Circuit board and lighting device

Abstract

Provided are a circuit board and lighting device making it possible to improve voltage resistance while still ensuring heat dissipation. A circuit board includes: a substrate (30) constituted of an insulating material; through hole wiring (33) formed penetrating from a first surface to a second surface of the substrate (30); a first wiring layer (31) formed on the first surface; and a second wiring layer (32) formed on the second surface. A protective layer (35) covering the second wiring layer (32) is formed on the second surface. Insulation ensuring sections (36) are formed on the second surface up to a location that is spaced farther apart from the second surface than the protective layer (35) is.

Description

Circuit board and lighting device

[0001] The present invention relates to a circuit board and a lighting device, and more particularly to a circuit board and a lighting device in which through-hole wiring is formed in a substrate.

[0002] In recent years, vehicle lamps using light-emitting diodes (LEDs) as light sources have become widespread. Furthermore, a lighting device for use in a vehicle lamp has been proposed in which a plurality of LEDs are arranged on a circuit board to emit light with a desired brightness and light distribution pattern (see, for example, Patent Document 1).

[0003] It is generally known that LEDs generate heat as they emit light, which causes a rise in temperature, resulting in a change in the wavelength of light emitted and a decrease in light emission efficiency. Therefore, in headlights and other devices that emit a large amount of light, it is important to effectively dissipate the heat generated by the LED to the outside and suppress temperature increases. Another proposal involves forming through-hole wiring and heat dissipation wiring on a circuit board made of an insulating material, effectively transferring heat from the LED to the heat dissipation wiring on the back side, and dissipating the heat from a heat dissipation member in contact with the heat dissipation wiring.

[0004] Japanese Patent Application Laid-Open No. 2018-073762

[0005] In such a heat dissipation structure using through-hole wiring and heat dissipation wiring, the heat dissipation wiring is covered with an insulating layer to electrically insulate the heat dissipation member from the heat dissipation wiring. However, at the edge where the heat dissipation wiring pattern is formed, a step occurs in the insulating layer due to the thickness of the heat dissipation wiring. This easily results in uneven thickness of the insulating layer, which can cause dielectric breakdown and reduce voltage resistance. Increasing the thickness of the insulating layer is effective in ensuring voltage resistance, but this reduces thermal conductivity between the heat dissipation wiring and the heat dissipation member, reducing the heat dissipation performance of the vehicle lamp.

[0006] The present invention has been made in consideration of the above-mentioned conventional problems, and has an object to provide a circuit board and a lighting device that can improve voltage resistance while ensuring heat dissipation properties.

[0007] In order to solve the above problem, the circuit board of the present invention is a circuit board having a base material made of an insulating material, through-hole wiring formed to penetrate from a first surface to a second surface of the base material, a first wiring layer formed on the first surface, and a second wiring layer formed on the second surface, wherein a protective layer covering the second wiring layer is formed on the second surface, and an insulation ensuring portion is formed on the second surface, even at a position farther from the second surface than the protective layer.

[0008] In such a circuit board of the present invention, an insulation ensuring portion is provided on the second surface of the circuit board, thereby ensuring the distance between the heat dissipation member arranged on the second surface side and the second wiring layer, thereby making it possible to improve voltage resistance while ensuring heat dissipation properties.

[0009] In one aspect of the present invention, the insulation ensuring portion is an ink layer or a resist layer formed on the surface of the protective layer.

[0010] In one aspect of the present invention, the insulation ensuring portion is provided at a position overlapping the second wiring layer in a plan view.

[0011] In one aspect of the present invention, the insulation ensuring portion is provided at a position corresponding to an edge portion of the second wiring layer electrically connected to the through-hole wiring.

[0012] In one aspect of the present invention, the through-hole wiring is filled with a resin material.

[0013] In one aspect of the present invention, the insulation ensuring portion has a thickness in the range of 5 μm to 50 μm.

[0014] In addition, in order to solve the above problem, the lighting device of the present invention is characterized by having any one of the circuit boards described above, a light-emitting element mounted at a position corresponding to the through-hole wiring on the first surface, a heat dissipation member arranged on the second surface side, and a heat conduction member provided between the second surface and the heat dissipation member.

[0015] The present invention can provide a circuit board and a lighting device that can improve voltage resistance while ensuring heat dissipation.

