JP7779009B2 - Surface light source and its manufacturing method - Google Patents

Description

This disclosure relates to a surface light source and a method for manufacturing the same.

When the number of semiconductor-equipped elements increases or when the elements are densely packed, wiring boards require multilayer wiring. Furthermore, while there is a strong demand for thin multilayer wiring boards, warping due to thinning is a concern.

Japanese Patent Application Laid-Open No. 2006-310541

The purpose of this disclosure is to provide a surface light source that can achieve multi-layer wiring while reducing warping, and a method for manufacturing the same.

According to one aspect of the present disclosure, a surface light source includes a first substrate, a first surface on which a first wiring layer is disposed on the first substrate, and a second surface on which a second wiring layer is disposed on the first substrate and located opposite the first surface, a first wiring board on which the first wiring layer and the second wiring layer are electrically connected, a light source electrically connected to the first wiring layer on the first surface of the first wiring board, and an electronic component electrically connected to the second wiring layer, a second substrate having an elastic modulus lower than that of the first substrate, and a third surface facing the second surface of the first wiring board, a fourth surface on which a third wiring layer is disposed on the second substrate and located opposite the third surface, and a first hole portion, and a second wiring board stacked on the first wiring substrate, wherein the electronic component is located in the first hole portion, and the third wiring layer is electrically connected to the second wiring layer.
According to one aspect of the present disclosure, a method for manufacturing a surface light source includes the steps of: preparing a first wiring board including a first substrate, the first substrate having a first surface on which a first wiring layer is disposed, and a second substrate having a second wiring layer disposed on the first substrate and positioned opposite the first surface, the first wiring layer and the second wiring layer being electrically connected; arranging a light source electrically connected to the first wiring layer on the first surface of the first wiring board; arranging an electronic component electrically connected to the second wiring layer on the second surface of the first wiring board; and adjusting the elasticity of the first substrate. and laminating a second wiring board on the first wiring board, the second wiring board having a second substrate having a lower elastic modulus than the second substrate, a third surface facing the second surface of the first wiring board, a fourth surface on which a third wiring layer is disposed on the second substrate and located on the opposite side of the third surface, and a first hole portion penetrating at least the second substrate, wherein in the step of laminating the second wiring board on the first wiring board, the electronic component disposed on the second surface of the first wiring board is positioned within the first hole portion, and the third wiring layer is electrically connected to the second wiring layer.
According to one aspect of the present disclosure, a method for manufacturing a surface light source includes the steps of: preparing a first wiring board including a first substrate, the first substrate having a first surface on which a first wiring layer is disposed, and a second substrate having a second wiring layer disposed on the first substrate and positioned opposite the first surface, the first wiring layer and the second wiring layer being electrically connected; arranging a light source electrically connected to the first wiring layer on the first surface of the first wiring board; and providing a second substrate and a third substrate having a modulus of elasticity lower than that of the first substrate, the third substrate facing the second surface of the first wiring substrate, and the third wiring layer being disposed on the second substrate. the third wiring layer and the fourth wiring layer are electrically connected; a step of stacking the second wiring board on the first wiring board so as to electrically connect the third wiring layer to the second wiring layer; and a step of placing an electronic component on the fourth surface of the second wiring board so as to be located in the first hole, and electrically connecting the electronic component to the third wiring layer.

This disclosure provides a surface light source and a manufacturing method thereof that can achieve multi-layer wiring while reducing warping.

3A and 3B are plan views of the upper surface of the surface light source of each embodiment. FIG. 2 is a plan view of a portion of the lower surface of the surface light source of the first embodiment. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 . FIG. 2 is a cross-sectional view illustrating an example of a light source according to each embodiment. FIG. 2 is a cross-sectional view illustrating an example of a light source according to each embodiment. FIG. 2 is a cross-sectional view illustrating an example of a light source according to each embodiment. FIG. 2 is a cross-sectional view illustrating an example of a light source according to each embodiment. FIG. 10 is a cross-sectional view of a surface light source according to a second embodiment. FIG. 10 is a cross-sectional view of a surface light source according to a third embodiment. FIG. 10 is a cross-sectional view of a surface light source according to a fourth embodiment. 4 is a flowchart illustrating an example of a method for manufacturing the surface light source according to the first embodiment. 4 is a flowchart illustrating an example of a method for manufacturing the surface light source according to the first embodiment. 4 is a flowchart illustrating an example of a method for manufacturing the surface light source according to the first embodiment.

Embodiments will be described below with reference to the drawings. In each drawing, the same components are designated by the same reference numerals. Note that, because each drawing is a schematic representation of an embodiment, the scale, spacing, or positional relationship of each component may be exaggerated, or some components may not be shown. Additionally, cross-sectional views may include end views showing only the cut surface.

In the following description, components having substantially the same functions are denoted by the same reference numerals, and their descriptions may be omitted. Furthermore, terms indicating specific directions or positions (for example, "upper," "lower," and other terms incorporating these terms) may be used. However, these terms are merely used to facilitate understanding of relative directions or positions in the referenced drawings. As long as the relative direction or positional relationship indicated by terms such as "upper" and "lower" in the referenced drawings is the same, drawings other than those disclosed herein, actual products, etc., do not necessarily have to be arranged in the same way as in the referenced drawings. In this specification, "parallel" includes not only cases where two lines, sides, surfaces, etc. do not intersect even when extended, but also cases where the angle between the two lines, sides, surfaces, etc. is within a range of 10°.

[First embodiment]
3, the surface light source 1 of the first embodiment includes a multilayer wiring substrate 9, a light source 20A, and an electronic component 41. The multilayer wiring substrate 9 includes a first wiring substrate 50 and a second wiring substrate 60. The first wiring substrate 50 includes a first substrate 51, and the second wiring substrate 60 includes a second substrate 61. The second wiring substrate 60 further includes a first hole H1 in which the electronic component 41 is disposed.

The surface light source 1 has a light source 20A arranged on a multilayer wiring substrate 9. Power is supplied to the light source 20A through the wiring layer of the multilayer wiring substrate 9. The multilayer wiring substrate 9 has a first wiring substrate 50 and a second wiring substrate 60.

The first wiring board 50 has a first substrate 51. The first substrate 51 is made of an insulating material. Resins that can be used for the first substrate 51 include, for example, the commonly used epoxy resin, as well as urethane resin, polyimide resin, polyamide resin, aromatic polyester resin (liquid crystal polymer), bismaleimide-triazine resin, polyphenylene sulfide resin, fluorine-based resin, and silicone resin. Derivatives or mixed resins of the above resins may also be used. Furthermore, it is desirable to use glass woven fabric, glass nonwoven fabric, or glass fiber as the core material to increase the rigidity of the substrate. The elastic modulus of the first substrate 51 is desirably 20 GPa or more and 30 GPa or less.

