Glass panel for wiring board and method of manufacturing wiring board

A glass panel for a wiring board, includes a first surface and a second surface, the second surface being opposite to the first surface; and an alignment mark constituted by a plurality of through holes each penetrating the glass panel from the first surface to the second surface, at least one of the plurality of through holes being configured such that a first diameter “t1” of a first opening at the first surface, a second diameter “t2” of a second opening at the second surface, and a minimum diameter “t3” between the first surface and the second surface satisfy t1>t3 and also t2>t3.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a glass panel for a wiring board and a method of manufacturing a wiring board.

2. Description of the Related Art

Conventionally, a glass panel is used in a wiring board that is used for an IC package board, an interposer and the like (Patent Document 1, for example). When performing a process at a specific position on the glass panel by identifying the position, an alignment mark is used for alignment.

However, when the alignment mark is constituted by through holes, as the glass panel is transparent, there is a concern that the alignment mark cannot be recognized by a camera. Thus, a technique capable of accurately recognizing the alignment mark is desired.

PATENT DOCUMENT

SUMMARY OF THE INVENTION

The present invention is made in light of the above problems.

According to an embodiment, there is provided a glass panel for a wiring board including a first surface and a second surface, the second surface being opposite to the first surface; and an alignment mark constituted by a plurality of through holes each penetrating the glass panel from the first surface to the second surface, at least one of the plurality of through holes being configured such that a first diameter “t1” of a first opening at the first surface, a second diameter “t2” of a second opening at the second surface, and a minimum diameter “t3” between the first surface and the second surface satisfy t1>t3 and also t2>t3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be noted that, in the explanation of the drawings, the same components are given the same reference numerals, and explanations are not repeated.

Embodiment

(Structure of Glass Panel for Wiring Board)

FIG. 1is a view for describing a glass panel10for a wiring board (hereinafter, simply referred to as “the glass panel10”) of the embodiment.FIG. 2is an enlarged schematic view of an alignment mark120.FIG. 4is a cross-sectional view illustrating a through hole125constituting the alignment mark120.

The glass panel10may be used for an IC package board, an interposer or the like, for example. As illustrated inFIG. 1, the glass panel10includes through holes (via holes)110to be filled and alignment marks120. In this embodiment, the glass panel10is made of a non-alkali glass, for example. Further, in this embodiment, the glass panel10has a substantially square shape whose length of each side may be 300 mm, for example. However, the glass panel10may have any shape and any size as long as the glass panel10can be used as a glass panel for wiring board. The thickness of the glass panel10may be greater than or equal to 0.15 mm, and preferably, greater than or equal to 0.3 mm. Further, the thickness of the glass panel10may be less than or equal to 1 mm, and preferably, less than or equal to 0.7 mm.

Each of the through holes110to be filled penetrates the glass panel10from a front surface11(referred to as a “first surface” as well) to a back surface12(referred to as a “second surface” as well) of the glass panel10. The back surface12is opposite to the front surface11.

The through holes110to be filled are used for a technique called TGV (Through-Glass Via) by which the through holes110are filled with an electrical conductive material. Hereinafter, the through hole110to be filled is simply referred to as the through hole110. In this embodiment, the plurality of through holes110may be provided at equal intervals.

The alignment mark120is a pattern provided at a specific position of the glass panel10. In this embodiment, the alignment marks120may be provided at four corners of the glass panel10, respectively. The alignment marks120are used for alignment of the glass panel10.

Each of the alignment marks120is formed by a plurality of through holes125each penetrating the glass panel10from the front surface11to the back surface12of the glass panel10. In this embodiment, the plurality of through holes125constituting each of the alignment marks120are provided on an outer periphery of a circle with a predetermined diameter “D”. In this embodiment, the diameter “D” is greater than or equal to 1 mm, for example. By setting the diameter “D” to be greater than or equal to 1 mm, recognition accuracy of the alignment mark120by a camera or the like can be improved. Meanwhile, the diameter “D” may be less than or equal to 2 mm. By setting the diameter “D” to be less than or equal to 2 mm, the number of the through holes125necessary for constituting each of the alignment marks120becomes small, and a manufacturing period necessary for forming the alignment marks120can be reduced. Each of the through holes110and the through holes125has a substantially circular shape in a planar view.

