Printed wiring board

Abstract

A printed wiring board comprises a base film, a first foundation layer, and a second foundation layer. The base film has a first surface and a second surface. The second surface is positioned opposite from the first surface. The first foundation layer is disposed on the first surface. The second foundation layer is disposed on the second surface. The base film and the first foundation layer are provided with a through-hole that reaches the second surface. The second foundation layer closes the through-hole. The through-hole is filled with a conductive member. The conductive member includes a first conductive part and a second conductive part. The second conductive part is disposed on the first conductive part. The second conductive part has a first interface with the first conductive part.

Description

printed wiring board

[0001] The present disclosure relates to a printed wiring board. This application claims priority to Japanese Patent Application No. 2024-153301, filed on September 5, 2024. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Japanese Patent Laid-Open Publication No. 2008-218540 (Patent Document 1) describes a printed wiring board in which through holes filled with a conductive material are formed in a base film.

[0003] JP 2008-218540 A

[0004] The printed wiring board according to the present disclosure comprises a base film, a first underlayer, and a second underlayer. The base film has a first surface and a second surface. The second surface is located opposite the first surface. The first underlayer is disposed on the first surface. The second underlayer is disposed on the second surface. The base film and the first underlayer have through holes that reach the second surface. The second underlayer blocks the through holes. The through holes are filled with a conductive member. The conductive member includes a first conductive portion and a second conductive portion. The second conductive portion is disposed on the first conductive portion. The second conductive portion has a first interface with the first conductive portion.

[0005] FIG. 1 is a schematic cross-sectional view of a printed wiring board according to the first embodiment. FIG. 2 is a flow diagram schematically showing a method for manufacturing a printed wiring board according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing one step of the method for manufacturing a printed wiring board according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing one step of the method for manufacturing a printed wiring board according to the first embodiment. FIG. 5 is a schematic cross-sectional view showing one step of the method for manufacturing a printed wiring board according to the first embodiment. FIG. 6 is a schematic cross-sectional view showing one step of the method for manufacturing a printed wiring board according to the first embodiment. FIG. 7 is a schematic cross-sectional view showing one step of the method for manufacturing a printed wiring board according to the first embodiment. FIG. 8 is a schematic cross-sectional view of a printed wiring board according to a second embodiment.

[0006] [Problem to be Solved by the Present Disclosure] Increasing the thickness of the base film improves the transmission characteristics of a printed wiring board. However, in a heat cycle test, the conductive material filling the through holes may peel off from the through holes due to repeated thermal expansion. Therefore, there is room for improvement in the reliability of the printed wiring board.

[0007] An object of the present disclosure is to provide a printed wiring board with improved reliability. [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a printed wiring board with improved reliability.

[0008] [Outline of the embodiment of the present disclosure] First, an outline of the embodiment of the present disclosure will be described.

[0009] (1) A printed wiring board according to the present disclosure includes a base film, a first underlayer, and a second underlayer. The base film has a first surface and a second surface. The second surface is located opposite the first surface. The first underlayer is disposed on the first surface. The second underlayer is disposed on the second surface. The base film and the first underlayer have through holes that reach the second surface. The second underlayer blocks the through holes. The through holes are filled with a conductive material. The conductive material includes a first conductive portion and a second conductive portion. The second conductive portion is disposed on the first conductive portion. The second conductive portion has a first interface with the first conductive portion. This prevents peeling of the conductive material filled in the through holes. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0010] (2) In the printed wiring board according to (1) above, the conductive member may include a third conductive portion disposed on the second conductive portion. The third conductive portion may have a second interface between the third conductive portion and the second conductive portion. The distance from the second surface to the second interface may be greater than the distance from the second surface to the first interface. This prevents peeling of the conductive member filled in the through hole. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0011] (3) In the printed wiring board according to (1) or (2), the distance from the first surface to the second surface may be 80 μm or more and 350 μm or less. This prevents the conductive material filled in the through holes from peeling off. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0012] (4) In the printed wiring board according to any one of (1) to (3), the distance from the second surface to the first interface may be 0.20 to 0.85 times the distance from the second surface to the first surface. This prevents peeling of the conductive material filled in the through hole. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0013] (5) In the printed wiring board according to any one of (1) to (4), the width of the through hole may be 50 μm or more and 200 μm or less. This prevents peeling of the conductive material filled in the through hole. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0014] (6) In the printed wiring board according to any one of (1) to (5) above, the aspect ratio may be the distance from the first surface to the second surface divided by the width of the through hole. The aspect ratio may be 0.8 or more and 4.0 or less. This prevents peeling of the conductive material filled in the through hole. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0015] (7) In the printed wiring board according to any one of (1) to (6) above, in a cross section of the base film taken along a direction perpendicular to the first surface, the first interface may be convex toward the second underlayer. This prevents peeling of the conductive material filled in the through hole. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0016] (8) In the printed wiring board according to any one of (1) to (7), the first interface may include a curved portion in a cross section of the base film taken along a direction perpendicular to the first surface. This prevents peeling of the conductive material filled in the through hole. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0017] (9) In the printed wiring board according to (8), the curved portion may be positioned at the center of the through hole in the width direction. This prevents the conductive material filled in the through hole from peeling off. As a result, the reliability of the printed wiring board in a heat cycle test is improved.

