generally set with a certain amount of clearance. However, such a setting requires the use of a thick heat-conducting rubber member 41 sandwiched between the second surface 40c of the circuit board 40 and the inner surface of the left side wall 6. The heat-conducting rubber member 41 has a lower thermal conductivity than metal members. Therefore, if the heat-conducting rubber member 41 is thick, the amount of heat transferred from the circuit board 40 to the left side wall 6 via the heat-conducting rubber member 41 decreases, resulting in a decrease in the heat dissipation efficiency of the second surface heat dissipation structure.

[0025] 6, in the PLC1 according to the first embodiment, an embossed portion 6a is provided on the left side wall 6 of the housing 2, and a heat-conducting rubber member 41 is sandwiched between the mounting back side area A1 on the second surface 40c of the substrate 40 and the embossed portion 6a on the left side wall 6. With this configuration, it is possible to use a heat-conducting rubber member 41 with a small thickness, and therefore it is possible to avoid a decrease in heat dissipation efficiency in the second surface side heat dissipation structure that would occur if a thicker heat-conducting rubber member 41 were used.

[0026] The heat-conducting rubber member 41 is deformable. Therefore, even if there is an error between the design value of the distance between the second surface 40c of the substrate 40 and the embossed portion 6a of the left side wall 6 and the actual distance, the heat-conducting rubber member 41 can be reliably brought into close contact with both the second surface 40c of the substrate 40 and the embossed portion 6a of the left side wall 6. Therefore, according to the PLC1, it is possible to avoid a decrease in the heat dissipation efficiency of the second-surface heat dissipation structure due to poor adhesion between the heat-conducting member and the second surface 40c of the substrate 40 or poor adhesion between the heat-conducting member and the embossed portion 6a of the left side wall 6.

[0027] The embossed portion 6a on the left side wall 6 is preferably formed by drawing using a NCT (Numerical Control Turret) punch press with a mold. The distance between the second surface 40c of the substrate 40 and the embossed portion 6a on the left side wall 6 is preferably set in the range of 3 mm to 6 mm.

[0028] The heat-conducting rubber member 41 is in close contact not only with the mounting back area A1 on the second surface 40c of the substrate 40, but also with the area surrounding the mounting back area A1. The heat-conducting rubber member 41 is sandwiched between the power supply module 90 mounted on the second surface 40c of the substrate 40 and the inner surface of the left side wall 6 (the inner surface of the housing) on the side of the embossed portion 6a of the left side wall 6.

[0029] The area of the heat-conducting rubber member 41 that is in close contact with the power supply module 90 absorbs heat from the power supply module 90 and transfers it to the left side wall 6. With this configuration of the PLC1, the second surface side heat dissipation structure can also be used as a heat sink that promotes heat dissipation from the power supply module 90.

[0030] 7 is a partially enlarged cross-sectional view of the CPU 18, the board 40, the heat-conducting rubber member 41, and the left side wall 6. The CPU 18 is a BGA (Ball Grid Array) package with a plurality of terminal pads arranged in an array on its bottom surface. Each terminal pad is soldered independently to the board 40 of the first electronic board 15 by solder 18a.

[0031] The substrate 40 has a plurality of through-hole vias 40a arranged in an array. Each through-hole via 40a functions as part of the second-surface heat dissipation structure and includes a through-hole 40a1, a first land 40a2, a second land 40a3, a peripheral plated portion 40a4, etc. The through-hole 40a1 is a through-hole that penetrates the substrate 40 in the thickness direction.

[0032] The first land 40a2, the second land 40a3, and the peripheral wall plated portion 40a4 are each made of a thin metal layer (e.g., a thin copper layer) formed by plating the substrate 40. The first land 40a2 is a land on the first surface side (first surface 40b side) of the through-hole via 40a and is made of a ring-shaped thin metal layer surrounding the opening of the through-hole 40a1 on the first surface side of the substrate. The second land 40a3 is a land on the second surface side (second surface 40c side) of the through-hole via 40a and is made of a ring-shaped thin metal layer surrounding the opening of the through-hole 40a1 on the second surface side of the substrate. The peripheral wall plated portion 40a4 is a cylindrical thin metal layer that surrounds the through-hole 40a1 and is connected to the first land 40a2 and the second land 40a3.

[0033] Solder 18a is interposed between the terminal pads arranged on the bottom surface of the CPU 18 and the first lands 40a2 of the through-hole vias 40a of the substrate 40. The solder 18a is welded to the terminal pads of the CPU 18 and also to the first lands 40a2 of the through-hole vias 40a. In other words, the terminal pads of the CPU 18 are soldered to the first lands 40a2 of the through-hole vias 40a. The heat-conducting rubber member 41 is in close contact with the second lands 40a3 of each of the multiple through-hole vias 40a.

[0034] Heat from the main body of the CPU 18 is transferred to the heat-conducting rubber member 41 via the solder 18a of the CPU 18 and the first land 40a2, peripheral wall plated portion 40a4, and second land 40a3 of the through-hole via 40a. The first land 40a2, peripheral wall plated portion 40a4, and second land 40a3 are each made of metal, and therefore have higher thermal conductivity than the insulating plate material of the substrate 40. Therefore, with the PLC1, more heat can be transferred from the CPU 18 to the heat-conducting rubber member 41 than in a configuration in which heat from the CPU 18 is transferred to the heat-conducting rubber member 41 only via the insulating plate material of the substrate 40, thereby improving the heat dissipation efficiency (cooling efficiency) of the second-surface heat dissipation structure.

