Wiring board

Abstract

To reduce the diameter of a connection terminal portion and suppress the peeling of the connection terminal portion in a wiring board in which at least a part of the connection terminal portion is exposed on the surface of an insulating board.SOLUTION: A wiring board 1 includes a ceramic board 11, via 31, and a connection pad 21. The ceramic board 11 has a front surface 11a (first surface) and a back surface 11b (second surface). The vias 31 are arranged in the ceramic board 11. The connection pads 21 are arranged in the ceramic board 11 and connected to the vias 31. At least a part of the connection pad 21 is exposed from the front surface 11a. Moreover, the connection pad 21 has a maximum width portion at a portion that enters inside the ceramic board 11. An equivalent circle diameter D1 of the end surface of the connection pad 21 exposed from the surface 11a is within the range of 30 μm or more and 100 μm or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a wiring board having a connection terminal portion for external connection.

Background Art

[0002] As a wiring board on which electronic components such as semiconductor elements are mounted, there is a ceramic board formed of ceramic which is a non-conductive material, and a conductive pattern formed using a conductive material such as metal inside and on the surface of the ceramic board. The conductive pattern formed on the wiring board functions as, for example, a wiring, a via, a connection terminal, etc. The connection terminal, also called a connection pad, is electrically connected to an external electronic component.

[0003] Patent Document 1 discloses a ceramic wiring board on which electronic components such as semiconductor elements and crystal oscillators are mounted. This ceramic wiring board has a ceramic insulating layer, a through conductor provided so as to penetrate the ceramic insulating layer in the thickness direction, and a conductor layer joined to the end face of the through conductor in the thickness direction. The conductor layer serves as a connection terminal for an electronic component when the electronic component is mounted on the ceramic board.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the ceramic wiring board disclosed in Patent Document 1, when viewed in cross section in the thickness direction, a part of the conductor layer 3 is embedded in the ceramic insulating layer 1 in an exposed state. When the exposed surface of the conductor layer 3 is defined as the first surface 3a and the surface on the side of the through conductor 5 is defined as the second surface 3b, the width w1 of the first surface 3a is larger than the width w2 of the second surface 3b, and the side surface 3s of the conductor layer 3 is an inclined surface 7 from the first surface 3a side to the second surface 3b side, and the angle between the inclined surface 7 and the side surface 5s of the through conductor 5 is larger than 90°.

[0006] However, if the shape of the conductor layer exposed on the surface of the ceramic wiring board is a shape that tapers from the surface toward the inner layer side, the conductor layer will easily come out of the ceramic insulating layer. In recent years, the demand for miniaturization of wiring boards has been increasing, and the conductor layer is also required to have a smaller diameter. However, as the diameter is reduced, the contact area with the ceramic substrate becomes smaller, so there has been a problem that the conductor layer easily comes out of the ceramic insulating layer even when miniaturized (miniaturized).

[0007] Therefore, the present invention aims to suppress peeling of the connection terminal portion while realizing miniaturization of the connection terminal portion in a wiring board in which at least a part of the connection terminal portion is exposed on the surface of the insulating substrate.

Means for Solving the Problems

[0008] A wiring board according to one aspect of the present invention includes an insulating substrate having a first surface and a second surface on the opposite side of the first surface in its thickness direction, a conductive via disposed in the insulating substrate, and a connection terminal portion disposed in the insulating substrate and connected to the via. In this wiring board, at least a part of the connection terminal portion is exposed from the first surface, and in a portion of the connection terminal portion that enters the interior of the insulating substrate, when the connection terminal portion is viewed in a cross-sectional view in the thickness direction, a maximum width portion where the width of the connection terminal portion in the surface direction orthogonal to the thickness direction is the largest is located inside the insulating substrate, and the width of the maximum width portion in the surface direction is larger than the width of the connection terminal portion in the surface direction at the position of the first surface. Further, the equivalent circle diameter of the end face of the connection terminal portion exposed from the first surface is in the range of 30 μm or more and 100 μm or less.

[0009] According to the above configuration, it is possible to obtain a wiring board with a reduced diameter of the connection terminal portion and a high definition. Further, even when the diameter of the connection terminal portion is reduced, by configuring the connection terminal portion as described above, it is possible to obtain a connection terminal portion that is difficult to peel off from the insulating substrate.

[0010] In the wiring board according to one aspect of the present invention described above, the via may have a shape that tapers toward the connection terminal portion.

