Wiring circuit board and manufacturing method thereof

Abstract

To provide a wiring circuit board having high flexibility and reduced impedance discontinuity and a manufacturing method thereof.SOLUTION: An insulating layer 30 has first and second main surfaces S1 and S2. A conductive layer 40 is provided on the first main surface S1. A metal thin film 20 is provided on the second main surface S2 and has a third main surface S3 facing in the opposite direction to the insulating layer 30. A metal support body 10 is made of a metal material different from that of the metal thin film 20. First and second regions A1 and A2 are defined on the first main surface S1 and the conductive layer 40 constitutes a wiring extending to pass through the first and second regions A1 and A2 on the first main surface S1. In the third main surface S3, when defining third and fourth regions A3 and A4 that overlap the first and second regions A1 and A2 of the first main surface S1 in plan view, the metal support body 10 is provided on the third main surface S3 so as not to cover the third region A3 and to cover the fourth region A4.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a wired circuit board and a method for manufacturing the same. [Background technology]

[0002] An example of a wired circuit board is a suspension board with a circuit in which an insulating layer is formed on a metal supporting board and a conductor layer as wiring is formed on the insulating layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-243382 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the applications of wired circuit boards have been expanding. Depending on the application of the wired circuit board, there are cases where higher flexibility is required for the wired circuit board. In the above-mentioned suspension board with a circuit, the metal supporting board has a relatively high rigidity compared to the insulating layer and the conductor layer. Therefore, it is considered that a wired circuit board having high flexibility can be realized by removing a part of the metal supporting board from the above-mentioned basic configuration of the suspension board with a circuit.

[0005] In the above-mentioned suspension board with circuit, in a portion where the conductor layer and the metal supporting board face each other with the insulating layer sandwiched therebetween, the metal supporting board reduces the impedance of the conductor layer (wiring). Therefore, when a part of the metal supporting board is removed, the impedance of the conductor layer cannot be reduced. In this case, the impedance of the conductor layer (wiring) deviates from a desired value, which may cause impedance mismatch between the conductor layer and an electronic component connected to the conductor layer.

[0006] Patent Document 1 describes an example of a flexible substrate for suspension (wired circuit board) in which an insulating layer and wiring are laminated in this order on a stainless steel metal supporting substrate having an opening region. In the following description, the direction in which the metal supporting substrate, insulating layer, and wiring are laminated in the flexible substrate for suspension of Patent Document 1 is referred to as the substrate lamination direction.

[0007] In the flexible substrate for suspension, an opening region of the metal supporting board overlaps with a portion of the wiring in the substrate stacking direction. Also, in the flexible substrate for suspension, a conductive film having a higher conductivity than the metal supporting board is formed in the opening region of the metal supporting board in order to reduce the impedance of the wiring. The conductive film overlaps with a portion of the wiring in the substrate stacking direction.

[0008] According to this configuration, a plurality of portions of the wiring overlap with the metal supporting board or the conductive film in the substrate lamination direction. This reduces the impedance of the wiring. However, in the flexure substrate for suspension of Patent Document 1, the metal supporting board and the conductive film are made of materials that at least have different electrical conductivity (electrical conductivity).

[0009] The degree to which the impedance can be reduced for the multiple parts of the wiring varies depending on the conductivity of the members (the conductive film and the metal supporting board in the above example) that face each of the multiple parts of the wiring in the substrate stacking direction with an insulating layer interposed therebetween. Therefore, there is a difference in the degree of impedance that can be reduced between a part of the wiring that overlaps the conductive film in the substrate stacking direction and another part of the wiring that overlaps the metal supporting board in the substrate stacking direction. The discontinuity in impedance in the wiring reduces the electrical characteristics of the wiring.

[0010] An object of the present invention is to provide a printed circuit board having high flexibility and reduced impedance discontinuity, and a method for manufacturing the same. [Means for solving the problem]

[0011] (1) A wired circuit board according to one aspect of the present invention comprises an insulating layer having a first main surface and a second main surface facing in opposite directions, a conductor layer provided on the first main surface of the insulating layer, a metal thin film provided on the second main surface of the insulating layer and having a third main surface facing in a direction opposite to the insulating layer, and a metal support made of a metal material different from the metal material of at least a portion of the metal thin film, wherein a first region and a second region different from each other are defined on the first main surface of the insulating layer, and at least a portion of the conductor layer forms wiring extending to pass through the first region and the second region of the first main surface, and when a third region and a fourth region are defined on the third main surface of the metal thin film, respectively overlapping the first region and the second region of the first main surface as viewed in an intersecting direction perpendicular to the first main surface, the metal support is provided on the third main surface so as not to cover the third region of the third main surface but to cover the fourth region.

[0012] In the wired circuit board, a portion of the wired circuit board overlapping the first region of the first main surface and the third region of the third main surface when viewed in the intersecting direction is called a first substrate portion, and another portion of the wired circuit board overlapping the second region of the first main surface and the fourth region of the third main surface when viewed in the intersecting direction is called a second substrate portion.

[0013] In this case, the first substrate part includes a portion of the conductor layer, a portion of the insulating layer, and a portion of the thin metal film, but does not include the metal support, while the second substrate part includes the other portion of the conductor layer, the other portion of the insulating layer, the other portion of the thin metal film, and the metal support.

[0014] As described above, the first substrate portion does not include a metal support. This ensures that the first substrate portion has higher flexibility than the second substrate portion. On the other hand, the second substrate portion includes a metal support. This ensures that the second substrate portion has a certain level of mechanical strength required to support the first substrate portion on another member or to mount another member thereon.