In this specification, as shown in Figure 3, two directions that are parallel to the top surface of the first substrate 51 and perpendicular to each other are referred to as the first direction X and the second direction Y. Furthermore, one direction perpendicular to the first direction X and the second direction Y is referred to as the third direction Z, with the direction of the arrow being the +Z side or upward, and the direction opposite the arrow being the -Z side or downward. In this specification, "planar view" refers to viewing an object in the direction of the third direction Z, an "upper surface" refers to the surface of the object viewed from the +Z side, and a "lower surface" refers to the surface of the object viewed from the -Z side. In this specification, the thickness direction refers to the third direction Z. In this specification, the positional relationship expressed as "above" includes cases where two or more objects are positioned in the third direction Z and are in contact or not in contact.

The first wiring board 50 has a first surface 50a, where a first wiring layer 52 is disposed on a first substrate 51, and a second surface 50b, where a second wiring layer 53 is disposed on the first substrate 51, located on the opposite side of the first surface 50a. In other words, the first surface 50a is the +Z side surface of the first wiring board 50, and the second surface 50b is the -Z side surface of the first wiring board 50.

The first wiring layer 52 and the second wiring layer 53 can be made of materials such as copper, nickel, and aluminum.

The first substrate 51 has a first through hole h1 penetrating the first substrate 51 in the thickness direction. A first conductive member 54 is provided in the first through hole h1. The first wiring layer 52 and the second wiring layer 53 are electrically connected by the first conductive member 54. Materials that can be used for the first conductive member 54 include, for example, copper, silver, nickel, tin, zinc, carbon, and other elements or alloys thereof, as well as materials such as resin powder or inorganic powder plated with conductive material. The first conductive member 54 may also be a mixture of a filler such as flake-, scale-, or bark-shaped silver powder or copper powder and a thermosetting binder resin such as epoxy resin, phenolic resin, urethane resin, or polyester resin. It is preferable to use a first conductive member 54 with as low a volume resistivity as possible and with as little binder resin or solvent content as possible.

The light source 20A is arranged on the first surface 50a of the first wiring substrate 50. Multiple light sources 20A are arranged on the first surface 50a, and the electrodes 24 of the light sources 20A are electrically connected to the first wiring layer 52 via first bonding members 91. The first bonding members 91 can be, for example, solder or conductive paste.

The second wiring board 60 is laminated on the first wiring board 50. The second wiring board 60 has a second base material 61. The second base material 61 is made of an insulating material. Materials that can be used for the second base material 61 include, for example, urethane resin, polyimide resin, polyamide resin, aromatic polyester resin (liquid crystal polymer), polyphenylene sulfide resin, fluorine-based resin, and silicone resin, all of which have an elastic modulus of 10 GPa or less. The elastic modulus of the second base material 61 is preferably 2 GPa or more and 5 GPa or less.

The second wiring board 60 has a third surface 60a facing the second surface 50b of the first wiring board 50, and a fourth surface 60b on the opposite side of the third surface 60a, where a third wiring layer 62 is disposed on the second base material 61. In other words, the third surface 60a is the +Z side surface of the second wiring board 60, and the fourth surface 60b is the -Z side surface of the second wiring board 60.

The third wiring layer 62 can be made of, for example, copper, nickel, aluminum, etc.

The first wiring board 50 and the second wiring board 60 are bonded via a first adhesive sheet 81 disposed between the first substrate 51 and the second substrate 61. As shown in FIG. 3, the first adhesive sheet 81 covers the second wiring layer 53. Alternatively, the first substrate 51 and the second substrate 61 may be bonded directly to each other. By bonding the first wiring board 50 and the second wiring board 60 so that the first adhesive sheet 81 covers the second wiring layer 53, it is possible to more easily reduce in-plane variations in the thickness of the surface light source 1 than when the first substrate 51 and the second substrate 61 are bonded directly to each other.

The first adhesive sheet 81 can be made of a thermoplastic resin such as acrylic resin, polyurethane resin, polycarbonate resin, cyclic polyolefin resin, polyethylene terephthalate resin, polyester resin, or aromatic polyester resin (liquid crystal polymer), or a thermosetting resin such as epoxy resin or silicone resin. It is preferable to use a highly flame-retardant material for the first adhesive sheet 81. The elastic modulus of the first adhesive sheet 81 is, for example, 100 MPa or more and 1 GPa or less. The thickness of the first adhesive sheet 81 is, for example, 0.01 mm or more and 0.1 mm or less. This range of elastic modulus and thickness can suppress warping while ensuring adhesion between the wiring boards.

The second substrate 61 has a second through hole h2, which penetrates at least the second substrate 61 in the thickness direction. When the first adhesive sheet 81 is disposed, for example, the second through hole h2 penetrates from the fourth surface 60b side through the third wiring layer 62, the second substrate 61, and the first adhesive sheet 81 between the second substrate 61 and the second wiring layer 53, and reaches the second wiring layer 53. A second conductive member 63 is provided inside the second through hole h2. The second wiring layer 53 and the third wiring layer 62 are electrically connected by the second conductive member 63. The second conductive member 63 is made of the same material as the first conductive member 54.

For example, the second substrate 61 may be at least one layer of polyimide resin and may be flexible. A portion of the second substrate 61 may extend outward from the light-emitting surface of the surface light source 1 as a flat cable 61a, as shown in FIG. 1. By connecting the third wiring layer 62 arranged on the flat cable 61a to an external connector, power can be supplied to the surface light source 1 from an external power source. The wiring layer closest to the -Z side of the second wiring board 60 may also be connected to the external connector.

The second wiring substrate 60 has a first hole H1. When the first adhesive sheet 81 is placed, the first hole H1 penetrates the second base material 61 and the first adhesive sheet 81 from the fourth surface 60b side and reaches the second surface 50b of the first wiring substrate 50. It is preferable that the first adhesive sheet 81 does not cover the second wiring layer 53 in the first hole H1.

An electronic component 41 is disposed on the second surface 50b of the first wiring substrate 50 within the first hole H1. The electrodes 42 of the electronic component 41 are electrically connected to the second wiring layer 53 on the second surface 50b via a second bonding member 92. The second bonding member 92 may be, for example, solder, an anisotropic conductive film (ACF), or an anisotropic conductive paste (ACP).

