Wiring board equipped with electronic component

Abstract

A wiring board (20) equipped with an electronic component is provided with: an insulating base material (31); a metal wiring part (32) which is formed above the insulating base material (31); an electronic component (21) which is mounted on the metal wiring part (32); and an overcoat layer (35) which covers the electronic component (21) and the metal wiring part (32). The wiring board (20) equipped with an electronic component does not include a solder resist.

Description

Wiring board with electronic components

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[0001] The present disclosure relates to a wiring board with electronic components.

[0002] Conventionally, a wiring board having a metal wiring portion and a solder resist layer formed on a substrate has been known (see, for example, Patent Document 1 and Patent Document 2). In such a wiring board, a metal containing copper is generally used for the metal wiring portion.

[0003] Japanese Unexamined Patent Application Publication No. 2023-37405 Japanese Unexamined Patent Application Publication No. Hei 8-51282 <i

[0004] By the way, in recent years, there has been a demand to reduce the manufacturing cost of wiring boards.

[0005] The present disclosure provides a wiring board capable of reducing manufacturing costs. <00000il>

[0006] Embodiments of the present disclosure relate to the following [1] to [5]. <i

[0007] [1] An insulating base material, A metal wiring portion formed on the insulating base material, An electronic component mounted on the metal wiring portion, An overcoat layer covering the electronic component and the metal wiring portion, A wiring board with electronic components that does not contain solder resist.

[0008] [2] The overcoat layer is directly formed on the metal wiring portion and on the electronic component, The wiring board with electronic components according to [1].

[0009] [3] The metal wiring portion is made of aluminum foil, and the thickness of the metal wiring portion is 5 μm or more and 200 μm or less, The wiring board with electronic components according to [1] or [2].

[0010] [4] In a plan view, the area of the region where the metal wiring portion is formed is 65% or more and 98% or less of the area of the insulating base material, The wiring board with electronic components according to any one of [1] to [3]. ​​​​According to this embodiment, the manufacturing cost of the wiring board can be reduced.

[0013] Figure 1 is a schematic diagram showing a wiring board with electronic components according to one embodiment. Figure 2 is a plan view showing a wiring board with electronic components according to one embodiment. Figure 3 is a cross-sectional view (cross-sectional view along line III-III in Figure 2) showing a wiring board with electronic components according to one embodiment. Figure 4 is a plan view showing the insulating substrate and metal wiring portion of a wiring board with electronic components according to one embodiment. Figure 5A is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 5B is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 5C is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 5D is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 5E is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 5F is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 5G is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 5H is a cross-sectional view showing a method for manufacturing a wiring board with electronic components according to one embodiment. Figure 6 is a schematic perspective view showing a plant cultivation factory according to one embodiment. Figure 7 is a schematic perspective view showing a plant growing shelf according to one embodiment. Figure 8 is a graph showing the reflectance of the wiring board in the embodiment. Figure 9 is a graph showing the emission spectrum of the LED chip used in the wiring board in the embodiment.

[0014] Hereinafter, one embodiment will be described in detail with reference to the drawings. The following figures are schematic representations. Therefore, the size and shape of each part are exaggerated as appropriate to facilitate understanding. Furthermore, it can be modified as appropriate without departing from the technical concept. In the following figures, the same parts are denoted by the same reference numerals, and some detailed explanations may be omitted. Also, the numerical values ​​such as dimensions and material names of each component described in this specification are examples of embodiments and can be selected and used as appropriate without being limited thereto. In this specification, terms that specify shapes and geometric conditions, such as parallel, orthogonal, and perpendicular, will be interpreted to include not only their strict meaning but also substantially the same state. In this specification, "plants and animals" means animals and / or plants. In the following, for convenience, the case of growing (cultivating) plants using a wiring board will be used as an example, but the wiring board for growing plants and animals according to this embodiment can also be applied to growing animals to the extent that it does not cause contradictions.

[0015] (Wiring board) The wiring board with electronic components (hereinafter also simply referred to as a wiring board) 20 shown in Figure 1 may be an LED lighting device for plant cultivation. That is, the wiring board 20 may be an LED lighting device installed in a plant cultivation factory 90 (Figure 6) using artificial light, as will be described later, for growing plants. A control unit 40 is electrically connected to such a wiring board 20.

[0016] As shown in Figures 1 and 2, the wiring board 20 is a so-called single-sided light-emitting, planar light source sheet. Multiple LED chips (electronic components) 21 are arranged on the light-emitting surface 20a side of this wiring board 20. By using such a direct-type wiring board 20, the light emitted from the LED chips 21 passes directly through the light-emitting surface 20a. Therefore, the emitted light reaches the plant directly below, increasing the light intensity and promoting plant growth. In addition, since the overall thickness of the wiring board 20 can be reduced compared to an LED bar light, the occurrence of shadows on the sides of the LED chips 21 can be suppressed.

