Manufacturing method of printed circuit boards

Abstract

The objective is to provide a method for manufacturing printed circuit boards that can maintain small via diameters and ensure sufficient adhesion between the insulating substrate and the conductor layer without roughening the surface of the insulating substrate. [Solution] We discovered that by using a laminate in which a first metal layer (M1) and a protective layer (PL) are laminated on an inner circuit board (A) and a curable resin layer (B) which is an insulating substrate, a printed wiring board can be obtained in which sufficient adhesion between the insulating substrate and the conductor layer can be ensured, and thus completed the present invention.

Description

Technical Field

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

Background Art

[0002] In recent years, miniaturization and high performance of electronic devices have been progressing. In order to achieve high-density mounting, multilayer printed wiring boards tend to have finer conductor wiring and smaller via sizes. As a method for forming high-density fine wiring on an insulating base material by a build-up process, a semi-additive method is known in which a thin copper conductive seed layer is formed on the entire surface by electroless copper plating, a pattern resist is formed on this thin seed layer, a conductor pattern layer is formed by electroplating copper, and then the unnecessary thin copper layer is removed by flash etching. The insulating base material is generally treated by a wet process called desmear treatment. Before the electroless copper plating process, smears in the formed via portions are removed, and at the same time, the surface is roughened to ensure adhesion to the conductive layer formed in the subsequent process. A general chemical solution used for desmear treatment is described in, for example, Patent Document 1.

[0003] If the surface roughness of the insulating substrate, which is roughened by the desmearing process, is small, the adhesion strength between the conductor layer and the insulating substrate tends to be low. As conductor wiring becomes smaller, the contact area of ​​the conductor layer on the insulating substrate decreases, so sufficient adhesion strength is required, and in order to ensure sufficient adhesion strength between the insulating substrate and the conductor layer, the surface roughness needs to be increased. For this reason, the desmearing process generally requires a longer processing time than the processing time required to remove smear from the via area. On the other hand, since desmearing also roughens the via walls, if the processing time is long, the via diameter will increase, which is counterproductive to the demand for miniaturization of via diameters. Furthermore, if the surface roughness of the insulating substrate is large, in the semi-additive process, there is a problem in that the plating deep inside the physical anchor cannot be removed in the flash etching process performed after the formation of the conductive layer. In addition, if the surface roughness of the conductor layer that transmits signals is large, it adversely affects the transmission of high-frequency band signals used in high-speed communication, so it is preferable that the surface roughness of the insulating substrate that forms the interface with the conductive layer is small. Therefore, there is a need for a technology that removes smear from inside vias through desmearing, reduces the surface roughness of the insulating substrate, and increases the interfacial adhesion strength with the conductor layer. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-282020 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The problem that this invention aims to solve is to provide a method for manufacturing a printed circuit board that can maintain a small via diameter and ensure sufficient adhesion between the insulating substrate and the conductor layer without roughening the surface of the insulating substrate.

[0006] In order to solve the above problems, the inventors of the present invention conducted diligent research and found that the above problems could be solved by using a laminate in which a first metal layer (M1) and a protective layer (PL) are laminated on a curable resin layer (B), which is an insulating substrate, in the manufacture of a printed circuit board, and thus completed the present invention.

[0007] In other words, the present invention is 1. Step 1: Forming a laminate (L1) on an inner layer circuit board (A) by stacking a curable resin layer (B), a first metal layer (M1), and a protective layer (PL) in that order. Step 2 involves forming vias connecting to the circuit metal portion (IM) of the inner layer circuit board (A) through the protective layer (PL) side of the laminate (L1), the protective layer (PL), the first metal layer (M1), and the curable resin layer (B). Step 3 is a desmearing process to remove the smear generated in step 2. Step 4 involves making the via layer conductive and forming an electrical connection between the circuit metal part (IM) of the inner layer circuit board (A) and the first metal layer (M1). Step 5 involves removing the protective layer (PL) to expose the first metal layer (M1). Step 6: Forming a pattern resist corresponding to the circuit pattern on the first metal layer (M1). Step 7: Forming a conductor layer (M2) of the circuit pattern inside the via and on the first metal layer (M1). Step 8: Stripping off the pattern resist. Step 9: Remove the first metal layer (UM1) of the circuit-free portion. A method for manufacturing a printed wiring board, characterized by having the following features. 2. The method for manufacturing a printed wiring board according to claim 1, characterized in that a curable resin layer (B), a first metal layer (M1), and a protective layer (PL), which are laminated on the inner circuit board (A), are formed on both sides of the inner circuit board (A). 3. The method for manufacturing a printed circuit board according to either claim 1 or 2, characterized in that step 1 is step 1' which manufactures a laminate (L1') in which a resin layer (C) is further present between the curable resin substrate (B) and the first metal layer (M1). 4. A method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the main component of the metal constituting the first metal layer (M1) is silver. 5. The method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the protective layer (M1) is a metal mainly composed of copper. 6. A method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the main component of the metal constituting the first metal layer (M1) is silver, and the protective layer (PL) is a metal mainly composed of copper. 7. The method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the desmear treatment performed in step 3 is dry desmear. [Effects of the Invention]