[0015] In the above-mentioned wired circuit board, a metal thin film faces a part of the wiring formed in the first region of the first main surface and another part of the wiring formed in the second region of the first main surface, with an insulating layer sandwiched between them. This allows the impedance of the part of the conductor layer and the impedance of the other part of the conductor layer to be adjusted by the common metal thin film. This reduces uneven adjustment of the impedance in multiple parts of the conductor layer.

[0016] As a result, a printed circuit board having high flexibility and reduced impedance discontinuity is realized.

[0017] (2) On the first main surface, the first region and the second region may be adjacent to each other. In this case, the first substrate portion and the second substrate portion are aligned continuously, so that the first substrate portion is appropriately supported by the second substrate portion.

[0018] (3) The metal thin film includes a first metal film and a second metal film stacked in a cross direction, and the metal material of at least one of the first metal film and the second metal film may be different from the metal material of the metal support.

[0019] In this case, a first metal film and a second metal film are used as the metal thin film. Therefore, by appropriately determining the metal materials used for the first metal film and the second metal film, a more suitable metal thin film can be formed to reduce the impedance of the conductor layer. Alternatively, a more suitable metal thin film can be formed to improve the adhesion of the metal thin film and the metal support to the insulating layer.

[0020] (4) The metal thin film may include a plating layer. The degree of reduction in impedance of the conductor layer varies depending on the thickness of the metal thin film. According to the above configuration, at least a part of the metal thin film includes a plating layer. When forming the plating layer, the thickness of the plating layer formed can be adjusted relatively easily by appropriately adjusting the plating processing conditions such as processing time. Therefore, it becomes possible to form a metal thin film having a more appropriate thickness for reducing the impedance of the conductor layer.

[0021] (5) The thickness of the metal thin film may be smaller than the thickness of the metal support, in which case greater flexibility is ensured in the first substrate portion.

[0022] (6) The metal thin film may have a thickness of 20 nm to 5 μm, in which case the impedance of the conductor layers formed on the first and second substrate portions is more appropriately adjusted.

[0023] (7) A method for manufacturing a wired circuit board according to another aspect of the present invention includes the steps of preparing a metal support, forming a metal thin film made of a metal material different from that of the metal support on the metal support, forming an insulating layer having a first main surface and a second main surface facing in opposite directions on the metal thin film such that the second main surface is in contact with the metal thin film, forming a conductor layer on the first main surface of the insulating layer, and removing a part of the metal support after the step of forming the metal thin film, wherein a first region and a second region different from each other are defined on the first main surface of the insulating layer, and the step of forming the conductor layer includes removing at least a part of the conductor layer. the step of removing a portion of the metal support includes forming wiring that extends through a first region and a second region of the first main surface using at least a portion of the metal support, the metal thin film having a third main surface facing in a direction opposite to the insulating layer and in contact with the metal support, and when a third region and a fourth region are defined on the third main surface of the metal thin film, the third region and the fourth region overlapping the first region and the second region of the first main surface, respectively, when viewed in a cross direction perpendicular to the first main surface, the step of removing a portion of the metal support includes removing a portion of the metal support located in the third region of the third main surface such that the metal support does not cover the third region of the third main surface but covers the fourth region.

[0024] In the wired circuit board produced by the above manufacturing method, a portion of the wired circuit board overlapping the first region of the first main surface and the third region of the third main surface when viewed in the intersecting direction is called a first substrate portion, and another portion of the wired circuit board overlapping the second region of the first main surface and the fourth region of the third main surface when viewed in the intersecting direction is called a second substrate portion.

[0025] In this case, the first substrate part includes a portion of the conductor layer, a portion of the insulating layer, and a portion of the thin metal film, but does not include the metal support, while the second substrate part includes the other portion of the conductor layer, the other portion of the insulating layer, the other portion of the thin metal film, and the metal support.

[0026] As described above, the first substrate portion does not include a metal support. This ensures that the first substrate portion has higher flexibility than the second substrate portion. On the other hand, the second substrate portion includes a metal support. This ensures that the second substrate portion has a certain level of mechanical strength required to support the first substrate portion on another member or to mount another member thereon.

[0027] In the above-mentioned wired circuit board, a metal thin film faces a part of the wiring formed in the first region of the first main surface and another part of the wiring formed in the second region of the first main surface, with an insulating layer sandwiched between them. This allows the impedance of the part of the conductor layer and the impedance of the other part of the conductor layer to be adjusted by the common metal thin film. This reduces uneven adjustment of the impedance in multiple parts of the conductor layer.

[0028] As a result, a printed circuit board having high flexibility and reduced impedance discontinuity is realized.

[0029] (8) The step of forming the thin metal film may include forming at least a portion of the thin metal film by sputtering.

[0030] In this case, the metal thin film can be easily formed. Also, the thickness of the sputtered film formed by sputtering can be made sufficiently small so as not to impair the flexibility of the wiring circuit board. Therefore, higher flexibility can be obtained in the first substrate portion.

[0031] (9) The step of forming the thin metal film may include forming at least a portion of the thin metal film by plating.

