Wiring boards and mounting structures

Abstract

To provide a wiring board that efficiently transmits signals, even high-frequency signals of 28 GHz or higher. [Solution] The wiring board according to this disclosure includes a core layer having a first surface and a second surface located opposite to the first surface, comprising a core insulating layer and a core conductor layer; a first build-up layer located on the first surface, comprising a first build-up insulating layer and a first build-up conductor layer; and a second build-up layer located on the second surface, comprising a second build-up insulating layer and a second build-up conductor layer. The core conductor layer, the first build-up conductor layer, and the second build-up conductor layer include a ground conductor and a differential wiring conductor.

Description

Technical Field

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

Background Art

[0002] A wiring board on which electronic components and the like are mounted may include differential wiring as described in, for example, Patent Document 1. When differential wiring is connected to pads located on the upper and lower surfaces of the wiring board, signals are transmitted through the differential wiring connected to these pads.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] High - frequency signals are easily affected by external noise. As a result, high - frequency signals (high - frequency signals of 28 GHz or more) may not be efficiently transmitted.

[0005] An object of the present disclosure is to provide a wiring board that can efficiently transmit signals even for high - frequency signals of 28 GHz or more.

Means for Solving the Problems

[0006] The wiring board according to this disclosure includes a core layer having a first surface and a second surface located opposite to the first surface, comprising a core insulating layer and a core conductor layer; a first build-up layer located on the first surface, comprising a first build-up insulating layer and a first build-up conductor layer; and a second build-up layer located on the second surface, comprising a second build-up insulating layer and a second build-up conductor layer. The core conductor layer, the first build-up conductor layer, and the second build-up conductor layer include a ground conductor and a differential wiring conductor. The differential wiring conductor has a wiring structure that connects a pair of first pads located on the surface of the first build-up layer to a pair of second pads located on the surface of the second build-up layer, and is arranged in parallel with each other. The differential wiring conductor comprises a through-hole conductor included in the core conductor layer, a first via-hole conductor included in the first build-up conductor layer and in contact with the through-hole conductor, and a second via-hole conductor included in the second build-up conductor layer and in contact with the through-hole conductor. The through-hole conductor, the first via-hole conductor, and the second via-hole conductor are each surrounded by a ground conductor in a planar perspective.

[0007] The implementation structure relating to this disclosure includes the above-mentioned wiring board and electronic components mounted on the wiring board. [Effects of the Invention]

[0008] The wiring board relating to this disclosure has a configuration as described in the means for solving the above problems, thereby efficiently transmitting signals even at high frequencies of 28 GHz or higher. [Brief explanation of the drawing]

[0009] [Figure 1] This is an enlarged explanatory diagram illustrating a mounting structure in which electronic components are mounted on a wiring board according to one embodiment of the present disclosure. [Figure 2A] This is an explanatory diagram illustrating the cross-section when the line AA shown in Figure 1 is cut. [Figure 2B] Figure 1 is an explanatory diagram illustrating the cross-section when the line BB is used for cutting. [Figure 2C]Figure 1 is an explanatory diagram illustrating the cross-section when the line CC is cut. [Figure 2D] Figure 1 is an explanatory diagram illustrating the cross-section when the line DD is used for cutting. [Figure 3] This is an explanatory diagram illustrating a modified example of a through-hole conductor. [Figure 4] Figures 4A to 4I are explanatory diagrams illustrating one embodiment of a method for forming a through-hole conductor, which is part of a differential wiring conductor, and a part of the ground conductor surrounding the through-hole conductor. [Modes for carrying out the invention]

[0010] A wiring board according to one embodiment of the present disclosure will be described with reference to Figures 1 to 3. Figure 1 is an enlarged explanatory diagram for illustrating a mounting structure 20 on which electronic components 7 are mounted on a wiring board 10 according to one embodiment of the present disclosure. Specifically, Figure 1 shows the main parts of the wiring board 10. The wiring board 10 according to one embodiment includes a first build-up layer 1, a second build-up layer 2, a core layer 3, and a solder resist 5.

