Printed wiring board and method for manufacturing printed wiring board

Abstract

This printed wiring board comprises: an insulating base material; and a wiring pattern including a first conductive layer disposed on at least one main surface of the base material, a plurality of metal particles disposed on a main surface on the opposite side of the first conductive layer from a main surface on the base material side, and a second conductive layer disposed directly above the metal particles.

Description

Printed Wiring Board and Method for Manufacturing Printed Wiring Board

[0001] The present disclosure relates to a printed wiring board and a method for manufacturing a printed wiring board.

[0002] Patent Document 1 discloses a method for manufacturing a printed wiring board having a fine wiring pattern. The printed wiring board produced in Patent Document 1 has a fine wiring pattern composed of a copper thin film whose surface disposed on an insulating layer is densely roughened with a specific etching solution and an electrolytic copper plating formed directly above the copper thin film.

[0003] Japanese Patent Application Laid-Open No. 2020-17747

[0004] The printed wiring board of the present disclosure includes an insulating base material, a first conductive layer disposed on at least one main surface of the base material, a plurality of metal particles disposed on the main surface of the first conductive layer opposite to the main surface on the base material side, and a wiring pattern including a second conductive layer disposed directly above the metal particles.

[0005] Figure 1 is a cross-sectional view of a printed circuit board according to Embodiment 1. Figure 2 is an enlarged view of the region near the wiring pattern 51 in Figure 1, and is a diagram illustrating an example of the form in which metal particles exist. Figure 3 is an enlarged view of the region near the wiring pattern 51 in Figure 1, and is a diagram illustrating an example of the form in which metal particles exist. Figure 4 is an enlarged view of the region near the wiring pattern 51 in Figure 1, and is a diagram illustrating an example of the form in which metal particles exist. Figure 5 is an enlarged view of the region near the wiring pattern 51 in Figure 1, and is a diagram illustrating an example of the form in which metal particles exist. Figure 6 is a manufacturing process diagram of a printed circuit board according to Embodiment 2. Figure 7 is a cross-sectional view illustrating the preparation process S1. Figure 8 is a cross-sectional view illustrating the first conductive layer formation process S2. Figure 9 is a cross-sectional view illustrating the metal particle arrangement process S3. Figure 10 is a diagram illustrating an example of the form in which metal particles exist. Figure 11 is a diagram illustrating an example of the form in which metal particles exist. Figure 12 is a cross-sectional view illustrating an example of a metal particle sintered body layer. Figure 13 is a cross-sectional view illustrating an example of a metal particle sintered body layer. Figure 14 is a cross-sectional view illustrating the resist pattern formation process S41. Figure 15 is a cross-sectional view illustrating the second conductive layer formation process S42. Figure 16 is a cross-sectional view illustrating the resist pattern removal process S43.

[0006] [Problems this disclosure aims to solve] In recent years, as electronic devices have become smaller, lighter, and more functional, there is an increasing demand for higher density wiring on printed circuit boards used in electronic devices. In order to miniaturize the wiring pattern, for example, it is necessary to thin the copper thin film which is the seed layer in the semi-additive process described in Patent Document 1. However, when the copper thin film is thin, it is partially lost during the roughening process, resulting in areas where the electroplating layer is not formed and causing circuit defects.

[0007] Therefore, the purpose of this disclosure is to provide a printed circuit board that has fewer circuit defects and enables high-density wiring.

[0008] [Effects of this disclosure] According to this disclosure, it is possible to provide a printed circuit board with fewer circuit defects and capable of high-density wiring.

[0009] [Description of Embodiments of the Disclosure] Embodiments of the Disclosure will be described first by listing them. (1) The printed circuit board of the Disclosure is a printed circuit board comprising an insulating substrate, a first conductive layer disposed on at least one main surface of the substrate, a plurality of metal particles disposed on the main surface of the first conductive layer opposite to the main surface on the substrate side, and a wiring pattern including a second conductive layer disposed directly above the metal particles.

[0010] According to this disclosure, it is possible to provide a printed circuit board with fewer circuit defects and capable of high-density wiring.

[0011] In the printed circuit board 100 of this disclosure, metal particles 41 are arranged between the first conductive layer 21 and the second conductive layer 31. Due to the fine anchoring effect of the metal particles 41, the adhesion between the first conductive layer 21 and the second conductive layer 31 is improved. Therefore, even in circuits with fine-pitch wiring patterns, peeling of the wiring pattern after the circuit formation process can be suppressed.

