Printed circuit board

Abstract

To provide a printed circuit board that offers excellent visibility of objects viewed through the board. [Solution] A printed wiring board according to one aspect of the present disclosure is a printed wiring board comprising a base layer and a conductive pattern disposed on the base layer, wherein the conductive pattern has one or more wirings with an average width of 15 μm or less, the conductive pattern has deformed portions in which the one or more wirings are bent, branched or intersected, and the average of the maximum widths in the deformed portions of the one or more wirings is 5 times or less the average width.

Description

Technical Field

[0001] The present disclosure relates to a printed wiring board.

Background Art

[0002] Printed wiring boards are widely used in electronic devices and the like. As a printed wiring board, a metal-clad laminate obtained by laminating a metal foil on a polyimide film having excellent transparency has been proposed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] A printed wiring board according to one aspect of the present disclosure is a printed wiring board including a base layer and a conductive pattern disposed on the base layer, wherein the conductive pattern has one or more wirings having an average width of 15 μm or less, the conductive pattern has a deformed portion where the one or more wirings are bent, branched, or crossed, and an average of the maximum widths in the deformed portion of the one or more wirings is 5 times or less the average width.

Brief Description of the Drawings

[0005] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a printed wiring board according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic plan view showing the arrangement of a plurality of wirings in the conductive pattern of the printed wiring board of FIG. 1. [Figure 3] FIG. 3 is a partially enlarged view of the conductive pattern of FIG. 2. [Figure 4] FIG. 4 is a schematic enlarged view showing a cross-section of a wiring in the printed wiring board of FIG. 1. [Figure 5]Figure 5 is a schematic plan view corresponding to Figure 2, showing the arrangement of multiple wires in the conductive pattern of the comparative example printed circuit board. [Figure 6] Figure 6 shows the visibility of the object in the embodiment with a printed circuit board in between. [Figure 7] Figure 7 shows the visibility of an object with a printed circuit board in place in a comparative example. [Figure 8] Figure 8 is a schematic diagram illustrating the width of the deformed portion in this disclosure. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] Today, with the development of XR (Cross Reality) technologies such as VR (Virtual Reality) and AR (Augmented Reality), there is a need for good visibility of objects viewed through printed circuit boards.

[0007] Patent Document 1 describes how to improve the transparency of a metal-clad laminate by using a transparent polyimide film. However, the invention described in Patent Document 1 cannot be said to have sufficiently good visibility of the object.

[0008] This disclosure is made based on the circumstances described above, and aims to provide a printed circuit board that offers excellent visibility of objects viewed through the printed circuit board.

[0009] [Effects of this disclosure] A printed circuit board according to one aspect of this disclosure offers excellent visibility of objects viewed through the printed circuit board.

[0010] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0011] (1) A printed wiring board according to one aspect of the present disclosure is a printed wiring board comprising a base layer and a conductive pattern disposed on the base layer, wherein the conductive pattern has one or more wirings with an average width of 15 μm or less, the conductive pattern has deformed portions in which the one or more wirings are bent, branched or intersected, and the average of the maximum widths in the deformed portions of the one or more wirings is 5 times or less the average width.

[0012] In this printed circuit board, the average width of one or more of the above-mentioned wirings is 15 μm or less, and the average of the maximum widths of the deformed portions of the one or more of the above-mentioned wirings is 5 times or less the average width. Therefore, when a viewer looks at an object through the printed circuit board, the conductive pattern is less likely to be noticed by the viewer. For this reason, the printed circuit board offers excellent visibility of objects viewed through it.

[0013] (2) In (1) above, the width of the deformed portion may be uniform. According to this embodiment, when a viewer looks at the object through the printed circuit board, the deformed portion becomes less noticeable to the viewer. As a result, the visibility of the object viewed through the printed circuit board can be improved.

[0014] (3) In (1) or (2) above, the variation in the width of the one or more of the wirings may be 5 μm or less. According to this embodiment, when a viewer looks at an object through the printed circuit board, the one or more of the wirings will be less noticeable to the viewer. As a result, the visibility of the object viewed through the printed circuit board can be improved.

[0015] (4) In any of (1) to (3) above, the one or more wirings may have a rectangular portion in cross-section where the thickness is greater than the width. According to this embodiment, the electrical resistance of the one or more wirings can be reduced.

[0016] (5) In any one of (1) to (4) above, the printed wiring board has a transparent region including the deformed portion in a plan view, and the transparent region may be a region in which each layer is formed mainly of a material having a total light transmittance of 85% or more excluding the conductive pattern. According to this aspect, the visibility of an object viewed through the printed wiring board can be improved.

