Method for manufacturing circuit board and circuit board

Abstract

In the method for manufacturing a circuit board, first, a glass laminate 10 having a first outer glass layer 11 including a first surface 10a and a first inner glass layer 13 bonded to the first outer glass layer 11 on a side opposite to the first surface 10a is prepared as a substrate serving as a core of a package substrate. In the method for manufacturing a circuit board, the first surface 10a is irradiated with a laser beam L to form a first hole H1 penetrating at least the first outer glass layer 11 and the first inner glass layer 13 from the first surface 10a toward the second surface 10b. In the method for manufacturing a circuit board, the light absorption rate of the first inner glass layer 13 is lower than the light absorption rate of the first outer glass layer 11. Thus, a hole for providing a connection member 40 for electrically connecting a first terminal 20 formed on the first surface 10a and a second terminal 30 formed on the second surface 10b can be easily formed.

Description

Circuit board manufacturing method and circuit board

[0001] The present disclosure relates to a method for manufacturing a circuit board and the circuit board.

[0002] Flip-chip mounting is a known method for mounting integrated circuits formed on a silicon wafer. In recent years, in flip-chip mounting, the use of a glass laminate as a core substrate of a package substrate has been considered in order to suppress warpage of the package substrate.

[0003] When flip-chip mounting is performed, the surface of the package substrate opposite to the mounting surface must be bonded to, for example, a motherboard in order to efficiently extract the terminals. In this case, it is necessary to form through-holes that penetrate the package substrate from the mounting surface to the opposite surface, and to provide connecting members for electrically connecting the terminals formed on the mounting surface and the opposite surface.

[0004] When the above-described glass laminate is used as a base material that becomes the core of a package substrate, a through hole for providing the above-described connecting member is formed in the glass laminate by irradiating the glass laminate with a laser beam. Non-Patent Document 1 discloses an example of a method for forming a through hole in a glass laminate by irradiating with a laser beam.

[0005] K. Demir et al., "First demonstration of copper-plated through-package-via (TPV) reliability in ultra-thin 3D glass interposers with double-side component assembly," 2015 IEEE 65th Electronic Components and Technology Conference (ECTC), pp. 666-671, 2015.

[0006] When forming the above-described through holes in a glass laminate by irradiating the glass laminate with laser light, the surface of the glass laminate is irradiated with laser light to form holes penetrating the glass layers constituting the glass laminate. During this process, it is necessary to allow vaporized components vaporized by the laser light irradiation to escape from the holes. Therefore, a method can be considered in which the glass layers constituting the glass laminate are sequentially punched one by one while changing the irradiation position of the laser light, thereby ensuring time for the vaporized components to migrate out of the holes. However, this method requires alignment each time the irradiation position of the laser light is changed, resulting in a problem of time-consuming laser light irradiation process. Therefore, there is a need for a method for manufacturing a circuit board that can easily form holes for providing connecting members in a circuit board including a glass laminate as a substrate.

[0007] The present disclosure addresses a need for a method for manufacturing a circuit board that can easily form holes for providing connecting members in a circuit board that includes a glass laminate as a substrate.

[0008] [1] One aspect of the present disclosure relates to a method for manufacturing a circuit board including a substrate having a first surface and a second surface opposite the first surface, a first terminal formed on the first surface, and a second terminal formed on the second surface and electrically connected to the first terminal. The method for manufacturing the circuit board includes the steps of: preparing a glass laminate having the first surface and the second surface and including a plurality of glass layers; and irradiating the glass laminate with laser light, wherein the preparing step includes preparing a glass laminate having the plurality of glass layers including a first outer glass layer including the first surface and a first inner glass layer joined to the first outer glass layer on a side opposite to the first surface; and irradiating the glass laminate with laser light to the first surface, wherein the irradiating step includes irradiating the first surface with laser light to form a first hole penetrating at least the first outer glass layer and the first inner glass layer from the first surface to the second surface, and wherein the light absorptance of the first inner glass layer is lower than the light absorptance of the first outer glass layer.

[0009] In this manufacturing method, the optical absorptance of the first inner glass layer is lower than that of the first outer glass layer. That is, in the irradiating step, the time required for the laser light to penetrate the first inner glass layer is longer than the time required for the laser light to penetrate the first outer glass layer. Meanwhile, the time required for the laser light to penetrate the first inner glass layer is shorter than the time required for aligning the laser light irradiation position. Therefore, by making the optical absorptance of the first inner glass layer lower than that of the first outer glass layer, the time required for the laser light irradiation step can be shortened during the process of forming the first hole, while allowing vaporized components to escape from the first hole as the laser light penetrates the first inner glass layer. From the above, the circuit board manufacturing method described in [1] above allows holes for providing connecting members to be easily formed.

[0010] [2] In the circuit board manufacturing method described in [1] above, the preparing step may include preparing a glass laminate in which a first inner glass layer includes a second surface. The irradiating step may include forming a first hole penetrating from the first surface to the second surface. In this case, even if the glass laminate has a two-layer structure including a first outer glass layer and a first inner glass layer, in the process of forming the first hole, vaporized components can be allowed to escape from the first hole as the laser light penetrates the first inner glass layer, thereby shortening the time required for the laser light irradiation step. Therefore, according to the circuit board manufacturing method described in [2] above, even if the glass laminate has a two-layer structure including a first outer glass layer and a first inner glass layer, holes for providing connecting members can be easily formed.

[0011] [3] In the circuit board manufacturing method described in [1] above, the preparing step may include preparing a glass laminate in which the plurality of glass layers further includes a second outer glass layer having a second surface. The irradiating step may further include forming a second hole that penetrates at least the second outer glass layer from the second surface toward the first surface and communicates with the first hole. In this case, even if the glass laminate has a three-layer or more structure including at least the first outer glass layer, the first inner glass layer, and the second outer glass, in the process of forming the first hole, vaporized components can escape from the first hole while the laser light penetrates the first inner glass layer, thereby shortening the time required for the laser light irradiation step. Therefore, according to the circuit board manufacturing method described in [3] above, even if the glass laminate has a three-layer or more structure including at least the first outer glass layer, the first inner glass layer, and the second outer glass, holes for providing connecting members can be easily formed.

[0012] [4] In the circuit board manufacturing method described in [3] above, the preparing step may prepare a glass laminate further including a second inner glass layer in which the plurality of glass layers are bonded to a second outer glass layer on the side opposite the second surface. The irradiating step may include irradiating the second surface with laser light to form a second hole penetrating the second outer glass layer and the second inner glass layer. The second inner glass layer may have a lower optical absorptivity than the second outer glass layer. In this case, by making the optical absorptivity of the second inner glass layer lower than that of the second outer glass layer, vaporized components can escape from the second hole while the laser light penetrates the second inner glass layer, thereby shortening the time required for the laser light irradiation step. Therefore, the circuit board manufacturing method described in [4] above can more easily form a hole for providing a connecting member.