[0011] According to the above configuration, it is possible to easily bring the entire end face of the via into contact with the end face of the connection terminal portion. Thereby, it is possible to suppress an increase in the resistance value that may occur when the via and the connection terminal portion are electrically connected in a state of being misaligned.

[0012] In the wiring board according to one aspect of the present invention described above, the end face of the connection terminal portion exposed from the first surface of the insulating substrate may be flush with the first surface of the insulating substrate.

[0013] According to the above configuration, an electronic component such as a semiconductor chip can be placed on the connection terminal portion in a stable state.

[0014] In the wiring board according to one aspect of the present invention described above, the connection terminal portion may have a tapered portion that tapers toward the first surface of the insulating substrate, and a columnar portion whose shape along the surface direction of the insulating substrate is substantially constant in the thickness direction of the insulating substrate.

[0015] According to the above configuration, a connection terminal portion that is less likely to peel off from the insulating substrate can be obtained.

[0016] Another aspect of the present invention relates to a method for manufacturing a wiring board. This wiring board includes a ceramic substrate, a conductive via disposed within the ceramic substrate, and a connection terminal portion disposed within the ceramic substrate and electrically connected to the via. The method for manufacturing this wiring board includes a hole forming step of irradiating a ceramic sheet before firing with a laser to form a hole at a location where the via is to be disposed, a filling step of filling the hole in the ceramic sheet with conductive ink, a pattern forming step of exposing and developing a film coated with a photosensitive conductive paste to form a conductive pattern for the connection terminal portion having a tapered shape toward the contact surface with the film, a transfer step of transferring the conductive pattern formed in the pattern forming step to the ceramic sheet that has undergone the filling step and electrically connecting the conductive ink and the conductive pattern, and a firing step of firing the ceramic sheet after the transfer step.

[0017] According to the above method, it is possible to manufacture a wiring board that can suppress peeling of the connection terminal portion while realizing a reduction in the diameter of the connection terminal portion.

[0018] In the method for manufacturing a wiring board according to one aspect of the present invention described above, in the hole forming step, the laser may be irradiated from the side opposite to the side of the ceramic sheet where the conductive pattern is to be transferred to form a hole.

[0019] According to the above method, a via having a tapered shape toward the connection terminal portion can be formed. As a result, it becomes easier to bring the entire end face of the via into contact with the end face of the connection terminal portion, so that the possibility of electrical connection in a state where the via and the connection terminal portion are misaligned can be reduced.

Advantages of the Invention

[0020] According to the wiring board according to one aspect of the present invention, it is possible to suppress peeling of the connection terminal portion while realizing a reduction in the diameter of the connection terminal portion. Further, according to the method for manufacturing a wiring board according to another aspect of the present invention, it is possible to manufacture a wiring board capable of suppressing peeling of the connection terminal portion while realizing a reduction in the diameter of the connection terminal portion.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0023] (Configuration of Wiring Substrate) In this embodiment, as an example of the wiring substrate according to the present invention, the wiring substrate 1 will be described. FIG. 1 is a schematic plan view showing the surface-side configuration of a part of the wiring substrate 1. FIG. 2 schematically shows the cross-sectional configuration of the wiring substrate 1. FIG. 2 is a cross-sectional view of the wiring substrate 1 shown in FIG. 1 when cut along the line A-A.

[0024] The wiring substrate 1 mainly includes a ceramic substrate (insulating substrate) 11 and a conductive pattern. The conductive pattern includes, for example, connection pads (connection terminal portions) 21, vias 31, and wiring portions 41.

[0025] The ceramic substrate 11 is a member serving as the base of the wiring substrate 1. The ceramic substrate 11 can be formed of, for example, a high-temperature fired ceramic mainly composed of alumina (Al2O3). In another embodiment, the ceramic sheet may be formed of a medium-temperature fired ceramic (MTCC) such as alumina with improved sinterability, or a low-temperature fired ceramic (LTCC).

[0026] The ceramic substrate 11 is obtained by firing one or a plurality of ceramic green sheets. When the ceramic substrate 11 is formed from a plurality of ceramic green sheets, the ceramic substrate 11 has a plurality of laminated ceramic layers. FIG. 2 shows a configuration example in which the ceramic substrate 11 is formed of one ceramic green sheet.