[0017] (6) In (5) above, the base layer may be a transparent polyimide layer or a transparent polyethylene naphthalate layer. According to this aspect, the visibility of an object viewed through the printed wiring board can be further improved.

[0018] (7) In (5) or (6) above, the printed wiring board further includes an insulating resin layer disposed on the conductive pattern, and the number of resin layers in the transparent region may be 3 or less. According to this aspect, the visibility of an object viewed through the printed wiring board can be further improved.

[0019] (8) In any one of (1) to (7) above, the conductive pattern may mainly contain copper. According to this aspect, the conductivity of the conductive pattern can be improved and the cost can be reduced, and the visibility of an object viewed through the printed wiring board is excellent.

[0020] In the present disclosure, the "width" of a wiring means the wiring width in a plan view. Also, when simply referring to the "width" of a wiring, it means the wiring width in a portion other than the above-described deformed portion. Further, the "average width" of a wiring means the average value of widths at any ten points. The "average of the maximum widths in one or more deformed portions of a wiring" means, when the number of deformed portions is ten or less, the average value of the maximum widths of all the deformed portions, and when the number of deformed portions exceeds ten, the average value of the maximum widths of the deformed portions at any ten points. "The width of the deformed portion is uniform" means, as shown in FIG. 8, when the corners formed when the wiring bends, branches, or crosses while maintaining the same width in the axial direction are defined as virtual corners A0, the curvature radius R at the edge A1 of the deformed portion intersecting the bisector of this virtual corner A0 is 15 μm or less, and the upper limit of this curvature radius R may be 13 μm or 11 μm.

[0021] The "variation width of the wiring width" means the difference between the maximum width and the minimum width of the wiring in a portion other than the above-described deformed portion. "Rectangle" is a concept including a substantially rectangle. The "total light transmittance" means a value measured in accordance with JIS-K7361-1 (1997). The "transparent polyimide layer" means a resin layer mainly composed of polyimide and having a light transmittance of 80% or more in the entire wavelength range from 450 nm to 800 nm measured in accordance with JIS-K0115 (2020). The "transparent polyethylene naphthalate layer" means a resin layer mainly composed of polyethylene naphthalate and having a light transmittance of 80% or more in the entire wavelength range from 450 nm to 800 nm measured in accordance with JIS-K0115 (2020). The "main component" means the component having the largest content in terms of mass conversion, for example, a component having a content of 50% by mass or more.

[0022] [Details of Embodiments of the Present Disclosure] Preferred embodiments of this disclosure will be described below with reference to the drawings. Note that, regarding the numerical values ​​described herein, it is possible to adopt only one of the upper or lower limits, or to combine the upper and lower limits as desired. This specification includes all possible numerical ranges that can be combined. Furthermore, the figures are schematic and may not correspond to actual shapes, dimensions, proportions, etc.

[0023] [First Embodiment] <Printed wiring board> The printed circuit board 1 shown in Figures 1 and 2 comprises a base layer 10 and a conductive pattern 11 disposed on the base layer 10. The conductive pattern 11 has one or more wirings 21 with an average width W of 15 μm or less. The conductive pattern 11 has deformed portions 22 where one or more wirings 21 are bent, branched, or intersecting. As shown in Figure 3, the average of the maximum widths Wmax in the deformed portions 22 of one or more wirings 21 is 5 times or less the average width W.

[0024] The printed circuit board 1 has an average width W of 15 μm or less for one or more wires 21, and the average of the maximum width Wmax in the deformed portion 22 of one or more wires 21 is 5 times or less of the average width W. Therefore, when a viewer looks at an object through the printed circuit board 1, the conductive pattern 11 is not easily noticeable to the viewer. For this reason, the printed circuit board 1 has excellent visibility of objects viewed through it.

[0025] The printed circuit board 1 is not particularly limited in its other structure, as long as the conductive pattern 11 is arranged on the base layer 10. As an example, Figure 1 describes a laminated structure in which coverlays 12 are laminated on both sides of the base layer 10. The coverlay 12 is a two-layer structure consisting of an adhesive layer 13 arranged on the base layer 10 and an insulating layer 14 arranged on the adhesive layer 13. That is, in Figure 1, the printed circuit board 1 is a five-layer structure in which the adhesive layer 13 and the insulating layer 14 are laminated in that order on both sides of the base layer 10. Note that the printed circuit board 1 in Figure 1 may have a five-layer structure in part, and may also have parts other than five layers. Also, although Figure 1 illustrates a structure in which the conductive pattern 11 is arranged on only one side of the base layer 10, the printed circuit board 1 may have the conductive pattern 11 arranged on both sides of the base layer 10. In this case, each of the conductive patterns 11 arranged on both sides of the base layer 10 may have one or more wirings 21 and deformable portions 22. Details of the conductive pattern 11, which is arranged on one or both sides of the base layer 10, will be described later.