[0017] The wiring board 20 in Figures 1 and 2 comprises a flexible insulating substrate 31 and a plurality of LED chips 21 regularly arranged on the insulating substrate 31. By using such an insulating substrate 31, a wiring board 20 with a relatively large surface area can be obtained. Generally, in plant and animal breeding factories and plant and animal breeding shelves, multiple wiring boards 20 are used in an arrangement. If the positions of adjacent wiring boards 20 are inconsistent, variations in light intensity may occur, potentially reducing the yield of plants and animals. A wiring board 20 with a relatively large surface area can reduce the number of wiring boards 20 used, thereby suppressing variations in light intensity caused by the arrangement of multiple wiring boards 20. Although Figures 1 and 2 show examples of wiring boards 20 equipped with a flexible insulating substrate 31, the wiring board is not limited to this, and the insulating substrate 31 may be a rigid substrate. When the insulating substrate 31 is a rigid substrate, the wiring board has higher resistance to stress and is less prone to damage. Note that the overcoat layer 35, which will be described later, is not shown in Figures 1 and 2.

[0018] In this case, the LED chips 21 are arranged regularly on the insulating substrate 31. Specifically, the LED chips 21 are arranged in a grid pattern in a plan view within the insulating substrate 31. That is, the LED chips 21 are arranged in a matrix with multiple rows and columns, and there are N rows of columns R of M LED chips 21 connected in series.

[0019] For example, in Figure 2, 14 LED chips (M=14) are connected in series along the first arrangement direction (X direction) of the LED chips 21. Furthermore, 10 rows (N=10) of these rows R, each containing 14 LED chips 21, are arranged in parallel along the second arrangement direction (Y direction) of the LED chips 21. Note that the number of LED chips 21 arranged is not limited to these.

[0020] The wiring board 20 is provided with a plurality of metal wiring sections 22. The plurality of metal wiring sections 22 are arranged along a first arrangement direction (X direction). Each of the plurality of metal wiring sections 22 arranged along the first arrangement direction (X direction) corresponds to each row R of the LED chip 21. Each LED chip 21 is arranged so as to straddle a pair of adjacent metal wiring sections 22 in the X direction. In addition, each terminal of the LED chip 21 (not shown) is electrically connected to a pair of metal wiring sections 22. The plurality of metal wiring sections 22 constitute a power supply section for the LED chip 21, and when power is supplied to the plurality of metal wiring sections 22, all the LED chips 21 arranged in the row R light up. The plurality of metal wiring sections 22 constitute a part of the metal wiring section 32, which will be described later.

[0021] The spacing Px between LED chips 21 in the first arrangement direction (X direction) may be 15 mm or more, and is preferably 25 mm or more. The spacing Px between LED chips 21 may be 100 mm or less, and is preferably 60 mm or less. The spacing Py between LED chips 21 in the second arrangement direction (Y direction) may be 15 mm or more, and is preferably 25 mm or more. The spacing Py between LED chips 21 may be 100 mm or less, and is preferably 75 mm or less. By setting the spacing between LED chips 21 within the above ranges, the brightness of the wiring board 20 can be made uniform across the plane. This suppresses variations in the light illuminating the space and reduces the power consumption of the wiring board 20.

[0022] The thickness of the thickest part of the wiring board 20 is preferably 5 mm or less. By making the wiring board 20 thinner in this way, the vertical spacing between the substrates 81 (Figure 7) on which the wiring boards 20 are installed can be narrowed, thereby increasing the number of substrates 81 per plant growing shelf 80 (Figure 7). As a result, the yield of plants per unit area can be increased. In addition, when plants and the wiring board 20 are in close proximity, variations in the relatively strong light irradiated onto the plants can be further suppressed.

[0023] The arrangement of the LED chips 21 is not limited to a grid pattern in plan view. Although not shown in the diagram, they may be arranged in a staggered pattern in plan view. Furthermore, the LED chips 21 do not need to be uniformly arranged within the plane of the wiring board 20. For example, although not shown in the diagram, the density of LED chips 21 may be higher at the periphery of the wiring board 20. This suppresses the decrease in brightness of the wiring board 20 at the periphery, makes the brightness of the wiring board 20 uniform within the plane, and suppresses the variation in light illuminating the space.

[0024] The overall shape of the wiring board 20 is rectangular in plan view, but the size and planar shape of the wiring board 20 are not particularly limited. Because the wiring board 20 offers a high degree of freedom in terms of size and shape processing, it can flexibly respond to various needs in this regard. Furthermore, because the wiring board 20 is flexible, it can be mounted not only on flat mounting surfaces but also on mounting surfaces of various shapes.

