Printed wiring board and method for manufacturing printed wiring board

Abstract

A printed wiring board according to one embodiment of the present disclosure comprises: a base film; a first through-hole provided in the base film; a land formed on a peripheral edge of the first through-hole on a surface of the base film; and a hole-filling resin filled in the first through-hole. A surface of the hole-filling resin is recessed with respect to a surface of the land, and the average depth of the surface of the hole-filling resin from the surface of the land is 5 μm or more.

Description

Printed wiring board and method for manufacturing printed wiring board

[0001] This disclosure relates to a printed wiring board and a method for manufacturing a printed wiring board. This application claims priority to Japanese Application No. 2023-119458, filed on July 21, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] A printed wiring board in which through holes are filled with a hole filling resin is known (Patent Document 1).

[0003] JP 2012-49160 A

[0004] A printed wiring board according to one embodiment of the present disclosure comprises a base film, a first through hole provided in the base film, a land formed on the surface of the base film around the periphery of the first through hole, and a hole-filling resin filled in the first through hole, wherein the surface of the hole-filling resin is recessed relative to the surface of the land, and the average depth of the surface of the hole-filling resin from the surface of the land is 5 μm or more.

[0005] FIG. 1 is a schematic cross-sectional view showing a printed wiring board according to an embodiment of the present disclosure. FIG. 2 is a partially enlarged cross-sectional view of a first through-hole in the printed wiring board of FIG. 1. FIG. 3 is a flow diagram showing a method for manufacturing the printed wiring board of FIG. 1. FIG. 4 is a schematic cross-sectional view of the printed wiring board after the step of filling a hole with a filling resin in FIG. 3. The printed wiring board shows a state in which the first through-hole is filled with the filling resin. FIG. 5 is a schematic cross-sectional view showing a printed wiring board according to an embodiment different from the printed wiring board of FIG. 1. FIG. 6 is a schematic cross-sectional view showing a printed wiring board according to an embodiment different from the printed wiring boards of FIGS. 1 and 5. FIG. 7 is a schematic cross-sectional view showing a printed wiring board according to an embodiment different from the printed wiring boards of FIGS. 1, 5, and 6.

[0006] [Problem to be Solved by the Present Disclosure] Patent Document 1 describes a method of depositing a plated conductor on the inner wall of a through-hole and on the surface of a copper-clad plate, and then filling the inside of the through-hole with a hole-filling resin. Patent Document 1 also describes a method of polishing and flattening the plated conductor laminated on the surface of the copper-clad plate and the hole-filling resin protruding from the through-hole after filling with the hole-filling resin.

[0007] However, with this configuration, the plated conductor is polished together with the filling resin, so that the surface of the filling resin and the surface of the plated conductor become even and smooth, and distortion is likely to occur on the surface of the plated conductor.

[0008] The present disclosure has been made in light of the above circumstances, and aims to provide a printed wiring board in which distortion is less likely to occur on the surface of a plated conductor and in which it is easy to form a substrate with improved dimensional accuracy.

[0009] Effect of the Present Disclosure In a printed wiring board according to one aspect of the present disclosure, distortion is less likely to occur on the surface of the plated conductor, making it easier to form a substrate with improved dimensional accuracy.

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

[0011] (1) A printed wiring board according to one aspect of the present disclosure comprises a base film, a first through hole provided in the base film, a land formed on the surface of the base film around the periphery of the first through hole, and a hole-filling resin filled in the first through hole, wherein the surface of the hole-filling resin is recessed relative to the surface of the land, and the average depth of the surface of the hole-filling resin from the surface of the land is 5 μm or more.

[0012] In the printed wiring board, the surface of the hole-filling resin is recessed relative to the surface of the land. This recess can be formed by selectively removing the surface layer of the hole-filling resin. Since there is no need to simultaneously polish the hole-filling resin and the land, distortion is less likely to occur on the surface of the land in the printed wiring board. Furthermore, in the printed wiring board, the average depth of the hole-filling resin surface from the surface of the land is 5 μm or more. This makes it easy to obtain an anchor effect when other components are placed on the hole-filling resin. Therefore, when the printed wiring board includes other components, adhesion between the hole-filling resin and the other components is improved.

[0013] (2) In the above (1), the arithmetic mean roughness Sa of the surface of the filling resin may be 1.0 μm or more and 10.0 μm or less. With this configuration, when another component is placed on the filling resin, an anchoring effect can be more reliably obtained.