[0026] (Base layer) The base layer 10 is insulating. The base layer 10 may or may not be flexible. If the base layer 10 is flexible, the printed circuit board 1 may be a flexible printed circuit board or a flex-rigid printed circuit board.

[0027] If the base layer 10 is flexible, it may be a resin layer mainly composed of resin. In this case, the base layer 10 may be a resin film. When the base layer 10 is a resin layer, examples of the main components of the base layer 10 include polyimide, polyethylene terephthalate, polyethylene naphthalate, liquid crystal polymer, and fluororesin. Among these, the base layer 10 may be a transparent polyimide layer or a transparent polyethylene naphthalate layer. By making the base layer 10 a transparent polyimide layer or a transparent polyethylene naphthalate layer, heat resistance and flexibility can be improved. Furthermore, by making the base layer 10 a transparent polyimide layer or a transparent polyethylene naphthalate layer, it becomes easier for the viewer to see the object through the base layer 10. As a result, the visibility of the object viewed through the printed circuit board 1 can be further improved.

[0028] When the base layer 10 is a transparent polyimide layer, the lower limit of the polyimide content in the base layer 10 may be 60% by mass, 70% by mass, 80% by mass, 90% by mass, or 95% by mass. Furthermore, the polyimide content in the base layer 10 may be 100% by mass. The higher the polyimide content of the base layer 10, the more transparent it can become.

[0029] When the base layer 10 is a transparent polyethylene naphthalate layer, the lower limit of the polyethylene naphthalate content in the base layer 10 may be 60% by mass, 70% by mass, 80% by mass, 90% by mass, or 95% by mass. Furthermore, the polyethylene naphthalate content in the base layer 10 may be 100% by mass. The higher the polyethylene naphthalate content of the base layer 10, the more transparent it can become.

[0030] The lower limit of the average thickness of the base layer 10 may be 3 μm, 5 μm, or 10 μm, from the viewpoint of increasing insulating strength and mechanical strength. On the other hand, the upper limit of the average thickness may be 70 μm or 50 μm, from the viewpoint of increasing light transmittance and flexibility. By having an average thickness of the base layer 10 below the above upper limit, it is easy to control the light transmittance of the base layer 10 to 800 μm or more in the entire range of wavelengths from 450 nm to 800 nm, as measured in accordance with JIS-K0115 (2020). In other words, by having an average thickness of the base layer 10 below the above upper limit, it is easy to form it as a transparent polyimide layer or a transparent polyethylene naphthalate layer. In this disclosure, "average thickness" means the average value of the thicknesses at any 10 points.

[0031] (Conductive pattern) As described above, the conductive pattern 11 is arranged on one or both sides of the base layer 10. The conductive pattern 11 may also be directly arranged on one or both sides of the base layer 10. The conductive pattern 11 can be formed, for example, by a semi-additive method. By forming the conductive pattern 11 by a semi-additive method, the shape of the deformed portion 22, described later, can be easily controlled.

[0032] As shown in Figure 4, the conductive pattern 11 includes, for example, a conductive underlayer 11a and a plating layer 11b laminated on the conductive underlayer 11a. The conductive underlayer 11a and the plating layer 11b are both conductive.

[0033] The conductive underlayer 11a can be formed, for example, by sputtering or electroless plating, and may be formed by sputtering. In other words, the conductive underlayer 11a may be a sputtered layer. Examples of materials for forming the conductive underlayer 11a include copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), or alloys thereof. In particular, the conductive underlayer 11a may contain one or both nickel and chromium, or it may contain a nickel-chromium alloy. The conductive underlayer 11a contains one or both nickel and chromium, which makes it easier to maintain adhesion with the base layer 10.

[0034] The conductive underlayer 11a may be a single-layer structure or a multi-layer structure. If the conductive underlayer 11a is a single-layer structure, it may be the sputtered layer described above. If the conductive underlayer 11a is a multi-layer structure, it may be a two-layer structure, for example, consisting of a sputtered layer and an electroless plating layer. The electroless plating layer may be, for example, an electroless copper plating layer mainly composed of copper.