[0032] In this case, the thickness of the plating layer formed by plating can be adjusted relatively easily, so that a metal thin film having a more appropriate thickness for reducing the impedance of the conductor layer can be formed. Effect of the Invention

[0033] According to the present invention, a printed circuit board having high flexibility and reduced impedance discontinuity is realized. [Brief description of the drawings]

[0034] [Figure 1] 1 is a top view of a printed circuit board according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a bottom view of the printed circuit board of FIG. [Diagram 3] 2 is a schematic cross-sectional view of a plurality of portions of the printed circuit board of FIG. 1. [Figure 4] 2 is a schematic cross-sectional view for explaining an example of a method for manufacturing the wired circuit board of FIG. 1. FIG. [Diagram 5] 2 is a schematic cross-sectional view for explaining an example of a method for manufacturing the wired circuit board of FIG. 1. FIG. [Figure 6] 2 is a schematic cross-sectional view for explaining an example of a method for manufacturing the wired circuit board of FIG. 1. FIG. [Figure 7] 1A to 1C are schematic cross-sectional views showing a printed circuit board having a metal thin film according to a first modified example, the printed circuit board being cut at a plurality of portions. [Figure 8] 11A to 11C are schematic cross-sectional views showing a plurality of cut portions of a printed circuit board having a metal thin film according to a second modified example. [Figure 9] FIG. 11 is a top view of a printed circuit board according to another embodiment. [Figure 10] 10 is a schematic cross-sectional view of a plurality of parts of the printed circuit board of FIG. 9. [Figure 11] FIG. 13 is a top view of a printed circuit board according to still another embodiment. [Figure 12]12 is a schematic cross-sectional view of a plurality of portions of the printed circuit board of FIG. 11. [Figure 13] 5A to 5C are schematic cross-sectional views of a printed circuit board according to still another embodiment, in which a plurality of portions are cut away. [Figure 14] 1 is a diagram showing measurement results of impedance of conductor layers of the wired circuit boards of Comparative Examples 1 and 2 and Examples 1 to 3. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A printed circuit board and a method for manufacturing the same according to an embodiment of the present invention will now be described with reference to the drawings.

[0036] 1. Basic structure of printed circuit board FIG. 1 is a top view of a wired circuit board according to an embodiment of the present invention. FIG. 2 is a bottom view of the wired circuit board 1 of FIG. 1. FIG. 3 is a schematic cross-sectional view of a plurality of parts of the wired circuit board 1 of FIG. 1 cut off. In FIG. 3, the AA line cross-sectional view, the BB line cross-sectional view, and the CC line cross-sectional view of FIG. 1 are shown in this order, arranged at the top, the center, and the bottom. Here, in order to make it easier to understand the configuration of the wired circuit board 1, the X direction, the Y direction, and the Z direction, which are mutually orthogonal, are defined. In each of the figures after FIG. 1, the X direction, the Y direction, and the Z direction are appropriately indicated by arrows. In this embodiment, the X direction and the Y direction are mutually orthogonal in a horizontal plane, and the Z direction corresponds to the vertical direction.

[0037] The wired circuit board 1 according to the present embodiment has a rectangular shape extending in one direction (X direction) in a plan view as shown in Figures 1 and 2. Moreover, the wired circuit board 1 has a configuration in which a metal support 10, a metal thin film 20, an insulating layer 30, and a conductor layer 40 are mainly laminated in this order in the Z direction as shown in Figure 3.

[0038] The insulating layer 30 is formed of, for example, photosensitive polyimide. The thickness (length in the Z direction) of the insulating layer 30 is, for example, 1 μm or more and 30 μm or less. The insulating layer 30 may be formed of other synthetic resins such as acrylic resin, polyethernitrile resin, polyethersulfone resin, epoxy resin, polyethylene terephthalate resin, polyethylene naphthalate resin, or polyvinyl chloride resin.

[0039] In addition, the insulating layer 30 has two main surfaces (upper and lower surfaces) facing in opposite directions. In the following description, one of the main surfaces (upper surface) of the insulating layer 30 is referred to as a first main surface S1, and the other main surface (lower surface) of the insulating layer 30 is referred to as a second main surface S2.

[0040] 1, in the insulating layer 30 of this example, a rectangular first region A1 and two rectangular second regions A2 are set on the first main surface S1. The first region A1 is located at the center of the wired circuit board 1 in the longitudinal direction (X direction) of the wired circuit board 1. The two second regions A2 are located at both ends of the wired circuit board 1 in the longitudinal direction (X direction) of the wired circuit board 1 and in the vicinity thereof. As a result, the second region A2 and the first region A1 on one side are adjacent to each other in the X direction, and the second region A2 and the first region A1 on the other side are adjacent to each other.

[0041] Two conductor layers 40 are provided on the first main surface S1 of the insulating layer 30. Each conductor layer 40 is mainly made of copper and is formed on the first main surface S1 of the insulating layer 30 by electrolytic plating. Each conductor layer 40 has a wiring portion 41 and two terminal portions 42. The two terminal portions 42 are respectively disposed in two second regions A2 at positions near both ends of the wiring circuit board 1. Each terminal portion 42 is used to connect other electronic components to the conductor layer 40 of the wiring circuit board 1. The wiring portion 41 extends continuously through one second region A2, the first region A1, and the other second region A2 so as to connect the two terminal portions 42. The thickness (length in the Z direction) of the conductor layer 40 is, for example, 0.25 μm or more and 50 μm or less. The width (length in the Y direction) of the wiring portion 41 of the conductor layer 40 is, for example, 0.25 μm or more and 300 μm or less.

[0042] A metal thin film 20 is provided on the second main surface S2 of the insulating layer 30, over the entire second main surface S2. The metal thin film 20 is formed of a metal or an alloy containing one or more elements selected from the group consisting of copper, chromium, nickel, titanium, iron, molybdenum, and tungsten. In this example, the metal thin film 20 is formed of a single layer made of copper or chromium. The thickness (length in the Z direction) of the metal thin film 20 is smaller than the thickness (length in the Z direction) of the metal support 10 described later, and is, for example, 20 nm or more and 5 μm or less, and preferably 20 nm or more and 3 μm or less.

[0043] The thin metal film 20 has two main surfaces (upper and lower surfaces) facing in opposite directions, similar to the insulating layer 30. In the following description, the main surface (lower surface) of the thin metal film 20 facing in the opposite direction to the insulating layer 30 is referred to as a third main surface S3.

