Printed wiring-board substrate and printed wiring-board

Abstract

This printed wiring-board substrate comprises: a base film having a main surface; and a conductive layer disposed on the main surface. The base film is formed of a fluororesin. The conductive layer contains a plurality of conductive particles which are bound to each other. The amount of nitrogen existing in the main surface is equal to or greater than 0.2 atom%.

Description

Substrate for printed wiring board and printed wiring board

[0001] This application claims priority to Japanese Patent Application No. 2022-097564, filed on June 16, 2022, and incorporates by reference all of the contents of that application.

[0002] Japanese Patent Laid-Open Publication No. 2006-69074 (Patent Document 1) describes a composite film. The composite film described in Patent Document 1 includes a resin film and a metal layer. The resin film has a main surface. The resin film is formed of, for example, a fluororesin. The metal layer is disposed on the main surface of the resin film. The metal layer is formed by sputtering.

[0003] Japanese Patent Application Laid-Open No. 2006-69074

[0004] The substrate for printed wiring boards of the present disclosure includes a base film having a main surface and a conductive layer disposed on the main surface. The base film is formed of a fluororesin. The conductive layer is a layer containing a plurality of conductive particles bonded to each other. The amount of nitrogen present on the main surface is 0.2 atomic percent or more.

[0005] FIG. 1 is a cross-sectional view of a substrate 100 for printed wiring boards. FIG. 2 is a cross-sectional view of a modified example of the substrate 100 for printed wiring boards. FIG. 3 is a manufacturing process diagram of the substrate 100 for printed wiring boards. FIG. 4 is a cross-sectional view illustrating a preparation step S1. FIG. 5 is a cross-sectional view illustrating a conductive layer formation step S2. FIG. 6 is a cross-sectional view of a printed wiring board 200. FIG. 7 is a cross-sectional view of a modified example of the printed wiring board 200. FIG. 8 is a manufacturing process diagram of the printed wiring board 200. FIG. 9 is a cross-sectional view illustrating a resist pattern formation step S4. FIG. 10 is a cross-sectional view illustrating an electrolytic plating step S5. FIG. 11 is a cross-sectional view illustrating a resist pattern removal step S6. FIG. 12 is an SEM image of a cross section of the substrate 100 for printed wiring boards.

[0006] [Problem to be Solved by the Present Disclosure] In the composite film described in Patent Document 1, water-soluble fluorides are formed at the interface between the metal layer and the resin film during sputtering. When attempting to form a printed wiring board using the composite film described in Patent Document 1 by a semi-additive process, it is necessary to remove a portion of the metal layer that does not constitute the wiring by wet etching. The fluorides corrode the metal layer that constitutes the wiring during this wet etching. Corrosion of the metal layer that constitutes the wiring causes a decrease in adhesion between the wiring and the base film.

[0007] The present disclosure has been made in view of the above-mentioned problems of the conventional art. More specifically, the present disclosure provides a substrate for a printed wiring board that can improve the adhesion of wiring.

[0008] [Advantages of the Present Disclosure] According to the substrate for printed wiring board of the present disclosure, it is possible to improve the adhesion of wiring.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) A substrate for a printed wiring board according to an embodiment includes a base film having a main surface and a conductive layer disposed on the main surface. The base film is formed of a fluororesin. The conductive layer is a layer containing a plurality of conductive particles bonded to each other. The amount of nitrogen present on the main surface is 0.2 atomic percent or more.

[0011] According to the substrate for printed wiring boards of (1) above, it is possible to improve the adhesion of wiring.

[0012] (2) In the substrate for printed wiring boards of (1) above, the conductive particles may be particles whose main component is copper or silver.

[0013] (3) In the substrate for printed wiring board of (1) or (2) above, the conductive layer may have a thickness of 0.05 μm or more and 2.0 μm or less.

[0014] (4) In the substrate for printed wiring board according to any one of (1) to (3) above, the conductive particles may have an average particle size of 1 nm or more and 500 nm or less.

