Printed wiring board

Abstract

This printed wiring board is provided with: a base film having a main surface; and a wiring disposed on the main surface. The wiring has a coil portion formed by winding the wiring in a spiral shape in plan view, and a connection portion connected to the coil portion. The connecting portion has a widened portion and a dummy portion. The width of the connecting portion increases at the widening portion. The dummy portion is connected to the broadened portion.

Description

Technical Field

[0001] This disclosure relates to printed wiring boards. This application claims priority based on Japanese Patent Application No. 2023-183235, filed October 25, 2023. Reference is made to the entire contents of that Japanese patent application, which are incorporated herein by reference. Background Technology

[0002] For example, International Patent Publication No. 2016 / 147993 (Patent Document 1) discloses a printed wiring board. The printed wiring board described in Patent Document 1 has an insulating base film and a conductive pattern. The insulating base film has a main surface. The conductive pattern is disposed on the main surface of the insulating base film. The conductive pattern has a planar coil element formed by the conductive pattern being wound into a vortex shape when viewed from above, and a connecting portion connected to the planar coil element.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2016 / 147993 Summary of the Invention

[0006] The printed wiring board disclosed herein comprises: a base film having a main surface; and wiring disposed on the main surface. The wiring has a coil portion formed by the wiring being wound into a spiral shape when viewed from above, and a connecting portion connected to the coil portion. The connecting portion has a widened portion and a dummy portion. The width of the connecting portion increases at the widened portion. The dummy portion is connected to the widened portion. Attached Figure Description

[0007] Figure 1 This is a top view of the printed wiring board 100.

[0008] Figure 2 yes Figure 1 The cross-sectional view at point II-II.

[0009] Figure 3 This is a manufacturing process diagram of the printed wiring board 100.

[0010] Figure 4 This is a cross-sectional diagram illustrating the non-electrolytic plating process S2.

[0011] Figure 5 This is a cross-sectional view illustrating the resist pattern formation process S3.

[0012] Figure 6 This is a cross-sectional diagram illustrating the electroplating process S4.

[0013] Figure 7 This is a cross-sectional view illustrating the resist pattern removal process S5.

[0014] Figure 8A This is a schematic diagram showing the structure of the connecting part 22 in sample 1.

[0015] Figure 8B This is a schematic diagram showing the structure of the connecting part 22 in sample 2.

[0016] Figure 9 This is a top view of the printed wiring board 200.

[0017] Figure 10 This is a top view of the printed wiring board 200 involved in the modified example. Detailed Implementation

[0018] [The technical problem this disclosure aims to solve]

[0019] In the printed wiring board described in Patent Document 1, the connecting portion has a first portion and a second portion that is wider than the first portion. In this case, since the width of the connecting portion changes at the boundary between the first portion and the second portion, stress concentration occurs at the boundary between the first portion and the second portion due to vibrations transmitted from the second portion to the first portion.

[0020] This disclosure is made in view of the problems of the prior art as described above. More specifically, this disclosure provides a printed wiring board capable of mitigating stress concentration at the boundaries of portions where wiring width varies.

[0021] [The Effects of This Disclosure]

[0022] According to the printed wiring board of this disclosure, stress concentration at the boundary of the portion where the wiring width changes can be mitigated.

[0023] [Description of embodiments of this disclosure]

[0024] First, embodiments of this disclosure will be described.

[0025] (1) The printed wiring board according to the embodiment includes: a base film having a main surface; and wiring disposed on the main surface. The wiring has a coil portion formed by the wiring being wound into a spiral shape when viewed from above, and a connecting portion connected to the coil portion. The connecting portion has a widened portion and a dummy portion. The width of the connecting portion is increased at the widened portion. The dummy portion is connected to the widened portion.

[0026] According to the printed wiring board of (1) above, stress concentration at the boundary of the part where the wiring width changes can be mitigated.

[0027] (2) The printed wiring board according to the embodiment includes: a base film having a main surface; and wiring disposed on the main surface. The wiring has a coil portion formed by the wiring being wound into a spiral shape when viewed from above, and a connecting portion connected to the coil portion. The connecting portion has a branch portion and a dummy portion. The connecting portion branches into multiple wiring portions at the branch portion. The dummy portion is connected to the branch portion.

