JP2018078244A - Manufacturing method of electronic device and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To electrically connect electronic components respectively placed on wiring boards to the wiring boards appropriately and stably.SOLUTION: A manufacturing method of an electronic device 1 having wiring boards 10 and 20 with different heat capacities is provided, comprising a step of preparing a wiring board 10, a step of preparing a wiring board 20 which has a heat capacity smaller that of the wiring board 10, and in which at least a part of the main surface 20a is covered with a low emissivity film 24 having a lower emissivity of infrared light than that of the wiring board 10, a step of placing and holding electronic components 17, 18, and 19 on a main surface 10a of the wiring board 10, a step of placing and holding electronic components 28 and 29 on a main surface 20a of the wiring board 20, a step of aligning the wiring board 10 and the wiring board 20 such that the main surface 10a and the main surface 20b are opposed to each other, and a step of irradiating the main surface 10a and the main surface 20a with infrared light to thereby heat the wiring boards 10 and 20.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an electronic device manufacturing method and an electronic device.

  Conventionally, when two wiring boards are electrically connected, conductive connection terminals (also called connection pins or connectors) are used. In addition, as a method that does not use connection terminals, a technique of directly joining two wiring boards via solder is also known. In either method, the wiring boards are electrically connected using a conductive bonding material such as solder.

  Specifically, first, an electronic component is placed on cream solder applied to the wiring board. Thereafter, each wiring board is set on a reflow jig and alignment between the wiring boards is performed. Thereafter, the wiring board is placed in a reflow furnace in a state set in a reflow jig, and the wiring board is heated by infrared irradiation. After completion of the heating process, the wiring board is cooled and the solder is cured.

  Patent Document 1 describes a wiring board whose base substrate is made of metal. In order to make it easy to raise the temperature of the wiring board during heating by infrared irradiation, a substance having good heat radiation (heat absorption) such as alumina or epoxy is applied to the exposed surface of the wiring board.

JP 63-133591 A

  By the way, when bonding wiring boards having different heat capacities, a temperature difference is generated between the wiring boards when heating in a reflow furnace. That is, the temperature of the wiring board having a large heat capacity is lower than the temperature of the wiring board having a small heat capacity. For example, when an aluminum substrate and a glass epoxy substrate are bonded, the glass epoxy substrate has a smaller heat capacity than the aluminum substrate. For this reason, when heating in a reflow furnace, the temperature of the glass epoxy substrate becomes higher than the temperature of the aluminum substrate.

  Therefore, when the heating temperature is adjusted to the glass epoxy substrate, the glass epoxy substrate is sufficiently heated and the solder on the glass epoxy substrate is melted. However, since the aluminum substrate is not sufficiently heated, the solder on the aluminum substrate is not sufficiently melted, and the soldering on the aluminum substrate may not be performed properly. On the other hand, if the heating temperature is adjusted to the aluminum substrate, soldering on the aluminum substrate is performed properly, but the temperature of the glass epoxy substrate may rise too much and damage or destroy electronic components on the glass epoxy substrate. is there. When wiring boards having different heat capacities are soldered in this way, it is difficult to properly solder each wiring board. In addition, said subject is the same also when using electroconductive joining materials other than solder, and more specifically, electroconductive joining materials which need to be melted by heating.

  Therefore, the present invention can electrically connect electronic components mounted on each wiring board to each wiring board appropriately and stably when manufacturing an electronic device having wiring boards having different heat capacities. An object of the present invention is to provide an electronic device manufacturing method and an electronic device.

An electronic device manufacturing method according to the present invention includes:
A method of manufacturing an electronic device having a plurality of wiring boards having different heat capacities,
Preparing a first wiring board having a first main surface and a second main surface opposite to the first main surface;
It has a fourth main surface opposite to the third main surface and the third main surface, and has a heat capacity smaller than that of the first wiring substrate, and at least a part of the third main surface is lower than that of the first wiring substrate. Preparing a second wiring board covered with a low emissivity film having a low infrared emissivity;
Placing a first electronic component on the first main surface of the first wiring board;
Placing a second electronic component on the third main surface of the second wiring board;
An alignment step of aligning the first wiring substrate and the second wiring substrate such that the first main surface of the first wiring substrate and the fourth main surface of the second wiring substrate face each other; ,
Irradiating the first main surface of the first wiring substrate and the third main surface of the second wiring substrate with infrared rays to heat the first and second wiring substrates;
It is characterized by providing.

