Wiring boards and mounting structures

Abstract

This invention provides a wiring board that reduces impedance mismatch and improves shielding effectiveness. [Solution] The wiring board according to this disclosure has a laminated structure having a first surface and a second surface opposite the first surface, wherein a plurality of insulating layers and a plurality of conductor layers are alternately laminated. The conductor layer includes a linear signal conductor, a land conductor connected to one end of the signal conductor, a first ground conductor located spaced apart around the signal conductor and the land conductor, and a pad located on the second surface. The pad has a larger area than the land conductor. In a plan view, the first ground conductor has an opening in the region overlapping with the pad. In a plan view, a portion of the signal conductor and the land conductor are located in the opening. A second ground conductor connected to the first ground conductor is located adjacent to the portion of the signal conductor and the land conductor located in the opening.

Description

[[Technical Field]]

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

[0002] In a conventional wiring board as described in Patent Document 1, a large clearance (opening) is provided in a ground conductor located in a region overlapping with a relatively large pad such as a ball grid array (BGA) pad in plan perspective. The presence of such a large clearance reduces the capacitance generated between the pad and the ground conductor. [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] International Publication No. 2016 / 067908 [[Disclosure of the Invention]] [[Problem to be Solved by the Invention]]

[0004] However, for example, when a signal conductor has a region adjacent to a ground conductor and a region located within a large clearance, the impedance of the signal conductor changes abruptly between the two regions. Therefore, high-frequency signals that are easily affected by impedance mismatch (high-frequency signals of 5 GHz or higher, the same applies hereinafter) may not be transmitted efficiently due to signal reflection or the like.

[0005] An object of the present disclosure is to provide a wiring board that reduces impedance mismatch and also improves the shielding effect. [[Means for Solving the Problem]]

[0006] The wiring board according to this disclosure has a laminated structure in which multiple insulating layers and multiple conductor layers are alternately laminated, and has a first surface and a second surface on the opposite side of the first surface. The conductor layer includes a linear signal conductor, a land conductor connected to one end of the signal conductor, a first ground conductor located spaced apart around the signal conductor and the land conductor, and a pad located on the second surface. The pad has a larger area than the land conductor. In a plan view, the first ground conductor has an opening in the region overlapping with the pad. In a plan view, a portion of the signal conductor and the land conductor are located in the opening. A second ground conductor connected to the first ground conductor is located adjacent to the portion of the signal conductor and the land conductor located in the opening.

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

[0008] The wiring board relating to this disclosure has the configuration described in the section on means for solving the problem, thereby reducing impedance mismatch and improving shielding effect. [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 2] This is an enlarged diagram illustrating one embodiment of region X shown in Figure 1. [Figure 3] Figure 1 is an enlarged diagram illustrating another embodiment of region X shown in Figure 1. [Figure 4] This is an enlarged diagram illustrating yet another embodiment of region X shown in Figure 1. [Figure 5] This is an enlarged diagram illustrating yet another embodiment of region X shown in Figure 1. [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 5. 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 a cross-section of a part of the mounting structure 20. The wiring board 10 according to one embodiment includes a laminated structure 1 and a solder resist 4, as shown in Figure 1.

[0011] The laminated structure 1 has a structure in which insulating layers 2 and conductive layers 3 are alternately laminated. As shown in Figure 1, in a wiring board 10 according to one embodiment, the laminated structure 1 includes a core layer and a build-up layer. The core layer includes a core insulating layer and a core conductive layer. The build-up layer includes a build-up insulating layer and a build-up conductive layer.

[0012] The core insulating layer is an insulating layer 2 located approximately in the center of the thickness direction of the laminated structure 1 and having a relatively large thickness. The core insulating 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, 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 is not particularly limited and may be, for example, 60 μm to 1600 μm.

[0013] The core insulating layer 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 may contain inorganic insulating fillers. Examples of inorganic insulating fillers include 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.

[0014] On both sides of the insulating layer for the core, a conductive layer for the core, which is part of the conductive layer 3, is located. The conductive layer for the core 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 conductive layer for the core is not limited and may be, for example, 10 μm or more and 30 μm or less.

[0015] As shown in Figure 1, the core insulating layer has through-hole conductors positioned to electrically connect the upper and lower surfaces of the core insulating layer. The through-hole conductors are located within through-holes that penetrate from the upper surface to the lower surface of the core insulating layer. The through-hole conductors are not particularly limited as long as they are made of a conductive material. Examples of conductive materials include metals such as copper. The through-hole conductors are also part of the conductor layer 3.

[0016] The through-hole conductor is connected to the core conductor layers located on both sides of the core insulating layer. The through-hole conductor may be integrally formed with the core insulating layer. The through-hole conductor may be located only on the inner wall surface of the through-hole, or it may be filled inside the through-hole.

