Wiring board and package structure using same

Abstract

A wiring board according to the present disclosure comprises an insulating layer having a first surface and a second surface that is positioned on the opposite side from the first surface, a conductor layer positioned on the first surface, a through-conductor that penetrates the insulating layer from the first surface to the second surface, and a tapered conductor that is positioned extending from the first surface of the insulating layer to the second-surface side. The conductor layer includes a linear conductor and a planar conductor that is positioned such that there is a gap between the linear conductor and the planar conductor. At least one end of the linear conductor has a portion that is connected to the through-conductor via the tapered conductor. When viewed in a cross-sectional view in the thickness direction of the insulating layer, the tapered conductor has a tapered shape in which the thickness-direction dimension gradually increases from the linear conductor toward the through-conductor.

Description

Wiring board and mounting structure using same

[0001] The present invention relates to a wiring board and a mounting structure using the same.

[0002] Conventionally, via-hole conductors are positioned in wiring boards to electrically connect between build-up insulating layers, and the via-hole conductors and wiring conductors are connected via lands on the surfaces of the build-up insulating layers, as described in Patent Document 1.

[0003] Japanese Patent Application Laid-Open No. 2014-204057

[0004] The wiring board according to the present disclosure includes an insulating layer having a first surface and a second surface opposite the first surface, a conductor layer located on the first surface, a through conductor penetrating the insulating layer from the first surface to the second surface, and a tapered conductor located extending from the first surface of the insulating layer toward the second surface. The conductor layer includes a linear conductor and a planar conductor located with a gap between them. At least one end of the linear conductor has a portion connected to the through conductor via the tapered conductor. When viewed cross-sectionally in the thickness direction of the insulating layer, the tapered conductor has a tapered shape in which the dimension in the thickness direction gradually increases from the linear conductor toward the through conductor.

[0005] A mounting structure according to the present disclosure includes the above-described wiring board and an electronic component located in a mounting area of ​​the wiring board.

[0006] 1A to 1F are explanatory diagrams illustrating a mounting structure in which electronic components are mounted on a wiring board according to an embodiment of the present disclosure. A schematic diagram illustrating an embodiment of the structure of a conductor layer in region X shown in FIG. 1. An explanatory diagram illustrating a main part of FIG. 2A. A schematic diagram illustrating another embodiment of the structure of a conductor layer in region X shown in FIG. 1. An explanatory diagram illustrating a main part of FIG. 3A. A schematic diagram illustrating another embodiment of the structure of a conductor layer in region X shown in FIG. 1. An explanatory diagram illustrating a main part of FIG. 4A. FIGS. 5A to 5F are explanatory diagrams illustrating an embodiment of a method for forming a linear conductor, a through conductor, and a tapered conductor. An explanatory diagram illustrating a simulation model used in Comparative Example 1. An explanatory diagram illustrating a simulation model used in Comparative Example 2. Data showing simulation results of electrical characteristics for wiring boards according to Embodiment 1, Embodiment 2, and Comparative Example 1. Data showing simulation results of electrical characteristics for wiring boards according to Embodiment 3 and Comparative Example 2.

[0007] As described above, in a wiring board, the via-hole conductor and the wiring conductor are connected via a land on the surface of the build-up insulating layer. In recent years, signal frequencies have been increasing, and the lands located at the connection points between the via-hole conductor and the wiring conductor have been causing increased signal reflection loss, which affects high-speed signal transmission. Therefore, there is a demand for wiring boards with low signal reflection loss and excellent transmission characteristics.

[0008] The wiring board according to the present disclosure has a configuration as described in the section on means for solving the above problems, and thus has small signal reflection loss and excellent transmission characteristics.

[0009] A wiring board according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram for describing a mounting structure 10 in which an electronic component S is mounted on a wiring board 1 according to an embodiment of the present disclosure. The wiring board 1 according to the embodiment includes a core layer, an insulating layer 2, and a conductor layer 3.

[0010] In the wiring board 1 shown in FIG. 1, the core layer is located approximately at the center in the thickness direction of the wiring board 1. The core layer is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. These resins may be used alone or in combination of two or more. The thickness of the core layer is not particularly limited and may be, for example, 100 μm or more and 1500 μm or less.