As illustrated inFIG. 4, in this embodiment, at least one of the through holes125is configured such that a first diameter “t1” of a first opening126at the front surface11, a second diameter “t2” of a second opening127at the back surface12, and a minimum diameter “t3” between the front surface11and the back surface12satisfy t1>t3 and also t2>t3. Hereinafter, a portion of the through hole125at which the diameter of the through hole125becomes the minimum diameter “t3” is referred to as a “portion128”. It is preferable that each of the through holes125is configured to satisfy the above relationship.

Specifically, with reference toFIG. 4, the first diameter “t1” of the first opening126of the through hole125is defined to be equal to a length of a tangent line “TG” (a distance between two intersection points of the tangent line “TG” and the front surface11) in a cross-section that passes a center of the through hole125. As the alignment mark120includes the plurality of through holes125in this embodiment, the first diameter “t1” of the first opening126is calculated by an average value of the diameters of the plurality of through holes125.

The second diameter “t2” of the second opening127at the back surface12of the glass panel10is similarly calculated. Further, a minimum diameter of the through hole125between the front surface11and the back surface12is defined as the minimum diameter “t3”. The first diameter “t1” may be within a range of 1 to 100 μm, and preferably, greater than or equal to 10 μm and less than or equal to 75 μm. More preferably, the first diameter “t1” may be less than or equal to 70 μm, furthermore preferably, less than or equal to 60 μm, and yet furthermore preferably, less than or equal to 50 μm. The second diameter “t2” may be within a range of 1 to 100 μm, and preferably, greater than or equal to 10 μm and less than or equal to 60 μm. More preferably, the second diameter “t2” may be less than or equal to 40 μm, furthermore preferably, less than or equal to 30 μm, and yet furthermore preferably, less than or equal to 20 μm. In this embodiment, as an example, the first diameter “t1” is 75 μm, the second diameter “t2” is 60 μm and the minimum diameter “t3” is 40 μm.

It is preferable that a pitch between the through holes125constituting the alignment mark120is greater than or equal to 1.5 times whichever of the first diameter “t1” and the second diameter “t2” is the larger. With this, even when the glass panel10is distorted when forming the through holes125, undesired connection of the through holes125can be suppressed. In other words, generation of cracking can be suppressed. In this embodiment, the pitch of the through holes125constituting the alignment mark120is 120 μm, which is greater than or equal to 1.5 times of the first diameter “t1”, for example.

Further, it is preferable that the pitches of the through holes125constituting the alignment mark120are equal intervals. With this configuration, the size of the alignment mark120can be made smaller compared with a case when the pitches of the through holes125constituting the alignment mark120are not equal intervals.

It is preferable that the minimum diameter “t3” of the through hole125is greater than or equal to 10 μm, more preferably, greater than or equal to 20 μm, and furthermore preferably, greater than or equal to 30 μm.

Here, if an alignment mark is formed by a single large through hole, cracking may be generated in the glass panel10due to distortion of the glass panel10when forming such a large through hole. However, according to the alignment mark120of the embodiment, as the alignment mark120is constituted by the plurality of small through holes, compared with a case when the alignment mark is constituted by the large through hole, generation of cracking can be suppressed.

As will be described later in detail with reference toFIG. 5B, when performing a process at a specific position on the glass panel10, the alignment marks120are used for alignment. As will be described later, when using the alignment marks120for alignment of the glass panel10, light is irradiated to recognize each of the alignment marks120.

According to the glass panel10of the embodiment, the above described relationships t1>t3 and also t2>t3 are satisfied. Thus, when the light is irradiated on the front surface11from a front surface11side, a part of the light entered in the through hole125is reflected by a sidewall of the through hole125. Similarly, when the light is irradiated on the back surface12from a back surface12side, a part of the light entered in the through hole125is reflected by the sidewall of the through hole125.