[0018] (10) The printed wiring board according to any one of (1) to (9) above may be made of any one of fluororesin, epoxy resin, polyimide, polyphenylene ether, and liquid crystal polymer, so that the printed wiring board can be used as a high-frequency substrate.

[0019] (11) The printed wiring board according to any one of (1) to (10) above includes a conductive layer formed on the surface of the first underlayer opposite to the base film, on the inner peripheral surfaces of the first underlayer and the base film that form the inner wall of the through hole, and on the surface of the second underlayer exposed at the bottom of the through hole, thereby electrically connecting the circuit formed on the first surface to the circuit formed on the second surface.

[0020] [Details of the embodiment of the present disclosure] Next, the details of the embodiment of the present disclosure will be described with reference to the drawings. Note that in the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0021] 1 is a schematic cross-sectional view of a printed wiring board 100 according to a first embodiment. The printed wiring board 100 is a printed wiring board used as a high-frequency substrate.

[0022] The printed wiring board 100 may be, for example, a printed wiring board on which a circuit (not shown) is formed. The printed wiring board 100 has a base film 1, a first underlayer 21, a second underlayer 22, a conductive layer 3, and a conductive member 4.

[0023] The base film 1 has a first surface 11 and a second surface 12. The second surface 12 is the surface located opposite the first surface 11. The first surface 11 and the second surface 12 are end surfaces of the base film 1 in the thickness direction (y direction). The base film 1 is formed of an electrically insulating material. Specific examples of materials that can be used to form the base film 1 include fluororesin, epoxy resin, polyimide, polyphenylene ether, and liquid crystal polymer (LCP). However, the materials that can be used to form the base film 1 are not limited to these.

[0024] A first underlayer 21 is disposed on the first surface 11 of the base film 1. A second underlayer 22 is disposed on the second surface 12 of the base film 1. The constituent material of the first underlayer 21 and the second underlayer 22 may be, for example, copper foil.

[0025] The first surface 11 of the base film 1 is provided with a through hole H that reaches the second surface 12. The shape of the through hole H in a plan view of the first surface 11 may be, for example, a circle centered on the central axis A. The shape of the through hole H in a plan view of the first surface 11 may be any shape, such as an ellipse or a rectangle.

[0026] An opening 21h is provided in the first underlayer 21. In a plan view of the first surface 11, the opening 21h is arranged at a position overlapping the through hole H. The shape of the opening 21h in a plan view of the first surface 11 may be the same as the shape of the through hole H in a plan view of the first surface 11, and may be, for example, circular. As shown in FIG. 1 , the inner circumferential surface of the opening 21h is continuous with the inner circumferential surface of the through hole H. Meanwhile, the second underlayer 22 blocks the through hole H. In other words, the surface of the second underlayer 22 is exposed from the first surface 11 where the through hole H is formed.

[0027] The width direction of the through-hole H is defined as the x direction, and the thickness direction of the base film 1 is defined as the y direction. The y direction is perpendicular to the x direction.

[0028] The greater the thickness of base film 1 in the y direction (distance T from first surface 11 to second surface 12), the more improved the transmission characteristics of printed wiring board 100. Therefore, the thickness of base film 1 in the y direction may be, for example, 80 μm or more, 100 μm or more, or 200 μm or more.