The electronic component 41 is electrically connected to the light source 20A via at least the second wiring layer 53, the first conductive member 54, and the first wiring layer 52. The electronic component 41 is, for example, a control element that controls the on/off and dimming of the light source 20A. The control element includes, for example, a transistor. Alternatively, the electronic component 41 is, for example, a protection element that protects the light source 20A from static electricity. A diode, for example, can be used as the protection element.

As shown in FIG. 2, an electronic component 41 is placed in the first hole H1. For example, the second wiring board 60 has multiple first hole H1. Therefore, the surface light source 1 has multiple electronic components 41. Multiple electronic components 41 may be placed in the first hole H1. Also, there may be a first hole H1 in which no electronic component 41 is placed.

In addition, a passive element 45 such as a resistor or capacitor can be placed within the first hole H1. The passive element 45 is placed on the second surface 50b of the first wiring substrate 50 within the first hole H1 and is electrically connected to the second wiring layer 53. The passive element 45 is electrically connected to the electronic component 41 via the second wiring layer 53.

It is preferable to place a resin member 32 inside the first hole H1. The resin member 32 covers at least the electronic component 41 and the passive element 45. The resin member 32 may also cover the connection between the electronic component 41 and the second wiring layer 53, and the connection between the passive element 45 and the second wiring layer 53. This protects them from moisture, dust, and the like. Epoxy resin, for example, can be used as the material for the resin member 32.

The elastic modulus of the second substrate 61 is lower than that of the first substrate 51. If, for example, glass cloth impregnated with epoxy resin is used as the material for the first substrate 51, the elastic modulus of the first substrate 51 is approximately 20 GPa to 30 GPa. The thickness of the first substrate 51 is, for example, 0.04 mm to 0.6 mm. If, for example, polyimide resin is used as the material for the second substrate 61, the elastic modulus of the second substrate 61 is approximately 2 GPa to 5 GPa. The thickness of the second substrate 61 is, for example, 0.012 mm to 0.1 mm. The difference between the elastic modulus of the first substrate 51 and the elastic modulus of the second substrate 61 is preferably 4 to 15 times. The thickness of the first substrate 51 is preferably at least twice the thickness of the second substrate 61.

The first substrate 51, which has a higher elastic modulus than the second substrate 61, is less likely to deform than the second substrate 61. For example, when substrates made of materials with high elastic moduli and different linear expansion coefficients are cured at a high temperature and then cooled, the substrates will pull against each other and warp due to differences in expansion and contraction caused by the properties of the materials. In contrast, this embodiment uses a second substrate 61 that has a lower elastic modulus than the first substrate 51, or in other words, is much softer than the first substrate 51. Therefore, despite differences in expansion and contraction caused by the properties of the materials, when cured at a high temperature and then cooled, the first substrate 51 and the second substrate 61 do not pull against each other, and the second substrate 61 follows the expansion and contraction of the first substrate 51, thereby reducing warping. Therefore, by arranging the light sources 20A on the first surface 50a of the first wiring board 50, which is located on the +Z side of the first substrate 51, the predetermined pitch between the multiple light sources 20A can be stably maintained. This reduces brightness unevenness in the surface light source 1 and improves the handleability of the surface light source 1.

In addition, while the planar light source 1 has an asymmetric layered structure in the thickness direction, with the light source 20A located on the +Z side of the first substrate 51 and the electronic component 41 located on the -Z side, by laminating the second substrate 61, which has a lower elastic modulus than the first substrate 51, onto the first substrate 51, the warping of the planar light source 1 can be reduced by the above-mentioned action. This makes it possible to achieve multi-layer wiring while reducing warping.

By placing the electronic component 41 closer to the light source 20A on the opposite side of the light-emitting surface rather than outside the light-emitting surface of the surface light source 1, the wiring distance between the electronic component 41 and the light source 20A can be shortened without blocking the light from the light source 20A. This enables stable control of the light source 20A with less noise.

The light source 20A and the electronic component 41 each generate heat during operation. Therefore, it is preferable that the light source 20A and the electronic component 41, both of which are heat sources, do not overlap in a planar view. In other words, it is preferable that the third surface 60a of the second wiring board 60 face the second surface 50b of the first wiring board 50 so that the light source 20A overlaps the second wiring board 60 by at least 80% of the area of the light source 20A in a planar view. This prevents the heat generated by the light source 20A and the electronic component 41 from concentrating.

Furthermore, as shown in FIG. 2, it is preferable that the electronic component 41 be located between at least two light sources 20A in a planar view. This allows the distances between the multiple light sources 20A and the electronic component 41 that controls them to be approximately equal in a planar view.

The electronic component 41 has a first main surface 41a facing the second surface 50b of the first wiring substrate 50 and a second main surface 41b located on the opposite side of the first main surface 41a in the thickness direction of the electronic component 41. The electrode 42 is disposed on the first main surface 41a. The second main surface 41b is preferably located within the first hole H1. The second main surface 41b being located within the first hole H1 means that, where d1 is the distance between the second main surface 41b and the second surface 50b of the first wiring substrate 50 in a direction perpendicular to the second surface 50b (third direction Z), and d2 is the distance between the fourth surface 60b of the second wiring substrate 60 and the second surface 50b of the first wiring substrate 50 in a direction perpendicular to the second surface 50b, d1≦d2. In other words, the electronic component 41 is embedded within the multilayer wiring substrate 9. This allows the electronic components 41 to be placed on the opposite side of the light-emitting surface of the surface light source 1, while still allowing the surface light source 1 to be made thinner.

A specific example of the light source 20A will be described below. As shown in FIG. 4A, the light source 20A includes a light-emitting element 21. The light-emitting element 21 includes a substrate, such as sapphire or gallium nitride, and a semiconductor structure disposed on the substrate. The semiconductor structure includes an n-type semiconductor layer, a p-type semiconductor layer, and an active layer sandwiched between them. The light-emitting element 21 also includes an n-side electrode electrically connected to the n-type semiconductor layer, and a p-side electrode electrically connected to the p-type semiconductor layer. The light source 20A also includes at least a pair of positive and negative electrodes 24 disposed on the underside. One of the pair of electrodes 24 is electrically connected to the p-side electrode, and the other is electrically connected to the n-side electrode. Note that the light-emitting element 21 may not include a substrate.