[0011] The core layer 3 includes a core insulating layer 31 and a core conductor layer 32. The core insulating layer 31 is located approximately in the center of the thickness direction of the wiring board 10. The core insulating layer 31 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, as well as glass. Only one of these insulating materials may be used, or two or more may be used in combination. The thickness of the core insulating layer 31 is not particularly limited and may be, for example, 800 μm or more and 1200 μm or less.

[0012] The core insulating layer 31 may contain reinforcing materials. Examples of reinforcing materials include insulating fabrics such as glass fibers, glass nonwoven fabrics, aramid nonwoven fabrics, aramid fibers, and polyester fibers. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the core insulating layer 31 may contain inorganic insulating fillers 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.

[0013] Core conductor layers 32 are located on both sides of the core insulating layer 31. The core conductor layer 32 is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper. The thickness of the core conductor layer 32 is not limited and may be, for example, 10 μm or more and 50 μm or less. In Figure 1, the core conductor layer 32 is located on both sides of the core insulating layer 31, but it is sufficient if it is located on at least one side of the core insulating layer 31.

[0014] As shown in Figure 1, a through-hole conductor 32T is located in the core insulating layer 31 to electrically connect the upper and lower surfaces of the core insulating layer 31. The through-hole conductor 32T is part of the differential wiring conductor 4 and has the function of transmitting high-frequency signals. The through-hole conductor 32T is located in a through-hole 311 for the differential wiring conductor that penetrates from the upper surface to the lower surface of the core insulating layer 31. The through-hole conductor 32T is made of a metal such as copper.

[0015] The through-hole conductor 32T is part of the core conductor layer 32 and is connected to the core conductor layer 32 formed on both sides of the core insulating layer 31. The through-hole conductor 32T may be formed integrally with the core conductor layer 32. The through-hole conductor 32T may be located only on the inner wall surface of the through-hole 311 for differential wiring conductors, or it may be filled inside the through-hole 311 for differential wiring conductors.

[0016] As shown in FIG. 1, the first build-up layer 1 is located on the first surface 3a of the core layer 3. The first surface 3a of the core layer 3 is the surface of the core conductor layer 32 where the surface of the core insulating layer 31 and the core conductor layer 32 are located, and is a concavo-convex surface. The first build-up layer 1 has a structure in which the first build-up insulating layer 11 and the first build-up conductor layer 12 are alternately laminated.

[0017] The first build-up insulating layer 11 is not particularly limited as long as it is a material having insulating properties. Examples of the material having insulating properties 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.

[0018] The first build-up insulating layers 11 may be the same resin or different resins. The first build-up insulating layer 11 and the core insulating layer 31 may be the same resin or different resins. The thickness of the first build-up insulating layer 11 is not particularly limited, and may be, for example, 20 μm or more and 50 μm or less. The first build-up insulating layers 11 may have the same thickness or different thicknesses.

[0019] The first build-up insulating layer 11 may contain a reinforcing material. Examples of the reinforcing material include insulating cloth materials such as glass fiber, glass non-woven fabric, aramid non-woven fabric, aramid fiber, and polyester fiber. The reinforcing material may be used alone or in combination of two or more. Further, the first build-up insulating layer 11 may contain inorganic insulating fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. The inorganic insulating fillers may be used alone or in combination of two or more.

[0020] On the surface of the first build-up insulating layer 11, a first build-up conductor layer 12 is located. The first build-up conductor layer 12 is not particularly limited as long as it is a material having conductivity. Examples of the material having conductivity include metals such as copper. The thickness of the first build-up conductor layer 12 is not limited, and may be, for example, 10 μm or more and 40 μm or less.

[0021] The first build-up conductor layers 12 may be the same metal or different metals. The first build-up conductor layer 12 and the core conductor layer 32 may be the same metal or different metals. The first build-up conductor layers 12 may have the same thickness or different thicknesses.

[0022] In the first build-up insulating layer 11, via hole conductors for electrically connecting the upper and lower surfaces of the first build-up insulating layer 11 are located. The via hole conductors are located in via holes penetrating from the upper surface to the lower surface of the first build-up insulating layer 11. The via hole conductors are not particularly limited as long as they are materials having conductivity. Examples of the material having conductivity include metals such as copper. The via hole conductors may be filled in the via holes or may be located only on the inner wall surface of the via holes. The via hole conductors located in the first build-up insulating layer 11 are part of the first build-up conductor layer 12. Among the via hole conductors located in the first build-up insulating layer 11, the via hole conductor that abuts on the through hole conductor 32T is defined as the "first via hole conductor 12V".

