Printed wiring board

Abstract

The invention provides a printed wiring board capable of improving transmission characteristics of high-frequency signals in a signal pattern. The printed wiring board includes a bent portion that is bendable in a bending direction in plan view and includes a first dielectric layer, a signal pattern, a second dielectric layer, a fabric, and a ground pattern. The first dielectric layer has a first main surface. The signal pattern is disposed on the first main surface. The second dielectric layer has a second main surface and a third main surface, and is disposed such that the second main surface faces the first main surface, and the third main surface faces the second main surface. The woven fabric is obtained by weaving a plurality of first reinforcing fibers and a plurality of second reinforcing fibers in a cloth shape, the plurality of first reinforcing fibers extending in a first direction in plan view, and the plurality of second reinforcing fibers extending in a second direction inclined with respect to the first direction in plan view.

Description

Technical Field

[0001] This disclosure relates to printed wiring boards. Background Technology

[0002] Japanese Patent Application Publication No. 2011-54919 (Patent Document 1) discloses a printed wiring board. The printed wiring board disclosed in Patent Document 1 has a first dielectric layer, a signal pattern disposed on the first dielectric layer, an adhesive layer disposed on the first dielectric layer to cover the signal pattern, a second dielectric layer disposed on the adhesive layer, and a ground pattern disposed on the second dielectric layer.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2011-54919 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] If the printed wiring board described in Patent Document 1 is bent such that the second dielectric layer is located on the inner side of the bend than the first dielectric layer, compressive stress is applied to the second dielectric layer. If the second dielectric layer is bent due to this compressive stress, the distance between the signal pattern and the ground pattern, and consequently the impedance of the signal pattern, will change, and the transmission characteristics of high-frequency signals in the signal pattern will deteriorate. This disclosure provides a printed wiring board capable of improving the transmission characteristics of high-frequency signals in a signal pattern.

[0008] Technical solutions for solving technical problems

[0009] The printed wiring board disclosed herein includes a bending portion. The bending portion, when viewed from above, is bendable along a bending direction and includes a first dielectric layer, a signal pattern, a second dielectric layer, a fabric, and a ground pattern. The first dielectric layer has a first main surface. The signal pattern is disposed on the first main surface. The second dielectric layer has a second main surface and a third main surface, arranged such that the second main surface faces the first main surface, and the third main surface is the surface opposite to the second main surface. The fabric is formed by weaving a plurality of first reinforcing fibers and a plurality of second reinforcing fibers into a fabric-like structure. When viewed from above, the plurality of first reinforcing fibers extend along a first direction, and the plurality of second reinforcing fibers extend along a second direction inclined relative to the first direction. The fabric is disposed within the second dielectric layer. The ground pattern is disposed on the third main surface. Both the first and second directions are inclined relative to the bending direction.

[0010] Invention Effects

[0011] The printed wiring board according to this disclosure can improve the transmission characteristics of high-frequency signals in signal patterns. Attached Figure Description

[0012] Figure 1 This is a schematic side view of the printed wiring board 100.

[0013] Figure 2 This is a top view of the printed wiring board 100.

[0014] Figure 3 yes Figure 2 The cross-sectional view at point III-III.

[0015] Figure 4 This is a schematic diagram showing the orientation of reinforcing fibers 51a and 51b in the fabric 51 within the dielectric layer 50 disposed in the bent portion 10 of the printed wiring board 100.

[0016] Figure 5 This is a cross-sectional view of the printed wiring board 100 involved in Modified Example 1.

[0017] Figure 6 This is a cross-sectional view of the printed wiring board 100 involved in Variation Example 2.

[0018] Figure 7 This is a manufacturing process diagram of the printed wiring board 100.

[0019] Figure 8 This is the first cross-sectional view illustrating the preparation process S1.

[0020] Figure 9 This is the second explanatory diagram illustrating the preparation process S1.

[0021] Figure 10 This is a cross-sectional view illustrating the patterning process S2.