In the method for manufacturing the electronic device,
As the second wiring board, a wiring board in which the low emissivity film is not provided in a bonding region between the first wiring board and the second wiring board may be prepared.

In the method for manufacturing the electronic device,
As the second wiring board, a wiring board in which the low emissivity film is provided so as to surround at least an electrode among electronic components mounted on the second wiring board may be prepared.

In the method for manufacturing the electronic device,
The low emissivity film may be a solder resist or a metal film provided on the solder resist.

In the method for manufacturing the electronic device,
As the first wiring board, a wiring board in which at least a part of the first main surface is covered with a high emissivity film having a higher emissivity than the low emissivity film may be prepared.

In the method for manufacturing the electronic device,
The high emissivity film may be a solder resist.

In the method for manufacturing the electronic device,
The solder resist of the low emissivity film may be white color, and the solder resist of the high emissivity film may be black color or green color.

In the method for manufacturing the electronic device,
The first wiring board is a metal base board having a metal base substrate, an insulating layer and a wiring pattern in this order,
The second wiring board may be a non-metallic base substrate having a non-metallic base substrate and a wiring pattern in this order.

In the method for manufacturing the electronic device,
The metal base substrate of the first wiring board may be made of aluminum, and the non-metal base substrate of the second wiring board may be made of glass epoxy.

In the method for manufacturing the electronic device,
In the positioning step, a first land portion provided at the edge portion of the first wiring board and a second land portion provided at the edge portion of the second wiring substrate are interposed via a conductive bonding material. The first wiring board and the second wiring board may be aligned so that they are connected.

An electronic device according to the present invention includes:
A first wiring board having a first main surface and a second main surface opposite to the first main surface;
A third main surface and a fourth main surface opposite to the third main surface, and electrically connected to the first wiring board so that the first main surface and the fourth main surface face each other A second wiring board,
The second wiring board has a heat capacity smaller than that of the first wiring board, and at least a part of the third main surface is covered with a low emissivity film having a lower infrared emissivity than the first wiring board. It is characterized by being.

In the electronic device,
The low emissivity film may not be provided in a bonding region between the first wiring board and the second wiring board.

In the electronic device,
The low emissivity film may be provided so as to surround at least the electrode of the electronic component placed on the second wiring board.

In the electronic device,
The low emissivity film may be a solder resist or a metal film provided on the solder resist.

In the electronic device,
At least a part of the first main surface of the first wiring board may be covered with a high emissivity film having a higher emissivity than the low emissivity film.

  In the present invention, for the second wiring board having a smaller heat capacity than the first wiring board, at least a part of the third main surface on which the electronic component is mounted has an infrared emissivity (absorption rate) than that of the first wiring board. Covered with a low emissivity film. For this reason, the temperature rise of the 2nd wiring board by infrared irradiation is suppressed, and the temperature difference with a 1st wiring board can be reduced. As a result, according to the present invention, when manufacturing an electronic device having wiring boards with different heat capacities, the electronic components placed on each wiring board are appropriately and stably electrically connected to each wiring board. Can do.

1 is a plan view of an electronic device 1 according to an embodiment of the present invention. FIG. 2 is a side view of the electronic device 1 as viewed from the direction A in FIG. 1. 4 is a plan view showing an example of a low emissivity film 24 provided on the wiring board 20. FIG. 6 is a plan view showing another example of the low emissivity film 24 provided on the wiring board 20. FIG. 3 is a flowchart illustrating a method for manufacturing the electronic device 1. 6 is a side view for explaining a method for manufacturing the electronic device 1. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the component which has an equivalent function in each figure.

<Electronic device 1>
An electronic device 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. In FIG. 1, the wiring pattern is omitted.

  The electronic device 1 according to this embodiment is a switching regulator (REG / RECT) that converts AC power output from an AC generator (AC generator: ACG) into DC power and outputs the DC power. The electronic device according to the present invention is not limited to a switching regulator.