[0012] (2) In (1) above, at least a portion of the metal particles may exist as a sintered metal particle body. This makes it less likely for the particles to fall off during transport in manufacturing processes such as dry film lamination.

[0013] (3) In (2) above, the metal particle sintered body exists as a metal particle sintered body layer, and the thickness of the metal particle sintered body layer may be 2 nm or more and 3 μm or less. If the average thickness of the metal particle sintered body layer is 2 nm or more, the effect of suppressing peeling of the wiring pattern is further improved. If the average thickness of the metal particle sintered body layer is 3 μm or less, productivity is improved.

[0014] (4) In any of (1) to (3) above, the metal particles may be made of copper. This suppresses ion migration.

[0015] (5) In any of (1) to (4) above, an electroless plating layer may be further provided between the first conductive layer and the metal particles. This allows for an electrical connection between the through-hole and the main surface of the substrate when the substrate has a through-hole.

[0016] (6) A method for manufacturing a printed circuit board according to the present disclosure is a method for manufacturing a printed circuit board according to any of (1) to (5) above, comprising the steps of: preparing the substrate; forming the first conductive layer on at least one main surface of the substrate; arranging the plurality of metal particles on the main surface of the first conductive layer opposite to the main surface on the substrate side; forming a resist pattern on the metal particles; forming the second conductive layer in the openings of the resist pattern by electroplating; removing the resist pattern; and forming the wiring pattern including the first conductive layer, the metal particles, and the second conductive layer by etching away the metal particles and the first conductive layer that were arranged between the resist pattern and the substrate.

[0017] In the method for manufacturing a printed circuit board according to the present disclosure, a plurality of metal particles are arranged on a first conductive layer, and a resist pattern is formed on the metal particles. As a result, even when the width of the resist becomes narrow when forming a circuit with a fine-pitch wiring pattern, the fine anchoring effect of the metal particles improves the adhesion between the first conductive layer and the resist, making it less likely for the resist to collapse even in the case of a fine pitch. Therefore, the method for manufacturing a printed circuit board according to the present disclosure is advantageous for forming circuits with a fine-pitch wiring pattern.

[0018] [Details of Embodiments of the Disclosure] Specific examples of the printed circuit board of the Disclosure will be described below with reference to the drawings. In the drawings of the Disclosure, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth have been modified as appropriate for clarity and simplification of the drawings and do not necessarily represent actual dimensional relationships.

[0019] In this disclosure, the notation "A to B" means A or greater and B or less. If no unit is specified for A, and only a unit is specified for B, then the unit for A and the unit for B are the same.

[0020] In this disclosure, when compounds and the like are represented by chemical formulas, unless otherwise specified, the atomic ratios should include all conventionally known atomic ratios and should not necessarily be limited to those within the stoichiometric range.

[0021] In this disclosure, if one or more numerical values ​​are listed as the lower limit and upper limit of a numerical range, any combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit shall also be disclosed.

[0022] In this disclosure, “equipment,” “includes,” “possesses,” and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the essential elements. The statement “consists of” is a closed term. However, even a configuration expressed in closed terms may include additional elements that are usually incidental or irrelevant to the subject technology.

[0023] [Embodiment 1: Printed Wiring Board] A printed wiring board 100 of one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to Figure 1. The printed wiring board 100 comprises an insulating substrate 10, a first conductive layer 21 disposed on at least one main surface of the substrate 10, a plurality of metal particles 41 disposed on the main surface of the first conductive layer 21 opposite to the main surface on the substrate 10 side, and a wiring pattern 51 including a second conductive layer 31 disposed directly above the metal particles 41.

[0024] <Base Material> The base material 10 has main surfaces consisting of 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 material 10. The second main surface 10b is the surface opposite to the first main surface 10a.

[0025] The base material 10 has insulating properties. The base material 10 may be formed from, for example, polyimide, liquid crystal polymer, fluororesin, etc. However, the constituent materials of the base material 10 are not limited to these.