[0022] Figure 11 This is a schematic diagram showing the orientation of reinforcing fibers 51a and 51b in the fabric 51 within the dielectric layer 50 disposed in the bent portion 10 of the printed wiring board 200.

[0023] Figure 12 It is the load-strain curve when the angle between the long side of each sample and the first direction DR1 changes.

[0024] Figure 13 It is a graph showing the relationship between the angle between the long side direction and the first direction DR1 in each sample and the fracture strain. Detailed Implementation

[0025] [Description of embodiments of this disclosure]

[0026] First, embodiments of this disclosure will be described.

[0027] (1) The printed wiring board according to the embodiment includes a bending portion. The bending portion can be bent along the bending direction when viewed from above, and has a first dielectric layer, a signal pattern, a second dielectric layer, a fabric, and a ground pattern. The first dielectric layer has a first main surface. The signal pattern is disposed on the first main surface. The second dielectric layer has a second main surface and a third main surface, and is disposed such that the second main surface faces the first main surface, and the third main surface is the surface opposite to the second main surface. The fabric is formed by weaving a plurality of first reinforcing fibers and a plurality of second reinforcing fibers into a cloth-like structure. When viewed from above, the plurality of first reinforcing fibers extend along a first direction, and the plurality of second reinforcing fibers extend along a second direction that is inclined relative to the first direction when viewed from above. The fabric is disposed within the second dielectric layer. The ground pattern is disposed on the third main surface. The first direction and the second direction are each inclined relative to the bending direction. According to the printed wiring board of (1) above, the transmission characteristics of high-frequency signals in the signal pattern can be improved.

[0028] (2) In the printed wiring board of (1) above, the first direction may be perpendicular to the second direction.

[0029] (3) In the printed wiring board of (2) above, the angle between the first direction and the bending direction when viewed from above is 30° or more.

[0030] (4) In the printed wiring board of (2) or (3) above, the angle between the first direction and the bending direction when viewed from above is 40° or more.

[0031] (5) In the printed wiring board of (1) to (4) above, the plurality of first reinforcing fibers and the plurality of second reinforcing fibers may also be formed of glass.

[0032] (6) In the printed wiring boards of (1) to (5) above, the second dielectric layer may also be formed of fluororesin.

[0033] (7) Alternatively, the printed wiring board of (1) to (6) above may also have an adhesive layer, which is disposed between the first main surface and the second main surface in a manner that covers the signal pattern.

[0034] (8) Alternatively, the printed wiring board described in (1) to (7) above may also include a second fabric disposed within the first dielectric layer. Alternatively, the second fabric may be formed by weaving a plurality of third reinforcing fibers and a plurality of fourth reinforcing fibers into a cloth-like structure, wherein the plurality of third reinforcing fibers extend along a third direction when viewed from above, and the plurality of fourth reinforcing fibers extend along a fourth direction inclined relative to the third direction when viewed from above. Alternatively, the third direction and the fourth direction may each be inclined relative to the bending direction.

[0035] (9) In the printed wiring board of (1) to (8) above, the bending portion may be bent in such a way that the second dielectric layer is compressed.

[0036] [Details of the embodiments of this disclosure]

[0037] Next, with reference to the accompanying drawings, details of the embodiments of this disclosure will be described. In the following drawings, the same or equivalent parts will be labeled with the same reference numerals, and repeated descriptions will not be given. The printed wiring board involved in the embodiments will be designated as printed wiring board 100.

[0038] (Composition of printed wiring board 100)

[0039] The following describes the structure of the printed wiring board 100.

[0040] like Figure 1 As shown, the printed wiring board 100 has a bending portion 10. The bending portion 10 can be bent along the bending direction BD when viewed from above.

[0041] like Figure 2 and Figure 3 As shown, the printed wiring board 100 has a dielectric layer 20, a signal pattern 30, a ground pattern 31, an adhesive layer 40, a dielectric layer 50, and a ground pattern 60 at the bend portion 10.

