printed wiring board

Abstract

A printed wiring board according to one aspect of the present disclosure is provided with: a substrate that has a penetrating hole; a land section that is disposed on an inner peripheral surface of the penetrating hole and on a surface of the substrate at a peripheral edge of the penetrating hole, and that has a through-hole conductor section; and wiring that is disposed on the surface of the substrate, one longitudinal end section of the wiring being electrically connected to the land section. The maximum length of the connecting portion of the wiring and the land section is at least the sum of the maximum diameter of the penetrating hole and the minimum wire width of the wiring.

Description

[Technical Field]

[0001] This disclosure relates to a printed wiring board. This application claims priority to Japanese Patent Application No. 2020-097435, filed on June 4, 2020, and the entire contents of the above-mentioned Japanese application are incorporated herein by reference. [Background technology]

[0002] Patent Document 1 describes a printed wiring board comprising a substrate, a through hole penetrating the substrate, a land portion disposed on the surface of the substrate and having a through-hole conductor portion, and wiring disposed on the surface of the substrate and having one longitudinal end electrically connected to the land portion (see JP 2011-146427 A). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-146427 Summary of the Invention

[0004] A printed wiring board according to one aspect of the present disclosure comprises a substrate having a through hole, a land portion having a through-hole conductor portion and arranged on the inner surface of the through hole and on the periphery of the through hole on the surface of the substrate, and wiring arranged on the surface of the substrate and having one longitudinal end electrically connected to the land portion, wherein the maximum length of the connection portion between the wiring and the land portion is equal to or greater than the sum of the maximum diameter of the through hole and the minimum line width of the wiring. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic plan view showing a printed wiring board according to a first embodiment. [Figure 2] FIG. 2 is a schematic end view showing the printed wiring board of FIG. 1, taken along the direction of the arrow AA in FIG. [Figure 3]FIG. 3 is a schematic plan view showing a printed wiring board according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] 2. Description of the Related Art Printed wiring boards are widely used to form circuits in various electronic devices. In recent years, as electronic devices have become smaller, printed wiring boards have become smaller and their wiring density has increased significantly.

[0007] As such a printed wiring board, for example, the printed wiring board described in Patent Document 1 mentioned above has been proposed.

[0008] [Problem to be solved by this disclosure] However, the above-described printed wiring boards are susceptible to shrinkage and warping of the substrate during manufacturing, which can lead to misalignment when forming through holes for the through-hole conductors. Such misalignment can lead to seat breaks. Even when seat breaks do not occur, the misalignment can lead to a reduction in the dimensions of the through-hole conductors. When stress is concentrated on the reduced-sized through-hole conductors due to handling or other reasons, microcracks can develop, potentially resulting in poor electrical continuity.

[0009] Therefore, an object of the present invention is to provide a printed wiring board in which poor conduction is suppressed.

[0010] [Effects of this disclosure] In a printed wiring board according to one aspect of the present disclosure, poor electrical conduction is suppressed.

[0011] [Description of the embodiments of the present disclosure] A printed wiring board according to one aspect of the present disclosure comprises a substrate having a through hole, a land portion having a through-hole conductor portion and arranged on the inner surface of the through hole and on the periphery of the through hole on the surface of the substrate, and wiring arranged on the surface of the substrate and having one longitudinal end electrically connected to the land portion, wherein the maximum length of the connection portion between the wiring and the land portion is equal to or greater than the sum of the maximum diameter of the through hole and the minimum line width of the wiring.

[0012] The present inventors have conducted extensive research and have found the following. Specifically, when manufacturing a printed wiring board using a subtractive method, first, a through hole for a through-hole conductor is formed in a substrate, and then a conductive base layer is plated on the inner surface of the through hole, the periphery of the through hole in the substrate, and other areas. Next, a plating layer for a land having a through-hole conductor and wiring is plated on this conductive base layer. Next, the areas of the plating layer for forming the land and wiring are masked with a resist pattern. Then, using this resist pattern as a mask, the plating layer is removed by etching using an etching solution, etc. That is, the plating layer and conductive base layer located in the openings of the resist pattern are removed. This forms the land and wiring. The positions where the resist pattern is formed are predetermined.