[0027] In this embodiment, for convenience, the surface (first surface) 11a of the substantially flat ceramic substrate 11 on which the connection pads 21 are provided is defined as the front surface, and the opposite surface is defined as the back surface (second surface) 11b. However, the definitions of the front and back surfaces of the ceramic substrate 11 are not limited to this and can be arbitrarily determined. Also, the surface direction of the ceramic substrate 11 is defined as the X direction, and the thickness direction of the ceramic substrate 11 is defined as the Y direction (see FIG. 2).

[0028] The conductive patterns are provided on the front surface 11a, back surface 11b, and inside of the ceramic substrate 11, etc. Each conductive pattern is formed in a predetermined shape and functions, for example, as a wiring portion, connection pad, via, and electrode.

[0029] The conductive pattern can be formed of, for example, a metal material such as copper (Cu), tungsten (W), silver (Ag), or molybdenum (Mo), or an alloy material mainly composed of these metal materials. When the ceramic substrate 11 is formed of a high-temperature fired ceramic, the conductive pattern preferably contains, for example, tungsten (W) or molybdenum (Mo) as a main component. When the ceramic substrate 11 is formed of a medium-temperature fired ceramic or a low-temperature fired ceramic, the conductive pattern preferably contains, for example, copper (Cu) or silver (Ag) as a main component.

[0030] A connection pad 21, which is an example of the conductive pattern, is used as a connection terminal to other electronic components (for example, semiconductor chips, etc.). The connection pad 21 is suitably used as a connection terminal, for example, when other electronic components are mounted on the wiring substrate 1 in a flip-chip method. When connecting a semiconductor chip to the wiring substrate 1 in a flip-chip method, bumps are formed on the connection pad 21 with solder or the like, and the connection pad 21 is electrically connected to the connection terminal of the semiconductor chip through these bumps.

[0031] In this embodiment, as shown in FIG. 2, a plurality of connection pads 21 are provided on the surface 11a side of the ceramic substrate 11. Also, in this embodiment, most of the connection pads 21 are embedded inside the ceramic substrate 11, and a part thereof is exposed from the surface 11a of the ceramic substrate 11. That is, the surface 21s of the connection pad 21 is exposed from the surface 11a of the ceramic substrate 11.

[0032] A via 31, which is an example of a conductive pattern, is embedded inside the ceramic substrate 11. In this embodiment, a plurality of vias 31 are provided on the back surface 11b side of the ceramic substrate 11. And each connection pad 21 is disposed on each via 31, and the via 31 and the connection pad 21 are electrically connected. As shown in FIG. 2, one connection pad 21 and one via 31 connected thereto are provided so as to penetrate the inside of the ceramic substrate 11 (that is, from the surface 11a to the back surface 11b).

[0033] A wiring portion 41, which is an example of a conductive pattern, is stretched over the surface 11a, the back surface 11b, and the inside of the ceramic substrate 11, etc. Some of these wiring portions 41 are joined to the vias 31 inside the ceramic substrate 11. Thereby, the via 31 and the wiring portion 41 are electrically connected. The wiring portion 41 can transmit and receive electrical signals to and from connection pads 21 and the like formed on the surface 11a side of the ceramic substrate 11 via the vias 31.

[0034] Subsequently, a more detailed configuration of the connection pad 21 and the via 31 will be described. FIG. 3 shows a cross-sectional shape of one of the connection pads 21 shown in FIG. 2 and one via 31 connected to this connection pad 21.

[0035] As shown in FIG. 1, the connection pad 21 is substantially circular in top view. The connection pad 21 is arranged so as to overlap the via 31 in top view. As shown in FIG. 3, the connection pad 21 has a tapered portion 22 and a columnar portion 23. The tapered portion 22 is located on the surface side (surface 11a in FIG. 3 etc.) of the ceramic substrate 11.

[0036] The tapered portion 22 tapers toward the surface 11a of the ceramic substrate 11. That is, the tapered portion 22 has a shape in which the cross-sectional area in the plane direction (X direction) of the ceramic substrate 11 increases as it moves away from the surface 11a of the ceramic substrate 11. In the present embodiment, the cross-sectional shape of the tapered portion 22 in the plane direction (X direction) is substantially circular.

[0037] The columnar portion 23 is located inside the ceramic substrate 11. The columnar portion 23 is in contact with the via 31. The cross-sectional shape of the columnar portion 23 along the plane direction (X direction) of the ceramic substrate 11 is substantially constant in the thickness direction (Y direction) of the ceramic substrate 11. In the present embodiment, the cross-sectional shape of the columnar portion 23 in the plane direction (X direction) is substantially circular.