[0013] [5] In the method for manufacturing a circuit board described in [4] above, the second inner glass layer may have a lower light absorptance than the first outer glass layer.

[0014] [6] In the method for manufacturing a circuit board according to [4] or [5] above, the preparing step may include preparing a glass laminate further including a plurality of third inner glass layers positioned between the first inner glass layer and the second inner glass layer. The irradiating step may include forming first holes penetrating the first outer glass layer, the first inner glass layer, and some of the third inner glass layers among the plurality of third inner glass layers, and forming second holes penetrating the second outer glass layer, the second inner glass layer, and the remaining third inner glass layers among the plurality of third inner glass layers. The optical absorptivities of the plurality of third inner glass layers may be lower than those of the first outer glass layer and the second outer glass layer. In this case, by making the optical absorptivities of the plurality of third inner glass layers lower than those of the first outer glass layer and the second outer glass layer, vaporized components generated by the laser beam can be allowed to escape to the outside of the first hole and the second hole in both the step of forming the first hole and the step of forming the second hole, thereby shortening the time required for the laser beam irradiation step. Therefore, according to the method for manufacturing a circuit board described in [6] above, holes for providing connection members can be easily formed.

[0015] [7] In the method for manufacturing a circuit board according to any one of [1] to [6] above, each of the plurality of glass layers may be a glass plate. According to the method for manufacturing a circuit board according to [7] above, a glass laminate in which a plurality of glass layers are stacked can be easily prepared.

[0016] [8] In the circuit board manufacturing method according to any one of [1] to [7] above, the glass layers may be bonded together with an adhesive. In this case, even if a defect or the like exists in one of the glass layers, the defect is unlikely to affect the other glass layers because the glass layers are bonded together with an adhesive. Therefore, the circuit board manufacturing method according to [8] above can improve the mechanical strength of the glass laminate.

[0017] [9] Another aspect of the present disclosure relates to a circuit board. The circuit board includes a glass laminate having a first surface and a second surface opposite the first surface, the glass laminate including multiple glass layers, a first terminal formed on the first surface, and a second terminal formed on the second surface and electrically connected to the first terminal. The multiple glass layers include a first outer glass layer including the first surface and a first inner glass layer joined to the first outer glass layer on the side opposite the first surface. A through hole is formed in the glass laminate, penetrating from the first surface to the second surface. The light absorptance of the first inner glass layer is lower than that of the first outer glass layer.

[0018]

[10] In the circuit board described in [9] above, the first inner glass layer may include a second surface.

[0019]

[11] In the circuit board described in [9], the plurality of glass layers may further include a second outer glass layer including a second surface, and the first inner glass layer may have a lower optical absorptance than the second outer glass layer.

[0020]

[12] In the circuit board described in

[11] above, the plurality of glass layers may further include a second inner glass layer bonded to the second outer glass layer on an opposite side to the second surface, and the second inner glass layer may have a lower optical absorptance than the second outer glass layer.

[0021]

[13] In the circuit board described in

[12] above, the second inner glass layer may have a lower light absorptance than the first outer glass layer.

[0022]

[14] In the circuit board according to the above

[12] or

[13] , the plurality of glass layers may further include a plurality of third inner glass layers positioned between the first inner glass layer and the second inner glass layer, and the light absorptance of the third inner glass layers may be lower than the light absorptance of the first outer glass layer and the light absorptance of the second outer glass layer.

[0023]

[15] In the circuit board according to any one of the above [9] to

[14] , each of the plurality of glass layers may be a glass plate.

[0024]

[16] In the circuit board according to any one of the above [9] to

[15] , each of the plurality of glass layers may be bonded to each other via an adhesive.

[0025] FIG. 1 shows an example of a circuit board according to a first embodiment of the present disclosure. (a) to (d) of FIG. 2 are cross-sectional views illustrating a method for manufacturing the circuit board shown in FIG. 1 . (a) to (d) of FIG. 3 are cross-sectional views illustrating a method for manufacturing the circuit board shown in FIG. 1 , illustrating steps performed after the step illustrated in FIG. 2 . FIG. 4 shows an example of a circuit board according to a second embodiment of the present disclosure. (a) to (d) of FIG. 5 are cross-sectional views illustrating a method for manufacturing the circuit board shown in FIG. 4 . (a) to (d) of FIG. 6 are cross-sectional views illustrating a method for manufacturing the circuit board shown in FIG. 4 , illustrating steps performed after the step illustrated in FIG. 5 . FIG. 7 shows an example of a circuit board according to a third embodiment of the present disclosure. (a) to (e) of FIG. 8 are cross-sectional views illustrating a method for manufacturing the circuit board shown in FIG. 7 .

[0026] Hereinafter, several embodiments of the present disclosure will be described in detail, with reference to the drawings as necessary. In the following description, identical or equivalent parts will be designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, right, etc. will be based on the positional relationships shown in the drawings unless otherwise specified. When terms such as "left," "right," "front," "back," "top," "bottom," "upper," and "lower" are used in the description and claims of this specification, these terms are intended for explanatory purposes and do not necessarily mean that these relative positions will always be the same. Furthermore, the dimensional ratios of the drawings are not limited to those shown. Furthermore, in this specification, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0027] First Embodiment A circuit board and a method for manufacturing the circuit board according to a first embodiment of the present disclosure will be described with reference to FIGS.

[0028] (Configuration of Circuit Board) First, the configuration of the circuit board according to the first embodiment will be described with reference to Fig. 1 . Fig. 1 shows an example of the circuit board according to the first embodiment. As shown in Fig. 1 , the circuit board 1 is a substrate that serves as the core of, for example, a package substrate, and includes a glass laminate 10, first terminals 20, second terminals 30, and a connecting member 40. In the circuit board 1, the glass laminate 10 functions as a substrate and has a first surface 10a and a second surface 10b located on the opposite side to the first surface 10a.

[0029] The glass laminate 10 is formed by laminating a plurality of glass layers, and in this embodiment, is formed by laminating four glass layers. As shown in Fig. 1 , the glass laminate 10 has the four glass layers: a first outer glass layer 11, a second outer glass layer 12, a first inner glass layer 13, and a second inner glass layer 14. In this embodiment, each of the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 is a glass plate.

[0030] The first outer glass layer 11 and the second outer glass layer 12 constitute the outermost layers of the glass laminate 10. Thus, in this embodiment, the first outer glass layer 11 includes a first surface 10a as its surface, and the second outer glass layer 12 includes a second surface 10b as its surface.