[0013] In this subtractive method, if the through-hole formation position deviates from the specified design position, the area masked by the resist pattern also deviates. This misalignment may cause the etchant to penetrate the inner surface of the through-hole conductor during etching. Because the etchant can remove the plating layer and the conductive base layer, the etchant that penetrates into the through-hole conductor will remove the through-hole conductor. Thus, in the subtractive method, if the through-hole formation position for the through-hole conductor deviates from the specified design position, the through-hole conductor is removed, which may result in a conduction failure, such as a disconnection, in the through-hole conductor. In addition, if the through-hole penetrates a region that will be the connection between the land and the wiring, or a region that will be part of the wiring, the conduction failure in the through-hole conductor may also result in a conduction failure in these connections or the wiring.

[0014] On the other hand, when manufacturing a printed wiring board using a semi-additive method, as with the subtractive method, first, through holes for through-hole conductors are formed in a substrate, and then a conductive base layer is plated on the substrate and the inner surfaces of the through holes. Next, a resist pattern for forming through-hole conductors, lands, and wiring is formed on the conductive base layer. Then, a plating layer for lands having through-hole conductors and wiring is plated in the openings of the resist pattern on the conductive base layer. That is, a plating layer is formed in the openings of the resist pattern. Next, the resist pattern is removed, and the conductive base layer is removed by etching using an etching solution using the plating layer as a mask. This forms lands having through-hole conductors and wiring. The position where the resist pattern is formed is predetermined.

[0015] Even with this semi-additive method, if the through-hole formation position deviates from the specified design position, the area masked by the resist pattern will also deviate. However, even if such misalignment occurs, as long as the misalignment is sufficient to allow the plating liquid to penetrate the through-hole (i.e., the through-hole formation position is not completely off-center), the plating liquid can flow into the conductive base layer in the through-hole, making it possible to form a plating layer on the conductive base layer inside the through-hole. Thus, with the semi-additive method, even if the formation position of the through-hole for the through-hole conductor is misaligned, poor conductivity in the through-hole conductor is unlikely to occur. Furthermore, even if the through-hole penetrates an area that will be the connection between the land portion and the wiring, or an area that will be part of the wiring, conductivity between the connection and part of the wiring can be ensured via the through-hole conductor.

[0016] Furthermore, if the position of the through hole is completely off (does not overlap) from the specified design position, it will be difficult to leave or form the through-hole conductor portion, whether using the subtractive method or the semi-additive method, and conductivity cannot be ensured.

[0017] As described above, by manufacturing a printed wiring board using the semi-additive method instead of the subtractive method, it is possible to reduce the occurrence of poor continuity in the through-hole conductors, even if the through-holes are misaligned, as long as the positions of the through-holes coincide with the specified design positions. Furthermore, even if a through-hole penetrates a connection between a land portion and a wiring or penetrates part of the wiring, causing the connection and the wiring to be severed, it is possible to ensure continuity between the connection and part of the wiring via the through-hole conductors.

[0018] However, since the conduction between the connection portion and part of the wiring via the through-hole conductor portion is unstable, it is preferable that the area of ​​the connection portion and the wiring that is penetrated by the through hole is small.

[0019] Therefore, the inventors conducted further intensive research and found that by making the maximum length of the connection portion between the wiring and the land portion in a planar view (i.e., the distance between the intersection points (two intersection points) of the land portion and the two outermost side edges of the wiring) equal to or greater than the sum of the maximum diameter of the inner surface of the through hole in the substrate and the minimum line width of the wiring, even if the positional misalignment of the through hole is relatively large, the extent to which the through hole penetrates the area that becomes the connection portion and the extent to which it penetrates the wiring can be reduced, thereby suppressing poor conductivity.

[0020] In this way, by having the maximum length of the connection portion within the above range, poor conductivity of the printed wiring board can be suppressed even if the formation position of the through hole for the through-hole conductor portion is shifted.