[0035] The plating layer 11b is, for example, an electroplated layer formed by electroplating. The plating layer 11b may be, for example, an electroplated copper layer with copper as the main component. The conductive underlayer 11a and the plating layer 11b can be layers containing different components.

[0036] When the plating layer 11b is mainly composed of copper, the conductive pattern 11 is formed mainly of copper. According to this embodiment, the conductivity of the conductive pattern 11 can be improved and costs can be reduced, and the visibility of objects viewed through the printed circuit board 1 is excellent.

[0037] (wiring) One or more wirings 21 are provided on the base layer 10 as part of a conductive pattern 11. The wiring 21 is, for example, a two-layer structure consisting of a conductive underlayer 11a and a plating layer 11b. In this disclosure, "wiring" means a linear, elongated portion and does not include, for example, pad portions or land portions.

[0038] The wiring 21 may have a large thickness relative to its width. The upper limit of the average width W of one or more wirings 21 can be 15 μm, as described above. The upper limit of the average width W may be 10 μm or 8 μm, from the viewpoint of further improving the visibility of objects viewed through the printed circuit board 1. The printed circuit board 1 can be easily made to have a smaller average width W by forming one or more wirings 21 using a semi-additive method. The lower limit of the average width W is not particularly limited, but from the viewpoint of preventing insufficient mechanical strength, it may be 4 μm or 6 μm, for example.

[0039] The upper limit of the variation in the width of one or more wires 21 may be 5 μm, 3 μm, or 2 μm, from the viewpoint of making it difficult for a viewer to notice the one or more wires 21 when they look at the object through the printed circuit board 1. Alternatively, the variation may be 0 μm. The smaller the variation in the width of one or more wires 21, the less likely they are to be noticed by a viewer.

[0040] The average thickness T of one or more wirings 21 may be greater than the average width W. The lower limit of the average thickness T may be 5 μm, 8 μm, or 10 μm. By increasing the average thickness T relative to the average width W, the printed circuit board 1 can reduce the electrical resistance of one or more wirings 21 while improving the visibility of objects viewed through the printed circuit board 1. The upper limit of the average thickness T is not particularly limited, but it may be 20 μm from the viewpoint of being able to sufficiently follow the flexible deformation of the base layer 10.

[0041] One or more wirings 21 may have the same thickness in the deformed portion 22 and in the portion other than the deformed portion 22. In this embodiment as well, the maximum width Wmax of the wirings 21 in the deformed portion 22 of the printed circuit board 1 can be sufficiently reduced.

[0042] As shown in Figure 4, one or more wirings 21 may have a rectangular portion Q in their cross-section (a cross-section perpendicular to the axis) where the thickness is greater than the width. The overall shape of one or more wirings 21 in the cross-section may consist of the rectangular portion Q, or a part of the shape in the cross-section may have the rectangular portion Q. The printed circuit board 1 can easily form the rectangular portion Q on one or more wirings 21 by, for example, forming the conductive pattern 11 by the semi-adhesive method. Having the rectangular portion Q on one or more wirings 21 can reduce their electrical resistance.

[0043] As shown in Figure 4, one or more wirings 21 have a bottom surface 21a fixed to the base layer 10 and a top surface 21b facing the bottom surface 21a. The top surface 21b may have rounded edges at both ends in the width direction. The printed circuit board 1 can be easily obtained in the above shape by, for example, using a semi-additive method. The printed circuit board 1 has the above shape, which makes it easier to fill gaps between multiple wirings 21 with coverlays 12, etc. As a result, the thickness of coverlays 12, etc. can be reduced, and the visibility of objects viewed through the printed circuit board 1 can be improved.

[0044] The conductive pattern 11 has a plurality of parallel wirings 21. More specifically, in the conductive pattern 11, the plurality of wirings 21 are arranged in a grid pattern, and more specifically, in a square grid pattern. The upper limit of the pitch P (see Figure 2) between adjacent wirings 21 can be set based on the application of the printed circuit board 1, but it may be, for example, 300 μm, 280 μm, 250 μm, or 220 μm. The printed circuit board 1 reduces the average width W of one or more wirings 21, and sets the average value of the maximum width Wmax in the deformed portion 22 of one or more wirings 21 to be 5 times or less the average width W of one or more wirings 21. Therefore, even if the pitch P between adjacent wirings 21 is reduced to be below the above upper limit (i.e., even if adjacent wirings 21 are densely arranged), the visibility of objects viewed through the printed circuit board 1 can be improved. On the other hand, the lower limit of the pitch P is not particularly limited, but may be, for example, 50 μm, 100 μm, 150 μm, or 180 μm. Note that "pitch between adjacent wirings" refers to the distance between the axes of adjacent wirings.