The active layer may have a structure having a single well layer, such as a double heterostructure or a single quantum well structure (SQW), or a structure having a group of well layers, such as a multiple quantum well structure (MQW). The active layer can emit visible light or ultraviolet light. The active layer can emit visible light ranging from blue to red. A semiconductor structure including such an active layer may include, for example, In _x Al _y Ga _1-x-y N (0≦x, 0≦y, x+y≦1). The semiconductor structure may include at least one active layer capable of emitting the above-described light. For example, the semiconductor structure may have a structure including one or more active layers between an n-type semiconductor layer and a p-type semiconductor layer, or may have a structure in which a structure including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer in that order is repeated multiple times. When the semiconductor structure includes multiple active layers, the active layers may have different emission peak wavelengths, or may have the same emission peak wavelength. Note that the same emission peak wavelength may have a variation of, for example, several nanometers. Such a combination of active layers can be appropriately selected, and for example, when the semiconductor structure includes two active layers, the active layers can be selected from a combination of blue light and blue light, green light and green light, red light and red light, ultraviolet light and ultraviolet light, blue light and green light, blue light and red light, or green light and red light, etc. Furthermore, the active layer may include a plurality of well layers having different emission peak wavelengths, or may include a plurality of well layers having the same emission peak wavelength.

The light source 20A may further include a wavelength conversion member 23. For example, in Figures 3 and 4A, the wavelength conversion member 23 covers the upper surface of the light emitting element 21. The wavelength conversion member 23 includes a light-transmitting resin and a phosphor. As the light-transmitting resin, for example, a silicone resin, an epoxy resin, or the like can be used. Examples of phosphors include yttrium aluminum garnet phosphors (e.g., _Y3 (Al,Ga) _5O12 :Ce), lutetium aluminum garnet phosphors (e.g., _Lu3 (Al,Ga _{)5O12 :} Ce), terbium aluminum garnet phosphors (e.g., _Tb3 (Al _{, Ga)5O12 :} Ce), CCA phosphors (e.g., _Ca10 ( _PO4 ) _{6C12 :} Eu), SAE phosphors (e.g., _Sr4Al14O25 : _Eu ), chlorosilicate phosphors ₍ e.g., _{Ca8MgSi4O16Cl2} :Eu), _and β-sialon phosphors (e.g., (Si,Al _{) 3} (O, _N ) ₄ oxynitride phosphors such as SLA phosphors (for example, SrLiAl ₃ N ₄ :Eu), CASN phosphors (for example, CaAlSiN ₃ :Eu) or SCASN phosphors (for example, (Sr,Ca)AlSiN ₃ :Eu), nitride phosphors such as KSF phosphors (for example, K ₂ SiF ₆ :Mn), KSAF phosphors ( _for example, K _{2 Si 0.99} Al _0.01 F _5.99 :Mn) or MGF phosphors (for example, 3.5MgO.0.5MgF ₂ .GeO ₂ Examples of the phosphor that can be used include a fluoride-based phosphor such as CsPb(F,Cl,Br,I) ₃ , a phosphor having a perovskite structure (e.g., CsPb(F,Cl,Br,I)3), and a quantum dot phosphor (e.g., CdSe, InP, _AgInS2 , or _AgInSe2 ). The wavelength conversion member 23 may include one type of phosphor or multiple types of phosphors.

The light source 20A may further include a covering member 22. For example, as shown in FIG. 4A, the covering member 22 covers the side surface of the light-emitting element 21. The covering member 22 is also disposed on the underside of the light-emitting element 21. The covering member 22 is disposed so that the underside of the electrode 24 of the light source 20A is exposed from the covering member 22. The covering member 22 not only protects the light-emitting element 21, but can also have functions such as wavelength conversion and light diffusion depending on the particles added to the covering member 22.

The covering member 22 includes, for example, light-scattering particles and a resin material. The light-scattering particles of the covering member 22 may be, for example, particles of titania, silica, alumina, zinc oxide, magnesium oxide, zirconia, yttria, calcium fluoride, magnesium fluoride, niobium pentoxide, barium titanate, tantalum pentoxide, barium sulfate, or glass. The resin material of the covering member 22 may be, for example, a thermoplastic resin such as acrylic resin, polycarbonate resin, cyclic polyolefin resin, polyethylene terephthalate resin, or polyester resin, or a thermosetting resin such as epoxy resin or silicone resin.

The light source in the surface light source 1 can be light source 20B shown in Figure 4B, light source 20C shown in Figure 4C, or light source 20D shown in Figure 4D.

The light source 20B shown in Figure 4B includes multiple light-emitting elements 21. The emission peak wavelengths of the multiple light-emitting elements 21 may be the same or different from each other.

The light source 20C shown in Figure 4C includes a wiring portion 25 disposed on the underside of the covering member 22. The wiring portion 25 is electrically connected to the electrode 24 below the light-emitting element 21. The wiring portion 25 extends from the connection with the electrode 24 to an area outside the area below the light-emitting element 21 (in other words, an area that does not overlap with the light-emitting element 21 in a top view). This facilitates electrical connection between the wiring portion 25 and the multilayer wiring board 9 when mounting the light source 20C on the multilayer wiring board 9.

The light source 20D shown in Figure 4D includes a wavelength conversion member 23 arranged on the upper and side surfaces of the light emitting element 21, and a covering member 22 arranged on the upper surface of the wavelength conversion member 23 and the lower surface of the light emitting element 21. An electrode 24 is provided below the light emitting element 21, and the side surfaces of the electrode 24 are covered by the covering member 22. The lower surface of the electrode 24 is exposed from the covering member 22.

The light source may not include a wavelength conversion member 23. The light source may not include a covering member 22. The light source may be a single light-emitting element 21.

The surface light source 1 only needs to have at least the light source 20 arranged on the multilayer wiring substrate 9, but a light-transmitting member 31 covering the light source 20 may also be provided on the multilayer wiring substrate 9, or a light-guiding member 10 may also be provided on the multilayer wiring substrate 9. Furthermore, as shown in FIG. 3, the surface light source 1 can also have a light-transmitting member 31 covering the light source 20 in addition to providing the light-guiding member 10 on the multilayer wiring substrate 9. Note that light source 20 is a collective term for light sources 20A, 20B, 20C, and 20D.

As described above, the surface light source 1 may include a light-guiding member 10. The light-guiding member 10 has an upper surface 11 and a lower surface 12 opposite the upper surface 11. As shown in FIG. 1, the upper surface 11 of the light-guiding member 10 can form part of the upper surface, which is the light-emitting surface of the surface light source 1. In a plan view, the outer shape of the light-guiding member 10 is, for example, a rectangle having two sides extending in the first direction X and two sides extending in the second direction Y. The light-guiding member 10 is disposed on the first surface 50a of the first wiring substrate 50. As shown in FIG. 1, the light-guiding member 10 has multiple second holes H2, and a light source 20A is disposed in each of the second holes H2. Multiple light sources 20A may be disposed in one second hole H2. Furthermore, among the multiple second holes H2, there may be a second hole H2 in which a light source 20A is not disposed.