[0023] As shown in FIG. 1, on the second surface 3b of the core layer 3, a second build-up layer 2 is located. The second surface 3b of the core layer 3 is located on the opposite side of the first surface 3a of the core layer 3. The second surface 3b of the core layer 3 is the surface of the core conductor layer 32 in the portion where the surface of the core insulating layer 31 and the core conductor layer 32 are located, and is a concavo-convex surface. The second build-up layer 2 has a structure in which second build-up insulating layers 21 and second build-up conductor layers 22 are alternately laminated.

[0024] The second build-up insulating layer 21 is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include epoxy resins, bismaleimide-triazine resins, polyimide resins, and polyphenylene ether resins. These resins may be used individually or in combination of two or more.

[0025] The second build-up insulating layer 21 may be made of the same resin or different resins. The second build-up insulating layer 21 and the core insulating layer 31 may be made of the same resin or different resins. The second build-up insulating layer 21 and the first build-up insulating layer 11 may be made of the same resin or different resins. The thickness of the second build-up insulating layer 21 is not particularly limited and may be, for example, 20 μm or more and 50 μm or less. The second build-up insulating layer 21 may have the same thickness or different thicknesses. The second build-up insulating layer 21 may have the same thickness as the first build-up insulating layer 11 or different thicknesses.

[0026] The second build-up insulating layer 21 may contain reinforcing materials. Examples of reinforcing materials include insulating fabrics such as glass fibers, glass nonwoven fabrics, aramid nonwoven fabrics, aramid fibers, and polyester fibers. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the second build-up insulating layer 21 may contain inorganic insulating fillers 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.

[0027] A second build-up conductor layer 22 is located on the surface of the second build-up insulating layer 21. The second build-up conductor layer 22 is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper. The thickness of the second build-up conductor layer 22 is not limited and may be, for example, 10 μm or more and 50 μm or less.

[0028] The second build-up conductor layers 22 may be made of the same metal or different metals. The second build-up conductor layers 22 and the core conductor layer 32 may be made of the same metal or different metals. The second build-up conductor layers 22 and the first build-up conductor layer 12 may be made of the same metal or different metals. The second build-up conductor layers 22 may have the same thickness or different thicknesses. The second build-up conductor layers 22 may have the same thickness as the first build-up conductor layer 12 or different thicknesses.

[0029] The second build-up insulating layer 21 contains via-hole conductors for electrically connecting the upper and lower surfaces of the second build-up insulating layer 21. The via-hole conductors located in the second build-up insulating layer 21 are described in the same way as the via-hole conductors located in the first build-up insulating layer 11 described above, and a detailed explanation is omitted. The via-hole conductors located in the second build-up insulating layer 21 are part of the second build-up conductor layer 22. Among the via-hole conductors located in the second build-up insulating layer 21, the via-hole conductor that is in contact with the through-hole conductor 32T is defined as the "second via-hole conductor 22V".

[0030] As shown in Figure 1, solder resist 5 may be located on the surfaces of the first build-up layer 1 and the second build-up layer 2. Solder resist 5 is formed of a resin, and examples of the resin include acrylic-modified epoxy resin.

[0031] The wiring board 10 includes a differential wiring conductor 4, as shown in Figure 1. The differential wiring conductor 4 has a wiring structure that connects a pair of first pads 41 located on the surface of the first build-up layer 1 to a pair of second pads 42 located on the surface of the second build-up layer 2, and is arranged in parallel with each other. Specifically, the differential wiring conductor 4 includes a first build-up conductor layer 12 including via-hole conductors, a second build-up conductor layer 22 including via-hole conductors, and a through-hole conductor 32T.

[0032] The first pad 41 is part of the first build-up conductor layer 12 and is exposed through an opening in the solder resist 5 located on the surface of the first build-up layer 1. The second pad 42 is part of the second build-up conductor layer 22 and is exposed through an opening in the solder resist 5 located on the surface of the second build-up layer 2.