[0008] In the method for manufacturing printed circuit boards of the present invention, it is possible to manufacture printed circuit boards that maintain small via diameters and ensure sufficient adhesion between the insulating substrate and the conductor layer without roughening the surface of the insulating substrate.

[0009] Therefore, the method for manufacturing printed circuit boards of the present invention is useful for manufacturing multilayer printed circuit boards such as flexible printed circuit boards, rigid printed circuit boards, semiconductor package substrates, ceramic package substrates, and glass package substrates, and in particular for manufacturing miniaturized, high-density mounting, and high-speed signal transmission printed circuit boards. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows the structure of the laminate (L1) produced in step 1. [Figure 2] This diagram shows the structure of the laminate formed by vias in step 2. [Figure 3] This diagram shows the structure of the laminate after smear removal in step 3. [Figure 4] This diagram shows the structure of a laminate in which the via layer is electrified in step 4, and an electrical connection is formed between the circuit metal part (B) of the inner layer circuit board (A) and the first metal layer (M1). [Figure 5]FIG. is a view showing the structure of a laminate in which the protective layer (PL) is removed and the first metal layer (M1) is exposed in Step 5. [Figure 6] FIG. is a view showing a laminate in which a pattern resist corresponding to a circuit pattern is formed on the first metal layer (M1) in Step 6. [Figure 7] FIG. is a view showing a laminate in which a conductor layer (M2) of a circuit pattern is formed inside the via and on the first metal layer (M1) in Step 7. [Figure 8] FIG. is a view showing a laminate from which the pattern resist has been peeled off in Step 8. [Figure 9] FIG. is a view showing a printed wiring board in which the first metal layer (UM1) of the unnecessary circuit portion has been removed in Step 9. [Figure 10] FIG. is a view showing the structure of the laminate (L1’) produced in Step 1. [Figure 11] FIG. is a view showing the structure of a laminate in which a via is formed in Step 2. [Figure 12] FIG. is a view showing the structure of a laminate in which smears are removed in Step 3. [Figure 13] FIG. is a view showing the structure of a laminate in which the via layer is electrified and an electrical connection between the circuit metal portion (B) of the inner layer circuit board (A) and the first metal layer (M1) is formed in Step 4. [Figure 14] FIG. is a view showing the structure of a laminate in which the protective layer (PL) is removed and the first metal layer (M1) is exposed in Step 5. [Figure 15] FIG. is a view showing a laminate in which a pattern resist corresponding to a circuit pattern is formed on the first metal layer (M1) in Step 6. [Figure 16] FIG. is a view showing a laminate in which a conductor layer (M2) of a circuit pattern is formed inside the via and on the first metal layer (M1) in Step 7. [Figure 17] FIG. is a view showing a laminate from which the pattern resist has been peeled off in Step 8. [Figure 18] FIG. is a view showing a printed wiring board in which the first metal layer (UM1) of the unnecessary circuit portion has been removed in Step 9. [Figure 19]This figure compares the surface morphology of the curable resin layer (B). (a) shows the surface morphology of Example 1, (b) shows the surface morphology of Comparative Example 2, and (c) shows the surface morphology of the curable resin layer (B) of Comparative Example 3. [Modes for carrying out the invention]

[0011] The present invention relates to a step 1 in which a laminate (L1) is formed by stacking a curable resin layer (B), a first metal layer (M1), and a protective layer (PL) in that order on an inner layer circuit board (A). Step 2 involves forming vias connecting to the circuit metal portion (IM) of the inner layer circuit board (A) through the protective layer (PL) side of the laminate (L1), the protective layer (PL), the first metal layer (M1), and the curable resin layer (B). Step 3 is a desmearing process to remove the smear generated in step 2. Step 4 involves making the via layer conductive and forming an electrical connection between the circuit metal part (IM) of the inner layer circuit board (A) and the first metal layer (M1). Step 5 to remove the protective layer (PL), Step 6: Forming a pattern resist corresponding to the circuit pattern on the first metal layer (M1). Step 7: Forming a conductor layer (M2) of the circuit pattern inside the via and on the first metal layer (M1). Step 8: Stripping off the pattern resist. Step 9: Remove the first metal layer (UM1) of the circuit-free portion. This is a method for manufacturing printed circuit boards, characterized by having [a specific feature].