[0015] (5) The substrate for printed wiring board according to any one of (1) to (4) above may further include a copper plating layer disposed on the conductive layer.

[0016] (6) In the substrate for printed wiring boards of (5) above, the copper plating layer may be an electroless copper plating layer or an electrolytic copper plating layer.

[0017] (7) In the substrate for printed wiring boards according to (1) to (6) above, the base film may be formed from a fluororesin containing a filler.

[0018] (8) In the substrate for printed wiring boards of (7) above, the filler may be made of silica.

[0019] (9) In the substrate for printed wiring boards described in (1) to (8) above, the fluororesin is polytetrafluoroethylene.

[0020] (10) A printed wiring board according to an embodiment includes a base film having a main surface and wiring disposed on the main surface. The base film is formed of a fluororesin. The wiring has a conductive layer disposed on the main surface. The conductive layer is a layer containing a plurality of conductive particles bonded to each other. The amount of nitrogen present on the main surface is 0.2 atomic percent or more.

[0021] [Details of the embodiment of the present disclosure] Next, details of the embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated. In the following, a substrate for a printed wiring board according to the embodiment will be referred to as a substrate for a printed wiring board 100, and a printed wiring board according to the embodiment will be referred to as a printed wiring board 200.

[0022] (Configuration of Substrate 100 for Printed Wiring Board) The configuration of the substrate 100 for printed wiring board will be described below.

[0023] 1 is a cross-sectional view of a substrate 100 for a printed wiring board. As shown in FIG. 1, the substrate 100 for a printed wiring board has a base film 10, a conductive layer 20, and a copper plating layer 30.

[0024] The base film 10 has a first main surface 10a and a second main surface 10b. The first main surface 10a and the second main surface 10b are end surfaces in the thickness direction of the base film 10. The second main surface 10b is the surface opposite to the first main surface 10a.

[0025] The base film 10 is made of a fluororesin. The fluororesin is, for example, PTFE (polytetrafluoroethylene). However, the fluororesin used for the base film 10 is not limited to this. The fluororesin used for the base film 10 may be PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer). The base film 10 may be made of a fluororesin containing a filler. The filler may be silica. However, the filler may be made of other materials.

[0026] The filler may be spherical. The average particle size of the filler may be 0.3 μm or more and 4.0 μm or less. The average particle size of the filler is measured by observing a cross section using a scanning electron microscope (SEM) and averaging the particle sizes of the filler observed in the cross section. The particle size of the filler may be calculated manually from the SEM image or by image processing. The area of ​​the cross section is 20 μm × 20 μm. Although the method for preparing a sample for the cross section observation is not particularly limited, the sample is prepared using, for example, a Cross Section Polisher (registered trademark) manufactured by JEOL Ltd. to accurately measure the particle size. The volume ratio of the filler to the fluororesin may be 1.2 or more, or 1.5 or more.

[0027] The filler and the conductive layer 20 may be in contact with each other, or there may be a distance between the filler and the conductive layer 20. When there is a distance between the filler and the conductive layer 20, a fluororesin may be present between the filler and the conductive layer 20. This distance may be 0.01 μm or more and 0.5 μm or less, or 0.05 μm or more and 0.3 μm or less. In any cross section perpendicular to the first main surface 10a, the total length along a direction parallel to the first main surface 10a of the fluororesin layer within the above-mentioned distance (0.01 μm or more and 0.5 μm or less) between the filler and the conductive layer 20 may be 5% or more, or 10% or more, of the entire length of the first main surface 10a in that cross section. In this case, the effect of improving adhesion is sufficiently ensured.

[0028] The conductive layer 20 is disposed on the first main surface 10a. The thickness of the conductive layer 20 is denoted by T. T may be 0.05 μm or more and 2.0 μm or less. If the thickness of the conductive layer 20 is less than 0.05 μm, the conductivity will be insufficient, and defects in the electroplated layer may occur or the thickness distribution of the electroplated layer may become more variable during the electroplating step (S5) described below. If the thickness of the conductive layer 20 exceeds 2.0 μm, the etching amount will be too large in the etching step (S7) described below, resulting in greater variation in the circuit width due to the variation in etching.