[0026] The thickness of the substrate 10 may be 5 μm or more and 100 μm or less, or 10 μm or more and 50 μm or less. If the thickness of the substrate 10 is 5 μm or more, the strength of the substrate 10 is sufficient. If the thickness of the substrate 10 is 100 μm or less, the substrate 10 can have good flexibility. In this disclosure, thickness means the average of the thickness measured at any five locations in the cross section in the direction along the normal to the main surface of the printed circuit board 100. The thickness of the first conductive layer 21, the second conductive layer 31 and the metal particle sintered body described later also have the same meaning.

[0027] <Wiring Pattern> The wiring pattern 51 includes a first conductive layer 21 disposed on at least one main surface of the substrate 10, a plurality of metal particles 41 disposed directly above the first conductive layer 21, and a second conductive layer 31 disposed directly above the metal particles 41. The wiring pattern 51 may be arranged so as to expose at least a portion of the main surface of the substrate 10.

[0028] <First conductive layer> The first conductive layer 21 is disposed on at least one main surface of the substrate 10. In Figure 1, the first conductive layer 21 is disposed on the first main surface 10a and the second main surface 10b of the substrate 10, but is not limited to this. The first conductive layer 21 may be disposed only on the first main surface 10a, or only on the second main surface 10b. The first conductive layer 21 may be disposed so as to expose at least a portion of the main surface of the substrate 10.

[0029] The first conductive layer 21 may be a sputtering, electroless plating, electroplating, rolled foil, or metal particle sintered layer, or a combination thereof. The main component of the first conductive layer 21 may be, but is not limited to, copper, silver, nickel, or gold. In this disclosure, "main component" means a component that is present in an amount of 60% by mass or more. From the viewpoint of cost and conductivity, the main component of the first conductive layer may be silver or copper.

[0030] From the viewpoint of suppressing ion migration, the main component of the first conductive layer 21 may be copper. As long as the effects of this disclosure are not impaired, the first conductive layer 21 may also contain, along with copper, at least one selected from the group consisting of nickel, chromium, silver, and titanium.

[0031] The thickness of the first conductive layer 21 may be 0.1 μm or more and 5 μm or less, or 0.2 μm or more and 1 μm or less.

[0032] <Metal Particles> Multiple metal particles 41 are arranged on the main surface of the first conductive layer 21 opposite to the main surface on the substrate 10 side. In Figure 1, the multiple metal particles 41 form a layer, but the form in which the metal particles exist is not limited to this.

[0033] As shown in Figure 2, at least some of the multiple metal particles 41 may be located on the main surface of the first conductive layer 21, with each metal particle separated from the others.

[0034] As shown in Figure 3, at least some of the multiple metal particles 41 are located on the main surface of the first conductive layer 21, with each metal particle 41 separated from the others, and the metal particles 41 may be fused to the first conductive layer 21. Fusion refers to a state in which at least some of the metal particles 41 have melted and become integrated with the first conductive layer 21.

[0035] The multiple metal particles 41 may be aggregated on the main surface of the first conductive layer 21. At least a portion of the multiple metal particles 41 may exist on the main surface of the first conductive layer 21 as a sintered metal particle body. The sintered metal particle body has a structure in which multiple metal particles are fixed by a metal oxide or the like. The sintered metal particle body may be continuous in the in-plane direction of the first conductive layer 21. The sintered metal particle body may be discontinuous in the in-plane direction of the first conductive layer 21. That is, the multiple sintered metal particle bodies may be spaced apart from each other in the in-plane direction of the first conductive layer 21.

[0036] In Figure 1, multiple metal particles 41 are arranged directly on the main surface of the first conductive layer 21, but the model is not limited to this. An electroless plating layer may be placed between the first conductive layer 21 and the metal particles 41. When a cross-section of the printed circuit board 100 in the direction along the normal to the main surface is analyzed using an energy-dispersive X-ray spectrometer attached to a scanning electron microscope, and palladium (Pd) is present between the first conductive layer 21 and the metal particles 41, it is determined that an electroless plating layer is placed between the first conductive layer 21 and the metal particles 41.

[0037] As shown in Figure 4, at least a portion of the plurality of metal particles 41 may exist as a metal particle sintered body layer 40 consisting of a layered metal particle sintered body having a layered structure on the main surface of the first conductive layer 21.