As a result, when checking the through hole125by the camera, the through hole125is effectively contrasted with a portion of the glass panel10where the through holes125are not formed, at both of the front surface11and the back surface12. As a result, the alignment mark can be accurately recognized by a camera at both of the front surface11and the back surface12.

It is preferable that a difference between the first diameter “t1” and the minimum diameter “t3”, in other words, “t1-t3” is greater than or equal to 5 μm, and more preferably, greater than or equal to 10 μm. Similarly, it is preferable that a difference between the second diameter “t2” and the minimum diameter “t3”, in other words, “t2-t3” is greater than or equal to 5 μm, and more preferably, greater than or equal to 10 μm. With this, a part of the light irradiated on each of the through holes125can reflect at the sidewall of the respective through holes125. As a result, the alignment mark can be accurately recognized by a camera at both of the front surface11and the back surface12.

In the glass panel10of the embodiment, the first diameter “t1” may be greater than or equal to 10 μm (t1≥10 μm), and more preferably, greater than or equal to 30 μm (t1≥30 μm). In addition, the second diameter “t2” may be greater than or equal to 10 μm (t2≥10 μm), and more preferably, greater than or equal to 30 μm (t2≥30 μm). With this configuration, when checking the through hole125by a camera, the through hole125is effectively contrasted with a portion of the glass panel10where the through holes125are not formed, at both of the front surface11and the back surface12. As a result, the alignment mark120can be more easily recognized at both of the front surface11and the back surface12.

In this embodiment, the through holes125constituting the alignment mark120are formed by following steps.

FIG. 3is a cross-sectional view illustrating the glass panel10after a first step is performed. In the first step, laser light is irradiated on the front surface11to form through holes125A each penetrating the glass panel10from the front surface11to the back surface12. The through holes110to be filled may be formed in the first step as well with the through holes125A.

CO2laser may be used as the laser light in the first step. An opening diameter of each of the through holes125A may be adjusted by a focal position of the laser light, energy of the laser light, and the like. For example, the opening diameter is increased by increasing the energy of the laser light and the like.

As illustrated inFIG. 3, at this time, the through hole125A is configured such that the first diameter “t1” of the first opening126at the front surface11is larger than a diameter “t4” of the second opening127at the back surface12. In other words, the through hole125A is formed to be tapered such that its diameter decreases from the front surface11toward the back surface12. This is because, as the laser light is irradiated from the front surface11side, an amount of heat received by the front surface11is greater than that by the back surface12.

Next, in a second step, laser light is irradiated on the back surface12to increase a diameter of the second opening127of each of the through holes125A at the back surface12. CO2laser may be used as the laser light in the second step as well. As a result, the through holes125as illustrated inFIG. 4are formed.

In the second step, by targeting a focal point of the CO2laser near the back surface12at each of the through holes125A, a chamfer portion “T” can be formed at the respective through holes125A near the back surface12of the glass panel10, as illustrated inFIG. 4. As a result, the diameter “t4” of the second opening127of each of the through holes125A becomes the second diameter “t2” (t2>t4) and the through holes125are formed.

By performing the second step in addition to the first step, the second diameter “t2” that is larger than the minimum diameter “t3” is formed. Thus, the through hole125is formed to be tapered off from the front surface11toward the back surface12, which means that the diameter decreases from the front surface11toward the portion128of the through hole125whose diameter becomes the minimum diameter “t3”, and also tapered off from the back surface12toward the front surface11, which means that the diameter decreases from the back surface12toward the portion128of the through hole125. Here, the minimum diameter “t3” may be larger than the diameter “t4” of the second opening127of the through hole125A.

As described above, according to the glass panel10of the embodiment, the through holes110are formed by the laser light same as the laser light used for forming the through holes125(through holes125A) of each of the alignment marks120. Thus, the glass panel10can be easily manufactured.

(Method of Manufacturing Wiring Board Using Glass Panel)

FIG. 5AtoFIG. 5Care views for describing manufacturing steps of a wiring board20using the glass panel10. As illustrated inFIG. 5A, the through holes110and the through holes125are formed in the glass panel10.