  As shown in FIG. 1, the electronic device 1 includes a wiring board 10 (first wiring board) and a wiring board 20 (second wiring board) having different heat capacities. Comparing the heat capacities of the wiring board 10 and the wiring board 20, the heat capacity of the wiring board 20 is smaller than the heat capacity of the wiring board 10. In the present embodiment, the wiring substrate 10 is an aluminum base aluminum substrate, and the wiring substrate 20 is a glass epoxy substrate.

  As shown in FIG. 2, the electronic device 1 is configured such that a wiring board 10 and a wiring board 20 having different heat capacities are directly joined via a conductive portion 33. That is, the wiring board 10 and the wiring board 20 are electrically connected via a conductive bonding material such as solder. Here, the conductive bonding material is solder in the present embodiment, but is not limited thereto, and may be any conductive bonding material that melts by heating and cures by cooling after heating. For example, a conductive paste such as a silver paste may be used, or a conductive adhesive in which conductive nanoparticles are dispersed in an adhesive may be used.

  The wiring board 10 and the wiring board 20 are not limited to direct bonding but may be electrically connected via a connector (connection pin) or the like.

  As described above, the electronic device 1 includes the wiring board 10 and the wiring board 20 that is directly bonded to the wiring board 10 via the conductive portion 33. Each component will be described in detail below.

  As shown in FIG. 2, the wiring board 10 has a main surface 10a (first main surface) and a main surface 10b (second main surface) opposite to the main surface 10a. In the present embodiment, the wiring board 10 is a metal base board having a metal base substrate 11, an insulating layer 12, and a wiring pattern 13 in this order. In the present embodiment, the base substrate 11 is made of aluminum.

  The base substrate 11 may be made of a metal other than aluminum. Further, the wiring substrate 10 may be a non-metallic base substrate such as a ceramic substrate.

  As shown in FIG. 2, the insulating layer 12 is provided so as to cover at least the upper surface of the base substrate 11. The wiring pattern 13 is provided on the insulating layer 12. The wiring pattern 13 has a land portion 13a. A plurality of land portions 13 a are provided along the side edges of the wiring substrate 10 so as to be associated with land portions 22 a (described later) of the wiring substrate 20.

  As shown in FIG. 1, electronic components 17, 18, and 19 are mounted on the main surface 10 a of the wiring board 10. The electronic component 17 is a chip-type electronic component such as a chip resistor or a chip capacitor. The electronic component 18 is a diode constituting a diode bridge. The electronic component 19 is a semiconductor switch element (MOSFET, IGBT, etc.) that constitutes a power conversion circuit that converts AC power input from the AC generator into DC power.

  In the present embodiment, the main surface 10b of the wiring board 10 functions as a heat radiating surface for radiating heat generated from a heat-generating component such as a diode or a semiconductor switch element. For this reason, the electronic component is not mounted on the main surface 10b.

  As shown in FIG. 1, the wiring board 10 is provided with three bus bars 15 and two bus bars 16. The bus bar 15 is a terminal for inputting three-phase AC power generated by an AC generator (ACG). The bus bar 16 is a terminal for outputting DC power obtained by power conversion. In the present embodiment, the bus bars 15 and 16 are provided so as to extend outward from the side end opposite to the side end of the wiring board 10 on which the land portion 13a is provided.

  As shown in FIG. 2, the wiring board 20 has a main surface 20a (third main surface) and a main surface 20b (fourth main surface) opposite to the main surface 20a. The wiring substrate 20 is electrically connected to the wiring substrate 10 such that the main surface 20b faces the main surface 10a of the wiring substrate 10. In the present embodiment, the wiring substrate 20 is directly bonded to the edge portion of the wiring substrate 10 via the conductive portion 33.

  Note that the wiring board 20 may be electrically connected to the wiring board 10 via connection terminals. Further, the wiring board 20 may be bonded onto the wiring board 10 so as to be included in the wiring board 10 in a plan view.

  In the present embodiment, the wiring board 20 is a non-metallic base board having a non-metallic base substrate 21 and a wiring pattern 23 in this order. In the present embodiment, the base substrate 21 is made of glass epoxy (FR-4). The wiring board 20 may be a metal-based wiring board such as an aluminum board. As shown in FIG. 2, the wiring board 20 has a wiring pattern 23 on the main surface 20a and a wiring pattern 22 on the main surface 20b.