[0031] In the glass laminate 10, the first inner glass layer 13 is bonded to the first outer glass layer 11 on the side opposite the first surface 10a, and the second inner glass layer 14 is bonded to the second outer glass layer 12 on the side opposite the second surface 10b. Furthermore, the first inner glass layer 13 and the second inner glass layer 14 are bonded to each other. Therefore, in the glass laminate 10, the first outer glass layer 11, the first inner glass layer 13, the second inner glass layer 14, and the second outer glass layer 12 are laminated in this order. In this embodiment, the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 are each bonded via adhesive A.

[0032] In the glass laminate 10, the light absorptance of the first outer glass layer 11 is different from that of the first inner glass layer 13, and the light absorptance of the second outer glass layer 12 is different from that of the second inner glass layer 14. Specifically, the light absorptance of the first inner glass layer 13 is lower than that of the first outer glass layer 11, and the light absorptance of the second inner glass layer 14 is lower than that of the second outer glass layer 12. The light absorptance of the second inner glass layer 14 may be lower than that of the first outer glass layer 11. Here, the light absorptance is a ratio indicating the degree to which each glass layer absorbs light when light is incident on the glass layer. The higher the light absorptance, the more easily the incident light is absorbed, and the lower the light absorptance, the less easily the incident light is absorbed. The light absorptance may be expressed, for example, using an extinction coefficient.

[0033] The light absorption rate of the first outer glass layer 11 is, for example, 0.5 cm －１ 3.5cm or more －１ The light absorption rate of the first inner glass layer 13 is, for example, 0.1 cm －１ 1.0cm or more －１ The light absorption coefficient of the second outer glass layer 12 is, for example, 0.5 cm －１ 3.5cm or more －１ The light absorption rate of the second inner glass layer 14 is, for example, 0.1 cm －１ 1.0cm or more －１ The following is the result.

[0034] As shown in Fig. 1 , a first terminal 20 is formed on the first surface 10a, and a second terminal 30 is formed on the second surface 10b. The first terminal 20 and the second terminal 30 are electrically connected to each other. In this embodiment, a through hole H is formed in the glass laminate 10, penetrating from the first surface 10a to the second surface 10b, and the first terminal 20 and the second terminal 30 are electrically connected to each other via a connecting member 40 disposed in the through hole H. The connecting member 40 may be, for example, a wiring or a conductive via.

[0035] (Method of Manufacturing Circuit Board) Next, a method of manufacturing the circuit board 1 will be described with reference to Fig. 2 and Fig. 3. Fig. 2(a) to (d) are cross-sectional views for explaining the method of manufacturing the circuit board shown in Fig. 1. Fig. 3(a) to (d) are cross-sectional views for explaining the method of manufacturing the circuit board shown in Fig. 1, showing steps performed after the steps shown in Fig. 2.

[0036] The circuit board 1 can be manufactured, for example, through the following steps (a) to (c). That is, the method for manufacturing the circuit board 1 includes the following steps (a) to (c): a) preparing a glass laminate as a substrate, the glass laminate having a first surface and a second surface and including a plurality of glass layers stacked together, the plurality of glass layers including a first outer glass layer including the first surface, a second outer glass layer including the second surface, a first inner glass layer bonded to the first outer glass layer on the side opposite to the first surface, and a second inner glass layer bonded to the second outer glass layer on the side opposite to the second surface; b) irradiating the glass laminate with laser light; and c) forming a connecting member, a first terminal, and a second terminal.

[0037] The step b) of irradiating the glass laminate with laser light includes the following steps: b1) irradiating a first surface with laser light to form a first hole that penetrates the first outer glass layer and the first inner glass layer from the first surface to the second surface; b2) repeating the step b1); b3) irradiating a second surface with laser light to form a second hole that penetrates the second outer glass layer and the second inner glass layer from the second surface to the first surface and that communicates with the first hole; and b4) repeating the step b3).

[0038] [Step (a)] Step (a) is a step of preparing a glass laminate 10. In step (a) of the present embodiment, a glass laminate 10 having a first surface 10a and a second surface 10b and including a plurality of laminated glass layers is prepared. The glass laminate 10 is, for example, a glass substrate. In this case, the glass laminate 10 may be, for example, a glass substrate having a thickness of 0.05 mm or more and 1.65 mm or less.

[0039] 2A, the glass laminate 10 prepared in step (a) of this embodiment has a plurality of glass layers, including a first outer glass layer 11, a second outer glass layer 12, a first inner glass layer 13, and a second inner glass layer 14. In the glass laminate 10 prepared in step (a), the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 are each a glass plate. The first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 are each made of glass, such as alkali silicate glass, alkali-free glass, or quartz glass.

[0040] The first outer glass layer 11 and the second outer glass layer 12 constitute the outermost layers of the glass laminate 10. Therefore, in the glass laminate 10 prepared in step (a), the first outer glass layer 11 includes a first surface 10a as its surface, and the second outer glass layer 12 includes a second surface 10b as its surface.

[0041] In the glass laminate 10 prepared in step (a), the first inner glass layer 13 is bonded to the first outer glass layer 11 on the side opposite the first surface 10a, and the second inner glass layer 14 is bonded to the second outer glass layer 12 on the side opposite the second surface 10b. Furthermore, the first inner glass layer 13 and the second inner glass layer 14 are bonded to each other. Therefore, in the glass laminate 10 prepared in step (a), the first outer glass layer 11, the first inner glass layer 13, the second inner glass layer 14, and the second outer glass layer 12 are laminated in this order. The first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 are each bonded via adhesive A.

[0042] In the glass laminate 10 prepared in step (a), the light absorptance of the first outer glass layer 11 is different from the light absorptance of the first inner glass layer 13, and the light absorptance of the second outer glass layer 12 is different from the light absorptance of the second inner glass layer 14. Specifically, the light absorptance of the first inner glass layer 13 is lower than the light absorptance of the first outer glass layer 11, and the light absorptance of the second inner glass layer 14 is lower than the light absorptance of the second outer glass layer 12. In the glass laminate 10 prepared in step (a), the light absorptance of the second inner glass layer 14 may be lower than the light absorptance of the first outer glass layer 11.

[0043] In the glass laminate 10 prepared in step (a), the light absorptance of the first outer glass layer 11 is, for example, 0.5 cm －１ 3.5cm or more －１ The light absorption rate of the first inner glass layer 13 is, for example, 0.1 cm －１ 1.0cm or more －１ In the glass laminate 10 prepared in step (a), the light absorptance of the second outer glass layer 12 is, for example, 0.5 cm －１ 3.5cm or more －１ The light absorption rate of the second inner glass layer 14 is, for example, 0.1 cm －１ 1.0cm or more －１ The following is the result.