[0012] The inner layer circuit board (A) used in the present invention is not particularly limited and can be appropriately selected according to the purpose and application of the printed wiring board to be manufactured, and is a core insulating substrate on which a circuit pattern or electrode pads are formed.

[0013] The curable resin layer (B) used in the present invention is an insulating substrate on which vias and conductor layers (M2) are formed in a subsequent process. The curable resin layer (B) is not particularly limited as long as it has the necessary insulating properties, heat resistance, and chemical resistance for a printed circuit board and can be cured under heating and pressurizing conditions. Commercially available materials called prepregs and build-up films can be suitably used. Suitable build-up films include, for example, the ABF series manufactured by Ajinomoto Fine Techno Co., Ltd. and build-up films manufactured by Sekisui Chemical Co., Ltd.

[0014] In the present invention, the first metal layer (M1) is a layer that serves as an electrode for electroplating when forming a conductor layer (M2) inside the via and on the first metal layer (M1) in step 7 of the method for manufacturing a printed circuit board of the present invention. The electrical resistance of the first metal layer (M1) only needs to have the conductivity required for an electrode in electroplating, and can be appropriately selected depending on the application and purpose of the product to be manufactured, the capacity and productivity of the manufacturing equipment, but from the viewpoint of the substrate size and capacity of the manufacturing equipment for general printed circuit board manufacturing, a surface resistance of 0.01Ω / □ to 10Ω / □ is preferable, and from the viewpoint of improving the efficiency of manufacturing and uniform electrodeposition of the conductor layer (M2), a surface resistance of 0.01Ω / □ to 5Ω / □ is preferable.

[0015] As described above, the first metal layer (M1) used in the present invention is used as an electrode for electroplating. In step 7, a pattern resist is formed on the first metal layer (M1) and used as a conductive seed layer for the semi-additive process. Therefore, the non-circuit pattern portion must ultimately be removed by etching. Due to the need to have sufficient conductivity as a conductive seed layer for the semi-additive process and to remove unwanted parts in subsequent processes, the thickness of the first metal layer (M1) used in the printed circuit board manufacturing method of the present invention is preferably 10 nm to 500 nm, and more preferably 10 nm to 300 nm from the viewpoint of efficiency in removing unwanted parts in subsequent processes.

[0016] The type of metal used to form the first metal layer (M1) in the present invention is not particularly limited as long as it functions as a conductive seed for the semi-additive method, and metals such as gold, silver, copper, and nickel can be suitably used. Among these metals, silver and copper are preferred from the viewpoint of conductivity as a conductive seed and cost-effectiveness, and silver is more preferable when copper is used as circuit wiring because it allows for the selection of a method that does not erode the wiring layer when removing the seed layer.

[0017] As described above, the first metal layer (M1) used in the present invention functions as a conductive seed for the semi-additive process and may be a bulk metal film or an aggregate film of metal particles, as long as the unnecessary parts can be removed in a later process.

[0018] In the method for manufacturing a printed circuit board of the present invention, a preferred uniform is one in which a resin layer (C) is further present between the curable resin substrate (B) and the first metal layer (M1). The resin layer (C) used in the present invention is a layer that promotes adhesion between the curable resin substrate (B) and the first metal layer (M1). As long as it has the heat resistance and chemical resistance required for the purpose and application of the printed circuit board to be manufactured, there are no restrictions, and it may be appropriately selected according to the type of curable resin substrate (B) and the type of first metal layer (M1).

[0019] In the method for manufacturing a printed circuit board of the present invention, the protective layer (PL) is laminated on the first metal layer (M1) and protects the first metal layer (M1) during the desmear treatment in step 2. The material forming the protective layer (PL) is not particularly limited as long as it protects the first metal layer (M1) during the desmear treatment and can be removed in a subsequent step. Resin films, metal films, etc., can be suitably used. When using a resin film for the protective layer (PL), commercially available film materials can be appropriately selected according to the purpose. For example, PET film, polystyrene film, OPP film, polyimide film, COP film, etc., can be used in the process. Since the protective layer (PL) is removed after the desmear treatment, it is preferable to form a release layer on the surface of the resin film facing the first metal layer (M1) in order to simplify the removal process. When using a resin film, the film thickness is preferably 20 μm to 300 μm from the viewpoint of handling and resistance in the desmear treatment process, and more preferably 20 μm to 100 μm from the viewpoint of via formation.