  As shown in FIG. 2, the wiring pattern 23 has a land portion 23a. Similarly, the wiring pattern 22 has a land portion 22a. In the present embodiment, as shown in FIG. 1, a plurality of land portions 22 a are provided along the side edges of the wiring board 20. Each land portion 22 a is associated with the land portion 13 a of the wiring board 10.

  As shown in FIG. 1, electronic components 28 and 29 are mounted on the upper surface (main surface 20 a) of the wiring board 20. The electronic component 28 is a chip-type electronic component such as a chip resistor or a chip capacitor. The electronic component 29 is a control IC for on / off control of the semiconductor switch element mounted on the wiring board 10. An electronic component such as a smoothing capacitor may be mounted on the lower surface (main surface 20b) of the wiring board 20. Further, the wiring board 20 may be provided with a through hole (not shown) for electrically connecting the land portion 22 a and the electronic components 28 and 29.

  As shown in FIG. 2, the wiring board 10 and the wiring board 20 are directly bonded via the conductive portion 33. In addition, the electronic component 17 disposed on the wiring board 10 is electrically connected to the land portion 13 a through the conductive portion 31. Similarly, the electronic component 28 disposed on the wiring board 20 is electrically connected to the land portion 23 a via the conductive portion 32. The conductive portions 31 to 33 are obtained by melting and hardening a conductive bonding material such as solder.

  As shown in FIG. 2, at least a part of the main surface 20 a of the wiring board 20 is covered with a low emissivity film 24. The low emissivity film 24 has an infrared emissivity (absorption rate) lower than that of the wiring substrate 10. For example, the low emissivity film 24 is a solder resist. In this case, the solder resist is a color having a low infrared absorptance (white color such as white or light gray). The low emissivity film 24 may be a metal film provided on a solder resist. The material of the metal film is, for example, aluminum, copper, gold or the like.

  As shown in FIG. 2, in the electronic device 1, the low emissivity film 24 may not be provided in the bonding region R between the wiring substrate 10 and the wiring substrate 20.

  Further, as shown in FIGS. 3A and 3B, the low emissivity film 24 may be provided so as to surround at least the electrode 28a of the electronic component 28 placed on the wiring board 20. In the example of FIG. 3A, the low emissivity film 24 is provided so as to cover the entire electronic component 28. In the example of FIG. 3B, the low emissivity film | membrane 24 is provided so that only the two electrodes 28a of the electronic component 28 may be included. In this manner, by providing the low emissivity film 24 so as to surround at least the electrode 28a of the electronic component 28, it is possible to suppress the temperature rise of the conductive bonding material applied on the land portion 23a.

  As shown in FIG. 2, at least a part of the main surface 10 a of the wiring board 10 is covered with a high emissivity film 14 having a higher emissivity than the low emissivity film 24. The high emissivity film 14 is, for example, a solder resist. In this case, the solder resist is a color having a high infrared absorptance (black color, green color, etc.). The high emissivity film 14 is preferably provided so as to surround at least the electrode of the electronic component placed on the wiring board 10. Thereby, the conductive bonding material applied on the land portion 13a can be easily melted.

<Method for Manufacturing Electronic Device>
Next, a method of manufacturing the electronic device 1 according to the present embodiment, that is, the electronic device 1 having a plurality of wiring boards (wiring boards 10 and 20) having different heat capacities will be described with reference to the flowchart of FIG.

  First, the wiring board 10 (first wiring board) and the wiring board 20 (second wiring board) are prepared (step S1). As described above, the heat capacity of the wiring board 20 is smaller than that of the wiring board 10, and at least a part of the main surface 20 a of the wiring board 20 is covered with the low emissivity film 24.

  Next, a conductive bonding material is applied to the land portion 13a of the wiring board 10 (step S2). The conductive bonding material is, for example, cream solder. Thereafter, the electronic component 17 (first electronic component) is placed on the conductive bonding material applied on the land portion 13a (step S3). The bus bars 15 and 16 and the electronic components 18 and 19 are also placed on the conductive bonding material applied on the corresponding land portions. By executing steps S2 and S3, the electronic components 17, 18, 19 are placed on the main surface 10a of the wiring board 10.

  Next, a conductive bonding material is applied to the land portions 22a and 23a of the wiring board 20 (step S4). Thereafter, the electronic component 28 is placed on the conductive bonding material applied on the land portion 23a (step S5). The electronic component 29 is also placed on the conductive bonding material applied on the corresponding land portion. By executing steps S4 and S5, the electronic components 28 and 29 are placed on the main surface 20a of the wiring board 20.