[0016] 4( a ) and 4 ( b ) are schematic cross-sectional views illustrating an overview of a lighting device 100 according to a first embodiment.

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[100] 8A and 8B are diagrams showing a simulation of heat dissipation performance with and without an insulation securing portion 36, in which FIG. 8A is a schematic plan view showing the arrangement of light-emitting elements 10 mounted on a circuit board 30, and FIG. 8B is a graph showing the simulation results.

[0017] First Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing will be denoted by the same reference numerals, and redundant description will be omitted where appropriate. In the following description, an illumination device 100 according to the present invention will be described, exemplarily, as applied to a vehicle lamp. FIG. 1 is a partially enlarged schematic cross-sectional view illustrating an overview of the illumination device 100 according to this embodiment. As shown in FIG. 1 , the illumination device 100 includes a light-emitting element 10, an electronic component 20, a circuit board 30, and a heat dissipation member 40. The circuit board 30 also includes a first wiring layer 31, a second wiring layer 32, through-hole wiring 33, a hole-filling resin 34, a protective layer 35, an insulation securing portion 36, and a heat-conducting member 37.

[0018] The light-emitting element 10 is a component mounted on the surface (first surface) of the circuit board 30 and emits light of a predetermined wavelength when a voltage is applied. While FIG. 1 illustrates a surface-mounted case in which the light-emitting element 10 is electrically connected to the first wiring layer 31 using solder 11, the light-emitting element 10 may be electrically connected to the first wiring layer 31 by wire bonding. For example, when the lighting device 100 is used as a headlamp for a vehicle lamp, a white LED may be used as the light-emitting element 10; when the lighting device 100 is used as a tail lamp or stop lamp, a red LED may be used; and when the lighting device 100 is used as a turn signal lamp, an amber LED may be used. The structure of the light-emitting element 10 is not limited, and may be a packaged LED chip or a bare LED chip directly mounted. Examples of white LEDs include a combination of a GaN-based LED emitting primary light in the blue to ultraviolet wavelength range and a phosphor, or a combination of RGB LED chips.

[0019] The electronic components 20 are mounted on the front surface (first surface) or back surface (second surface) of the circuit board 30, and are components that constitute an electronic circuit by realizing various functions when supplied with power and control signals. While Fig. 1 illustrates a surface-mounted case in which the electronic components 20 are electrically connected to the first wiring layer 31 using solder 11, they may also be electrically connected to the first wiring layer 31 by wire bonding using wires. The type and number of the electronic components 20 are not limited, and known components such as resistors, capacitors, and integrated circuits can be used.

[0020] The circuit board 30 is a plate-like member having a substantially plate-like base material on which a first wiring layer 31, a second wiring layer 32, through-hole wiring 33, a hole-filling resin 34, a protective layer 35, and an insulation ensuring portion 36 are formed. A thermally conductive member 37 is disposed between the circuit board 30 and the heat dissipation member 40. The material constituting the base material of the circuit board 30 is not particularly limited, but it is preferable to use a resin material with excellent electrical insulation properties, such as a glass epoxy resin used in ordinary printed wiring boards, such as FR4 (Flame Retardant Type 4).

[0021] The heat dissipation member 40 is made of a material with a higher thermal conductivity than the base material of the circuit board 30, and is disposed on the rear surface (second surface) of the circuit board 30 to dissipate heat from the circuit board 30. The material constituting the heat dissipation member 40 is not limited, but metals such as anodized aluminum or copper can be used, for example. In FIG. 1 , the heat dissipation member 40 is shown in a shape in which a plurality of heat dissipation fins are erected from a plate-like portion, but the shape and structure are not limited.

[0022] The first wiring layer (element wiring) 31 is a wiring pattern formed on the surface (first surface) of the circuit board 30. A part of the first wiring layer 31 functions as a land portion on which the light emitting element 10 or the electronic component 20 is mounted, and as a terminal portion to which a wire is electrically connected. The light emitting element 10 or the electronic component 20 is electrically connected to the first wiring layer 31, and an electronic circuit is formed on the circuit board 30. In the first wiring layer 31, a through-hole wiring 33 is formed in the region of the land portion on which the light emitting element 10 is mounted.