[0014] (3) In the above (1) or (2), the filling resin may contain a filler. This configuration makes it easier to form irregularities on the surface of the filling resin. As a result, when another component is placed on the filling resin, the anchoring effect can be more reliably obtained.

[0015] (4) In any one of (1) to (3) above, an adhesive member may be further provided that is in close contact with the surface of the hole-filling resin. With this configuration, the adhesive strength of the adhesive member to the hole-filling resin can be improved.

[0016] (5) In any of (1) to (4) above, a second through hole may be further provided, the interior of which is not filled with resin. The printed wiring board can be formed by selectively removing the surface layer of the hole-filling resin. Even if the second through hole is provided, distortion due to the removal of the surface layer does not occur in the second through hole. Therefore, the second through hole can be easily formed into a desired shape.

[0017] (6) In any of (1) to (5) above, the average depth of the surface of the filling resin from the surface of the land may be 200 μm or less. With this configuration, when another component is placed on the filling resin, the filling resin and the other component can be easily and reliably adhered to each other.

[0018] (7) A method for manufacturing a printed wiring board according to another aspect of the present disclosure includes the steps of forming a first through-hole in a base film, filling the first through-hole formed in the forming step with a hole-filling resin, and removing the surface layer of the hole-filling resin filled in the filling step with a laser.

[0019] In the method for manufacturing a printed wiring board, the removing step can selectively remove only the surface layer of the filling resin, which makes it easier to form a printed wiring board with improved dimensional accuracy and reduces distortion on the surface of the plated conductor.

[0020] (8) In the method of (7) above, a step of forming a conductive pattern on the surface of the base film may be included before the removing step. The method for manufacturing a printed wiring board can form a desired conductive pattern by performing the removing step after the conductive pattern forming step.

[0021] (9) In the above (7) or (8), a step of forming a second through hole in the base film, the second through hole having an interior not filled with resin, may be further included. With this configuration, even when the second through hole is provided, distortion does not occur in the second through hole.

[0022] (10) In the above (9), the step of forming the first through-hole and the step of forming the second through-hole may be performed simultaneously.

[0023] The "average depth" is determined as follows: The depth is measured at any 10 points. From the obtained measurements, the largest depth, the second largest depth, the smallest depth, and the second smallest depth are excluded. The average value of the remaining six depths is the "average depth." The "arithmetic mean roughness Sa" is a value measured in accordance with ISO 25178.

[0024] [Details of the embodiment of the present disclosure] Preferred embodiments of the present disclosure will be described below with reference to the drawings. Note that each drawing is a schematic view and may not correspond to the actual shape, dimensions, ratio, etc. Furthermore, in this disclosure, the terms "first," "second," etc. are used to distinguish the components to which they are attached, and do not limit the number, order, priority, etc.

[0025] [First Embodiment] <Printed Wiring Board> The printed wiring board includes a base film and a first through-hole. The first through-hole is provided in the base film. The printed wiring board further includes a first land formed on the surface of the base film around the periphery of the first through-hole. The printed wiring board further includes a filling resin filled in the first through-hole. More specifically, as shown in FIG. 1 , the printed wiring board 10 includes a first base film 1a and a second base film 1b. The printed wiring board 10 further includes a first through-hole 2 provided in the first base film 1a and the second base film 1b. The printed wiring board 10 further includes a first land 3 disposed on the surface of the first base film 1a and the second base film 1b around the periphery of the first through-hole 2. The printed wiring board 10 further includes a filling resin 4 filled in the first through-hole 2. The printed wiring board 10 also includes a circuit (not shown) disposed on the surface of the first base film 1a and the second base film 1b. The printed wiring board 10 is a multilayer printed wiring board in which a first base film 1a and a second base film 1b are laminated. The first lands 3 are arranged at both axial ends of the first through holes 2. An intermediate land 5 may be arranged between both axial ends of the first through holes 2. The first through holes 2 may be through-holes that penetrate all of the base films stacked in multiple layers in the printed wiring board 10. In this disclosure, the term "through holes" includes not only through-holes but also interstitial via holes that penetrate only some layers. Interstitial via holes include blind via holes provided in the outermost base film and buried via holes provided in base films other than the outermost layer.