[0044] The third main surface S3 of the metal thin film 20 has a third region A3 and a fourth region A4, which correspond to the first region A1 and the second region A2, respectively, of the first main surface S1 of the insulating layer 30. Specifically, the third region A3 of the third main surface S3 is a region that overlaps with the first region A1 of the first main surface S1 in a plan view in the Z direction. Moreover, the fourth region A4 of the third main surface S3 is a region that overlaps with the second region A2 of the first main surface S1 in a plan view in the Z direction.

[0045] The metal support 10 is provided on the third main surface S3 of the metal thin film 20 so as not to cover the third region A3 and to cover the fourth region A4. The metal support 10 is made of a metal material different from that of the metal thin film 20, and is formed of a metal or alloy containing one or more elements selected from the group consisting of copper, chromium, nickel, titanium, iron, molybdenum, and aluminum. Here, the metal material of the metal support 10 and the metal thin film 20 being different means that at least one of the electrical conductivity and the relative magnetic permeability is different between the two metal materials to such an extent that they cannot be regarded as substantially the same. In this embodiment, the metal support 10 is formed of stainless steel. The thickness (length in the Z direction) of the metal support 10 is, for example, 10 μm or more and 250 μm or less.

[0046] 2. Manufacturing method of the wired circuit board 1 Figures 4 to 6 are schematic cross-sectional views for explaining one example of a manufacturing method for the wired circuit board 1 of Figure 1. In each of Figures 4 to 6, similar to the example of Figure 3, three cross-sectional views (corresponding cross-sectional views) respectively corresponding to the lines AA, BB, and CC in Figure 1 are shown lined up in that order at the top, center, and bottom.

[0047] First, as shown in Fig. 4, a metal thin film 20 is formed on the upper surface of the metal support 10. The metal thin film 20 is formed by a film formation technique such as sputtering, electrolytic plating, electroless plating, chemical vapor deposition, or physical vapor deposition. As described above, the metal thin film 20 in this example is made of copper or chromium. The lower surface of the metal thin film 20 that contacts the metal support 10 is the third main surface S3.

[0048] Next, as shown in FIG. 5, an insulating layer 30 made of photosensitive polyimide is formed on the upper surface of the metal thin film 20. The insulating layer 30 is formed by applying a precursor of the photosensitive polyimide to the entire upper surface of the metal thin film 20, exposing the precursor to light, and developing the precursor. The formed insulating layer 30 is then subjected to a curing treatment by heating. The upper surface of the insulating layer 30 exposed upward is the first main surface S1, and the lower surface of the insulating layer 30 in contact with the metal thin film 20 is the second main surface S2. As described above, the first area A1 and the second area A2 are set on the first main surface S1, and the third area A3 and the fourth area A4 are set on the third main surface S3.

[0049] 6, one or more (two in this example) conductor layers 40 are formed on the first main surface S1 of the insulating layer 30. Specifically, the conductor layers 40 are formed as follows.

[0050] First, a seed layer made of, for example, a thin chromium film and a thin copper film is formed on the first main surface S1 of the insulating layer 30 by sputtering or electroless plating. Next, a plating resist having a predetermined pattern (a reverse pattern to the two conductor layers 40 in FIG. 1) is formed on the seed layer. Next, a plating layer made of copper is formed by electrolytic plating on the seed layer exposed through the openings in the plating resist.

[0051] Thereafter, the plating resist is peeled off, and the exposed portion of the seed layer (the portion on which the plating layer is not formed) is removed by etching. This forms a conductor layer 40 consisting of the seed layer and the plating layer. In Figs. 1 and 6 and Figs. 8, 10, 12, and 13 described below, the seed layer and the plating layer constituting the conductor layer 40 are not shown.

[0052] A barrier layer for suppressing copper diffusion may be formed on the exposed outer surface of the conductor layer 40. For example, a nickel thin film may be used as the barrier layer. The nickel thin film may be formed by, for example, sputtering or electroless plating. A protective film for protecting the wiring parts 41 may be formed on the first main surface S1 of the insulating layer 30 so as to cover the wiring parts 41 and not cover the terminal parts 42. For example, a photosensitive polyimide may be used as the material of the protective film. The protective film made of photosensitive polyimide may be formed by the same method as that of the insulating layer 30.

[0053] Finally, the portion of the metal support 10 located on the third region A3 of the third main surface S3 is removed, for example, by wet etching. The etching solution used at this time is an etching solution capable of dissolving the metal support 10 at a higher etching rate than the metal thin film 20. As a result, the third region A3 of the metal thin film 20 is exposed downward, and the wired circuit board 1 of FIGS. 1 to 3 is completed.

[0054] The above series of processes may be performed by a roll-to-roll method. In this case, for example, a roll (hereinafter referred to as a pay-out roll) on which a long metal plate made of stainless steel is wound is prepared. The metal plate is paid out from the prepared pay-out roll. The metal plate paid out from the pay-out roll is wound up on another roll. By performing the above series of processes on each part of the metal plate moving from the pay-out roll to the other roll, it becomes possible to efficiently manufacture a large number of wired circuit boards 1.

[0055] 3.Effects (1) In the above-mentioned wired circuit board 1, a portion of the wired circuit board 1 overlapping the first region A1 of the first main surface S1 and the third region A3 of the third main surface S3 in a plan view in the Z direction is called a first substrate portion. In addition, in the above-mentioned wired circuit board 1, another portion of the wired circuit board 1 overlapping the second region A2 of the first main surface S1 and the fourth region A4 of the third main surface S3 in a plan view in the Z direction is called a second substrate portion.