[0023] The second wiring layer (heat dissipation wiring) 32 is a wiring pattern formed on the back surface (second surface) of the circuit board 30. As shown in FIG. 1 , the second wiring layer 32 may be provided with a region electrically connected to the first wiring layer 31 by the through-hole wiring 33 and a region electrically isolated from the through-hole wiring 33, in different regions. The region of the second wiring layer 32 connected to the through-hole wiring 33 functions as a heat dissipation path, as described below. Furthermore, the region of the second wiring layer 32 electrically isolated from the through-hole wiring 33 may be connected to a ground potential.

[0024] The through-hole wiring 33 is an electrically conductive wiring formed on the inner wall of a through-hole (penetrating hole) that penetrates from the front surface side to the back surface side of the circuit board 30. A conventionally known plating method or the like can be used as a method for forming the through-hole wiring 33. The through-hole wiring 33 is electrically connected to a part of the first wiring layer 31 and a part of the second wiring layer 32. There are no limitations on the region in which the through-hole wiring 33 is provided, but by providing the through-hole wiring 33 at a position in the first wiring layer 31 that corresponds to the land portion on which the light-emitting element 10 is mounted, heat generated by light emission can be efficiently transmitted to the back surface side.

[0025] The hole-filling resin 34 is a resin material that fills the through-holes in which the through-hole wiring 33 is formed. There are no limitations on the material that constitutes the hole-filling resin 34, and a thermosetting epoxy resin can be used as an example. In addition, in order to improve the thermal conductivity of the hole-filling resin 34, a filler with high thermal conductivity may be mixed into the resin material.

[0026] The protective layer 35 is formed on the back surface of the circuit board 30 to cover the second wiring layer 32, and is a layer made of an insulating material. The material for the protective layer 35 is not limited, and a conventionally known resist material can be used. Although not shown in FIG. 1 , the protective layer 35 may also be formed on the front surface of the circuit board 30 to cover a portion of the first wiring layer 31. In the example shown in FIG. 1 , the protective layer 35 is formed over the entire back surface of the circuit board 30, but the back surface of the circuit board 30 may be partially exposed as long as it covers at least the area where the second wiring layer 32 is formed.

[0027] The insulation ensuring portion 36 is made of an insulating material and is a portion formed on the back surface side of the circuit board 30. The height of the insulation ensuring portion 36 from the back surface of the circuit board 30 is greater than the height of the protective layer 35 from the back surface of the circuit board 30. In other words, the insulation ensuring portion 36 is formed to a position farther from the back surface of the circuit board 30 than the protective layer 35. By forming the insulation ensuring portion 36 to a position farther from the back surface of the circuit board 30 than the protective layer 35, it is possible to ensure the distance from the second wiring layer 32 to the heat dissipation member 40 without increasing the thickness of the protective layer 35, and it is possible to improve the voltage resistance while ensuring heat dissipation.

[0028] The material for forming the insulation ensuring portion 36 is not limited, but an ink layer formed in a predetermined pattern using known silk screen printing can be used. Alternatively, a resist layer applied to the entire rear surface of the circuit board 30 using a known spin coating method may serve as the insulation ensuring portion 36. Furthermore, the insulation ensuring portion 36 may be formed by patterning a material such as a resist layer using known photolithography technology.

[0029] In the example shown in FIG. 1 , the insulation ensuring portion 36 is formed on the protective layer 35. By forming the insulation ensuring portion 36 on the protective layer 35, it is possible to ensure the distance from the second wiring layer 32 to the heat dissipation member 40 even if the film thickness of the insulation ensuring portion 36 is thin. While FIG. 1 shows an example in which the insulation ensuring portion 36 is formed on the protective layer 35, the insulation ensuring portion 36 may also be formed in an area where the back surface of the circuit board 30 is exposed. As shown in FIG. 1 , by forming the insulation ensuring portion 36 in a predetermined pattern and making it protrude from the surface of the protective layer 35, a gap is provided between the protective layer 35 and the heat dissipation member 40, and a thermally conductive member 37 can be disposed in the gap.

[0030] 1 , the insulation securing portion 36 is provided at a position overlapping the second wiring layer 32 in a plan view. By forming the insulation securing portion 36 at a position overlapping the second wiring layer 32, the thickness of the insulation securing portion 36 plus the thickness of the protective layer 35 ensures a sufficient distance from the second wiring layer 32 to the heat dissipation member 40. If the thickness of the insulation securing portion 36 is thinner than 5 μm, the distance from the second wiring layer 32 to the heat dissipation member 40 becomes too small, making it difficult to improve voltage resistance. If the thickness of the insulation securing portion 36 is thicker than 50 μm, the distance from the second wiring layer 32 to the heat dissipation member 40 becomes too large, resulting in reduced heat dissipation. Therefore, the thickness of the insulation securing portion 36 is preferably in the range of 5 μm to 50 μm.