[0028] According to the printed wiring board described in (2) above, stress concentration at the boundary of the part where the number of wiring portions constituting the wiring changes can be mitigated.

[0029] (3) In the printed wiring board of (1) or (2) above, the wiring may have a substrate layer and an electroplated layer. Alternatively, the substrate layer may be disposed on the main surface. Alternatively, the electroplated layer may be disposed on the substrate layer.

[0030] According to the printed wiring board described in (3) above, even when the wiring has an electrolytic plating layer and high hardness, it is possible to alleviate stress concentration at the boundary of the part where the wiring width changes or the number of wiring parts constituting the wiring changes.

[0031] [Details of the embodiments of this disclosure]

[0032] Next, 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 the description will not be repeated.

[0033] (First Implementation)

[0034] The printed wiring board according to the first embodiment will be described. The printed wiring board according to the first embodiment is designated as printed wiring board 100.

[0035] <Composition of Printed Wiring Board 100>

[0036] The following describes the structure of the printed wiring board 100.

[0037] Figure 1 This is a top view of the printed wiring board 100. Figure 2 yes Figure 1 The cross-sectional view at point II-II. (See diagram below.) Figure 1 and Figure 2 As shown, the printed wiring board 100 has a base film 10, wiring 20 and wiring 30.

[0038] The base film 10 has a main surface 10a and a main surface 10b. Main surfaces 10a and 10b are end faces of the base film 10 in the thickness direction. Main surface 10b is the surface opposite to main surface 10a. The base film 10 is made of a flexible, electrically insulating material. Polyimide is a specific example of the material constituting the base film 10.

[0039] Wiring 20 is disposed on the main surface 10a. Wiring 20 also has a coil portion 21 and a connecting portion 22. The coil portion 21 is formed by winding the wiring 20 into a spiral shape when viewed from above. The coil portion 21 has a pad 21a. The pad 21a is located at the innermost circumference of the coil portion 21. The pad 21a constitutes one end of the wiring 20. The connecting portion 22 is connected to the coil portion 21. The connecting portion 22 is connected to the outermost circumference of the coil portion 21. From another angle, the connecting portion 22 is located closer to the other end of the wiring 20 than the coil portion 21. The thickness of the wiring 20 may be, for example, 30µm or more and 200µm or less. The width of the wiring 20 at the coil portion 21 may be, for example, 10µm or more and 100µm or less. The spacing between portions of adjacent wiring 20 may be, for example, 5µm or more and 100µm or less.

[0040] The connecting portion 22 has a widened portion 22a and a dummy portion 22b. The width of the connecting portion 22 increases at the widened portion 22a. The dummy portion 22b is connected to the widened portion 22a. The end of the widened portion 22a located on the coil portion 21 side, that is, the position where the width of the connecting portion 22 begins to widen in the direction from one end of the wiring 20 to the other end, is called the starting end of the widened portion 22a. Preferably, the dummy portion 22b is connected to the starting end of the widened portion 22a. The number of dummy portions 22b may also be multiple. The dummy portion 22b is not connected to the portion of the connecting portion 22 located between the starting end of the widened portion 22a and the coil portion 21, nor to the coil portion 21.

[0041] The width of the connecting portion 22 at the widened portion 22a is set to width W1. Furthermore, the width of the connecting portion 22 located closer to the coil portion 21 than the starting end of the widened portion 22a is set to width W2. The width of the connecting portion 22 at the dummy portion 22b is set to width W3. The sum of width W2 and width W3 (in the case of multiple dummy portions 22b, the sum of the widths W3 of all dummy portions 22b) can be at least 0.5 times the width W1, or at least 0.8 times the width W1. The sum of width W2 and width W3 is, for example, less than or equal to 1 times the width W1. Widths W2 and W3 can also be, for example, 10µm or more and less than 100µm.

[0042] Wiring 30 is disposed on main surface 10b. Wiring 30 has coil portion 31. Although not shown, coil portion 31 is formed by winding wiring 30 into a spiral shape when viewed from above. Wiring 30 is electrically connected to wiring 20. More specifically, the pad located at the innermost periphery of coil portion 31 overlaps with pad 21a when viewed from above and is electrically connected to pad 21a.