[0056] In this case, the first substrate portion includes a part of the conductor layer 40, a part of the insulating layer 30, and a part of the metal thin film 20, but does not include the metal support 10. On the other hand, the second substrate portion includes the other part of the conductor layer 40, the other part of the insulating layer 30, the other part of the metal thin film 20, and the metal support 10.

[0057] In this way, the first substrate portion does not include the metal support 10. This ensures that the first substrate portion has higher flexibility than the second substrate portion. On the other hand, the second substrate portion includes the metal support 10. This ensures that the second substrate portion has a certain level of mechanical strength required to support the first substrate portion on another member or to mount another member thereon.

[0058] In the above-described wired circuit board 1, the metal thin film 20 faces a part of the wiring portion 41 formed in the first region A1 of the first main surface S1 and another part of the wiring portion 41 formed in the second region A2 of the first main surface S1, with the insulating layer 30 sandwiched therebetween. This allows the impedance of the part of the wiring portion 41 and the impedance of the other part of the wiring portion 41 to be adjusted by the common metal thin film 20. This reduces uneven adjustment of the impedance in multiple parts of the wiring portion 41.

[0059] As a result, a wired circuit board 1 having high flexibility and reduced impedance discontinuity is realized.

[0060] (2) The first region A1 is adjacent to each of the two second regions A2 on the first main surface S1 of the insulating layer 30. As a result, the first substrate portion and the second substrate portion are continuously aligned in the longitudinal direction (X direction) of the wired circuit board 1, and the first substrate portion is appropriately supported by the second substrate portion.

[0061] (3) The thickness of the metal thin film 20 is smaller than that of the metal support 10, and is 20 nm or more and 5 μm or less. In this case, higher flexibility is ensured in the first substrate portion. Also, the impedance of the wiring portion 41 of the conductor layer 40 formed on the first substrate portion and the second substrate portion is more appropriately adjusted.

[0062] 4. Modifications of the thin metal film 20 (1) First Modification The metal thin film 20 provided on the wired circuit board 1 may be composed of multiple layers. Fig. 7 is a schematic cross-sectional view of multiple parts of the wired circuit board 1 including the metal thin film 20 according to the first modification. In Fig. 7, similar to the example of Fig. 3, three cross-sectional views corresponding to the lines AA, BB, and CC in Fig. 1 are shown lined up in this order at the top, center, and bottom.

[0063] 7, the metal thin film 20 according to the first modification is composed of a first thin film layer 20a and a second thin film layer 20b. The first thin film layer 20a and the second thin film layer 20b are each formed using a film formation technique such as sputtering, electrolytic plating, electroless plating, chemical vapor deposition, or physical vapor deposition.

[0064] The first thin film layer 20a and the second thin film layer 20b may be a chromium thin film and a copper thin film, respectively, formed by sputtering on the upper surface of the metal support 10. Alternatively, the first thin film layer 20a and the second thin film layer 20b may be a copper thin film and a chromium thin film, respectively, formed by sputtering on the upper surface of the metal support 10.

[0065] Alternatively, one of the first thin film layer 20a and the second thin film layer 20b may be formed by electrolytic plating. For example, when producing the wired circuit board 1, the first thin film layer 20a made of copper may be formed by electrolytic plating on the upper surface of the metal support 10 in the step shown in Fig. 4 above. Furthermore, the second thin film layer 20b made of a chromium thin film may be formed on the first thin film layer 20a so as to cover the first thin film layer 20a.

[0066] As described below, the degree of reduction in the impedance of the wiring portion 41 varies depending on the thickness of the metal thin film 20. In electrolytic plating, the thickness of the plating layer formed can be adjusted relatively easily by appropriately adjusting the processing conditions such as the processing time. Therefore, when one of the first thin film layer 20a and the second thin film layer 20b is formed by electrolytic plating as described above, it is possible to form the metal thin film 20 having a thickness more appropriate for reducing the impedance of the wiring portion 41.

[0067] Furthermore, as described above, when the upper surface of the thin metal film 20 is formed of the second thin film layer 20b made of a thin chromium film, the insulating layer 30 is further formed on the second thin film layer 20b, thereby improving the adhesion between the first thin film layer 20a and the insulating layer 30. When the first thin film layer 20a is formed of a thin copper film, the second thin film layer 20b may be any of a thin nickel film, a thin titanium film, a thin molybdenum film, and a thin tungsten film formed by sputtering, instead of a thin chromium film. In this case as well, the adhesion between the first thin film layer 20a and the insulating layer 30 is improved.

[0068] (2) Second modified example Fig. 8 is a schematic cross-sectional view of a printed circuit board 1 including a metal thin film 20 according to a second modified example, in which a plurality of portions are cut. In Fig. 8, similarly to the example of Fig. 3, three cross-sectional views corresponding to the lines AA, BB, and CC in Fig. 1 are shown arranged in this order at the top, center, and bottom.

[0069] As shown in Fig. 8, the metal thin film 20 according to the second modification is composed of a first thin film layer 20a, a second thin film layer 20b, and a third thin film layer 20c. The first thin film layer 20a, the second thin film layer 20b, and the third thin film layer 20c are each formed by a film formation technique such as sputtering, electrolytic plating, electroless plating, chemical vapor deposition, or physical vapor deposition. The first thin film layer 20a, the second thin film layer 20b, and the third thin film layer 20c are each composed of a metal thin film such as a copper thin film, a chromium thin film, a nickel thin film, a titanium thin film, a molybdenum thin film, or a tungsten thin film.

