Wiring board and mounting structure

Abstract

A wiring board that reduces signal transmission loss and noise and allows mounted electronic components to operate stably and normally is provided. [Solution] A wiring board according to the present disclosure includes an insulating layer having a first surface and a second surface located on the opposite side to the first surface, first and second grooves recessed from the first surface toward the second surface, and a first conductor layer located in the first and second grooves. The first conductor layer has a signal conductor located in the first groove and a ground conductor located along the signal conductor and in the second groove. The ground conductor has a thickness that is greater than or equal to the thickness of the signal conductor at least in a first region along the signal conductor, and has a portion that is thinner than the thickness of the first region in a second region away from the first region.

Description

[Technical Field]

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

[0002] Conventionally, in wiring boards (circuit structures) such as those described in Patent Document 1, conductor layers are connected to each other by via conductors. The ground conductors included in the conductor layers include portions with relatively wide widths and portions with narrow widths. Therefore, in order to connect the layers using the ground conductor portions, via conductors are arranged in the portions with relatively wide widths and are not arranged in the portions with narrow widths. As a result, the via conductors are not arranged at the desired pitch, or thin ground conductors with open ends are formed between signal conductors, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7013579 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] If via conductors are not arranged at the desired pitch, or if thin ground conductors with open ends are formed between signal conductors, the return current path in the ground conductors will be obstructed for high-frequency signals, resulting in increased signal transmission loss and noise, and preventing the mounted electronic components from operating stably and normally.

[0005] An object of the present disclosure is to provide a wiring board that reduces signal transmission loss and noise and enables electronic components mounted thereon to operate stably and normally. [Means for solving the problem]

[0006] The wiring board according to the present disclosure includes an insulating layer having a first surface and a second surface located on the opposite side to the first surface, first and second grooves recessed from the first surface toward the second surface, and a first conductor layer located in the first and second grooves. The first conductor layer has a signal conductor located in the first groove and a ground conductor located along the signal conductor and in the second groove. The ground conductor has a thickness that is greater than or equal to the thickness of the signal conductor at least in a first region along the signal conductor, and has a portion thinner than the thickness of the first region in a second region away from the first region.

[0007] A mounting structure according to the present disclosure includes the above-described wiring board and an electronic component mounted on the wiring board. [Effects of the Invention]

[0008] The wiring board and mounting structure according to the present disclosure have the above-described configuration, thereby reducing signal transmission loss and noise, and allowing mounted electronic components to operate stably and normally. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram illustrating a wiring substrate according to an embodiment of the present disclosure. [Figure 2] 2 is an enlarged explanatory view for explaining an embodiment of a region X shown in FIG. 1 (however, an insulating layer is omitted). FIG. [Figure 3] 1. FIG. 4 is an enlarged explanatory view for explaining another embodiment of the region X shown in FIG. 1 (however, the insulating layer is omitted). [Figure 4] 1. FIG. 4 is an enlarged explanatory view for explaining still another embodiment of the region X shown in FIG. 1 (however, the insulating layer is omitted). [Figure 5] 5A to 5D are explanatory views for explaining one embodiment of a method for forming a first conductor layer. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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 illustrating a wiring board 100 according to an embodiment of the present disclosure. The wiring board 100 according to the embodiment includes a core layer and a build-up layer. The core layer includes a core insulating layer 4, a core conductor layer 4a, and a through-hole conductor 4b. The build-up layer includes an insulating layer 3, a first conductor layer 1, a second conductor layer 2, and a solder resist 5.

[0011] In the wiring board 100 shown in FIG. 1, the core layer is located approximately at the center in the thickness direction of the wiring board 100. The core layer includes a core insulating layer 4, a core conductor layer 4a, and a through-hole conductor 4b. The core insulating layer 4 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 insulating layer 4 is not particularly limited and may be, for example, 100 μm or more and 1.2 mm or less.

[0012] The core insulating layer 4 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 insulating layer 4 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.

[0013] Core conductor layers 4a are located on both sides of the core insulating layer 4. The core conductor layer 4a 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 4a is not limited and may be, for example, 10 μm or more and 50 μm or less. Although the core conductor layers 4a are shown in FIG. 1 to be located on both sides of the core insulating layer 4, they may be located on at least one side of the core insulating layer 4.

[0014] As shown in FIG. 1, a through-hole conductor 4b is located in the core insulating layer 4, electrically connecting the top and bottom surfaces of the core insulating layer 4. The through-hole conductor 4b is located in a through-hole that penetrates from the top surface to the bottom surface of the core insulating layer 4. The through-hole conductor 4b is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper. The through-hole conductor 4b is connected to the core conductor layers 4a formed on both sides of the core insulating layer 4. The through-hole conductor 4b may be located only on the inner wall surface of the through-hole, or may fill the through-hole. The through-hole conductor 4b may be made of the same metal as the core conductor layer 4a, or a different metal.