[0029] The height of the through hole H corresponds to the distance T from the first surface 11 to the second surface 12. The opening of the through hole H formed in the first surface 11 may be considered to be the first surface 11. The surface of the second underlayer 22 exposed from the lower end of the through hole H may be considered to be the second surface 12. From a different perspective, the height of the through hole H is the distance from the surface of the second underlayer 22 exposed from the lower end of the through hole H to the opening of the through hole H formed in the first surface 11.

[0030] If the height of the through hole H (the distance T from the first surface 11 to the second surface 12) is large, when the conductive member 4 is formed in the through hole H by electroplating, the through hole H cannot be filled with the conductive member 4. Therefore, the thickness of the base film 1 in the y direction (the distance T from the first surface 11 to the second surface 12) may be 350 μm or less.

[0031] If the width W of the through hole H in the x direction is small, when forming the conductive member 4 in the through hole H by electroplating, the plating solution will have difficulty entering the through hole H, and there is a risk of voids being formed in the through hole H. Therefore, the width W of the through hole H in the x direction may be, for example, 50 μm or more.

[0032] If the width W of the through hole H in the x direction exceeds 200 μm, when forming the conductive member 4 in the through hole H by electroplating, the through hole H cannot be filled with the conductive member 4. Therefore, the width W of the through hole H in the x direction may be, for example, 200 μm or less. Note that when the shape of the through hole H in the plan view of the first surface 11 is circular, the width W of the through hole H in the x direction is the diameter of the through hole H.

[0033] The thickness of the through hole H (the distance T from the first surface 11 to the second surface 12) and the width W of the through hole H in the x direction can be measured by observing a cross section exposed using a CP (Cross Section Polisher) process with a SEM (Scanning Electron Microscope).

[0034] The aspect ratio AS is the value obtained by dividing the height of the through hole H (the distance T from the first surface 11 to the second surface 12) by the width W of the through hole H. The aspect ratio AS may be 0.8 or more and 4.0 or less.

[0035] The conductive layer 3 is formed on the first underlayer 21 (specifically, the surface of the first underlayer 21 opposite the base film 1), the inner surface of the through hole H (specifically, the inner surface of the first underlayer 21 and base film 1 constituting the through hole H), and the second underlayer 22 exposed at the bottom end of the through hole H (specifically, the surface of the second underlayer 22 exposed at the bottom of the through hole H). The conductive layer 3 is formed of a conductor such as a metal material. The conductive layer 3 is a plated layer formed, for example, by electroless plating. Specific examples of the material of the conductive layer 3 include copper and copper alloys. However, the material of the conductive layer 3 is not limited to these.

[0036] The through holes H are filled with a conductive member 4. The conductive member 4 is a plating layer formed by, for example, electrolytic plating. Specific examples of the material of the conductive member 4 include copper and copper alloys. However, the material of the conductive member 4 is not limited to these.

[0037] The conductive member 4 includes a first conductive portion 41 and a second conductive portion 42. The first conductive portion 41 is formed on the conductive layer 3. A portion of the first conductive portion 41 fills the through hole H. A portion of the first conductive portion 41 may be formed on the first surface 11.

[0038] The second conductive portion 42 is disposed on the first conductive portion 41. A portion of the second conductive portion 42 fills the through hole H. A portion of the second conductive portion 42 may be formed on the first surface 11. The first conductive portion 41 is disposed between the second conductive portion 42 and the conductive layer 3. Therefore, the second conductive portion 42 is disposed so as not to come into contact with the conductive layer 3, and is spaced apart from the conductive layer 3.

[0039] The second conductive portion 42 has a first interface B1 with the first conductive portion 41. As shown in Fig. 1 , in a cross section of the base film 1 taken along a direction perpendicular to the first surface 11 (the y direction), the first interface B1 includes a straight line portion B1a and a curved line portion B1b. Note that when the shape of the through hole H in the plan view of the first surface 11 is circular, as shown in Fig. 1 , the cross section is a cross section taken along the central axis A and passes through the center of the circle.