[0033] The size (area) of the first pad 41 and the size (area) of the second pad 42 are not limited. For example, the sizes of the first pad 41 and the second pad 42 may be the same or different. For example, if the first pad 41 is smaller than the second pad 42, the first pad 41 may be a flip-chip attach (FCA) and the second pad 42 may be a ball grid array (BGA).

[0034] Of the differential wiring conductors 4, the through-hole conductor 32T, the first via-hole conductor 12V in contact with the through-hole conductor 32T, and the second via-hole conductor 22V in contact with the through-hole conductor 32T are each surrounded by a ground conductor G in a planar perspective. Specifically, the through-hole conductor 32T is surrounded by a ground conductor 32G included in the core conductor layer 32. The first via-hole conductor 12V is surrounded by a ground conductor 12G included in the first build-up conductor layer 12. The second via-hole conductor 22V is surrounded by a ground conductor 22G included in the second build-up conductor layer 22.

[0035] Figures 2A and 2B show the state in which the through-hole conductor 32T included in the differential wiring conductor 4 is surrounded by the ground conductor 32G included in the core conductor layer 32. Figure 2C shows the state in which the first via-hole conductor 12V included in the differential wiring conductor 4 is surrounded by the ground conductor 12G included in the first build-up conductor layer 12. Figure 2D shows the state in which the second via-hole conductor 22V included in the differential wiring conductor 4 is surrounded by the ground conductor 22G included in the second build-up conductor layer 22. Figure 2A is an explanatory diagram to show the cross-section when cut along the AA line shown in Figure 1. Figure 2B is an explanatory diagram to show the cross-section when cut along the BB line shown in Figure 1. Figure 2C is an explanatory diagram to show the cross-section when cut along the CC line shown in Figure 1. Figure 2D is an explanatory diagram to show the cross-section when cut along the DD line shown in Figure 1.

[0036] When the through-hole conductor 32T, the first via-hole conductor 12V, and the second via-hole conductor 22V included in the differential wiring conductor 4 are surrounded by the ground conductor G (12G, 22G, 32G), external noise is reflected by the ground conductor G. As a result, the differential wiring conductor 4 becomes less susceptible to noise. Consequently, even high-frequency signals above 28GHz can be transmitted efficiently. In particular, the first via-hole conductor 12V and the second via-hole conductor 22V have relatively large surface areas within the differential wiring conductor 4. Therefore, being surrounded by the ground conductor G (12G, 22G) is advantageous in that it can relatively and significantly reduce the noise mixed into the differential wiring conductor 4.

[0037] Because the core layer 3 and the insulating layer laminated on top of the core layer 3 have different CTEs (coefficient of thermal expansion), stress tends to concentrate at their boundary. Furthermore, the signal wiring through which high-frequency signals are transmitted is very fine. Therefore, surrounding it with a ground conductor G improves its mechanical strength and reduces the likelihood of breakage.

[0038] If the through-hole conductor 32T, the first via-hole conductor 12V, and the second via-hole conductor 22V included in the differential wiring conductor 4 are surrounded by the ground conductor G, they may be continuously surrounded or intermittently surrounded with partial gaps, as shown in Figures 2A to 2D. When the through-hole conductor 32T, the first via-hole conductor 12V, and the second via-hole conductor 22V included in the differential wiring conductor 4 are continuously surrounded by the ground conductor G, the aforementioned external noise is less likely to be mixed in. As a result, even high-frequency signals of 28 GHz or higher are transmitted more efficiently.

[0039] In the wiring board 10, at least the through-hole conductor 32T, the first via-hole conductor 12V, and the second via-hole conductor 22V included in the differential wiring conductor 4 should be surrounded by a ground conductor G. For example, as shown in Figure 1, the differential wiring conductor 4 may be surrounded by ground conductors G (12G, 22G, 32G) from the first pad 41 to the second pad 42. When the differential wiring conductor 4 is surrounded by ground conductors G from the first pad 41 to the second pad 42, the aforementioned external noise is less likely to be mixed in. As a result, even high-frequency signals of 28 GHz or higher can be transmitted more efficiently.