[0020] When a metal is used for the protective layer (PL), gold, silver, copper, aluminum, etc., can be suitably used as the metal, but from the viewpoint of applicability to general printed circuit board manufacturing methods, it is preferable to use a metal mainly composed of copper. When a metal protective layer is used as the protective layer (PL), the thickness of the protective layer is preferably 0.1 μm to 100 μm, and more preferably 0.1 to 50 μm from the viewpoint of ease of removal in subsequent processes. Furthermore, from the viewpoint of via formation, it is preferable to have a thickness of 0.1 to 10 μm, but in step 1, a thicker protective layer (PL) may be formed, and before via formation in step 2, the film thickness may be thinned to 0.1 to 10 μm by a method such as half etching.

[0021] The surface of the protective layer (PL) in contact with the first metal layer (M1) is a smooth surface, and specifically, the surface roughness (maximum height Sz) measured with a laser microscope is preferably in the range of 0.001 to 30 μm, preferably in the range of 0.01 to 20 μm, and more preferably in the range of 0.05 to 10 μm. The surface roughness (maximum height Sz) is measured using the evaluation method described in ISO 25178 and represents the distance from the highest point to the lowest point on the surface.

[0022] For the aforementioned conductor layer (M2), it is preferable to form a copper conductor layer (M2) due to its versatility as a printed circuit board.

[0023] In step 1 of the method for manufacturing a printed circuit board of the present invention, a laminate (L1) is produced by laminating a curable resin layer (B), a first metal layer (M1), and a protective layer (PL) in this order on an inner circuit board (A). Alternatively, a laminate (L2) may be produced by stacking a curable resin layer (B) on an inner circuit board (A), heating and pressurizing it, thereby creating a laminate (L2) on which a laminate (B) having a partially cured or cured insulating layer of curable resin (B) is laminated on the inner circuit board (A), and then laminating the first metal layer (M1) and protective layer (PL) on top of this laminate (L2) (Lamination method 1). Alternatively, a laminate (L3) may be produced in advance with the first metal layer (M1) formed on top of the protective layer (PL), and then the inner circuit board (A), curable resin layer (B), and laminate (L3) may be stacked to produce the laminate (L1) (Lamination method 2).

[0024] When producing a laminate (L1') in which a resin layer (C) is further present between the curable resin substrate (B) and the first metal layer (M1), a laminate (L2') may be produced by laminating the resin layer (C), the first metal layer (M1), and the protective layer (PL) in that order on top of the laminate (L2) (Lamination Method 1'). Alternatively, a laminate (L3') may be produced in advance by forming the first metal layer (M1) and the resin layer (C) in that order on top of the protective layer (PL), and then the laminate (L1') may be produced by stacking the inner layer circuit board (A), the curable resin layer (B), and the laminate (L3) (Lamination Method 2').

[0025] In the lamination methods 1 and 1' described above, when producing the laminate (L2), the surface of the laminate (L2) must be a smooth surface that is not roughened. As a method for smoothing the surface of the laminate (L2), smooth metal foils such as copper foil or aluminum foil, or heat-resistant films such as smooth polyimide film or fluororesin film are used as smoothing treatment substrates. The smooth surfaces of these smoothing treatment substrates are heat-pressed and bonded to the surfaces of the inner circuit substrate (A) and the curable resin layer (B), and then peeled off to transfer the smooth surface to the surface of the laminate (L2), thereby performing the smoothing treatment.

[0026] The smooth surface of the smoothed substrate preferably has a surface roughness (maximum height Sz) in the range of 0.001 to 30 μm, more preferably in the range of 0.01 to 20 μm, and more preferably in the range of 0.05 to 10 μm, as measured by a laser microscope. The surface roughness (maximum height Sz) is measured using the evaluation method described in ISO 25178 and represents the distance from the highest point to the lowest point on the surface.

[0027] The resin layer (C) may be a single layer or may consist of two or more layers. When two or more resin layers (C) are formed, for example, the resin layer (C) in contact with the curable resin layer (B) should be selected to improve adhesion with the curable resin layer (B), while the resin layer (C) in contact with the first metal layer (M1) should be selected to improve adhesion with the first metal layer (M1).