[0038] In the present embodiment, the diameter D1 of the surface 21s of the connection pad 21, which is substantially circular in top view, is smaller than the diameter D2 of the columnar portion 23 of the connection pad 21, which is substantially circular in top view (see FIG. 1).

[0039] That is, when the shape of the connection pad 21 is viewed in a cross-sectional view in the Y direction (thickness direction), the maximum width portion (corresponding to the columnar portion 23 in the present embodiment) where the width in the X direction (plane direction) of the connection pad 21 is the largest is located inside the ceramic substrate 11. And the width of this maximum width portion in the X direction (plane direction) (corresponding to the diameter D2 of the columnar portion 23 in the present embodiment) is larger than the width of the connection pad 21 in the X direction (plane direction) at the position of the surface 11a of the ceramic substrate 11 (corresponding to the diameter D1 of the surface 21s of the tapered portion 22 in the present embodiment).

[0040] Since the connection pad 21 has such a shape, it is possible to configure the connection pad 21 so that it is difficult to come off from the ceramic substrate 11.

[0041] In addition, in the present embodiment, the side surface of the tapered portion 22 located in the surface layer portion of the ceramic substrate 11 has a curved shape (rounded shape) in a cross-sectional view (see FIG. 3 and the like). Thereby, in the portion where the connection pad 21 is embedded in the ceramic substrate 11, the contact area between the tapered portion 22 and the ceramic layer can be increased. Therefore, the bonding strength of the connection pad 21 to the ceramic substrate 11 increases, and the connection pad 21 is less likely to come off from the ceramic substrate 11.

[0042] The via 31 has a shape that tapers toward the connection pad 21. That is, the cross-sectional area of the portion of the via 31 located on the back surface 11b side of the ceramic substrate 11 in the plane direction (X direction) is larger than the cross-sectional area of the portion in contact with the connection pad 21 in the plane direction (X direction). In the present embodiment, the cross-sectional shape of the via 31 in the plane direction (X direction) is substantially circular.

[0043] As will be described later, the via 31 can be formed by filling a hole 10a formed in the ceramic sheet 10 with a conductive material using a laser or the like. Thereby, the cross-sectional diameter of the via 31 in the plane direction (X direction) can be made smaller, for example, to about 30 μm or less. Further, a wiring board 1 in which a plurality of vias 31 are arranged at a narrow interval (for example, about 50 μm) can be obtained.

[0044] Also, by forming a via formation hole 10a in the ceramic substrate 11 using a laser, a via 31 having a shape that tapers toward the connection pad 21 can be formed. By making the via 31 have a shape that tapers toward the connection pad 21, it is possible to easily bring the entire end surface of the via 31 into contact with the end surface of the connection pad 21. Thereby, it is possible to suppress an increase in the resistance value that may occur when the via 31 and the connection pad 21 are electrically connected in a state of being misaligned.

[0045] Further, most of the connection pad 21 is in a state of being buried in the ceramic substrate 11, and at least a part of the connection pad 21 is exposed from the surface 11a of the ceramic substrate 11.

[0046] And, the equivalent circle diameter D1 of the top surface (end face) of the connection pad 21 exposed from the surface 11a of the ceramic substrate 11 is in the range of 30 μm or more and 100 μm or less. By the diameter D1 being 30 μm or more, in the hole forming step (S10) of the manufacturing method of the wiring board 1 described later, holes 10a having a uniform diameter can be stably formed. Also, by the diameter D1 being 100 μm or less, high fineness of the connection pad 21 can be realized.

[0047] Furthermore, in the wiring board 1 according to the present embodiment, it is preferable that the entire connection pad 21 is in a state of being buried in the ceramic substrate 11. Thereby, a connection pad 21 that is more difficult to come off from the ceramic substrate 11 can be obtained. Also, the surface 21s of the connection pad 21 may be flush with the surface of the ceramic substrate 11 (in the example shown in FIG. 3 and the like, the surface 11a). Thereby, electronic components such as semiconductor chips can be placed on the connection pad 21 in a stable state.

[0048] (Manufacturing method of wiring board) Subsequently, the manufacturing method of the wiring board 1 will be described. Here, the description will be centered on the step of forming conductive patterns such as the connection pad 21 and the via 31. For the manufacturing method of the wiring board 1 other than this step, a conventionally known manufacturing method of a wiring board can be applied.