[0070] The first thin film layer 20a and the second thin film layer 20b may be a chromium thin film and a copper thin film, respectively, formed by sputtering on the upper surface of the metal support 10. In this case, the third thin film layer 20c may be a copper plating layer formed by electrolytic plating on the copper thin film of the second thin film layer 20b.

[0071] Alternatively, the first thin film layer 20a may be a copper plating layer formed by electrolytic plating on the upper surface of the metal support 10. In this case, the second thin film layer 20b and the third thin film layer 20c may be a copper thin film and a chromium thin film, respectively, formed by sputtering on the plating layer of the first thin film layer 20a.

[0072] Alternatively, the first thin film layer 20a may be a copper thin film formed by sputtering on the upper surface of the metal support 10. In this case, the second thin film layer 20b may be a copper plating layer formed by electrolytic plating on the upper surface of the metal support 10. Furthermore, the third thin film layer 20c may be a chromium thin film formed by sputtering on the plating layer of the second thin film layer 20b.

[0073] 5. Other embodiments (1) In the first main surface S1 of the insulating layer 30 according to the above embodiment, one of the two second regions A2, the first region A1, and the other of the two second regions A2 are arranged in this order in the X direction. However, the present invention is not limited to the above example. In the first main surface S1 of the insulating layer 30, the first region A1 and the second region A2 may be arranged as follows.

[0074] Fig. 9 is a top view of a wired circuit board 1 according to another embodiment. Fig. 10 is a schematic cross-sectional view in which a plurality of parts of the wired circuit board 1 of Fig. 9 are cut. In Fig. 10, a cross-sectional view along line AA, a cross-sectional view along line BB, and a cross-sectional view along line CC of Fig. 9 are shown in this order, arranged at the top, the center, and the bottom. The wired circuit board 1 of Figs. 9 and 10 will be described in terms of differences from the wired circuit board 1 of Fig. 1.

[0075] In the wired circuit board 1 of FIG. 9, one first region A1 and one second region A2 are set on the first main surface S1 of the insulating layer 30. The first region A1 is set in an island shape in the center in the longitudinal direction (X direction) and the lateral direction (Y direction) of the wired circuit board 1. On the other hand, the second region A2 is set so as to surround the first region A1. As in the wired circuit board 1 of FIG. 1, most of the wiring parts 41 of the two conductor layers 40 are located on the first region A1. The remaining parts of the wiring parts 41 of the two conductor layers 40 and the terminal parts 42 of the two conductor layers 40 are located on the second region A2.

[0076] As described above, the first region A1 and the second region A2 are set on the first main surface S1. As a result, in the wired circuit board 1 of this example, a third region A3 (not shown) is set on the third main surface S3 of the metal thin film 20, overlapping the first region A1 of the first main surface S1 in a plan view in the Z direction. Also, a fourth region A4 (not shown) is set on the second region A2 of the first main surface S1 in a plan view in the Z direction.

[0077] 10, in the wired circuit board 1 of this example, at least a portion of the metal support 10 is located on the third main surface S3 of the metal thin film 20 over the entire area in the X direction. Specifically, in the wired circuit board 1 of this example, as shown in the center of FIG. 10, a linear metal support 10 is provided in a position near the wiring portion 41 of each conductor layer 40 so as to extend parallel to the wiring portion 41. This makes it possible to obtain mechanical strength as required in the area near the wiring portion 41.

[0078] In this way, by appropriately providing metal supports 10 at multiple portions of the wired circuit board 1, it is possible to impart the desired flexibility and mechanical strength to each of the multiple portions of the wired circuit board 1.

[0079] (2) Although the wired circuit board 1 according to the above embodiment has a rectangular shape extending in one direction (X direction) in a plan view, the present invention is not limited to this. The wired circuit board 1 may have the following shapes.

[0080] Fig. 11 is a top view of a wired circuit board 1 according to still another embodiment. Fig. 12 is a schematic cross-sectional view in which a plurality of parts of the wired circuit board 1 of Fig. 11 are cut. In Fig. 12, a cross-sectional view along line AA, a cross-sectional view along line BB, and a cross-sectional view along line CC of Fig. 11 are shown arranged in this order at the top, the center, and the bottom. The wired circuit board 1 of Figs. 11 and 12 will be described in terms of differences from the wired circuit board 1 of Fig. 1.

[0081] As shown in Figs. 11 and 12, the wired circuit board 1 of this example is formed so that the width (length in the Y direction) of the insulating layer 30 changes stepwise in the direction in which the wiring parts 41 of the two conductor layers 40 extend. Specifically, the insulating layer 30 is formed so that it is large at both ends and their neighboring parts in the longitudinal direction (X direction) of the wired circuit board 1 and is small in other parts. As a result, the width (length in the Y direction) of the first region A1 set on the first main surface S1 is smaller than the width (length in the Y direction) of the second region A2. With this configuration, it is possible to obtain higher flexibility in the part of the wired circuit board 1 located between the two second regions A2.

[0082] (3) In the wired circuit board 1 according to the above embodiment, the metal thin film 20 is formed on the upper surface of the metal support 10, but the present invention is not limited to this. A new insulating layer 31 may be formed between the metal support 10 and the metal thin film 20.

[0083] Fig. 13 is a schematic cross-sectional view of a plurality of parts of a wired circuit board 1 according to yet another embodiment. The top view of the wired circuit board 1 of this example is the same as the top view of the wired circuit board 1 of Fig. 1. In Fig. 13, similarly to the example of Fig. 3, three cross-sectional views corresponding to the lines AA, BB, and CC in Fig. 1 are shown lined up in this order at the top, center, and bottom.