[0028] Various known and conventional coating and printing methods can be used for coating or printing the resin layer (C). As a method for forming the first metal layer (M1) on the laminate (L2) or laminate (L2'), a dry method such as vapor deposition or sputtering may be used, or it may be formed by coating with a coating of metal particles that form the first metal layer. As the coating of metal particles used in the present invention, various commercially available metal particles may be made into coatings and used, metal particles may be manufactured and made into coatings, or commercially available metal particle coatings may be used. The size of the metal particles used in the present invention may be appropriately selected according to the thickness of the first metal layer (M1), but the average particle diameter is preferably 1 nm to 100 nm, and more preferably 1 nm to 80 nm from the viewpoint of forming a dense first metal layer (M1). The average particle diameter can be determined, for example, by dynamic light scattering using "NanoTrack UPA-150" manufactured by MicroTrack. The first metal layer (M1) may also be formed by coating or printing a metal complex coating of the metal that forms the first metal layer (M1).

[0029] In the method for manufacturing a printed circuit board of the present invention, a particularly preferred method for forming the first metal layer (M1) is to apply a silver particle coating. The silver particle coating is a mixture of silver particles dispersed in a solvent. The shape of the silver particles is not particularly limited as long as it can form the first metal layer (M1) well, and various shapes of silver particles can be used, such as spherical, lenticular, polyhedral, flat, rod-shaped, and wire-shaped. These silver particles can be used as a single shape or in combination of two or more different shapes.

[0030] As the solvent used in the dispersion of the silver particles, an aqueous medium or an organic solvent can be used. Examples of the aqueous medium include distilled water, deionized water, pure water, and ultrapure water. Examples of the organic solvent include alcohol compounds, ether compounds, ester compounds, and ketone compounds.

[0031] The solvent is not particularly limited as long as it can stably disperse the silver particles and form the first metal layer (M1) well. Furthermore, the solvent can be used alone or in combination of two or more.

[0032] The silver particle dispersion preferably maintains long-term dispersion stability without the silver particles agglomerating, fusing, or precipitating in the various solvents, and preferably contains a dispersant for dispersing the silver particles in the various solvents. Such a dispersant is preferably one having a functional group that coordinates to the silver particles, such as a carboxyl group, amino group, cyano group, acetoacetyl group, phosphorus atom-containing group, thiol group, thiocyanato group, or glycinato group.

[0033] As the dispersant, commercially available or independently synthesized low molecular weight or high molecular weight dispersants can be used, and can be appropriately selected according to the purpose, such as the type of solvent for dispersing the silver particles, the curable resin (B) for coating with the silver particle paint, or the type of protective layer (PL). For example, dodecanethiol, 1-octanthiol, triphenylphosphine, dodecylamine, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, polyvinylpyrrolidone; fatty acids such as myristic acid, octanoic acid, and stearic acid; and polycyclic hydrocarbon compounds having carboxyl groups such as cholic acid, glycyrrhizic acid, and avintic acid are preferably used. Here, when a resin layer (C) is formed between the curable resin (B) and the first metal layer (M1), it is preferable to use a compound having a reactive functional group [Y] that can form a bond with the reactive functional group [X] of the resin used in the resin layer (C), which will be described later, in order to ensure good adhesion between these resin layers (C) and the first metal layer (M1).

[0034] Examples of compounds having a reactive functional group [Y] include compounds having amino groups, amide groups, alkylolamide groups, carboxyl groups, anhydrous carboxyl groups, carbonyl groups, acetoacetyl groups, epoxy groups, alicyclic epoxy groups, oxetane rings, vinyl groups, allyl groups, (meth)acryloyl groups, (blocked) isocyanate groups, (alkoxy)silyl groups, and silsesquioxane compounds. In particular, a basic nitrogen atom-containing group is preferred for the reactive functional group [Y] because it can further improve the adhesion between the resin layer (C) and the primary metal layer (M1). Examples of the basic nitrogen atom-containing group include imino groups, primary amino groups, and secondary amino groups.

[0035] The basic nitrogen atom-containing groups may be present in one or more quantities in a single molecule of the dispersant. By including multiple basic nitrogen atoms in the dispersant, some of the basic nitrogen atom-containing groups contribute to the dispersion stability of the metal particles through interaction with the metal particles, while the remaining basic nitrogen atom-containing groups contribute to improving adhesion to the insulating substrate (A). Furthermore, if a resin having a reactive functional group [X] is used in the resin layer (C) described later, the basic nitrogen atom-containing groups in the dispersant can form bonds with this reactive functional group [X], which is preferable because it further improves the adhesion of the conductive layer (M2) to the curable resin layer (B).

[0036] The dispersant is preferable to be a polymer dispersant because it provides stability and coating properties for the silver particle dispersion, and allows for the formation of a first metal layer (M1) that exhibits good adhesion to the curable resin layer (B). Preferred polymer dispersants include polyalkylene imines such as polyethyleneimine and polypropyleneimine, and compounds in which polyoxyalkylene is added to the polyalkylene imine.