[0035] To improve the insulation between the metal housing 2 and the electronic circuit of the first electronic board 15, an insulating sheet may be interposed between the second surface 40c of the board 40 and the inner surface of the left side wall 6 of the housing 2. This insulating sheet has a through-hole penetrating through it in the thickness direction. The insulating sheet is disposed between the second surface 40c of the board 40 and the inner surface of the left side wall 6 of the housing 2, with the heat-conducting rubber member 41 passing through the through-hole. The insulating sheet does not need to be in contact with both the second surface 40c of the board 40 and the left side wall 6 of the housing 2, and may be disposed in a non-contact state with either of them. The thickness of the insulating sheet is preferably in the range of 0.1 mm to 0.5 mm.

[0036] Next, a second embodiment of the PLC 1 to which the present invention is applied will be described. Unless otherwise specified below, the configuration of the PLC 1 according to the second embodiment is the same as that of the first embodiment. 8 is an enlarged cross-sectional view of the CPU 18 and its surroundings of the PLC 1 according to the second embodiment. The left side wall 6 of the housing 2 of the PLC 1 according to the second embodiment does not have an embossed portion, and its inner surface is a flat surface.

[0037] The first surface of the heat-conducting rubber member 41 of the second-surface-side heat dissipation structure is in close contact with the mounting back area A1 on the second surface 40c of the substrate 40. A heat-conducting metal plate 42 serving as a heat-conducting member is sandwiched between the heat-conducting rubber member 41 and the flat inner surface of the left side wall 6 of the housing 2. The heat-conducting metal plate 42, which has a thickness similar to that of the left side wall 6, is fixed to the left side wall 6 by spot welding, screwing, or the like. As with the embossed portion of the PLC1 according to the first embodiment, the heat-conducting metal plate 42 serving as a metal member can avoid a decrease in heat dissipation efficiency of the second-surface-side heat dissipation structure due to the use of a thick heat-conducting rubber member 41. The distance between the second surface 40c of the substrate 40 and the left side wall 6 is preferably set to a range of 3 mm to 6 mm.

[0038] 9 is a cross-sectional view showing the CPU 18, the board 40, the heat-conducting rubber member 41, and the left side wall 6, each divided into two parts. The CPU 18 is a DIP (Dual In-line Package) package, and has a plurality of connection terminals 18b extending toward the board 40 on each of two opposing side surfaces. Each connection terminal 18b is soldered independently to the board 40 of the first electronic board 15. The bottom surface of the CPU 18 has a heat dissipation pad 18c instead of a terminal pad. Note that the configuration of the CPU 18 is not limited to that of a DIP package.

[0039] The substrate 40 includes a first-side thin metal layer 40d, a second-side thin metal layer 40e, multiple hollows 40f, and multiple cylindrical thin metal layers 40g. The first-side thin metal layer 40d is a thin metal layer (e.g., a copper thin layer) provided on the first side 40b of the substrate 40. The second-side thin metal layer 40e is a thin metal layer (e.g., a copper thin layer) provided on the second side 40c of the substrate 40. Each of the multiple hollows 40f is provided in the substrate 40 between the first-side thin metal layer 40d and the second-side thin metal layer 40e and extends in the thickness direction of the substrate, and is cylindrical in shape. Each of the multiple cylindrical thin metal layers 40g forms the peripheral wall of the hollow 40f and is a thin metal layer (e.g., a copper thin layer) connected to the first-side thin metal layer 40d and the second-side thin metal layer 40e.

[0040] The first-surface thin metal layer 40d, the second-surface thin metal layer 40e, and the cylindrical thin metal layer 40g are each formed on the substrate 40 by, for example, plating. For example, 10 to 20 pairs of hollows 40f and the cylindrical thin metal layers 40g surrounding them are provided and arranged in an array. The first-surface thin metal layer 40d, the second-surface thin metal layer 40e, the plurality of hollows 40f, and the plurality of cylindrical thin metal layers 40g each constitute a part of the second-surface heat dissipation structure.

[0041] The metallic heat dissipation pad 18c of the CPU 18 is soldered to the first surface thin metal layer 40d of the substrate 40. The heat conductive rubber member 41 sandwiched between the second surface 40c of the substrate 40 and the heat conductive metal plate 42 is in close contact with the second surface thin metal layer 40e of the substrate 40.

[0042] Heat from the main body of the CPU 18 is transferred to the left side wall 6 via the heat dissipation pad 18c of the CPU 18, the first-surface thin metal layer 40d, the cylindrical thin metal layer 40g, and the second-surface thin metal layer 40e of the substrate 40, the heat-conducting rubber member 41, and the heat-conducting metal plate 42. The first-surface thin metal layer 40d, the cylindrical thin metal layer 40g, and the second-surface thin metal layer 40e are each made of metal, and therefore have higher thermal conductivity than the insulating plate material of the substrate 40. Therefore, with the PLC1, more heat can be transferred from the CPU 18 to the heat-conducting rubber member 41 than in a configuration in which heat from the CPU 18 is transferred to the heat-conducting rubber member 41 only via the insulating plate material of the substrate 40, thereby improving the heat dissipation efficiency (cooling efficiency) of the second-surface heat dissipation structure.

[0043] In order to improve the insulation between the metal housing 2 and the electronic circuit of the first electronic board 15, an insulating sheet may be interposed between the second surface 40c of the board 40 and the inner surface of the left side wall 6 of the housing 2, as in the first embodiment. The thickness of the insulating sheet is preferably in the range of 0.1 mm to 0.5 mm.