[0044] To achieve such a configuration in which the first outer glass layer 11 and the first inner glass layer 13 have different light absorptivities, for example, the first outer glass layer 11 and the first inner glass layer 13 may be made different in color. Similarly, to achieve such a configuration in which the second outer glass layer 12 and the second inner glass layer 14 have different light absorptivities, for example, the second outer glass layer 12 and the second inner glass layer 14 may be made different in color.

[0045] In the glass laminate 10 prepared in step (a), the thicknesses of the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 may be the same or different from one another. The thicknesses of the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 are, for example, 0.035 mm or more and 0.7 mm or less, preferably 0.05 mm or more and 0.5 mm or less, and more preferably 0.1 mm or more and 0.3 mm or less.

[0046] [Step (b)] Step (b) is a step of irradiating the glass laminate 10 with laser light. In step (b), first, the first surface 10a of the glass laminate 10 is irradiated with laser light. In step (b) of this embodiment, as shown in FIG. 2(b), a laser irradiation device 100 is used to irradiate the first surface 10a with laser light L. In this case, the laser irradiation device 100 recognizes positioning marks that have been provided in advance on the first surface 10a, and irradiates the positioning marks with laser light L. In this embodiment, a plurality of the positioning marks are provided on the first surface 10a. The positioning marks are provided, for example, by etching or laser processing the first surface 10a.

[0047] The laser irradiation device 100 may be, for example, a Nd:YAG (Neodymium-doped Yttrialuminum Garnet) laser, a laser that combines a Nd:YAG laser with wavelength conversion and covers the near-infrared region, the visible region, and even the ultraviolet region, a KrF excimer laser with a wavelength of 248 nm, an ArF excimer laser with a wavelength of 193 nm, or an F ２ A known laser irradiation device such as an excimer laser can be used. From the viewpoint of processability, it is preferable to use an Nd:YAG laser as the laser irradiation device 100. When an Nd:YAG laser is used as the laser irradiation device 100, a third harmonic laser (wavelength 355 nm) is used. Furthermore, when an Nd:YAG laser is used as the laser irradiation device 100, the pulse width of the Nd:YAG laser is set to, for example, 100 fs or more and 1 ns or less.

[0048] In step (b) of the present embodiment, by irradiating the first surface 10a with laser light L as described above, a first hole H1 is formed in the glass laminate 10, penetrating the first outer glass layer 11 and the first inner glass layer 13 from the first surface 10a toward the second surface 10b, as shown in (c) of Fig. 2. That is, in step (b) of the present embodiment, the first hole H1 is formed by irradiating the first surface 10a with laser light L. The first hole H1 formed by the above method has a diameter of, for example, 0.02 mm or more and 0.15 mm or less.

[0049] Subsequently, the above-described formation of the first holes H1 by irradiation with the laser light L is repeated. As a result, a plurality of first holes H1 are formed in the glass laminate 10, as shown in Fig. 2(d). The pitch of the plurality of first holes H1 is, for example, 0.04 mm or more and 1.0 mm or less. In the example shown in Fig. 2(d), three first holes H1 are formed in the glass laminate 10.

[0050] Next, the glass laminate 10 is turned upside down, and the second surface 10b of the glass laminate 10 is irradiated with laser light. In step (b) of this embodiment, as shown in FIG. 3A, a laser irradiation device 100 is used to irradiate the second surface 10b with laser light L. In this case, similar to the irradiation of the first surface 10a with laser light L, the laser irradiation device 100 recognizes a positioning mark provided in advance on the second surface 10b and irradiates the positioning mark with laser light L. Here, the positioning mark provided on the second surface 10b is provided at a position corresponding to the positioning mark provided on the first surface 10a.

[0051] In step (b) of the present embodiment, by irradiating the second surface 10b with laser light L, a second hole H2 is formed in the glass laminate 10, penetrating the second outer glass layer 12 and the second inner glass layer 14 from the second surface 10b toward the first surface 10a. That is, in step (b) of the present embodiment, the second hole H2 is formed by irradiating the second surface 10b with laser light L. The diameter of the second hole H2 formed by irradiating the second surface 10b with laser light L is the same as the diameter of the first hole H1.

[0052] As described above, the positioning mark provided on the second surface 10b is provided at a position corresponding to the positioning mark provided on the first surface 10a. Therefore, the second hole H2 and the first hole H1 formed in step (b) communicate with each other, thereby forming a through hole H that penetrates from the first surface 10a to the second surface 10b in the glass laminate 10. In step (b) of this embodiment, the through hole H is formed penetrating the first outer glass layer 11, the first inner glass layer 13, the second inner glass layer 14, and the second outer glass layer 12 from the first surface 10a to the second surface 10b.

[0053] Subsequently, the formation of the second holes H2 by irradiation with the laser light L described above is repeated. As a result, a plurality of second holes H2 are formed in the glass laminate 10, and a plurality of through holes H are formed, as shown in FIG. 3C. The pitch of the plurality of second holes H2 is, for example, the same as the pitch of the plurality of first holes H1. That is, the pitch of the plurality of through holes H in this embodiment is, for example, the same as the pitch of the plurality of first holes H1. In the example shown in FIG. 3C, three through holes H are formed in the glass laminate 10.

[0054] [Step (c)] Step (c) is a step of forming the first terminal 20, the second terminal 30, and the connection member 40 in the glass laminate 10. In step (c) of the present embodiment, first, a conductive material is filled into the through hole H to form a conductive via as the connection member 40. In this case, the connection member 40 is formed by filling the through hole H with a conductive paste as the conductive material. The conductive paste contains, for example, copper.

[0055] Next, the first terminal 20 is formed on the first surface 10a, and the second terminal 30 is formed on the second surface 10b so as to be electrically connected to the first terminal 20. In step (c) of this embodiment, the second terminal 30 is formed on the second surface 10b so as to be electrically connected to the first terminal 20 via the connecting member 40. In this way, the first terminal 20 and the second terminal 30 are formed so as to be electrically connected to each other by the connecting member 40, as shown in (d) of FIG.

[0056] Through the above steps, the circuit board 1 shown in FIG. 1 is manufactured.