[0037] The compound obtained by adding polyoxyalkylene to the polyalkylene imine may be one in which polyethyleneimine and polyoxyalkylene are linked in a linear manner, or it may be one in which polyoxyalkylene is grafted onto the side chains of a main chain made of polyethyleneimine.

[0038] Specific examples of compounds in which polyoxyalkylene is added to the polyalkylene imine include, for example, block copolymers of polyethyleneimine and polyoxyethylene, compounds in which a polyoxyethylene structure is introduced by adding ethylene oxide to some of the imino groups present in the main chain of polyethyleneimine, and compounds obtained by reacting the amino groups of polyalkylene imine with the hydroxyl groups of polyoxyethylene glycol and the epoxy groups of epoxy resin.

[0039] Examples of commercially available polyalkyleneimines include "PAO2006W," "PAO306," "PAO318," and "PAO718" from the "Epomin (registered trademark) PAO series" manufactured by Nippon Shokubai Co., Ltd.

[0040] The number-average molecular weight of the polyalkyleneimine is preferably in the range of 3,000 to 30,000.

[0041] The amount of dispersant required to disperse the metal particles is preferably in the range of 0.01 to 50 parts by mass per 100 parts by mass of the metal particles. Furthermore, since a metal particle layer (M1) exhibiting good adhesion can be formed on the insulating substrate (A) or on the primer layer (B) described later, it is preferably in the range of 0.1 to 10 parts by mass per 100 parts by mass of the metal particles. Moreover, since the plating properties of the metal particle layer (M1) can be improved, it is more preferably in the range of 0.1 to 5 parts by mass.

[0042] The silver particles may be partially replaced by other metals or mixed with other metal components, as long as they do not interfere with the plating process using the first metal layer (M1), described later, as a cathode, or impair the ease of removal of the metal particle layer (UM1) in the circuit-free section, described later, by the etching solution. Examples of metals to be substituted or mixed include one or more metallic elements selected from the group consisting of gold, platinum, palladium, ruthenium, tin, copper, nickel, iron, cobalt, titanium, indium, and iridium. The ratio of the metal to be substituted or mixed is preferably 5% by mass or less in the silver particles, and more preferably 2% by mass or less from the viewpoint of the plating properties and ease of removal by etching solution of the metal particle layer (M1).

[0043] The silver particle content in the silver particle coating can be appropriately adjusted to a concentration that allows the first metal layer (M1) to be properly formed using any coating method, and to a viscosity that has optimal coating suitability depending on the coating method. However, a range of 0.1 to 50% by mass is preferred, a range of 0.5 to 20% by mass is more preferred, and a range of 0.5 to 15% by mass is even more preferred. The amount of dispersant required to disperse the silver particles is preferably in the range of 0.01 to 50 parts by mass per 100 parts by mass of the silver particles. A first metal layer (M1) that exhibits good adhesion to the curable resin layer (B) or to the resin layer (C) can be formed, so a range of 0.1 to 10 parts by mass per 100 parts by mass of the silver particles is preferable, and a range of 0.1 to 5 parts by mass is even more preferable, as it can improve the plating deposition properties on the first metal layer (M1).

[0044] There are no particular limitations on the method for manufacturing the silver particle coating, and it can be manufactured using various methods. For example, silver particles manufactured using a gas-phase method such as evaporation in a low vacuum gas may be dispersed in a solvent, or a dispersion of silver particles may be directly prepared by reducing a silver compound in the liquid phase and used as the coating. In both gas-phase and liquid-phase methods, the solvent composition of the dispersion during manufacturing and the coating during application can be changed as appropriate and necessary by solvent exchange or solvent addition. Of the gas-phase and liquid-phase methods, the liquid-phase method is particularly preferable due to the stability of the dispersion and the simplicity of the manufacturing process. As an example of the liquid-phase method, it can be manufactured by reducing silver ions in the presence of the polymer dispersant.

[0045] The dispersion of metal particles may further contain, if necessary, organic compounds such as surfactants, leveling agents, viscosity modifiers, film-forming aids, defoamers, and preservatives. Various known and conventional coating and printing methods can be used to coat or print the paint onto the first metal layer (M1).

[0046] Furthermore, in a more preferred embodiment of the printed circuit board manufacturing method of the present invention, a laminate (L1') is used in which a resin layer (C), a first metal layer (M1), and a protective layer (PL) are sequentially laminated on a curable resin layer (B). Printed circuit boards with this resin layer (C) are preferred because the adhesion of the conductor layer (M2) on the curable resin layer (B) can be further improved.