[0044] 10 is a front view showing the main components of the PLC 1 with the front wall 7 removed. The thick arrows in the figure indicate the direction of heat transfer. On the first surface side of the first electronic board 15, the first heat sink 19 promotes heat dissipation from the CPU 18, as in the first embodiment.

[0045] The second surface heat dissipation structure is composed of a metal housing 2, a heat-conducting rubber member 41 as a heat-conducting member, a heat-conducting metal plate 42 as a heat-conducting member and a metal member, a first surface thin metal layer (40d in FIG. 9), a second surface thin metal layer (40e in FIG. 9), a cylindrical thin metal layer (40g in FIG. 9), etc. The second surface heat dissipation structure transfers heat transferred from the CPU 18 to the board 40 (including each thin metal layer) to the left side wall 6 via the heat-conducting rubber member 41 and the heat-conducting metal plate 42. The heat transferred to the left side wall 6 is released into the outside air and rises. With a PLC 1 configured as described above, the metal housing 2 can function as a heat sink.

[0046] Depending on the layout of the components within the housing 2, multiple embossed portions may be provided on each wall (3, 4, 5, 6, 7, 8) of the housing 2. In the PLC 1 according to the first embodiment, if multiple embossed portions are provided by drawing in addition to the embossed portion (6a) of the second-surface heat dissipation structure, this may cause distortion in the left side wall 6, degrading the dimensional accuracy of each portion of the left side wall 6. For example, if multiple embossed portions measuring 20 mm × 20 mm × 1.5 mm in height are provided by drawing on the left side wall 6, which measures 100 mm × 150 mm, in order to individually cool each of the multiple electronic components, this may cause significant distortion of the left side wall 6. In this case, only one embossed portion may be formed to suppress distortion, resulting in a problem in which only one electronic component can be cooled.

[0047] On the other hand, according to the PLC1 of the second embodiment, the embossed portion of the second surface side heat dissipation structure is not provided on the left side wall 6, so that multiple electronic components can be cooled by the second surface side heat dissipation structure without distorting the left side wall 6 by drawing.

[0048] Next, a third embodiment of the PLC 1 to which the present invention is applied will be described. Unless otherwise specified below, the configuration of the PLC 1 according to the third embodiment is the same as that of the first embodiment. 11 is an enlarged cross-sectional view of PHY 28 and its surroundings in PLC 1 according to the third embodiment. The left side wall 6 of the housing 2 of PLC 1 according to the third embodiment does not have an embossed portion, and its inner surface is flat. PHY 28 is disposed on the second surface side (left side wall 6 side) of second heat sink 29.

[0049] The heat-conducting rubber member 41 of the second-surface-side heat dissipation structure has its first surface in close contact with the mounting back area A2 on the second surface 40c of the substrate 40. A heat-conducting metal plate 42 serving as a heat-conducting member is sandwiched between the heat-conducting rubber member 41 and the flat inner surface of the left side wall 6 of the housing 2. The heat-conducting metal plate 42, which has a thickness similar to that of the left side wall 6, is fixed to the left side wall 6 by spot welding, screwing, or the like. As with the embossed portion of the PLC1 according to the first embodiment, the heat-conducting metal plate 42 serving as a metal member can avoid a decrease in heat dissipation efficiency in the second-surface-side heat dissipation structure due to the use of a thick heat-conducting rubber member 41. The distance between the second surface 40c of the substrate 40 and the left side wall 6 is preferably set within a range of 3 mm to 6 mm.

[0050] 12 is a view of the mounting surface of the copper inlay portion 43 as seen from the PHY 28 side. A cylindrical copper inlay portion 43 having the same thickness as the substrate 40 is disposed on the left side wall 6 side of the heat dissipation pad 28c. The diameter of the copper inlay portion 43 is approximately the same as the length of one side of the heat dissipation pad 28c, and is at least 90% or more of the length of one side of the heat dissipation pad 28c.

[0051] In addition to the copper inlay portion 43, four vias 40v are formed in the substrate 40 adjacent to the heat dissipation pad 28c. The vias 40v electrically connect the first surface thin metal layer 40d and the second surface thin metal layer 40e of the substrate 40. The copper inlay portion 43 is also electrically connected to the first surface thin metal layer 40d and the second surface thin metal layer 40e.

[0052] The metallic heat dissipation pad 28c of the PHY 28 is soldered to the first-surface thin metal layer 40d and the copper inlay portion 43 of the substrate 40. Specifically, after the resist is removed to expose the first-surface thin metal layer 40d (and the second-surface thin metal layer 40e) of the substrate 40, the heat dissipation pad 28c is soldered to the first-surface thin metal layer 40d and the copper inlay portion 43 of the substrate 40.

[0053] FIG. 13 is a cross-sectional view showing the PHY 28, the substrate 40, the copper inlay portion 43, the heat-conducting rubber member 41, and the left side wall 6, each divided into two parts. The second heat sink 29 in FIG. 11 is omitted in FIG. 13. FIG. 13 is a cross-sectional view taken along line XX in FIG. 12. The PHY 28 has a QFN (Quad Flat No-lead package) or QFP (Quad Flat Package) configuration. In this embodiment, the QFN configuration will be described as an example. The bottom surface of the PHY 28 has a heat dissipation pad 28c, as described above.

[0054] As described above, the copper inlay portion 43 is disposed on the board 40 in most of the position sandwiched between the heat dissipation pad 28c and the heat conductive rubber member 41. In this manner, in this embodiment, the copper inlay portion 43, which has a higher heat dissipation effect, is disposed on the board 40 instead of the thermal via.