Specific examples of the light-guiding member 10 are described below.

The light-guiding member 10 has multiple light-emitting units 10a separated from each other in the first direction X and the second direction Y by multiple grooves 14. Each light-emitting unit 10a can be used as a driving unit for local dimming, for example.

In the example shown in FIG. 3, the groove 14 penetrates from the upper surface 11 to the lower surface 12 of the light-guiding member 10. Alternatively, the groove 14 may be a bottomed groove that has an opening on the upper surface 11 side and whose bottom does not reach the lower surface 12. Alternatively, the groove 14 may be a bottomed groove that has an opening on the lower surface 12 side and whose bottom does not reach the upper surface 11.

A partition member that is reflective to the light emitted by the light source 20A can be placed within the groove 14. The partition member can contain, for example, light-scattering particles and a resin material. The light-scattering particles of the partition member can be, for example, particles of titania, silica, alumina, zinc oxide, magnesium oxide, zirconia, calcium carbonate, or glass. The resin material of the partition member can be, for example, a thermoplastic resin such as acrylic resin or polycarbonate resin, or a thermosetting resin such as epoxy resin or silicone resin. The partition member can also be made of a metal such as aluminum or silver.

The light-guiding member 10 is translucent and transmits the light emitted by the light source 20A. The transmittance of the light-guiding member 10 for the light emitted by the light source 20A is preferably 50% or more, and more preferably 70% or more.

The light-guiding member 10 can be made of a thermoplastic resin such as acrylic resin, polycarbonate resin, cyclic polyolefin resin, polyethylene terephthalate resin, or polyester resin; a thermosetting resin such as epoxy resin or silicone resin; or glass.

The thickness of the light-guiding member 10 in the third direction Z is preferably, for example, 150 μm or more and 800 μm or less. In this specification, the thickness of each member refers to the thickness of the portion of each member where no holes, recesses, or grooves are formed. The light-guiding member 10 may be composed of a single layer in the thickness direction, or may be composed of a laminate of multiple layers. When the light-guiding member 10 is composed of a laminate, a translucent adhesive layer may be disposed between each layer. Each layer of the laminate may use a different type of main material. Examples of materials that can be used for the adhesive layer include thermoplastic resins such as acrylic resin, polycarbonate resin, cyclic polyolefin resin, polyethylene terephthalate resin, or polyester resin, or thermosetting resins such as epoxy resin or silicone resin.

The light-guiding member 10 has a second hole H2 that penetrates from the upper surface 11 to the lower surface 12. In plan view, the shape of the second hole H2 can be, for example, circular. Furthermore, in plan view, the second hole H2 can be, for example, elliptical or polygonal, such as triangular, rectangular, hexagonal, or octagonal. The second hole H2 may also be a recess with an opening on the lower surface 12 side.

Specific examples of the translucent member 31 are described below.

The light-transmitting member 31 is disposed between the side surface of the light source 20A and the light-guiding member 10 in the second hole portion H2 of the light-guiding member 10, and above the light source 20A. The light-transmitting member 31 covers the top and side surfaces of the light source 20A. It is preferable that the light-transmitting member 31 contacts the light-guiding member 10 and the light source 20A. This makes it easier to guide light from the light source 20A to the light-guiding member 10.

The light-transmitting member 31 is translucent and transmits light emitted by the light source 20A. The transmittance of the light-transmitting member 31 for the peak wavelength of the light source 20A is preferably 50% or more, and more preferably 70% or more. The light-transmitting member 31 contains a resin, and can be, for example, the same resin as the material of the light-guiding member 10 or a resin with a small difference in refractive index from the material of the light-guiding member 10.

The light-transmitting member 31 may be composed of a single layer in the thickness direction of the light-guiding member 10, or may be composed of a laminate of multiple layers. The light-transmitting member 31 may also contain phosphors, light-scattering particles, etc. For example, the light-transmitting member 31 may be composed of a layer containing phosphors and a layer not containing phosphors.

A light-reflecting member 85 may also be disposed on the first surface 50a of the first wiring substrate 50. The light-reflecting member 85 is located between the lower surface 12 of the light-guiding member 10 and the first surface 50a of the first wiring substrate 50.

The light-reflecting member 85 has reflectivity and reflects the light emitted by the light source 20A. The light-reflecting member 85 can be made of, for example, a resin containing numerous air bubbles or a resin containing light-scattering particles. The light-scattering particles and resin material contained in the light-reflecting member 85 can be the same as those used for the covering member 22.

Next, an example of a method for manufacturing the surface light source 1 of the first embodiment will be described.

Figure 8 is a flowchart that includes the steps of preparing a first wiring board 50, placing a light source 20A on the first wiring board 50, and placing an electronic component 41 on the first wiring board 50.

In step S1, the first wiring substrate 50 is prepared. As described above, the first wiring substrate 50 has a first base material 51, a first wiring layer 52, and a second wiring layer 53. The first wiring layer 52 and the second wiring layer 53 are electrically connected via a first conductive member 54 provided inside the first through hole h1 of the first wiring substrate 50. As an example, the first conductive member 54 is provided by printing using a mask with an opening slightly larger than the first through hole h1, so that it has a filled portion that fills the first through hole h1 and a printed portion on the surface of the second wiring layer 53 with a volume approximately equal to the opening of the mask.

Step S1 is followed by steps S2, S3, and S4. Step S3 can be performed after step S2, and step S4 can be performed after step S3. Alternatively, step S4 can be performed after step S3, and step S2 can be performed after step S4. Note that step S2 may be omitted.

In step S2, the light-reflecting member 85 is placed on the first surface 50a of the first wiring board 50. The light-reflecting member 85 is adhered to the first surface 50a directly or via an adhesive sheet. The light-reflecting member 85 is formed, for example, by printing a developable highly reflective solder resist on the first surface 50a of the first wiring board 50, or by laminating a developable highly reflective white solder resist, followed by patterning through exposure and development.

In step S3, a first bonding member 91 is placed on the first wiring layer 52 of the first wiring board 50 on which the light source 20A is mounted. The first bonding member 91 used to mount the light source 20A is placed on the first wiring layer 52 by printing using a metal mask or by applying paste using a dispenser.