[0011] The core layer may contain a reinforcing material. Examples of reinforcing materials include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the core layer may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0012] A through-hole conductor is located in the core layer to electrically connect the upper and lower surfaces of the core layer. The through-hole conductor is located in a through-hole that penetrates the upper and lower surfaces of the core layer. The through-hole conductor is formed of a metal such as copper, specifically a metal plating such as copper plating. The through-hole conductor may be formed only on the inner wall surface, or may fill the through-hole. The through-hole conductor is connected to a core conductor layer located on the upper and lower surfaces of the core layer. The core conductor layer is not limited as long as it is a conductor such as a metal. Specifically, the core conductor layer is formed of a metal foil such as copper foil, or a metal plating such as copper plating.

[0013] Build-up layers are located on the top and bottom surfaces of the core layer. The build-up layers have a structure in which an insulating layer 2 and a conductor layer 3 are laminated. The conductor layer 3 is located on the first surface of the insulating layer 2. In this specification, the "first surface of the insulating layer 2" refers to the surface of both surfaces of the insulating layer 2 that is farther from the core layer. The "second surface of the insulating layer 2" refers to the surface opposite to the first surface, i.e., the surface closer to the core layer.

[0014] The insulating layer 2 is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. These resins may be used alone or in combination of two or more. The insulating layers 2 may be made of the same resin or different resins. The insulating layer 2 and the core layer may be made of the same resin or different resins. The thickness of the insulating layer 2 is not particularly limited and may be, for example, 10 μm or more and 50 μm or less. The insulating layers 2 may have the same thickness or different thicknesses.

[0015] The insulating layer 2 may contain a reinforcing material. Examples of reinforcing materials include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the insulating layer 2 may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0016] The conductor layer 3 is not limited to any material as long as it is a conductor such as a metal. Specifically, the conductor layer 3 is formed of a metal foil such as a copper foil, or a metal plating such as a copper plating. The thickness of the conductor layer 3 is not particularly limited and is, for example, 5 μm or more and 25 μm or less.

[0017] The conductor layer 3 includes a linear conductor 31 and a planar conductor 32. The linear conductor 31 is used, for example, as a signal conductor. The planar conductor 32 is located with a gap between it and the linear conductor 31 and is used, for example, as a ground conductor and a power conductor. The conductor layer 3 may be located on the first surface of the insulating layer 2, or may be located in a recess 21 in the first surface as shown in FIG. 1 . For example, if the conductor layer 3 is located in the recess 21 in the first surface, peeling of the linear conductor 31 from the insulating layer 2 can be reduced, especially during the wiring formation process, when the linear conductor 31 is fine. The conductor layer 3 may be located so as to fill the recess 21, or may be located up to a height partway along the depth direction of the recess 21.

[0018] 1, a solder resist 4 may be located on the surface of the build-up layer. The solder resist 4 is made of a resin, such as an acrylic-modified epoxy resin. The solder resist 4 has openings for electrically connecting the conductor layer 3 to electrodes of the electronic component S via solder 5. Examples of the electronic component S include semiconductor integrated circuit elements and optoelectronic elements.

[0019] The insulating layer 2 has a through conductor 33 positioned therein, penetrating from the first surface to the second surface. The through conductor 33 is also not limited as long as it is a conductor such as a metal. The through conductor 33 includes a through conductor connected to the linear conductor 31. Specifically, as shown in FIGS. 2A and 2B , at least one end of the linear conductor 31 has a portion connected to the through conductor 33 via a tapered conductor 34. FIG. 2A is a schematic diagram showing one embodiment of the structure of the conductor layer 3 in region X shown in FIG. 1. FIG. 2B is an explanatory diagram for explaining the main parts of FIG. 2A .

[0020] When viewed in cross section in the thickness direction of the insulating layer 2, the tapered conductor 34 has a tapered shape in which the dimension in the thickness direction gradually increases from the linear conductor 31 toward the through conductor 33. The linear conductor 31 and the through conductor 33 are connected via the tapered conductor 34 having such a structure. This reduces abrupt changes in impedance at the connection between the linear conductor 31 and the through conductor 33. As a result, signal reflection loss is small, and excellent transmission characteristics are exhibited.

[0021] The shape of the tapered conductor 34 is not limited as long as it is a tapered shape in which the dimension in the thickness direction gradually increases from the linear conductor 31 toward the through conductor 33. When viewed in cross section in the thickness direction of the insulating layer 2, the end of the tapered conductor 34 on the through conductor 33 side may have a length that is, for example, half or more of the length (depth) of the through conductor 33. That is, when the length of the through conductor 33 is Ha, the length Hb of the end of the tapered conductor 34 on the through conductor 33 side may satisfy 0.5Ha≦Hb≦Ha. When the length Hb of the end of the tapered conductor 34 on the through conductor 33 side satisfies this range, a sudden change in impedance at the connection between the linear conductor 31 and the through conductor 33 is further alleviated.