[0029] The conductive layer 20 is a layer of multiple conductive particles bonded to one another. The thickness of the conductive layer 20 can be measured by the following method: A sample is embedded in resin, and the processed surface is pre-finished by mechanical polishing. This processed surface is cross-sectionally processed using an Ar ion beam (cross-section polisher), and a 2 nm carbon coating is applied. The thickness of the conductive layer 20 is measured in an image obtained using a high-resolution scanning electron microscope (SU8020, manufactured by Hitachi High-Technologies Corporation). The thickness is the average value of measurements taken at 10 arbitrary points.

[0030] The conductive layer 20 is a porous body. In the conductive layer 20, two adjacent conductive particles are bonded to each other. The bonded conductive particles may be sintered. The conductive layer 20 may have a portion where two adjacent conductive particles are not bonded to each other. The plurality of conductive particles at the interface with the first main surface 10a are fixed to the first main surface 10a. However, some of the plurality of conductive particles at the interface with the first main surface 10a may not be fixed to the first main surface 10a.

[0031] The conductive particles are formed from a conductive material. The conductive particles are particles whose main component is, for example, copper (Cu). The conductive particles may also be particles whose main component is silver (Ag). Note that copper being the main component of the conductive particles means that the copper content in the conductive particles is greater than 50 mass percent. The same applies when silver is used. The conductive layer 20 may contain multiple types of conductive particles made of different materials. The average particle diameter of the conductive particles is, for example, 1 nm or more and 500 nm or less. If the average particle diameter of the conductive particles is less than 1 nm, oxidation is likely to progress, resulting in reduced conductivity. Furthermore, during the electroplating step (S5) described below, defects in the electroplated layer may occur, and the thickness distribution of the electroplated layer may become more variable. If the average particle diameter of the conductive particles exceeds 500 nm, it is difficult to achieve interparticle bonding by firing, resulting in reduced conductivity. Furthermore, during the electroplating step (S5) described below, defects in the electroplated layer may occur, and the thickness distribution of the electroplated layer may become more variable. The average particle size of the conductive particles is measured using a particle size distribution device (for example, Microtrac particle size distribution meter UPA-150EX manufactured by Nikkiso Co., Ltd.).

[0032] The amount of nitrogen present on the first major surface 10a is 0.2 atomic percent or more. The amount of nitrogen present on the first major surface 10a is measured by XPS (X-ray photoelectron spectroscopy) analysis. More specifically, the conductive layer 20 disposed on the first major surface 10a is removed using an acidic solution, and then the first major surface 10a is subjected to XPS analysis. The amount of nitrogen present per unit area on the first major surface 10a is obtained based on the peak area of ​​the spectrum representing the nitrogen 1s orbital obtained as a result.

[0033] The copper plating layer 30 is disposed on the conductive layer 20. The copper plating layer 30 is a copper layer formed by plating. The copper plating layer 30 is, for example, an electroless copper plating layer, i.e., a copper layer formed by electroless plating. The copper plating layer 30 may also be an electrolytic copper plating layer, i.e., a copper layer formed by electrolytic plating. Note that the printed wiring board substrate 100 does not necessarily have to have the copper plating layer 30.

[0034] 2 is a cross-sectional view of a modified example of the substrate 100 for printed wiring boards. As shown in Fig. 2, the substrate 100 for printed wiring boards may also have a conductive layer 20 disposed on the second main surface 10b. When the conductive layer 20 is disposed on the second main surface 10b, a copper plating layer 30 may be disposed on the conductive layer 20 on the second main surface 10b.

[0035] (Method for Manufacturing the Substrate 100 for Printed Wiring Board) A method for manufacturing the substrate 100 for printed wiring board will be described below.