[0031] The heat conduction member 37 is a member with high thermal conductivity that is disposed between the circuit board 30 and the heat dissipation member 40. In order to improve the voltage resistance of the lighting device 100, it is preferable that the heat conduction member 37 be insulating. There are no restrictions on the material that constitutes the heat conduction member 37, but one example is heat dissipation grease mixed with a filler of metal particles or metal oxide particles. Alternatively, a heat conduction sheet molded into a sheet shape may be used as the heat conduction member 37.

[0032] 2A and 2B are schematic plan views showing an example structure of a circuit board 30 according to this embodiment, in which FIG. 2A shows the formation pattern of the second wiring layer 32, FIG. 2B shows the formation pattern of the protective layer 35, and FIG. 2C shows the positional relationship between the formation pattern of the insulation ensuring portion 36 and the second wiring layer 32 in a plan view. As shown in FIG. 2A, the second wiring layer 32 is connected to the through-hole wiring 33, forming a region on the back surface of the region where the light-emitting element 10 is mounted and a large-area region electrically isolated from the through-hole wiring 33. Also, as shown in FIG. 2B, the protective layer 35 is formed over the entire back surface of the circuit board 30 and covers the second wiring layer 32. In the example shown in FIG. 2C, a plurality of insulation ensuring portions 36 are formed in a dot-like pattern at positions overlapping the second wiring layer 32 in a plan view.

[0033] 1 and 2 , the light emitting element 10 emits light when power and a control signal are transmitted to an electronic circuit configured by the first wiring layer 31, the light emitting element 10, and the electronic component 20. Heat generated by the light emission of the light emitting element 10 is transmitted to the heat dissipation member 40 via the first wiring layer 31, the through-hole wiring 33, the second wiring layer 32, the protective layer 35, and the heat conduction member 37. The heat dissipation member 40 dissipates the heat to the outside of the lighting device 100, thereby cooling the lighting device 100.

[0034] At this time, because the first wiring layer 31 and the second wiring layer 32 are electrically connected by through-hole wiring 33, a potential is also applied to the second wiring layer 32. On the back surface of the circuit board 30, the second wiring layer 32 is covered with a protective layer 35, ensuring electrical insulation. However, because the second wiring layer 32 has a thickness of approximately several tens of micrometers, the protective layer 35 formed by a method such as spin coating has a step at the edge of the second wiring layer 32 (not shown). The step in the protective layer 35 at this edge has an inclined surface to fill the step, resulting in a partial thinning of the film thickness (not shown). Because the protective layer 35 is thinner at these edge portions than in other regions, its voltage resistance is likely to decrease.

[0035] More specifically, if the second wiring layer 32 is about 50 to 60 μm thick and the protective layer 35 is about 10 to 30 μm thick, the thickness of the inclined surface at the edge portion may be about 5 to 15 μm. In order to make the thickness of the edge portion about 10 to 30 μm, the thickness of the protective layer 35 in other regions needs to be about 20 to 60 μm, which increases the thickness of the protective layer 35 in the above-mentioned heat dissipation path and reduces heat dissipation.

[0036] However, in the lighting device 100 and circuit board 30 of this embodiment, the insulation ensuring portion 36 is provided on the back side of the circuit board 30 to ensure the distance between the second wiring layer 32 and the heat dissipation member 40, so that heat resistance can be ensured even if the thickness of the protective layer 35 is about 10 to 30 μm. Furthermore, since there is no need to make the protective layer 35 thick, a decrease in heat dissipation performance can also be suppressed.

[0037] Furthermore, since the insulating portions 36 are arranged in a dot pattern, the proportion of the insulating portions 36 in the total area of ​​the circuit board 30 can be reduced, ensuring an area for applying the thermally conductive member 37, and further improving heat dissipation. In the example shown in Figure 2(c), multiple insulating portions 36 are provided around the area of ​​the second wiring layer 32 connected to the through-hole wiring 33. This allows the multiple insulating portions 36 to ensure a distance between the heat dissipation member 40 and the protective layer 35, making the film thickness of the thermally conductive member 37 arranged between them uniform and improving heat dissipation.