[0022] The angle θ between the tapered conductor 34 and the linear conductor 31 may be, for example, 30° or more and 60° or less. If the angle θ is 30° or more and 60° or less, it becomes easier to obtain a tapered conductor 34 that satisfies the above-mentioned 0.5Ha≦Hb≦Ha. Furthermore, a sudden change in impedance at the connection between the linear conductor 31 and the through conductor 33 becomes easier to alleviate.

[0023] As shown in Figures 3A and 3B, the end of the linear conductor 31 connected to the through conductor 33 may include a land portion 311. In this case, the linear conductor 31 includes the land portion 311 and a linear portion 312. Figure 3A is a schematic diagram showing another embodiment of the structure of the conductor layer 3 in region X shown in Figure 1. Figure 3B is an explanatory diagram for explaining the main parts of Figure 3A.

[0024] Including the land portion 311 at the end of the linear conductor 31 increases the width (area) of the end of the linear conductor 31. This makes it easy to ensure the connection area between the linear conductor 31 (land portion 311) and the through conductor 33, further improving electrical connectivity. The shape of the land portion 311 is not limited as long as the periphery of the through conductor 33 is located inside the periphery of the land portion 311. Examples of the shape of the land portion 311 when viewed from above include a circle, an ellipse, and a polygon (such as a triangle, a rectangle, a pentagon, or a hexagon).

[0025] Furthermore, as shown in Figures 4A and 4B, the shape of the land portion 311 may have a region in which the width gradually decreases from the through conductor 33 toward the linear conductor 31 when viewed from above. Figure 4A is a schematic diagram showing another embodiment of the structure of the conductor layer 3 in region X shown in Figure 1. Figure 4B is an explanatory diagram for explaining the main part of Figure 4A.

[0026] If the land portion 311 has a region whose width gradually decreases from the through conductor 33 toward the linear conductor 31, this is advantageous in that it reduces the change in impedance between the land portion 311 and the linear portion 312. In Fig. 4B , the region whose width gradually decreases from the through conductor 33 toward the linear conductor 31 has a width that gradually decreases from two directions from the through conductor 33 toward the linear conductor 31. However, the region whose width gradually decreases from the through conductor 33 toward the linear conductor 31 may also be a region whose width gradually decreases in only one direction from the through conductor 33 toward the linear conductor 31.

[0027] The sheet conductor 32 has a clearance hole 32a, for example, as shown in FIG. 2A . The clearance hole 32a is intended to adjust the electrostatic capacitance between the sheet conductor 32 and the linear conductor 31 (signal conductor) to achieve impedance matching of the signal conductor. The clearance hole 32a refers to, for example, a circular region of the sheet conductor 32 where no conductor is present. When the clearance hole 32a is viewed in a plan view, the through conductor 33 and the tapered conductor 34 may be located within the circular region. When the clearance hole 32a is viewed in a plan view, the clearance hole 32a may have a shape other than a circle, such as a square, in order to match the impedance of the signal conductor.

[0028] Next, one embodiment of a method for forming the linear conductors 31, the through conductors 33, and the tapered conductors 34 will be described with reference to Figures 5A to 5F. Figures 5A to 5F are explanatory diagrams for describing one embodiment of a method for forming the linear conductors 31, the through conductors 33, and the tapered conductors 34.

[0029] First, as shown in Fig. 5A, an insulating layer 2 is prepared below the insulating layer 2 on which the linear conductor 31 is to be formed. A conductor layer 3 (through conductor 33) is located in the lower insulating layer 2. Next, as shown in Fig. 5B, the insulating layer 2 on which the linear conductor 31 is to be formed is laminated on the lower insulating layer 2.

[0030] Next, as shown in FIG. 5C , through holes are formed so as to penetrate the top and bottom surfaces of the insulating layer 2. Specifically, the through holes are formed so that the conductor layer 3 located in the underlying insulating layer 2 forms the bottom. The size and number of the through holes are set appropriately depending on the size of the wiring board 1 to be finally obtained, etc. Simultaneously with or after the formation of the through holes, recesses 21 are formed in which the linear conductors 31 and tapered conductors 34 are to be located. The through holes and recesses 21 are formed using, for example, a drill, a laser, or a blast. Desmearing or the like is performed as necessary to remove resin residue and the like.

