Wiring boards and mounting structures

Abstract

The present invention provides a wiring board that enables efficient signal transmission even when there are differences in the wiring width and thickness of the wiring conductors embedded in the insulating layer. [Solution] The wiring board according to this disclosure includes a laminated structure having a structure in which a plurality of insulating layers and a plurality of conductor layers are alternately stacked. The insulating layer includes a first insulating layer having a first surface, a second surface located opposite to the first surface, and a groove recessed from the first surface toward the second surface. The groove includes a first region and a second region that is narrower and shallower than the first region. The conductor layer includes a first wiring conductor located in the groove. The first wiring conductor has a first portion located in the first region and a second portion located in the second region. In cross-sectional view, the thickness of the first portion is greater than the thickness of the second portion, and a third portion having an inclined portion is located from the bottom of the first portion toward the bottom of the second portion.

Description

Technical Field

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

[0002] Conventionally, as described in Patent Document 1, a wiring board in which a wiring conductor is embedded in a recess located on a surface of an insulating layer has been used. Prior Art Literature Patent Literature

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2004-149926 Disclosure of the Invention Problem to be Solved by the Invention

[0004] When the wiring conductor is relatively thin (for example, 5 µm or less), forming the wiring conductor in a groove provided in the insulating layer can stably increase the wiring density. However, when there is a difference in width and thickness between wires, impedance matching tends to be difficult, and as a result, signal transmission efficiency decreases.

[0005] An object of the present disclosure is to provide a wiring board that allows efficient signal transmission even when there is a difference in the wiring width and thickness of wiring conductors embedded in an insulating layer. Means for Solving the Problem

[0006] The wiring board according to this disclosure includes a laminated structure having a structure in which a plurality of insulating layers and a plurality of conductor layers are alternately stacked. The insulating layer includes a first insulating layer having a first surface, a second surface located opposite the first surface, and a groove recessed from the first surface toward the second surface. The groove includes a first region and a second region that is narrower and shallower than the first region. The conductor layer includes a first wiring conductor located in the groove. The first wiring conductor has a first portion located in the first region and a second portion located in the second region. In cross-sectional view, the thickness of the first portion is greater than the thickness of the second portion, and a third portion having an inclined portion is located from the bottom of the first portion toward the bottom of the second portion.

[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 the configuration described in the section on means for solving the problem, thereby enabling efficient signal transmission even when there are differences in the wiring width and thickness of the wiring conductors embedded in the insulating layer. [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 2 is an enlarged diagram illustrating the shape of the groove in region Y. [Figure 4] A perspective view showing an example of a first wiring conductor (the insulating layer is omitted). [Figure 5] A perspective view showing another example of the first wiring conductor (with the insulating layer omitted). [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 5, 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, 100 μm or more and 1.2 mm or less.

[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 50 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 layer located on both sides of the core insulating layer. The through-hole conductor may be integrally formed with the core conductor 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 alone, or two or more of them may be used in combination.

[0020] The build-up insulating layers may each 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, 10 µm or more and 50 µm or less. The build-up insulating layers may each 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 alone, 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 inorganic insulating filler may be used alone, or two or more inorganic insulating fillers may be used in combination.

[0022] Any one layer of the build-up insulating layer (insulating layer 2) is defined as a first insulating layer 21. One surface of the first insulating layer 21 is a first surface 21a, and the surface located on the opposite side to the first surface 21a is a second surface 21b. The first surface 21a is the surface farther from the core layer, and the second surface 21b is the surface closer to the core layer. The first insulating layer 21 has a groove 4 recessed from the first surface 21a toward the second surface 21b.

[0023] A build-up conductor layer, which is part of the conductor layer 3, is located in groove 4. The build-up conductor layer is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper. The build-up conductor layers may be made of the same metal or different metals. The build-up conductor layer and the core conductor layer may be made of the same metal or different metals.

[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, a solder resist 5 may be located on the surface of the laminated structure 1. The solder resist 5 is made of resin, such as an acrylic-modified epoxy resin. The solder resist 5 is provided with openings to electrically connect the conductive layer 3 located on the surface of the build-up layer to the electrodes of the electronic component 7 via solder 6. Examples of the electronic component 7 include semiconductor integrated circuit elements and optoelectronic elements.

[0026] The groove 4 located in the first insulating layer 21 includes a first region 41 and a second region 42, as shown in Figure 2. Figure 2 is an enlarged explanatory diagram illustrating one embodiment of region X shown in Figure 1. As shown in Figure 3, the second region 42 has a narrower width and shallower depth than the first region 41. Figure 3 is an enlarged explanatory diagram illustrating the shape of the groove 4 in region Y shown in Figure 2. Figure 3 is shown using a line drawing with only lines to make the shape of the groove 4 easier to understand.