[0042] The dielectric layer 20 has a main surface 20a and a main surface 20b. The main surface 20b is the surface opposite to the main surface 20a. The main surfaces 20a and 20b are end faces in the thickness direction of the dielectric layer 20. The dielectric layer 20 is formed of a dielectric material. For example, the dielectric layer 20 is formed of a fluoropolymer resin.

[0043] Signal pattern 30 is disposed on dielectric layer 20 (main surface 20a). Signal pattern 30 extends, for example, along the curvature direction BD when viewed from above. High-frequency signals flow, for example, within signal pattern 30. Signal pattern 30 is formed of a conductive material. Signal pattern 30 is formed, for example, of copper or a copper alloy.

[0044] A grounding pattern 31 is disposed on the dielectric layer 20 (main surface 20b). The grounding pattern 31 represents a ground potential. The grounding pattern 31 is formed of a conductive material. For example, the grounding pattern 31 is formed of copper or a copper alloy.

[0045] The adhesive layer 40 is disposed on the dielectric layer 20 (main surface 20a) in a manner that covers the signal pattern 30. The adhesive layer 40 is formed of an adhesive.

[0046] The dielectric layer 50 has a main surface 50a and a main surface 50b. The main surface 50b is the surface opposite to the main surface 50a. The main surfaces 50a and 50b are end faces of the dielectric layer 50 in the thickness direction. The dielectric layer 50 is disposed on the adhesive layer 40 with the main surface 50a facing the adhesive layer 40. The bent portion 10 is bent such that the dielectric layer 50 is located on the inner side of the bend than the dielectric layer 20.

[0047] A grounding pattern 60 is disposed on the dielectric layer 50 (main surface 50b). The grounding pattern 60 represents a ground potential. The grounding pattern 60 is formed of a conductive material. For example, the grounding pattern 60 is formed of copper or a copper alloy.

[0048] A fabric 51 is disposed within the dielectric layer 50. For example... Figure 4 As shown, fabric 51 has a plurality of reinforcing fibers 51a and a plurality of reinforcing fibers 51b. When viewed from above, the reinforcing fibers 51a extend along a first direction DR1, and the reinforcing fibers 51b extend along a second direction DR2, which is inclined relative to the first direction DR1. Fabric 51 is formed by weaving the plurality of reinforcing fibers 51a and 51b into a cloth-like structure. The reinforcing fibers 51a and 51b are, for example, formed of glass (glass fibers). That is, fabric 51 is, for example, glass cloth.

[0049] When viewed from above, the angle between the first direction DR1 and the second direction DR2 is, for example, 90°. However, as long as the first direction DR1 is tilted relative to the second direction DR2 when viewed from above, the angle between the first direction DR1 and the second direction DR2 may not be 90°.

[0050] When viewed from above, the first direction DR1 and the second direction DR2 are tilted relative to the curvature direction BD. The angle between the first direction DR1 and the curvature direction BD when viewed from above is, for example, 15° or more. The angle between the first direction DR1 and the curvature direction BD when viewed from above can be 30° or more, or 40° or more. If the angle between the first direction DR1 and the second direction DR2 is 90° when viewed from above, then ideally the angle between the first direction DR1 and the curvature direction BD is 45°. It should be noted that the angle between the first direction DR1 and the curvature direction BD when viewed from above is the smaller of the two angles formed by the two directions when viewed from above.

[0051] Although not shown, the fabric may also be disposed within the dielectric layer 20. The reinforcing fibers forming the fabric disposed within the dielectric layer 20 may also be oriented in the same manner as reinforcing fibers 51a and 51b. That is, the extension direction of one reinforcing fiber forming the fabric disposed within the dielectric layer 20 and the extension direction of the other reinforcing fiber forming the fabric disposed within the dielectric layer 20 are inclined relative to the bending direction BD. It should be noted that the extension direction of one reinforcing fiber may or may not be parallel to the first direction DR1. The extension direction of the other reinforcing fiber may or may not be parallel to the second direction DR2.