[0049] FIG. 4 shows, in the order of processes, a part of the manufacturing process of the wiring board 1. In FIG. 4, mainly, each process from the hole forming process (S10) to the firing process (S50) is shown. FIG. 5 schematically shows, in the order of processes, the state in which the hole forming process (S10) and the filling process (S20) for forming vias 31 and the like are performed. FIG. 6 schematically shows, in the order of processes, the state in which the pattern forming process (S30) for forming the connection pads 21 is performed. FIG. 7 schematically shows, in the order of processes, the state in which the transfer process (S40) for transferring the conductive pattern for the connection pads 21 to the ceramic sheet is performed.

[0050] In performing each process shown in FIG. 4, first, the ceramic sheet 10 is prepared. The ceramic sheet 10 can be obtained, for example, by kneading a powder of a ceramic material containing alumina (Al2O3) or the like together with an organic solvent, a binder, and the like to prepare a slurry and then forming it into a sheet shape.

[0051] After the ceramic sheet 10 is prepared, first, a conductive pattern for the via 31 is formed at a predetermined position within the ceramic sheet 10. Specifically, the hole forming process (S10) and the filling process (S20) are performed. FIG. 5 schematically shows the state in which the hole forming process (S10) and the filling process (S20) are performed.

[0052] In the hole forming process (S10), as in process A shown in FIG. 5, the hole forming laser 51 is irradiated onto a predetermined position (the position where the via 31 is to be formed) of the ceramic sheet 10 to form a plurality of holes 10a in the ceramic sheet 10. As shown in FIG. 5, a masking film 52 is disposed on the back surface 10d (the surface opposite to the laser irradiation surface 10c) of the ceramic sheet 10. In the subsequent filling process (S20), the conductive ink is filled from the side where the masking film 52 is disposed.

[0053] In the hole forming step (S10), in the subsequent transfer step (S40), a laser 51 is irradiated from the side opposite to the side where the conductive pattern in the ceramic sheet 10 is to be transferred to form holes 10a. As a result, as shown in FIG. 5, holes 10a having a shape in which the diameter of the holes 10a in the plane direction of the ceramic sheet 10 gradually decreases from the laser irradiation surface 10c toward the back surface 10d are formed.

[0054] As the laser 51, for example, a CO2 laser, a UV laser, etc. can be used. By forming holes in the ceramic sheet 10 using the laser 51, the diameter of the holes 10a can be reduced and the distance between adjacent holes can be reduced.

[0055] After the hole forming step (S10), a filling step (S20) is performed. In the filling step (S20), as shown in step B of FIG. 5, the conductive ink 54 for via formation is filled into each hole 10a from the back surface 10d side of the ceramic sheet 10 on which the masking film 52 is disposed, using a squeegee 53 or the like. As a result, a conductive pattern 30 for the via 31 having a tapered shape from the laser irradiation surface 10c to the back surface 10d (laser emission surface) of the ceramic sheet 10 can be formed.

[0056] Subsequently, a pattern forming step (S30) is performed. FIG. 6 schematically shows the state in which the pattern forming step (S30) is performed. The pattern forming step (S30) includes an exposure step (S31) and a development step (S31). Step A in FIG. 6 shows the exposure step (S31). Step B in FIG. 6 shows the development step (S31).

[0057] In performing the exposure step (S31), first, a carrier film 61 and a photosensitive conductive paste 62 are prepared. As the carrier film 61, for example, a transparent film made of a resin such as PEN (polyethylene naphthalate) or PET (polyethylene terephthalate) can be used.

[0058] The conductive paste 62 contains, for example, metal powder containing copper (Cu), tungsten (W), silver (Ag), or molybdenum (Mo), and a photosensitive resin. As the photosensitive resin, a negative photosensitive material that is photocured when irradiated with ultraviolet light is used. In the present embodiment, for example, a bisazide compound is used. By including a photosensitive resin in the conductive paste, a conductive pattern having a predetermined shape can be formed by photolithography. Therefore, for example, compared with the case of forming a conductive pattern by a screen printing method, a conductive pattern having a higher definition pattern shape can be formed.

[0059] The conductive paste 62 is applied onto the carrier film 61. The application of the conductive paste 62 can be performed using a conventionally known screen printing apparatus or the like. Thereby, a film body with conductive paste attached (hereinafter referred to as a film body) is obtained.

[0060] In the exposure step (S31), for example, light L is irradiated onto the conductive paste 62 applied on the carrier film 61 using an exposure apparatus equipped with a UV light source or the like.