[0015] Buildup layers are located on the upper and lower surfaces of the core layer. The buildup layer has a structure in which an insulating layer 3 and a conductor layer are laminated. The insulating layer 3 has a first surface 31 and a second surface 32. In this specification, the "first surface 31 of the insulating layer 3" refers to the surface of the insulating layer 3 that is farther from the core layer. The "second surface 32 of the insulating layer 3" refers to the surface opposite the first surface 31, i.e., the surface closer to the core layer. In this specification, the conductor layer located on the first surface 31 of the insulating layer 3 is defined as the "first conductor layer 1," and the conductor layer adjacent to the second surface 32 of the insulating layer 3 is defined as the "second conductor layer 2." In the insulating layer 3 adjacent to the core insulating layer 4, the conductor layer adjacent to the second surface 32 of the insulating layer 3 is the core conductor layer 4a, which may correspond to the "second conductor layer 2."

[0016] The insulating layer 3 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 3 may be made of the same resin or different resins. The insulating layer 3 and the core insulating layer 4 may be made of the same resin or different resins. The thickness of the insulating layer 3 is not particularly limited and may be, for example, 10 μm or more and 50 μm or less. The insulating layers 3 may have the same thickness or different thicknesses.

[0017] The insulating layer 3 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 3 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.

[0018] The first conductor layer 1 and the second conductor layer 2 are not particularly limited as long as they are made of a conductive material. Examples of conductive materials include metals such as copper. The thicknesses of the first conductor layer 1 and the second conductor layer 2 are not limited and may be, for example, 5 μm or more and 25 μm or less.

[0019] A via-hole conductor is located in the insulating layer 3, electrically connecting the upper and lower surfaces of the insulating layer 3. The via-hole conductor is located in a via hole that penetrates the upper and lower surfaces of the insulating layer 3. The via-hole conductor is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper. The via-hole conductor is connected to a first conductor layer 1 located on a first surface 31 of the insulating layer 3 and a second conductor layer 2 located on a second surface 32 of the insulating layer 3. The via-hole conductor may be filled in the via hole, or may be located only on the inner surface of the via hole. The via-hole conductor may be made of the same metal as the first conductor layer 1 and the second conductor layer 2, or may be made of a different metal.

[0020] As shown in Fig. 1, a solder resist 5 may be located on the surface of the buildup layer. The solder resist 5 is made of a resin, such as an acrylic-modified epoxy resin. The solder resist 5 has openings for electrically connecting the conductor layer located on the surface of the buildup layer to the electrodes of the electronic component 7 via solder 6. Examples of the electronic component 7 include a semiconductor integrated circuit element and an optoelectronic element.

[0021] As shown in Fig. 2, the first conductor layer 1 includes a signal conductor 1s and a ground conductor 1g. This is an enlarged explanatory view for explaining one embodiment of the region X shown in Fig. 1. Specifically, Fig. 2 is a perspective view of the region X shown in Fig. 1 seen from above, in which the reference numeral for the insulating layer 3 is indicated by a dashed line, and the insulating layer 3 itself is not shown.

[0022] The signal conductor 1s is located in a first groove 3a recessed from the first surface 31 toward the second surface 32 of the insulating layer 3. The first groove 3a does not penetrate from the first surface 31 to the second surface 32, and the bottom of the first groove 3a is located within the insulating layer 3.

[0023] The thickness of the signal conductor 1s, i.e., the depth of the first groove 3a, is not limited as long as it penetrates from the first surface 31 to the second surface 32. The thickness of the signal conductor 1s (the depth of the first groove 3a) may be, for example, 20% to 80% of the thickness of the insulating layer 3. The width of the signal conductor 1s is not limited and may be, for example, 2 μm to 20 μm. The signal conductor 1s may be a differential wiring or a single wiring.

[0024] The ground conductor 1g is located in a second groove 3b recessed from the first surface 31 toward the second surface 32 of the insulating layer 3. The ground conductor 1g is located along the signal conductor 1s and typically has a solid structure. An example of the first groove 3a and the second groove 3b is specifically illustrated in FIG. 5B, which will be described later.

[0025] The ground conductor 1g has a first region 11 and a second region 12. The first region 11 refers to a region along the signal conductor 1s. In this specification, the "region along the signal conductor" can be defined as, for example, a region adjacent to the signal conductor 1s and having a width of 2 μm to 20 μm (or the same width as the signal conductor 1s). The second region 12 refers to a region away from the first region 11, specifically, a region of the ground conductor 1g other than the first region 11.