[0026] In the printed wiring board 10, the surface of the filling resin 4 is recessed relative to the surface of the first land 3. As shown in FIG. 2 , the average depth D1 of the surface 4a of the filling resin 4 relative to the surface 3a of the first land 3 is 5 μm or more. The printed wiring board 10 has first lands 3 at both axial ends of the first through hole 2. Of the two first lands 3, the surface 4a of the filling resin 4 may be recessed relative to the surface 3a of the first land 3 at only one end. Alternatively, the surface 4a of the filling resin may be recessed relative to the surface 3a of the first land 3 at both ends. When the surface 4a of the filling resin is recessed relative to the surface 3a of the first land 3 at both ends, the average depth D1 of at least one surface 4a of the filling resin 4 may be within the above range.

[0027] As described above, in the printed wiring board 10, the surface 4 a of the filling resin 4 is recessed relative to the surface 3 a of the first land 3. This recess can be formed, for example, by selectively removing the surface layer of the filling resin 4. In the printed wiring board 10, there is no need to polish the first land 3 when removing the surface layer of the filling resin 4. Therefore, distortion is less likely to occur in the surface 3 a of the first land 3. Furthermore, in the printed wiring board 10, the average depth D1 of the surface 4 a of the filling resin 4 relative to the surface 3 a of the first land 3 is 5 μm or more, which makes it easy to obtain an anchor effect when placing other components on the filling resin 4. Therefore, when the printed wiring board 10 includes other components, adhesion between the filling resin 4 and the other components is improved.

[0028] (Base Film) The first base film 1a and the second base film 1b (hereinafter, the first base film 1a and the second base film 1b are also referred to as "base films 1a, 1b") have insulating properties. The base films 1a, 1b may be flexible. When the base films 1a, 1b are flexible, the printed wiring board 10 can be a flexible printed wiring board. When the base films 1a, 1b are flexible, the main component of the base films 1a, 1b is, for example, polyimide, polyethylene terephthalate, liquid crystal polymer, or fluororesin. The base films 1a, 1b do not need to be flexible. In this case, the main component of the base films 1a, 1b is, for example, glass epoxy, paper phenol, paper epoxy, glass composite, or glass. Note that the "main component" refers to the component with the largest content in terms of mass, for example, a component with a content of 50 mass% or more.

[0029] The lower limit of the average thickness of each base film 1a, 1b may be 3 μm, 5 μm, or 10 μm from the viewpoint of increasing the insulating strength and mechanical strength. The upper limit of the average thickness may be 200 μm, 150 μm, or 100 μm from the viewpoint of reducing the thickness of the printed wiring board 10. In the present disclosure, the "average thickness" refers to the average value of thicknesses at any 10 points.

[0030] (First Through Hole) The first through hole 2 includes a through hole 2a penetrating the base films 1a and 1b and a conductor layer 2b laminated on the inner surface of the through hole 2a. The diameter of the through hole 2a may be uniform along its axis. The cross-sectional shape perpendicular to the axis of the through hole 2a is, for example, circular. The conductor layer 2b is cylindrical. The conductor layer 2b includes an electroless plating layer laminated directly on the inner surface of the through hole 2a and an electroplating layer laminated on the electroless plating layer. The main component of the conductor layer 2b is not particularly limited, but copper may be mentioned as an example. The conductor layer 2b may be formed by electroless copper plating and electrolytic copper plating, in that order, on the inner surface of the through hole 2a. The conductor layer 2b protrudes from the surface of the base films 1a and 1b along the axis of the first through hole 2. A first land 3 extends from the outer periphery of this protruding portion.

[0031] The lower limit of the average diameter D2 of the first through holes 2 may be 100 μm, 200 μm, or 250 μm, from the viewpoint of easily filling the first through holes 2 with the hole-filling resin 4. The upper limit of the average diameter D2 may be 1000 μm, 800 μm, or 500 μm, from the viewpoint of sufficiently blocking the first through holes 2 with the hole-filling resin 4. As shown in FIG. 2 , the average diameter D2 is an average diameter based on the inner circumferential surface of the conductor layer 2b. Note that the "diameter" refers to the diameter of a perfect circle having an area equal to the area of ​​a cross section perpendicular to the axis of the through hole. Furthermore, the "average diameter" refers to the average value of diameters at any five points along the axis.

[0032] (First Land) The first land 3 is provided integrally with the conductor layer 2b. The first land 3 and the conductor layer 2b are provided in a connected state. The first land 3 is formed, for example, by electroless plating and electroplating on a conductive underlayer such as copper foil arranged on the surface of the base films 1a, 1b. The first land 3 is formed simultaneously with the conductor layer 2b when the conductor layer 2b is formed on the inner surface of the through hole 2a.