[0025] In Figure 2, the length Lx of the wiring board 20 in the first arrangement direction (X direction) is preferably 500 mm or more, and more preferably 550 mm or more. Furthermore, the length Lx of the wiring board 20 in the first arrangement direction (X direction) is preferably 750 mm or less, and more preferably 650 mm or less. The length Ly of the wiring board 20 in the second arrangement direction (Y direction) is preferably 300 mm or more, and more preferably 350 mm or more. Furthermore, the length Ly of the wiring board 20 in the second arrangement direction (Y direction) is preferably 500 mm or less, and more preferably 450 mm or less. By ensuring that the size of each wiring board 20 is not excessively small, the amount of light emitted from the wiring board 20 can be increased. Also, by ensuring that the size of each wiring board 20 is not excessively large, the impact on other LED chips 21 when a specific LED chip 21 is damaged can be minimized. Therefore, it is possible to prevent the overall illuminance of the wiring board 20 from decreasing drastically, and to limit the range in which the illuminance decreases.

[0026] Next, the control unit 40 will be described. As shown in Figure 1, the control unit 40 supplies power to the wiring board 20 and controls the illumination of the wiring board 20. The control unit 40 is detachably connected to the wiring board 20 via a first connector 44A provided on the wiring board 20. In other words, the control unit 40 is configured separately from the wiring board 20 and is connected to the wiring board 20 externally. To put it another way, the control unit 40 is not integrated with the wiring board 20. This allows the control unit 40, which is a heat source, to be separated from the wiring board 20, and prevents the heat from the control unit 40 from affecting plant growth.

[0027] The control unit 40 also includes a power input unit 41, an AC / DC converter (driver) 42, and a PWM control unit 43. The power input unit 41 is supplied with an AC voltage having any voltage between 100V and 240V, for example. The AC / DC converter 42 converts the AC voltage between 100V and 240V into a constant voltage (for example, 44V) DC voltage. The PWM control unit 43 adjusts the brightness of the LED chips 21 on the wiring board 20 by arbitrarily changing the pulse width of the constant voltage waveform from the AC / DC converter 42. In other words, the PWM control unit 43 also functions as a dimming control unit that controls the dimming of the wiring board 20. The constant voltage output from the PWM control unit 43 is applied to the wiring board 20 via the first connector 44A.

[0028] When adjusting the illuminance of the LED chip 21, for example, the illuminance of the wiring board 20 may be adjusted according to the growth stage of the plant. This allows for adjustment of the degree of plant growth. For example, in the early stages of growth when the plant leaves are small, the illuminance of the wiring board 20 may be lowered, and in the later stages of growth when the plant leaves are large, the illuminance of the wiring board 20 may be increased. Alternatively, in the early stages of growth when the plant is short, the distance between the plant and the LED chip 21 is greater, so the illuminance of the wiring board 20 may be increased. Also, in the later stages of growth when the plant is taller, the distance between the plant and the LED chip 21 is closer, so the illuminance of the wiring board 20 may be lowered. Other examples of adjusting the illuminance of the wiring board 20 include increasing the illuminance for plant species that require high illuminance, and decreasing it for plant species that can be grown with low illuminance. Furthermore, the illuminance may be increased to expedite shipping, and decreased to delay shipping.

[0029] A regulator 45 is provided on the wiring board 20. In this case, a regulator 45 is provided for each row of LED chips 21, specifically, 10 regulators 45 are provided for each of the 10 rows of LED chips 21. The role of this regulator 45 is to maintain a constant current flowing through the multiple LED chips 21 in each row. This prevents excessive current from flowing to the LED chips 21 in other rows even if one LED chip 21 is damaged, thus preventing damage to the LED chips 21 in other rows. As a result, it is possible to prevent an extreme decrease in the overall illuminance of the wiring board 20 and to suppress variations in the light illuminating the space.

[0030] Furthermore, a power supply line 46 is provided on the wiring board 20, branching from the first connector 44A. A second connector 44B is also provided on the wiring board 20. The power supply line 46 is not electrically connected to the LED chip 21 on the wiring board 20, but is electrically connected to the wiring of another wiring board 200 having the same configuration as the wiring board 20. That is, the power supply line 46 is detachably connected to the wiring of the wiring board 200 via the second connector 44B and another first connector 44A provided on the other wiring board 200. Current from the power supply line 46 is supplied to the other wiring board 200 via the second connector 44B and the other first connector 44A. This allows two wiring boards 20 and 200 to be connected and simultaneously controlled by a single control unit 40. By being able to simultaneously control multiple wiring boards 20 and 200 with a single control unit 40, the number of control units 40 can be reduced. Therefore, variations in plant growth due to heat from the control unit 40 are less likely to occur, and a decrease in yield can be suppressed.

[0031] (Each component of the wiring board) Next, the components constituting the wiring board 20 will be described. As shown in Figure 3, the wiring board 20 comprises an insulating substrate 31, a metal wiring section 32 formed on the insulating substrate 31, LED chips (electronic components) 21 mounted on the metal wiring section 32, and an overcoat layer 35 covering the LED chips 21 and the metal wiring section 32. The metal wiring section 32 is laminated on the insulating substrate 31 via an adhesive layer 33. A joint section 36 is also provided on the metal wiring section 32. Each LED chip 21 is electrically connected to the metal wiring section 32 via the joint section 36.