[0055] At a position sandwiched between the heat dissipation pad 28c of the substrate 40 and the heat conductive rubber member 41, where electrical connection between the heat dissipation pad 28c and the substrate 40 is essential, there is a via 40v including a first surface thin metal layer 40d, a second surface thin metal layer 40e, a hollow 40f, a cylindrical thin metal layer 40g, etc. This embodiment is configured to have four vias 40v. The specific configuration of each part that makes up the via 40v is omitted as it is the same as in the second embodiment.

[0056] The heat-conducting rubber member 41 sandwiched between the second surface 40c of the substrate 40 and the heat-conducting metal plate 42 is in close contact with the thin metal layer 40e on the second surface of the substrate 40.

[0057] Heat from the body of the PHY 28 is transferred to the left sidewall 6 via the thermal pad 28c of the PHY 28, the copper inlay 43, the thermally conductive rubber member 41, and the thermally conductive metal plate 42. At the same time, in the area where the copper inlay 43 is not welded to the thermal pad 28c, heat from the body of the PHY 28 is transferred to the left sidewall 6 via the thermal pad 28c of the PHY 28, the first-surface thin metal layer 40d, the cylindrical thin metal layer 40g, and the second-surface thin metal layer 40e of the substrate 40, the thermally conductive rubber member 41, and the thermally conductive metal plate 42. The first-surface thin metal layer 40d, the cylindrical thin metal layer 40g, and the second-surface thin metal layer 40e are each made of metal, and therefore have higher thermal conductivity than the insulating plate material of the substrate 40. Thus, the location where the copper inlay 43 is located can reduce the temperature rise by approximately 5 K compared to when a thermal via is used. Furthermore, since the vias 40v are made of metal, they have a higher thermal conductivity than the insulating plate material of the substrate 40.

[0058] Therefore, according to PLC1, more heat can be transferred from PHY28 to the heat-conducting rubber member 41 than in a configuration in which the heat from PHY28 is transferred to the heat-conducting rubber member 41 only through the insulating plate material of the substrate 40, thereby improving the heat dissipation efficiency (cooling efficiency) of the second surface side heat dissipation structure.

[0059] In order to improve the insulation between the metal housing 2 and the electronic circuit of the first electronic board 15, an insulating sheet may be interposed between the second surface 40c of the board 40 and the inner surface of the left side wall 6 of the housing 2, as in the first embodiment. The thickness of the insulating sheet is preferably in the range of 0.1 mm to 0.5 mm.

[0060] As described above, the configuration of the PLC1 of the third embodiment promotes heat transfer similarly to the configuration of the PLC1 of the second embodiment. Specifically, on the first surface side of the PHY 28, the second heat sink 29 promotes heat dissipation from the PHY 28, similar to the first embodiment. Meanwhile, on the second surface side, heat transferred from the PHY 28 to the substrate 40 (including each thin metal layer) is transferred to the left side wall 6 via the heat-conducting rubber member 41 and the heat-conducting metal plate 42. The heat transferred to the left side wall 6 is released into the outside air and rises. This configuration of the PLC1 allows the metal housing 2 to function as a heat sink. In particular, the copper inlay portion 43 arranged on the substrate 40 has a higher thermal conductivity than thermal vias, thereby improving the heat dissipation effect compared to the structure exemplified in the second embodiment. Meanwhile, in areas where electrical connection is essential between the thermal dissipation pad 28c and the ground pattern of the substrate 40, the vias 40v, which provide a more reliable electrical connection than copper inlays, are arranged, thereby ensuring the reliability of the electronic circuit.

[0061] Furthermore, in the PLC1 according to the third embodiment, the embossed portion of the second-surface-side heat dissipation structure is not provided on the left side wall 6, but this is not limited to this. For example, as in the first embodiment, the embossed portion 6a may be provided on the left side wall 6 by drawing. Thus, according to the third embodiment, in particular, by providing the copper inlay portion 43, the electronic components can be cooled more efficiently by the second-surface-side heat dissipation structure.

[0062] Next, a description will be given of a PLC 1 according to a fourth embodiment. Unless otherwise specified below, the configuration of the PLC 1 according to the fourth embodiment is the same as that of the first embodiment. 14 is a front view showing the PLC 1 with the front wall 7 removed. The PLC 1 includes an external-housing heat sink 50 as an external-housing radiator disposed outside the housing 2. The external-housing heat sink 50 includes a heat sink plate 50a and a through-hole 50b, and is fixed to the outer surface of the left side wall 6. The left side wall 6 of the housing 2 includes a through-hole 6b. Of the entire external-housing heat sink 50, only the through-hole 50b passes through the through-hole 6b in the left side wall 6 and is positioned inside the housing 2, as shown in the figure. The through-hole 50b of the external-housing heat sink 50 sandwiches a thermally conductive rubber member 41 between itself and the mounting back-side area A1 of the second surface 40c of the substrate 40.

[0063] FIG. 15 is an enlarged cross-sectional view of the CPU 18 and its surroundings. The CPU 18 is a BGA package, as in the first embodiment. The substrate 40 includes a plurality of through-hole vias 40a arranged in an array, as in the first embodiment. A plate-shaped heat-conducting rubber member 41, which constitutes part of the second-surface heat dissipation structure, is sandwiched between the second surface 40c of the substrate 40 and the opening 50b of the external heat sink 50, while being in close contact with the back-side mounting area A1 on the second surface 40c of the substrate 40. The heat-conducting rubber member 41 promotes heat conduction from the back-side mounting area A1 on the second surface 40c of the substrate 40 to the external heat sink 50, which is made of metal (e.g., aluminum).