A copper interconnect130may be formed by using either of a subtractive method and an additive method. In this embodiment, an example is described in which the subtractive method is used for forming the copper interconnect130.

Firstly, a metal layer130A is formed on the front surface11and the back surface12of the glass panel10, and also over a sidewall of each of the through holes110. The metal layer130A may be formed by the following steps, for example. The metal layer130A may be made of copper.

A thin copper (Cu) film is formed on the front surface11and the back surface12of the glass panel10, and also over a sidewall of each of the through holes110and the through holes125by electroless copper (Cu) plating. Then, a copper (Cu) film is formed on the thin copper (Cu) film to increase the thickness of the copper (Cu) film by electrolytic copper (Cu) plating.

Thereafter, after covering the through holes110with films each having resistance against etchant, the metal layer130A formed on and around the through holes125is removed by wet etching and the like to expose the alignment marks120.FIG. 5Aillustrates this state.

The metal layer130A formed on and around the through holes125need not be removed. However, by removing the metal layer130A formed on and around the through holes125as illustrated inFIG. 5A, positions of the through holes125are more clearly recognized and recognition accuracy of the alignment mark120by a camera is improved. Further, as described later in detail, if the metal layer130A is left on and around the through holes125, it is preferable that the metal layer130A will not be discontinuous in order to facilitate recognition accuracy of the alignment mark120by a camera.

Next, as illustrated inFIG. 5B, by processing the metal layer130A, a copper interconnect130is formed in each of the through holes110. The copper interconnects130may be formed by the following steps, for example.

First, a resist layer (photoresist, not illustrated) is formed on the front surface11of the glass panel10. Thereafter, positional information of the glass panel10is obtained by recognizing the alignment marks120at the front surface11by a camera while irradiating light, and using positional information of the alignment marks120. Then, using the positional information of the glass panel10, the resist layer is processed. Specifically, the resist layer is exposed and developed. Thereafter, using the resist layer as a mask, the metal layer130A at the front surface11that is not covered by the mask is etched. Then, the resist layer is removed.

Then, a resist layer (photoresist, not illustrated) is formed on the back surface12of the glass panel10. Thereafter, positional information of the glass panel10is obtained by recognizing the alignment marks120at the back surface12by a camera while irradiating light, and using positional information of the alignment marks120. Then, using the positional information of the glass panel10, the resist layer is processed. Specifically, the resist layer is exposed and developed. Thereafter, using the resist layer as a mask, the metal layer130A at the back surface12is etched. Then, the resist layer is removed.FIG. 5Billustrates this state.

It is preferable that wavelength of the light irradiated on the alignment mark120for recognizing the alignment mark120at the front surface11or the back surface12is greater than or equal to 400 nm. With this configuration, the resist layer is not cured by the light.

Thereafter, after performing a roughing process on a surface of each of the copper interconnects130, at either of or both of the front surface11and the back surface12, an insulation resin layer140that covers the copper interconnects130are formed. With these steps, a wiring board20is completed. By performing the roughing process, the surfaces of the copper interconnects130are roughed, and adhesion between the copper interconnects130and the insulation resin layer140is increased.

FIG. 5Cis a view for describing the wiring board20after forming the insulation resin layer140. Further, by a so-called build-up process, a multi-layered wiring board may be manufactured. According to the method of manufacturing the wiring board20of the embodiment, as the alignment marks120are accurately recognized by the camera, at both of the front surface11and the back surface12, the wiring board20is accurately manufactured.

Modified Examples

When forming the through holes125of each of the alignment marks120by the CO2laser, short pulse laser whose wavelength is less than or equal to 800 nm may be used. Further, in such a case, it is preferable that the pulse width is less than 1 ns, more preferably, less than or equal to 100 ps, and furthermore preferably, less than or equal to 10 ps.

Although the CO2laser is used for forming the through holes125of each of the alignment marks120in the above embodiment, this is not limited as such. Instead of the CO2laser, for example, the through holes125may be formed by UV-YAG laser, He:Ne laser, Ar ion laser, excimer XeF laser, Er:YAG laser, Nd:YAG laser, second high frequency of Nd:YAG laser, third high frequency of Nd:YAG laser, ruby laser, fiber laser, spark erosion, etching, sand blasting or drilling.