[0021] The one end of the wiring may have a plurality of branched portions, and the maximum length of the connection portion may be the distance between the two intersections of the two outermost edges of the plurality of branched portions in the width direction and the land portion.

[0022] In this way, by having the plurality of branched portions at the one end of the wiring, even if the through hole is misaligned, poor conduction can be more reliably suppressed.

[0023] Here, "the maximum length of the connection portion" refers to the length between the two intersections of the two outermost edges of the wiring and the land portion. Specifically, if the end of the wiring on the land portion side is not branched, "the maximum length of the connection portion" corresponds to the entire length of the connection portion between the wiring and the land portion. If the end of the wiring on the land portion side is branched, "the maximum length of the connection portion" corresponds to the length of the connection portion including the spacing between the branch portions, i.e., the length between the outermost intersections of the connection portion between the branch portions and the land portion. "The maximum diameter of the through hole" refers to the largest diameter of the inner surface of the through hole. "Width" refers to the dimension of the wiring in the direction perpendicular to the longitudinal direction, and "minimum width" refers to the smallest width of the wiring in the longitudinal direction.

[0024] [Details of the embodiments of the present disclosure] Hereinafter, an embodiment of a printed wiring board according to the present disclosure will be described in detail with reference to the drawings. In this embodiment, the "surface" refers to the surface on which wiring is arranged in the thickness direction of the board, and the front and back of this embodiment do not determine the front and back of the printed wiring board when in use.

[0025] [First embodiment] [Printed wiring board] 1 and 2, a printed wiring board 1 of this embodiment includes a base film 3 as a substrate having a through hole 5, a first land portion 20 having a through-hole conductor portion 30 and disposed on the inner surface of the through hole 5 and on the periphery of the through hole 5 on the surface 3a of the base film 3, and a first wiring 11 disposed on the surface 3a of the base film 3 and having one longitudinal end electrically connected to the land portion 20. The printed wiring board 1 also includes a second land portion 21 disposed on the inner surface of the through hole 5 and on the back surface 3b of the base film 3 and sharing the through-hole conductor portion 30 with the first land portion 20, and a second wiring 13 disposed on the back surface 3b of the base film 3 and having one longitudinal end electrically connected to the second land portion 21.

[0026] (base film) The base film 3 is a layer made of an insulating synthetic resin. The base film 3 is a substrate for forming the first wiring 11 and the second wiring 13. The base film 3 may be flexible. The material for forming the base film 3 is not particularly limited as long as it has insulating properties, and for example, a low-dielectric-constant synthetic resin film formed in a sheet shape can be used. Examples of the main component of this synthetic resin film include polyimide, polyethylene terephthalate, liquid crystal polymer, and fluororesin. The "main component" refers to the component with the highest content, and for example, a component that accounts for 50% by mass or more of the forming material. The base film 3 may contain other resins besides the exemplified resins such as polyimide, an antistatic agent, etc.

[0027] The lower limit of the average thickness of the base film 3 is not particularly limited, but is preferably 5 μm, more preferably 10 μm. The upper limit of the average thickness of the base film 3 is not particularly limited, but is preferably 200 μm, more preferably 150 μm, even more preferably 100 μm, and particularly preferably 50 μm. If the average thickness of the base film 3 is below the lower limit, the insulating strength and mechanical strength of the base film 3 may be insufficient. On the other hand, if the average thickness of the base film 3 exceeds the upper limit, the printed wiring board 1 may be unnecessarily thick. Here, the "average thickness" of the base film 3 means the average value of thicknesses measured at any ten points.

[0028] The maximum diameter R of the through hole 5 is not particularly limited, and can be set appropriately so that the maximum length D described later satisfies a relationship equal to or greater than the sum of this maximum diameter R and the minimum line width Wa of the first wiring 11 described later.

[0029] (First Land Section) The first land portion 20 is disposed on the inner circumferential surface of the through hole 5 in the base film 3 and on the periphery of the through hole 5 on the surface 3a of the base film 3, and has a through-hole conductor portion 30. The first land portion 20 is formed from the same type of metal so that the through-hole conductor portion 30 and the portions other than the through-hole conductor portion 30 are integrated.