[0033] The lower limit of the average thickness T of the first lands 3 may be 5 μm or 10 μm from the viewpoint of maintaining the conductivity of the first through-holes 2 (i.e., from the viewpoint of maintaining a sufficient thickness of the conductor layer 2 b). The upper limit of the average thickness T of the first lands 3 may be 150 μm, 60 μm, or 40 μm from the viewpoint of preventing the conductor layer 2 b from becoming too thick so that the filling resin 4 can be sufficiently filled in the first through-holes 2.

[0034] The average thickness T of the first lands 3 may be greater than the average thickness of the conductor layer 2b. As described above, the first lands 3 can be formed on a conductive base layer by electroless plating and electroplating. Here, the thickness of the plating layer formed by electroless plating and electroplating is equal to the thickness of the conductor layer 2b. As described below, the printed wiring board 10 can be formed by selectively removing the surface layer of the filling resin 4 with a laser. The surface layer is a layer close to the surface of the filling resin 4 and includes the portion overflowing from the axial end of the first through hole 2 and the portion filling the end of the first through hole 2. In other words, the printed wiring board 10 does not require polishing the first lands 3 to remove the surface layer of the filling resin 4. Therefore, the printed wiring board 10 can have the average thickness T of the first lands 3 greater than the average thickness of the conductor layer 2b by approximately the thickness of the conductive base layer. As a result, it is easier to form a desired circuit.

[0035] (Filling Resin) The internal space of the first through-hole 2 is filled with a filling resin 4. The filling resin 4 blocks the inside of the first through-hole 2. The filling resin 4 is fixed to the inner circumferential surface of the conductor layer 2b. The main component of the filling resin 4 is, for example, a thermosetting resin such as an epoxy resin.

[0036] The filling resin 4 may contain a filler. Examples of fillers include copper, silica, alumina, and calcium carbonate. When the filling resin 4 contains a filler, it becomes easier for unevenness to form on the surface 4a. When the printed wiring board 10 is formed by removing the surface layer of the filling resin 4 with a laser, micro-recesses are formed on the surface 4a of the filling resin 4. The reason for the formation of micro-recesses is that the filler exposed by removing the surface layer may fall off. Another reason for the formation of micro-recesses is that thermosetting resins are more easily removed by a laser than fillers. When another component is placed on the filling resin 4, the micro-recesses can more reliably obtain an anchoring effect.

[0037] The lower limit of the arithmetic mean roughness Sa of the surface 4 a of the filling resin 4 may be 0.1 μm, 1.0 μm, or 3.0 μm from the viewpoint of improving the anchoring effect when another component is placed on the filling resin 4. The upper limit of the arithmetic mean roughness Sa may be 10.0 μm or 6.0 μm from the viewpoint of easily roughening only the surface 4 a of the filling resin 4 by controlling the laser output. As described above, the printed wiring board 10 does not require polishing of the first lands 3 to remove the surface layer of the filling resin 4. Therefore, the arithmetic mean roughness Sa of the surface 3 a of the first lands 3 may be smaller than the arithmetic mean roughness Sa of the surface 4 a of the filling resin 4.

[0038] The lower limit of the average depth D1 of the surface 4a of the filling resin 4 from the surface 3a of the first land 3 is 5 μm as described above, but may also be 10 μm or 20 μm, from the viewpoint of easily obtaining an anchoring effect when another component is disposed on the filling resin 4. The upper limit of the average depth D1 may also be 200 μm or 100 μm, from the viewpoint of easily and reliably adhering the filling resin 4 to the other component.

[0039] 2, the surface 4a of the filling resin 4 has a peripheral portion, and the peripheral portion is connected to the conductor layer 2b. The surface 4a of the filling resin 4 may have a recess 4b on the peripheral portion. This recess 4b can be formed by removing the surface layer of the filling resin 4 with a laser. This configuration makes it easier to improve the anchor effect when placing another component on the filling resin 4.

[0040] <Method for Manufacturing a Printed Wiring Board> Next, an example of a method for manufacturing a printed wiring board 10 will be described with reference to FIG. 3 . The method for manufacturing a printed wiring board includes a step S1 of forming first through holes in a base film, a step S3 of filling the first through holes formed in the step S1 with a hole-filling resin, and a step S4 of removing the surface layer of the hole-filling resin filled in the filling step S3 with a laser. The method for manufacturing a printed wiring board also includes a step S2 of forming a conductive pattern on the surface of the base film before the removing step S4. The step S2 of forming the conductive pattern can be performed after the step S1 of forming the first through holes. FIG. 3 also illustrates a procedure in which the step S2 of forming the conductive pattern is performed before the step S3 of filling. However, the step S2 of forming the conductive pattern can also be performed after the step S3 of filling.