Although the diameter “t4” of the second opening127of the through hole125A is increased by irradiating the laser light from the back surface12side in the above embodiment (seeFIG. 3), this is not limited as such. For example, after forming the through hole125A as described above, a film may be provided at the front surface11of the glass panel10to cover the through hole125A at the front surface11, and the diameter “t4” of the second opening127of the through hole125A may be increased by wet etching using hydrofluoric acid or the like.

Alternatively, when forming the through holes125A, a film of PET or the like may be formed at the back surface12. By forming such a film, when irradiating the laser light from the front surface11side to form the through holes125, the chamfer portion T may be formed at each of the through holes125at the back surface12by heat of fusion of the film.

Although the metal layer130A is formed by, after forming the thin copper (Cu) film by the electroless copper (Cu) plating, increasing the thickness of the copper (Cu) film by the electrolytic copper (Cu) plating in the above embodiment, this is not limited as such. For example, before forming the electroless copper (Cu) plating, an adhesion layer made of titanium (Ti), tin (Sn), zinc (Zn) or the like may be formed. Further, instead of using the electroless copper (Cu) plating, the thin copper (Cu) film may be formed by sputtering copper (Cu) on an adhesion layer made of titanium (Ti), nickel (Ni), chromium (Cr) or the like.

Although the copper interconnect130is formed as a conformal via, in which the metal layer is formed on the sidewall of each of the through holes110but does not fill each of the through holes110, in each of the through holes110in the above embodiment, the copper interconnect130may be formed to completely fill each of the through holes110without a space.

Further, the second step as described above with reference toFIG. 4need not be performed for the through holes110to be filled. Alternatively, the second step may be performed for the through holes110to be filled similarly as for the through holes125. Furthermore alternatively, the through holes110to be filled may be separately formed from the through holes125.

Although the resist layer is formed on each of the front surface11and the back surface12of the glass panel10in manufacturing the wiring board20in the above embodiment, this is not limited as such. The resist layer may be formed on either of the front surface11and the back surface12of the glass panel10.

Although each of the alignment marks120is constituted by the plurality of through holes125in the above embodiment, this is not limited as such. Each of the alignment marks120may be formed by holes that do not penetrate the glass panel10, for example.

Although the through holes125constituting the alignment mark120are provided on the outer periphery of the circle in the above embodiment, this is not limited as such. For example, the through holes125constituting the alignment mark120may be provided along an outer periphery of a rectangular or square shape.

The alignment mark120may have various configurations.

For example, the plurality of through holes125constituting the alignment mark125may be provided on an outer periphery of a certain graphic pattern, or on the outer periphery of the certain graphic pattern and also within the certain graphic pattern.

FIG. 6Ais a view illustrating an example of the alignment mark120seen from the front surface11, and illustrates a case where the certain graphic pattern is a circle150. The through holes125are provided on the outer periphery of the circle150. Here, the through holes125provided on the outer periphery of the circle150include a first through hole125aand a second through hole125b. A distance between centers of the first openings of the first through hole125aand the second through hole125bmay be greater than or equal to 1 mm.

In other words, in each of the alignment marks120, the plurality of through holes125provided on the outer periphery of the certain graphic pattern (circle150, for example) may be configured such that the maximum length “dmax” of a length “d” of a straight line connecting centers of first openings of any two of the through holes125at the front surface11is greater than or equal to 1 mm.

Furthermore, the through holes125provided on the outer periphery of the circle150further include a third through hole125cand a fourth through hole125d. Provided that the first through hole125aand the second through hole125bare provided on a first straight line “L1”, the third through hole125cand the fourth through hole125dare provided on a second straight line “L2” that is perpendicular to the first straight line “L1” and also that passes through a midpoint between the first through hole125aand the second through hole125bon the first straight line “L1”. Accordingly, in each of the alignment marks120, a distance between centers of the first openings of the third through hole125cand the fourth through hole125dat the front surface11may be greater than or equal to 1 mm.