  Next, as shown in FIG. 5, the wiring substrate 10 and the wiring substrate 20 are aligned so that the main surface 10a of the wiring substrate 10 and the main surface 20b of the wiring substrate 20 face each other (step S6). This alignment is performed, for example, by setting the wiring boards 10 and 20 on a reflow jig (not shown).

  In the alignment step of step S6, as shown in FIG. 5, the land portion 13a provided at the edge portion of the wiring substrate 10 and the land portion 22a provided at the edge portion of the wiring substrate 20 are electrically conductively bonded. The wiring board 10 and the wiring board 20 are aligned so that they are connected via a material. Note that the land portion 13a and the land portion 22a are not limited to being directly bonded only through the conductive bonding material, but the land portion 13a and the land portion 22a are electrically connected via a connector (connection pin) or the like. May be.

  Next, as shown in FIG. 5, the main surfaces 10a of the wiring substrate 10 and the main surface 20a of the wiring substrate 20 are irradiated with infrared rays to heat the wiring substrates 10 and 20 (step S7). Specifically, the wiring boards 10 and 20 set in the reflow jig are placed in a reflow furnace, and the wiring boards 10 and 20 are irradiated with infrared rays and heated. Thus, the conductive bonding material applied on the land portions 13a, 22a, and 23a is melted. In addition, about the setting of heating temperature, it sets so that the wiring board 10 may become predetermined temperature, for example. After the heating process of step S7, the wiring boards 10 and 20 are cooled to cure the conductive bonding material.

  Through the above steps, the wiring board 10 and the electronic components 17, 18, 19 are electrically connected by the conductive bonding material, and the wiring board 20 and the electronic components 28, 29 are electrically connected by the conductive bonding material. Connecting.

  In the manufacturing method of the electronic device according to the present embodiment, at least a part of the main surface 20a of the wiring board 20 smaller than the heat capacity of the wiring board 10 is the low emissivity film 24 having a lower infrared emissivity than the wiring board 10. Since it is covered, the temperature rise of the wiring board 20 due to infrared irradiation is suppressed, and the temperature difference from the wiring board 10 can be reduced. As a result, according to this embodiment, when manufacturing the electronic device 1 having the wiring substrates 10 and 20 having different heat capacities, the electronic components 17, 18 and 19 and the electronic components placed on the wiring substrates 10 and 20, respectively. 28 and 29 can be appropriately and stably electrically connected to the wiring boards 10 and 20 by the conductive bonding material. That is, the electronic components 17, 18, and 19 placed on the wiring board 10 can be appropriately and stably electrically connected to the wiring board 10, and the electronic component 28 placed on the wiring board 20. 29 can be electrically connected to the wiring board 20 appropriately and stably.

  In the wiring substrate preparation step (step S1), the wiring substrate 20 in which the low emissivity film 24 is not provided in the bonding region R between the wiring substrate 10 and the wiring substrate 20 may be prepared. Thereby, in the heating process (step S7), it is prevented that heat is not easily transmitted to the conductive bonding material (that is, the conductive bonding material to be the conductive portion 33) for electrically bonding the wiring board 10 and the wiring board 20. it can. In other words, the mounting region in which the electronic components 28 and 29 are provided suppresses the temperature rise by the low emissivity film 24, and the bonding region R is sufficiently heated, so that the wiring substrate 10 and the wiring Bonding defects between the substrates 20 can be prevented.

  Further, in the wiring substrate preparation step (step S1), a wiring substrate in which the low emissivity film 24 is provided so as to surround at least the electrode 28a of the electronic component 28 placed on the wiring substrate 20 may be prepared. (See FIGS. 3A and 3B). This makes it difficult for heat to be transferred from the wiring board 20 to the electronic component 28 during the heating process (step S7) by infrared irradiation. Thereby, even when the heating temperature is set high according to the wiring board 10, damage or destruction of the electronic component 28 can be suppressed.

  Further, in the wiring substrate preparation step (step S1), as the wiring substrate 10, a wiring substrate in which at least a part of the main surface 10a is covered with the high emissivity film 14 having higher emissivity than the low emissivity film 24 is used. You may prepare. Thereby, in the heating process (step S7) by infrared irradiation, the temperature of the wiring board 10 is likely to rise, so that the temperature difference between the wiring board 10 and the wiring board 20 can be further reduced.