[0045] The lower limit of the ratio (P / W) of the pitch P between adjacent wirings 21 to the average width W of multiple wirings 21 may be 20, 23, or 25. On the other hand, the upper limit of the above ratio (P / W) may be 35, 32, or 30. By setting the above ratio (P / W) within the above range, it is easier to improve the visibility of objects viewed through the printed circuit board 1 while densely arranging multiple wirings 21.

[0046] (Deformed part) As described above, the deformed portion 22 is a portion where one or more wires 21 are bent, branched, or crossed.

[0047] The deformed portion 22 is formed by the bent portion of one wiring 21 or the connection portion of two or more wirings 21 (in Figures 2 and 3, the deformed portion 22 is formed by the intersection of two wirings 21). The bending angle of the wiring 21 in the deformed portion 22 or the angle between the wirings 21 (hereinafter also referred to as "bending angle, etc.") may be 80° to 100°, 85° to 95°, or 90°, from the viewpoint of reducing the maximum width Wmax. If the bending angle, etc. is outside the above range, the deformed portion 22 tends to be wider than other parts. If the width of the deformed portion 22 is large, for example, when viewing an object through the printed circuit board 1, the viewer's attention tends to be drawn to the deformed portion 22, reducing the visibility of the object. The printed circuit board 1 can easily reduce the average of the maximum width Wmax in the deformed portions 22 of one or more wirings 21 by reducing the maximum width Wmax in each deformed portion 22. From this perspective, the ratio of deformed portions 22 whose bending angle, etc., is within the above range to the total number of deformed portions 22 may be 50% or more, 70% or more, 80% or more, 90% or more, or 100%.

[0048] Corners 22a are formed at the edges of the deformed portion 22 by the bending of one wire 21 or by the connection of two or more wires 21. Corners 22a may be bent at an obtuse angle, a right angle, or an acute angle. Corners 22a may be formed by two straight sides, or they may be rounded. If corners 22a are rounded, the width of the wire 21 may be partially increased in the deformed portion 22.

[0049] In Figures 2 and 3, a deformed section 22 is formed by the intersection of two wires 21, and in the deformed section 22, the wires 21 are widened on both sides. The upper limit of the average value of the maximum width Wmax in the deformed section 22 of one or more wires 21 is 5 times the average width W of one or more wires 21, but may also be 4 times, 3.5 times, or 3.2 times, from the viewpoint of avoiding the viewer's attention being drawn to the deformed section 22. Here, "maximum width" in the deformed section of the wire means the maximum width in a cross-section (transverse plane) perpendicular to the axis of the wire, and in Figures 2 and 3, it means the maximum value of the widening width of the deformed section 22 in the cross-section. Furthermore, if only one side of the wire 21 is widened, such as when the deformed section 22 is formed by the bending of one wire 21, the maximum width Wmax of the wire 21 in the deformed section 22 may be smaller than when the wire 21 is widened on both sides. For example, the upper limit of the maximum width Wmax of the wiring 21 in the deformed portion 22 may be 3 times, 2.5 times, or 2.2 times the average width W of one or more wirings 21.

[0050] The width of the deformed portion 22 may be uniform. That is, the edge of the deformed portion 22 may substantially coincide with a virtual edge formed when the wiring 21 bends, branches, or intersects while maintaining the same width in the axial direction. According to this embodiment, when a viewer looks at an object through the printed circuit board 1, the deformed portion 22 becomes less noticeable to the viewer. As a result, the visibility of the object viewed through the printed circuit board 1 can be improved.

[0051] If the corner formed when the wiring 21 bends, branches, or intersects while maintaining the same width in the axial direction is defined as a virtual corner A0, the upper limit of the distance L (see Figure 3) between the virtual corner A0 and the edge A1 of the deformed portion 22 that intersects with the bisector of the virtual corner A0 may be 10 μm, 8 μm, or 6 μm, from the viewpoint of avoiding the viewer's attention being drawn to the deformed portion 22. On the other hand, the lower limit of the above distance L is not particularly limited and may be 0 μm.