[0084] 13, a new insulating layer 31 different from the insulating layer 30 is further formed on the upper surface of the metal support 10. Even in this case, the metal thin film 20 is formed so as to face the entire conductor layer 40 with the insulating layer 30 interposed therebetween, so that the same effect as in the above embodiment can be obtained.

[0085] (4) In manufacturing the wired circuit board 1, the insulating layer 30 may be formed using a photosensitive carrier film. Specifically, the insulating layer 30 may be formed by attaching an insulating film made of photosensitive polyimide onto the upper surface of the metal thin film 20.

[0086] (5) In the wired circuit board 1 according to the above embodiment, the thin metal film 20 is formed to overlap the entire insulating layer 30 in a plan view. However, it is sufficient that the thin metal film 20 overlaps the entire conductor layer 40.

[0087] For example, the first region A1 and the second region A2 may be set to be separated from each other in the X direction on the first main surface S1 of the wired circuit board 1 according to the above embodiment, with another new region sandwiched therebetween. Here, when the wiring portion 41 of the conductor layer 40 is located on the other new region, the metal thin film 20 is formed so as to overlap the first region A1 and the second region A2 and to overlap the other new region in a plan view in the Z direction. On the other hand, when the wiring portion 41 of the conductor layer 40 is not located on the other new region, the metal thin film 20 may be formed so as to overlap the first region A1 and the second region A2 and not to overlap the other new region in a plan view in the Z direction.

[0088] 5. Correspondence between each component of the claims and each part of the embodiment Below, examples of the correspondence between each component of the claims and each element of the embodiment will be described, but the present invention is not limited to the following examples. Various other elements having the configuration or function described in the claims can also be used as each component of the claims.

[0089] In the above embodiment, the wired circuit board 1 is an example of a wired circuit board, the first main surface S1 is an example of a first main surface, the second main surface S2 is an example of a second main surface, the insulating layer 30 is an example of an insulating layer, the conductor layer 40 is an example of a conductor layer, the third main surface S3 is an example of a third main surface, and the metal thin film 20 is an example of a metal thin film.

[0090] In addition, the first region A1 is an example of a first region, the second region A2 is an example of a second region, the wiring portion 41 is an example of wiring, the third region A3 is an example of a third region, the fourth region A4 is an example of a fourth region, the first thin film layer 20a is an example of a first metal film, and the second thin film layer 20b is an example of a second metal film.

[0091] 6. Testing the impedance reduction effect of the wiring portion 41 by the metal thin film 20 The present inventors produced wired circuit boards of Comparative Examples 1 and 2 and Examples 1 to 3 in order to confirm a plurality of types of thin metal films 20 and the degree of reduction in impedance of the wiring portion 41 according to those types.

[0092] Specifically, the inventors produced a wired circuit board of Comparative Example 1, which has the same configuration as the wired circuit board 1 of Figures 1 to 3, except that it does not have the metal support 10 and the metal thin film 20.

[0093] 1 to 3 except that the metal thin film 20 is not included and the metal support 10 is provided so as to be in contact with the entire second main surface S2 of the insulating layer 30. In the wired circuit board of Comparative Example 2, the thickness (length in the Z direction) of the metal support 10 was 18 μm.

[0094] The present inventors also produced a wired circuit board of Example 1, which had the same configuration as the wired circuit board 1 of Figures 1 to 3 and in which the metal thin film 20 was formed of a single layer made of chromium. The metal thin film 20 of chromium was formed by sputtering. In the wired circuit board of Example 1, the thickness (length in the Z direction) of the metal thin film 20 was 50 nm.

[0095] The present inventors also produced a wired circuit board of Example 2, which had the same configuration as the wired circuit board 1 of Figures 1 to 3 and in which the metal thin film 20 was formed of a single layer made of copper. The copper metal thin film 20 was formed by sputtering. In the wired circuit board of Example 2, the thickness (length in the Z direction) of the metal thin film 20 was 50 nm.

[0096] The present inventors also produced a wired circuit board having the same configuration as the wired circuit board 1 in FIG. 7 as a wired circuit board of Example 3. The first thin film layer 20a was made of chromium and formed by sputtering. The second thin film layer 20b was made of copper and formed by sputtering. In the wired circuit board of Example 3, the thickness (length in the Z direction) of the first thin film layer 20a was 50 nm, and the thickness (length in the Z direction) of the second thin film layer 20b was 50 nm. Therefore, the thickness (length in the Z direction) of the metal thin film 20 was 100 nm.

[0097] The dimensions of each part, such as the length, width, interval, and thickness, of the two wiring parts 41 are equal between the wired circuit boards of Comparative Examples 1 and 2 and Examples 1 to 3. The thickness of the insulating layer 30 is also equal between the wired circuit boards of Comparative Examples 1 and 2 and Examples 1 to 3.

[0098] For the plurality of wired circuit boards fabricated as described above, the impedance of the conductor layer 40 was measured by a TDR (Time Domain Reflectometry) method. Fig. 14 is a diagram showing the measurement results of the impedance of the conductor layer 40 of the wired circuit boards of Comparative Examples 1 and 2 and Examples 1 to 3.

[0099] In FIG. 14, the impedance measurement results are shown in a graph. In the graph, the vertical axis represents impedance, and the horizontal axis represents time. In the graph of FIG. 14, the impedance measurement results corresponding to the conductor layer 40 of Comparative Example 1 are shown by a dotted line, and the impedance measurement results corresponding to the conductor layer 40 of Comparative Example 2 are shown by a solid line. In addition, the impedance measurement results corresponding to the conductor layer 40 of Example 1 are shown by a thick solid line, the impedance measurement results corresponding to the conductor layer 40 of Example 2 are shown by a thick dotted line, and the impedance measurement results corresponding to the conductor layer 40 of Example 3 are shown by a thick two-dot chain line. In the graph of FIG. 14, the impedance shown in the range of about 200 ps or more and about 400 ps or less on the horizontal axis (time axis) represents the impedance corresponding to the wiring portion 41 of each printed circuit board.