[0038] As shown in Figure 5, at least a portion of the plurality of metal particles 41 exist as a metal particle sintered body layer 40 consisting of a layered metal particle sintered body on the main surface of the first conductive layer 21, and the metal particles 41 may be fused to the first conductive layer 21.

[0039] The thickness of the metal particle sintered body layer may be 2 nm to 3 μm, 20 nm to 1 μm, or 50 nm to 0.2 μm.

[0040] Examples of metals that make up the metal particles include copper, silver, nickel, and gold. From the viewpoint of cost and conductivity, the metal may be silver or copper. From the viewpoint of suppressing ion migration, the metal may be copper. In other words, the metal particles may be made of copper.

[0041] The average particle size of the metal particles may be 1 nm to 900 nm, 10 nm to 500 nm, or 30 nm to 100 nm. When the average particle size of the metal particles is 1 nm or more, the dispersibility and stability of the metal particles in the conductive ink containing the metal particles used to form the metal particles are good. When the average particle size of the metal particles is 900 nm or less, the precipitation of metal particles in the conductive ink is suppressed, and the uniformity of the density of metal particles is improved when the conductive ink is applied. In this disclosure, the average particle diameter means the particle diameter at which the volume integrated value in the particle diameter distribution measured by laser diffraction is 50%.

[0042] <Second conductive layer> The second conductive layer 31 is placed directly on top of the plurality of metal particles 41. The second conductive layer 31 may include at least electroplating.

[0043] The main component of the second conductive layer 31 may be, but is not limited to, copper, silver, nickel, or gold. From the viewpoint of cost and conductivity, the main component of the second conductive layer may be silver or copper.

[0044] The thickness of the second conductive layer 31 may be 1 μm or more and 200 μm or less, may be 5 μm or more and 100 μm or less, or may be 10 to 50 μm or less.

[0045] [Embodiment 2: Method for manufacturing a printed wiring board] A method for manufacturing a printed wiring board according to Embodiment 2 will be described. FIG. 6 is a manufacturing process diagram of the printed wiring board according to Embodiment 2. As shown in FIG. 6, the method for manufacturing the printed wiring board 100 includes a preparation step S1, a first conductive layer formation step S2, a metal particle placement step S3, and a wiring pattern formation step S4.

[0046] <Preparation step S1> As shown in FIG. 7, in the preparation step S1, a base material 10 having insulating properties is prepared. The configuration of the base material 10 is as described in Embodiment 1.

[0047] <First conductive layer formation step S2> As shown in FIG. 8, in the first conductive layer formation step S2, a first conductive layer 21 is formed on at least one main surface of the base material 10. In FIG. 8, the first conductive layer 21 is formed on the first main surface 10a and the second main surface 10b of the base material 10, but is not limited thereto. The first conductive layer 21 may be formed only on the first main surface 10a, or may be formed only on the second main surface 10b.

[0048] A first conductive layer 21 made of a rolled foil may be attached to at least one main surface of the base material 10 to form the first conductive layer 21. The metal constituting the first conductive layer 21 may be laminated on at least one main surface of the base material 10 by (a) only sputtering, (b) sputtering and electrolytic plating, (c) sputtering, electrolytic plating and electroless plating, or (d) sputtering and electroless plating to form the first conductive layer 21. A metal particle sintered layer may be formed on at least one main surface of the base material 10 to form the first conductive layer 21. The metal constituting the first conductive layer 21 is as described in Embodiment 1.

[0049] <Metal particle placement step S3> As shown in FIG. 6, the metal particle placement step S3 includes a conductive ink application step S31, a drying step S32, and a firing step S33.

[0050] <Conductive Ink Coating Process S31> As shown in Figure 9, in the metal particle arrangement process S3, firstly, a conductive ink containing metal particles is applied (also referred to as "conductive ink coating process S31") to the main surface of the first conductive layer 21 opposite to the main surface on the substrate 10 side. Conventional known coating methods such as spin coating, spray coating, bar coating, die coating, slit coating, roll coating, and dip coating can be used as coating methods.

[0051] The average particle size of the metal particles contained in the conductive ink may be between 1 nm and 900 nm.

[0052] The metal particle content of the conductive ink may be 5% by mass or more and 50% by mass or less. When the metal particle content of the conductive ink is 5% by mass or more, it is easy to form a dense metal particle sintered body containing the metal particles 41. When the metal particle content of the conductive ink is 50% by mass or less, the film thickness of the metal particle sintered body layer containing the metal particles 41 can be made more uniform.