[0040] Even when the differential wiring conductor 4 is surrounded by a ground conductor G from the first pad 41 to the second pad 42, the differential wiring conductor 4 may be continuously surrounded by the ground conductor G, or it may be intermittently surrounded with partial gaps. When the differential wiring conductor 4 is continuously surrounded by the ground conductor G from the first pad 41 to the second pad 42, the aforementioned external noise is less likely to be mixed in. As a result, even high-frequency signals of 28 GHz or higher are transmitted more efficiently.

[0041] The core insulating layer 31 may contain reinforcing materials such as glass cloth, as described above. However, the region of the core insulating layer 31 in which the through-hole conductor 32T included in the differential wiring conductor 4 is surrounded by the ground conductor 32G does not need to have glass cloth. If the region of the core insulating layer 31 surrounded by the ground conductor 32G does not have glass cloth, the variation in dielectric constant is reduced. As a result, differences in the signal transmission speed in the differential wiring conductor 4 can be reduced.

[0042] The first build-up insulating layer 11 and the second build-up insulating layer 21 may contain reinforcing materials such as glass cloth, as described above. However, the first build-up insulating layer 11 and the second build-up insulating layer 21 often do not contain reinforcing materials such as glass cloth. For example, if the first build-up insulating layer 11 and the second build-up insulating layer 21 do not contain glass cloth, then in the core insulating layer 31, the region where the through-hole conductor 32T included in the differential wiring conductor 4 is surrounded by the ground conductor 32G may be filled with at least one of the first build-up insulating layer 11 and the second build-up insulating layer 21.

[0043] The through-hole conductor 32T included in the differential wiring conductor 4 is located in the through-hole 311 for the differential wiring conductor included in the core insulating layer 31. The ground conductor 32G surrounding the through-hole conductor 32T included in the differential wiring conductor 4 is located in the through-hole 312 for the ground conductor included in the core insulating layer 31. The through-holes 311 for the differential wiring conductor and the through-hole 312 for the ground conductor are not limited, but the inner wall surface of the through-hole 312 for the ground conductor may be rougher than the inner wall surface of the through-hole 311 for the differential wiring conductor. When the inner wall surface of the through-hole 312 for the ground conductor is rougher than the inner wall surface of the through-hole 311 for the differential wiring conductor, good adhesion between the ground conductor 32G and the through-hole 312 for the ground conductor is ensured, and high-frequency signals can be transmitted with good characteristics even when the skin effect occurs when transmitting through the through-hole conductor 32T included in the differential wiring conductor 4.

[0044] The inner wall surface of the through-hole 311 for differential wiring conductors may have an arithmetic surface roughness of, for example, 0.3 μm to 0.5 μm. The inner wall surface of the through-hole 312 for ground conductors may have an arithmetic surface roughness of, for example, 0.3 μm to 0.7 μm.

[0045] The shape of the through-hole conductor 32T included in the differential wiring conductor 4 is not limited. The through-hole conductor 32T included in the differential wiring conductor 4 may have the same diameter from the first surface 3a to the second surface 3b of the core insulating layer 31, or it may have different diameters. If the through-hole conductor 32T has different diameters, it may have a tapered shape, for example, and may have a shape that gradually increases from the center in the thickness direction of the core insulating layer 31 toward the first surface 3a and the second surface 3b, as shown in Figure 3. Figure 3 is an explanatory diagram illustrating a modified example of the through-hole conductor 32T.

[0046] To minimize impedance changes, it is ideal for the through-hole conductor 32T to have the same diameter from the first surface 3a to the second surface 3b of the core insulating layer 31. However, it is difficult to form the through-hole conductor 32T to have the same diameter from the first surface 3a to the second surface 3b. For example, if the through-hole conductor 32T has a shape that gradually increases in diameter from the center of the core insulating layer 31 in the thickness direction toward the first surface 3a and the second surface 3b, the change in the diameter of the through-hole conductor 32T in the thickness direction of the core insulating layer 31 becomes small. Therefore, the change in distance between the through-hole conductor 32T and the ground conductor 32G surrounding it becomes small. As a result, impedance changes are reduced. The center of the core insulating layer 31 in the thickness direction can be defined, for example, as a range of 10% of the thickness of the core insulating layer 31 from the middle of the core insulating layer 31 toward the first surface 3a and the second surface 3b, respectively.

