Wiring board and mounting structure using the same

Abstract

To provide a wiring board that can reduce breaking in a through-hole conductor at a narrowest part of a through-hole and also reduce short circuit.SOLUTION: A wiring board includes: an insulating layer having a first surface and a second surface located opposite the first surface; a through-hole penetrating the first surface and the second surface of the insulating layer; and a through-hole conductor located at least in the through-hole. The through-hole has a narrowest portion where the inner diameter of the through-hole is smallest, and a widest portion where the inner diameter is largest. The through-hole conductor includes a first portion located on at least the inner wall surface of the through hole, and a second portion located to extend from the inner wall surface to the inside of the insulating layer. The second portion is located in the insulating layer adjacent to at least the narrowest portion in a sectional view in a penetration direction of the through-hole, and is located between a first virtual line and a second virtual line when the first virtual line is defined as a virtual line that passes through the narrowest portion of the inner wall surface and extends in parallel to a thickness direction of the insulating layer, and the second virtual line is defined as a virtual line that passes through the widest portion of the inner wall surface and extends in parallel to the thickness direction of the insulating layer.SELECTED DRAWING: Figure 2A

Description

[Technical field]

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

[0002] At least one through hole is formed in the insulating layer of the wiring board to electrically connect the upper surface side and the lower surface side of the wiring board. When viewed in cross section in the depth direction, the through hole may have a constricted shape and include a wide portion and a narrow portion, depending on the formation method, as described in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-213296 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0004] When a through-hole has a constricted shape, stress tends to concentrate in the narrow portion, which makes the through-hole conductor more susceptible to breakage in the narrow portion.

[0005] An object of the present disclosure is to provide a wiring board that can reduce breakage of through-hole conductors in the narrowest parts of the through-holes where stress is likely to concentrate, and also reduce the risk of short circuits. [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, a through hole penetrating the insulating layer from the first surface to the second surface, and at least a through hole conductor located in the through hole. The through hole has a narrowest portion where the inner diameter of the through hole is the narrowest, and a widest portion where the inner diameter is the widest. The through hole conductor includes at least a first portion located on the inner wall surface of the through hole, and a second portion located from the inner wall surface to within the insulating layer. The second portion is located in the insulating layer adjacent to at least the narrowest portion in a cross-sectional view in the penetration direction of the through hole, and is located between the first virtual line and the second virtual line when the first virtual line is defined as a virtual line that passes through the narrowest portion of the inner wall surface and extends parallel to the thickness direction of the insulating layer, and the second virtual line is defined as a virtual line that passes through the widest portion of the inner wall surface and extends parallel to the thickness direction of the insulating layer.

[0007] A mounting structure according to the present disclosure includes the above-mentioned wiring board and an electronic component located in a mounting area of ​​the wiring board. Effect of the Invention

[0008] By having a configuration as described in the section on means for solving the problems, the wiring board of the present disclosure can reduce breakage of the through-hole conductor at the narrowest part of the through-hole where stress is likely to concentrate, and can also reduce the risk of short circuits. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is an explanatory diagram for explaining a wiring board according to an embodiment of the present disclosure. [Diagram 2] 2A is an enlarged explanatory diagram for explaining region X shown in FIG. 1, FIG. 2B is a planar perspective view of region A shown in FIG. 2A as viewed from the direction of arrow A, and FIG. 2C is an explanatory diagram showing another embodiment. [Diagram 3] 3A to 3H are explanatory views for explaining one embodiment of a method for forming a through-hole conductor located in region X shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A wiring board according to an embodiment of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is an explanatory diagram for explaining a wiring board 1 according to an embodiment of the present disclosure. As shown in Figure 1, the wiring board 1 according to the embodiment includes an insulating layer 21, a build-up insulating layer 22, a conductor layer 3, and a solder resist 4.

[0011] The insulating layer 21 has a first surface 211 and a second surface 212 located on the opposite side to the first surface 211. The insulating layer 21 is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include insulating resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. Two or more of these insulating resins may be mixed for use. The thickness of the insulating layer 21 is not particularly limited. The insulating layer 21 may have a thickness of, for example, 30 μm or more and 400 μm or less.