[0061] In the exposure step (S31), light L is irradiated onto the conductive paste 62 on the carrier film 61 using the glass mask 70, and the photosensitive resin in the conductive paste 62 is photocured in accordance with the pattern shape of the connection pad 21 formed on the wiring board 1. In FIG. 6, the surface of the conductive paste 62 far from the carrier film 61 is defined as the first surface 62a, and the contact surface with the carrier film 61 is defined as the second surface 62b.

[0062] In the exposure step (S31), the glass mask 70 is disposed above the conductive paste 62. The glass mask 70 is provided with a light-shielding film 72 on a flat plate-shaped glass in accordance with the shape of the conductive pattern 20 to be formed. In the exposure step, light L (for example, ultraviolet light) that photocures the photosensitive resin contained in the conductive paste 62 is irradiated onto the conductive paste 62 on the carrier film 61 through the glass mask 70.

[0063] As a result, the conductive paste 62 in the region where the light-shielding film 72 is not provided is irradiated with the light L, while the conductive paste 62 in the region where the light-shielding film 72 is provided is not irradiated with the light L. As a result, in the conductive paste 62 on the carrier film 61, only the photosensitive resin existing in the region irradiated with the light L is photocured, and the photosensitive resin existing in the region where the light is blocked by the light-shielding film 72 remains on the carrier film 61 without being photocured.

[0064] Note that when the light L is irradiated in this way, since the light is scattered by the metal powder contained in the conductive paste 62, a part of the irradiated light L does not reach the conductive paste 62 on the side closer to the carrier film 61 (that is, the second surface 62b side). Therefore, the photosensitive resin in the conductive paste 62 on the side closer to the carrier film 61 (that is, the second surface 62b side) tends to have its photocuring inhibited.

[0065] That is, the region where the conductive paste 62 is photocured becomes narrower as it is farther from the side where the light L is incident (that is, the first surface 62a side). As a result, a photocured region having a tapered shape toward the contact surface with the carrier film 61 is formed in the conductive paste 62.

[0066] Thereafter, a developing process (S32) is performed. In the developing process (S32), a conductive pattern 20 is formed on the carrier film 61. Specifically, the conductive paste 62 is treated with a developer 75 to remove the non-photosensitive portion of the conductive paste 62. As a result, only the photocured region of the conductive paste 62 remains on the carrier film 61, and a conductive pattern 20 is formed on the carrier film 61 (see step B in FIG. 6). The conductive pattern 20 has a tapered portion 22 located on the carrier film 61 side and a columnar portion 23 located on the side far from the carrier film 61.

[0067] As described above, the pattern forming process (S30) is performed. As a result, a conductive pattern 20 having a predetermined shape is formed on the carrier film 61.

[0068] Subsequently, a transfer process (S40) is performed. FIG. 7 schematically shows the state in which the transfer process (S40) is performed. In the transfer process (S40), the conductive pattern 20 formed in the patterning process (S30) is transferred onto the ceramic sheet 10 that has undergone the filling process (S20), and the conductive pattern 30 for the via 31 and the conductive pattern 20 for the connection pad 21 are electrically connected.

[0069] Specifically, as shown in step A of FIG. 7, an adhesive solvent (for example, an alcohol-based solvent) is applied to the surface of the ceramic sheet 10 using an inkjet device 55 or the like, and a part of the ceramic sheet 10 is made into a paste. Here, an adhesive material is applied from the back surface 10d (corresponding to the surface 11a of the ceramic substrate 11) side of the ceramic sheet 10, and a part of the ceramic sheet is made into a paste. In FIG. 7, in the ceramic sheet 10, the pasted ceramic portion is indicated by 10b.

[0070] Next, as shown in step B of FIG. 7, with the surface of the carrier film 61 on which the conductive pattern 20 is formed facing the ceramic sheet 10 side, the carrier film 61 is placed on the back surface 10d of the ceramic sheet 10, and pressure and heat are applied using a hot press device 56. At this time, the carrier film 61 is aligned with the ceramic sheet 10 so that the positions of the respective conductive patterns 30 formed on the ceramic sheet 10 side and the positions of the respective conductive patterns 20 formed on the carrier film 61 side match. Thereby, electrical connection between the conductive pattern 30 and the conductive pattern 20 becomes possible.

[0071] Thereafter, as shown in step C of FIG. 7, by peeling off the carrier film 61, the conductive pattern 20 is transferred onto the ceramic sheet 10. Here, at least a part of the conductive pattern 20 is in a state of being embedded in the ceramic sheet 10.