[0053] The solvent in the conductive ink described above is not particularly limited, and various solvents that can effectively disperse metal particles can be used. Examples of solvents include water and various water-soluble organic solvents. Specific examples of organic solvents include alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; ketones such as acetone and methyl ethyl ketone; polyhydric alcohols such as ethylene glycol and glycerin; other esters; and glycol ethers such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether.

[0054] Conductive inks may contain dispersants in addition to metal particles. The dispersant is not particularly limited, and various dispersants capable of effectively dispersing metal particles can be used. Examples of dispersants include amine-based polymeric dispersants such as polyethyleneimine and polyvinylpyrrolidone; hydrocarbon-based polymeric dispersants having carboxyl groups in their molecules, such as polyacrylic acid and carboxymethylcellulose; and polymeric dispersants having polar groups, such as polyvinyl alcohol (PVA), styrene-maleic acid copolymers, olefin-maleic acid copolymers, and copolymers having polyethyleneimine and polyethylene oxide moieties in their molecules.

[0055] <<Drying Process S32>> Following the conductive ink coating process S31, a drying process S32 is performed in which the solvent contained in the coated conductive ink is dried. The drying method can be, for example, blowing air at a temperature of room temperature (23°C) or higher. The upper limit of the drying temperature may be 100°C from the viewpoint of suppressing crack formation due to rapid drying.

[0056] <<Firing Process S33>> Following the drying process S32, a firing process S33 is performed in which the dried conductive ink is fired. As a result, the metal particles contained in the dried conductive ink are fired, and as shown in Figure 9, the metal particles 41 are arranged on the first conductive layer 21.

[0057] In the firing process S33, the metal particles contained in the conductive ink may be sintered with each other to form a sintered metal particle body.

[0058] As shown in Figure 10, the multiple metal particles 41 may be arranged on the main surface of the first conductive layer 21, with each metal particle separated from the others.

[0059] As shown in Figure 11, the multiple metal particles 41 are located on the main surface of the first conductive layer 21, with each metal particle 41 separated from the others, and the metal particles 41 may be fused to the first conductive layer 21.

[0060] As shown in Figure 12, at least a portion of the plurality of metal particles 41 may exist as a metal particle sintered body layer 40 consisting of a layered metal particle sintered body having a layered structure on the main surface of the first conductive layer 21.

[0061] As shown in Figure 13, at least a portion of the plurality of metal particles 41 exist as a metal particle sintered body layer 40 consisting of a layered metal particle sintered body on the main surface of the first conductive layer 21, and the metal particles 41 may be fused to the first conductive layer 21.

[0062] The firing temperature may be between 150°C and 500°C, or between 250°C and 400°C. A firing temperature of 150°C or higher can improve the adhesion between the first conductive layer 21 and the metal particles 41. A firing temperature of 250°C or higher can form a sintered metal particle layer. A firing temperature of 500°C or lower can suppress deformation of the substrate 10. The firing time is not particularly limited, but may be, for example, between 30 minutes and 600 minutes. The firing atmosphere may be a nitrogen atmosphere, or a reducing atmosphere such as hydrogen-containing nitrogen. The firing method may be photo-firing, plasma irradiation, etc.

[0063] <Wiring Pattern Formation Process S4> As shown in Figure 6, the wiring pattern formation process S4 comprises a resist pattern formation process S41, a second conductive layer formation process S42, a resist pattern removal process S43, and an etching process S44.

[0064] <<Resist Pattern Formation Process S41>> As shown in Figure 14, in the resist pattern formation process S41, a resist pattern 71 is formed on the first conductive layer 21.

[0065] In the resist pattern formation process S41, first, a resist is applied to the metal particles 41. The fine anchoring effect of the metal particles 41 improves the adhesion between the metal particles 41 and the resist. This makes it possible to reduce the minimum resist width and enable the formation of fine-pitch circuits. Next, the applied resist is exposed and developed. As a result, the remaining resist that was not removed becomes the resist pattern 71, and the removed resist becomes an opening 71a.

[0066] The type of resist is not particularly limited. For example, dry film resists or liquid resists can be used, and either negative or positive types are acceptable.