[0057] As described above, in the manufacturing method of the circuit board 1 according to this embodiment, the light absorptance of the first inner glass layer 13 is lower than that of the first outer glass layer 11. That is, in step (b), the time required for the laser light L to penetrate the first inner glass layer 13 is longer than the time required for the laser light L to penetrate the first outer glass layer 11. Meanwhile, the time required for the laser light L to penetrate the first inner glass layer 13 is shorter than the time required for aligning the irradiation position of the laser light L. Therefore, by making the light absorptance of the first inner glass layer 13 lower than that of the first outer glass layer 11, in the process of forming the first hole H1, vaporized components can escape to the outside of the hole while the laser light L penetrates the first inner glass layer 13, thereby shortening the time required for the laser light L irradiation step. As described above, the manufacturing method of the circuit board 1 makes it possible to easily form the through hole H for providing the connecting member 40.

[0058] In the manufacturing method of circuit board 1, even in a glass laminate having a structure of three or more layers such as glass laminate 10, in the process of forming first hole H1, vaporized components can be allowed to escape to the outside of first hole H1 while laser light L penetrates first inner glass layer 13, thereby shortening the time required for the irradiation step of laser light L. Therefore, according to the manufacturing method of circuit board 1, even if the glass laminate has a structure of three or more layers, it is possible to easily form through hole H for providing connecting member 40.

[0059] In the manufacturing method of circuit board 1, the light absorptance of second inner glass layer 14 is lower than the light absorptance of second outer glass layer 12. In this case, even in the process of forming second hole H2, vaporized components can be allowed to escape to the outside of second hole H2 while laser light L penetrates second inner glass layer 14, thereby shortening the time required for the irradiation step of laser light L. Therefore, according to the manufacturing method of circuit board 1, it is possible to more easily form through hole H for providing connecting member 40.

[0060] In the method for manufacturing the circuit board 1, the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 are each a glass plate. Therefore, according to the method for manufacturing the circuit board 1, in step (a), the glass laminate 10 in which a plurality of glass layers are stacked can be easily prepared.

[0061] In the manufacturing method of circuit board 1, the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14 are each bonded via adhesive A. In this case, even if a defect or the like exists in any of the glass layers among the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14, the defect is unlikely to affect the other glass layers because the glass layers are bonded via adhesive A. Therefore, the manufacturing method of circuit board 1 can improve the mechanical strength of the glass laminate 10.

[0062] Second Embodiment Next, a circuit board and a method for manufacturing a circuit board according to a second embodiment of the present disclosure will be described with reference to Figures 4 to 6. Below, differences from the first embodiment will be mainly described, and descriptions similar to or overlapping with the first embodiment may be omitted.

[0063] (Configuration of Circuit Board) First, the configuration of a circuit board 1A according to the second embodiment will be described with reference to Fig. 4 . Fig. 4 shows an example of a circuit board according to the second embodiment of the present disclosure. As shown in Fig. 4 , the circuit board 1A is a substrate that serves as the core of, for example, a package substrate, and includes a glass laminate 10A, a first terminal 20, a second terminal 30, and a connecting member 40. Like the glass laminate 10, the glass laminate 10A has a first surface 10a and a second surface 10b.

[0064] Like the glass laminate 10, the glass laminate 10A is configured by stacking multiple glass layers, and in this embodiment, it is configured by stacking six glass layers. As shown in Fig. 4, the glass laminate 10A has six glass layers: a first outer glass layer 11, a second outer glass layer 12, a first inner glass layer 13, a second inner glass layer 14, and multiple third inner glass layers 15a, 15b. In this embodiment, the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, the second inner glass layer 14, and the multiple third inner glass layers 15a, 15b are each a glass plate.

[0065] In the glass laminate 10A, the first outer glass layer 11 and the second outer glass layer 12 constitute the outermost layers. Therefore, in this embodiment as well, the first outer glass layer 11 includes a first surface 10a as its surface, and the second outer glass layer 12 includes a second surface 10b as its surface.

[0066] In the glass laminate 10A, the multiple third inner glass layers 15a, 15b are located between the first inner glass layer 13 and the second inner glass layer 14. Specifically, the third inner glass layer 15a is bonded to the first inner glass layer 13 on the side opposite to the first surface 10a, and the third inner glass layer 15b is bonded to the second inner glass layer 14 on the side opposite to the second surface 10b. Furthermore, the third inner glass layer 15a and the third inner glass layer 15b are bonded to each other. Therefore, in the glass laminate 10A, the first outer glass layer 11, the first inner glass layer 13, the third inner glass layer 15a, the third inner glass layer 15b, the second inner glass layer 14, and the second outer glass layer 12 are laminated in this order. In this embodiment, the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, the second inner glass layer 14, and the multiple third inner glass layers 15a, 15b are each bonded together via adhesive A.

[0067] In the glass laminate 10A, the light absorptance of the third inner glass layers 15a, 15b is different from the light absorptance of the first outer glass layer 11 and the light absorptance of the second outer glass layer 12. Specifically, the light absorptance of the third inner glass layers 15a, 15b is lower than the light absorptance of the first outer glass layer 11 and the light absorptance of the second outer glass layer 12.

[0068] The light absorption coefficient of the third inner glass layers 15a and 15b is, for example, 0.1 cm －１ 1.0cm or more －１ The light absorptance of the third inner glass layer 15a and the light absorptance of the third inner glass layer 15b may be the same as or different from each other.

[0069] The configurations of the first terminal 20, the second terminal 30, and the connecting member 40 in the glass laminate 10A are the same as the configurations of the first terminal 20, the second terminal 30, and the connecting member 40 in the glass laminate 10, so detailed explanations are omitted.

[0070] (Method of Manufacturing Circuit Board) Next, a method of manufacturing the circuit board 1A will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a cross-sectional view for explaining the method of manufacturing the circuit board shown in Fig. 4. Fig. 6 is a cross-sectional view for explaining the method of manufacturing the circuit board shown in Fig. 4, showing a step subsequent to the step shown in Fig. 5.

[0071] The circuit board 1A can be manufactured through, for example, the following steps (d) to (f). That is, the manufacturing method of the circuit board 1A includes the following steps (d) to (f): d) preparing a glass laminate as a substrate having a first surface and a second surface and including a plurality of laminated glass layers, the plurality of glass layers including a first outer glass layer including the first surface, a second outer glass layer including the second surface, a first inner glass layer bonded to the first outer glass layer on the side opposite to the first surface, a second inner glass layer bonded to the second outer glass layer on the side opposite to the second surface, and a plurality of third inner glass layers positioned between the first inner glass layer and the second inner glass layer; e) irradiating the glass laminate with laser light; and f) forming a connecting member, a first terminal, and a second terminal.

[0072] Furthermore, the above-mentioned e) step of irradiating the glass laminate with laser light includes the following steps: e1) a step of irradiating the first surface with laser light to form a first hole penetrating the first outer glass layer, the first inner glass layer, and some of the plurality of third inner glass layers from the first surface toward the second surface; e2) a step of repeating the above-mentioned e1); e3) a step of irradiating the second surface with laser light to form a second hole penetrating the second outer glass layer, the second inner glass layer, and some of the plurality of third inner glass layers from the second surface toward the first surface and communicating with the first hole; and e4) a step of repeating the above-mentioned e3).