[0030] For example, the first land portion 20 is formed by a conductive base layer disposed on the through-hole 5 and the surface 3a of the base film 3, and a plating layer disposed on the conductive base layer.

[0031] Examples of materials for forming the conductive underlayer include copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), alloys of these, and stainless steel.

[0032] For example, the lower limit of the average thickness of the conductive underlayer is preferably 10 nm. The upper limit of the average thickness of the conductive underlayer is preferably 12,500 nm. If the average thickness of the conductive underlayer is less than the lower limit, the adhesion of the plating layer formed on the conductive underlayer to the conductive underlayer may be insufficient. On the other hand, if the average thickness of the conductive underlayer exceeds the upper limit, after forming a plating layer on the conductive underlayer, when removing the conductive underlayer using the plating layer as a mask, the conductive underlayer may not be sufficiently removed, resulting in a short circuit between adjacent wirings. The "average thickness" of the conductive underlayer refers to the average value of thicknesses measured at any ten points.

[0033] Examples of metal materials for forming the plating layer include copper, aluminum, silver, gold, nickel, alloys thereof, etc. Among these, copper or copper alloys are preferred from the viewpoints of improving conductivity and reducing costs.

[0034] The average thickness of the plating layer can be appropriately set in consideration of the average thickness of the conductive base layer so that the average thickness of the first land portion 20 falls within the range described below.

[0035] The through-hole conductor portion 30 penetrates the base film 3 and is electrically connected to the second land portion 21.

[0036] The inner diameter and shape of the through-hole conductor portion 30 can be set appropriately depending on the inner diameter and shape of the through hole 5. For example, the lower limit of the average thickness of the through-hole conductor portion 30 from the inner peripheral surface of the through hole 5 is preferably 5 μm. If the average thickness is less than the lower limit, there may be areas in the through-hole conductor portion 30 where the conductor (conductive base layer and plating layer) is not present, which may result in poor conductivity. On the other hand, the upper limit of the average thickness of the through-hole conductor portion 30 is less than the radius of the through hole 5.

[0037] The average thickness of the portion of the first land portion 20 other than the through-hole conductor portion 30 (hereinafter also referred to as the "flat portion") is not particularly limited and can be set appropriately. For example, the lower limit of the average thickness of the flat portion of the first land portion 20 is preferably 5 μm. The upper limit of the average thickness of the flat portion of the first land portion 20 is preferably 100 μm. If the average thickness of the flat portion of the first land portion 20 is less than the above-mentioned lower limit, there may be areas in the flat portion of the first land portion 20 where no conductor (conductive base layer and plating layer) is present, which may result in poor conductivity. On the other hand, if the average thickness of the flat portion of the first land portion 20 exceeds the above-mentioned upper limit, it may take a long time to form the plating layer, which may lead to increased costs.

[0038] The shape of the first land portion 20 in a plan view is not particularly limited and can be set as appropriate. The dimensions of the first land portion 20 in a plan view are not particularly limited and can be set as appropriate depending on the size of the through hole 5, etc.

[0039] (1st wiring) The first wiring 11 is disposed on the surface 3a of the base film 3, and one longitudinal end 11a thereof is electrically connected to the first land portion 20. The first wiring 11 is disposed on the surface 3a of the base film 3 directly or via another layer. Examples of the first wiring 11 include a signal line for transmitting a signal, a current line for transmitting a current for power supply, and a current line for transmitting a current for generating a magnetic field.

[0040] The first wiring 11 is formed by a conductive underlayer disposed on the surface 3a of the base film 3 and a plating layer disposed on the conductive underlayer.

[0041] The lower limit of the average line width of the first wiring 11 is preferably 10 μm, more preferably 15 μm, and even more preferably 20 μm. The upper limit of the average line width of the first wiring 11 is preferably 50 μm, more preferably 45 μm, and even more preferably 40 μm. If the average line width of the first wiring 11 is less than the above-mentioned lower limit, it may be difficult to form the first wiring 11. In addition, the adhesion strength between the base film 3 and the first wiring 11 may decrease, resulting in the first wiring 11 peeling off from the base film 3. On the other hand, if the average line width of the first wiring 11 exceeds the above-mentioned upper limit, the required wiring density may not be met. Here, the "average line width" of the first wiring 11 refers to the value obtained by averaging the maximum width in a cross section perpendicular to the longitudinal direction of the first wiring 11 in the longitudinal direction of the wiring 11.