[0032] (Insulating Substrate) In this embodiment, the insulating substrate 31 is flexible. The insulating substrate 31 can be a flexible resin film. In this specification, "flexible" means "having a radius of curvature when bent of at least 1 m, preferably 50 cm, more preferably 30 cm, even more preferably 10 cm, and particularly preferably 5 cm."

[0033] As the material for the insulating substrate 31, a thermoplastic resin with high heat resistance and insulating properties may be used. As such a resin, polyimide resin (PI) or polyethylene naphthalate (PEN), which have excellent heat resistance, dimensional stability when heated, mechanical strength, and durability, can be used. Among these, polyethylene naphthalate (PEN) whose heat resistance and dimensional stability have been improved by heat resistance improvement treatment such as annealing treatment is preferably used. Alternatively, polyethylene terephthalate (PET) whose flame retardancy has been improved by adding flame-retardant inorganic fillers may also be used.

[0034] The thickness of the insulating substrate 31 is not particularly limited. From the viewpoint of not becoming a bottleneck in the heat dissipation path, having heat resistance and insulating properties, and balancing manufacturing costs, the thickness of the insulating substrate 31 is preferably about 10 μm or more, and more preferably 50 μm or more. Furthermore, the thickness of the insulating substrate 31 is preferably 500 μm or less, and more preferably 250 μm or less. Also, from the viewpoint of maintaining good productivity when manufacturing by a roll-to-roll method, it is preferable that the thickness of the insulating substrate 31 be within the above thickness range.

[0035] (Adhesive layer) The adhesive forming the adhesive layer 33 may be any known resin-based adhesive. Among these resin adhesives, urethane-based, polycarbonate-based, silicone-based, ester-based, or epoxy-based adhesives are particularly preferred.

[0036] (Metal Wiring Section) The metal wiring section 32 is a wiring pattern formed on the surface of the insulating substrate 31 (the surface on the light-emitting surface 20a side) using a conductive substrate such as metal foil. Preferably, the metal wiring section 32 is formed on the surface of the insulating substrate 31 via an adhesive layer 33 by a dry lamination method. The metal wiring section 32 includes the plurality of metal wiring sections 22 described above. The plurality of metal wiring sections 22 include a first metal wiring section 22A and a second metal wiring section 22B spaced apart from the first metal wiring section 22A. LED chips 21 are mounted on the first metal wiring section 22A and the second metal wiring section 22B, and the LED chips 21 are electrically connected to the first metal wiring section 22A and the second metal wiring section 22B. The LED chips 21 light up when power is supplied to the first metal wiring section 22A and the second metal wiring section 22B.

[0037] The metal wiring section 32 preferably achieves a high level of both heat dissipation and electrical conductivity. For example, aluminum foil or copper foil can be used for the metal wiring section 32. When aluminum foil is used for the metal wiring section 32, since aluminum is inexpensive and lightweight, it is possible to reduce the weight of the wiring board 20 while lowering the manufacturing cost of the wiring board 20. In particular, the price of copper has been soaring in recent years. Furthermore, due to the limited reserves of copper, a further increase in the price of copper is expected. For this reason, if aluminum foil is used instead of copper for the metal wiring section 32, the manufacturing cost of the wiring board 20 can be effectively reduced. In addition, since aluminum has a high light reflectivity, the light reflectivity of the wiring board 20 can be increased even if the wiring board 20 does not contain solder resist as described later. In this case, it is preferable that the light reflectivity of the metal wiring section 32 is 80% or more, and more preferably 85% or more, in the wavelength range of 400 nm to 780 nm.

[0038] As for the aluminum, for example, aluminum of grade A1N30 or A8079 may be used.

[0039] Aluminum has lower electrical conductivity compared to metals such as copper. Therefore, when aluminum foil is used for the metal wiring section 32, the thickness of the metal wiring section 32 may be increased and the width of the metal wiring section 32 may be increased compared to when copper foil is used. This makes it possible to improve the electrical conductivity of the metal wiring section 32 even when aluminum foil is used. In this case, the electrical conductivity of the metal wiring section 32 can be increased to a level comparable to that when copper is used. In this case, the thickness of the metal wiring section 32 may be between 5 μm and 200 μm. By having a thickness of 5 μm or more for the metal wiring section 32, the electrical conductivity can be increased. By having a thickness of 200 μm or less for the metal wiring section 32, the manufacturing cost of the wiring board 20 can be reduced while maintaining sufficient flexibility of the insulating substrate 31, and a decrease in handling performance due to increased weight can be suppressed.

[0040] When copper foil is used in the metal wiring section 32, heat dissipation from the LED chip 21 is stabilized, preventing an increase in electrical resistance. This reduces variations in light emission between the LED chips 21, enabling stable light emission. The lifespan of the LED chip 21 is also extended. Furthermore, deterioration of surrounding components such as the insulating substrate 31 due to heat is prevented, thus extending the product lifespan of the wiring board 20. Examples of metals used to form the metal wiring section 32 include, in addition to the above-mentioned aluminum and copper, gold, silver, and other metals.