[0040] The straight line portion B1a is formed by a portion that follows the inner circumferential surface of the through hole H and a portion that follows the first surface 11. The curved line portion B1b is continuous with the straight line portion B1a, and is disposed between the first surface 11 and the second surface 12 in the y direction.

[0041] The curved portion B1b is located at the center of the through hole H in the width direction (x direction). From a different perspective, the curved portion B1b is the portion of the first interface B1 that faces the second underlayer 22 located at the bottom of the through hole H. The curved portion B1b has a bottom point p1. The bottom point p1 is the point on the curved portion B1b that is farthest from the first surface 11 in the y direction. From a different perspective, the bottom point p1 is the point on the curved portion B1b that is closest to the second surface 12 in the y direction. The central axis A of the through hole H may pass through the bottom point p1. In other words, the bottom point p1 may be located at the center of the through hole H in the width direction (x direction). Thus, as shown in FIG. 1 , in a cross section of the base film 1 taken along a direction perpendicular to the first surface 11, at least a portion of the first interface B1 may be convex toward the second underlayer 22.

[0042] The distance T1 in the y direction from the second surface 12 to the first interface B1 may be 0.20 to 0.85 times the distance T in the y direction from the second surface 12 to the first surface 11. When the first interface B1 is convex toward the second underlayer 22, the distance T1 from the second surface 12 to the first interface B1 corresponds to the distance in the y direction from the second surface 12 to the bottom point p1.

[0043] In this way, the presence of the first interface B1 inside the through hole H can cause a small gap to form between the first conductive portion 41 and the second conductive portion 42. Therefore, even if the first conductive portion 41 and the second conductive portion 42 thermally expand during a heat cycle test, the first interface B1 can alleviate the stress caused by the thermal expansion. As a result, peeling of the first conductive portion 41 and the second conductive portion 42 from the through hole H is prevented.

[0044] (Method for manufacturing printed wiring board) Next, a method for manufacturing the printed wiring board 100 according to the first embodiment will be described. Fig. 2 is a flow diagram that schematically shows the method for manufacturing the printed wiring board 100 according to the first embodiment. Figs. 3 to 7 are schematic cross-sectional views that show one step of the method for manufacturing the printed wiring board 100 according to the first embodiment.

[0045] As shown in FIG. 2, the manufacturing method of the printed wiring board 100 according to the first embodiment mainly includes a step (S1) of preparing a base film 1, a step (S2) of forming a through hole H, a step (S3) of forming a conductive layer 3, a step (S4) of forming a first conductive portion 41, and a step (S5) of forming a second conductive portion 42.

[0046] First, a step (S1) of preparing a base film 1 is performed. In this step (S1), the base film 1 is prepared as shown in Fig. 3. A first underlayer 21 and a second underlayer 22 are provided as copper foil on a first surface 11 and a second surface 12 of the base film 1, respectively. The thickness of the base film 1 in the y direction (the distance T from the first surface 11 to the second surface 12) is, for example, not less than 80 µm and not more than 350 µm.

[0047] Next, a step (S2) of forming through holes H is performed. In this step (S2), as shown in FIG. 4 , openings 21h are formed in the first underlayer 21. Specifically, a resist pattern (not shown) is formed on the first underlayer 21, and the openings 21h are formed by etching using the resist pattern as a mask. The resist pattern is formed by applying a dry film resist to the first underlayer 21 and then exposing and developing the applied dry film resist. The openings 21h are formed in the first underlayer 21 at locations where the through holes H are to be formed. Note that, although not shown, the second underlayer 22 may be patterned at locations where the through holes H are not to be formed by etching using the resist pattern as a mask.

[0048] 5, through holes H are formed in the first surface 11 of the base film 1 exposed from the openings 21h, reaching the second surface 12. The through holes H are formed, for example, by irradiating with a laser. The width W of the through holes H in the x direction is, for example, not less than 50 μm and not more than 200 μm.

[0049] Next, a step (S3) of forming a conductive layer 3 is carried out. In this step (S3), as shown in Fig. 6 , the conductive layer 3 is formed on the first underlayer 21, on the inner circumferential surface of the through hole H, and on the second underlayer 22 exposed at the lower end of the through hole H. The conductive layer 3 is formed by, for example, electroless plating.