[0042] The lower limit of the average thickness of the first wiring 11 is preferably a value obtained by subtracting 10% of the average thickness of the flat portion of the first land portion 20. Specifically, for example, the lower limit of the average thickness of the first wiring 11 is preferably 4.5 μm. If the average thickness of the first wiring 11 is less than the above lower limit, cracks may occur in the connection portion between the first wiring 11 and the first land portion 20. On the other hand, the upper limit of the average thickness of the first wiring 11 is preferably a value approximately the same as the average thickness of the flat portion of the first land portion 20.

[0043] When the printed wiring board 1 has multiple first wirings 11, the upper limit of the average spacing between adjacent first wirings 11 is preferably 50 μm, more preferably 40 μm, even more preferably 30 μm, and particularly preferably 25 μm. If the average spacing between each first wiring 11 is less than the above lower limit, there is a risk of short-circuiting between the wirings 11. On the other hand, if the average spacing between each first wiring 11 exceeds the above upper limit, there is a risk of the wiring density not meeting the required level. Here, the "average spacing" of the first wirings 11 refers to the minimum distance between the opposing side edges of adjacent first wirings 11 in a cross section perpendicular to the longitudinal direction of the first wirings 11, averaged in the longitudinal direction of the first wirings 11.

[0044] (Second Land Section) The second land portion 21 can be formed, for example, using the same material and having the same dimensions as the first land portion 20. The second land portion 21 and the first land portion 20 share the through-hole conductor portion 30.

[0045] (2nd wiring) The second wiring 13 is formed using, for example, the same material as the first wiring 11. Although not shown in the drawings, in this embodiment, the end 13a of the second wiring 13 on the second land portion 21 side is formed to have the same dimensions as the first wiring 11.

[0046] <Relationship between the first land and the first wiring> In this embodiment, the maximum length D of the connection portion between the first wiring 11 and the first land portion 20 (the distance between the two intersection points P1, P2 between the two outermost edges 11b, 11c of the first wiring 11 in the width direction and the outer peripheral edge 20a of the first land portion 20) is greater than or equal to the sum of the maximum diameter R of the through hole 5 and the minimum line width Wa of the first wiring 11.

[0047] <Relationship between the second land and the second wiring> Although not shown in the figures, in this embodiment, the maximum length D of the connection portion between the second wiring 13 and the second land portion 21 (the distance between the two intersections of the two outermost edges in the width direction of the second wiring 13 and the outer peripheral edge 21a of the second land portion 21) is greater than or equal to the sum of the maximum diameter R of the through hole 5 and the minimum line width Wa of the second wiring 13.

[0048] <Printed wiring board manufacturing method> Next, a method for manufacturing the printed wiring board of this embodiment will be described.

[0049] The method for manufacturing a printed wiring board of this embodiment includes a through hole forming process for forming a through hole 5 in a base film 3; a first forming process for forming a conductive base layer by electrolessly plating the front surface 3a, the back surface 3b, and the through hole 5 of the base film 3; after the first forming process, a resist pattern forming process for forming a resist pattern on each of the conductive base layers on the front surface 3a and the back surface 3b of the base film; a second forming process for forming a first land portion 20, a second land portion 21, a first wiring 11, and a second wiring 13 by electrolytic plating the conductive base layer of the through hole 5 and non-laminated areas of the resist pattern on each of the conductive base layers on the front surface 3a and the back surface 3b; and after the second forming process, a removal process for removing the resist pattern and each non-laminated area of ​​the first land portion 20, the second land portion 21, the first wiring 11, and the second wiring 13 on each of the conductive base layers on the front surface 3a and the back surface 3b of the base film 3.

[0050] As the base film 3, the above-mentioned base film 3 is used.