[0047] When a resin having a reactive functional group [Y] is used as the dispersant for the silver particles, the resin forming the resin layer (C) is preferably a resin having a reactive functional group [X] that is reactive with the reactive functional group [Y]. Examples of the reactive functional group [X] include amino groups, amide groups, alkylolamide groups, carboxyl groups, anhydrous carboxyl groups, carbonyl groups, acetoacetyl groups, epoxy groups, alicyclic epoxy groups, oxetane rings, vinyl groups, allyl groups, (meth)acryloyl groups, (blocked) isocyanate groups, (alkoxy)silyl groups, and the like.

[0048] In particular, when the reactive functional group [Y] in the dispersant is a basic nitrogen atom-containing group, the adhesion of the conductive layer (M2) on the curable resin layer (B) can be further improved. Therefore, the resin forming the resin layer (C) is preferably one having a carboxyl group, carbonyl group, acetoacetyl group, epoxy group, alicyclic epoxy group, alkylolamide group, isocyanate group, vinyl group, (meth)acryloyl group, or allyl group as the reactive functional group [X].

[0049] Examples of resins that form the aforementioned resin layer (C) include urethane resin, acrylic resin, core-shell type composite resin with urethane resin as the shell and acrylic resin as the core, epoxy resin, imide resin, amide resin, melamine resin, phenol resin, urea-formaldehyde resin, blocked isocyanate polyvinyl alcohol obtained by reacting polyisocyanate with a blocking agent such as phenol, and polyvinylpyrrolidone. The core-shell type composite resin with urethane resin as the shell and acrylic resin as the core can be obtained, for example, by polymerizing acrylic monomers in the presence of urethane resin. Furthermore, these resins can be used individually or in combination of two or more.

[0050] Among the resins that form the resin layer (C) described above, resins that generate reducing compounds upon heating are preferred because they can further improve the adhesion of the conductive layer (M2) to the curable resin layer (B). Examples of the reducing compounds include phenol compounds, aromatic amine compounds, sulfur compounds, phosphoric acid compounds, and aldehyde compounds. Among these reducing compounds, phenol compounds and aldehyde compounds are preferred.

[0051] The paint used to form the resin layer (C) preferably contains 1 to 70% by mass of the resin, and more preferably contains 1 to 20% by mass of the resin, from the viewpoint of coating properties and film-forming properties.

[0052] Furthermore, suitable solvents for the paint used to form the resin layer (C) include various organic solvents and aqueous media. Examples of organic solvents include toluene, ethyl acetate, methyl ethyl ketone, and cyclohexanone, while examples of aqueous media include water, organic solvents miscible with water, and mixtures thereof.

[0053] Examples of organic solvents that are miscible with water include alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, ethyl carbitol, ethyl cellosolve, and butyl cellosolve; ketone solvents such as acetone and methyl ethyl ketone; alkylene glycol solvents such as ethylene glycol, diethylene glycol, and propylene glycol; polyalkylene glycol solvents such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; and lactam solvents such as N-methyl-2-pyrrolidone.

[0054] Furthermore, the resin forming the resin layer (C) may optionally have functional groups that contribute to the crosslinking reaction, such as alkoxysilyl groups, silanol groups, hydroxyl groups, and amino groups.

[0055] In the lamination method 1 or 1' described above, a metal protective layer is preferred as the protective layer (PL) formed on the first metal layer (M1). The protective metal layer formed in lamination method 1 or 1' may be formed by a dry method such as vapor deposition or sputtering, or it may be formed by wet plating on the first metal layer (M1). Wet plating can be performed by electroless plating, electrolytic plating, or a combination of electroless plating and electrolytic plating. As mentioned above, copper is preferred as the metal used for the protective layer, and copper plating is preferred.

[0056] When forming a laminate (L1) using the lamination method 2 described above, a laminate (L3) is prepared by first forming a first metal layer (M1) on top of a protective layer (PL). When forming a laminate (L1) using the lamination method 2' described above, a laminate (L3') is prepared by first forming a first metal layer (M1) and a resin layer (C) on top of a protective layer (PL) in that order.

[0057] When producing a laminate (L3 or L3') using the lamination method 2 or 2' described above, the method for forming the first metal layer (M1) on the protective layer (PL) used may be to apply the metal to form the first metal layer (M1) to the smooth surface of the protective layer (PL) using a dry method such as vapor deposition or sputtering, or to form the first metal layer by coating or printing a coating of metal particles. The coating of metal particles, coating, and printing methods used in the present invention can preferably be those described in the lamination method 1 or 1' described above. In the lamination method 2 or 2' described above, when metal is used as the protective layer (PL), commercially available metal foil can be suitably used.