[0043] Wiring 20 and wiring 30 each have a substrate layer 41 and an electroplated layer 42. The substrate layer 41 may have, for example, a seed layer 41a and an electroplated layer 41b.

[0044] A seed layer 41a is disposed on the main surfaces (main surface 10a, main surface 10b) of the base film 10. An electroless plating layer 41b is disposed on the seed layer 41a. The electroless plating layer 41b is a layer formed by electroless plating. Specific examples of materials constituting the seed layer 41a include nickel-chromium alloys. Specific examples of materials constituting the electroless plating layer 41b include copper or copper alloys.

[0045] The electroplated layer 42 is a layer formed by electroplating. A specific example of the constituent material of the electroplated layer 42 is copper or a copper alloy.

[0046] Although not shown, through-holes are formed in the base film 10 and the seed layer 41a. The through-holes penetrate the base film 10 in the thickness direction. When viewed from above, the through-holes overlap with the pads 21a and the pads of the coil portion 31. An electroless plating layer 41b is also disposed on the inner wall surface of the through-holes. The wiring 20 and wiring 30 (pads 21a and the pads of the coil portion 31) are electrically connected to each other through the electroless plating layer 41b and the electrolytic plating layer 42 disposed on the inner wall surface of the through-holes.

[0047] <Manufacturing Method of Printed Wiring Board 100>

[0048] The manufacturing method of the printed wiring board 100 will be described below.

[0049] Figure 3 This is a manufacturing process diagram of printed wiring board 100. (Example) Figure 3 As shown, the manufacturing method of the printed wiring board 100 includes a preparation step S1, an electroless plating step S2, a resist pattern forming step S3, an electrolytic plating step S4, a resist pattern removal step S5, and an etching step S6.

[0050] Electroless plating step S2 is performed after preparation step S1, and resist pattern formation step S3 is performed after electroless plating step S2. Electrolytic plating step S4 is performed after resist pattern formation step S3, and resist pattern removal step S5 is performed after electrolytic plating step S4. Etching step S6 is performed after resist pattern removal step S5.

[0051] In preparation step S1, a base film 10 is prepared. It should be noted that a seed layer 41a is disposed on the main surfaces 10a and 10b of the base film 10 prepared in preparation step S1. Before the electroless plating step S2, through-holes are formed in the base film 10 and the seed layer 41a. These through-holes are formed, for example, by laser irradiation.

[0052] Figure 4 This is a cross-sectional view illustrating the non-electrolytic plating process S2. For example... Figure 4 As shown, in the electroless plating process S2, an electroless plating layer 41b is formed on the seed layer 41a by an electroless plating method. At this time, the electroless plating layer 41b is also formed on the inner wall surface of the through hole formed on the base film 10 and the seed layer 41a.

[0053] Figure 5 This is a cross-sectional view illustrating the resist pattern formation process S3. For example... Figure 5 As shown, in the resist pattern forming process S3, a resist pattern 50 is formed on the substrate layer 41. In the resist pattern forming process S3, firstly, a dry film resist is adhered to the substrate layer 41, for example. Secondly, the adhered dry film resist is exposed and developed. As a result, the exposed portion of the dry film resist is removed, becoming the opening 51, while the unexposed portion of the dry film resist remains as the resist pattern 50. It should be noted that the substrate layer 41 is exposed from the opening 51.

[0054] Figure 6 This is a cross-sectional diagram illustrating the S4 electroplating process. For example... Figure 6 As shown, in the electroplating process S4, an electroplating layer 42 is formed on the substrate layer 41 exposed from the opening 51 by electroplating.

[0055] Figure 7 This is a cross-sectional view illustrating the resist pattern removal process S5. For example... Figure 7 As shown, in the resist pattern removal step S5, the resist pattern 50 is removed. During the removal of the resist pattern 50, an alkaline solution is sprayed onto the resist pattern 50, for example. As a result, the resist pattern 50 swells and is extruded from between portions of adjacent electroplated layers 42. The extruded resist pattern 50 is removed by a suitable method.