[0041] When a metal other than aluminum foil is used for the metal wiring section 32, the thickness of the metal wiring section 32 can be appropriately set according to the current resistance required for the insulating substrate 31. The thickness of the metal wiring section 32 is preferably 10 μm or more, and more preferably 20 μm or more. On the other hand, the thickness of the metal wiring section 32 is preferably 100 μm or less, and more preferably 60 μm or less. This allows for sufficient flexibility of the insulating substrate 31 to be maintained and prevents a decrease in handling performance due to increased weight.

[0042] (Joint) The joint 36 joins the metal wiring part 32 and the LED chip 21. This joint 36 may be formed of a conductive paste (conductive adhesive (conductive formulations)), an anisotropic conductive film (ACF), or a mounting solder paste. As described above, when an aluminum foil is used for the metal wiring part 32, since the surface of the aluminum foil oxidizes immediately, it is preferable that the joint 36 is formed of a conductive paste or an anisotropic conductive film (ACF).

[0043] (LED Chip) The LED chip 21 is mounted in a manner that enables conduction with the metal wiring part 32. In this wiring board 20, since the LED chip 21 is mounted on the insulating base material 31, a plurality of LED chips 21 can be arranged at a desired high density.

[0044] The LED chip 21 is a light-emitting element that utilizes light emission at a PN junction where a P-type semiconductor and an N-type semiconductor are joined. As the LED chip 21, a structure in which a P-type electrode and an N-type electrode are provided on the upper surface and the lower surface of the element, respectively, may be used, or a structure in which both the P-type electrode and the N-type electrode are provided on one side of the element may be used.

[0045] Also, it is preferable to select an LED chip 21 with high luminous efficiency. Specifically, as the LED chip 21, it is preferable to use one having a luminous efficiency of 150 lm / W or more, and more preferably one having a luminous efficiency of 180 lm / W or more. By increasing the luminous efficiency of the LED chip 21 to 150 lm / W or more, the number (density) of mounted LED chips 21 can be reduced, and heat generation due to Joule heat from the LED chip 21 can be decreased. Therefore, deterioration of peripheral members such as the insulating base material 31 due to heat from the LED chip 21 can be prevented.

[0046] As described above, the wiring board 20 directly mounts the LED chip 21 on the metal wiring portion 32 that can exhibit high heat dissipation. Thereby, even when the LED chips 21 are arranged at a high density, excessive heat generated when the LED chips 21 are lit can be quickly diffused through the metal wiring portion 32. For this reason, deterioration of peripheral members such as the insulating base material 31 due to heat from the LED chip 21 can be prevented.

[0047] (Overcoat layer) The overcoat layer 35 is formed on the outermost surface of the wiring board 20 so as to cover the LED chip 21. The overcoat layer 35 is formed directly on the metal wiring portion 32 and on the LED chip 21 and covers the metal wiring portion 32 and the LED chip 21. The overcoat layer 35 is a resinous film formed on its outermost surface (the surface located on the most light-emitting surface 20a side) mainly for ensuring the waterproofness and insulation of the wiring board 20 and protecting the metal wiring portion 32. In the present embodiment, the overcoat layer 35 has waterproofness and transparency. Due to the waterproofness of the overcoat layer 35, intrusion of water into the wiring board 20 can be prevented. When a highly efficient LED chip 21 having a luminous efficiency of, for example, 150 lm / W or more is selected as the LED chip 21, in the wiring board 20, the influence when a specific LED chip 21 is damaged becomes large. Therefore, making the LED chip 21 as difficult to be damaged as possible is important from the viewpoint of risk management.

[0048] The overcoat layer 35 can be formed of various resin compositions having an acrylic-based polyurethane resin or the like as a base resin. As the base resin of the resin composition used to form the overcoat layer 35, in addition to the acrylic-based polyurethane resin, urethane-based resins, polyester-based resins, phenol-based resins, fluorine-based resins, silicone-based resins, epoxy-based resins, etc. can be appropriately used.

[0049] The thickness of the overcoat layer 35 is 5 μm or more, preferably 10 μm or more, and more preferably 15 μm or more. Alternatively, the thickness of the overcoat layer 35 may be 100 μm or less, preferably 60 μm or less, and more preferably 40 μm or less. By setting the thickness of the overcoat layer 35 within the above range, the good flexibility, thinness, lightness, and good optical properties required in emergencies of the wiring board 20 can be maintained. Furthermore, sufficient waterproofing and insulation required in emergencies can be ensured for the wiring board 20, and sufficient protective performance, such as abrasion resistance, can be provided to the metal wiring portion 32 in emergencies.

[0050] The water resistance of the wiring board 20 provided by the overcoat layer 35 is not particularly limited, as long as it is sufficient to suppress the degradation of the LED chips 21 when water is sprayed onto the wiring board 20. Such water resistance is preferably IPX4 or higher according to the waterproof and dustproof protection standards set by the IEC (International Electrotechnical Commission). IPX4 or higher waterproofing means that the LED chips 21 are not adversely affected by water splashes from any direction. Specifically, this means that when water is sprayed from a spray nozzle at a rate of 10 L / min over the entire range of ±180° relative to the normal direction of the wiring board 20 for 5 minutes, the LED chips 21 are not adversely affected.