[0050] Next, a step (S4) of forming a first conductive portion 41 is performed. In this step (S4), as shown in FIG. 7 , the first conductive portion 41 is formed as the conductive member 4 that fills the through hole H. The first conductive portion 41 is formed by electrolytic plating. The plating solution used when forming the first conductive portion 41 by electrolytic plating contains copper sulfate pentahydrate with a concentration of 50 g / L or more and 150 g / L or less and sulfuric acid with a concentration of 125 g / L or more and 225 g / L or less. The concentration of copper contained in the plating solution is 50 g / L or more and 250 g / L or less.

[0051] Next, a step (S5) of forming a second conductive portion 42 is performed. In this step (S5), the second conductive portion 42 is formed on the first conductive portion 41. The second conductive portion 42 is formed by electrolytic plating. The plating solution used to form the second conductive portion 42 by electrolytic plating contains copper sulfate pentahydrate with a concentration of 150 g / L to 250 g / L and sulfuric acid with a concentration of 30 g / L to 100 g / L. The copper concentration in the plating solution is 100 g / L to 250 g / L. In this way, as shown in FIG. 1 , the second conductive portion 42 having a first interface B1 with the first conductive portion 41 is formed on the first conductive portion 41.

[0052] (Effects) A printed wiring board 100 according to the present disclosure includes a base film 1, a first underlayer 21, and a second underlayer 22. The base film 1 has a first surface 11 and a second surface 12. The second surface 12 is located opposite the first surface 11. The first underlayer 21 is disposed on the first surface 11. The second underlayer 22 is disposed on the second surface 12. The base film 1 and the first underlayer 21 have through holes H that reach the second surface 12. The second underlayer 22 blocks the through holes H. A conductive member 4 is filled in the through holes H. The conductive member 4 includes a first conductive portion 41 and a second conductive portion 42. The second conductive portion 42 is disposed on the first conductive portion 41. The second conductive portion 42 has a first interface B1 with the first conductive portion 41.

[0053] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0054] According to the above-described printed wiring board 100, the distance T from the first surface 11 to the second surface 12 is not less than 80 μm and not more than 350 μm.

[0055] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0056] According to the above-described printed wiring board 100, the distance T1 from the second surface 12 to the first interface B1 is 0.20 to 0.85 times the distance T from the second surface 12 to the first surface 11.

[0057] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0058] According to the printed wiring board 100, the width W of the through hole H is not less than 50 μm and not more than 200 μm.

[0059] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0060] According to the above-described printed wiring board 100, the aspect ratio AS is the value obtained by dividing the distance T from the first surface 11 to the second surface 12 by the width W of the through hole H. The aspect ratio AS is equal to or greater than 0.8 and equal to or less than 4.0.

[0061] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0062] According to the above-described printed wiring board 100 , in a cross section of the base film 1 taken along a direction perpendicular to the first surface 11 , the first interface B1 is convex toward the second underlayer 22 .

[0063] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0064] According to the above-described printed wiring board 100, in a cross section of the base film 1 taken along a direction perpendicular to the first surface 11, the first interface B1 includes a curved portion B1b.

[0065] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0066] According to the printed wiring board 100, the curved portion B1b is disposed at the center of the through hole H in the width direction (x direction).

[0067] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0068] According to the printed wiring board 100, the material is any one of fluororesin, epoxy resin, polyimide, polyphenylene ether, and liquid crystal polymer.

[0069] As a result, printed wiring board 100 is used as a high-frequency substrate. Printed wiring board 100 includes conductive layer 3. Conductive layer 3 is formed on the surface of first underlayer 21 opposite base film 1, on the inner circumferential surface of first underlayer 21 and base film that form the inner wall of through hole H, and on the surface of second underlayer 22 exposed at the bottom of through hole H.

[0070] This allows electrical continuity between the circuit formed on the first surface 11 and the circuit formed on the second surface 12 .

[0071] Second Embodiment <Configuration of Printed Wiring Board> Next, the configuration of a printed wiring board 100 according to a second embodiment will be described. The printed wiring board 100 according to the second embodiment differs from the printed wiring board 100 according to the first embodiment mainly in that the conductive member 4 includes a third conductive portion 43, but is otherwise similar to the printed wiring board 100 according to the first embodiment. The following description will focus on the configuration that differs from the printed wiring board 100 according to the first embodiment.