In other words, in each of the alignment marks120, a length “ddgl” of a second line segment (L2) that passes through a midpoint of a first line segment (L1) connecting the two through holes whose distance takes the maximum length “dmax” and that is perpendicular to the first line segment (L1) is greater than or equal to 1 mm.

Although not specifically limited, each of the distance between the centers of the first openings of the first through hole125aand the second through hole125b, and the distance between the centers of the first openings of the third through hole125cand the second through hole125d, may be less than or equal to 2 mm.

FIG. 6Bis a view illustrating another example of the alignment mark120seen from the front surface11, and illustrates a case where the certain graphic pattern is a circle150. In the alignment mark120ofFIG. 6B, the through hole125is provided within the circle150in addition to the through holes125provided on the outer periphery of the circle150.

FIG. 7AtoFIG. 7Care views each illustrating another example of the alignment mark120seen from the front surface11, and illustrates a case where the certain graphic pattern is a square shape152.FIG. 7AandFIG. 7Beach illustrate the alignment mark120in which the through holes125are provided on the outer periphery of the square shape152. In the alignment mark120ofFIG. 7C, the through hole125is provided within the square shape152in addition to the through holes125provided on the outer periphery of the square shape152.

It is preferable that each of the alignment marks120is constituted by eight or more of the through holes125. With this configuration an error in recognition of the alignment mark120can be reduced.

Furthermore, the certain graphic pattern may have various shapes such as a cross shape, in addition to the circle and the rectangular or square shape.

The glass panel10may have various configurations, and the alignment marks120may be provided on the glass panel10in various ways.

For example, the glass panel10may have a substantially rectangular or square shape having four corners and four sides in a planar view. At this time, the alignment mark120may be provided at least at each of two corners among the four corners of the glass panel10.FIG. 1illustrates an example in which the alignment mark120is provided at each of the four corners of the glass panel10. Alternatively, the alignment mark120may be provided at least along each of two sides among the four sides of the glass panel10.FIG. 8Aillustrates an example in which the alignment mark120is provided at each of the four sides of the glass panel10.

As alignment accuracy is improved when a distance between the alignment marks120is long, it is preferable to provide the alignment marks120along an outer periphery of the glass panel10such as the corners or the sides. It is preferable to provide three of the alignment marks120, and more preferably, four or more of the alignment marks120may be provided.

FIG. 8Billustrates an example in which the alignment mark120is provided at each of the four corners and each of the four sides of the glass panel10.

Furthermore, the alignment mark120may be further provided substantially at a center of the glass panel10. With this configuration, even when the glass panel10is large, the alignment mark120can be included in a screen taken by a camera.

FIG. 9Aillustrates an example in which the alignment mark120is provided at a center in addition to each of the four corners of the glass panel10.FIG. 9Billustrates an example in which the alignment mark120is provided at the center in addition to each of the four corners and each of the four sides of the glass panel10.

Furthermore, although not illustrated, the glass panel10may have a circular shape such as a wafer. In such a case as well, the alignment marks120may be provided along the outer periphery of the glass panel10, at four positions, for example.

Furthermore, a distance between an outer edge of the glass panel10and the through hole125constituting the alignment mark120that is nearest to the outer edge of the glass panel10may be greater than or equal to 1 mm, and more preferably, may be greater than or equal to 5 mm. With this configuration, cracking and chipping of the glass panel10can be prevented.

As illustrated inFIG. 4, in the at least one of the through holes125, an inner wall surface is a substantially curved surface from the portion128of the through hole125whose diameter becomes the minimum diameter “t3” to the back surface12.FIG. 10specifically illustrates this feature of the through hole125. An inner surface129of the through hole125is curved from the portion128to the second opening127.

With this configuration, when the light is irradiated to recognize each of the alignment marks120, the light is reflected at the curved surface and an edge of the through hole125is easily recognized. Furthermore, as stress can be dispersed, the glass panel10will not break.