[0051] The insulating properties of the overcoat layer 35 are ensured by adjusting the resin composition and the thickness of the overcoat layer 35. According to "Appendix 4, 1 (2), Re (Ro), b (a)" of the Technical Standards for Electrical Appliances, for example, when the operating voltage exceeds 30V but is 150V or less, the insulating standard is that it must withstand an applied 1000V for 60 seconds or more. Therefore, the insulating properties of the overcoat layer 35 are designed to meet this standard.

[0052] Regarding the abrasion resistance of the overcoat layer 35, it is preferable that the overcoat layer 35 has a hardness of 2H or higher in the scratch hardness (pencil method) test. The test method for the scratch hardness (pencil method) test is in accordance with JIS K5600-5-4.

[0053] Regarding the flexibility of the overcoat layer 35, it is preferable that the overcoat layer 35 has a flexibility that allows it to be measured by the cylindrical mandrel method to have a diameter of 20 mm or less, and more preferably a flexibility that allows it to be measured by the cylindrical mandrel method to have a diameter of 10 mm or less. The test method for the cylindrical mandrel method is in accordance with JIS K5600-5-1.

[0054] Such a wiring board 20 does not contain solder resist. Therefore, manufacturing costs can be reduced. Here, as shown in Figure 4, in a plan view, the area of ​​the region where the metal wiring portion 32 is formed (shaded area) may be 65% to 98% of the area of ​​the insulating substrate 31, and for example, it may be 90%. Here, the metal wiring portion 32 is a part that has a higher light reflectivity compared to the insulating substrate 31. In particular, when the metal wiring portion 32 is made of aluminum foil, the light reflectivity of the metal wiring portion 32 becomes very high. Therefore, in a plan view, by having the area of ​​the region where the metal wiring portion 32 is formed be 65% of the area of ​​the insulating substrate 31, the light reflectivity of the wiring board 20 can be effectively increased. In other words, even if the wiring board 20 does not contain solder resist to increase light reflectivity, the light reflectivity of the wiring board 20 can be increased. In this case, in a plan view, if the area of ​​the region where the metal wiring portion 32 is formed is 80% or more of the area of ​​the insulating substrate 31, the light reflectivity of the wiring board 20 can be more effectively increased. Also, if the area of ​​the region where the metal wiring portion 32 is formed is 98% or less of the area of ​​the insulating substrate 31 in a plan view, the difficulty in manufacturing the metal wiring portion 32 can be suppressed.

[0055] (Manufacturing Method for Wiring Boards) Next, the manufacturing method for the wiring board 20 according to this embodiment will be described with reference to Figures 5A to 5H.

[0056] First, an insulating substrate 31 is prepared (Figure 5A). Next, a metal foil 32A, such as aluminum foil or copper foil, which will be the material for the metal wiring section 32, is laminated onto the surface of the insulating substrate 31 (Figure 5B). The metal foil 32A is bonded to the surface of the insulating substrate 31 by an adhesive layer 33, such as a urethane-based adhesive. Alternatively, the metal foil 32A may be directly formed on the surface of the insulating substrate 31 by an electrolytic plating method or a vapor deposition method (sputtering, ion plating, electron beam deposition, vacuum deposition, chemical deposition, etc.). Alternatively, the insulating substrate 31 may be directly welded to the metal foil 32A.

[0057] Next, an etching mask 37 patterned to the shape required for the metal wiring portion 32 is formed on the surface of the metal foil 32A (Figure 5C). This etching mask 37 is provided so that the portion of the metal foil 32A corresponding to the wiring pattern that will become the metal wiring portion 32 is not corroded by the etching solution. The method for forming the etching mask 37 is not particularly limited; for example, the etching mask 37 may be formed by exposing a photoresist or dry film to light through a photomask and then developing it. Alternatively, the etching mask 37 may be formed on the surface of the metal foil 32A using printing technology such as an inkjet printer.

[0058] Next, the metal foil 32A located in areas not covered by the etching mask 37 is removed by immersion (Figure 5D). This removes the parts of the metal foil 32A other than those that will become the metal wiring section 32.

[0059] Subsequently, the etching mask 37 is removed using an alkaline stripping solution. This removes the etching mask 37 from the surface of the metal wiring portion 32 (Figure 5E).

[0060] Next, the LED chip 21, regulator 45, and connectors 44A and 44B are mounted on the metal wiring section 32 (Figures 5F and 5G). Note that in Figures 5F, 5G, and Figure 5H (described later), the regulator 45 and other components are omitted for clarity. In this case, the LED chip 21 is bonded to the metal wiring section 32 via a joint 36. The joint 36 may be formed from a conductive paste (conductive formulations), an anisotropic conductive film (ACF), or solder paste for mounting. For example, first, a conductive paste 36a is layered on the metal wiring section 32 (Figure 5F). Next, the LED chip 21 is placed on the conductive paste 36a (Figure 5G). Then, by heating the conductive paste 36a, the LED chip 21 is mounted on the metal wiring section 32 via the joint 36.