[0027] As shown in Figure 3, the first region 41 of the groove 4 has a relatively wide width W1, for example, it may have a width W1 of 15 μm or more at its widest point, or it may have a width W1 of 20 μm or more and 100 μm or less. The depth D1 of the first region 41 is not limited. The first region 41 may have a depth D1 of, for example, 25% or more and 75% or less of the thickness of the first insulating layer 21. The width W1 is defined as, for example, the length of the first region 41 in a direction perpendicular to the extending direction of the second region 42, as shown in Figure 3. The depth D1 is defined as the length from the first surface 21a in the thickness direction of the first insulating layer 21 to the deepest part of the groove 4 of the first region 41.

[0028] As shown in Figure 3, the second region 42 of the groove 4 has a width W2 that is narrower than the first region 41, and its depth D2 is not limited as long as it is shallower than the depth D1. The second region 42 may have a width W2 of 7 μm or less at its widest point, or it may have a width W2 of 2 μm or more and 5 μm or less. The second region 42 may have a depth D2 of 20% to 70% of the thickness of the first insulating layer 21. The width W2 is defined as, for example, the length of the second region 42 in a direction perpendicular to the extension direction of the second region 42, as shown in Figure 3. The depth D2 is defined as the length from the first surface 21a in the thickness direction of the first insulating layer 21 to the deepest part of the groove 4 in the second region 42.

[0029] As shown in Figure 2, a portion of the conductor layer 3 includes a first wiring conductor 31 located in the groove 4. The first wiring conductor 31 includes a first portion 311 located in the first region 41 of the groove 4 and a second portion 312 located in the second region 42 of the groove 4. The width and thickness of the first portion 311 are approximately the same as the width W1 and depth D1 of the first region 41, and the width and thickness of the second portion 312 are approximately the same as the width W2 and depth D2 of the second region 42. That is, the first portion 311 may have a width of 15 μm or more, or a width of 20 μm or more and 100 μm or less, and a thickness of 25% or more and 75% or less of the thickness of the first insulating layer 21. The second portion 312 may have a width of 7 μm or less, or a width of 2 μm or more and 5 μm or less, and a thickness of 20% or more and 70% or less of the thickness of the first insulating layer 21.

[0030] In cross-sectional view, the first wiring conductor 31 has a third portion 313 with an inclined portion 31a extending from the bottom of the first portion 311 to the bottom of the second portion 312. In the groove 4, the first region 41 and the second region 42 are connected, and as shown in Figure 3, this connection is inclined rather than vertical. Therefore, in the first wiring conductor 31 located in the groove 4, the first portion 311 and the second portion 312 are integrally connected via the third portion 313 with the inclined portion 31a.

[0031] In the first wiring conductor 31, the third portion 313, which has a sloping portion 31a extending from the bottom of the first portion 311 to the bottom of the second portion 312, facilitates impedance matching between, for example, the first portion 311 and the second portion 312. As a result, signals are transmitted efficiently regardless of the wiring width of the first wiring conductor 31.

[0032] The angle of the inclined portion 31a is not limited to being perpendicular to the bottom of the first portion 311 and the bottom of the second portion 312. For example, the angle between the bottom of the first portion 311 and the inclined portion 31a may be between 110° and 150°.

[0033] In the first wiring conductor 31, the first portion 311, the second portion 312, and the third portion 313 may be separate components or have an integrated structure, as long as they can transmit signals. For example, if the first portion 311, the second portion 312, and the third portion 313 have an integrated structure, there are no connections between the first portion 311 and the third portion 313, or between the second portion 312 and the third portion 313. Therefore, cracks and other defects are less likely to occur in the first wiring conductor 31, and signals are transmitted more efficiently.

[0034] The first wiring conductor 31 may be a signal wiring conductor, a ground conductor, or a power supply conductor. Considering the effect of efficiently transmitting signals, the first wiring conductor 31 may be a signal wiring conductor. Furthermore, the first wiring conductor 31 may be a single wiring conductor as shown in Figure 4, or a differential wiring conductor as shown in Figure 5. Figure 4 is a perspective view showing an example of the first wiring conductor 31. Figure 5 is a perspective view showing another example of the first wiring conductor 31. In Figures 4 and 5, the insulating layer 2 is omitted.

[0035] As shown in Figure 2, the insulating layer 2 further includes a second insulating layer 22 located on the first surface 21a of the first insulating layer 21. The second insulating layer 22 includes a plurality of via-hole conductors 3V located in via-holes that penetrate the upper and lower surfaces of the second insulating layer 22. At least some of the via-hole conductors 3V are in contact with the first portion 311 on the first surface 21a side. In this way, the via-hole conductors 3V are in contact with the first portion 311 on the first surface 21a side, which is at the same height as the second portion 312, thereby enabling more efficient signal transmission.

[0036] A method for manufacturing such a wiring board 10 is shown. First, through holes are formed in the core insulating layer by drilling or laser. Then, for example, through-hole conductors and core conductor layers are formed by subtractive method.