[0038] As described above, in the lighting device 100 and circuit board 30 of this embodiment, an insulation ensuring portion 36 is provided on the second surface of the circuit board 30, thereby ensuring the distance between the heat dissipation member 40 arranged on the second surface side and the second wiring layer 32, thereby making it possible to improve voltage resistance while ensuring heat dissipation.

[0039] Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. 3 to 5. Description of content that overlaps with the first embodiment will be omitted. FIG. 3 is a partially enlarged schematic cross-sectional view illustrating an overview of a lighting device 110 according to this embodiment. This embodiment differs from the first embodiment in that the insulation ensuring portion 36 is formed at an edge portion of the second wiring layer 32.

[0040] 3 , in the lighting device 110 and the circuit board 30 of this embodiment, the insulation ensuring portion 36 is provided at a position corresponding to an edge portion of the second wiring layer 32. Because the second wiring layer 32 is covered with the protective layer 35, the insulation ensuring portion 36 is formed on the protective layer 35, covering a step (not shown) in the protective layer 35 generated at the edge portion of the second wiring layer 32.

[0041] FIG. 4 is a schematic plan view showing the positional relationship between the formation pattern of the insulation securing portions 36 according to this embodiment and the second wiring layer 32 in a plan view. FIG. 4( a) shows an example in which the insulation securing portions 36 are arranged in isolated dots, and FIG. 4( b) shows an example in which the insulation securing portions 36 are arranged in a continuous line. The formation pattern of the second wiring layer 32 is the same as that shown in FIG. 2( a), and the formation pattern of the protective layer 35 is the same as that shown in FIG. 2( b). In the example shown in FIG. 4( a), the insulation securing portions 36 are arranged in multiple dots, thereby reducing the proportion of the insulation securing portions 36 relative to the total area of ​​the circuit board 30, thereby ensuring an area for applying the thermal conductive member 37 and further improving heat dissipation. In the example shown in FIG. 4( b), the insulation securing portions 36 are arranged in a continuous line, thereby covering a wide area of ​​the edge portions of the second wiring layer 32 with the insulation securing portions 36, further improving voltage resistance.

[0042] 4(a) and 4(b), an insulating portion 36 is provided at the edge of the region of the second wiring layer 32 connected to the through-hole wiring 33. This ensures the distance between the heat dissipation member 40 and the protective layer 35 with the insulating portion 36, and makes it possible to make the film thickness of the heat conduction member 37 disposed between them uniform and improve heat dissipation.

[0043] 5 is a schematic cross-sectional view illustrating the overlap between the edge portion of the second wiring layer 32 and the insulation ensuring portion 36. As shown in Fig. 5, at the edge portion of the second wiring layer 32, a step occurs in the protective layer 35 due to the thickness of the second wiring layer 32. The insulation ensuring portion 36 is formed so as to cover the step portion of the protective layer 35 from the region where the second wiring layer 32 is not provided to the region where the second wiring layer 32 is provided.

[0044] In this case, if the width W of the overlapping portion between the insulation ensuring portion 36 and the second wiring layer 32 is set to be equal to or greater than 0.2 mm and equal to or less than 1.0 mm, it is preferable that W be set in the range of 0.2 mm to 1.0 mm. If the overlapping width W between the insulation ensuring portion 36 and the second wiring layer 32 is less than 0.2 mm, it becomes difficult to improve the voltage resistance by compensating for the reduction in film thickness at the edge portions caused by the steps in the protective layer 35. Furthermore, if the overlapping width W between the insulation ensuring portion 36 and the second wiring layer 32 is greater than 1.0 mm, the area of ​​the second wiring layer 32 covered by the insulation ensuring portion 36 becomes large, making it difficult to maintain good heat dissipation.

[0045] In the lighting device 110 and circuit board 30 of this embodiment, an insulation ensuring portion 36 is provided on the second surface of the circuit board 30, thereby ensuring the distance between the heat dissipation member 40 arranged on the second surface side and the second wiring layer 32, thereby making it possible to improve voltage resistance while ensuring heat dissipation.