[0052] <Variation Example 1>

[0053] like Figure 5 As shown, the printed wiring board 100 may also have a cover layer 70 and a cover layer 71. The cover layer 70 has an adhesive layer 70a and a film 70b. The adhesive layer 70a is disposed on the ground pattern 60. The film 70b is disposed on the adhesive layer 70a. The cover layer 71 has an adhesive layer 71a and a film 71b. The adhesive layer 71a is disposed on the ground pattern 31. The film 71b is disposed on the adhesive layer 71a.

[0054] <Variation Example 2>

[0055] like Figure 6 As shown, the printed wiring board 100 may also have an adhesive layer 80, a dielectric layer 81, a signal pattern 82, an adhesive layer 90, a dielectric layer 91, and a grounding pattern 92.

[0056] An adhesive layer 80 is disposed on the grounding pattern 31. The adhesive layer 80 is formed of an adhesive. A dielectric layer 81 has a main surface 81a and a main surface 81b, and is disposed on the adhesive layer 80 with the main surface 81a facing the adhesive layer 80, and the main surface 81b is the surface opposite to the main surface 81a. The dielectric layer 81 is formed of a dielectric material, such as fluoropolymer. A signal pattern 82 is disposed on the main surface 81b. The signal pattern 82 is formed of a conductive material, such as copper or a copper alloy.

[0057] An adhesive layer 90 is disposed on a main surface 81b to cover the signal pattern 82. The adhesive layer 90 is formed of an adhesive. A dielectric layer 91 has a main surface 91a and a main surface 91b, and is disposed on the adhesive layer 90 with the main surface 91a facing the adhesive layer 90, the main surface 91b being the surface opposite to the main surface 91a. The dielectric layer 91 is formed of a dielectric material, such as fluoropolymer. A ground pattern 92 is disposed on the main surface 91b. The ground pattern 92 is formed of a conductive material, such as copper or a copper alloy. In this way, multiple layers of signal patterns can be disposed on the inner layers of the printed wiring board 100.

[0058] (Manufacturing method of printed wiring board 100)

[0059] The manufacturing method of the printed wiring board 100 will be described below.

[0060] like Figure 7 As shown, the manufacturing method of the printed wiring board 100 includes a preparation step S1, a patterning step S2, and a dielectric layer bonding step S3. The patterning step S2 is performed after the preparation step S1, and the dielectric layer bonding step S3 is performed after the patterning step S2.

[0061] like Figure 8 As shown, in fabrication step S1, a dielectric layer 20 is fabricated. In the dielectric layer 20 fabricated in fabrication step S1, a copper layer 32 is disposed on the main surface 20a, and a grounding pattern 31 is disposed on the main surface 20b. For example... Figure 9 As shown, in fabrication step S1, a dielectric layer 50 is also fabricated. In the dielectric layer 50 fabricated in fabrication step S1, an adhesive layer 40 is disposed on the main surface 50a, and a grounding pattern 60 is disposed on the main surface 50b. It should be noted that at this stage, the adhesive layer 40 is not yet cured.

[0062] like Figure 10 As shown, in the patterning process S2, a signal pattern 30 is formed by patterning the copper layer 32. In the patterning process S2, firstly, a resist pattern is formed on the copper layer 32. For example, a resist pattern is formed by attaching a dry film resist to the copper layer 32 and exposing and developing the dry film resist. Secondly, the copper layer 32 exposed from the openings of the resist pattern is removed by etching. Thus, the copper layer 32 is patterned to form the signal pattern 30.

[0063] In the dielectric layer bonding process S3, the dielectric layer 50 is bonded. In the dielectric layer bonding process S3, firstly, the dielectric layer 50 is arranged such that the adhesive layer 40 covers the signal pattern 30. Secondly, the dielectric layer 50 is hot-pressed onto the dielectric layer 20. That is, while heated, pressure is applied to the dielectric layer 50 towards the dielectric layer 20. As a result, the adhesive layer 40 cures, and the dielectric layer 50 is bonded to the dielectric layer 20 through the adhesive layer 40. Through the above processes, a dielectric layer 50 is formed. Figure 2 and Figure 3 The structure of the printed wiring board 100 shown is illustrated.