[0012] The insulating layer 21 may function as, for example, an insulating layer for a core in the wiring board 1. When the insulating layer 21 functions as a core, it may contain a reinforcing material to improve rigidity. Examples of the reinforcing material include insulating cloth materials such as glass fiber, glass nonwoven fabric, aramid fiber, aramid nonwoven fabric, and polyester fiber. Two or more types of reinforcing materials may be used in combination. Furthermore, the insulating layer 21 may have inorganic insulating fillers dispersed therein, such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide.

[0013] A build-up layer in which conductor layers 3 and build-up insulating layers 22 are alternately laminated is located on the first surface 211 and the second surface 212 of the insulating layer 21. The build-up insulating layers 22 are not particularly limited as long as they are made of an insulating material, similar to the insulating layer 21. As with the insulating layer 21, examples of insulating materials include insulating resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. Two or more of these insulating resins may be mixed together.

[0014] The build-up insulating layers 22 may each be made of the same insulating resin or different insulating resins. The build-up insulating layers 22 and the insulating layers 21 constituting the build-up layer may each be made of the same insulating resin or different insulating resins. The thickness of the build-up insulating layers 22 is not particularly limited. The build-up insulating layers 22 may have a thickness of, for example, 5 μm or more and 40 μm or less. The build-up insulating layers 22 may each be made of the same thickness or different thicknesses.

[0015] The build-up insulating layer 22 may contain a reinforcing material, similar to the insulating layer 21. Examples of the reinforcing material include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid fiber, aramid nonwoven fabric, and polyester fiber. Two or more types of reinforcing materials may be used in combination. Furthermore, the build-up insulating layer 22 may contain inorganic insulating fillers, such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide, dispersed therein, similar to the insulating layer 21.

[0016] The conductor layer 3 is not limited as long as it is a conductor such as a metal. The conductor layer 3 is formed of a metal such as copper. The thickness of the conductor layer 3 is not particularly limited, and is, for example, 3 μm or more and 20 μm or less. The conductor layer 3 includes a power conductor, a ground conductor, and a signal conductor.

[0017] A via-hole conductor 3a for electrically connecting the upper and lower surfaces of the build-up insulating layer 22 is located in the build-up insulating layer 22. The via-hole conductor 3a is located in a via hole formed to penetrate the build-up insulating layer 22. The via-hole conductor 3a is a part of the conductor layer 3 and is formed of a metal such as copper.

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

[0019] A through-hole conductor 2a is located in the insulating layer 21 to electrically connect the upper and lower surfaces of the insulating layer 21. The through-hole conductor 2a is located in a through-hole 23 that penetrates from the first surface 211 to the second surface 212 of the insulating layer 21. The through-hole conductor 2a is formed by, for example, metal plating such as copper plating.

[0020] As shown in Fig. 2A, through-hole conductor 2a is located only on the inner wall surface of through-hole 23. Fig. 2A is an enlarged explanatory view for illustrating region X shown in Fig. 1. In through-hole 23, resin 2b is located in addition to through-hole conductor 2a. Resin 2b is located so as to be surrounded by through-hole conductor 2a. Resin 2b is a filling resin that fills the space surrounded by through-hole conductor 2a.

[0021] Resin 2b is not limited, and examples thereof include insulating resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin, as in insulating layer 21. Two or more of these insulating resins may be mixed. Although wiring board 1 is filled with resin 2b, through-hole conductor 2a may be filled in through-hole 23 instead of resin 2b.

[0022] Through hole 23 does not have the same inner diameter from first surface 211 to second surface 212. As shown in Fig. 2A, through hole 23 has narrowest portion 231 where the inner diameter is the narrowest and widest portion 232 where the inner diameter is the widest.

[0023] When through-hole 23 is viewed in cross section in the penetration direction, narrowest portion 231 may be located closer to first surface 211 or second surface 212 than the halfway position of insulating layer 21 in the thickness direction. For example, as shown in FIG. 2A, in wiring board 1, narrowest portion 231 is located closer to second surface 212 than the halfway position of insulating layer 21 in the thickness direction. In FIG. 2A, the halfway position of insulating layer 21 is indicated by line L3. When a high-density mounting region of semiconductor elements is located on the first surface 211 side, it is advantageous in terms of easily obtaining a stress relaxation effect by positioning narrowest portion 231 on the first surface 211 side where stress is likely to concentrate.