[0052] (Coverlay) As described above, the coverlay 12 has an adhesive layer 13 and an insulating layer 14. The adhesive layer 13 is arranged so as to sandwich the conductive pattern 11 between it and the base layer 10. The upper limit of the average thickness of the adhesive layer 13 (average thickness relative to the surface of the base layer 10) is sufficient as long as it is greater than the average thickness T of the multiple wirings 21, for example it may be 40 μm or 30 μm. By keeping the average thickness of the adhesive layer 13 below the above upper limit, the visibility of the object viewed through the printed circuit board 1 can be improved. The lower limit of the average thickness of the adhesive layer 13 may be, for example, 10 μm or 15 μm.

[0053] The insulating layer 14 has insulating properties. The insulating layer 14 is a resin layer mainly composed of resin. That is, the insulating layer 14 is an insulating resin layer placed on the conductive pattern 11. The insulating layer 14 may also be a resin film. The main component of the insulating layer 14 is the same resin as described for the base layer 10. In particular, the insulating layer 14 may be a transparent polyimide layer or a transparent polyethylene naphthalate layer. The insulating layer 14 being a transparent polyimide layer or a transparent polyethylene naphthalate layer improves heat resistance and flexibility. Furthermore, the insulating layer 14 being a transparent polyimide layer or a transparent polyethylene naphthalate layer makes it easier for the observer to see the object through the insulating layer 14.

[0054] The printed circuit board 1 allows for easy control of the composition of the insulating layer 14 by using a coverlay 12. As a result, the visibility of objects viewed through the printed circuit board 1 can be further improved.

[0055] If the insulating layer 14 is a transparent polyimide layer, the polyimide content in the insulating layer 14 can be the same as the polyimide content described in the base layer 10 above. Also, if the insulating layer 14 is a transparent polyethylene naphthalate layer, the polyethylene naphthalate content in the insulating layer 14 can be the same as the polyethylene naphthalate content described in the base layer 10 above.

[0056] The lower limit of the average thickness of the insulating layer 14 may be 3 μm, 5 μm, or 10 μm, from the viewpoint of increasing the insulating strength. On the other hand, the upper limit of the average thickness of the insulating layer 14 may be 50 μm, 30 μm, or 20 μm, from the viewpoint of increasing the light transmittance.

[0057] (transparent area) The printed circuit board 1 may have a transparent region S including a deformed portion 22 in a plan view (see Figure 2). The transparent region S is a region in which each layer is formed mainly of a material with a total light transmittance of 85% or more, excluding the conductive pattern 11. The transparent region S may be a region in which all layers except the conductive pattern 11 are mainly composed of a material with a total light transmittance of 85% or more. The transparent region S is a region in which coverlays 12 are arranged on both sides of the base layer 10. The transparent region S is a region consisting of a three-layer structure of the base layer 10 and a pair of coverlays 12, or more specifically, a five-layer structure of the base layer 10, a pair of adhesive layers 13, and a pair of insulating layers 14. Each of the above layers in the transparent region S may be the base layer 10 and the pair of insulating layers 14. Alternatively, each of the above layers may be the base layer 10, the pair of adhesive layers 13, and the pair of insulating layers 14. By having a transparent region S, the printed circuit board 1 can improve the visibility of objects viewed through the printed circuit board 1.

[0058] The number of resin layers (resin films) in the transparent region S is 3 or less. Furthermore, the resin layers included in the transparent region S may all be either the transparent polyimide layer or the transparent polyethylene naphthalate layer. By having 3 or fewer resin layers in the transparent region S, the visibility of objects viewed through the printed circuit board 1 can be further improved. It is sometimes desirable for the visibility of objects viewed through the printed circuit board 1 to be high in the transparent region S. Therefore, it is sometimes desirable for the bending angle, etc., to be controlled in the transparent region S. Specifically, in the transparent region S, the proportion of deformed portions 22 with a bending angle, etc., of 80° to 100°, 85° to 95°, or 90° relative to the total number of deformed portions 22 may be 70% or more, 80% or more, 90% or more, or 100%.

[0059] <Manufacturing method for printed circuit boards> Next, an example of a method for manufacturing the printed circuit board 1 will be described. The method for manufacturing the printed circuit board comprises a step S1 of forming a conductive pattern on a base layer, and a step S2 of laminating an insulating layer on the conductive pattern formed in step S1. The conductive pattern has one or more wirings with an average width W of 15 μm or less. The conductive pattern also has deformed portions where the one or more wirings are bent, branched, or intersecting. The average of the maximum widths Wmax in the deformed portions of the one or more wirings is 5 times or less the average width W.

