JP2022163905A - Electronic apparatus - Google Patents

Abstract

To improve heat dissipation from heating components 8A, 8B to a heat sink 9.SOLUTION: Heating components 8A, 8B are mounted on a second surface 3B of a circuit board 3. A case body 4 is formed with a heat sink 9 in correspondence with the heating components 8A, 8B, and a first surface 3A of the circuit board 3 is in contact with a top face 9a. A surface layer of the first surface 3A is formed with a circuit pattern through etching of a metal foil layer 21A. An insulating coating 25 covering the circuit pattern has a thermal conductivity of 0.5 W/m K or more and has a constant thickness in a portion other than the heat sink 9. In an area in contact with the heat sink 9, the thickness of the insulating coating 25 in a portion not overlapping the circuit pattern is larger than the thickness of the insulating coating 25 on the circuit pattern by the thickness of a metal foil of the metal foil layer 21A. As a result, a surface of the insulating coating 25C in contact with the top face 9a of the heat sink 9 is flat regardless of the presence or absence of the circuit pattern, which improves adhesion.SELECTED DRAWING: Figure 3

Description

The present invention relates to an electronic device in which a circuit board is accommodated in a housing, and more particularly to improvement of an electronic device in which a heat sink for heat dissipation is provided on the housing side so as to be in contact with the circuit board.

In order to promote heat dissipation from the heat-generating components mounted on the circuit board, for example, a heat sink with a large heat capacity formed in a block of metal material is provided on the housing side, and the heat of the circuit board is transferred to this heat sink. Electronic devices are known.

In such a configuration, one problem is the adhesion between the surface of the circuit board and the surface of the heat sink, which are uneven due to the circuit pattern on the surface layer. In Patent Document 1, a window-shaped recess is formed in an insulating layer on the surface of a circuit board, and silicon resin having excellent thermal conductivity is held in the recess so as to improve adhesion between the heat sink and the surface of the circuit board. is disclosed.

JP 2007-109866 A

In the configuration of Patent Document 1, the silicon resin is held by the window-shaped recess. likely to occur. In addition, since the silicon resin is applied or filled in accordance with the position of the recess, it is difficult to align the position.

In one aspect of the present invention, a circuit board having a circuit pattern made of metal foil on its surface layer and an insulating coating covering the circuit pattern; an electronic device comprising a housing having a heat sink in contact with a surface thereof, wherein the insulating coating has a thermal conductivity of 0.5 W/mK or more, and at least in a region in contact with the heat sink, Compared to the thickness of the insulating coating on the circuit pattern, the thickness of the insulating coating at a portion not overlapping with the circuit pattern is larger by the thickness of the metal foil.

According to the configuration of the present invention, by increasing the thickness of the insulating coating at other locations by the thickness of the metal foil as compared with the thickness of the insulating coating on the circuit pattern, it comes into contact with the heat sink. The surface of the insulating coating is basically flat and smooth. Therefore, the inherent adhesion with the heat sink is improved, and the heat dissipation by the heat sink is high.

1 is a cross-sectional view of an electronic device according to an embodiment; FIG. The top view of a case main body. FIG. 2 is an enlarged cross-sectional view of the main part of the first embodiment; The enlarged sectional view of the principal part of 2nd Example. The enlarged sectional view of the principal part of 3rd Example.

An embodiment in which the present invention is applied to an electronic device for automobiles will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view of an electronic device 1 that is an embodiment of the invention. The electronic device 1 is mounted at an appropriate position in a vehicle as, for example, a controller of an automatic transmission for a vehicle, and includes a housing 2 and a circuit board 3 accommodated inside the housing 2. there is The housing 2 consists of a metal case body 4 in the shape of a substantially rectangular plate, and a synthetic resin bulge to cover one side of the case body 4 (the upper side in FIG. 1). A connector 6 attached to one end of the circuit board 3 is sandwiched between the case body 4 and the cover 5 . The circuit board 3 is attached to the case body 4 via a plurality of screws 7 . A gasket 11 is provided between the case body 4 and the cover 5 , and another gasket 12 is provided between the periphery of the connector 6 and the housing 2 .