[0056] In etching step S6, the substrate layer 41 located beneath the resist pattern 50 is removed by etching. Thus, in the manufacturing method of the printed wiring board 100, wiring 20 and wiring 30 are formed by a semi-additive process. As described above, forming... Figure 1 and Figure 2 The structure of the printed wiring board 100 shown is illustrated.

[0057] <Effect of Printed Wiring Board 100>

[0058] The following describes the effect of the printed wiring board 100.

[0059] When vibration is transmitted from one end of the wiring 20 toward the other, the vibration is transmitted from the widened portion 22a to the portion of the connection 22 located between the starting end of the widened portion 22a and the coil portion 21. If the connection 22 does not have a dummy portion 22b, the width of the portion of the connection 22 located between the coil portion 21 and the connection portion 22 cannot withstand the aforementioned vibration, and cracks may sometimes occur at this portion.

[0060] For example, during the manufacturing process of the printed wiring board 100, the aforementioned vibrations can be generated by the spraying of alkaline solution in the resist pattern removal process S5. Furthermore, these vibrations can also occur during the transport of the printed wiring board 100. Moreover, when the wiring 20 has a high-hardness electrolytic plating layer 42, cracks are particularly prone to occur due to the aforementioned vibrations and stress concentration.

[0061] However, in the printed wiring board 100, since the connection portion 22 has a dummy portion 22b, the aforementioned vibration is dispersed not only in the portion of the connection portion 22 located between the starting end of the widening portion 22a and the coil portion 21, but also in the dummy portion 22b. Therefore, in the printed wiring board 100, stress concentration at the starting end of the widening portion 22a, i.e., the portion where the width of the connection portion 22 changes abruptly, can be mitigated, and crack formation at that portion can be suppressed.

[0062] <Example>

[0063] The effectiveness of the printed wiring board 100 was confirmed using Sample 1 and Sample 2. Figure 8A This is a schematic diagram showing the structure of the connecting part 22 in sample 1. Figure 8B This is a schematic diagram showing the structure of the connecting part 22 in sample 2. Figure 8A As shown, in sample 1, the connecting portion 22 does not have a dummy portion 22b. On the other hand, in sample 2, multiple dummy portions 22b are connected to the starting end of the widened portion 22a. That is, sample 2 has a configuration corresponding to the connecting portion 22 in the printed wiring board 100. It should be noted that in Figure 8A and Figure 8B In this diagram, the wiring portion that constitutes the connection portion 22, which is not a dummy portion 22b, is shown as the wiring portion 23.

[0064] In Sample 1, since the vibration of the widened portion 22a is dispersed among the multiple wiring portions 23 connected to the starting end of the widened portion 22a, no crack is generated at the starting end of the widened portion 22a. However, in Sample 1, at the location where the multiple wiring portions 23 merge into one wiring portion 23, cracks are generated at that location because the total width of the wiring portion 23 decreases sharply. More specifically, 105 cases of Sample 1 were observed, and cracks were found to have occurred in all of them.

[0065] On the other hand, in sample 2, the vibration of the widened portion 22a is dispersed among one wiring portion 23 and multiple dummy portions 22b. Furthermore, in sample 2, unlike sample 1, there is no point where multiple wiring portions 23 merge into a single wiring portion 23. Therefore, 120 cases of sample 2 were observed, and none of them showed crack formation. Based on this comparison, it was experimentally confirmed that connecting the dummy portions 22b to the widened portion 22a mitigates stress concentration and thus suppresses crack formation.

[0066] (Second Implementation)

[0067] The printed wiring board according to the second embodiment will be described. The printed wiring board according to the second embodiment is designated as printed wiring board 200. Here, the differences from printed wiring board 100 will be mainly described, and repeated descriptions will not be given.

[0068] <Composition of Printed Wiring Board 200>

[0069] Figure 9 This is a top view of the printed wiring board 200. (Example) Figure 9 As shown, the printed wiring board 200 has a base film 10 and wiring 20. It should be noted that, although not shown, the printed wiring board 200 also has wiring 30. In these respects, the configuration of the printed wiring board 200 is common to that of the printed wiring board 100.

[0070] In the printed wiring board 200, the connector 22 has a branch 22c. In the branch 22c, the connector 22 branches into multiple wiring sections 22ca. Figure 9 In the example shown, there are two wiring sections 22ca.