[0037] Next, a predetermined number of build-up insulating layers and build-up conductor layers are alternately stacked. In the build-up insulating layer (first insulating layer 21), via holes and grooves 4 are formed, for example, by excimer laser processing, with the lower conductor layer 3 as the bottom surface. By using an excimer laser with a mask when irradiating with laser light, it becomes easier to form inclined portions 31a between the first region 41 and the second region 42 in the grooves 4. Then, plating metal is deposited in the via holes and grooves 4, for example, by a semi-additive method. Then, by chemical mechanical polishing, for example, excess plating metal is formed in the first insulating layer 21, and the first portion 311, second portion 312, and third portion 313 of the first wiring conductor 31 are formed in the grooves 4 to have an integrated structure.

[0038] Then, if necessary, solder resist 5 is formed on the top and bottom build-up insulating layers to form a wiring board 10 as shown in Figure 1.

[0039] 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.

[0040] Figure 1 shows a state in which the wiring board 10 and the electronic component 7 are not connected. By connecting the electronic component connection pad (part of the conductor layer 3) exposed from an opening in the solder resist 5 located on one surface of the wiring board 10 to the electrodes of the electronic component 7 via solder 6, a mounting structure 20 according to one embodiment is obtained. Examples of electronic components 7 include semiconductor integrated circuit elements and optoelectronic elements. In the mounting structure 20 according to one embodiment, electronic components 7 may also be connected via solder 6 to other pads (part of the conductor layer 3) exposed from openings in the solder resist 5 located on the other surface of the wiring board 10. Alternatively, a motherboard, for example, may be connected to other pads of the wiring board 10 via solder 6.

[0041] 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 (6) below.

[0042] (1) The wiring board according to the present disclosure includes a laminated structure having a structure in which a plurality of insulating layers and a plurality of conductor layers are alternately stacked. The insulating layer includes a first insulating layer having a first surface, a second surface located opposite to the first surface, and a groove recessed from the first surface toward the second surface. The groove includes a first region and a second region that is narrower and shallower than the first region. The conductor layer includes a first wiring conductor located in the groove. The first wiring conductor has a first portion located in the first region and a second portion located in the second region. In cross-sectional view, the thickness of the first portion is greater than the thickness of the second portion, and a third portion having an inclined portion is located from the bottom of the first portion toward the bottom of the second portion. (2) In the wiring board described in (1) above, the first wiring conductor has an integrated structure in the first part, the second part and the third part. (3) In the wiring board described in (1) or (2) above, the first portion has a wiring width of 15 μm or more, and the second portion has a wiring width of 7 μm or less. (4) In the wiring board described in any of (1) to (3) above, the insulating layer further includes a second insulating layer located on the first surface of the first insulating layer. The second insulating layer includes a plurality of via-hole conductors located in via-holes penetrating the upper and lower surfaces of the second insulating layer. At least some of the via-hole conductors are in contact with the first portion. (5) In the wiring board described in any of (1) to (4) above, the first wiring conductor is a signal wiring conductor. (6) The implementation structure relating to this disclosure includes a wiring board as described in any of (1) to (5) above, and an electronic component connected to the wiring board. [Explanation of Symbols]

[0043] 1. Laminated structure 2. Insulating layer 21 First insulating layer 21a 1st page 21b 2nd side 3 Conductor layers 31 First Wiring Conductor 311 Part 1 312 Part 2 313 Part 3 31a Slope 4 grooves 41 First area 42 Second area 5 Solder Resist 6 Handa 7 Electronic Components 10 Wiring board 20 Implementation Structures

Claims

1. The laminated structure includes a structure in which multiple insulating layers and multiple conductive layers are alternately stacked, The insulating layer includes a first surface, a second surface located opposite to the first surface, and a first insulating layer having a groove that is recessed from the first surface toward the second surface. The groove includes a first region and a second region that is narrower in width and shallower in depth than the first region. The conductor layer includes a first wiring conductor located in the groove, The first wiring conductor has a first portion located in the first region and a second portion located in the second region. In a cross-sectional view, the thickness of the first portion is greater than the thickness of the second portion, and a third portion having an inclined portion is located from the bottom of the first portion to the bottom of the second portion. Wiring board.

2. The wiring board according to claim 1, wherein the first wiring conductor has an integral structure in the first portion, the second portion and the third portion.

3. The wiring board according to claim 1, wherein the first portion has a wiring width of 15 μm or more, and the second portion has a wiring width of 7 μm or less.

4. The insulating layer further includes a second insulating layer located on the first surface of the first insulating layer. The second insulating layer includes a plurality of via-hole conductors located in via-holes that penetrate the upper and lower surfaces of the second insulating layer. At least some of the via-hole conductors are in contact with the first portion. The wiring board according to claim 1.

5. The wiring board according to claim 1, wherein the first wiring conductor is a signal wiring conductor.

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

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