[0060] According to the method for manufacturing printed circuit boards, the above-mentioned printed circuit board 1 can be easily manufactured.

[0061] (Formation process S1) In forming step S1, a conductive pattern is formed using a semi-additive method. In forming step S1, a conductive pattern 11 having the deformed portion 22 described above is formed. First, in forming step S1, a laminate is prepared in which a conductive underlayer is laminated on a base layer 10. Then, in forming step S1, a resist pattern is placed on the conductive underlayer in the laminate. The resist pattern may be formed using, for example, a photosensitive dry film resist.

[0062] Next, in the forming step S1, a plating layer is formed by electroplating onto the conductive underlayer after the resist pattern has been placed. The electroplating may be, for example, electroplated copper.

[0063] Next, in forming step S1, after electroplating, the resist pattern and the conductive underlayer overlapping the resist pattern are removed. As a result, one or more wirings 21 are formed on the base layer 10, with the conductive underlayer 11a and the plating layer 11b stacked in this order.

[0064] (Lamination process S2) In lamination step S2, an insulating layer 14 is laminated so as to sandwich the conductive pattern 11 between it and the base layer 10. In lamination step S2, the insulating layer 14 may also be laminated on both sides of the base layer 10. The insulating layer 14 laminated in lamination step S2 is, for example, the transparent polyimide layer or the transparent polyethylene naphthalate layer described above.

[0065] In the lamination process S2, the coverlay 12 may be laminated on the base layer 10. In this case, in the lamination process S2, the coverlay 12 is laminated on the base layer 10 such that an adhesive layer 13 is placed on the base layer 10, and an insulating layer 14 is placed on this adhesive layer 13.

[0066] In the lamination step S2, a transparent region S may be formed in the resulting printed circuit board 1 by laminating an insulating layer 14 on the base layer 10. This transparent region S includes the deformed portion 22 described above in a plan view. By forming the transparent region S in the lamination step S2, the visibility of objects viewed through the resulting printed circuit board 1 can be improved.

[0067] [Other embodiments] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is not limited to the configurations of the embodiments described above, but is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0068] For example, Figures 2 and 3 illustrate a deformed portion formed by the intersection of multiple wires, but in this disclosure, the deformed portion may be formed by the bending of a single wire, or by the branching of multiple wires.

[0069] The printed circuit board may have wiring with an average width exceeding 15 μm. For example, if the printed circuit board has the transparent region and a portion other than the transparent region, the average width of the wiring in the portion other than the transparent region may also exceed 15 μm.

[0070] The width of the deformed portion of the printed circuit board can be made non-uniform, provided that it does not affect the visibility of the object.

[0071] In the above embodiment, one or more wirings have a rectangular portion in cross-section. On the other hand, depending on the application of the printed circuit board, the wirings do not need to have a rectangular portion in cross-section.

[0072] The printed circuit board can have four or more resin layers, provided that the visibility of the object viewed through the printed circuit board is satisfactory. Furthermore, although the above embodiment described an insulating layer using a coverlay, the insulating layer may be formed using, for example, a solder resist. Examples of solder resists include photosensitive liquid solder resist and photosensitive dry film solder resist.

[0073] In the above embodiment, a two-layer structure consisting of a conductive underlayer and a plating layer was exemplified as the conductive pattern, but the layer structure of the conductive pattern is not limited to the structure described in the above embodiment. Furthermore, in the above embodiment, the conductive underlayer was described as being formed by sputtering or electroless plating, but the conductive underlayer may be attached to the base layer using an adhesive, or it may be formed by a sintered body using copper nanoparticles.

[0074] In the above embodiment, a procedure for forming a conductive pattern by a semi-additive method was described, but in this disclosure, it is also possible to form a conductive pattern by a subtractive method. [Examples]

[0075] The present disclosure will be described in detail below based on examples, but the present disclosure should not be construed as being limited based on the description of these examples.

[0076] [Examples] A conductive pattern was formed on one side of a copper-clad laminate with a transparent polyethylene naphthalate layer as the base layer, using a subtractive etching method. Furthermore, coverlays consisting of an adhesive layer and an insulating layer were laminated on both sides of the laminate with the conductive pattern on the base layer. A resin film made of transparent polyimide was used as the insulating layer. In the example, the average thickness of the base layer was 25 μm, the average thickness of the adhesive layer was 25 μm, and the average thickness of the insulating layer was 12.5 μm. The conductive pattern in the example had multiple wires arranged in the configuration shown in Figure 2 (square grid), with an average width W of 7.5 μm and an average maximum width Wmax of 23.9 μm in the deformed portions of the wires. In this conductive pattern, the pitch P between adjacent wires was 200 μm, and the radius of curvature R in the deformed portions was 10.4 μm. Furthermore, the multiple wires had rectangular portions in cross-section where the height was greater than the width.