[0047] The ground conductors 12G and 22G surrounding the first via-hole conductor 12V and the second via-hole conductor 22V included in the differential wiring conductor 4 may have a greater width in the direction parallel to the first surface 3a than the ground conductor 32G surrounding the through-hole conductor 32T included in the differential wiring conductor 4. Having such a configuration is advantageous in that it can reduce the occurrence of cracks in the ground conductors 12G and 22G in the first build-up layer 1 and the second build-up layer 2, which have greater thermal expansion and contraction than the core layer 3.

[0048] In a wiring board 10 according to one embodiment, a method for forming a through-hole conductor 32T surrounded by a ground conductor 32G, which is part of a differential wiring conductor 4 surrounded by a ground conductor G, will be explained with reference to Figures 4A to 4I. Figures 4A to 4I are explanatory diagrams illustrating one embodiment of a method for forming a through-hole conductor 32T, which is part of the differential wiring conductor 4, and a part of the ground conductor 32G surrounding the through-hole conductor 32T.

[0049] First, as shown in Figure 4A, a through-hole 312 for a ground conductor is formed in the core insulating layer 31, penetrating from the first surface 3a to the second surface 3b. The through-hole 312 for the ground conductor is formed by drilling and laser processing. When laser processing is used, examples of lasers include excimer lasers, YAG lasers, and carbon dioxide lasers. After forming the hole by drilling and laser processing, it may be subjected to desmearing. Examples of desmearing include chemical desmearing and plasma desmearing.

[0050] Next, as shown in Figure 4B, a seed layer 32a is formed on the first surface 3a, the second surface 3b of the core insulating layer 31, and the inner wall surface of the through-hole 312 for the ground conductor. The seed layer 32a is formed, for example, by electroless plating. For electroless plating, electroless copper plating is used, for example.

[0051] After forming the seed layer 32a, an electroplating layer 32b is formed on the surface of the seed layer 32a, as shown in Figure 4C. The electroplating layer 32b is formed, for example, by electrolytic copper plating. Next, as shown in Figure 4D, the unnecessary portions of the seed layer 32a and the electroplating layer 32b are removed. Specifically, the seed layer 32a and the electroplating layer 32b formed on the first surface 3a and the second surface 3b are removed so that the seed layer 32a and the electroplating layer 32b are positioned on the inner wall surface of the ground conductor through hole 312. The unnecessary portions of the seed layer 32a and the electroplating layer 32b are removed, for example, by polishing.

[0052] Next, as shown in Figure 4E, the resin film 31a is attached to the first surface 3a and the second surface 3b and then heat-pressed. During heat-pressing, the resin film 31a flows into and fills the through-hole 312 for the ground conductor. The resin film 31a does not necessarily contain reinforcing materials such as glass cloth.

[0053] Next, as shown in Figure 4F, the resin film 31a located on the first surface 3a and the second surface 3b is removed, leaving the resin film 31a only in the ground conductor through-hole 312. The method for removing the resin film 31a is not limited and can be, for example, by buffing or roller polishing.

[0054] Next, as shown in Figure 4G, through holes 311 for differential wiring conductors are formed in the resin film 31a filled in the ground conductor through hole 312. The through holes 311 for differential wiring conductors are formed by drilling and laser processing. When laser processing is used, examples of lasers include excimer lasers, YAG lasers, and carbon dioxide lasers. After forming the holes by drilling and laser processing, the film may be subjected to desmearing. Examples of desmearing include chemical desmearing and plasma desmearing.

[0055] The resin film 31a filling the ground conductor through-hole 312 is different from the core insulating layer 31, but it is located in the ground conductor through-hole 312 formed in the core insulating layer 31. Therefore, the resin film 31a filling the ground conductor through-hole 312 is also considered part of the core insulating layer 31, and the differential wiring conductor through-hole 311 formed in the resin film 31a is considered to be formed in the core insulating layer 31.