[0064] The heat-conducting rubber member 41 is sandwiched between the power supply module 90 mounted on the second surface 40c of the substrate 40 and the main body of the external-housing heat sink 50, on the side of the opening through portion 50b of the external-housing heat sink 50. The area of the heat-conducting rubber member 41 that is in close contact with the power supply module 90 absorbs heat from the power supply module 90 and transfers it to the external-housing heat sink 50. With the PLC1 configured as described above, the external-housing heat sink 50 can also be used as a heat sink that promotes heat dissipation from the power supply module 90.

[0065] 16 is a front view showing the main components of the PLC 1 with the front wall (7) removed. The thick arrows in the figure indicate the direction of heat transfer. On the first surface side of the first electronic board 15, the first heat sink 19 promotes heat dissipation from the CPU 18, as in the first embodiment.

[0066] In the PLC1 according to the fourth embodiment, the second surface side heat dissipation structure is composed of a heat conductive rubber member 41, which is a heat conductive member, through-hole vias 40a, an external housing heat sink 50, and the like. The second surface side heat dissipation structure transfers heat transferred from the CPU 18 to the board 40 (including the through-hole vias 40a) to the external housing heat sink 50 via the heat conductive rubber member 41. The heat transferred to the external housing heat sink 50 is released into the outside air and rises. With the PLC1 having such a configuration, by using the external housing heat sink 50 with a structure suitable for heat dissipation, it is possible to improve heat dissipation efficiency (cooling efficiency) compared to the first and second embodiments in which the housing 2 also functions as a heat sink.

[0067] In order to improve the insulation between the metal housing 2 and the electronic circuit of the first electronic board 15, an insulating sheet may be interposed between the second surface 40c of the board 40 and the inner surface of the left side wall 6 of the housing 2, as in the first embodiment.

[0068] In the fourth embodiment, the housing 2 does not also function as a heat sink, so it is not necessarily required to make the housing 2 from a metal material. However, since the external heat sink 50 is fixed to the left side wall 6, the housing 2 may be made from a metal material to provide the strength to withstand its weight. In this case, it is possible to use an inexpensive metal material that does not have excellent heat resistance (for example, iron or stainless steel).

[0069] Next, an example will be described in which a more characteristic configuration is added to the PLC1 according to the first, second, third, or fourth embodiment. Unless otherwise specified below, the configuration of the PLC1 according to the example is the same as that of the first, second, third, or fourth embodiment.

[0070] PLC1 is designed to be used with the bottom wall 3 facing downward (the direction of gravity Z) and the top wall 4 facing upward. The following describes the configuration of PLC1 according to the embodiment using the figures. The term "vertical direction" refers to the direction in which the bottom wall 3 and the top wall 4 face each other, regardless of the orientation of PLC1 shown in each figure. The term "upward" refers to the direction facing "upward" along the vertical direction, regardless of the orientation of PLC1 shown in each figure. The term "downward" refers to the direction facing "downward" along the vertical direction, regardless of the orientation of PLC1 shown in each figure. The term "left-right direction" refers to the direction in which the left wall 6 and the right wall 5 face each other, regardless of the orientation of PLC1 shown in each figure. The term "front-rear direction" refers to the direction in which the front wall 7 and the rear wall 8 face each other, regardless of the orientation of PLC1 shown in each figure.

[0071] 17 is an exploded perspective view showing the PLC 1 from the side of the bottom wall 3. The bottom wall 3 is provided with a plurality of intake openings 3e as openings arranged in a honeycomb structure.

[0072] The top wall 4 is provided with a plurality of exhaust openings 4e as openings arranged in a honeycomb structure.

[0073] The PLC 1 includes a first electronic board 15, a second electronic board 16, and a third electronic board 17. Each of the first electronic board 15, the second electronic board 16, and the third electronic board 17 includes a board on which wiring patterns, lands, through-holes, etc. are formed, and a plurality of electronic components mounted on the board. The configuration of the first electronic board 15 is the same as that of the first, second, third, or fourth embodiment.

[0074] Electronic components such as the CPU 18 and the PHYs 28 of the three LAN port units 24 are mounted on a first surface of the first electronic board 15. Each of the three LAN port units 24 has two Ethernet ports 24a. A first heat sink 19 made of aluminum is fixed to the first surface of the first electronic board 15. The first heat sink 19 is in close contact with the CPU 18 via a thermally conductive sheet or thermally conductive grease and functions as a first heat sink that promotes heat dissipation from the CPU 18. The first electronic board 15 is fixed inside the housing 2 with the second surface, which does not have the CPU 18 mounted thereon, facing the left wall 6 of the housing 2.

[0075] Electronic components such as an RS-422A port 21 and an RS-485 port 22 are mounted on a first surface of the second electronic board 16. The second electronic board 16 is fixed inside the housing 2 in an orientation in which the second surface, which does not have the RS-422A port 21 and the like mounted thereon, faces the first surface of the first electronic board 15.

[0076] Electronic components such as a 5-pin connector 23 are mounted on a first surface of the third electronic board 17. A power supply circuit is provided on the third electronic board 17. The third electronic board 17 is fixed inside the housing 2 in an orientation in which the first surface, of the first and second surfaces, on which the 5-pin connector 23 and other components are mounted, faces the first surface of the second electronic board 16.