[0026] The thickness T1 of the first region 11 of the ground conductor 1g is equal to or greater than the thickness Ts of the signal conductor 1s. The thickness T2 of the second region 12 of the ground conductor 1g has a portion that is thinner than the thickness T1 of the first region 11. Specifically, the thickness T2 of the second region 12 of the ground conductor 1g may be thinner than the thickness Ts of the signal conductor 1s, or may be equal to or greater than the thickness Ts of the signal conductor 1s, as long as it is thinner than the thickness T1 of the first region 11.

[0027] The ground conductor 1g has the first region 11 and the second region 12, which ensures a good return current path for the ground conductor 1g. This reduces signal transmission loss and noise, ensuring stable and normal operation of the mounted electronic component 7. If the second region 12 has a thickness thinner than the thickness Ts of the signal conductor 1s, the stress applied to the wiring board 100 by the ground conductor 1g is reduced. As a result, warping of the wiring board 100 and the occurrence of cracks are further reduced.

[0028] The first region 11 is not limited to a specific thickness as long as it has a thickness equal to or greater than the thickness Ts of the signal conductor 1s, but as shown in Fig. 3, at least a portion of the first region 11 may be in contact with the second conductor layer 2. That is, at least a portion of the second groove 3b in which the first region 11 is located may penetrate from the first surface 31 to the second surface 32. Fig. 3 is an enlarged explanatory view for explaining another embodiment of the region X shown in Fig. 1. Specifically, Fig. 3 is a perspective view of the region X shown in Fig. 1 seen from above, in which the reference numeral for the insulating layer 3 is indicated by a dashed line and the insulating layer 3 itself is not shown.

[0029] If at least a part of the first region 11 is in contact with the second conductor layer 2, it is advantageous in that, for example, the problem of noise being mixed into the signal conductor 1s can be reduced.

[0030] When at least a portion of the first region 11 is in contact with the second conductor layer 2, the portion of the first region 11 in contact with the second conductor layer 2 may be located intermittently along the signal conductor 1s. In such a structure, as shown in Fig. 3, the length H1 of the gap 11a between the portions of adjacent first regions 11 may be equal to or less than ¼ of the wavelength of the signal flowing through the signal conductor 1s. When the length H1 of the gap 11a between the portions of adjacent first regions 11 is equal to or less than ¼ of the wavelength of the signal flowing through the signal conductor 1s, the shielding effect of the ground conductor 1g is improved with respect to the signal flowing through the signal conductor 1s.

[0031] Furthermore, as shown in Fig. 4, the first region 11 may be in continuous contact with the second conductor layer 2. That is, the second groove 3b in which the first region 11 is located may penetrate from the first surface 31 to the second surface 32. Fig. 4 is an enlarged explanatory view for explaining still another embodiment of the region X shown in Fig. 1. Specifically, Fig. 4 is a perspective view of the region X shown in Fig. 1 seen from above, in which the reference numeral for the insulating layer 3 is indicated by a dashed line and the insulating layer 3 itself is not shown.

[0032] When the first region 11 is in continuous contact with the second conductor layer 2, the shielding effect of the ground conductor 1g is further improved with respect to signals flowing through the signal conductor 1s, and the operability of the electronic component 7 is improved by expanding the return current path.

[0033] In one wiring board 100, all of the first regions 11 may have the same shape or different shapes. That is, in one wiring board 100, for example, first regions 11 that are in continuous contact with the second conductor layer 2 as shown in Fig. 4 and first regions 11 that are in discontinuous contact with the second conductor layer 2 as shown in Fig. 3 may be mixed. Furthermore, as shown in Fig. 2, when the second groove 3b does not penetrate from the first surface 31 to the second surface 32, the second conductor layer 2 does not necessarily have to be located in the portion where the second groove 3b does not penetrate.

[0034] Next, one embodiment of a method for forming the first conductor layer 1 on the insulating layer 3 will be described with reference to Figures 5A to 5D. Figures 5A to 5D are explanatory views for explaining one embodiment of a method for forming the first conductor layer 1.

[0035] 5A, an insulating layer 3 is prepared. Although a second conductor layer 2 is located on the second surface 32 of the insulating layer 3, the second conductor layer 2 does not necessarily have to be located in a portion where the second groove 3b does not penetrate from the first surface 31 to the second surface 32.

[0036] 5B, first grooves 3a and second grooves 3b are formed in the insulating layer 3. The first grooves 3a and second grooves 3b are formed taking into consideration the arrangement of the signal conductors 1s and the ground conductors 1g. The first grooves 3a and second grooves 3b are formed by irradiating a laser such as an excimer laser, for example.

[0037] By adjusting the output or irradiation amount of the laser, the first groove 3a is formed so as not to penetrate from the first surface 31 to the second surface 32. In the second groove 3b, a portion corresponding to the first region 11 of the ground conductor 1g is formed deeper than the first groove 3a, and a portion corresponding to the second region 12 of the ground conductor 1g is formed shallower than the portion corresponding to the first region 11.