[0064] (The effect of printed wiring board 100)

[0065] The effect of printed wiring board 100 will be explained below by comparing it with the printed wiring board involved in the comparative example. It should be noted that the printed wiring board involved in the comparative example is referred to as printed wiring board 200.

[0066] Fluoropolymers are suitable as materials for the dielectric layer 50 due to their low dielectric constant, which is beneficial for improving the transmission characteristics of high-frequency signals flowing in the signal pattern 30. However, fluoropolymers have a high coefficient of thermal expansion. Therefore, to suppress the thermal expansion of the dielectric layer 50, it is considered to place a fabric 51 within the dielectric layer 50.

[0067] like Figure 11 As shown, in the bent portion 10 of the printed wiring board 200, when viewed from above, the first direction DR1 is parallel to the bending direction BD, and the second direction DR2 is perpendicular to the bending direction BD. The bent portion 10 is bent such that the dielectric layer 50 is located on the inner side of the bend than the dielectric layer 20. Therefore, in the printed wiring board 200, as the bent portion 10 bends, compressive stress acts on the fabric 51 disposed within the dielectric layer 50. Consequently, in the bent portion 10 of the printed wiring board 200, since the first direction DR1 is parallel to the bending direction BD, the reinforcing fiber 51a is bent due to the aforementioned compressive stress, and consequently, the dielectric layer 50 and the grounding pattern 60 disposed on the main surface 50b are also bent. As a result, in the printed wiring board 200, the distance between the grounding pattern 60 and the signal pattern 30 changes, and consequently, the impedance of the signal pattern 30 changes.

[0068] On the other hand, in the bent portion 10 of the printed wiring board 100, when viewed from above, both the first direction DR1 and the second direction DR2 are inclined relative to the bending direction BD. Therefore, the aforementioned compressive stress will not concentrate on either the reinforcing fiber 51a or the reinforcing fiber 51b, and bending of the reinforcing fiber 51a and the reinforcing fiber 51b is less likely. Consequently, according to the printed wiring board 100, the distance between the ground pattern 60 and the signal pattern 30, as well as the impedance of the signal pattern 30, are less likely to change, and the signal transmission characteristics of the signal pattern 30 are improved.

[0069] To investigate the effect of the angle between the first direction DR1 and the bending direction BD on the load-strain curve of the dielectric layer 50 when viewed from above, samples 1 to 4 were prepared as samples of the dielectric layer 50. Each sample is rectangular in shape, measuring 10 mm × 50 mm when viewed from above. The direction with a length of 50 mm in each sample is referred to as the long side direction.

[0070] In Sample 1, the angle between the first direction DR1 and the long side direction is 0° when viewed from above (the first direction DR1 is parallel to the bending direction BD). In Sample 2, the angle between the first direction DR1 and the long side direction is 15° when viewed from above. In Sample 3, the angle between the first direction DR1 and the long side direction is 30° when viewed from above. In Sample 4, the angle between the first direction DR1 and the long side direction is 45° when viewed from above. It should be noted that in Samples 1 to 4, the angle between the first direction DR1 and the second direction DR2 is 90° when viewed from above.

[0071] Tensile tests were performed on samples 1 through 4. In the tensile tests, each sample was stretched along its long side, and load-strain curves were obtained. Figure 12 and Figure 13 As shown, the fracture strain of each sample increases as the angle between the long side and the first direction DR1 increases when viewed from above.

[0072] When the bending portion 10 is bent, tensile stress is applied to the dielectric layer 20. Figure 12 and Figure 13 The results clearly show that stress is less likely to concentrate on one of the reinforcing fibers of the fabric disposed within the dielectric layer 20, thus reducing the likelihood of fiber breakage. Furthermore, when the bending portion 10 is bent, compressive stress is applied to the dielectric layer 50 to induce bending, but similarly to the case of tensile stress, stress is less likely to concentrate on one of the reinforcing fibers of the fabric disposed within the dielectric layer 50, thus reducing the likelihood of fiber bending. Therefore, it is clear that by tilting the first direction DR1 and the second direction DR2 relative to the bending direction BD when viewed from above, bending of the dielectric layer 50 is less likely, consequently reducing the impedance change of the signal pattern 30 and improving its signal transmission characteristics.