[0041] In the method for manufacturing a printed wiring board, the removing step S4 can selectively remove only the surface layer of the filling resin filled in the filling step S3. Therefore, in this method for manufacturing a printed wiring board, since neither the filling resin nor the conductor layer 2b is polished, distortion is less likely to occur in the conductor layer 2b.

[0042] Furthermore, in the method for manufacturing a printed wiring board, even when the removing step S4 is performed after the conductive pattern forming step S2, defects in the conductive pattern are unlikely to occur due to the removing step S4. Therefore, the method for manufacturing a printed wiring board can form the conductive pattern with good dimensional accuracy, and this effect is particularly noticeable when a semi-additive method is used.

[0043] (Step of Forming First Through Holes) In step S1 of forming first through holes, the first through holes are formed in a laminate having, for example, a base film and a conductive underlayer such as copper foil disposed on the surface of the base film. In step S1 of forming first through holes, through-holes are formed in the laminate in the thickness direction, and then a conductor layer is laminated on the inner surface of the through-hole to form the first through holes. The conductor layer can be formed, for example, by performing electroless plating and electroplating in this order on the inner surface of the through-hole. The specific configuration of the first through holes formed in step S1 of forming first through holes may be the same as that of the first through holes 2 described in printed wiring board 10.

[0044] (Conductive Pattern Forming Process) In the conductive pattern forming process S2, a conductive pattern is formed on the surface of the base film by, for example, a semi-additive process or a subtractive process. This conductive pattern includes a circuit and the first lands described above. In the conductive pattern forming process S2, the semi-additive process is used, which makes it easier to achieve a finer pitch for the circuit while reducing defects.

[0045] A procedure for using a semi-additive method in step S2 of forming a conductive pattern will be described below. The procedure for performing step S2 of forming a conductive pattern in parallel with the formation of a conductor layer in step S1 of forming a first through hole will be described below.

[0046] First, in the conductive pattern forming step S2, an electroless plated layer is laminated on the conductive base layer by the electroless plating performed in the first through-hole forming step S1. Next, in the conductive pattern forming step S2, a resist pattern is formed on the electroless plated layer. Then, electroplating is performed on the electroless plated layer exposed by the resist pattern. This electroplating is performed simultaneously with the electroplating performed in the first through-hole forming step S1. As a result, an electroplated layer is laminated on the electroless plated layer. Next, the resist pattern is removed, and the electroless plated layer exposed between the electroplated layers and the conductive base layer disposed below the electroless plated layer are removed by etching. As a result, a conductive pattern is formed on the base fill. The specific configuration of the first land formed in the conductive pattern forming step S2 may be the same as the first land 3 described in the printed wiring board 10.

[0047] In step S3 of filling the hole with the hole filling resin (hereinafter, sometimes referred to as step S3 of filling), the space within the first through-hole formed in step S1 of forming the first through-hole is filled with the hole filling resin. The components of the hole filling resin filled in step S3 may be the same as those of the hole filling resin 4 described in connection with printed wiring board 10.

[0048] 4 , in the filling step S3, the hole filling resin 14 is filled so as to overflow from the axial end of the first through hole 2. At this time, the hole filling resin 14 may be disposed up to the surface of the first land 3.

[0049] (Step of Removing Surface Layer of Filling Resin) In step S4 of removing the surface layer 14a of the filling resin 14 (hereinafter sometimes referred to as the removing step), the surface layer 14a of the filling resin 14 filled in step S3 is removed. More specifically, in the removing step S4, the portion of the filling resin 14 filled in step S3 that overflows from the axial end of the first through hole 2 and the portion that fills the end of the first through hole 2 are removed with a laser. In the removing step S4, the filling resin 14 is selectively removed so as not to cause defects in the first through hole 2 and the first land 3. In the removing step S4, the filling resin 14 can be selectively removed by controlling the wavelength, output, repetition frequency, irradiation diameter, etc. of the laser. In the removing step S4, the filling resin 14 can be selectively removed. As a result, the precision of the conductive pattern formed in step S2 of forming the conductive pattern can be maintained.