[0017] Although the laminated structure 1 shown in Figure 1 includes a core layer, the core layer is not an essential component. For example, in the case of a coreless substrate, the laminated structure 1 may not include a core layer.

[0018] As shown in Figure 1, build-up layers are located on both sides of the core layer. The build-up layer has a structure in which build-up insulating layers and build-up conductive layers are alternately stacked. As described above, in the case of laminated structure 1 that does not include a core layer, the laminated structure 1 includes only the build-up layer.

[0019] The build-up insulating layer is an insulating layer 2 other than the core insulating layer. The build-up insulating layer is not particularly limited as long as it is an insulating material. Examples of the insulating material include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin and polyphenylene ether resin. Only one of these resins may be used, or two or more of them may be used in combination.

[0020] Each build-up insulating layer may be formed of the same resin, or may be formed of different resins. The build-up insulating layer and the core insulating layer may be formed of the same resin, or may be formed of different resins. The thickness of the build-up insulating layer is not particularly limited, and may be, for example, 20 µm or more and 50 µm or less. Each build-up insulating layer may have the same thickness, or may have different thicknesses.

[0021] The build-up insulating layer may contain a reinforcing material. Examples of the reinforcing material include insulating cloth materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber and polyester fiber. Only one reinforcing material may be used, or two or more reinforcing materials may be used in combination. Furthermore, the build-up insulating layer may contain an inorganic insulating filler. Examples of the inorganic insulating filler include silica, barium sulfate, talc, clay, glass, calcium carbonate and titanium oxide. Only one type of the inorganic insulating filler may be used, or two or more types may be used in combination.

[0022] On the surface of the build-up insulating layer, a build-up conductor layer that is a part of the conductor layer 3 is disposed. The build-up conductor layer is not particularly limited as long as it is a material having conductivity. Examples of the conductive material include metals such as copper. The thickness of the build-up conductor layer is not limited, and may be, for example, 10 µm or more and 30 µm or less.

[0023] The build-up conductor layers may be made of the same metal or different metals. The build-up conductor layers and the core conductor layer may be made of the same metal or different metals. The build-up conductor layers may have the same thickness or different thicknesses.

[0024] The build-up insulating layer contains via-hole conductors 3V for electrically connecting the upper and lower surfaces of the build-up insulating layer. The via-hole conductors 3V are located within via holes that penetrate from the upper surface to the lower surface of the build-up insulating layer. The via-hole conductors 3V are not particularly limited as long as they are made of a conductive material. Examples of conductive materials include metals such as copper. The via-hole conductors 3V may be filled into the via holes or may be located only on the inner wall surface of the via holes. The via-hole conductors 3V are part of the build-up conductor layer.

[0025] As shown in Figure 1, solder resist 4 may be located on the first surface 11 and the second surface 12 of the laminated structure 1. The solder resist 4 is made of resin, and examples of the resin include acrylic-modified epoxy resin.

[0026] The conductor layer 3, as shown in Figures 1 and 2, includes a linear signal conductor 3S, a land conductor 31 connected to one end of the signal conductor 3S, a first ground conductor 3G1 spaced apart around the signal conductor 3S and the land conductor 31, and a pad 32 located on the second surface 12. Figure 2 is an enlarged diagram illustrating one embodiment of region X shown in Figure 1. The pad 32 has a larger area than the land conductor 31.

[0027] As shown in Figure 2, the first ground conductor 3G1 has an opening 5 in a plan view that overlaps with the pad 32. The size of the opening 5 is not limited; for example, the opening 5 may be large enough to accommodate the entire pad 32 in a plan view, i.e., large enough so that the entire pad 32 is exposed from the opening 5. As shown in Figure 2, a portion of the signal conductor 3S and the land conductor 31 are located in the opening 5 in a plan view.

[0028] The second ground conductor 3G2 is located in the opening 5. The second ground conductor 3G2 is part of the conductor layer 3 and is connected to the first ground conductor 3G1. The second ground conductor 3G2 located in the opening 5 is positioned adjacent to a part of the signal conductor 3S located in the opening 5 and the land conductor 31. This configuration allows for a gradual change in impedance between the signal conductor 3S located within the relatively large opening 5 and the signal conductor 3S located outside the opening 5. Therefore, even for high-frequency signals that are susceptible to impedance mismatch, the gradual change in impedance reduces the impact of impedance mismatch. As a result, signal reflections are reduced, and even high-frequency signals are transmitted efficiently. Furthermore, the second ground conductor 3G2 also has the effect of reducing noise interference to the signal conductor 3S within the opening 5 (shielding effect).