[0024] Through-hole conductor 2a includes first portion 2a1 located on the inner wall surface of through-hole 23, and second portion 2a2 located from the inner wall surface of through-hole 23 to within insulating layer 21. It is sufficient that first portion 2a1 is located at least on the inner wall surface of through-hole 23, and through-hole conductor 2a located so as to fill through-hole 23 also corresponds to first portion 2a1.

[0025] As shown in FIG. 2A, the second portion 2a2 is located at least in the insulating layer 21 adjacent to the narrowest portion 231 in a cross-sectional view in the penetration direction of the through-hole 23. When the second portion 2a2 is located in the insulating layer 21 adjacent to the narrowest portion 231, the breakage of the through-hole conductor 2a is reduced. Specifically, when the second portion 2a2 exists, the adhesion of the through-hole conductor 2a is improved in the narrowest portion 231 where stress is likely to concentrate. As a result, the breakage of the through-hole conductor 2a is reduced. The cross-sectional view in the penetration direction may be a cross-sectional view passing through the center of the through-hole 23. For example, if the opening of the through-hole 23 is circular in a plan view, the center of the through-hole 23 can be defined as a cross-section passing through the center of the circle, and if the opening is rectangular, the center of the through-hole 23 can be defined as a cross-section passing through the intersection of the diagonals of the rectangle.

[0026] As shown in FIG. 2B, the second portions 2a2 may be located intermittently on the periphery of the through-hole 23 in a planar perspective view. FIG. 2B is a planar perspective view of the region A shown in FIG. 2A as viewed from the direction of the arrow A. The second portions 2a2 may be arranged at equal intervals, for example, or may have the same length. When the second portions 2a2 are located intermittently on the periphery of the through-hole 23, the adhesion of the through-hole conductor 2a is further improved. As a result, breakage of the through-hole conductor 2a is further reduced.

[0027] 2A, the second portion 2a2 is located between the first virtual line L1 and the second virtual line L2 in a cross-sectional view in the penetration direction of the through hole 23. Since the second portion 2a2 is located between the first virtual line L1 and the second virtual line L2, the shortest distance H2 between adjacent second portions 2a2 is not smaller than the shortest wall-to-wall distance H1 between adjacent through holes 23. Thus, by setting the shortest wall-to-wall distance H1 between adjacent through holes 23 to a predetermined value, the shortest distance H2 between adjacent second portions 2a2 can be sufficiently secured, thereby reducing the risk of a short circuit.

[0028] 2A , first virtual line L1 refers to a virtual line that passes through narrowest part 231 of the inner wall surface of through hole 23 and extends parallel to the thickness direction of insulating layer 21. The thickness direction of insulating layer 21 can be defined as, for example, a direction perpendicular to at least one of first surface 211 or second surface 212 of insulating layer 21. Second virtual line L2 refers to a virtual line that passes through widest part 232 of the inner wall surface of through hole 23 and extends parallel to the thickness direction of insulating layer 21.

[0029] When the insulating layer 21 is formed of an insulating resin as described above and contains glass fiber as a reinforcing material, the second portion 2a2 may be located at least in one of the following locations: in the glass fiber, between the glass fiber and the insulating resin, and in the insulating resin. When the second portion 2a2 is located in the glass fiber, the second portion 2a2 is firmly fixed to the glass fiber, which is advantageous for improving the connectivity between the through-hole conductor 2a and the insulating layer 21. Furthermore, the shape of the through-hole 23 in the cross-sectional view in the penetration direction may be a shape as shown in FIG. 2C. In the shape shown in FIG. 2C, the narrowest portion 231' is located between the line L3 indicating the half-way position of the thickness of the insulating layer 21 and the second surface 212 of the insulating layer 21. The first virtual line L1', the second virtual line L2', and the widest portion 232' shown in FIG. 2C correspond to the first virtual line L1, the second virtual line L2, and the widest portion 232 described above, respectively, and detailed description thereof will be omitted.