  Based on the above description, those skilled in the art may be able to conceive additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the individual embodiments described above. . You may combine suitably the component covering different embodiment. Various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Electronic device 10, 20 Wiring board 10a, 10b, 20a, 20b Main surface 11, 21 Base base material 12 Insulating layer 13, 22, 23 Wiring pattern 13a, 22a, 23a Land part 14 High emissivity film 24 Low emissivity film 15, 16 Busbars 18, 19, 28, 29 Electronic components 17a, 28a Electrodes 31, 32, 33 Conductive part A Direction R Joint region

Claims (15)

A method of manufacturing an electronic device having a plurality of wiring boards having different heat capacities,
Preparing a first wiring board having a first main surface and a second main surface opposite to the first main surface;
It has a fourth main surface opposite to the third main surface and the third main surface, and has a heat capacity smaller than that of the first wiring substrate, and at least a part of the third main surface is lower than that of the first wiring substrate. Preparing a second wiring board covered with a low emissivity film having a low infrared emissivity;
Placing a first electronic component on the first main surface of the first wiring board;
Placing a second electronic component on the third main surface of the second wiring board;
An alignment step of aligning the first wiring substrate and the second wiring substrate such that the first main surface of the first wiring substrate and the fourth main surface of the second wiring substrate face each other; ,
Irradiating the first main surface of the first wiring substrate and the third main surface of the second wiring substrate with infrared rays to heat the first and second wiring substrates;
An electronic device manufacturing method comprising:   2. The electron according to claim 1, wherein the second wiring board is prepared as a wiring board in which the low emissivity film is not provided in a bonding region between the first wiring board and the second wiring board. Device manufacturing method.   2. The wiring board in which the low emissivity film is provided as the second wiring board so as to surround at least an electrode among electronic components placed on the second wiring board. 3. A method for manufacturing an electronic device according to 2.   The method for manufacturing an electronic device according to claim 1, wherein the low emissivity film is a solder resist or a metal film provided on the solder resist.   2. The wiring board in which at least a part of the first main surface is coated with a high emissivity film having a higher emissivity than the low emissivity film is prepared as the first wiring board. The manufacturing method of the electronic device in any one of -4.   6. The method of manufacturing an electronic device according to claim 5, wherein the high emissivity film is a solder resist.   7. The method of manufacturing an electronic device according to claim 6, wherein the solder resist of the low emissivity film is a white color, and the solder resist of the high emissivity film is a black color or a green color. The first wiring board is a metal base board having a metal base substrate, an insulating layer and a wiring pattern in this order,
The method for manufacturing an electronic device according to claim 1, wherein the second wiring board is a non-metallic base substrate having a non-metallic base substrate and a wiring pattern in this order.   9. The electronic device according to claim 8, wherein the metal base base material of the first wiring board is made of aluminum, and the non-metal base base material of the second wiring board is made of glass epoxy. Manufacturing method.   In the positioning step, a first land portion provided at the edge portion of the first wiring board and a second land portion provided at the edge portion of the second wiring substrate are interposed via a conductive bonding material. The method for manufacturing an electronic device according to claim 1, wherein the first wiring board and the second wiring board are aligned so as to be connected to each other. A first wiring board having a first main surface and a second main surface opposite to the first main surface;
A third main surface and a fourth main surface opposite to the third main surface, and electrically connected to the first wiring board so that the first main surface and the fourth main surface face each other A second wiring board,
The second wiring board has a heat capacity smaller than that of the first wiring board, and at least a part of the third main surface is covered with a low emissivity film having a lower infrared emissivity than the first wiring board. An electronic device characterized by being made.   The electronic device according to claim 11, wherein the low emissivity film is not provided in a bonding region between the first wiring board and the second wiring board.   The electronic device according to claim 11, wherein the low emissivity film is provided so as to surround at least an electrode among electronic components placed on the second wiring board.   The electronic device according to claim 11, wherein the low emissivity film is a solder resist or a metal film provided on the solder resist.   The at least part of the first main surface of the first wiring board is covered with a high emissivity film having an emissivity higher than that of the low emissivity film. An electronic device according to 1.

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