In step S4, the light source 20A is placed on the first wiring layer 52, on which the first bonding member 91 of the first wiring substrate 50 is placed, so that the electrode 24 of the light source 20A is in contact with the first bonding member 91. The light source 20A is placed on the first wiring layer 52 via the first bonding member 91.

After step S4, in step S5A, a second bonding member 92 is placed on the second wiring layer 53 of the first wiring board 50 on which the electronic component 41 is mounted. The second bonding member 92 used to mount the electronic component 41 is placed on the second wiring layer 53 by printing using a metal mask, applying paste using a dispenser, or crimping an ACF.

After step S5A, in step S6A, an electronic component 41 is placed on the second surface 50b of the first wiring substrate 50. The electrodes 42 of the electronic component 41 are placed on the second wiring layer 53 via the second bonding member 92.

After step S6A, in step S7A, the first bonding member 91 and the second bonding member 92 are reflowed simultaneously. That is, the electrode 24 of the light source 20A is bonded to the first bonding member 91, and the electrode 42 of the electronic component 41 is bonded to the second bonding member 92 simultaneously. As a result, the light source 20A is electrically connected to the first wiring layer 52 via the first bonding member 91, and the electronic component 41 is electrically connected to the second wiring layer 53 via the second bonding member 92.

After step S4, in step S5B, only the first bonding member 91 may be reflowed first. After the electrode 24 of the light source 20A and the first bonding member 91 are bonded by reflowing the first bonding member 91, in step S6B, the second bonding member 92 is placed on the second wiring layer 53, and in step S7B, the electronic component 41 is placed on the second surface 50b.

Then, in step S8B, the second bonding member 92 is reflowed to bond the electrodes 42 of the electronic component 41 to the second bonding member 92. It is preferable that the second bonding member 92 have a lower melting point than the first bonding member 91 so that the first bonding member 91 does not melt when the second bonding member 92 is reflowed.

Figure 9 is a flowchart showing the process for preparing the second wiring substrate 60.

In step S11, the second substrate 61 and the third wiring layer 62 are prepared. As mentioned above, the elastic modulus of the second substrate 61 is lower than the elastic modulus of the first substrate 51.

When the second wiring board 60 is laminated to the first wiring board 50 via an adhesive sheet, in step S12, the first adhesive sheet 81, which is in a soft, adhesive state before hardening, is placed on the third surface 60a of the second wiring board 60. The first adhesive sheet 81 is adhered to the third surface 60a.

In step S13, the first hole H1 and the second through hole h2 are formed. The first hole H1 and the second through hole h2 are formed by penetrating at least the second substrate 61 and the first adhesive sheet 81. By forming the first hole H1 and the second through hole h2 while the first adhesive sheet 81 is adhered to the second substrate 61, misalignment of the first hole H1 and the second through hole h2 between the second substrate 61 and the first adhesive sheet 81 is suppressed.

In step S14, a second conductive member 63 is placed in the second through hole h2. The second conductive member 63 is formed by supplying a conductive paste containing, for example, resin and metal particles to the second through hole h2 using printing in the same manner as for the first conductive member 54 described above, and then thermally curing the conductive paste, thereby placing the second conductive member 63 in the second through hole h2.

The process shown in Figure 8 results in a first wiring board 50 on which the light source 20A and electronic components 41 are arranged. The process shown in Figure 9 results in a second wiring board 60 on which the first adhesive sheet 81 is arranged. After these processes, in step S21 shown in Figure 10, the second wiring board 60 is laminated on the first wiring board 50.

A first adhesive sheet 81 is placed between the first substrate 51 and the second substrate 61, and the second wiring board 60 is laminated to the first wiring board 50 via the first adhesive sheet 81. The first adhesive sheet 81 covers the second wiring layer 53 of the first wiring board 50. The second conductive member 63 reaches the second wiring layer 53, and the second wiring layer 53 is electrically connected to the third wiring layer 62 via the second conductive member 63.

The second wiring board 60 is stacked on the first wiring board 50 so that the electronic component 41 arranged on the second surface 50b of the first wiring board 50 is located within the first hole H1 in a planar view. At this time, it is preferable that the second main surface 41b of the electronic component 41 is also located within the first hole H1 in the third direction Z. It is also preferable that the third surface 60a of the second wiring board 60 faces the second surface 50b of the first wiring board 50 so that the light source 20A overlaps the second wiring board 60 in a planar view. This allows the light source 20A and the electronic component 41 to be positioned so that the heat generated by each is not locally concentrated.

After laminating the second wiring board 60 on the first wiring board 50, in step S22, if the first wiring board 50 and the second wiring board 60 are bonded using a first adhesive sheet 81 made of, for example, urethane resin, the first adhesive sheet 81 is hardened by heat pressing at 80°C to 120°C for 5 minutes to 1 hour. If the second main surface 41b of the electronic component 41 is located inside the opening of the first hole portion H1 in the third direction Z (d1 < d2), no stress is applied to the electronic component 41 even when pressure is applied during heat pressing. If another material is used for the first adhesive sheet 81, the heat pressing conditions are not limited to those described above. In addition, if the second main surface 41b of the electronic component 41 is located at the same position as the opening of the first hole H1 in the third direction Z, or is located outside the first hole H1 (d1≧d2), then a spacer having an opening in a plan view can be positioned on the fourth surface 60b of the second wiring board 60 so that the first hole H1 is included, and then hot-pressed.

After step S22, in step S23, the light-guiding member 10 may be placed on the first surface 50a of the first wiring substrate 50. If a light-reflecting member 85 is placed on the first surface 50a, the light-guiding member 10 is placed on the light-reflecting member 85. At this time, the light source 20A on the first surface 50a is positioned within the second hole H2 of the light-guiding member 10 in a planar view.

After step S23, in step S24, a resin member 32 may be placed in the first hole H1 of the second wiring substrate 60, thereby sealing the electronic component 41. Also, a light-transmitting member 31 may be placed in the second hole H2 of the light-guiding member 10, thereby sealing the light source 20A.

Second Embodiment
A surface light source 2 according to a second embodiment will now be described. Note that the same names and symbols as those in the first embodiment indicate the same or similar components, and detailed descriptions thereof will be omitted as appropriate. This also applies to the following embodiments.

Figure 5 is a cross-sectional view of the surface light source 2 of the second embodiment. The electronic component 41 in the surface light source 2 of the second embodiment has an electrode 43 arranged on the second main surface 41b. The electrode 43 is electrically connected to the second wiring layer 53 via a wire 94. The electronic component 41 is arranged on the second surface 50b of the first wiring board 50 with the first main surface 41a facing the second surface 50b via a third bonding member 93.