[0050] Examples of the laser include a UV laser and a carbon dioxide laser. By using a UV laser as the laser, it is easy to remove the desired area of ​​the filling resin 14 with high precision.

[0051] The specific shape of the filling resin 14 after the removing step S4 may be the same as that of the filling resin 4 described in relation to the printed wiring board 10 .

[0052] Second Embodiment <Printed Wiring Board> The printed wiring board 20 of Fig. 5 includes base films 1a, 1b and first through holes 2 provided in the base films 1a, 1b. The printed wiring board 20 further includes first lands 3 formed on the surfaces of the base films 1a, 1b around the peripheries of the first through holes 2. The printed wiring board 20 further includes a filling resin 4 filled in the first through holes 2. The printed wiring board 20 further includes an adhesive member 21 that adheres to the surface of the filling resin 4. The printed wiring board 20 may have the same configuration as the printed wiring board 10 of Fig. 1 except for the adhesive member 21. Therefore, only the adhesive member 21 will be described below.

[0053] (Adhesive Member) The adhesive member 21 is in close contact with the filling resin 4. The adhesive member 21 is fitted into a recess 22 defined by the filling resin 4 and the first through-hole 2. Examples of the adhesive member 21 include an insulating layer such as a solder resist, and solder that connects an electronic component to the first through-hole 2 (an insulating layer is shown in FIG. 5 ).

[0054] The adhesive member 21 is fitted into the recess 22 and is also disposed on the surface of the first land 3. The adhesive member 21 may be fitted into only a portion of the recess 22, or may be fitted into the entire recess 22.

[0055] In the printed wiring board 20, the surface of the filling resin 4 is recessed relative to the surface of the first land 3, and the average depth of the surface of the filling resin 4 from the surface of the first land 3 is 5 μm or more, which improves the adhesive strength of the adhesive member 21 to the filling resin 4 and the first land 3. Furthermore, when the above-mentioned solder is used as the adhesive member 21, for example, the shear strength of the printed wiring board 20 can be improved.

[0056] <Method for manufacturing printed wiring board> Printed wiring board 20 can be manufactured by adhering adhesive member 21 to the surface of filling resin 4 in printed wiring board 10 of Fig. 1. That is, the method for manufacturing a printed wiring board further includes a step of adhering an adhesive member to the surface of the filling resin after removing step S4 of Fig. 3.

[0057] (Bonding process) In the bonding process, an adhesive member is placed so as to fill the recess defined by the hole-filling resin and the first through-hole. In the bonding process, the adhesive member is placed on the surface of the first land while being placed in the recess. In the bonding process, the adhesive member may be placed so as to fill only a portion of the recess. In the bonding process, the adhesive member may be placed so as to fill the entire recess.

[0058] Third Embodiment <Printed Wiring Board> The printed wiring board 30 of Figure 6 includes a first base film 31a and a second base film 31b, first through holes 32 (penetrating through holes) provided in the first base film 31a and the second base film 31b, and first through holes 33 (interstitial via holes) provided in the first base film 31a. The printed wiring board 30 further includes first lands 34 formed on the surfaces of the first base film 31a and the second base film 31b around the edges of the first through holes 32. The printed wiring board 30 further includes first lands 35 formed on the surface of the first base film 31a around the edges of the first through holes 33. The printed wiring board 30 further includes hole-filling resins 36 and 37 filled in the first through holes 32 and 33, respectively. The printed wiring board 30 has a plurality of first through holes. The first through holes 33 are interstitial via holes. 1 except for the inclusion of first through-hole 33. Therefore, only the configuration relating to first through-hole 33 will be described below.

[0059] (First Through Hole) The first through hole 33 is an interstitial via hole, more specifically, a blind via hole. The upper and lower limits of the average diameter of the first through hole 33 may be the same as those of the average diameter D2 of the first through hole 2 in FIG. 1 . The surface of the filling resin 37 filled in the first through hole 33 is recessed relative to the surface of the first land 35. The upper and lower limits of the average depth of the surface of the filling resin 37 from the surface of the first land 35 may be the same as those of the average depth D1 of the surface 4a of the filling resin 4 relative to the surface 3a of the first land 3 in FIG. 1 . The first through hole 33 has a through hole 33a penetrating the first base film 31a and a conductor layer 33b laminated on the inner surface of the through hole 33a. The specific configuration of the through hole 33a may be the same as that of the through hole 2a in FIG. 1 , except that the through hole 33a does not penetrate the second base film 31b. The specific configuration of the conductor layer 33b may be the same as that of the conductor layer 2b in FIG. 1 . The specific configuration of the first land 35 may be the same as that of the first land 3 in FIG.