The circuit board 3 is composed of a multi-layer (for example, four layers) printed wiring board as will be described later. and have A plurality of electronic components 8 including heat-generating components 8A and 8B such as FETs are surface-mounted on the second surface 3B. On the bottom surface 4a of the case body 4 facing the first surface 3A of the circuit board 3, heat sinks 9 are formed at positions corresponding to the heat generating components 8A and 8B that generate a large amount of heat. The heat sink 9 has a large heat capacity by partially thickening the bottom wall of the metal case body 4, and is formed in the shape of a rectangular block protruding from the bottom surface 4a toward the circuit board 3. . A top surface 9 a of each heat sink 9 is smoothly formed along the same plane, and each top surface 9 a is in contact with the first surface 3 A of the circuit board 3 .

FIG. 2 is a plan view of the case body 4. FIG. In the illustrated example, heat sinks 9 are formed at four locations on the bottom surface 4a. The case body 4 has a pair of tongue-shaped mounting pieces 10 for mounting to the vehicle body, and through holes 13 at the four corners into which mounting pins (not shown) of the cover 5 are inserted and thermally crimped. is provided. Further, threaded holes 14 into which the screws 7 described above are screwed are arranged at the four corners on the inner peripheral side of the gasket groove 14 in which the gasket 11 described above is held. 1 corresponds to a cross section taken along line AA shown in FIG.

FIG. 3 is an enlarged cross-sectional view of a part of FIG. 1 showing the first embodiment. The circuit board 3 is a multilayer printed wiring board, specifically, a so-called four-layer printed wiring board having four metal foil layers 21 (for example, copper foil layers). This multilayer printed wiring board is manufactured by laminating several layers of base material 22, for example, made of glass epoxy, having metal foil layers 21 on one side or both sides thereof via prepregs (adhesive layers) (not shown), and applying heat and pressure. It is configured by integrating with A desired circuit pattern is formed by etching each metal foil layer 21 and forming vias 23 extending in the stacking direction. That is, the metal foil layer 21 includes a first metal foil layer 21A, a second metal foil layer 21B, a third metal foil layer 21C, and a fourth metal foil layer 21D in order from the first surface 3A side. The first metal foil layer 21A and the fourth metal foil layer 21D are on the surface layers of the first surface 3A and the second surface 3B, respectively, and the second metal foil layer 21B and the third metal foil layer 21C are on the inner layers. These metal foil layers 21 are removed by etching at portions other than the desired circuit pattern. As a result, for example, in the fourth metal foil layer 21D on the second surface 3B side, lands 21D1, 21D2, 21D3, and 21D4 to which the terminals of the electronic components 8 (heat generating components 8A and 8B) are connected, and a plurality of narrow wirings. The portion 21D5 or the like remains as a circuit pattern projecting from the surface of the substrate 22. FIG. Similarly, in the first metal foil layer 21A on the first surface 3A side, the land 21A1 connected to the plated layer 23a of the via 23, a plurality of narrow wiring portions 21A2, and the like are formed from the surface of the base material 22 as a circuit pattern. It remains in a prominent shape.

Insulating coatings 25 and 26 covering the circuit patterns are further provided on the first surface 3A and the second surface 3B provided with the circuit patterns made of the metal foil layers 21A and 21D. The insulating coatings 25 and 26 are made of a so-called solder resist ink, and are printed by a printing technique such as screen printing, leaving the lands 21D1, etc. to be soldered and the outer peripheral edge of the circuit board 3. is coated on the entire surface. Here, at least the insulating coating 25 on the first surface 3A is made of a material with a high thermal conductivity. It has a thermal conductivity of about /m·K. As the insulating coating 26 of the second surface 3B, it is desirable to use the same high thermal conductivity material as that of the first surface 3A, but a material with relatively low thermal conductivity may also be used.