[0031] 5D , a seed layer 3a is formed on the surface of the insulating layer 2 on which the linear conductors 31 are formed, on the surface of the recesses 21, and on the surfaces of the through holes. The seed layer 3a is formed by electroless metal plating, such as electroless copper plating. The presence of the seed layer 3a allows metals that will become conductors such as the linear conductors 31 and the through conductors 33 to be efficiently deposited by electrolytic plating.

[0032] Next, as shown in Fig. 5E, a plating layer 3b is formed on the surface of the seed layer 3a, filling the recesses 21 and the through holes with the plating layer 3b. The plating layer 3b is formed, for example, by electrolytic metal plating such as electrolytic copper plating. Next, as shown in Fig. 5F, excess plating layer 3b formed on the surface of the insulating layer 2 is removed to form the linear conductors 31, the through conductors 33, and the tapered conductors 34. The excess plating layer 3b is removed, for example, by polishing.

[0033] In this manner, the linear conductors 31, the through conductors 33, and the tapered conductors 34 are formed in the insulating layer 2. 5A to 5F illustrate an embodiment in which the end of the linear conductor 31 includes a land portion 311. However, the presence or absence of the land portion 311 and the shape of the land portion 311 may be appropriately designed when forming the recess 21. Furthermore, although the linear conductors 31, the through conductors 33, and the tapered conductors 34 are described as individual conductors, the linear conductors 31, the through conductors 33, and the tapered conductors 34 may be integrally formed, as in the above-described embodiment.

[0034] A mounting structure according to the present disclosure will be described with reference to Fig. 1 . As shown in Fig. 1 , a mounting structure 10 according to one embodiment includes a wiring board 1 according to one embodiment and an electronic component S located in a mounting area of ​​the wiring board 1. A conductor layer 3 in an opening of a solder resist 4 located on the surface of a build-up layer is connected to an electrode of the electronic component S via solder 5. As described above, examples of the electronic component S include semiconductor integrated circuit elements and optoelectronic elements. In the mounting structure 10 according to one embodiment, the electronic component S may be located on both surfaces of the wiring board 1, or the electronic component S may be located on one surface and, for example, a motherboard may be located on the other surface.

[0035] Next, the electrical characteristics of the wiring board 1 according to the embodiment were verified by simulation. The verification results are shown in FIGS.

[0036] As simulation models, there were prepared: embodiment 1 in which the linear conductor 31, the through conductor 33, and the tapered conductor 34 have the structure shown in Fig. 2B; embodiment 2 in which the structure shown in Fig. 3B; and embodiment 3 in which the structure shown in Fig. 4B. Furthermore, as simulation models for comparative examples, there were prepared comparative example 1, which is embodiment 2 without the tapered conductor 34 as shown in Fig. 6A; and comparative example 2, which is embodiment 3 without the tapered conductor 34 as shown in Fig. 6B.

[0037] In the first to third embodiments, as shown in FIG. 1, the wiring board 1 has a core layer on the top and bottom surfaces of which are built-up layers each having five insulating layers 2 stacked thereon. The core layer and insulating layer 2 are made of epoxy resin. When viewed from above, the core layer and insulating layer 2 have a rectangular shape of 50 mm x 50 mm. The core layer has a thickness of 800 μm. The insulating layer 2 has a thickness of 35 μm or more and 40 μm or less, although there may be some variation in the thickness of each layer.

[0038] The conductor layer 3 and the through conductor 33 are made of copper and are located on both surfaces of the core layer and in recesses 21 formed in the insulating layer 2. The conductor layer 3 has a thickness of 15 μm or more and 20 μm or less. The through conductor 33 has a circular shape in plan view and a diameter of 50 μm or more and 70 μm or less.

[0039] The tapered conductor 34 is included in a conductor layer 3 formed on an insulating layer 2 located one layer below the uppermost insulating layer 2. The tapered conductor 34 is positioned so that the angle θ between the tapered conductor 34 and the linear conductor 31 is approximately 45°, and the length Ha of the through conductor 33 is approximately the same as the length Hb of the end of the tapered conductor 34 on the through conductor 33 side. Wiring boards were obtained in the same manner in Comparative Examples 1 and 2, except that the tapered conductor 34 was not formed.