[0030] Next, one embodiment of a method for forming a through-hole conductor 2a in an insulating layer 21 will be described with reference to Fig. 3A to Fig. 3H. Fig. 3A to Fig. 3H are explanatory diagrams for explaining one embodiment of a method for forming a through-hole conductor 2a located in region X shown in Fig. 1.

[0031] First, as shown in Fig. 3A, recesses 23' are formed in insulating layer 21. Specifically, after first surface 211 of insulating layer 21 is covered with resist 6, recesses 23' are formed, for example, by blasting. Examples of resist 6 include dry film resist. The size and number of recesses 23' will be the size and number of through holes 23 that will be finally formed, and are appropriately set depending on the size of wiring board 1, etc.

[0032] Next, as shown in FIG. 3B, the recess 23' is penetrated from the first surface 211 to the second surface 212 of the insulating layer 21 to form the through hole 23. Specifically, the resist 6 is removed, the recess 23' is irradiated with a laser, and the recess 23' is penetrated from the first surface 211 to the second surface 212 of the insulating layer 21 to form the through hole 23. In order to remove the resin residue, etc., a desmearing process is performed as necessary. The inner diameter of the through hole 23 is not uniform, and there are parts with narrow inner diameters and parts with wide inner diameters. As shown in FIG. 2A, the part with the narrowest inner diameter is the narrowest part 231, and the part with the widest inner diameter is the widest part 232. The inner diameter of the through hole 23 can be measured, for example, by a hole analyzer, X-ray observation, ultrasonic observation, or cross-sectional observation.

[0033] In the through-hole 23, a gap 23a is formed from the inner wall surface of the through-hole 23 to the inside of the insulating layer 21. The gap 23a is formed mainly during laser processing, particularly in the vicinity of the narrowest part 231 of the through-hole 23. When the insulating layer 21 contains glass fiber as a reinforcing material, the gap 23a is also formed in the glass fiber.

[0034] 3C, a seed layer 31 is formed on the first surface 211 and the second surface 212 of the insulating layer 21 and the inner wall surface of the through hole 23. The formation of the seed layer 31 allows metal to be efficiently deposited by electrolytic plating. The seed layer 31 is formed of a metal such as copper by, for example, electroless plating. The seed layer 31 is also formed in the above-mentioned gap 23a.

[0035] 3D, a portion of the seed layer 31 formed on the first surface 211 and the second surface 212 of the insulating layer 21 is covered with a resist 6. The resist 6 is as described above, and a detailed description thereof will be omitted. The resist 6 has an opening at a position where the conductor layer 3 is to be formed.

[0036] 3E, an electrolytic plating layer 32 is formed on the surface of the seed layer 31. Specifically, the electrolytic plating layer 32 is formed in the openings of the resist 6. The electrolytic plating layer 32 is formed, for example, by precipitating a metal such as copper by electrolytic plating. The precipitated portion of the electrolytic plating layer 32 corresponds to the conductor layer 3. The electrolytic plating layer 32 is also formed in the gaps 23a described above.

[0037] Next, as shown in Fig. 3F, the resist 6 is removed. After the resist 6 is removed, the seed layer 31 covered with the resist 6 is removed as shown in Fig. 3G. The method for removing the seed layer 31 is not limited, and examples thereof include an etching process such as flash etching.

[0038] 3H, build-up insulating layer 22 is laminated so as to cover first surface 211 and second surface 212 of insulating layer 21 and conductor layer 3 formed on first surface 211 and second surface 212. Build-up insulating layer 22 is as described above, and a detailed description thereof will be omitted.

[0039] When the build-up insulating layer 22 is laminated, a part of the resin forming the build-up insulating layer 22 is filled into the through-hole 23. This filled resin corresponds to the resin 2b. The resin 2b may be filled before the build-up insulating layer 22 is laminated. In this case, the resin may be the same as the resin forming the build-up insulating layer 22, or may be a different resin. The resin 2b is as described above, and a detailed description is omitted. When it is desired to connect the via-hole conductor 3a in series to the through-hole conductor 2a, a cap plating may be formed on the resin 2b, or the through-hole conductor 2a may be filled into the through-hole 23 instead of the resin 2b.