The insulating coating 26 on the second surface 3B is applied with a constant thickness. Specifically, each part is coated with a constant thickness (first thickness) with a minimum thickness necessary for desired insulation, durability, and the like. Therefore, the surface shape of the insulating coating 26 is an uneven shape reflecting the wiring portion 21D5 and the like left by etching.

The insulating coating 25 on the first surface 3A, except for the area in contact with the top surface 9a of the heat sink 9, is applied to each part with a constant thickness (first thickness) like the insulating coating 26 on the second surface 3B. there is Therefore, the area other than the area in contact with the top surface 9a of the heat sink 9 has an uneven shape reflecting the circuit pattern left by the etching. On the other hand, in the regions (indicated by reference numerals 25A and 25B) in contact with the top surface 9a of the heat sink 9, the thickness (first thickness) of the insulating coating 25 on the circuit pattern (for example, the wiring portion 21A2) left by etching is , the thickness (second thickness) of the insulating coating 25 at the portion not overlapping the circuit pattern is increased by the thickness of the metal foil of the first metal foil layer 21A. As a result, the surfaces of the insulating coatings 25A and 25B in contact with the top surface 9a of the heat sink 9 are flat regardless of the presence or absence of circuit patterns. The insulating coatings 25A and 25B having different thicknesses can be easily realized by, for example, coating multiple times. Alternatively, it is possible to apply a sufficient thickness in one coat and then cure the coating while adjusting it so that the coating becomes a flat surface, or cure the coating while it is uneven and then machine the coating into a flat surface.

To give a specific example, the thickness of the metal foil layer 21 that forms the circuit pattern is about 18 to 35 μm, and the thickness (first thickness) of the insulating coatings 25 and 26 applied thereon is 15 μm. degree. Therefore, the thickness (second thickness) of the insulating coatings 25A and 25B in the regions in contact with the top surface 9a of the heat sink 9, which does not overlap the circuit pattern, is approximately 33 to 50 μm.

The thickness of the insulating coating 26 on the second surface 3B side may be slightly different from the thickness (first thickness) of the insulating coating 25 on the first surface 3A other than the heat sink 9 . In addition, the thickness (first thickness) of the insulating coating 25 on the circuit pattern in the insulating coatings 25A and 25B in the regions corresponding to the heat sink 9 is basically the thickness of the insulating coating 25 in the portions other than the heat sink 9. Although it is equal to (the first thickness), both may be slightly different from each other due to processing restrictions and the like.

In the first embodiment, the top surface 9a of the heat sink 9 is in direct contact with the surfaces of the insulating coatings 25A and 25B which basically form smooth surfaces as described above, without intervening heat dissipation grease or the like. Since the surfaces of the insulating coatings 25A and 25B are smooth without irregularities due to the circuit pattern, sufficiently good adhesion can be obtained. to the heat sink 9 more reliably. Since the insulation films 25 and 26 made of solder resist ink have some elasticity even in a cured state, sufficient adhesion can be obtained without using heat dissipation grease or the like.

In the present invention, heat dissipation grease may be applied to the contact surfaces between the insulating coatings 25A and 25B and the top surface 9a of the heat sink 9 as necessary. It can be set thin (for example, 100 μm or less).

In the first embodiment, since the thickness of the insulating coating 25 is constant (first thickness) in the region not corresponding to the heat sink 9, the amount of material used for the insulating coating 25 does not excessively increase.