[0036] 3 is a manufacturing process diagram of the substrate 100 for printed wiring boards. As shown in FIG. 3, the manufacturing method of the substrate 100 for printed wiring boards includes a preparation step S1, a conductive layer forming step S2, and a plating step S3. The conductive layer forming step S2 is performed after the preparation step S1. The plating step S3 is performed after the conductive layer forming step S2. Note that if the substrate 100 for printed wiring boards does not have a copper plating layer 30, the plating step S3 is omitted.

[0037] 4 is a cross-sectional view illustrating the preparation step S1. As shown in FIG. 4, in the preparation step S1, a base film 10 is prepared. Note that the base film 10 prepared in the preparation step S1 does not have a conductive layer 20 formed on its first main surface 10a. Furthermore, the base film 10 prepared in the preparation step S1 may or may not be subjected to a pretreatment (e.g., alkali treatment or plasma treatment) on its first main surface 10a before being subjected to the conductive layer forming step S2.

[0038] 5 is a cross-sectional view illustrating the conductive layer forming step S2. In the conductive layer forming step S2, as shown in FIG. 5, a conductive layer 20 is formed on the first main surface 10a. In the conductive layer forming step S2, first, ink in which a plurality of conductive particles are dispersed is applied to the first main surface 10a. The surfaces of the conductive particles contained in the ink are coated with an organic material. The organic material contains nitrogen and hydrogen.

[0039] Secondly, in the conductive layer forming step S2, the ink applied to the first main surface 10a is heated and pressurized. The heating and pressurization are performed in a vacuum environment. The heating and pressurization are performed using, for example, a vacuum press. The heating and pressurization volatilize the solvent in the ink and decompose the organic material coating the surfaces of the conductive particles, causing sintering between the conductive particles and adhesion of the conductive particles to the first main surface 10a. In this way, the conductive layer 20 is formed on the first main surface 10a. When pressurization is performed, a plate member made of a metal material such as aluminum is placed between the head of the vacuum press and the ink.

[0040] In the plating step S3, a copper plating layer 30 is formed on the conductive layer 20. The copper plating layer 30 is formed by, for example, electroless plating. The copper plating layer 30 may also be formed by electrolytic plating. In this manner, the printed wiring board substrate 100 having the structure shown in FIG. 1 is formed.

[0041] <Modifications> In the above example, ink having dispersed conductive particles is applied to the first main surface 10a in the conductive layer forming step S2, but the ink may also be applied to the surface of a plate member made of a metal material such as aluminum. In this case, the base film 10 is placed on the applied ink, and then the ink is heated and pressurized. Note that when ink is applied to the surface of a plate member made of a metal material such as aluminum, it is less likely to be repelled than when ink is applied to the surface of a base film 10 made of fluororesin.

[0042] (Configuration of Printed Wiring Board 200) The configuration of the printed wiring board 200 will be described below.

[0043] 6 is a cross-sectional view of a printed wiring board 200. As shown in FIG. 6, the printed wiring board 200 has a base film 10 and wiring 50. The wiring 50 is disposed on the first main surface 10a. The wiring 50 has a conductive layer 20, a copper plating layer 30, and an electrolytic copper plating layer 40. The electrolytic copper plating layer 40 is disposed on the copper plating layer 30. The electrolytic copper plating layer 40 is a copper layer formed by electrolytic plating. The printed wiring board 200 does not necessarily have to have the copper plating layer 30.

[0044] 7 is a cross-sectional view of a modified example of printed wiring board 200. As shown in Fig. 7, in printed wiring board 200, wiring 50 may also be arranged on second main surface 10b. In this case, printed wiring board 200 does not need to have copper plating layer 30.

[0045] (Method of Manufacturing Printed Wiring Board 200) A method of manufacturing the printed wiring board 200 will be described below.