[0072] 8 is a schematic cross-sectional view of a printed wiring board 100 according to the second embodiment. As shown in FIG. 8, the conductive member 4 includes a first conductive portion 41, a second conductive portion 42, and a third conductive portion 43.

[0073] The third conductive portion 43 is disposed on the second conductive portion 42. A portion of the third conductive portion 43 fills the through hole H. A portion of the third conductive portion 43 may be formed on the first surface 11. The second conductive portion 42 is disposed between the third conductive portion 43 and the first conductive portion 41. Therefore, the third conductive portion 43 is disposed so as not to contact the first conductive portion 41, and is spaced apart from the first conductive portion 41.

[0074] The third conductive portion 43 has a second interface B2 with the second conductive portion 42. As shown in Fig. 8 , in a cross section of the base film 1 taken along a direction perpendicular to the first surface 11 (the y direction), the second interface B2 includes a straight portion B2a and a curved portion B2b.

[0075] The straight line portion B2a is formed by a portion that follows the inner circumferential surface of the through hole H and a portion that follows the first surface 11. The curved line portion B2b is continuous with the straight line portion B2a and is disposed between the first surface 11 and the second surface 12 in the y direction. The curved line portion B2b may be disposed at a position farther from the second surface 12 in the y direction than the first surface 11.

[0076] The curved portion B2b is disposed at the center of the through hole H in the width direction (x direction). The curved portion B2b has a bottom point p2. The bottom point p2 is the point on the curved portion B2b that is farthest from the first surface 11 in the y direction. From a different perspective, the bottom point p2 is the point on the curved portion B2b that is closest to the second surface 12 in the y direction. The central axis A of the through hole H may pass through the bottom point p2. In other words, the bottom point p2 may be located at the center of the through hole H in the width direction (x direction). In this way, as shown in FIG. 8 , in a cross section of the base film 1 taken along a direction perpendicular to the first surface 11, at least a portion of the second interface B2 may be convex toward the second underlayer 22.

[0077] A distance T2 from the second surface 12 to the second interface B2 in the y direction is greater than a distance T1 from the second surface 12 to the first interface B1. When the second interface B2 is convex toward the second underlayer 22, the distance T2 from the second surface 12 to the second interface B2 corresponds to the distance from the second surface 12 to the bottom point p2 in the y direction.

[0078] The third conductive portion 43 is formed by performing the step (S6) of forming the third conductive portion 43 after the step (S5) of forming the second conductive portion 42. The third conductive portion 43 is formed by electrolytic plating.

[0079] (Operation and Effect) According to the above-described printed wiring board 100, the conductive member 4 includes the third conductive portion 43 disposed on the second conductive portion 42. The third conductive portion 43 has a second interface B2 with the second conductive portion 42. The distance T2 from the second surface 12 to the second interface B2 is greater than the distance T1 from the second surface 12 to the first interface B1.

[0080] This prevents peeling of the conductive member 4 filled in the through hole H. As a result, the reliability of the printed wiring board 100 in a heat cycle test is improved.

[0081] (Heat Cycle Test) In order to verify the effects of the printed wiring board 100 described above, the following heat cycle test was carried out.

[0082] In the heat cycle test, the filling rate of the conductive member 4 in the through holes H, the transmission characteristics, and the reliability were evaluated for the printed wiring boards 100 manufactured using the electrolytic plating method. The test subjects were printed wiring boards 100 from sample 1 to sample 14. Samples 1 and 2 were printed wiring boards 100 manufactured using the electrolytic plating method once. Samples 3 to 14 were printed wiring boards 100 manufactured using the electrolytic plating method two or more times.

[0083] <Results>

[0084]

[0085]

[0086] The manufacturing conditions and test results of the printed wiring board 100 are shown in Tables 1 and 2. In Tables 1 and 2, from the top to the bottom, the manufacturing conditions include the number of times electrolytic plating was performed, the thickness of the base film 1 (the distance T from the first surface 11 to the second surface 12), the width W of the through hole H in the x direction, the aspect ratio AS, and the ratio (T1 / T) of the distance T1 from the second surface 12 to the first interface B1 to the thickness of the base film 1 (the distance T from the first surface 11 to the second surface 12), and the test results include the filling rate of the conductive member 4 in the through hole H, the transmission characteristics, and the reliability.