[Third embodiment]
FIG. 6 is a cross-sectional view of a surface light source 3 according to the third embodiment.

The second wiring board 70 of the surface light source 3 of the third embodiment further includes a third base material 71 in addition to the configuration of the second wiring board 60 of the surface light source 1 of the first embodiment.

The third substrate 71 is made of an insulating material. The elastic modulus of the third substrate 71 is lower than that of the first substrate 51. The material of the third substrate 71 can be, for example, the same material as that of the second substrate 61. The thickness of the third substrate 71 is, for example, 0.012 mm or more and 0.1 mm or less.

The second wiring board 70 includes a second substrate 61 and has a third surface 70a facing the second surface 50b of the first wiring board 50, and a fourth surface 70b located on the opposite side of the third surface 70a in the thickness direction of the second substrate 61. Furthermore, the second wiring board 70 includes a third substrate 71 and has a fifth surface 70c facing the fourth surface 70b, and a sixth surface 70d located on the opposite side of the fifth surface 70c in the thickness direction of the third substrate 71. In other words, the third surface 70a and the fifth surface 70c are the +Z side surfaces of the second wiring board 70, and the fourth surface 70b and the sixth surface 70d are the -Z side surfaces of the second wiring board 70.

The second wiring board 70 has a third wiring layer 62 on the fourth surface 70b. The second wiring board 70 further has a fourth wiring layer 72 on the sixth surface 70d. In other words, the second wiring board 70 of the third embodiment has a greater number of wiring layers than the second wiring board 60 of the first embodiment.

The third substrate 71 is laminated on the second substrate 61. The second substrate 61 and the third substrate 71 can be directly bonded to each other. Alternatively, the second substrate 61 and the third substrate 71 can be bonded to each other via a second adhesive sheet 82 disposed between the second substrate 61 and the third substrate 71. In this case, the third wiring layer 62 can be covered with the second adhesive sheet 82. This makes it easier to reduce in-plane variation in the thickness of the surface light source 3 compared to when the second substrate 61 and the third substrate 71 are directly bonded to each other. The material for the second adhesive sheet 82 can be selected from, for example, the resins listed above as materials for the first adhesive sheet 81. Like the first adhesive sheet 81, the second adhesive sheet 82 is preferably made of a material with high flame retardancy. The elastic modulus of the second adhesive sheet 82 is, for example, 100 MPa or more and 1 GPa or less. The thickness of the second adhesive sheet 82 is, for example, 0.01 mm or more and 0.1 mm or less.

The second wiring board 70 has a first hole H1 that penetrates the third substrate 71 and the second substrate 61. When the first adhesive sheet 81 and the second adhesive sheet 82 are arranged, the first hole H1 penetrates from the sixth surface 70d through at least the third substrate 71, the second adhesive sheet 82, the second substrate 61, and the first adhesive sheet 81 to reach the second surface 50b of the first wiring board 50.

A third through hole h3 is formed in the third substrate 71. When the second adhesive sheet 82 is placed, the third through hole h3 penetrates from the sixth surface 70d side through the fourth wiring layer 72, the third substrate 71, and the second adhesive sheet 82 between the third substrate 71 and the third wiring layer 62, reaching the third wiring layer 62. A third conductive member 73 is provided in the third through hole h3. The third wiring layer 62 and the fourth wiring layer 72 are electrically connected by the third conductive member 73. The third conductive member 73 can be made of the same material as the second conductive member 63.

The electronic component 41 is disposed on the second surface 50b of the first wiring substrate 50 within the first hole H1. The electrode 42 of the electronic component 41 is electrically connected to the second wiring layer 53 on the second surface 50b via the second bonding member 92. In this embodiment, too, it is preferable that the second main surface 41b of the electronic component 41 is disposed within the first hole H1. This makes it easier to reduce the thickness of the surface light source 3 while still disposing the electronic component 41 on the back side of the light-emitting surface of the surface light source 3.

In the process of laminating the second wiring substrate 70 of the surface light source 3 of the third embodiment onto the first wiring substrate 50 (step S21 in FIG. 10 described above), the laminate of the second base material 61, the third base material 71, the first adhesive sheet 81, and the second adhesive sheet 82 is laminated onto the first wiring substrate 50.

[Fourth embodiment]
FIG. 7 is a cross-sectional view of a surface light source 4 according to the fourth embodiment.

The second wiring substrate 70 of the surface light source 4 of the fourth embodiment also has a third base material 71, a fourth wiring layer 72, and a third conductive member 73, similar to the surface light source 3 of the third embodiment.

The first hole H1 penetrates the third substrate 71 and the second adhesive sheet 82 and reaches the fourth surface 70b of the second wiring board 70. The first hole H1 does not penetrate the second substrate 61 or the first adhesive sheet 81. This allows for a wider area for the third wiring layer 62 on the fourth surface 70b of the second wiring board 70 than in the third embodiment.

The electronic component 41 is disposed on the fourth surface 70b of the second wiring board 70 within the first hole H1. The electrode 42 of the electronic component 41 is electrically connected to the third wiring layer 62 on the fourth surface 70b via the second bonding member 92. In this embodiment, too, it is preferable that the second main surface 41b of the electronic component 41 is disposed within the first hole H1. This makes it easier to reduce the thickness of the surface light source 4 while still disposing the electronic component 41 on the back side of the light-emitting surface of the surface light source 4.

Embodiments of the present disclosure have been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. All forms that a person skilled in the art could implement by appropriately modifying the design based on the above-described embodiments of the present disclosure also fall within the scope of the present disclosure, as long as they encompass the gist of the present disclosure. In addition, within the scope of the concept of the present disclosure, a person skilled in the art may come up with various modifications and alterations, and these modifications and alterations also fall within the scope of the present disclosure.