[0061] Next, an overcoat layer 35 is formed to cover the metal wiring section 32, LED chip 21, regulator 45, and connectors 44A and 44B (Figure 5H). This overcoat layer 35 is preferably formed by a method of spraying a transparent resin composition (hereinafter referred to as the "spray coating method"), a curtain coating method, or a dip method. The overcoat layer 35 can be formed by the spray coating method, for example, by spraying a coating liquid for spray coating containing an acrylic polyurethane resin onto a desired area on the insulating substrate 31 using a spray coating machine to form a coating film. The overcoat layer 35 can be formed by the curtain coating method, for example, by dropping a coating liquid for curtain coating containing an acrylic polyurethane resin onto a desired area on the insulating substrate 31 using a curtain coating machine to form a coating film. The overcoat layer 35 can be formed by the dip method, for example, as follows. First, the entire member on which the components are mounted (the member shown in Figure 5G) is immersed in a coating liquid for dip coating containing an acrylic polyurethane resin stored in a dip tank. Subsequently, the component immersed in the coating solution is removed from the coating solution. In this way, a coating film (overcoat layer 35) may be formed.

[0062] Furthermore, the wiring board 20 according to this embodiment is not limited to the method described above, but can also be manufactured by conventionally known flexible wiring boards for LED chips, or by known methods for manufacturing various wiring boards on which LED chips are mounted.

[0063] (Plant cultivation factory and plant cultivation shelves) Figure 6 is a schematic diagram showing the configuration of a plant cultivation factory 90 using the wiring board 20 according to this embodiment. The plant cultivation factory 90 comprises a building 91 and a plurality of plant cultivation shelves 80 arranged inside the building 91.

[0064] As shown in Figure 7, the plant cultivation shelf 80 has a plurality (four) of support posts 82 and a plurality of substrates 81 arranged vertically at intervals along the support posts 82. The upper surface of each substrate 81, except for the uppermost substrate 81, is provided with a growing medium area for cultivating plant PLs. The lower surface of each substrate 81, except for the lowest substrate 81, forms a ceiling surface relative to the substrate 81 located below it. Wiring boards 20 are attached to the lower side of each substrate 81, except for the lowest substrate 81, and the wiring boards 20 are arranged in parallel. In this case, the control unit 40 is located at a sufficient distance from the wiring boards 20. Therefore, there is little risk of variations in growth due to heat from the control unit 40 between plant PLs located close to the control unit 40 and those located far away. In addition, the substrates 81 and the wiring boards 20 attached to the substrates 81 constitute the shelf boards 83 for the plant cultivation shelf.

[0065] Because the wiring board 20 according to this embodiment is flexible and lightweight, it can be attached to the underside of each board 81 more easily than with conventional straight-tube lighting devices. Furthermore, because the wiring board 20 is flexible, it can be attached to ceiling surfaces of various sizes and shapes. As a result, the wiring board 20 according to this embodiment can be applied to various plant cultivation shelves 80 and plant cultivation factories 90.

[0066] Furthermore, the wiring board 20 is thinner compared to conventional straight-tube lighting devices. This allows for a narrower spacing between the boards 81 in the vertical direction, increasing the number of boards 81 included in each plant growing shelf 80. As a result, the yield of plant PL per unit area can be increased.

[0067] Although not shown in the diagram, the wiring board 20 may be placed not only on the underside of the substrate 81 but also on the side of the substrate 81. The wiring board 20 on the side may hang down from the substrate 81 located above it toward the substrate 81 located below it. In this case, the wiring board 20 may reach the substrate 81 located below it. Alternatively, the wiring board 20 may not reach the substrate 81 located below it, but may only cover the upper part of the space located between the upper and lower substrates 81. By further placing the wiring board 20 on the side of the substrate 81 in this way, the amount of light at the periphery of the substrate 81, where illumination tends to be weaker, can be supplemented, and the brightness of the wiring board 20 can be made uniform across the surface. As a result, plant growth can be made uniform across the surface, and the yield of the plants being grown can be improved.

[0068] As described above, according to this embodiment, the wiring board 20 comprises an insulating substrate 31, a metal wiring portion 32 formed on the insulating substrate 31, an LED chip 21 mounted on the metal wiring portion 32, and an overcoat layer 35 covering the LED chip 21 and the metal wiring portion 32. The wiring board 20 does not contain solder resist. In this way, the manufacturing cost of the wiring board 20 can be reduced by not including solder resist. Furthermore, because the wiring board 20 is equipped with an overcoat layer 35 covering the metal wiring portion 32, oxidation of the metal wiring portion 32 can be effectively suppressed even if the wiring board 20 does not contain solder resist. In particular, when aluminum foil is used for the metal wiring portion 32, the surface of the aluminum foil oxidizes quickly. However, because the wiring board 20 is equipped with an overcoat layer 35 covering the metal wiring portion 32, oxidation of the metal wiring portion 32 can be effectively suppressed even when aluminum foil is used for the metal wiring portion 32.