[0056] Next, although not shown in the drawing, a seed layer 32a is formed on the first surface 3a, the second surface 3b of the core insulating layer 31, and the inner wall surface of the through-hole 311 for the differential wiring conductor. The seed layer 32a is formed, for example, by electroless plating. For example, electroless copper plating is used as the electroless plating. After forming the seed layer 32a, a dry film resist is formed to obtain the desired pattern (core conductor layer 32).

[0057] Next, an electroplating layer 32b is formed on the surface of the seed layer 32a and the surface of the dry film resist. The electroplating layer 32b is formed, for example, by electrolytic copper plating. After forming the electroplating layer 32b, the dry film resist is peeled off, and the portion of the seed layer 32a that was covered by the dry film resist is removed, for example, by etching. Through this procedure, as shown in Figure 4H, a through-hole conductor 32T is formed in the through-hole 311 for differential wiring conductors, and a core conductor layer 32 is formed on the first surface 3a and the second surface 3b.

[0058] Next, as shown in Figure 4I, a first build-up insulating layer 11 and a second build-up insulating layer 21 are formed to cover the first surface 3a, the second surface 3b, and the core conductor layer 32. Subsequently, via holes and via hole conductors including the first via hole conductor 12V and the second via hole conductor 22V can be formed in accordance with the method for forming through holes 311 for differential wiring conductors and through-hole conductors 32T.

[0059] Next, the mounting structure according to this disclosure will be described with reference to Figure 1. The mounting structure 20 according to one embodiment includes a wiring board 10 according to one embodiment and an electronic component 7 located in the mounting area of ​​the wiring board 10.

[0060] As shown in Figure 1, in the mounting area on which the electronic component 7 is mounted, a mounting structure 20 according to one embodiment is obtained by connecting the first pad 41 (first build-up conductor layer 12) exposed from an opening in the solder resist 5 located on the surface of the first build-up layer 1 to the electrodes of the electronic component 7 via solder 6. Examples of electronic components 7 include semiconductor integrated circuit elements and optoelectronic elements. A second pad 42 (second build-up conductor layer 22) exposed from an opening in the solder resist 5 located on the surface of the second build-up layer 2 may be connected to a motherboard, for example, via solder 6. Alternatively, further electronic components 7 may be connected via solder 6.

[0061] The embodiments of this disclosure have been described above. However, the invention relating to this disclosure is not limited to the embodiments described above, and various modifications and improvements are possible within the scope of this disclosure as shown in (1) to (10) below.

[0062] (1) The wiring board according to the present disclosure includes a core layer having a first surface and a second surface located opposite to the first surface, and including a core insulating layer and a core conductor layer; a first build-up layer located on the first surface, and including a first build-up insulating layer and a first build-up conductor layer; and a second build-up layer located on the second surface, and including a second build-up insulating layer and a second build-up conductor layer. The core conductor layer, the first build-up conductor layer, and the second build-up conductor layer include a ground conductor and a differential wiring conductor. The differential wiring conductor has a wiring structure that connects a pair of first pads located on the surface of the first build-up layer to a pair of second pads located on the surface of the second build-up layer, and is parallel to each other. The differential wiring conductor comprises a through-hole conductor included in the core conductor layer, a first via-hole conductor included in the first build-up conductor layer and in contact with the through-hole conductor, and a second via-hole conductor included in the second build-up conductor layer and in contact with the through-hole conductor. The through-hole conductor, the first via-hole conductor, and the second via-hole conductor are each surrounded by a ground conductor in a planar perspective. (2) In the wiring board described in (1) above, the differential wiring conductors are such that at least the through-hole conductor, the first via-hole conductor, and the second via-hole conductor are continuously surrounded by a ground conductor. (3) In the wiring board described in (1) or (2) above, the differential wiring conductor is surrounded by a ground conductor from the first pad to the second pad. (4) In the wiring board described in (3) above, the differential wiring conductor is continuously surrounded by a ground conductor from the first pad to the second pad. (5) In the wiring board described in any of (1) to (4) above, the core insulating layer includes through holes for differential wiring conductors where through-hole conductors are located and through holes for ground conductors where ground conductors are located. The inner wall surface of the ground conductor through hole is rougher than the inner wall surface of the differential wiring conductor through hole. (6) In the wiring board described in any of (1) to (5) above, the region of the core insulating layer surrounded by the ground conductor does not have glass cloth. (7) In the wiring board described in (6) above, the region of the core insulating layer surrounded by the ground conductor is filled with at least one of the first build-up insulating layer or the second build-up insulating layer. (8) In the wiring board described in any of (1) to (7) above, the diameter of the through-hole conductors gradually increases from the center in the thickness direction of the core insulating layer toward the first and second surfaces. (9) In the wiring board described in any of (1) to (8) above, the ground conductor surrounding the first via hole conductor and the second via hole conductor has a greater width in the direction parallel to the first surface than the ground conductor surrounding the through hole conductor. (10) The implementation structure relating to this disclosure includes a wiring board as described in any of (1) to (9) above, and electronic components connected to the wiring board. [Explanation of symbols]