1-4...Surface light source, 9...Multilayer wiring board, 10...Light-guiding member, 10a...Light-emitting portion, 14...Groove, 20A-20C...Light source, 31...Translucent member, 32...Resin member, 41...Electronic component, 41a...First main surface, 41b...Second main surface, 50...First wiring board, 50a...First surface, 50b...Second surface, 51...First base material, 52...First wiring layer, 53...Second wiring layer, 54...First conductive member, 60...Second wiring board, 60a... Third surface, 60b...fourth surface, 61...second substrate, 62...third wiring layer, 63...second conductive member, 70...second wiring substrate, 70a...third surface, 70b...fourth surface, 70c...fifth surface, 70d...sixth surface, 71...third substrate, 72...fourth wiring layer, 81...first adhesive sheet, 82...second adhesive sheet, 85...light reflecting member, H1...first hole, H2...second hole, h1...first through hole, h2...second through hole, h3...third through hole

Claims (19)

a first wiring board including a first base material, the first surface having a first wiring layer disposed on the first base material, and a second surface having a second wiring layer disposed on the first base material and positioned opposite to the first surface, the first wiring layer and the second wiring layer being electrically connected;
a light source electrically connected to the first wiring layer on the first surface of the first wiring substrate;
an electronic component electrically connected to the second wiring layer;
a second wiring board laminated on the first wiring board, the second wiring board including a second base material having a modulus of elasticity lower than that of the first base material, the second wiring board having a third surface facing the second surface of the first wiring board, a fourth surface on which a third wiring layer is disposed on the second base material and which is located opposite to the third surface, and a first hole;
Equipped with
the electronic component is located in the first hole,
The third wiring layer is electrically connected to the second wiring layer. The surface light source described in claim 1, wherein a first adhesive sheet is provided between the first substrate and the second substrate, and the second wiring layer is covered with the first adhesive sheet. A surface light source according to claim 1 or 2, wherein the third surface of the second wiring board faces the second surface of the first wiring board so that the light source overlaps the second wiring board in a plan view. A surface light source according to any one of claims 1 to 3, wherein the first substrate has a first through-hole, a first conductive member is provided in the first through-hole, and the second wiring layer is connected to the first conductive member in the first through-hole. The second wiring substrate is
a third base material, a fifth surface facing the fourth surface of the second wiring board, and a sixth surface on which a fourth wiring layer is disposed on the third base material and which is located opposite the fifth surface;
5. The surface light source according to claim 1, wherein the fourth wiring layer is electrically connected to the third wiring layer. A surface light source according to any one of claims 1 to 5, wherein the electronic component is disposed on the second surface of the first wiring substrate and is electrically connected to the second wiring layer on the second surface. A surface light source according to any one of claims 1 to 5, wherein the electronic component is disposed on the fourth surface of the second wiring substrate and is electrically connected to the third wiring layer on the fourth surface. A surface light source according to claim 5, claim 6 or claim 7 which cites claim 5, wherein a second adhesive sheet is provided between the second substrate and the third substrate, and the third wiring layer is covered with the second adhesive sheet. At least two of the light sources are disposed on the first surface;
9. The surface light source according to claim 1, wherein the electronic component is located between at least two of the light sources in a plan view. a light guide member disposed on the first surface of the first wiring substrate and having a second hole portion;
10. The surface light source according to claim 1, wherein the light source is located inside the second hole. A surface light source according to any one of claims 1 to 10, wherein the electronic component has a first main surface facing the second surface of the first wiring board, and a second main surface opposite the first main surface and positioned within the first hole. A surface light source according to any one of claims 1 to 11, wherein the second substrate is at least one layer of polyimide resin, and the third wiring layer is connected to an external connector. a step of preparing a first wiring board including a first base material, the first base material having a first surface on which a first wiring layer is disposed, and a second surface on which a second wiring layer is disposed on the first base material and is positioned opposite to the first surface, the first wiring layer and the second wiring layer being electrically connected;
a step of arranging a light source electrically connected to the first wiring layer on the first surface of the first wiring substrate;
a step of arranging an electronic component electrically connected to the second wiring layer on the second surface of the first wiring substrate;
a step of laminating a second wiring board on the first wiring board, the second wiring board including a second base material having a modulus of elasticity lower than that of the first base material, the second wiring board having a third surface facing the second surface of the first wiring board, a fourth surface on which a third wiring layer is disposed on the second base material and which is positioned opposite to the third surface, and a first hole portion penetrating at least the second base material;
Equipped with
In the step of stacking the second wiring substrate on the first wiring substrate,
the electronic component disposed on the second surface of the first wiring substrate is positioned within the first hole;
The method for manufacturing a surface light source includes electrically connecting the third wiring layer to the second wiring layer. The second wiring substrate is
a fifth surface facing the fourth surface of the second wiring board, and a sixth surface on which a fourth wiring layer is disposed on the third base material and which is located on the opposite side of the fifth surface;
and
the fourth wiring layer is electrically connected to the third wiring layer,
The method of manufacturing a surface light source according to claim 13 , wherein the first hole portion penetrates the second base material and the third base material. The method for manufacturing a surface light source according to claim 13 or 14, wherein in the step of laminating the second wiring substrate on the first wiring substrate, a first adhesive sheet is disposed between the first base material and the second base material, and the second wiring layer is covered with the first adhesive sheet. A method for manufacturing a surface light source according to any one of claims 13 to 15, wherein in the step of stacking the second wiring board on the first wiring board, the third surface of the second wiring board is opposed to the second surface of the first wiring board so that the light source overlaps the second wiring board in a planar view. a step of preparing a first wiring board including a first base material, the first base material having a first surface on which a first wiring layer is disposed, and a second surface on which a second wiring layer is disposed on the first base material and is positioned opposite to the first surface, the first wiring layer and the second wiring layer being electrically connected;
a step of arranging a light source electrically connected to the first wiring layer on the first surface of the first wiring substrate;
a step of preparing a second wiring board including a second substrate and a third substrate each having a modulus of elasticity lower than that of the first substrate, and having a third surface opposite the second surface of the first wiring board, a fourth surface on which a third wiring layer is disposed on the second substrate and located opposite the third surface, a fifth surface opposite the fourth surface, a sixth surface on which a fourth wiring layer is disposed on the third substrate and located opposite the fifth surface, and a first hole portion penetrating the third substrate, wherein the third wiring layer and the fourth wiring layer are electrically connected;
laminating the second wiring substrate on the first wiring substrate so that the third wiring layer is electrically connected to the second wiring layer;
a step of placing an electronic component on the fourth surface of the second wiring substrate so that the electronic component is positioned in the first hole portion and electrically connecting the electronic component to the third wiring layer;
A method for manufacturing a surface light source comprising: The method for manufacturing a surface light source according to claim 17, wherein, in the step of laminating the second wiring substrate on the first wiring substrate, a first adhesive sheet is disposed between the first base material and the second base material, and the second wiring layer is covered with the first adhesive sheet. The method for manufacturing a surface light source described in claim 17 or 18, wherein, in the step of stacking the second wiring board on the first wiring board, the third surface of the second wiring board is opposed to the second surface of the first wiring board so that the light source overlaps the second wiring board in a planar view.