[0069] Furthermore, according to this embodiment, the overcoat layer 35 is formed directly on the metal wiring portion 32 and the LED chip 21. In this case as well, oxidation of the metal wiring portion 32 can be effectively suppressed.

[0070] Furthermore, according to this embodiment, the metal wiring section 32 is made of aluminum foil, and the thickness of the metal wiring section 32 is 5 μm or more and 200 μm or less. When aluminum foil is used for the metal wiring section 32, since aluminum is inexpensive and lightweight, it is possible to reduce the weight of the wiring board 20 while lowering the manufacturing cost of the wiring board 20. In addition, since aluminum has a high light reflectivity, when aluminum foil is used for the metal wiring section 32, the light reflectivity of the wiring board 20 can be increased even if the wiring board 20 does not contain solder resist as described above. Also, by having a thickness of 5 μm or more for the metal wiring section 32, the electrical conductivity can be effectively increased even when aluminum foil is used for the metal wiring section 32. Furthermore, by having a thickness of 200 μm or less for the metal wiring section 32, it is possible to maintain sufficient flexibility of the insulating substrate 31 while lowering the manufacturing cost of the wiring board 20, and a decrease in handling performance due to increased weight can be suppressed.

[0071] Although the example described uses an LED chip 21 as the electronic component, it is not limited to this. For example, the electronic component may be a microphone or a heating element, or a temperature sensor, humidity sensor, pressure sensor, or acceleration sensor.

[0072] Furthermore, while an example has been described in which the wiring board with electronic components (wiring board) 20 is an LED lighting device for plant cultivation, it is not limited to this. For example, the wiring board 20 may be used as a heater, defroster, etc.

[0073] [Examples] Next, specific examples of this embodiment will be described.

[0074] (Example 1) A wiring board as shown in Figure 3 was fabricated. In this case, aluminum foil was used for the metal wiring. Also, the aluminum foil was arranged so that the glossy side of the aluminum foil faced the overcoat layer.

[0075] (Example 2) A wiring board 20 was manufactured in the same manner as in Example 1, except that the aluminum foil was arranged so that the matte side of the aluminum foil faced the overcoat layer.

[0076] (Example 3) A wiring board was manufactured in the same manner as in Example 1, except that copper foil was used for the metal wiring section.

[0077] (Comparative Example) A wiring board was manufactured in the same manner as in Example 1, except that copper foil was used for the metal wiring portion, and a solder resist containing white pigment (manufactured by Taiyo Ink Mfg. Co., Ltd., product name HDE-020) was placed between the metal wiring portion and the overcoat layer.

[0078] Next, the reflectance of the wiring boards of Example 1 to Comparative Example was measured. The reflectance was measured using a spectrophotometer (Konica Minolta, Inc., CM-3600d). The reflectance was measured from the light-emitting side. The measurement point was the surface of the wiring board in an area where no components were mounted.

[0079] The results are shown in Figures 8 and 9. Figure 8 is a graph showing the reflectance of each wiring board. Figure 9 is a graph showing the emission spectrum of the LED chips used in the wiring board.

[0080] As a result, as shown in Figure 8, the wiring boards according to Examples 1 and 2 were able to obtain a higher reflectivity than the wiring board containing solder resist (the wiring board according to the comparative example). Therefore, it was found that by using aluminum foil as the metal wiring portion, the manufacturing cost of the wiring board can be reduced while increasing the light reflectivity of the wiring board.

[0081] Furthermore, as shown in Figure 8, the wiring substrate according to Example 3 achieved a higher reflectivity than the wiring substrate containing solder resist (the wiring substrate according to the comparative example) at wavelengths of approximately 600 nm or higher. Therefore, it was found that even when copper foil is used as the metal wiring portion, the light reflectivity of the wiring substrate can be increased in a specific wavelength range while reducing the manufacturing cost of the wiring substrate.

[0082] The multiple components disclosed in the above embodiments and variations can be combined as needed. Alternatively, some components may be removed from all the components shown in the above embodiments and variations.

Claims

1. A wiring board with electronic components, comprising an insulating substrate, a metal wiring portion formed on the insulating substrate, an electronic component mounted on the metal wiring portion, and an overcoat layer covering the electronic component and the metal wiring portion, wherein solder resist is not included.

2. The wiring board with electronic components according to claim 1, wherein the overcoat layer is formed directly on the metal wiring portion and the electronic components.

3. The wiring board with electronic components according to claim 1, wherein the metal wiring portion is made of aluminum foil, and the thickness of the metal wiring portion is 5 μm or more and 200 μm or less.

4. In a plan view, the area of ​​the region where the metal wiring portion is formed is 65% or more and 98% or less of the area of ​​the insulating substrate, as described in claim 1.

5. The wiring board with an electronic component according to claim 1, wherein the electronic component is an LED chip.

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