Next, FIG. 4 is an enlarged cross-sectional view of a main part showing a second embodiment. In this second embodiment, the thickness of the insulating coating 25 (first thickness) on the circuit pattern is smaller than the thickness of the insulating coating 25 on the circuit pattern even in the area other than the area in contact with the top surface 9a of the heat sink 9 of the circuit board 3. The thickness (second thickness) of the insulating coating 25 at the portion not overlapping the pattern is increased by the thickness of the metal foil of the first metal foil layer 21A. That is, on the entire surface of the circuit board 3, compared to the thickness of the insulating coating 25 on the circuit pattern, the thickness of the insulating coating 25 at a portion not overlapping with the circuit pattern is less than the thickness of the metal foil of the first metal foil layer 21A. is larger by the thickness of As a result, the surface of the insulating coating 25 is flat over the entire surface of the circuit board 3 regardless of the presence or absence of the circuit pattern. As described above, the insulating film 25 is not applied to the portions that require soldering.

By making the entire surface of the insulating coating 25 have the same structure, the coating of the insulating coating 25 and smoothing of the surface can be facilitated.

Furthermore, in the second embodiment shown in FIG. 4, the insulation coating 26 is locally thickened in the region where the packages of the heat-generating components 8A and 8B are overlapped in the insulation coating 26 on the second surface 3B. In FIG. 4, the locally thickened portions of the insulating coating 26 are indicated by reference numerals 26A and 26B. Preferably, the thickness of these insulating coatings 26A, 26B is set so that the bottom surface of the package is in close contact with the surfaces of the insulating coatings 26A, 26B. Moreover, it is desirable to use a material having high thermal conductivity as the insulating coating 26 on the second surface 3B, like the insulating coating 25 on the first surface 3A.

By increasing the thickness of the insulating coatings 26A and 26B so as to contact the packages of the heat generating components 8A and 8B, the heat transfer from the heat generating components 8A and 8B to the heat sink 9 becomes more effective. Even if the surfaces of the insulating coatings 26A and 26B are not in complete contact with the bottom surface of the package, increasing the thickness of the insulating coatings 26A and 26B allows them to be positioned close to each other, thereby improving heat conduction. Improve efficiency.

Next, FIG. 5 is an enlarged cross-sectional view of a main portion showing a third embodiment of the invention. In this third embodiment, the heat sink 9 is provided at positions corresponding to a plurality of vias 31 (so-called thermal vias) provided for heat transfer, not at positions overlapping the heat generating components 8A. The vias 31 extend in the stacking direction of the circuit board 3, and the inner plated layer 31a thermally connects the metal foil layer 21A on the first surface 3A and the metal foil layer 21D on the second surface 3B. Therefore, at the opening edge of the via 31, lands 21A3 and 21D6 having an annular shape or an appropriate shape remain as part of the metal foil layers 21A and 21D, respectively. The land 21A3 on the first surface 3A corresponds to part of the circuit pattern in the claims.

A plurality of electronic components 8 including a heat-generating component 8A are mounted on the second surface 3B of the circuit board 3, and some electronic components 8 are also mounted on the first surface 3A. The heat sink 9 is formed at a position laterally displaced from the position of the heat generating component 8A in order to avoid interference with the electronic component 8 on the first surface 3A. A via 31 is provided to secure a heat transfer path from the heat generating component 8A to the heat sink 9. As shown in FIG.

The insulating coating 25 provided on the first surface 3A of the circuit board 3 is applied to a constant thickness (first thickness) except for the area in contact with the top surface 9a of the heat sink 9, as in the first embodiment. It is Therefore, the area other than the area in contact with the top surface 9a of the heat sink 9 has an uneven shape reflecting the circuit pattern left by the etching. On the other hand, in the area (indicated by reference numeral 25C) in contact with the top surface 9a of the heat sink 9, the thickness (first thickness) of the insulating coating 25 on the circuit pattern (for example, the land 21A3) left by etching is smaller than that of the insulating coating 25. Thus, the thickness (second thickness) of the insulating coating 25 at the portion not overlapping the circuit pattern is increased by the thickness of the metal foil of the first metal foil layer 21A. As a result, the surface of the insulating coating 25C in contact with the top surface 9a of the heat sink 9 is flat regardless of the presence or absence of the circuit pattern.