[0046] 8 is a manufacturing process diagram of printed wiring board 200. As shown in Fig. 8, the manufacturing method of printed wiring board 200 includes a resist pattern forming step S4, an electrolytic plating step S5, a resist pattern removing step S6, and an etching step S7. Printed wiring board 200 is formed using printed wiring board substrate 100.

[0047] 9 is a cross-sectional view illustrating the resist pattern forming step S4. As shown in FIG. 9, in the resist pattern forming step S4, a resist pattern 60 is formed on the conductive layer 20. The resist pattern 60 has openings 61. The copper plating layer 30 is exposed from the openings 61. The resist pattern 60 is formed, for example, by patterning a dry film resist through exposure and development. Note that if the printed wiring board 200 does not have the copper plating layer 30, the conductive layer 20 is exposed from the openings 61.

[0048] 10 is a cross-sectional view illustrating the electrolytic plating step S5. As shown in Fig. 10, in the electrolytic plating step S5, an electrolytic copper plating layer 40 is formed on the copper plating layer 30 exposed from the opening 61 (or on the conductive layer 20 exposed from the opening 61 if no copper plating layer 30 is present). The electrolytic copper plating layer 40 is formed by passing a current through the conductive layer 20 and the copper plating layer 30 to perform electrolytic plating on the copper plating layer 30 exposed from the opening 61.

[0049] 11 is a cross-sectional view illustrating the resist pattern removal step S6. As shown in FIG. 11, in the resist pattern removal step S6, the resist pattern 60 is removed. In the etching step S7, the conductive layer 20 and the copper plating layer 30 between two adjacent electrolytic copper plating layers 40 are removed by wet etching. In this manner, the printed wiring board 200 having the structure shown in FIG. 6 is formed.

[0050] (Effects of the Substrate 100 for Printed Wiring Board) The effects of the substrate 100 for printed wiring board will be described below.

[0051] In the substrate 100 for printed wiring boards, in the conductive layer formation step S2, the organic material coating the surfaces of the conductive particles reacts with fluorine contained in the fluororesin of the base film 10 to generate a fluorine compound. Because the organic material coating the surfaces of the conductive particles contains hydrogen, this fluorine compound is hydrogen fluoride. Because hydrogen fluoride is a gas, the fluorine compound generated in the conductive layer formation step S2 is discharged to the outside through the porous conductive layer 20 and is unlikely to remain at the interface between the conductive layer 20 and the first main surface 10a. In other words, it does not corrode the conductive layer 20, unlike water-soluble fluorides that form at the interface between a metal layer and a resin film during sputtering.

[0052] When forming printed wiring board 200 using substrate 100 for printed wiring board, conductive layer 20 that does not constitute wiring 50 is removed by wet etching. In substrate 100 for printed wiring board, fluorine compound is unlikely to remain at the interface between conductive layer 20 and first main surface 10a, so conductive layer 20 that constitutes wiring 50 is unlikely to corrode when wet etching is performed. Therefore, substrate 100 for printed wiring board can prevent peeling of wiring 50.

[0053] In the conductive layer formation step S2, nitrogen contained in the organic material coating the surfaces of the conductive particles at the interface with the first main surface 10a bonds with carbon contained in the fluororesin of the base film 10, thereby adhering the conductive layer 20 to the first main surface 10a. Therefore, when the amount of nitrogen present on the first main surface 10a is measured by XPS analysis after removing the conductive layer 20 with an acidic solution, it is 0.2 atomic percent or more. Therefore, the printed wiring board substrate 100 and the printed wiring board 200 exhibit excellent adhesion between the base film 10 and the conductive layer 20. The XPS analysis was performed using a Quantera SXM manufactured by ULVAC PHI under X-ray irradiation conditions of 100 μmφ, 25 W, and 15 kV.

[0054] If the base film 10 is made of a fluororesin containing a filler, the base film 10 is less likely to deform when pressure is applied in the conductive layer forming step S2, and pressure is applied more uniformly to the ink. Therefore, in this case, the conductive layer 20 can be formed more uniformly.