[0077] The first electronic board 15, the second electronic board 16, and the third electronic board 17 form a board unit with a three-tier structure arranged in the "left-right direction." Note that the number of tiers of electronic boards in the board unit is not limited to three, and may be any number of tiers as long as it is two or more tiers including at least the first electronic board 15 and the second electronic board 16.

[0078] 18 is an exploded perspective view showing PLC1 with some components removed. As shown in Fig. 18, a USB port 26 and three LAN port units 24 are mounted on the front end of the first surface of the first electronic board 15 in the front-to-rear direction, and are aligned in the up-down direction.

[0079] The first heat sink 19 fixed to the first electronic board 15 includes a plurality of heat dissipation plates 19a. The first electronic board 15 is fixed inside the housing 2 in an orientation in which the heat dissipation plates 19a of the first heat sink 19 extend in the "up-down direction."

[0080] Fig. 19 is a perspective view showing the first electronic board 15. The first electronic board 15 shown in Fig. 19 is inside the PLC 1 in a normal position. Therefore, the multiple heat dissipation plates 19a of the first heat sink 19 shown in Fig. 19 extend in the "up-down direction" and also in the direction of gravity Z.

[0081] The multiple heat sinks 19a of the first heat sink 19 are arranged in a matrix on an imaginary plane extending in the "up-down direction" and "front-rear direction." Of the multiple heat sinks 19a arranged in a matrix, the distance between adjacent heat sinks 19a arranged in the "up-down direction" is about several millimeters. In contrast, the distance between adjacent heat sinks 19a arranged in the "front-rear direction" is about 1 cm, and an inter-plate space S is formed between adjacent heat sinks 19a.

[0082] On the first surface of the first electronic board 15, three PHYs (Physical Layers) 28 are mounted at predetermined intervals along the up-down direction in front of the CPU 18 in the front-to-back direction. The PHYs 28 are physical layers of an Ethernet controller electrically connected to the LAN port unit 24. The three PHYs 28 are an example of electronic components according to the present invention.

[0083] A second heat sink 29 made of aluminum is fixed to the first surface of the first electronic board 15 with its heat sink 29a extending in the vertical direction. The second heat sink 29 is in close contact with each of the three PHYs 28 via thermally conductive adhesive or thermally conductive grease to promote heat dissipation from the three PHYs 28. The heat sink 29a of the second heat sink 29 faces the heat sinks 19a of the first heat sink 19. The heat sink 29a also faces a space below the first heat sink 19 in the vertical direction. Hereinafter, this space will be referred to as the "lower space." Note that the number of PHYs 28 is merely an example and does not necessarily have to be three. For example, six PHYs 28 may be mounted, or any other number may be mounted.

[0084] When the temperature of the first heat sink 19 rises due to heat conduction from the CPU 18, the air in the inter-plate space S of the first heat sink 19 rises in temperature due to heat dissipation from the heat sink 19a. The heated air gains buoyancy and becomes an ascending air current, rising straight upward while being guided by the heat sink 19a extending in the "vertical direction." As a result, a "lower space" located "below" the first heat sink 19 becomes negative pressure, and air outside the housing 2 is drawn into the "lower space" through the intake opening 3e in the bottom wall 3 shown in FIG. 17.

[0085] Air taken into the "lower space" through the intake opening 3e of the bottom wall 3 is attracted by the ascending air current generated in the inter-plate space S of the first heat sink 19 shown in FIG. 19 and rises toward the inter-plate space S. At this time, the movement of the air toward the heat sink 29a of the second heat sink 29 is hindered by the heat sink 29a, suppressing vortexes, and the heat sink 29a guides the air to move linearly from "below" to "upward." Therefore, within the housing 2, the airflow passing through the intake opening (3e in FIG. 17), the "lower space," the inter-plate space S, and the exhaust opening (4e in FIG. 17) flows smoothly from "below" to "upward." Therefore, according to the PLC 1, the CPU 18 can be cooled by natural airflow without providing a duct inside the housing 2.

[0086] 17, the second electronic board 16 is fixed inside the housing 2 in an orientation in which the second surface faces the first surface of the first electronic board 15. The air taken into the housing 2 through the intake opening 3e of the bottom wall 3 is prevented from moving toward the second electronic board 16 by the second electronic board 16, thereby suppressing vortexes. In addition, the second electronic board 16 guides the air to move linearly from "below" to "upward." Therefore, according to the PLC1, the second electronic board 16 further promotes a smooth flow of air from "below" to "upward," thereby further improving the efficiency of natural cooling of the CPC 19.

[0087] 20 is a perspective view showing the three electronic boards from the bottom wall side (3 in FIG. 17). Inside the housing (2 in FIG. 1), the third electronic board 17 is fixed in an orientation in which its first surface faces the first surface of the second electronic board 16. A first connector 30 is mounted on the first surface of the third electronic board 17. Meanwhile, a second connector 31 is mounted on the first surface of the second electronic board 16. When the third electronic board 17 and the second electronic board 16 are connected via the hexagonal support 34, the first connector 30 of the third electronic board 17 and the second connector 31 of the second electronic board 16 are connected, enabling communication between the third electronic board 17 and the second electronic board 16.