[0046] Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIGS. 6 and 7. Description of content that overlaps with the first embodiment will be omitted. FIG. 6 is a partially enlarged schematic cross-sectional view illustrating an overview of a lighting device 120 according to this embodiment. This embodiment differs from the first embodiment in that the insulation ensuring portion 36 is formed on the entire surface of the region connected to the through-hole wiring 33 of the second wiring layer 32.

[0047] As shown in Fig. 6 , in the lighting device 120 and circuit board 30 of this embodiment, the insulation ensuring portion 36 is provided over the entire area of ​​the second wiring layer 32 connected to the through-hole wiring 33, corresponding to the position where the light-emitting element 10 is mounted. In addition, the heat conducting member 37 is provided between the heat dissipation member 40 and covers the insulation ensuring portion 36. While Fig. 6 shows an example in which the heat conducting member 37 is provided partially on the back surface side of the circuit board 30, the heat conducting member 37 may be provided over the entire back surface side of the circuit board 30. In this embodiment, the path of heat dissipation from the light-emitting element 10 in the lighting device 120 is the first wiring layer 31, the through-hole wiring 33, the second wiring layer 32, the protective layer 35, the insulation ensuring portion 36, the heat conducting member 37, and the heat dissipation member 40.

[0048] 6 shows an example in which the insulation ensuring portion 36 covers an area substantially the same as the area of ​​the second wiring layer 32 connected to the through-hole wiring 33, but the insulation ensuring portion 36 may be formed to be larger than the area of ​​the area of ​​the second wiring layer 32 connected to the through-hole wiring 33. In this case, the insulation ensuring portion 36 can cover the step in the protective layer 35 generated at the edge portion of the second wiring layer 32, thereby further improving the voltage resistance.

[0049] 7 is a schematic plan view showing the positional relationship between the formation pattern of the insulation ensuring portion 36 according to this embodiment and the second wiring layer 32 in a plan view. The formation pattern of the second wiring layer 32 is the same as that shown in FIG. 2( a), and the formation pattern of the protective layer 35 is the same as that shown in FIG. 7( b). As shown in FIG. 7, the insulation ensuring portion 36 is formed in a planar shape corresponding to the region of the second wiring layer 32 connected to the through-hole wiring 33.

[0050] 7, the insulation ensuring portion 36 is arranged in a planar shape, which improves the voltage resistance over the entire area of ​​the second wiring layer 32 connected to the through-hole wiring 33. Furthermore, the insulation ensuring portion 36 is formed only in the area of ​​the second wiring layer 32 connected to the through-hole wiring 33, so the ratio of the insulation ensuring portion 36 to the entire area of ​​the circuit board 30 is small, and heat dissipation can be ensured from the area where the insulation ensuring portion 36 is not formed via the heat conduction member 37 and the heat dissipation member 40.

[0051] In the lighting device 120 and circuit board 30 of this embodiment, an insulation ensuring portion 36 is provided on the second surface of the circuit board 30, thereby ensuring the distance between the heat dissipation member 40 arranged on the second surface side and the second wiring layer 32, thereby making it possible to improve voltage resistance while ensuring heat dissipation.

[0052] (Regarding Heat Dissipation) FIG. 8 shows a simulation of heat dissipation with and without the insulation ensuring portion 36. FIG. 8(a) is a schematic plan view showing the arrangement of light-emitting elements 10 mounted on a circuit board 30, and FIG. 8(b) is a graph showing the simulation results. As shown in FIG. 8(a), multiple light-emitting elements 10 were mounted on a circuit board 30, and temperature was simulated before and after the insulation ensuring portion 36 was formed on the back surface by silk printing. Among the simulation results, FIG. 8(b) shows the temperatures of the light-emitting elements 10 at positions indicated as Tc_1 and Tc_2 in the figure. In the table of FIG. 8(b), "No. 1" indicates a sample in which the insulation ensuring portion 36 is formed in a dot-like shape on the edge portion shown in FIG. 4(a), "No. 3" indicates a sample in which the insulation ensuring portion 36 is formed in a planar shape shown in FIG. 7, and "AVE." indicates the average value of No. 1 and No. 3. In addition, in the table of Figure 8 (b), "with silk" indicates the measurement results of each sample when the insulation ensuring section 36 was formed, and "without silk" indicates the measurement results of each sample when the insulation ensuring section 36 was not formed.