[0072] Thus, in the transfer step (S40), the film body that has undergone the development step (S32) is pressed against the ceramic sheet 10 on which the conductive pattern 30 is formed at a predetermined position, and the conductive pattern 20 is transferred onto the ceramic sheet 10. As a result, the conductive pattern 20 connected to the conductive pattern 30 is formed on the ceramic sheet 10.

[0073] In the case of the wiring board 1 having a plurality of ceramic layers, after forming a plurality of ceramic sheets 10 by the above method, the sheets are laminated in a determined order.

[0074] Thereafter, a firing step (S50) is performed. In the firing step (S50), the ceramic sheet 10 or the laminate thereof on which the conductive patterns 20 and 30 are formed is co-fired (simultaneously fired). As a result, the ceramic sheet 10 becomes the ceramic substrate 11. Note that by performing the firing step (S50), the photosensitive resin contained in the conductive pattern 20 is burned out.

[0075] When the firing step (S50) is completed, post-processes such as a plating step are performed. The plating step is carried out by a conventionally known electrolytic plating method. By performing the electrolytic plating method, a plating film can be formed on the surface of the conductive pattern (for example, the connection pad 21) exposed from the ceramic substrate 11.

[0076] As described above, in the manufacturing method of the wiring board 1 according to the present embodiment, by exposing and developing the carrier film 61 coated with the photosensitive conductive paste 62, the conductive pattern 20 having a tapered shape toward the contact surface with the carrier film 61 is formed. This conductive pattern 20 is transferred onto the ceramic sheet 10 on which the conductive pattern 30 for the via 31 is formed, and the conductive pattern 30 and the conductive pattern 20 are electrically connected.

[0077] By forming the conductive pattern 20 using such a manufacturing method, a finer conductive pattern can be formed. Therefore, according to the manufacturing method according to the present embodiment, for example, a wiring board 1 having high-definition connection pads 21 with a diameter of the connection pads 21 of about 30 μm and an interval between adjacent connection pads 21 of about 60 μm can be obtained.

[0078] Further, in the exposure step (S31) of the above-described pattern forming step (S30), a tapered portion 22 can be formed in the conductive pattern 20 by utilizing the characteristic that the region where the conductive paste 62 is photocured becomes narrower as it moves away from the side where the light L is incident. This tapered portion 22 becomes the tapered portion 22 of the connection pad 21. By forming the tapered portion 22 on the surface 11a side of the ceramic substrate 11 in the connection pad 21, it is possible to make it difficult for the connection pad 21 to come off from the ceramic substrate 11.

[0079] Also, in the hole forming step (S10), by forming the holes 10a in the ceramic sheet 10 using the laser 51, the diameter of the holes 10a can be reduced, and the interval between adjacent holes can be reduced. For example, by forming the holes 10a using a CO2 laser, the diameter of the holes 10a can be reduced to about 30 μm. Also, by forming the holes 10a using a UV laser, the diameter of the holes 10a can be reduced to about 20 μm. Further, by using a CO2 laser or a UV laser, the interval between adjacent holes 10a can be narrowed to about 50 μm.

[0080] As described above, in the hole forming step (S10), it is preferable to form the holes 10a by irradiating the laser 51 from the side opposite to the side (i.e., the back surface 10d side) where the conductive pattern 30 in the ceramic sheet 10 is transferred (i.e., the laser irradiation surface 10c side).

[0081] As a result, it is possible to form the hole 10a having a shape in which the diameter of the hole 10a in the plane direction of the ceramic sheet 10 gradually decreases from the laser irradiation surface 10c toward the back surface 10d (see FIG. 5). By filling the hole 10a having such a shape with the conductive ink 54, it is possible to form the via 31 having a tapered shape toward the connection pad 21. Thereby, the area of the via 31 at the contact portion with the connection pad 21 becomes small, and it becomes easy to bring the entire end surface of the via 31 into contact with the connection pad 21. Therefore, it is possible to suppress an increase in the resistance value that may occur due to misalignment of the positions of the via 31 and the connection pad 21 at the contact portion therebetween.

[0082] Further, in the hole forming step (S10), on the back surface 10d side of the ceramic sheet 10 that becomes the emission surface of the laser 51, there may be variations in the diameter of the hole 10a compared to the laser irradiation surface 10c side. As a result, the diameter of the via 31 may become unstable on the back surface 10d side. In the present embodiment, the conductive pattern 20 of the connection pad 21 is transferred to the side where the diameter of the via 31 may become unstable and is embedded in the ceramic substrate 11. On the other hand, it is possible to reduce the variation in the diameter of the via 31 exposed on the back surface 11b of the ceramic substrate 11 on the laser irradiation surface 10c side.