[0088] The second electronic board 16 is fixed in a position where its second surface faces the first surface of the first electronic board 15. A third connector 32 is mounted on the second surface of the second electronic board 16. Meanwhile, a fourth connector 33 is mounted on the first surface of the first electronic board 15. When the second electronic board 16 and the first electronic board 15 are connected via the hexagonal support 34, the third connector 32 of the second electronic board 16 and the fourth connector 33 of the first electronic board 15 are connected, enabling communication between the second electronic board 16 and the first electronic board 15. Note that the direction in which the third connector 32 and the fourth connector 33 are connected is along the opposing direction of the first electronic board 15 and the second electronic board 16, as shown in FIG. 20 .

[0089] The side surfaces of the third connector 32 and the fourth connector 33 and the heat sink 29a of the second heat sink 29 face each other with the first heat sink 19 positioned therebetween. In this configuration, as shown in Fig. 20, the first electronic board 15, the heat sink 29a of the second heat sink 29, the second electronic board 16, the third connector 32, and the fourth connector 33 surround the first heat sink 19 like a duct. Therefore, according to the PLC1, a chimney effect is produced, and sufficient ventilation can be obtained, similar to a configuration in which the first heat sink is disposed inside a duct.

[0090] 21 is a perspective view partially illustrating the first electronic board 15 with some electronic components removed. As shown in FIG. 21, in the area above the CPU 18 on the first surface of the first electronic board 15, a plate-shaped memory module 35 that communicates with the CPU 18 and a covering member 36 made of a resin sheet are arranged. The memory module 35 is attached to the first electronic board 15 in an orientation in which the first surface of the memory module 35 faces the first surface of the first electronic board 15. The covering member 36 covers the "lower" side of the memory module 35 and the second surface of the memory module 35.

[0091] In this configuration, the plate-like memory module 35 is oriented to face the first electronic board 15, so that the ascending air current that passes through the inter-plate space (S in FIG. 20) of the first heat sink 19 does not strike the first or second surface of the memory module. Therefore, PLC1 can prevent a decrease in ventilation efficiency caused by the ascending air current striking the first or second surface of the memory module.

[0092] The memory module 35 covered by the covering member 36 does not come into direct contact with the rising air current. Therefore, according to the PLC 1, it is possible to prevent the temperature of the memory module 35 from rising due to contact with the heated rising air current. For convenience, the covering member 36 is not shown in Figures 18 and 19.

[0093] The present invention is not limited to the above-described embodiments and examples, and configurations different from those of the embodiments and examples may be adopted within the scope of the application of the configuration of the present invention. The present invention provides unique effects for each of the aspects described below.

[0094] [First aspect] The first aspect is an electronic device (e.g., PLC1) including a substrate (e.g., substrate 40), an electronic board (e.g., first electronic board 15) having a heat sink (e.g., second heat sink 29) that is in close contact with an electronic component (e.g., PHY 28) mounted on a first surface (e.g., first surface 40b) of the substrate to promote heat dissipation from the electronic component, and a housing (e.g., housing 2) that houses the electronic board, and further including a second surface side heat dissipation structure that promotes heat dissipation from the electronic component from a second surface (e.g., second surface 40c) of the substrate, wherein the second surface side heat dissipation structure: The second surface side heat dissipation structure includes at least the metal housing, and a heat conductive member (for example, a heat conductive rubber member 41) that is in close contact with a mounting back area (for example, a mounting back area A2) that is an area of the entire second surface of the board that is located behind the mounting area of the electronic component on the first surface of the board, and that promotes heat conduction from the mounting back area to the housing, and the second surface side heat dissipation structure includes a heat conductive rubber member made of insulating rubber as the heat conductive member, and a metal member made of metal that is fixed to the inner surface of the housing and is interposed between the inner surface and the heat conductive rubber member. a first surface thin metal layer (e.g., first surface thin metal layer 40d) which is a thin metal layer provided on the first surface of the substrate; a second surface thin metal layer (e.g., second surface thin metal layer 40e) which is a thin metal layer provided on the second surface of the substrate; and a plurality of hollows (e.g., hollows 40a, 40b) which are provided in the substrate in a manner extending in the thickness direction of the substrate between the first surface thin metal layer and the second surface thin metal layer. 0f), and a plurality of cylindrical thin metal layers (e.g., cylindrical thin metal layers 40g) that individually form the hollow peripheral walls of each and are connected to the first surface thin metal layer and the second surface thin metal layer, the electronic component has a heat dissipation pad (e.g., heat dissipation pad 18c) on its bottom surface, the heat dissipation pad is soldered to the copper inlay portion and the first surface thin metal layer with the first surface thin metal layer and the second surface thin metal layer exposed, and the heat conductive rubber member is in close contact with the second surface thin metal layer.

[0095] In the first aspect, in addition to promoting heat dissipation from electronic components on the first surface side of the substrate by a heat sink, heat dissipation from electronic components on the second surface side of the substrate is promoted by a second surface side heat dissipation structure. According to this first aspect, electronic components can be naturally cooled without providing a duct inside the housing. Furthermore, heat from the electronic components can be transferred to the housing via the substrate and the thermally conductive member. Furthermore, since the embossed portion of the second surface side heat dissipation structure is not provided on the housing, multiple electronic components can be cooled by the second surface side heat dissipation structure without distorting the housing through drawing. Furthermore, compared to a configuration in which heat from electronic components is transferred to the thermally conductive rubber member only through the insulating plate material of the substrate, more heat can be transferred from the electronic components to the thermally conductive rubber member, thereby improving the heat dissipation efficiency (cooling efficiency) of the second surface side heat dissipation structure. Furthermore, the copper inlay portion has lower thermal resistance than the portion with the cylindrical thin metal layer, further reducing thermal resistance. Furthermore, the cylindrical thin metal layer provides a more reliable electrical connection than the copper inlay portion, so that the electrical connection with the heat dissipation pad can be ensured, resulting in a highly reliable electronic circuit.