[0038] After forming the first groove 3a and the second groove 3b, the conductor 10 is formed as shown in FIG. 5C. The conductor 10 is formed on the entire surface of the insulating layer 3 so as to fill the first groove 3a and the second groove 3b. The conductor 10 may be formed, for example, of a base metal layer formed by electroless plating and an electroplated layer formed by electrolytic plating on the surface of the base metal layer. The conductor 10 corresponds to the first conductor layer 1. Therefore, as described above, the conductor 10 is not particularly limited as long as it is made of a conductive material. An example of the conductive material is a metal such as copper.

[0039] 5D, unnecessary portions of the surface of the conductor 10 and the surface of the insulating layer 3 are removed, and the signal conductor 1s is formed in the first groove 3a, and the ground conductor 1g is formed in the second groove 3b. The unnecessary portions of the surface of the conductor 10 and the surface of the insulating layer 3 are removed by polishing, for example, by chemical mechanical polishing (CMP).

[0040] Next, a mounting structure according to the present disclosure will be described with reference to Fig. 1. The mounting structure according to one embodiment includes a wiring board 100 according to one embodiment and an electronic component 7 located in a mounting area of ​​the wiring board 100.

[0041] FIG. 1 shows a state in which the wiring board 100 and the electronic component 7 are not connected. The mounting structure according to the present disclosure is obtained by connecting the first conductor layer 1 exposed through an opening in the solder resist 5 located on the surface of the build-up layer to the electrodes of the electronic component 7 via solder 6. As described above, examples of the electronic component 7 include semiconductor integrated circuit devices and optoelectronic devices. In the mounting structure according to one embodiment, the electronic components 7 may be located on both surfaces of the wiring board 100, or the electronic components 7 may be located on one surface and, for example, a motherboard may be located on the other surface.

[0042] Although the embodiments of the present disclosure have been described above, 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) and (5) below.

[0043] (1) A wiring board according to the present disclosure includes an insulating layer having a first surface and a second surface located on the opposite side to the first surface, first and second grooves recessed from the first surface toward the second surface, and a first conductor layer located in the first and second grooves. The first conductor layer has a signal conductor located in the first groove and a ground conductor located along the signal conductor and in the second groove. The ground conductor has a thickness that is greater than or equal to the thickness of the signal conductor at least in a first region along the signal conductor, and has a portion that is thinner than the thickness of the first region in a second region away from the first region.

[0044] The present disclosure further discloses the following embodiments (2) to (4).

[0045] (2) In the wiring board described in (1) above, a second conductor layer is further disposed on the second surface, and at least a portion of the first region of the ground conductor is in contact with the second conductor layer. (3) In the wiring board described in (2) above, the portions of the first region that contact the second conductor layer are located intermittently along the signal conductor, and the length of the gap between adjacent portions of the first region is 1 / 4 or less of the wavelength of the signal flowing through the signal conductor. (4) In the wiring board described in (2) above, the first region is in continuous contact with the second conductor layer.

[0046] (5) A mounting structure according to the present disclosure includes the wiring board according to any one of (1) to (4) above, and an electronic component mounted on the wiring board. [Explanation of symbols]

[0047] 1 First conductor layer 1s signal conductor 1g Ground conductor 11 First area 11a Gap 12 Second area 2 Second conductor layer 3. Insulation layer 31 Page 1 32 2nd page 3a 1st groove 3b 2nd groove 4 Core insulation layer 4a Core conductor layer 4b Through-hole conductor 5 Solder resist 6 Solder 7. Electronic Components 10 Conductors 100 wiring board Ts Signal conductor thickness T1 Thickness of the first section of the ground conductor T2 Thickness of the second region of the ground conductor H1: Length of the gap between parts of the first region 11

Claims

1. an insulating layer having a first surface and a second surface opposite the first surface; a first groove and a second groove recessed from the first surface toward the second surface; a first conductor layer located in the first groove and the second groove; Including, the first conductor layer has a signal conductor located in the first groove and a ground conductor located along the signal conductor and located in the second groove; The ground conductor has a thickness equal to or greater than the thickness of the signal conductor at least in a first region along the signal conductor, and has a portion in a second region away from the first region that is thinner than the thickness of the first region. Wiring board.

2. a second conductor layer is further located on the second surface; At least a portion of the first region of the ground conductor is in contact with the second conductor layer. The wiring board according to claim 1 .

3. 3. The wiring board according to claim 2, wherein the portions of the first region that contact the second conductor layer are located intermittently along the signal conductor, and the length of the gap between adjacent portions of the first region is 1 / 4 or less of the wavelength of the signal flowing through the signal conductor.

4. The wiring board according to claim 2 , wherein the first region is in continuous contact with the second conductor layer.

5. A mounting structure comprising the wiring board according to any one of claims 1 to 4 and an electronic component mounted on the wiring board.

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