[0055] When the filler is made of silica, silica is inexpensive, which can reduce the cost of the base film 10. When the average particle size of the filler is 0.3 μm or more and 4.0 μm or less, deformation of the base film 10 during pressure application can be suppressed while suppressing increase in unevenness of the first main surface 10 a (second main surface 10 b) due to the pressure application in the conductive layer formation step S2. When the volume ratio of the filler to the fluororesin is 1.2 or more, the conductive layer 20 can be formed more uniformly.

[0056] FIG. 12 is an SEM image of a cross section of a printed wiring board substrate 100. FIG. 12 shows an SEM image of a cross section perpendicular to the first main surface 10a. The cross section in FIG. 12 was processed using a Cross-Section Polisher (registered trademark). In FIG. 12, the base film 10 is formed of PTFE containing a silica filler. As shown in FIG. 12, if a fluororesin is present between the filler and the conductive layer 20, high pressure is applied between the fluororesin and the conductive layer 20 during the pressurization in the conductive layer formation step S2, improving adhesion between the conductive layer 20 and the base film 10. If the thickness of the fluororesin is less than 0.01 μm, the conductive layer 20 may come into contact with the filler. If the thickness of the fluororesin is greater than 0.5 μm, the pressure increase effect is reduced. Therefore, if the thickness of the fluororesin is 0.01 μm or more and 0.5 μm or less, adhesion between the conductive layer 20 and the base film 10 is particularly improved.

[0057] When the filler is spherical, a uniform distance from the conductive layer 20 can be easily achieved along a portion of the filler's surface. Furthermore, when the filler is spherical, the filler is less likely to break through the conductive layer 20 when pressure is applied in the conductive layer forming step S2. The aforementioned effect of improving adhesion is sufficiently ensured when, in any cross section perpendicular to the first main surface 10a, the length along the first main surface 10a of the fluororesin layer between the filler and the conductive layer 20 is 5% or more of the width of the cross section. Alternatively, in any cross section perpendicular to the first main surface 10a, the total length along a direction parallel to the first main surface 10a of the fluororesin layer within the above-mentioned distance (0.01 μm or more and 0.5 μm or less) between the filler and the conductive layer 20 may be 5% or more, or even 10% or more, of the entire length of the first main surface 10a in the cross section. In this case, the aforementioned effect of improving adhesion is sufficiently ensured.

[0058] <Examples> Samples 1 to 7 were prepared as examples, and Sample 8 was prepared as a comparative example. In Samples 1 to 6 and Sample 8, the base film 10 was formed of PTFE containing a filler. In Sample 7, the base film 10 was formed of PTFE containing no filler.

[0059] Copper particles having an average particle size of 70 nm were used as the conductive particles in Samples 1 to 4 and Samples 6 and 7. In Sample 5, copper particles having an average particle size of 30 nm were used as the conductive particles.

[0060] For Samples 1 to 8, the pressure applied to the ink in the conductive layer forming step S2 was changed. For Sample 8, this pressure was 0. That is, for Sample 8, no pressure was applied to the ink during the conductive layer forming step S2. For Samples 1 to 8, the maximum heating temperature (maximum heating temperature of the hot plate of the press device) in the conductive layer forming step S2 was 350°C. Samples 1 to 8 were heated from room temperature to 350°C at a temperature increase rate of 5°C / min, held at 350°C for 10 minutes, and then cooled to room temperature at a temperature decrease rate of 5°C / min.

[0061] In Samples 1 to 5, 7, and 8, ink was applied to the first main surface 10a when the conductive layer forming step S2 was performed. In Sample 6, ink was applied to the surface of an aluminum plate member when the conductive layer forming step S2 was performed. In Samples 1 to 8, no pretreatment was performed on the first main surface 10a. Details of Samples 1 to 8 are shown in Table 1.