[0040] In this manner, the through-hole conductor 2a is formed in the insulating layer 21.

[0041] The mounting structure according to the present disclosure includes a wiring board 1 according to one embodiment and an electronic component S located on the surface of the wiring board 1. A conductor layer 3 in an opening of a solder resist 4 and an electrode of the electronic component S are connected via solder 5. As described above, examples of the electronic component S include a semiconductor integrated circuit element and an optoelectronic element. In the mounting structure according to the present disclosure, the electronic component S may be located on both sides of the wiring board 1, or the electronic component S may be located on one surface and, for example, a motherboard may be located on the other surface.

[0042] The embodiments of the present disclosure have been described above. However, 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, a through hole penetrating the insulating layer from the first surface to the second surface, and at least a through hole conductor located in the through hole. The through hole has a narrowest portion where the inner diameter of the through hole is the narrowest, and a widest portion where the inner diameter is the widest. The through hole conductor includes at least a first portion located on an inner wall surface of the through hole, and a second portion located from the inner wall surface to within the insulating layer. The second portion is located in the insulating layer adjacent to at least the narrowest portion in a cross-sectional view in the penetration direction of the through hole, and is located between the first virtual line and the second virtual line when the first virtual line is defined as a virtual line that passes through the narrowest portion of the inner wall surface and extends parallel to the thickness direction of the insulating layer, and the second virtual line is defined as a virtual line that passes through the widest portion of the inner wall surface and extends parallel to the thickness direction of the insulating layer.

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

[0045] (2) In the wiring board according to (1) above, the second portion is located discontinuously on the periphery of the through hole in a planar perspective view. (3) In the wiring board described in (1) or (2) above, when viewed in cross-section in the direction of penetration of the through hole, the narrowest part is located closer to the first surface or the second surface than the position halfway through the thickness of the insulating layer. (4) In the wiring board described in any one of (1) to (3) above, the insulating layer contains glass fibers and insulating resin, and the second portion is located in at least one of the following locations: within the glass fibers, between the glass fibers and the insulating resin, and within the insulating resin.

[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 located in a mounting area of ​​the wiring board. [Explanation of symbols]

[0047] 1. Wiring board 21 Insulating layer 211 Page 1 212 2nd page 22 Build-up insulation layer 23 Through Hole 231, 231' narrowest part 232, 232' widest part 23' Recess 23a Gap 2a through hole conductor 2a1 Part 1 2a2 2nd part 2b resin 3 Conductor Layer 3a Via hole conductor 31 Seed Layer 32 Electrolytic plating layer 4 Solder resist 5 Solder 6. Resist

Claims

1. an insulating layer having a first surface and a second surface opposite the first surface; a through hole penetrating the insulating layer from the first surface to the second surface; a through-hole conductor located at least in the through-hole; Including, the through hole has a narrowest portion where the inside diameter of the through hole is the narrowest, and a widest portion where the inside diameter of the through hole is the widest, the through-hole conductor includes at least a first portion located on an inner wall surface of the through-hole and a second portion located from the inner wall surface to within the insulating layer; the second portion is located at least in the insulating layer adjacent to the narrowest portion in a cross-sectional view in the penetration direction of the through hole, and is located between the first virtual line and the second virtual line when a first virtual line is defined as a virtual line that passes through the narrowest portion of the inner wall surface and extends parallel to the thickness direction of the insulating layer, and a second virtual line is defined as a virtual line that passes through the widest portion of the inner wall surface and extends parallel to the thickness direction of the insulating layer. Wiring board.

2. The wiring board according to claim 1 , wherein the second portion is located intermittently around the periphery of the through hole in a plan view.

3. The wiring board according to claim 1 , wherein when the through hole is viewed in cross section in the penetrating direction, the narrowest portion is located closer to the first surface or the second surface than a position halfway through the thickness of the insulating layer.

4. the insulating layer includes glass fiber and an insulating resin; The wiring board according to claim 1 , wherein the second portion is located at least in one of the following locations: within the glass fiber, between the glass fiber and the insulating resin, and within the insulating resin.

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

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