[0087] In addition, in the filling rate, transmission characteristics, and reliability of the conductive member 4 in the through hole H shown in Tables 1 and 2, A, B, and C indicate the evaluation of each item. B indicates that it is better than C. A indicates that it is better than B. In other words, A indicates that it is the best evaluation result among A, B, and C.

[0088] When the through hole H is sufficiently filled with the conductive member 4, the filling rate of the conductive member 4 is evaluated as A. When the through hole H is not sufficiently filled with the conductive member 4 or when a void is formed in the through hole H, the filling rate of the conductive member 4 is evaluated as C.

[0089] If the conductive member 4 does not peel off from the through hole H in the heat cycle test, the reliability of the printed wiring board 100 is rated A. If the conductive member 4 peels off from the through hole H in the heat cycle test, the reliability of the printed wiring board 100 is rated C.

[0090] As can be seen from Tables 1 and 2, in the printed wiring boards 100 of Samples 1 to 14, the thickness of the base film 1 (the distance T from the first surface 11 to the second surface 12) is 80 μm or more, and therefore the transmission characteristics are rated A.

[0091] In the printed wiring boards 100 of Samples 1 and 2, the electrolytic plating method was performed once. Therefore, the reliability of the printed wiring boards 100 of Samples 1 and 2 was evaluated as C. On the other hand, the electrolytic plating method was performed twice or more in the printed wiring boards 100 of Samples 3 to 14. Therefore, the reliability of the printed wiring boards 100 of Samples 3 to 14 was evaluated as A or B. This is thought to be because the first interface B1 and the second interface B2 are present inside the through hole H, which has improved the reliability of the printed wiring boards 100 of Samples 3 to 14.

[0092] In the printed wiring board 100 of Sample 4, the ratio (T1 / T) of the distance T1 from the second surface 12 to the first interface B1 to the thickness of the base film 1 (the distance T from the first surface 11 to the second surface 12) is 0.5. In the printed wiring board 100 of Sample 5, the ratio (T1 / T) is 0.85. The reliability of the printed wiring boards 100 of Samples 4 and 5 is evaluated as A. On the other hand, the ratio (T1 / T) of the printed wiring board 100 of Sample 6 is 0.9. The reliability of the printed wiring board 100 of Sample 6 is evaluated as B. Thus, if the ratio (T1 / T) of the distance T1 from the second surface 12 to the first interface B1 to the thickness of the base film 1 (the distance T from the first surface 11 to the second surface 12) is 0.85 or less, the reliability of the printed wiring board 100 is improved.

[0093] In the printed wiring board 100 of Sample 7, the ratio (T1 / T) is 0.2. The filling rate of the conductive member 4 in the printed wiring board 100 of Sample 7 is evaluated as A. On the other hand, in the printed wiring board 100 of Sample 8, the ratio (T1 / T) is 0.15. The filling rate of the conductive member 4 in the printed wiring board 100 of Sample 8 is evaluated as C. Thus, if the ratio (T1 / T) of the distance T1 from the second surface 12 to the first interface B1 to the thickness of the base film 1 (the distance T from the first surface 11 to the second surface 12) is 0.2 or more, the conductive member 4 is sufficiently filled in the through hole H.

[0094] In the printed wiring board 100 of sample 9, the thickness of the base film 1 is 350 μm, and the electrolytic plating method has been performed twice. The filling rate of the conductive member 4 in the printed wiring board 100 of sample 9 is evaluated as C. In the printed wiring board 100 of sample 10, the thickness of the base film 1 is 350 μm, and the electrolytic plating method has been performed three times. The filling rate of the conductive member 4 in the printed wiring board 100 of sample 10 is evaluated as A. In the printed wiring board 100 of sample 11, the thickness of the base film 1 is 400 μm, and the electrolytic plating method has been performed three times. The filling rate of the conductive member 4 in the printed wiring board 100 of sample 11 is evaluated as C.