[0051] (Through hole formation process) In this step, through holes 5 are formed in the base film 3 by punching or the like.

[0052] (1st formation step) In this step, a conductive underlayer is formed by electroless plating the front surface 3a, the back surface 3b, and the through holes 5 of the base film 3. In forming the conductive underlayer, the same material as that of the above-mentioned conductive underlayer is used, and a conductive underlayer having the same average thickness as that of the above-mentioned conductive underlayer is formed.

[0053] <Resist pattern formation process> In this process, after the first formation process, resist patterns are formed on the conductive underlayers on the front surface 3a and back surface 3b of the base film. The shape and dimensions of the openings in the resist pattern can be appropriately set so that the plated layers of the first land portion 20, the second land portion 21, the first wiring 11, and the second wiring 13 described above are formed. Specifically, resist films are laminated on the conductive underlayers on the front surface 3a and back surface 3b of the base film 3, and then exposed and developed to form resist patterns having predetermined patterns. Examples of methods for laminating the resist films include a method of applying a resist composition to the conductive underlayers and a method of laminating a dry film photoresist on the conductive underlayers. The exposure and development conditions for the resist film can be appropriately adjusted depending on the resist composition used, etc. As described above, the shape of the opening of the resist pattern formed on the front surface 3a is appropriately set so that the maximum length D of the connection portion between the first wiring 11 and the first land portion 20 (the distance between two intersections P1, P2 between the outer periphery 20a of the first land portion 20 and both end edges 11b, 11c of the first wiring 11) is equal to or greater than the sum of the maximum diameter R of the through hole 5 and the minimum line width Wa of the first wiring 11. In addition, in this embodiment, the shape of the opening of the resist pattern formed on the back surface 3b is appropriately set so that the maximum length D of the connection portion between the second wiring 13 and the second land portion 21 (the distance between two intersections between the outer periphery 21a of the second land portion 21 and both end edges of the second wiring 13) is equal to or greater than the sum of the maximum diameter R of the through hole 5 and the minimum line width Wa of the second wiring 13, although not shown.

[0054] <Second formation process> In this step, the first land portion 20, the second land portion 21, the first wiring 11, and the second wiring 13 are formed by electroplating the non-laminated regions of the resist pattern in each of the conductive base layers. As described above, examples of the electroplating material include copper, aluminum, silver, gold, nickel, and alloys thereof. Among these, copper or a copper alloy is preferred from the viewpoints of improving conductivity and reducing costs. The plating solution is not particularly limited as long as it allows electroplating of the metal onto the conductive base layer, and any known plating solution can be used.

[0055] <Removal process> In this process, after the second forming process, the resist pattern and the non-laminated regions of the first land portion 20, the second land portion 21, the first wiring 11, and the second wiring 13 in each of the conductive base layers are removed. Specifically, this process includes a peeling process of peeling off the resist pattern and an etching process of etching the non-laminated regions of the plating layer in the conductive base layer.

[0056] (peeling process) In this process, after the electrolytic plating process, the resist patterns are stripped from the conductive underlayers. Specifically, the resist patterns are stripped using a stripping solution. Known stripping solutions can be used, such as aqueous alkaline solutions of sodium hydroxide, potassium hydroxide, etc., organic acid solutions of alkylbenzenesulfonic acid, etc., and mixtures of organic amines, such as ethanolamine, with polar solvents.

[0057] (etching process) In this process, after the peeling process, the conductive underlayer is etched using each plating layer as a mask. This etching process results in a laminate in which plating layers are laminated on the front surface 3a and back surface 3b of the base film 3 via the conductive underlayer, resulting in the first land portion 20, the second land portion 21, the first wiring 11, and the second wiring 13. Simultaneously with the formation of the first land portion 20 and the second land portion 21, the through-hole conductor portion 30 is also formed. For this etching process, a known etching solution is used that corrodes the metal forming the conductive underlayer but does not corrode the plating layer. In this manner, in this embodiment, the printed wiring board 1 can be manufactured using a semi-additive method. That is, the printed wiring board 1 is preferably formed using a semi-additive method.