As a result, the surface of the insulating coating 25C covering the land 21A3 at the end of the via 31 and the top surface 9a of the heat sink 9 can be highly adhered to each other, and heat can be reliably transferred from the heat generating component 8A to the heat sink 9 via the via 31. be done. As described above, heat dissipation grease or the like is not required between the surface of the insulating coating 25C and the top surface 9a of the heat sink 9, but heat dissipation grease may be thinly applied as necessary.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, although the heat sink 9 is formed as part of the bottom wall of the case body 4 in the above embodiment, the heat sink may have any form. Moreover, the insulating film is not limited to the solder resist ink.

As described above, the electronic device of the present invention includes a circuit board having a circuit pattern made of metal foil on its surface layer and an insulating coating covering the circuit pattern, and a housing having a heat sink in contact with a surface of the electronic device, wherein the insulating coating has a thermal conductivity of 0.5 W/m·K or more, and at least in a region in contact with the heat sink (2) The thickness of the insulating coating at the portion not overlapping with the circuit pattern is larger by the thickness of the metal foil than the thickness of the insulating coating on the circuit pattern.

In one specific aspect of the present invention, in the entire surface of the circuit board including the region in contact with the heat sink, the thickness of the insulating coating on the circuit pattern is greater than the thickness of the insulating coating on the circuit pattern, and the portion not overlapping the circuit pattern is The thickness of the insulating coating is as large as the thickness of the metal foil.

In another aspect of the present invention, in a region in contact with the heat sink, the thickness of the insulating coating at a location not overlapping the circuit pattern is greater than the thickness of the insulating coating on the circuit pattern. , is greater by the thickness of the metal foil, and in other regions of the circuit board, the thickness of the insulating coating is a constant thickness equal to the thickness of the insulating coating on the circuit pattern.

In a preferred aspect of the present invention, as part of the circuit pattern, a land at the end of the via is included in the area contacting the heat sink.

In a preferred aspect of the present invention, a heat-generating component is mounted on a second surface of the circuit board opposite to the heat sink, and a region of the second surface where the package of the heat-generating component overlaps. In addition, the insulating coating is locally thickened.

DESCRIPTION OF SYMBOLS 1... Electronic device, 2... Housing, 3... Circuit board, 4... Case main body, 5... Cover, 8A, 8B... Heat-generating component, 9... Heat sink, 9a... Top surface, 21... Metal foil layer, 21A2... Wiring part , 21A3... land, 25, 26... insulating film, 31... via.

Claims (5)

A circuit board having a circuit pattern made of metal foil on its surface and an insulating coating covering the circuit pattern;
a housing containing the circuit board and having a heat sink in contact with a surface of a portion of the circuit board;
An electronic device comprising
The insulating coating has a thermal conductivity of 0.5 W/m·K or more,
At least in a region in contact with the heat sink, the thickness of the insulating coating at a portion not overlapping with the circuit pattern is greater than the thickness of the insulating coating on the circuit pattern by the thickness of the metal foil. ,
electronic device. Over the entire surface of the circuit board, including the area in contact with the heat sink, the thickness of the insulating coating at locations not overlapping the circuit pattern is greater than the thickness of the insulating coating on the circuit pattern. larger by the thickness,
An electronic device according to claim 1 . In the region in contact with the heat sink, the thickness of the insulating coating at a portion not overlapping with the circuit pattern is greater than the thickness of the insulating coating on the circuit pattern by the thickness of the metal foil,
In other regions of the circuit board, the thickness of the insulating coating is a constant thickness equal to the thickness of the insulating coating on the circuit pattern.
An electronic device according to claim 1 . A land at the end of the via as part of the circuit pattern is included in a region in contact with the heat sink,
The electronic device according to any one of claims 1 to 3. A heat-generating component is mounted on a second surface opposite to the heat sink of the circuit board,
An insulating coating is locally thickly formed in a region of the second surface where the package of the heat-generating component overlaps.
The electronic device according to any one of claims 1 to 4.

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