[0073] [Step (d)] Step (d) is a step of preparing a glass laminate 10A. In step (d) of this embodiment, a glass laminate 10A having a first surface 10a and a second surface 10b and including a plurality of glass layers is prepared. The glass laminate 10A is, for example, a glass substrate. In this case, the glass laminate 10A may be, for example, a glass substrate having a thickness of 0.05 mm or more and 1.65 mm or less.

[0074] 5A, the glass laminate 10A prepared in step (d) of this embodiment includes a first outer glass layer 11, a second outer glass layer 12, a first inner glass layer 13, a second inner glass layer 14, and a plurality of third inner glass layers 15a, 15b as glass layers. Each of the third inner glass layers 15a, 15b is also made of glass such as alkali silicate glass, alkali-free glass, or quartz glass.

[0075] In the glass laminate 10A, the first outer glass layer 11 and the second outer glass layer 12 also constitute the outermost layers. Therefore, in the glass laminate 10A prepared in step (d), the first outer glass layer 11 includes the first surface 10a as its surface, and the second outer glass layer 12 includes the second surface 10b as its surface.

[0076] In the glass laminate 10A prepared in step (d), the plurality of third inner glass layers 15a, 15b are located between the first inner glass layer 13 and the second inner glass layer 14. Specifically, the third inner glass layer 15a is bonded to the first inner glass layer 13 on the side opposite to the first surface 10a, and the third inner glass layer 15b is bonded to the second inner glass layer 14 on the side opposite to the second surface 10b. Furthermore, the third inner glass layer 15a and the third inner glass layer 15b are bonded to each other. Therefore, in the glass laminate 10A prepared in step (d), the first outer glass layer 11, the first inner glass layer 13, the third inner glass layer 15a, the third inner glass layer 15b, the second inner glass layer 14, and the second outer glass layer 12 are laminated in this order. The first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, the second inner glass layer 14, and the plurality of third inner glass layers 15a, 15b are each bonded together via adhesive A.

[0077] In the glass laminate 10A prepared in step (d), the light absorptance of the third inner glass layers 15a, 15b is different from the light absorptance of the first outer glass layer 11 and the light absorptance of the second outer glass layer 12. Specifically, the light absorptance of the third inner glass layers 15a, 15b is lower than the light absorptance of the first outer glass layer 11 and the light absorptance of the second outer glass layer 12. Note that the relationship between the light absorptance of the first outer glass layer 11 and the light absorptance of the first inner glass layer 13, and the relationship between the light absorptance of the second outer glass layer 12 and the light absorptance of the second inner glass layer 14 are similar to those in the glass laminate 10, and therefore detailed description thereof will be omitted.

[0078] In the glass laminate 10A prepared in step (d), the light absorptance of the third inner glass layers 15a and 15b is, for example, 0.1 cm －１ 1.0cm or more －１ In the glass laminate 10A, the ranges of the light absorptance of the first outer glass layer 11, the ranges of the light absorptance of the second outer glass layer 12, the ranges of the light absorptance of the first inner glass layer 13, and the ranges of the light absorptance of the second inner glass layer 14 are the same as those in the glass laminate 10, and therefore detailed description thereof will be omitted.

[0079] In order to realize such a configuration in which the light absorbance of the first outer glass layer 11, the light absorbance of the second outer glass layer 12, and the light absorbance of the multiple third inner glass layers 15a, 15b are different from each other, for example, the color of the first outer glass layer 11, the color of the second outer glass layer 12, and the colors of the multiple third inner glass layers 15a, 15b may be different from each other.

[0080] In the glass laminate 10A prepared in step (d), the thicknesses of the plurality of third inner glass layers 15a, 15b may be the same as or different from the thicknesses of the first outer glass layer 11, the second outer glass layer 12, the first inner glass layer 13, and the second inner glass layer 14. The thicknesses of the plurality of third inner glass layers 15a, 15b are, for example, 0.035 mm or more and 0.7 mm or less, preferably 0.05 mm or more and 0.5 mm or less, and more preferably 0.1 mm or more and 0.3 mm or less.

[0081] [Step (e)] Step (e) is a step of irradiating glass laminate 10A with laser light. In step (e), first, laser light is irradiated onto first surface 10a of glass laminate 10A. In step (e) of the present embodiment, as shown in Fig. 5(b), laser irradiation device 100 is used to irradiate first surface 10a with laser light L.

[0082] In step (e) of this embodiment, by irradiating the first surface 10a with laser light L, a first hole H1A is formed in the glass laminate 10A, penetrating the first outer glass layer 11, the first inner glass layer 13, and the third inner glass layer 15a from the first surface 10a toward the second surface 10b, as shown in Fig. 5(c). The diameter of the first hole H1A is the same as the diameter of the first hole H1, for example.

[0083] Subsequently, the above-described formation of the first holes H1A by irradiation with the laser light L is repeated. As a result, as shown in Fig. 5(d), a plurality of first holes H1A are formed in the glass laminate 10A. The pitch of the plurality of first holes H1 is, for example, the same as the pitch of the plurality of first holes H1. In the example shown in Fig. 5(d), three first holes H1 are formed in the glass laminate 10A.

[0084] Next, the glass laminate 10A is turned upside down, and the second surface 10b of the glass laminate 10A is irradiated with laser light. In step (e) of the present embodiment, as shown in (a) of Fig. 6, the second surface 10b is irradiated with laser light L using a laser irradiation device 100.

[0085] In step (e) of the present embodiment, a second hole H2A is formed in the glass laminate 10A by irradiating the second surface 10b with laser light L, penetrating the second outer glass layer 12, the second inner glass layer 14, and the third inner glass layer 15b from the second surface 10b toward the first surface 10a. That is, in step (e) of the present embodiment, the second hole H2A is formed by irradiating the second surface 10b with laser light L. The diameter of the second hole H2A formed by irradiating the second surface 10b with laser light L is the same as the diameter of the first hole H1A, for example.

[0086] The second hole H2A and the first hole H1A formed in step (e) are connected to each other, thereby forming a through hole H that penetrates from the first surface 10a to the second surface 10b. In step (e) of the present embodiment, the through hole H is formed penetrating the first outer glass layer 11, the first inner glass layer 13, the third inner glass layer 15a, the second inner glass layer 14, the third inner glass layer 15b, and the second outer glass layer 12 from the first surface 10a to the second surface 10b.