[0063] 1. First build-up layer 11. First build-up insulating layer 12. First build-up conductor layer 12G Ground Conductor 12V First via hole conductor 2. Second build-up layer 21. Second build-up insulating layer 22. Second build-up conductor layer 22G Ground Conductor 22V Second via hole conductor 3 Core Layers 31. Insulating layer for core 311 Through-hole for differential wiring conductors 312 Through-hole for ground conductor 31a Resin film 32 Conductor layers for core 32G Ground Conductor 32T Through-Hole Conductor 32a Seed layer 32b Electroplating layer 3a 1st page 3b 2nd side 4 Differential wiring conductors 41 First pad 42 Second pad 5 Solder Resist 6 Handa 7 Electronic Components G Ground Conductor 10 Wiring board 20 Implementation Structures

Claims

1. A core layer comprising a core insulating layer and a core conductive layer, having a first surface and a second surface located opposite to the first surface, The first build-up layer includes a first build-up insulating layer and a first build-up conductor layer, and the first build-up layer is located on the first surface, The second build-up layer includes a second build-up insulating layer and a second build-up conductive layer, and the second build-up layer is located on the second surface, Includes, The core conductor layer, the first build-up conductor layer, and the second build-up conductor layer include a ground conductor and a differential wiring conductor. The differential wiring conductors have a wiring structure that connects a pair of first pads located on the surface of the first build-up layer to a pair of second pads located on the surface of the second build-up layer, and are arranged in parallel with each other. The differential wiring conductor comprises a through-hole conductor included in the core conductor layer, a first via-hole conductor included in the first build-up conductor layer and in contact with the through-hole conductor, and a second via-hole conductor included in the second build-up conductor layer and in contact with the through-hole conductor, wherein the through-hole conductor, the first via-hole conductor, and the second via-hole conductor are each surrounded by the ground conductor in a planar perspective. Wiring board.

2. The wiring board according to claim 1, wherein in the differential wiring conductor, at least the through-hole conductor, the first via-hole conductor, and the second via-hole conductor are continuously surrounded by the ground conductor.

3. The wiring board according to claim 1, wherein the differential wiring conductor is surrounded by the ground conductor from the first pad to the second pad.

4. The wiring board according to claim 3, wherein the differential wiring conductor is continuously surrounded by the ground conductor from the first pad to the second pad.

5. The core insulating layer includes through holes for differential wiring conductors where the through-hole conductors are located and through holes for ground conductors where the ground conductors are located. The inner wall surface of the through-hole for the ground conductor is rougher than the inner wall surface of the through-hole for the differential wiring conductor. The wiring board according to claim 1.

6. The wiring board according to claim 1, wherein the region surrounded by the ground conductor in the core insulating layer does not have glass cloth.

7. The wiring board according to claim 6, wherein in the core insulating layer, the region surrounded by the ground conductor is filled with at least one of the first build-up insulating layer or the second build-up insulating layer.

8. The wiring board according to claim 1, wherein the diameter of the through-hole conductor gradually increases from the center in the thickness direction of the core insulating layer toward the first and second surfaces.

9. The wiring board according to claim 1, wherein the ground conductor surrounding the first via hole conductor and the second via hole conductor has a greater width in the direction parallel to the first surface than the ground conductor surrounding the through hole conductor.

10. A mounting structure comprising a wiring board according to any one of claims 1 to 9 and an electronic component connected to the wiring board.

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