[0029] In the opening 5, the gap between the signal conductor 3S (land conductor 31) and the second ground conductor 3G2 is not limited, as long as the second ground conductor 3G2 is located adjacent to the signal conductor 3S and the land conductor 31. For example, the gap between the signal conductor 3S (land conductor 31) and the second ground conductor 3G2 may be between 10 μm and 100 μm. If the gap between the signal conductor 3S (land conductor 31) and the second ground conductor 3G2 is within this range, the change in impedance becomes more gradual.

[0030] The gap between the signal conductor 3S (land conductor 31) and the second ground conductor 3G2 may have a constant width or an irregular width. In this specification, "constant width" does not need to be exactly the same width; any width within ±5 μm of a reference width is considered "constant width". For example, if 100 μm is the reference, the range of 95 μm to 105 μm is considered a constant width of 100 μm. When the gap between the signal conductor 3S (land conductor 31) and the second ground conductor 3G2 has a constant width, the change in impedance becomes more gradual.

[0031] Although the width of the second ground conductor 3G2 is not limited, considering that a relatively large opening 5 is provided to reduce capacitance, it is preferable to reduce the proportion of the opening 5 occupied by the second ground conductor 3G2. The second ground conductor 3G2 may have a width of, for example, 1 to 5 times the wiring width of the signal conductor 3S located in the opening 5. Having such a width for the second ground conductor 3G2 results in a more gradual change in impedance without affecting the effect of reducing capacitance.

[0032] As shown in Figure 3, the opening 5 may also contain a first conductor 3a that is not connected to the signal conductor 3S and the second ground conductor 3G2. Figure 3 is an enlarged explanatory diagram illustrating another embodiment of region X shown in Figure 1. The presence of the first conductor 3a reduces the recess caused by the overlapping of the openings 5 ​​located in each layer of the laminated structure 1. Specifically, for example, the region on the first surface 11 where the openings 5 ​​overlap vertically is prone to recession. However, the presence of the first conductor 3a reduces the recess on the first surface 11.

[0033] The position of the first conductor 3a is not limited as long as it is located in the opening 5. The first conductor 3a may be located along the edge of the opening 5, as shown in Figure 3. When the first conductor 3a is located along the edge of the opening 5, in addition to reducing the aforementioned recess, the first ground conductor 3G1 above the via hole conductor 3V located around the opening 5 is less likely to become convex. Specifically, when forming the via hole conductor 3V around the opening 5, electrolytic plating tends to deposit more around the opening 5. As a result, the via hole conductor 3V located around the opening 5 is more raised than the via hole conductor 3V located in other areas, and the first ground conductor 3G1 located above it is more likely to have a convex shape. If the first ground conductor 3G1 is raised in a convex shape, it will affect the formation of the conductor layer 3 and impair electrical reliability. Therefore, when the first conductor 3a is located along the edge of the opening 5, the aforementioned recess is reduced without impairing electrical reliability.

[0034] When the first conductor 3a is located along the edge of the opening 5, it may be located at a distance of 30 μm to 50 μm from the first ground conductor 3G1. When the first conductor 3a is located at a distance of 30 μm to 50 μm from the first ground conductor 3G1, the above-mentioned recess is further reduced with little effect on electrical reliability.

[0035] Although the width of the first conductor 3a is not limited, as mentioned above, considering the reduction of capacitance, it is preferable to reduce the proportion occupied by the second ground conductor 3G2 in the opening 5. The first conductor 3a may have a width of, for example, 1 to 3 times the wiring width of the signal conductor 3S located in the opening 5. Having such a width for the first conductor 3a reduces the recess without affecting the effect of reducing capacitance. When the first conductor 3a is located along the edge of the opening 5, the recess is reduced without impairing electrical reliability.

[0036] In Figures 2 and 3, the signal conductor 3S is a differential wiring conductor. When the signal conductor 3S is a differential wiring conductor, the effect of smoother impedance changes when transmitting high-frequency signals is more pronounced. The signal conductor 3S is not limited to a differential wiring conductor; as shown in Figures 4 and 5, it may also be a single wiring conductor. Figures 4 and 5 are enlarged explanatory diagrams illustrating yet another embodiment of region X shown in Figure 1. In Figures 4 and 5, the configuration is the same as in Figures 2 and 3, except that the signal conductor 3S is a single wiring conductor, and a detailed explanation is omitted.

[0037] The method for manufacturing the wiring board 10 according to one embodiment is not limited. For example, first, through holes are formed in the core insulating layer by drilling or laser. Next, through-hole conductors and core conductor layers are formed by, for example, a subtractive method. Then, a predetermined number of build-up insulating layers and build-up conductor layers are alternately stacked. In the build-up insulating layer, via holes are formed, for example, by laser processing with the lower conductor layer 3 as the bottom surface. Then, via-hole conductors 3V and build-up conductor layers can be formed by, for example, a semi-additive method. Pads 32, which are part of the build-up conductor layer, are formed on the second surface 12 of the build-up insulating layer. A first ground conductor 3G1, a second ground conductor 3G2, and a signal conductor 3S, which are part of the build-up conductor layer, are formed in each layer. Then, if necessary, solder resist 4 is formed on the first surface 11 and the second surface 12 to form the wiring board 10 shown in Figure 1.