[0071] Figure 10 This is a top view of the printed wiring board 200 involved in the modified example. For example... Figure 10 As shown, in the printed wiring board 200, the connection portion 22 may also have multiple branches 22c. In the branch 22c located closest to the coil portion 21, the connection portion 22 branches into multiple wiring portions 22ca, and in other branches 22c, one of the multiple wiring portions 22ca further branches into multiple wiring portions 22ca.

[0072] The end of the branch 22c located on the coil section 21 side, i.e., the position where the connecting section 22 branches into multiple wiring sections 22ca (or the position where one wiring section 22ca branches into multiple wiring sections 22ca), is called the starting end of the branch 22c. In the printed wiring board 200, the connecting section 22 also has a dummy section 22d. The dummy section 22d is connected to the branch 22c. Preferably, the dummy section 22d is connected to the starting end of the branch 22c. The dummy section 22d is not connected to the portion of the connecting section 22 located between the starting end of the branch 22c and the coil section 21, nor to the coil section 21.

[0073] The number of dummy units 22d plus one can be, for example, more than 0.5 times the number of wiring units 22ca, or more than 0.7 times the number of wiring units 22ca. The number of dummy units 22d plus one can be, for example, less than one time the number of wiring units 22ca. In these aspects, the configuration of the printed wiring board 200 differs from that of the printed wiring board 100.

[0074] <Effect of Printed Wiring Board 200>

[0075] The following describes the effect of the printed wiring board 200.

[0076] When vibration is transmitted from one end of the wiring 20 toward the other, the vibration is transmitted from the branch 22c to the portion of the connection 22 located between the starting end of the branch 22c and the coil portion 21. In the portion of the connection 22 located between the branch 22c and the coil portion 21, stress concentration is likely to occur because the number of wiring portions is reduced.

[0077] However, in the printed wiring board 200, since the connection portion 22 has a dummy portion 22d, the aforementioned vibration is dispersed not only in the portion of the connection portion 22 located between the branch portion 22c and the coil portion 21, but also in the dummy portion 22d. Therefore, in the printed wiring board 200, stress concentration at the starting end of the branch portion 22c, i.e., the portion where the number of wiring portions constituting the connection portion 22 changes drastically, can be mitigated, and crack generation at that portion can be suppressed.

[0078] It should be understood that the embodiments disclosed herein are illustrative in all respects and not restrictive. 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.

[0079] Explanation of reference numerals in the attached figures

[0080] 10: Base film; 10a, 10b: Main surface; 20: Wiring; 21: Coil section; 21a: Pad; 22: Connection section; 22a: Widening section; 22b: Dummy section; 22c: Branch section; 22ca: Wiring section; 22d: Dummy section; 23: Wiring section; 30: Wiring; 31: Coil section; 41: Substrate layer; 41a: Seed layer; 41b: Electroless plating layer; 42: Electrolytic plating layer; 50: Resist pattern; 51: Opening; 100, 200: Printed wiring board; S1: Preparation process; S2: Electroless plating process; S3: Resist pattern formation process; S4: Electrolytic plating process; S5: Resist pattern removal process; S6: Etching process; W1, W2, W3: Width.

Claims

1. A printed wiring board, comprising: Base film, having a main surface; and Wiring, configured on the main surface, The wiring has a coil portion and a connecting portion. The coil portion is formed by the wiring being wound into a spiral shape when viewed from above. The connecting portion is connected to the coil portion. The connecting portion has an enlarged portion and a dummy portion. The width of the connecting portion increases at the widening portion. The dummy part is connected to the widened part.

2. A printed wiring board, comprising: Base film, having a main surface; and Wiring, configured on the main surface, The wiring has a coil portion and a connecting portion. The coil portion is formed by the wiring being wound into a spiral shape when viewed from above. The connecting portion is connected to the coil portion. The connecting part has a branch and a dummy part. The connecting part branches into multiple wiring parts at the branch section. The virtual part is connected to the branch part.

3. The printed wiring board according to claim 1 or 2, wherein, The wiring has a base layer and an electroplated layer. The base layer is disposed on the main surface. The electroplated layer is disposed on the substrate layer.

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