[0067] The resist pattern 71 has an opening 71a. The opening 71a penetrates the resist pattern 71 along the thickness direction. In Figure 14, metal particles 41 are exposed from the opening 71a, but are not limited to this. If metal particles are not arranged on a part of the main surface of the first conductive layer 21, both the metal particles 41 and the first conductive layer 21 may be exposed from the opening 71a.

[0068] ≪Second conductive layer formation step S42≫ Following the resist pattern formation step S41, the second conductive layer formation step S42 is performed as shown in Figure 15. In the second conductive layer formation step S42, the second conductive layer 31 is formed on the metal particles 41 exposed from the opening 71a, or on the metal particles 41 and the first conductive layer 21. The second conductive layer 31 is formed by electroplating the first conductive layer 21 and the metal particles 41 by passing an electric current through them in a plating solution.

[0069] <<Resist Pattern Removal Process S43>> Following the second conductive layer formation process S42, the resist pattern 71 is removed as shown in Figure 16. In the resist pattern removal process, the resist pattern 71 is removed from the metal particles 41. As a result, the metal particles 41, or the metal particles 41 and the first conductive layer 21, are exposed between two adjacent second conductive layers 31.

[0070] ≪Etching Process S44≫ Following the resist pattern removal process, etching is performed. In the etching process, the metal particles 41 and the first conductive layer 21, which are positioned between the resist pattern and the substrate and exposed between two adjacent second conductive layers 31, are removed by etching. The presence of the metal particles 41 in the first conductive layer 21 and the second conductive layer 31 acts as an anchor, suppressing delamination between the first conductive layer 21 and the second conductive layer 31. As a result, a wiring pattern 51 including the first conductive layer 21, the metal particles 41, and the second conductive layer 31 is formed, and a printed circuit board 100 of Embodiment 1 having the structure shown in Figure 1 is obtained.

[0071] This embodiment will be described in more detail by reference to examples. However, this embodiment is not limited by these examples.

[0072] [Samples 1 to 10] A substrate 10 made of polyimide was prepared (see Figure 7). The average thickness of the substrate 10 was 25 μm.

[0073] A first conductive layer 21 containing copper was formed on both main surfaces of the substrate 10 by sputtering (see Figure 8). The average thickness of the first conductive layer 21 was 0.2 μm.

[0074] Next, a conductive ink 61 containing copper particles with an average particle size of 63 nm was applied onto the first conductive layer 21 using a bar coater. The application speed was 0.6 m / min.

[0075] Next, the substrate 10 was air-dried at room temperature (23°C).

[0076] Next, the dried conductive ink 61 was fired at the firing temperature shown in Table 1 for 60 minutes to form metal particles 41 (see Figure 9). In all samples, the metal particles 41 existed in both forms: as a sintered metal particle layer and as individual metal particles separated from each other. The average thickness of the sintered metal particle body is shown in Table 1.

[0077] Next, a dry film resist (12 μm thick) was attached to the metal particles 41. Then, the attached dry film resist was exposed to light and developed to remove a portion of the dry film resist and form a resist pattern 71 (see Figure 14). For each sample, the following two types of resist patterns 71 were prepared.

[0078] ≪Resist Pattern 1≫ The resist width was set at 0.5 μm intervals between 1.0 μm and 10.0 μm (for example, 1.0 μm, 1.5 μm, 2.0 μm, etc.). Table 1 shows the minimum resist width at which resist could be formed without resist peeling or resist collapse in each sample. The smaller the minimum resist width, the finer the pitch of the circuit that can be formed, and the higher the density of the wiring on the printed circuit board.

[0079] <<Resist Pattern 2>> The spacing between circuits was fixed at 10 μm, and resist patterns were fabricated in 0.5 μm increments so that the finished circuit width was 2 μm to 10 μm, and the presence or absence of circuit collapse was checked. The smallest circuit width in which no circuit collapse occurred is shown in Table 1. The smaller the minimum circuit width, the finer the pitch of the circuit formation is possible, and the higher the density of the wiring on the printed circuit board can be achieved.

[0080] Next, a second conductive layer 31 (material: copper) was formed by electroplating on the metal particles 41 exposed from the opening 71a, or on the metal particles 41 and the first conductive layer 21 (see Figure 15). The second conductive layer 31 was formed by electroplating the first conductive layer 21 and the metal particles 41 in a plating solution. The average thickness of the second conductive layer 31 was 8 μm.