[0060] The internal space of the first through-hole 2 is filled with a hole filling resin 37. The hole filling resin 37 blocks the inside of the first through-hole 33. The hole filling resin 37 is fixed to the inner peripheral surface of the conductor layer 33b. The specific configuration of the hole filling resin 37 may be the same as that of the hole filling resin 4 in FIG. 1. For example, the components of the hole filling resin 37 may be the same as those of the hole filling resin 4 in FIG. 1, and the arithmetic mean roughness Sa of the surface of the hole filling resin 37 may be the same as that of the hole filling resin 4 in FIG. 1. Furthermore, the hole filling resin 37 may have a recess in the peripheral portion connected to the conductor layer 33b.

[0061] Even when the printed wiring board 30 has an interstitial via hole as the first through hole 33, like the printed wiring board 10 in Figure 1, distortion is less likely to occur on the surfaces of the first through hole 32, the conductor layer 33b, the first land 34, and the first land 35, making it easier to form a board with improved dimensional accuracy.

[0062] The printed wiring board 30 has a plurality of first through holes 32, 33 filled with hole filling resins 36, 37. The surface of each hole filling resin 36, 37 is recessed relative to the surface of the first lands 34, 35, and the average depth of the surface of each hole filling resin 36, 37 from the surface of the first lands 34, 35 is 5 μm or more. This makes it possible to easily improve the adhesive strength of an adhesive member by, for example, disposing an adhesive member across the plurality of first through holes 32, 33.

[0063] <Method for manufacturing printed wiring board> The printed wiring board 30 can be manufactured by forming a plurality of first through holes in the above-mentioned first through-hole forming step S1, filling the plurality of first through-holes with a hole filling resin in the above-mentioned filling step S3, and removing the surface layer of each hole filling resin filled in the plurality of first through-holes with a laser in the above-mentioned removing step S4.

[0064] 7 includes a first base film 41 a, a second base film 41 b, and a first through-hole 42 provided in the first base film 41 a and the second base film 41 b. The printed wiring board 40 further includes a first land 43 disposed on the surface of the first base film 41 a and the second base film 41 b around the periphery of the first through-hole 42, and a hole-filling resin 44 filled in the first through-hole 42.

[0065] Printed wiring board 40 further includes second through holes 45 that are not filled with resin. Printed wiring board 40 may have the same configuration as printed wiring board 10 in Fig. 1 except for including second through holes 45. Therefore, only second through holes 45 will be described below.

[0066] (Second Through Hole) The second through hole 45 is provided in the first base film 41a. The second through hole 45 is an interstitial via hole, more specifically a blind via hole. The second through hole 45 has a through hole 45a penetrating the first base film 41a and a conductor layer 45b laminated on the inner surface of the through hole 45a. A second land 46 is formed around the periphery of the second through hole 45 on the surface of the first base film 41a.

[0067] Even when printed wiring board 40 has second through holes 45 that are not filled with resin, like printed wiring board 10 in Figure 1, distortion is less likely to occur on the surfaces of first through holes 42, second through holes 45, first lands 43, and second lands 46, making it easier to form a board with improved dimensional accuracy.

[0068] In the past, after filling the first through-holes with filler resin, the filler resin was polished together with the plating layer laminated on the surface of the base film. With this configuration, if the base film has second through-holes that are not filled with resin, the surfaces of the second through-holes are also polished at the same time. As a result, unintended distortion is likely to occur in the second through-holes. In contrast, the printed wiring board 40 can be formed by selectively removing the surface layer of the filler resin 44 that fills the first through-holes 42. Therefore, even if the printed wiring board 40 includes second through-holes 45 and second lands 46, distortion due to the removal of the surface layer does not occur in the second through-holes 45 and second lands 46. Therefore, the second through-holes 45 and second lands 46 can be easily formed into the desired shape.

[0069] <Method for manufacturing a printed wiring board> A method for manufacturing a printed wiring board includes the steps of forming first through holes in a base film, forming second through holes in the base film, filling the first through holes formed in the step of forming the first through holes with a hole-filling resin, and removing the surface layer of the hole-filling resin filled in the filling step with a laser. The method for manufacturing a printed wiring board also includes the step of forming a conductive pattern on the surface of the base film before the removing step. In the method for manufacturing a printed wiring board, the steps of forming the first through holes and forming the second through holes may be performed simultaneously. In the method for manufacturing a printed wiring board, the steps of forming the first through holes, filling, removing, and forming the conductive pattern can be performed in the same manner as the step S1 of forming the first through holes, the step S3 of filling, the step S4 of removing, and the step S2 of forming the conductive pattern in FIG.