Further, when a thin metal film such as the metal layer130A is formed on the inner surface of the through hole125, it is preferable that the thin metal film will not be discontinuous. Furthermore, even when the conductive material is not filled in the through hole125, if the thin metal film is evenly deposited on the curved inner surface129of the through hole125, the light is easily reflected by the inner surface. Thus, an edge of the through hole125can be easily recognized.

Furthermore, as illustrated inFIG. 4, the portion128of the through hole125whose diameter becomes the minimum diameter “t3” may be positioned between a center of the glass panel10in its thickness direction and the back surface12.

Furthermore, a distance between the portion128of the through hole125whose diameter becomes the minimum diameter “t3” and the back surface12may be less than or equal to 50 μm, preferably, less than or equal to 30 μm, more preferably, less than or equal to 20, furthermore preferably, less than or equal to 10, and yet furthermore preferably, less than or equal to 5.

Furthermore, the first diameter “t1” of the first opening126is larger than the second diameter “t2” of the second opening127.

As long as the above described relationships t1>t3 and also t2>t3 are satisfied, the through hole125may have various shapes, in addition to the structure specifically illustrated inFIG. 4and the like. Furthermore, as long as the through hole125is formed to be tapered off from the front surface11such that its diameter decreases from the front surface11toward the portion128of the through hole125whose diameter becomes the minimum diameter “t3”, and also tapered at the back surface12side such that its diameter decreases from the back surface12toward the portion128of the through hole125, the through hole125may have various shapes.

For example, the through holes125may be formed by irradiating laser on the front surface11of the glass panel10to form through holes and/or modified regions at positions at which the through holes125are to be formed, and then performing wet etching using hydrofluoric acid or the like from both of the front surface11side and the back surface12side.

Further, a difference between the first diameter “t1” of the first opening126of the through hole125constituting the alignment mark120and a diameter of an opening of each of the through holes110to be filled at the front surface11may be within 15 μm, preferably, within 15 μm, and more preferably, within 5 μm. The through holes125each constituting the alignment mark120and the through holes110to be filled may be formed by the same laser irradiation condition from the front surface11side. With this configuration, as the through holes125and the through holes110are formed by the same program, the through holes125and the through holes110can be easily formed by a short period.

Although irradiating the laser light from the back surface12in the second step is not performed on the through holes110in the above embodiment, the laser light such as the CO2laser may be irradiated on the through holes110from the back surface as well. With this configuration, a conductive material is easily filled in each of the through holes110.

Various aspects of the subject-matter described herein are set out non-exhaustively in the following numbered clauses:

1. A glass panel for a wiring board, comprising:

a first surface and a second surface, the second surface being opposite to the first surface; and

an alignment mark constituted by a plurality of through holes each penetrating the glass panel from the first surface to the second surface,

at least one of the plurality of through holes being configured such that a first diameter “t1” of a first opening at the first surface, a second diameter “t2” of a second opening at the second surface, and a minimum diameter “t3” between the first surface and the second surface satisfy t1>t3 and also t2>t3.

With this configuration, the alignment mark can be accurately recognized.

2. In the above described glass panel for the wiring board, the plurality of through holes constituting the alignment mark may be provided on an outer periphery of a certain graphic pattern with a diameter greater than or equal to 1 mm. With this configuration, the alignment mark can be furthermore accurately recognized.

3. In the above described glass panel for the wiring board, both of the first diameter “t1” of the first opening and the second diameter “t2” of the second opening may be greater than or equal to 10 μm. With this configuration, the alignment mark can be furthermore accurately recognized.

4. A method of manufacturing a wiring board, including:

forming a resist layer on at least one of the first surface and the second surface of the above described glass panel for the wiring board; and

processing the resist layer by using positional information of the alignment mark. With this configuration, the alignment mark can be accurately recognized. As a result, the wiring board can be accurately manufactured.

Although a preferred embodiment of the glass panel for a wiring board and the method of manufacturing a wiring board has been specifically illustrated and described, it is to be understood that minor modifications may be made therein without departing from the spirit and scope of the invention as defined by the claims.

The present invention is not limited to the specifically disclosed embodiments, and numerous variations and modifications may be made without departing from the spirit and scope of the present invention.