[0058] <Advantages> Since the maximum length D of the connection portion of the printed wiring board 1 is within the above range, poor conduction can be suppressed even if the formation position of the through hole 5 for the through-hole conductor portion 30 is shifted.

[0059] [Second embodiment] A printed wiring board 1a of this embodiment has third wiring 15, instead of first wiring 11, on a surface 3a of a base film 3 serving as a substrate having through holes 5. One end 15a of the third wiring 15 on the first land portion 20 side has a plurality of branch portions 17 branched therefrom, and the maximum length D of the connection portion between the plurality of branch portions 17 of the third wiring 15 and the first land portion 20 is the distance between two intersection points P1 and P2 between two outermost edges 17a, 17b in the width direction of the plurality of branch portions 17 and the outer peripheral edge 20a of the first land portion 20. Since the other configurations are exactly the same as those of the first embodiment, a detailed description of the printed wiring board 1a will be omitted.

[0060] An end 15a of the third wiring 15 on the first land portion 20 side has a plurality of (here, two) branch portions 17. Two outermost edges 17a, 17b in the width direction of the branch portion 17 intersect with an outer peripheral edge 20a of the first land portion 20 at two intersections P1, P2. The distance between these two intersections P1, P2 is the maximum length D of the connection portion between the branch portion 17 and the first land portion 20, and this maximum length D is equal to or greater than the sum of the maximum diameter R of the through hole 5 and the minimum line width Wa of the third wiring 15.

[0061] <Advantages> Since the maximum length D of the connection portion of the printed wiring board 1a is within the above range, poor conductivity can be suppressed even if the formation position of the through hole 5 for the through-hole conductor portion 30 in the base film 3 is shifted.

[0062] In addition, in this embodiment, since the one end 15a of the third wiring 15 has the multiple branch portions 17, it is possible to more reliably suppress poor conductivity even if the through hole 5 is misaligned.

[0063] The printed wiring board according to the embodiment of the present disclosure can suppress poor conductivity even if the formation position of the through hole for the through-hole conductor portion is misaligned, and therefore can be suitably used in small electronic devices, etc.

[0064] [Other embodiments] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0065] In the first embodiment, the case where the maximum length D of the land portions and wiring on both sides of the base film is equal to or greater than the sum of the maximum diameter R and the minimum line width Wa was described, but the maximum length D may also be equal to or greater than the sum of the maximum diameter R and the minimum line width Wa on either the front or back surface.

[0066] In the above second embodiment, a case was described in which the end of the wiring on the surface of the base film on the land portion side has multiple branch portions, but in addition to the end on the surface of the base film, the end of the wiring on the back side on the land portion side may also have multiple branch portions.

[0067] In the second embodiment, the wiring has two branched portions, but the wiring may have three or more branched portions. [Explanation of symbols]

[0068] 1, 1a Printed wiring board 3 Base film (substrate) 3a surface 3b back side 5 through holes 11 1st wiring 11a: End of the first wiring on the land portion side 13 2nd wiring 13a End of the second wiring on the land portion side 20 First Land Section 20a outer edge 21 Second Land Section 21a outer edge 30 Through-hole conductor P1, P2 intersection D Maximum length of the connection part (distance between intersections) R Maximum diameter of through hole Wa Minimum line width

Claims

[Claim 1] a substrate having a through hole; a land portion having a through-hole conductor portion, the land portion being disposed on an inner peripheral surface of the through-hole and on a periphery of the through-hole on the surface of the substrate; a wiring arranged on the surface of the substrate, one end of which in the longitudinal direction is electrically connected to the land portion; Equipped with the maximum length of the connection portion between the wiring and the land portion is equal to or greater than the sum of the maximum diameter of the through hole and the minimum line width of the wiring, the wiring has a main body portion having a uniform line width and a plurality of branch portions branching from the main body portion, each of the branch portions having a uniform line width; the line width of the branch portion is equal to or less than the line width of the main body portion, A printed wiring board in which the maximum length of the connection portion is the distance between two intersections between the two outermost edges of the plurality of branch portions in the width direction and the land portion.

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