[0062]

[0063] For Samples 1 to 8, the amount of nitrogen present on the first main surface 10a and the adhesion of the conductive layer 20 to the first main surface 10a were measured. To measure the adhesion of the conductive layer 20 to the first main surface 10a, first, an electrolytic copper-plated layer was formed on the conductive layer 20. The average total thickness of the conductive layer 20 and the electrolytic copper-plated layer was 20 μm. Second, in accordance with JIS-C6471 (1995), the base film 10 was fixed to a glass epoxy plate with double-sided tape, and the conductive layer 20 and the electrolytic copper-plated layer were peeled off in a direction 180° relative to the base film 10. The measurement device used was an Autograph AGS-X / 500N manufactured by Shimadzu Corporation, with a sample width of 5 mm, a peeling rate of 50 mm / min, and a measurement temperature of 25±3°C. The peel strength during this peeling was taken as the adhesion of the conductive layer 20 to the first main surface 10a. The amount of nitrogen present in the base film was measured by etching away the copper layer using a copper etching solution containing 1 mol / L copper chloride and 0.5 mol / L hydrochloric acid, followed by XPS analysis. The XPS analysis was performed using a Quantera SXM (manufactured by ULVAC PHI) under X-ray irradiation conditions of 100 μmφ, 25 W, and 15 kV. The results are shown in Table 2.

[0064]

[0065] As shown in Table 2, the amount of nitrogen present in the first main surface 10a was 0.2 atomic percent or more in Samples 1 to 7. On the other hand, the amount of nitrogen present in the first main surface 10a was less than 0.2 atomic percent in Sample 8. This demonstrates that the application of pressure in the conductive layer forming step S2 causes the amount of nitrogen present in the first main surface 10a to be 0.2 atomic percent or more.

[0066] The adhesion of conductive layer 20 to first main surface 10a in Samples 1 to 7 was greater than the adhesion of conductive layer 20 to first main surface 10a in Sample 8. This comparison revealed that the adhesion of conductive layer 20, and therefore the adhesion of wiring 50, is improved when the amount of nitrogen present on first main surface 10a is 0.2 atomic percent or more.

[0067] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0068] REFERENCE SIGNS LIST 10 base film 10a first main surface 10b second main surface 20 conductive layer 30 copper plating layer 40 electrolytic copper plating layer 50 wiring 60 resist pattern 61 opening 100 printed wiring board substrate 200 printed wiring board S1 preparation step S2 conductive layer forming step S3 plating step S4 resist pattern forming step S5 electrolytic plating step S6 resist pattern removing step S7 etching step T thickness

Claims

1. A base film having a main surface; a conductive layer disposed on the major surface; The base film is formed of a fluororesin, the conductive layer is a layer including a plurality of conductive particles bonded to each other; The amount of nitrogen present on the main surface of the substrate for printed wiring boards is 0.2 atomic percent or more.

2. 2. The substrate for printed wiring board according to claim 1, wherein the conductive particles are particles whose main component is copper or silver.

3. 2. The substrate for printed wiring board according to claim 1, wherein the conductive layer has a thickness of 0.05 μm or more and 2.0 μm or less.

4. 2. The substrate for printed wiring board according to claim 1, wherein the conductive particles have an average particle size of 1 nm or more and 500 nm or less.

5. The substrate for printed wiring board according to claim 1 , further comprising a copper plating layer disposed on the conductive layer.

6. The substrate for printed wiring board according to claim 5 , wherein the copper plating layer is an electroless copper plating layer or an electrolytic copper plating layer.

7. 2. The substrate for printed wiring board according to claim 1, wherein the base film is made of a fluororesin containing a filler.

8. The substrate for printed wiring board according to claim 7 , wherein the filler is made of silica.

9. The substrate for printed wiring board according to claim 1 , wherein the fluororesin is polytetrafluoroethylene.

10. A base film having a main surface; wiring disposed on the main surface; The base film is formed of a fluororesin, the wiring has a conductive layer disposed on the main surface; the conductive layer is a layer including a plurality of conductive particles bonded to each other; The amount of nitrogen present on the main surface is 0.2 atomic percent or more.