[0040] The electrical characteristics were examined for the wiring boards 1 of embodiments 1 to 3 and the wiring boards of comparative examples 1 and 2. FIG. 7 shows data illustrating the results of a simulation of the electrical characteristics for the wiring boards 1 of embodiments 1 and 2 and the wiring board of comparative example 1. FIG. 8 shows data illustrating the results of a simulation of the electrical characteristics for the wiring board 1 of embodiment 3 and the wiring board of comparative example 2. The return loss shown in FIGS. 7 and 8 is a measurement of a signal that is reflected back from the input terminal when a signal is input to the input terminal. A smaller dB value indicates better electrical characteristics.

[0041] 7 and 8, it can be seen that the wiring boards 1 of Embodiments 1 to 3 have smaller dB values ​​and superior electrical characteristics than the wiring boards of Comparative Examples 1 and 2. The wiring board 1 of Embodiment 2 and the wiring board of Comparative Example 1 have the same shape of land portion 311, and the difference in reflection loss due to the presence or absence of tapered conductor 34 was verified. The same is true for the wiring board 1 of Embodiment 3 and the wiring board of Comparative Example 2. The wiring board 1 of Embodiment 1 was verified to have low reflection loss (small dB value) even though it does not have land portion 311.

[0042] The embodiments of the present disclosure have been described above. However, the invention according to the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) to (6) below.

[0043] (1) A wiring board according to the present disclosure includes an insulating layer having a first surface and a second surface opposite the first surface, a conductor layer located on the first surface, a through conductor penetrating the insulating layer from the first surface to the second surface, and a tapered conductor extending from the first surface to the second surface of the insulating layer. The conductor layer includes a linear conductor and a planar conductor located with a gap between them. At least one end of the linear conductor has a portion connected to the through conductor via the tapered conductor. When viewed cross-sectionally in the thickness direction of the insulating layer, the tapered conductor has a tapered shape whose thickness dimension gradually increases from the linear conductor toward the through conductor. (2) In the wiring board described in (1) above, the linear conductor includes a linear portion and a land portion at an end. When viewed from above in a perspective view of the land portion, the periphery of the through conductor is located inside the periphery of the land portion. (3) In the wiring board described in (2) above, when the land portion is viewed in a plane, the land portion has a region whose width gradually decreases from the penetrating conductor toward the linear portion. (4) In the wiring board described in any of (1) to (3) above, the first surface has a recess. The conductor layer is located within the recess. (5) In the wiring board described in any of (1) to (4) above, the planar conductor has a clearance hole including a circular region. When the clearance hole is viewed in a plane, the penetrating conductor and the tapered conductor are located within the circular region. (6) A mounting structure according to the present disclosure includes the wiring board described in any of (1) to (5) above and an electronic component located in the mounting region of the wiring board.

[0044] REFERENCE SIGNS LIST 1 wiring substrate 2 insulating layer 21 recess 3 conductor layer 31 linear conductor 311 land portion 312 linear portion 32 planar conductor 32a clearance hole 33 through conductor 34 tapered conductor 3a seed layer 3b plating layer 4 solder resist 5 solder 10 mounting structure

Claims

1. A wiring board comprising: an insulating layer having a first surface and a second surface located opposite the first surface; a conductor layer located on the first surface; a through conductor penetrating the insulating layer from the first surface to the second surface; and a tapered conductor located extending from the first surface of the insulating layer toward the second surface, wherein the conductor layer includes a linear conductor and a planar conductor located with a gap between the linear conductor and at least one end of the linear conductor has a portion connected to the through conductor via the tapered conductor, and when viewed in cross section in the thickness direction of the insulating layer, the tapered conductor has a tapered shape whose dimension in the thickness direction gradually increases from the linear conductor toward the through conductor.

2. The wiring board according to claim 1, wherein the linear conductor includes a linear portion and a land portion at the end, and when the land portion is viewed in a plan view, the periphery of the through conductor is located inside the periphery of the land portion.

3. The wiring board according to claim 2, wherein, in a plan view of the land portion, the land portion has a region whose width gradually decreases from the through conductor toward the linear portion.

4. The wiring board according to any one of claims 1 to 3, wherein the first surface has a recess, and the conductor layer is located within the recess.

5. A wiring board as described in any one of claims 1 to 4, wherein the planar conductor has a clearance hole including a circular area, and when the clearance hole is viewed in a plane, the through conductor and the tapered conductor are located within the circular area.

6. A mounting structure comprising the wiring board according to any one of claims 1 to 5 and an electronic component located in a mounting area of ​​the wiring board.

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