[0077] [Comparative Example] A conductive pattern was formed on one side of a copper-clad laminate with a transparent polyethylene naphthalate layer as the base layer, similar to that in the example, by a subtractive etching method. Furthermore, coverlays consisting of an adhesive layer and an insulating layer were laminated on both sides of the laminate with the conductive pattern on the base layer. The conductive pattern 101 in the comparative example had multiple wirings 102 arranged in the configuration shown in Figure 5 (square grid), with an average width W of 15 μm and an average maximum width Wmax of 168.8 μm in the deformed portion 103 of the multiple wirings 102. In this conductive pattern 101, the pitch P between adjacent wirings 102 was 300 μm, and the radius of curvature R in the deformed portion 103 was 49.5 μm. Furthermore, the multiple wirings 102 were approximately trapezoidal in cross-section.

[0078] (Visibility of the object) Figure 6 shows the object 200 as viewed through the printed circuit board of the embodiment, and Figure 7 shows the object 200 as viewed through the printed circuit board of the comparative example. Comparing Figure 6 and Figure 7, in Figure 6, the average of the maximum widths in the deformed parts of multiple wires is small, so even if the pitch P between adjacent wires is reduced, the viewer's attention is less likely to be drawn to the wires. Also, with respect to the printed circuit board of the embodiment, when the object 200 is viewed through the printed circuit board with the naked eye, the wires are almost imperceptible. In contrast, in Figure 7, the average of the maximum widths in the deformed parts of multiple wires is large, so even if the pitch P between adjacent wires is increased, the viewer's attention is more likely to be drawn to the wires.

[0079] Thus, with the printed circuit board of this disclosure, when the object 200 is viewed through the printed circuit board, the viewer's attention is easily directed towards the object 200. Therefore, the printed circuit board of this disclosure offers excellent visibility of the object 200 when viewed through the printed circuit board. [Explanation of symbols]

[0080] 1 Printed circuit board 10 Base Layer 11 Conductive Patterns 11a Conductive underlayer 11b Plating layer 12 Coverlays 13 Adhesive layer 14. Insulating layer 21 Wiring 21a Bottom 21b Top surface 22 Deformed parts 22a Corner 101 Conductive Pattern 102 Wiring 103 Deformed part 200 Objects L is the distance between the virtual angle and the edge of the deformed portion where it intersects with the angle bisector of the virtual angle. P: Pitch between adjacent wires Q rectangular part R: Radius of curvature at the edge of the deformed portion S transparent area Average thickness of T wiring W average width of wiring Wmax: Maximum width of wiring in the deformed section A0 Virtual corner A1 Edge of the deformed portion intersecting the angle bisector of the virtual angle

Claims

1. A printed wiring board comprising a base layer and a conductive pattern disposed on the base layer, The above conductive pattern has one or more wirings with an average width of 15 μm or less. The conductive pattern described above has deformed portions in which the one or more of the above-mentioned wirings are bent, branched, or intersected. A printed circuit board in which the average of the maximum widths in the deformed portions of the one or more of the above-mentioned wirings is five times or less the average width.

2. The printed circuit board according to claim 1, wherein the width of the deformed portion is uniform.

3. The printed circuit board according to claim 1 or claim 2, wherein the variation in the width of the one or more of the above-mentioned wirings is 5 μm or less.

4. The printed circuit board according to claim 1 or claim 2, wherein the one or more of the above-mentioned wirings have rectangular portions in cross-section where the thickness is greater than the width.

5. In a plan view, it has a transparent region that includes the deformed portion described above. The printed circuit board according to claim 1, wherein the transparent region is a region in which each layer is formed mainly of a material with a total light transmittance of 85% or more, excluding the conductive pattern.

6. The printed circuit board according to claim 5, wherein the base layer is a transparent polyimide layer or a transparent polyethylene naphthalate layer.

7. The device further comprises an insulating resin layer disposed on the conductive pattern described above. The printed circuit board according to claim 5 or claim 6, wherein the number of resin layers in the transparent region is three or less.

8. The above conductive pattern is a printed circuit board according to claim 1 or claim 2, with copper as the main component.

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