[0083] (Summary of the embodiment) As described above, the wiring board 1 according to the present embodiment includes a ceramic substrate 11, vias 31, and connection pads 21. The ceramic substrate 11 has a front surface 11a (first surface) and a back surface 11b (second surface). The vias 31 are disposed within the ceramic substrate 11. The connection pads 21 are disposed within the ceramic substrate 11 and are connected to the vias 31. At least a part of the connection pads 21 is exposed from the front surface 11a. Further, the connection pads 21 have a maximum width portion (specifically, a columnar portion 23) in a portion that enters the interior of the ceramic substrate 11. The width of the maximum width portion in the X direction (plane direction) (specifically, the diameter D2 of the columnar portion 23) is larger than the width of the connection pads 21 in the X direction (plane direction) (specifically, the diameter D1 of the surface 21s of the tapered portion 22) at the position of the front surface 11a of the ceramic substrate 11.

[0084] According to the above configuration, since the maximum width portion of the connection pads 21 is in a state of being embedded in the ceramic substrate 11, peeling of the connection pads 21 can be suppressed.

[0085] Further, in the manufacturing method of the wiring board 1 according to the present embodiment, a conductive pattern 20 for the connection pads 21 is formed by photolithography including the exposure step (S31) and the development step (S32) described above. Thereby, the equivalent circle diameter D1 of the end face of the connection pads 21 exposed from the front surface 11a can be, for example, in the range of 30 μm or more and 100 μm or less.

[0086] As described above, according to the present embodiment, it is possible to obtain a wiring board 1 with reduced diameter of the connection pads 21 and high definition. Further, according to the present embodiment, even when the diameter of the connection pads 21 is reduced, by forming the connection pads 21 in the shape as described above, it is possible to form connection pads 21 that are difficult to peel from the ceramic substrate 11.

[0087] In addition, when forming the connection pad 21 using the transfer process (S40) as in the manufacturing method of the present embodiment, the flatness of the surface of the connection pad can be improved as compared with the case where the connection pad is formed using the screen printing method. Therefore, when the conductive pattern formed using the manufacturing method of the present embodiment is used as the connection pad 21, the connection reliability with the connection terminal of the semiconductor chip can be improved. Accordingly, the wiring board 1 according to the present embodiment is suitably used, for example, for a wiring board to which a semiconductor chip or the like is connected by a flip chip method.

[0088] The disclosed embodiments should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is defined not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included. Also, the configurations obtained by combining the configurations of the respective embodiments described in this specification with each other are also included in the scope of the present invention.

Explanation of Reference Numerals

[0089] 1: Wiring board 10: Ceramic sheet 10a: Hole formed in the ceramic sheet 11: Ceramic substrate (insulating substrate) 11a: Surface of the ceramic substrate (first surface) 11b: Back surface of the ceramic substrate (second surface) 20: Conductive pattern for connection pad 21: Connection pad (connection terminal portion) 21s: Surface of the connection pad 22: Tapered portion 23: Columnar portion (maximum width portion) 30: Conductive pattern for via 31: Via 51: Laser 54: Conductive ink 61: Carrier film (film) 62: Conductive paste

Claims

1. A ceramic substrate, a conductive via disposed within the ceramic substrate, and a connection terminal portion disposed within the ceramic substrate and electrically connected to the via, wherein the method for manufacturing a wiring board comprises: a hole forming step of irradiating a ceramic sheet before firing with a laser to form a hole at a location where the via is to be disposed; a filling step of filling the hole in the ceramic sheet with a conductive ink; a pattern forming step of exposing and developing a film coated with a photosensitive conductive paste to form a conductive pattern for the connection terminal portion having a tapered shape toward the contact surface with the film; after pasting a surface of the ceramic sheet on which the conductive pattern is to be transferred, transferring the conductive pattern formed in the pattern forming step to the ceramic sheet that has undergone the filling step, embedding a maximum width portion of the conductive pattern inside the ceramic sheet, and electrically connecting the conductive ink and the conductive pattern; a firing step of firing the ceramic sheet after the transfer step; The method for manufacturing a wiring board includes the above steps.

2. In the hole forming step, the laser is irradiated from a side opposite to the side of the ceramic sheet on which the conductive pattern is to be transferred to form a hole. The method for manufacturing a wiring board according to Claim 1.

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