[0095] When the thickness of the base film 1 is 350 μm or more, even if the electrolytic plating method is used twice, the through holes H cannot be sufficiently filled with the conductive member 4. Therefore, when the thickness of the base film 1 is 350 μm or more, by using the electrolytic plating method three times, the through holes H can be sufficiently filled with the conductive member 4. However, when the thickness of the base film 1 is 400 μm or more, even if the electrolytic plating method is used three times, the through holes H cannot be sufficiently filled with the conductive member 4.

[0096] In the printed wiring board 100 of Sample 12, the width W of the through hole H is 50 μm, and the electrolytic plating method has been performed twice. The filling rate of the conductive member 4 in the printed wiring board 100 of Sample 12 is evaluated as A. In the printed wiring board 100 of Sample 13, the width W of the through hole H is 40 μm, and the electrolytic plating method has been performed twice. The filling rate of the conductive member 4 in the printed wiring board 100 of Sample 12 is evaluated as C. Thus, if the width W of the through hole H is 50 μm or more, the plating solution can easily enter the through hole H, and the conductive member 4 can be formed in the through hole H using the electrolytic plating method.

[0097] In the printed wiring board 100 of Sample 14, the width W of the through hole H is 60 μm and the thickness of the base film 1 is 300 μm, so the aspect ratio AS is 5. The filling rate of the conductive member 4 in the printed wiring board 100 of Sample 14 is evaluated as C. When the aspect ratio AS of the through hole H is 5 or more, the through hole H could not be filled with the conductive member 4 even when the electrolytic plating method was used twice.

[0098] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0099] 1 base film, 3 conductive layer, 4 conductive member, 11 first surface, 12 second surface, 21 first base layer, 21h opening, 22 second base layer, 41 first conductive portion, 42 second conductive portion, 43 third conductive portion, 100 printed wiring board, A central axis, AS aspect ratio, B1 first interface, B1a straight portion, B1b curved portion, B2 second interface, B2a straight portion, B2b curved portion, H through hole, p1 bottom point, p2 bottom point, T distance, T1 distance, T2 distance, W width.

Claims

1. A printed wiring board comprising: a base film having a first surface and a second surface opposite the first surface; a first foundation layer disposed on the first surface; and a second foundation layer disposed on the second surface, wherein the base film and the first foundation layer have through holes that reach the second surface, the second foundation layer blocks the through holes, and the through holes are filled with a conductive material, the conductive material including a first conductive portion and a second conductive portion disposed on the first conductive portion, and the second conductive portion has a first interface with the first conductive portion.

2. The printed wiring board according to claim 1, wherein the conductive member includes a third conductive portion disposed on the second conductive portion, the third conductive portion has a second interface between itself and the second conductive portion, and the distance from the second surface to the second interface is greater than the distance from the second surface to the first interface.

3. The printed wiring board according to claim 1 or 2, wherein the distance from the first surface to the second surface is 80 μm or more and 350 μm or less.

4. A printed wiring board according to any one of claims 1 to 3, wherein the distance from the second surface to the first interface is 0.20 to 0.85 times the distance from the second surface to the first surface.

5. The printed wiring board according to any one of claims 1 to 4, wherein the width of the through hole is 50 μm or more and 200 μm or less.

6. A printed wiring board according to any one of claims 1 to 5, wherein, when the aspect ratio is the value obtained by dividing the distance from the first surface to the second surface by the width of the through hole, the aspect ratio is equal to or greater than 0.8 and equal to or less than 4.

0.

7. A printed wiring board according to any one of claims 1 to 6, wherein in a cross section of the base film taken along a direction perpendicular to the first surface, the first interface is convex toward the second underlayer.

8. A printed wiring board according to any one of claims 1 to 7, wherein in a cross section of the base film taken along a direction perpendicular to the first surface, the first interface includes a curved portion.

9. The printed wiring board according to claim 8, wherein the curved portion is disposed at the center of the through hole in the width direction.

10. A printed wiring board according to any one of claims 1 to 9, wherein the material constituting the base film is one of fluororesin, epoxy resin, polyimide, polyphenylene ether, and liquid crystal polymer.

11. A printed wiring board as described in any one of claims 1 to 10, comprising a conductive layer formed on the surface of the first underlayer opposite to the base film, the inner surfaces of the first underlayer and the base film that form the inner wall of the through hole, and the surface of the second underlayer exposed at the bottom of the through hole.

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