[0100] 14, the impedance of wiring portion 41 of Comparative Example 1 is higher than the impedance of wiring portion 41 of Comparative Example 2 and Examples 1 to 3. In contrast, the impedance of wiring portion 41 of Comparative Example 2 is sufficiently lower than the impedance of wiring portion 41 of Comparative Example 1 and Examples 1 to 3.

[0101] The impedance of the wiring portion 41 in Examples 1 and 2 is approximately the same, sufficiently lower than the impedance of the wiring portion 41 in Comparative Example 1, and slightly higher than the impedance of the wiring portion 41 in Comparative Example 2 and Example 3. The impedance of the wiring portion 41 in Example 3 is sufficiently lower than the impedance of the wiring portion 41 in Comparative Example 1, and lies between the impedance of the wiring portion 41 in Comparative Example 2 and the impedance of the wiring portion 41 in Examples 1 and 2.

[0102] Here, in the wired circuit board of Comparative Example 2, the portion of the metal support 10 overlapping each wiring portion 41 in plan view in the Z direction functions as an impedance-reducing layer that reduces the impedance of the wiring portion 41. On the other hand, in each of the wired circuit boards of Examples 1 to 3, the portion of the metal thin film 20 overlapping each wiring portion 41 in plan view functions as an impedance-reducing layer that reduces the impedance of the wiring portion 41.

[0103] The thickness of the metal support 10 functioning as an impedance reducing layer in the wiring circuit board of Comparative Example 2 is greater than the thickness of the metal thin film 20 functioning as an impedance reducing layer in the wiring circuit boards of Examples 1 to 3. The thickness of the metal thin film 20 functioning as an impedance reducing layer in the wiring circuit board of Example 3 is greater than the thickness of the metal thin film 20 functioning as an impedance reducing layer in the wiring circuit boards of Examples 1 and 2. Considering these points, it was found that the degree of reduction in impedance of the wiring portion 41 is greater as the impedance reducing layer is thicker and is smaller as the impedance reducing layer is thinner. Therefore, when producing the wiring circuit board 1 according to the present invention, it is preferable to adjust the thickness of the metal thin film 20 overlapping the wiring portion 41 in a plan view according to the required degree of impedance reduction. [Explanation of symbols]

[0104] 1...wired circuit board, 10...metal support, 20...metal thin film, 20a...first thin film layer, 20b...second thin film layer, 20c...third thin film layer, 30...insulating layer, 31...insulating layer, 40...conductor layer, 41...wiring portion, 42...terminal portion, A1...first region, A2...second region, A3...third region, A4...fourth region, S1...first main surface, S2...second main surface, S3...third main surface

Claims

1. an insulating layer having a first main surface and a second main surface facing in opposite directions; a conductor layer provided on the first main surface of the insulating layer; a metal thin film provided on the second main surface of the insulating layer and having a third main surface facing in a direction opposite to the insulating layer; a metal support made of a metal material different from at least a part of the metal thin film; a first region and a second region that are different from each other are defined on the first main surface of the insulating layer; at least a portion of the conductor layer constitutes a wiring extending through the first region and the second region of the first main surface; a third region and a fourth region are defined on the third main surface of the metal thin film, the third region and the fourth region overlapping the first region and the second region of the first main surface, respectively, when viewed in a cross direction perpendicular to the first main surface, and the metal support is provided on the third main surface so as not to cover the third region of the third main surface and to cover the fourth region.

2. The printed circuit board according to claim 1 , wherein the first region and the second region are adjacent to each other on the first main surface.

3. the metal thin film includes a first metal film and a second metal film stacked in the intersecting direction, 3. The printed circuit board according to claim 1, wherein a metal material of at least one of said first metal film and said second metal film is different from a metal material of said metal support.

4. 3. The printed circuit board according to claim 1, wherein the thin metal film includes a plating layer.

5. 3. The printed circuit board according to claim 1, wherein the metal thin film has a thickness smaller than that of the metal support.

6. 3. The printed circuit board according to claim 1, wherein the metal thin film has a thickness of 20 nm or more and 5 [mu]m or less.

7. Providing a metal support; forming a metal thin film on the metal support, the metal thin film being made of a metal material different from the metal support; forming an insulating layer having a first main surface and a second main surface facing in opposite directions on the metal thin film such that the second main surface is in contact with the metal thin film; forming a conductor layer on the first major surface of the insulating layer; and removing a portion of the metal support after the step of forming the metal thin film. a first region and a second region that are different from each other are defined on the first main surface of the insulating layer; the step of forming the conductor layer includes forming a wiring line extending through the first region and the second region of the first main surface by using at least a portion of the conductor layer; the metal thin film has a third main surface facing away from the insulating layer and in contact with the metal support; A method for manufacturing a wired circuit board, wherein, when a third region and a fourth region are defined on the third main surface of the metal thin film, the third region and the fourth region overlapping the first region and the second region of the first main surface, respectively, when viewed in a cross direction perpendicular to the first main surface, the step of removing a portion of the metal support includes removing a portion of the metal support located in the third region of the third main surface such that the metal support does not cover the third region of the third main surface but covers the fourth region.

8. The step of forming the metal thin film includes: The method for producing a printed circuit board according to claim 7, further comprising forming at least a part of the thin metal film by sputtering.

9. The step of forming the metal thin film includes:

9. The method for producing a wired circuit board according to claim 7, further comprising forming at least a part of the thin metal film by plating.

Images