[0096] [Second aspect] The second aspect has the configuration of the first aspect, and is characterized in that the housing has an embossed portion (e.g., embossed portion 6a on the left side wall 6) that is recessed toward the inside of the housing on the outer surface of the housing and protrudes toward the inside of the housing on the inner surface of the housing, and the heat conduction member is a heat conduction rubber member (e.g., heat conduction rubber member 41) made of insulating rubber, and is sandwiched between the mounting back side area of the board and the embossed portion.

[0097] According to the second aspect, heat from the electronic component is transferred to the substrate, the heat-conducting rubber member, and the housing, allowing the housing to double as a heat sink. Furthermore, since a thin heat-conducting rubber member can be used, it is possible to avoid a decrease in the heat dissipation efficiency (cooling efficiency) of the second-surface-side heat dissipation structure that would occur if a thicker heat-conducting rubber member were used. Additionally, it is possible to avoid a decrease in the heat dissipation efficiency (cooling efficiency) of the second-surface-side heat dissipation structure that would occur if a poor contact between the heat-conducting member and the second surface of the substrate or between the heat-conducting member and the housing.

[0098] [Third aspect] The third aspect has the configuration of the first or second aspect, and is characterized in that the second surface side heat dissipation structure comprises at least an external housing heat sink (e.g., an external housing heat sink 50) that is a heat sink arranged outside the housing, and a heat-conducting rubber member made of insulating rubber that is in close contact with a mounting back area, which is an area of the entire second surface of the board that is located behind the mounting area of the electronic components on the first surface of the board, and that promotes heat conduction from the mounting back area to the external housing heat sink, and the external housing heat sink has an opening-through portion (e.g., opening-through portion 50b) that passes through a through opening (e.g., through opening 6b) provided in the housing and sandwiches the heat-conducting rubber member between the external housing heat sink and the mounting back area.

[0099] According to the third aspect, by using an external heat sink with a structure suitable for heat dissipation as part of the second surface side heat dissipation structure, the heat dissipation efficiency (cooling efficiency) of the second surface side heat dissipation structure can be improved compared to the first and second aspects in which the housing is also used as a heat sink.

[0100] [Fourth aspect] The fourth aspect is characterized in that the housing has the configuration of any one of the first to third aspects, and that the top wall (e.g., top wall 4) or bottom wall (e.g., bottom wall 3) of the housing has a honeycomb structure formed by arranging regular hexagonal openings (e.g., exhaust openings 4e or intake openings 3e).

[0101] According to the fourth aspect, it is possible to maximize the opening ratio of the plurality of openings while allowing the top wall or bottom wall to exhibit the desired strength, thereby achieving excellent ventilation efficiency. [Industrial Applicability]

[0102] The present invention is applicable to electronic devices that include a control unit, such as a PLC. [Explanation of symbols]

[0103] 1: PLC (electronic device), 2: housing (part of second-surface side heat dissipation structure), 3: bottom wall (part of second-surface side heat dissipation structure), 3e: intake opening, 4: top wall (part of second-surface side heat dissipation structure), 4e: exhaust opening, 5: right-hand side wall (part of second-surface side heat dissipation structure, side wall of housing), 6: left-hand side wall (part of second-surface side heat dissipation structure, side wall of housing), 6a: embossed portion, 6b: through opening, 15: first electronic board, 16: second electronic board, 18: CPU (electronic component), 18a: solder, 18b: connection terminal, 18c: heat dissipation pad, 19: first heat sink (heat sink), 19a: heat sink, 24: LAN port unit, 28: PHY (electronic component), 29: second heat sink (heat sink), 29a: heat sink, 32: third connector, 33: fourth connector, 35: memory module, 36: covering member, 40: substrate, 40a: through-hole via (part of second surface side heat dissipation structure), 40a1: through-hole, 40a2: first land (land on first surface side), 40a3: second land (land on second surface side), 40a4: peripheral wall plated portion, 40b: first surface, 40c: second surface, 40d: first surface thin metal layer, 40e: second surface thin metal layer, 40f: hollow, 40g: cylindrical thin metal layer, 41: thermally conductive rubber member (part of second surface side heat dissipation structure thermally conductive member), 43: copper inlay portion, 50: external housing heat sink (external housing heat sink), 50a: heat sink, 50b: opening through portion, 90: power supply module (electronic component), A1: Back side area, A2: Back side area

Claims

1. An electronic device comprising: an electronic substrate having a substrate and a heat sink that is in close contact with an electronic component mounted on a first surface of the substrate to promote heat dissipation from the electronic component; and a housing that houses the electronic substrate, a second surface side heat dissipation structure that promotes heat dissipation from the electronic component from the second surface side of the substrate; The second surface side heat dissipation structure includes at least an external heat sink that is a heat sink disposed outside the housing; a thermally conductive rubber member made of insulating rubber that is in close contact with a mounting rear region, which is a region of the entire second surface of the substrate that is located behind the mounting region of the electronic component on the first surface of the substrate, and that promotes heat conduction from the mounting rear region to the external heat sink; The electronic device is characterized in that the external heat sink has an opening-through portion that passes through a through opening provided in the housing and sandwiches the heat-conducting rubber member between the external heat sink and the mounting backside area.

2. 2. The electronic device according to claim 1, wherein the top wall or the bottom wall of the housing has a honeycomb structure formed by arranging regular hexagonal openings.

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