[0087] Subsequently, the formation of the second holes H2A by irradiation with the laser light L described above is repeated. As a result, as shown in FIG. 6C, a plurality of second holes H2A are formed in the glass laminate 10A, and a plurality of through holes H are formed. The pitch of the plurality of second holes H2A is, for example, the same as the pitch of the plurality of first holes H1A. That is, in this embodiment, the pitch of the plurality of through holes H is, for example, the same as the pitch of the plurality of first holes H1A. In the example shown in FIG. 6C, three through holes H are formed in the glass laminate 10A.

[0088] [Step (f)] Step (f) is a step of forming the first terminal 20, the second terminal 30, and the connecting member 40 on the glass laminate 10A. In step (f) of the present embodiment, the first terminal 20 and the second terminal 30 are formed electrically connected to each other by the connecting member 40 in a manner similar to step (c), as shown in FIG. 6(d).

[0089] Through the above steps, the circuit board 1A shown in FIG. 4 is manufactured.

[0090] As described above, in the manufacturing method of circuit board 1A, the light absorptance of the plurality of third inner glass layers 15a, 15b is lower than that of the first outer glass layer 11 and that of the second outer glass layer 12. In the manufacturing method of circuit board 1A, by making the light absorptance of the plurality of third inner glass layers 15a, 15b lower than that of the first outer glass layer 11 and that of the second outer glass layer 12, it is possible to reduce the time required for the irradiation step of laser light L while allowing vaporized components generated by laser light L to escape to the outside of first hole H1A and second hole H2A in both the process of forming first hole H1A and the process of forming second hole H2A. Therefore, the manufacturing method of circuit board 1A can easily form through hole H for providing connecting members.

[0091] Third Embodiment Next, a circuit board and a method for manufacturing a circuit board according to a third embodiment of the present disclosure will be described with reference to Fig. 7 and Fig. 8. Below, differences from the first embodiment will be mainly described, and descriptions similar to or overlapping with the first embodiment may be omitted.

[0092] (Configuration of Circuit Board) First, the configuration of a circuit board 1B according to the third embodiment will be described with reference to Fig. 7 . Fig. 7 shows an example of a circuit board according to the third embodiment. As shown in Fig. 7 , the circuit board 1B is a substrate that serves as the core of, for example, a package substrate, and includes a glass laminate 10B, first terminals 20, second terminals 30, and a connecting member 40. Like the glass laminate 10, the glass laminate 10B has a first surface 10a and a second surface 10b.

[0093] Like the glass laminate 10, the glass laminate 10B is also formed by stacking a plurality of glass layers, and in this embodiment, it is formed by stacking two glass layers. As shown in Fig. 7 , the glass laminate 10B has two glass layers, a first outer glass layer 11 and a first inner glass layer 13. In this embodiment, each of the first outer glass layer 11 and the first inner glass layer 13 is also a glass plate.

[0094] In the glass laminate 10B, the first outer glass layer 11 and the first inner glass layer 13 constitute the outermost layers. Therefore, in this embodiment, the first outer glass layer 11 includes a first surface 10a as its surface, and the first inner glass layer 13 includes a second surface 10b as its surface. In the glass laminate 10B, the first outer glass layer 11 and the first inner glass layer 13 are laminated in this order. In this embodiment, the first outer glass layer 11 and the first inner glass layer 13 are also bonded together via adhesive A.

[0095] The configurations of the first terminal 20, the second terminal 30, and the connecting member 40 in the glass laminate 10B are the same as the configurations of the first terminal 20, the second terminal 30, and the connecting member 40 in the glass laminate 10, so detailed explanations are omitted.

[0096] (Method of Manufacturing Circuit Board) Next, a method of manufacturing the circuit board 1B will be described with reference to Fig. 8. Fig. 8 is a cross-sectional view for explaining a method of manufacturing the circuit board shown in Fig. 7.

[0097] The circuit board 1B can be manufactured through, for example, the following steps (g) to (i). That is, the manufacturing method of the circuit board 1B includes the following steps (g) to (i): g) preparing a glass laminate as a substrate, the glass laminate having a first surface and a second surface, and including a plurality of glass layers stacked together, the plurality of glass layers including a first outer glass layer including the first surface and a first inner glass layer including the second surface; h) irradiating the glass laminate with laser light; i) forming a connecting member, a first terminal, and a second terminal.

[0098] The step h) of irradiating the glass laminate with laser light includes the following steps: h1) irradiating the first surface with laser light to form a first hole penetrating the first outer glass layer and the first inner glass layer from the first surface to the second surface, and h2) repeating the step h1).

[0099] [Step (g)] Step (g) is a step of preparing a glass laminate 10B. In step (g) of this embodiment, a glass laminate 10B having a first surface 10a and a second surface 10b and including a plurality of glass layers is prepared. The glass laminate 10B is, for example, a glass substrate. In this case, the glass laminate 10B may be, for example, a glass substrate having a thickness of 0.05 mm or more and 1.65 mm or less.

[0100] 8A, the glass laminate 10B prepared in step (g) of the present embodiment has, as a plurality of glass layers, a first outer glass layer 11 and a first inner glass layer 13. The materials of the glass layers in the glass laminate 10B are the same as those of the glass layers in the glass laminate 10, and therefore detailed description thereof will be omitted.

[0101] In the glass laminate 10B, the first outer glass layer 11 and the first inner glass layer 13 constitute the outermost layers. Therefore, in the glass laminate 10B prepared in step (g), the first outer glass layer 11 includes the first surface 10a as its surface, and the first inner glass layer 13 includes the second surface 10b as its surface. As described above, the first inner glass layer 13 is bonded to the first outer glass layer 11 on the side opposite to the first surface 10a. Therefore, in the glass laminate 10B prepared in step (g), the first outer glass layer 11 and the first inner glass layer 13 are laminated in this order.

[0102] [Step (h)] Step (h) is a step of irradiating glass laminate 10B with laser light. In step (h), first, laser light is irradiated onto first surface 10a of glass laminate 10B. In step (h) of the present embodiment, as shown in (b) of FIG. 8 , laser irradiation device 100 is used to irradiate first surface 10a of glass laminate 10B with laser light L.

[0103] In step (h) of the present embodiment, by irradiating the first surface 10a with laser light L, a first hole H1B is formed in the glass laminate 10B, penetrating the first outer glass layer 11 and the first inner glass layer 13 from the first surface 10a toward the second surface 10b, as shown in (c) of FIG. 8 . The diameter of the first hole H1B is, for example, the same as the diameter of the first hole H1. As described above, in the present embodiment, the glass laminate 10B has the first outer glass layer 11 and the first inner glass layer 13 as two glass layers. Therefore, in step (h) of the present embodiment, the first hole H1B becomes a through hole H penetrating from the first surface 10a toward the second surface 10b. In other words, in step (h) of the present embodiment, it can be said that the through hole H is formed by irradiating the glass laminate 10B with laser light.