[0073] It should be understood that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the invention is set forth not by the above embodiments but by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0074] Explanation of reference numerals in the attached figures

[0075] 10. Bending section

[0076] 20 Dielectric layer

[0077] 20a, 20b Main face

[0078] 30 signal patterns

[0079] 31 Grounding pattern

[0080] 32 copper layers

[0081] 40 Adhesive layer

[0082] 50 Dielectric layer

[0083] 50a, 50b Main face

[0084] 51 Fabrics

[0085] 51a and 51b reinforcing fibers

[0086] 60 Grounding pattern

[0087] 70 Covering layer

[0088] 70a Adhesive Layer

[0089] 70b film

[0090] 71 Covering layer

[0091] 71a Adhesive layer

[0092] 71b thin film

[0093] 80 Adhesive layer

[0094] 81 Dielectric layer

[0095] 81a, 81b main surface

[0096] 82 signal patterns

[0097] 90 Adhesive layer

[0098] 91 Dielectric layer

[0099] 91a, 91b Main face

[0100] 92 Grounding pattern

[0101] 100, 200 Printed Wiring Boards

[0102] BD bending direction

[0103] DR1 First Direction

[0104] DR2 Second Direction

[0105] S1 preparation process

[0106] S2 Patterning Process

[0107] S3 Dielectric layer bonding process.

Claims

1. A printed wiring board having a bending portion, The bent portion can be bent along the bending direction when viewed from above, and has a first dielectric layer, a signal pattern, a second dielectric layer, a first fabric, and a grounding pattern. The first dielectric layer has a first main surface. The signal pattern is disposed on the first main surface. The second dielectric layer has a second main surface and a third main surface, and is configured such that the second main surface faces the first main surface, and the third main surface is the surface opposite to the second main surface. The first fabric is formed by weaving a plurality of first reinforcing fibers and a plurality of second reinforcing fibers into a fabric shape. When viewed from above, the plurality of first reinforcing fibers extend along a first direction, and the plurality of second reinforcing fibers extend along a second direction inclined relative to the first direction when viewed from above. The first fabric is disposed within the second dielectric layer. The grounding pattern is disposed on the third main surface. The first direction and the second direction are each inclined relative to the bending direction.

2. The printed wiring board according to claim 1, wherein, The first direction is perpendicular to the second direction.

3. The printed wiring board according to claim 2, wherein, When viewed from above, the angle between the first direction and the bending direction is greater than 30°.

4. The printed wiring board according to claim 2, wherein, When viewed from above, the angle between the first direction and the bending direction is greater than 40°.

5. The printed wiring board according to claim 1, wherein, The plurality of first reinforcing fibers and the plurality of second reinforcing fibers are formed of glass.

6. The printed wiring board according to claim 1, wherein, The second dielectric layer is formed of fluororesin.

7. The printed wiring board according to claim 1, wherein, The printed wiring board also includes an adhesive layer disposed between the first main surface and the second main surface in a manner that covers the signal pattern.

8. The printed wiring board according to claim 1, wherein, The printed wiring board further includes a second fabric disposed within the first dielectric layer. The second fabric is formed by weaving together a plurality of third reinforcing fibers and a plurality of fourth reinforcing fibers into a fabric shape. When viewed from above, the plurality of third reinforcing fibers extend along a third direction, and the plurality of fourth reinforcing fibers extend along a fourth direction inclined relative to the third direction when viewed from above. The third direction and the fourth direction are each inclined relative to the bending direction.

9. The printed wiring board according to any one of claims 1 to 8, wherein, The bent portion can be bent in such a way that the second dielectric layer is compressed.

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