[0081] Next, after removing the resist pattern 71 (see Figure 16), the metal particles 41 and the first conductive layer 21 exposed between the two adjacent second conductive layers 31 were removed by etching. This resulted in a printed circuit board 100 having the cross-sectional structure shown in Figure 1.

[0082] [Sample 1-1] A printed circuit board was fabricated in the same manner as Sample 1, except that metal particles were not formed.

[0083]

[0084] <Measurement of Resist Adhesion> For each sample, a dry film resist (12 μm thick) was applied to the entire surface of the metal particles 41 and / or the sintered metal particle layer 40 (first conductive layer in sample 1-1), and then exposed and developed to prepare a sample with a resist formed. Double-sided tape was attached to a support made of glass epoxy. The resist surface of each sample was attached to the double-sided tape, the substrate side was grasped with the chuck of a tensile testing machine, and the tensile testing machine was used to pull at a constant speed of 50 mm / min in a 180° direction at room temperature. The peel force between the substrate and the resist when pulled was measured. No patterning was done during exposure, and the entire surface was exposed. The substrate was 2 cm wide. The results are shown in Table 1.

[0085] <Discussion> The printed circuit boards of Samples 1 to 10 correspond to the examples. The printed circuit board of Sample 1-1 corresponds to the comparative example. It was confirmed that the printed circuit boards of Samples 1 to 10 have a smaller minimum resist width than the printed circuit board of Sample 1-1, enabling the formation of fine-pitch circuits and high-density wiring on the printed circuit boards. This is presumed to be because the resist adhesion force of Samples 1 to 10 is greater than that of Sample 1-1.

[0086] The printed circuit boards of Samples 1 to 10 had a smaller minimum circuit width and allowed for the formation of fine-pitch circuits compared to the printed circuit board of Sample 1-1, confirming that high-density wiring of the printed circuit boards was possible. This is presumed to be because, in the printed circuit boards of Samples 1 to 10, metal particles and / or a sintered metal particle layer are present between the seed layer and the electroplating layer in the circuit, making the circuit less prone to peeling.

[0087] The printed circuit boards of samples 1 to 10 were found to have few circuit defects and were confirmed to allow for high-density wiring.

[0088] While embodiments and examples of this disclosure have been described above, it is intended from the outset that the configurations of each of the embodiments and examples described above may be combined or modified in various ways as appropriate. The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalences.

[0089] 10 Substrate, 10a First main surface, 10b Second main surface, 21 First conductive layer, 31 Second conductive layer, 40 Metal particle sintered layer, 41 Metal particles, 51 Wiring pattern, 61 Conductive ink, 71 Resist pattern, 71a Opening, 100 Printed wiring board.

Claims

1. A printed circuit board comprising: an insulating substrate; a first conductive layer disposed on at least one main surface of the substrate; a plurality of metal particles disposed on the main surface of the first conductive layer opposite to the main surface on the substrate side; and a wiring pattern including a second conductive layer disposed directly above the metal particles.

2. The printed circuit board according to claim 1, wherein at least a portion of the metal particles exist as a sintered metal particle body.

3. The printed circuit board according to claim 2, wherein the metal particle sintered body exists as a metal particle sintered body layer, and the thickness of the metal particle sintered body layer is 2 nm or more and 3 μm or less.

4. The printed circuit board according to any one of claims 1 to 3, wherein the metal particles are made of copper.

5. The printed circuit board according to any one of claims 1 to 4, further comprising an electroless plating layer disposed between the first conductive layer and the metal particles.

6. A method for manufacturing a printed circuit board according to any one of claims 1 to 5, comprising: a step of preparing the substrate; a step of forming the first conductive layer on at least one main surface of the substrate; a step of arranging the plurality of metal particles on the main surface of the first conductive layer opposite to the main surface on the substrate side; a step of forming a resist pattern on the metal particles; a step of forming the second conductive layer in the openings of the resist pattern by electroplating; a step of removing the resist pattern; and a step of forming the wiring pattern including the first conductive layer, the metal particles, and the second conductive layer by etching away the metal particles and the first conductive layer that were arranged between the resist pattern and the substrate.

Images