[0104] Subsequently, the formation of first holes H1B (through holes H) by irradiation with the laser light L described above is repeated. As a result, as shown in (d) of Fig. 8, a plurality of first holes H1B are formed as through holes H in the glass laminate 10B. The pitch of the plurality of first holes H1B is, for example, the same as the pitch of the plurality of first holes H1. In the example shown in (d) of Fig. 8, three first holes H1B (through holes H) are formed in the glass laminate 10B.

[0105] [Step (i)] Step (i) is a step of forming a first terminal 20, a second terminal 30, and a connecting member 40 on the glass laminate 10B. In step (i) of the present embodiment, the first terminal 20 and the second terminal 30 that are electrically connected to each other by the connecting member 40 are formed in a manner similar to step (c), as shown in (e) of Fig. 8 .

[0106] Through the above steps, the circuit board 1B shown in FIG. 7 is formed.

[0107] As described above, in the method for manufacturing circuit board 1B, the light absorptance of first inner glass layer 13 is also lower than that of first outer glass layer 11. Therefore, even in a glass laminate having a two-layer structure such as glass laminate 10B, in the process of forming first hole H1B (through hole H), vaporized components can be allowed to escape to the outside of first hole H1B while punching first inner glass layer 13 with laser light L, thereby shortening the time required for the step of applying laser light L. Therefore, the method for manufacturing circuit board 1B makes it possible to easily form a hole for providing connecting member 40.

[0108] 1, 1A, 1B...circuit board, 10, 10A, 10B...glass laminate, 10a...first surface, 10b...second surface, 11...first outer glass layer, 12...second outer glass layer, 13...first inner glass layer, 14...second inner glass layer, 15a, 15b...third inner glass layer, 20...first terminal, 30...second terminal, A...adhesive, H...through hole, H1, H1A, H1B...first hole, H2, H2A...second hole, L...laser light.

Claims

1. A method for manufacturing a circuit board comprising a substrate having a first surface and a second surface opposite to the first surface, a first terminal formed on the first surface, and a second terminal formed on the second surface and electrically connected to the first terminal, the method comprising the steps of: preparing a glass laminate having the first surface and the second surface as the substrate, the glass laminate including a plurality of glass layers; and irradiating the glass laminate with laser light, wherein the preparing step includes preparing a glass laminate including the plurality of glass layers having a first outer glass layer including the first surface and a first inner glass layer joined to the first outer glass layer on the side opposite to the first surface, and wherein the irradiating step includes irradiating the first surface with the laser light to form a first hole penetrating at least the first outer glass layer and the first inner glass layer from the first surface to the second surface, and wherein the light absorptance of the first inner glass layer is lower than the light absorptance of the first outer glass layer.

2. The method for manufacturing a circuit board as described in claim 1, wherein in the preparing step, the glass laminate is prepared, in which the first inner glass layer includes the second surface, and in the irradiating step, the first hole penetrating from the first surface to the second surface is formed.

3. A method for manufacturing a circuit board as described in claim 1, wherein the preparing step includes preparing a glass laminate in which the plurality of glass layers further includes a second outer glass layer including the second surface, and the irradiating step further includes forming a second hole that at least penetrates the second outer glass layer from the second surface toward the first surface and communicates with the first hole.

4. A method for manufacturing a circuit board as described in claim 3, wherein in the preparing step, the glass laminate further includes a second inner glass layer joined to the second outer glass layer on the side opposite to the second surface, and in the irradiating step, the second surface is irradiated with the laser light to form the second hole penetrating the second outer glass layer and the second inner glass layer, and the light absorptance of the second inner glass layer is lower than the light absorptance of the second outer glass layer.

5. The method for manufacturing a circuit board according to claim 4, wherein the optical absorptivity of the second inner glass layer is lower than the optical absorptivity of the first outer glass layer.

6. A method for manufacturing a circuit board as described in claim 4 or 5, wherein the preparing step includes preparing the glass laminate further having a plurality of third inner glass layers located between the first inner glass layer and the second inner glass layer, and the irradiating step includes forming the first hole penetrating the first outer glass layer, the first inner glass layer, and some of the third inner glass layers among the plurality of third inner glass layers, and forming the second hole penetrating the second outer glass layer, the second inner glass layer, and the remaining third inner glass layers among the plurality of third inner glass layers, and the light absorbance of the plurality of third inner glass layers is lower than the light absorbance of the first outer glass layer and the light absorbance of the second outer glass layer.

7. The method for manufacturing a circuit board according to any one of claims 1 to 6, wherein each of the plurality of glass layers is a glass plate.

8. The method for manufacturing a circuit board according to any one of claims 1 to 7, wherein each of the plurality of glass layers is bonded to each other via an adhesive.

9. A circuit board comprising: a glass laminate having a first surface and a second surface opposite to the first surface, the glass laminate being formed with a plurality of glass layers; a first terminal formed on the first surface; and a second terminal formed on the second surface and electrically connected to the first terminal, the plurality of glass layers comprising: a first outer glass layer including the first surface; and a first inner glass layer joined to the first outer glass layer on the side opposite to the first surface, the glass laminate having a through hole penetrating from the first surface to the second surface, and the first inner glass layer having a lower light absorptance than the first outer glass layer.

10. The circuit board of claim 9, wherein said first inner glass layer comprises said second surface.

11. The circuit board of claim 9, wherein the plurality of glass layers further comprises a second outer glass layer including the second surface, and wherein the optical absorptivity of the first inner glass layer is lower than the optical absorptivity of the second outer glass layer.

12. The circuit board of claim 11, wherein said plurality of glass layers further comprises a second inner glass layer bonded to said second outer glass layer on a side opposite said second surface, and wherein said second inner glass layer has a lower optical absorptivity than said optical absorptivity of said second outer glass layer.

13. The circuit board of claim 12, wherein the optical absorptivity of the second inner glass layer is less than the optical absorptivity of the first outer glass layer.

14. The circuit board of claim 12 or 13, wherein the plurality of glass layers further comprises a plurality of third inner glass layers positioned between the first inner glass layer and the second inner glass layer, and the light absorptivity of the plurality of third inner glass layers is lower than the light absorptivity of the first outer glass layer and the light absorptivity of the second outer glass layer.

15. The circuit board according to any one of claims 9 to 14, wherein each of the plurality of glass layers is a glass plate.

16. The circuit board according to any one of claims 9 to 15, wherein each of the plurality of glass layers is bonded to each other via an adhesive.

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