[0053] The simulation was performed using the finite element method. A 0.8 mm thick glass epoxy was used as the base material for the circuit board 30, with a vertical width of 55.5 mm and a horizontal width of 53.7 mm in FIG. 8(a). Gold was used for the first wiring layer 31, the second wiring layer 32, and the through-hole wiring 33, and the thicknesses of the first wiring layer 31 and the second wiring layer 32 were 60 μm. A 30 μm thick white resist was used as the protective layer 35, and a thermosetting epoxy resin was used as the hole-filling resin 34. A 15 μm thick ink layer formed by silkscreen printing was used as the insulation securing portion 36. The diameter of the through-holes was 250 μm, and the through-hole pitch was 550 μm. The thermal conductivity was determined based on the material used for each component.

[0054] As shown in Figure 8(b), in sample No. 1, in which the insulating ensuring portion 36 was provided in a dot pattern, the temperature at position Tc_1 was 70.63°C without the insulating ensuring portion 36 and 71.2°C with the insulating ensuring portion 36. At position Tc_2, the temperature was 66.41°C without the insulating ensuring portion 36 and 68.26°C with the insulating ensuring portion 36. At position Tc_1, in sample No. 3, in which the insulating ensuring portion 36 was provided in a planar pattern, the temperature was 70.86°C without the insulating ensuring portion 36 and 71.3°C with the insulating ensuring portion 36. At position Tc_2, the temperature was 66.29°C without the insulating ensuring portion 36 and 69.24°C with the insulating ensuring portion 36. Therefore, even when the insulating ensuring portion 36 was provided, the temperature rise of the light-emitting element 10 was within 3°C, confirming that good heat dissipation was maintained.

[0055] Furthermore, in the case where the insulation ensuring portion 36 was not provided, a short circuit occurred between the second wiring layer 32 and the heat dissipation member 40 in samples No. 1 and No. 3 at a voltage difference of 800 V. In contrast, in the case where the insulation ensuring portion 36 was provided, a short circuit did not occur between the second wiring layer 32 and the heat dissipation member 40 in samples No. 1 and No. 3, even at a voltage difference of 1000 V. Therefore, it was confirmed that by providing the insulation ensuring portion 36 on the back side of the circuit board 30, the voltage resistance was improved while ensuring heat dissipation.

[0056] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0057] This international application claims priority based on Japanese Patent Application No. 2024-021569, filed on February 15, 2024, the entire contents of which are incorporated herein by reference.

[0058] The above descriptions of specific embodiments of the present invention have been presented for purposes of illustration. They are not intended to be exhaustive or to limit the invention to the precise forms described. Numerous modifications and variations will be apparent to those skilled in the art in light of the above description.

[0059] DESCRIPTION OF SYMBOLS 100, 110, 120... Illumination device 10... Light emitting element 11... Solder 20... Electronic component 30... Circuit board 31... First wiring layer 32... Second wiring layer 33... Through-hole wiring 34... Hole filling resin 35... Protective layer 36... Insulation ensuring portion 37... Heat conducting member 40... Heat dissipation member

Claims

1. A circuit board having a base material made of an insulating material, through-hole wiring formed penetrating from a first surface to a second surface of the base material, a first wiring layer formed on the first surface, and a second wiring layer formed on the second surface, wherein a protective layer covering the second wiring layer is formed on the second surface, and an insulation ensuring portion is formed on the second surface, extending to a position farther from the second surface than the protective layer.

2. The circuit board according to claim 1, wherein the insulation ensuring portion is an ink layer or a resist layer formed on the surface of the protective layer.

3. A circuit board according to claim 1, wherein the insulation ensuring portion is provided at a position overlapping the second wiring layer in a plan view.

4. A circuit board according to claim 1, characterized in that the insulation ensuring portion is provided at a position corresponding to an edge portion of the second wiring layer electrically connected to the through-hole wiring.

5. The circuit board according to claim 1, wherein the through-hole wiring is filled with a resin material.

6. The circuit board according to claim 1, wherein the insulation ensuring portion has a thickness in the range of 5 μm to 50 μm.

7. A lighting device comprising: a circuit board according to any one of claims 1 to 6; a light-emitting element mounted on the first surface at a position corresponding to the through-hole wiring; a heat dissipation member disposed on the second surface; and a heat conduction member provided between the second surface and the heat dissipation member.

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