[0070] [Other Embodiments] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configuration of the embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0071] The printed wiring board has a hole-filling resin filled in the first through hole, the surface of the hole-filling resin is recessed relative to the surface of the first land, and the average depth of the surface of the hole-filling resin from the surface of the first land is 5 μm or more, so long as the other specific configurations are not particularly limited.

[0072] The printed wiring board may include only an interstitial via hole as the first through hole. Also, when the printed wiring board includes a plurality of first through holes, each of the first through holes may be a through-hole, a blind via hole, or a buried via hole.

[0073] When the first through hole is an interstitial via hole, the adhesive member that adheres to the hole-filling resin filled in the first through hole may be another base film laminated on the base film in which the first through hole is provided.

[0074] When the printed wiring board has a plurality of first through holes, the surface of the filling resin for all of the first through holes may be recessed relative to the surface of the first land, and the average depth of the surface of the filling resin from the surface of the first land may be 5 μm or more. However, this disclosure does not exclude a configuration in which the surface of the filling resin for some of the first through holes is not recessed relative to the surface of the first land, or a configuration in which the average depth of some of the first through holes is less than 5 μm.

[0075] The printed wiring board may include a through-hole as the second through-hole. Also, the printed wiring board may include a plurality of second through-holes. In this case, each second through-hole may be a through-hole, a blind via hole, or a buried via hole.

[0076] In the embodiment, the configuration in which the printed wiring board is a multilayer printed wiring board has been described. However, the printed wiring board may be a single-layer printed wiring board. Furthermore, when the printed wiring board is a multilayer printed wiring board, the number of layers of the printed wiring board is not particularly limited.

[0077] The method for manufacturing a printed wiring board may also include a step of forming a conductive pattern after the above-mentioned removing step.

[0078] 1a, 31a, 41a First base film 1b, 31b, 41b Second base film 2, 32, 33, 42 First through hole 2a, 33a Through hole 2b, 33b Conductive layer 3, 34, 35, 43 First land 3a Surface of first land 4, 14, 36, 37, 44 Filling resin 4a Surface of filling resin 4b Depression 5 Intermediate land 10, 20, 30, 40 Printed wiring board 14a Surface layer of filling resin 21 Adhesive member 22 Depression 45 Second through hole 45a Through hole 45b Conductive layer 46 Second land D1 Average depth of surface of filling resin from surface of first land D2 Average diameter of first through hole T Average thickness of first land

Claims

1. A printed wiring board comprising: a base film; a first through hole provided in the base film; a land formed on the surface of the base film around the periphery of the first through hole; and a hole-filling resin filled in the first through hole, wherein the surface of the hole-filling resin is recessed relative to the surface of the land, and the average depth of the surface of the hole-filling resin from the surface of the land is 5 μm or more.

2. The printed wiring board according to claim 1, wherein the arithmetic mean roughness Sa of the surface of said hole-filling resin is 1.0 μm or more and 10.0 μm or less.

3. The printed wiring board according to claim 1 or 2, wherein the hole-filling resin contains a filler.

4. The printed wiring board according to any one of claims 1 to 3, further comprising an adhesive member that adheres closely to the surface of the filling resin.

5. The printed wiring board according to any one of claims 1 to 4, further comprising a second through hole the interior of which is not filled with resin.

6. The printed wiring board according to any one of claims 1 to 5, wherein the average depth from the surface of the land to the surface of the filling resin is 200 µm or less.

7. A method for manufacturing a printed wiring board comprising the steps of: forming a first through hole in a base film; filling the first through hole formed in the forming step with a hole filling resin; and removing, with a laser, the surface layer of the hole filling resin filled in the filling step.

8. The method for producing a printed wiring board according to claim 7, further comprising the step of forming a conductive pattern on the surface of said base film prior to said removing step.

9. The method for manufacturing a printed wiring board according to claim 7 or 8, further comprising the step of forming a second through hole in the base film, the inside of which is not filled with resin.

10. The method for manufacturing a printed wiring board according to claim 9, wherein the step of forming the first through-hole and the step of forming the second through-hole are carried out simultaneously.

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