[0038] 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.

[0039] In the mounting area where the electronic component 7 is mounted, a mounting structure 20 according to one embodiment is obtained by connecting the conductive layer 3 exposed from an opening in the solder resist 4 located on the surface of the build-up layer to the electrodes of the electronic component 7 via solder 6. Examples of electronic components 7 include semiconductor integrated circuit elements and optoelectronic elements. In the mounting structure 20 according to one embodiment, a conductive layer 3 (pad 32) exposed from an opening in the solder resist 4 is also located on the surface (second surface 12) opposite to the surface (first surface 11) on which the electronic component 7 is mounted. A motherboard, for example, may be connected to this pad 32 via solder 6, and further electronic components 7 may be connected via solder 6.

[0040] 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.

[0041] (1) The wiring board according to the present disclosure has a laminated structure having a first surface and a second surface on the opposite side of the first surface, wherein a plurality of insulating layers and a plurality of conductor layers are alternately laminated. The conductor layers include a linear signal conductor, a land conductor connected to one end of the signal conductor, a first ground conductor located spaced apart around the signal conductor and the land conductor, and a pad located on the second surface. The pad has a larger area than the land conductor. In a plan view, the first ground conductor has an opening in the region overlapping with the pad. In a plan view, a portion of the signal conductor and the land conductor are located in the opening. A second ground conductor connected to the first ground conductor is located adjacent to the portion of the signal conductor and the land conductor located in the opening. (2) In the wiring board described in (1) above, the entire pad is contained within the opening when viewed from above. (3) In the wiring board described in (1) or (2) above, the gap between the signal conductor and the second ground conductor in the opening has a certain width. (4) In the wiring board described in any of (1) to (3) above, the second ground conductor has a width of 1 to 5 times the wiring width of the signal conductor located in the opening. (5) In the wiring board described in any of (1) to (4) above, a first conductor that is not connected to the signal conductor and the second ground conductor is further located in the opening. (6) In the wiring board described in (5) above, the first conductor is located along the edge of the opening. (7) In the wiring board described in (5) or (6) above, the first conductor has a width of 1 to 3 times the wiring width of the signal conductor located in the opening. (8) In the wiring board described in any of (5) to (7) above, the first conductor is located at a distance of 30 μm or more and 50 μm or less from the first ground conductor. (9) In the wiring board described in any of (1) to (8) above, at least a portion of the signal conductors are differential wiring conductors. (10) The implementation structure relating to this disclosure includes a wiring board as described in any of (1) to (9) above, and an electronic component connected to the wiring board. [Explanation of Symbols]

[0042] 1. Laminated structure 11 Page 1 12 Side 2 2. Insulating layer 3 Conductor layers 31 Land conductor 32 pads 3a First conductor 3G1 First ground conductor 3G2 Second ground conductor 3S signal conductor 3V via hole conductor 4 Solder Resist 5 aperture 6 Handa 7 Electronic Components 10 Wiring board 20 Implementation Structures

Claims

1. The laminated structure has multiple insulating layers and multiple conductive layers stacked alternately, and has a first surface and a second surface on the opposite side of the first surface. The conductor layer includes a linear signal conductor, a land conductor connected to one end of the signal conductor, a first ground conductor spaced apart around the signal conductor and the land conductor, and a pad located on the second surface. The pad has a larger area than the land conductor, In a planar perspective view, the first ground conductor has an opening in the region overlapping with the pad. In a plan view, a portion of the signal conductor and the land conductor are located in the opening. The second ground conductor, which connects to the first ground conductor, is located adjacent to the area around the part of the signal conductor located in the opening and the land conductor. Wiring board.

2. The wiring board according to claim 1, wherein, in a planar perspective view, the entire pad is housed within the opening.

3. The wiring board according to claim 1, wherein the gap between the signal conductor and the second ground conductor in the opening has a certain width.

4. The wiring board according to claim 1, wherein the second ground conductor has a width of 1 to 5 times the wiring width of the signal conductor located in the opening.

5. The wiring board according to claim 1, wherein a first conductor, which is not connected to the signal conductor and the second ground conductor, is further positioned in the opening.

6. The wiring board according to claim 5, wherein the first conductor is located along the edge of the opening.

7. The wiring board according to claim 5, wherein the first conductor has a width of one to three times the wiring width of the signal conductor located in the opening.

8. The wiring board according to claim 5, wherein the first conductor is located at a distance of 30 μm or more and 50 μm or less from the first ground conductor.

9. The wiring board according to claim 1, wherein at least a portion of the signal conductors are differential wiring conductors.

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.

Images