[0058] When forming a laminate (L1) using the lamination method 2 or 2' described above, the laminate (L1 or L1') can be manufactured by layering the inner circuit board (A) and the curable resin layer (B) with the protective layer (PL) of the laminate (L3 or L3') facing the outer layer, and then bonding them together using heat and pressure. In this lamination method, the inner circuit board (A) and the curable resin layer (B) may be pre-laminated, and the laminate (L3 or L3') may be laminated onto this laminate. When laminating the laminate (L3 or L3') onto the curable resin layer (B), the curable resin layer (B) may be laminated in an already cured state, or it may be in a semi-cured state and cured when the laminate (L3 or L3') is laminated.

[0059] The method of bonding using heat and pressure is not particularly limited, but for example, thermal lamination, thermal roll transfer, and vacuum pressing can be used.

[0060] In the method for manufacturing a printed circuit board of the present invention, step 2 is a step of forming vias that connect to the circuit metal portion (IM) of the inner layer circuit board (A) from the protective layer (PL) side of the laminate (L1) through the protective layer (PL), the first metal layer (M1), and the curable resin layer (B).

[0061] Furthermore, if a resin layer (C) exists between the curable resin substrate (B) and the first metal layer (M1), step 2 is a step of forming vias that connect to the circuit metal portion (IM) of the inner layer circuit board (A) from the protective layer (PL) side of the laminate (L1') through the protective layer (PL), the first metal layer (M1), the resin layer (C), and the curable resin layer (B).

[0062] As a method for forming vias, via formation using laser light irradiation is preferred. As for the type of laser light, IR lasers, NIR lasers, visible light lasers, and UV lasers can be used, and can be appropriately selected depending on the required via diameter and the material used. However, when the protective layer (PL) is made of a resin material, a CO2 laser, which is an IR laser, can be suitably used. Furthermore, when the protective layer is made of metal, especially copper, it is preferable to use a UV laser. In addition, for forming small diameter vias, it is preferable to use a UV laser or a visible light laser, and a short-pulse laser with a short pulse width can also be used.

[0063] In the method for manufacturing a printed circuit board of the present invention, step 3 is a desmearing step. Normally, in the desmearing step, smear removal of the via portion is performed simultaneously with roughening the surface of the insulating substrate. In the present invention, the insulating substrate surface is the surface of the curable resin substrate (B). In the method for manufacturing a printed circuit board of the present invention, by forming a first metal layer (M1) on the curable resin substrate (B), roughening of the surface of the curable resin substrate (B) is not required in order to ensure the adhesion strength between the curable resin substrate (B) and the conductor layer (M2). Therefore, the processing time for the desmearing step can be shortened. Since the desmearing step also etches the sides of the vias, shortening the time can suppress the widening of the via diameter due to the desmearing step.

[0064] Desmearing can be performed using wet treatment with chemicals, dry treatment using plasma or UV irradiation, or a combination of wet and dry treatments. As described above, in the method for manufacturing printed circuit boards of the present invention, it is sufficient to remove smear from the via portion, and roughening of the insulating substrate surface is not required by the desmearing treatment, so it is preferable to perform a short-time wet desmearing or dry desmearing treatment. By performing a short-time wet desmearing or dry desmearing treatment, it is possible to suppress the expansion of the via diameter.

[0065] In the method for manufacturing a printed circuit board of the present invention, step 4 is a step of making the via layer conductive and forming an electrical connection between the circuit metal part (B) of the inner circuit board (A) and the first metal layer (M1). As a method for making the via layer conductive and electrically connecting the circuit metal part (IM) of the inner circuit board (A) and the first metal layer (M1), electroless copper plating, direct plating, and sputtering methods can be appropriately selected depending on the purpose. However, when the metal constituting the first metal layer (M1) is silver and the material forming the protective layer (PL) is copper, it is particularly preferable to perform the electrical connection by direct plating. Among direct plating methods, a method using a carbon material as the conductive material is particularly preferable, and MacDermid's Black Hole Process and Shadow Process can be used particularly suitably.

[0066] In the method for manufacturing a printed circuit board of the present invention, step 5 is a step of removing the protective layer (PL) to expose the first metal layer (M1). If the protective layer (PL) is a resin film, the resin film laminated on the first metal layer (M1) can be mechanically peeled off. If the protective layer (PL) is made of metal, the method for peeling off the protective layer (PL) can be appropriately selected from a method of mechanically peeling off the protective layer (PL) or a method of chemically removing it by etching.

[0067] In the aforementioned lamination method 2 or 2', if a metal foil is used for the protective layer (PL), a method of mechanical removal can be selected. Alternatively, in the method of chemical removal by etching, an etching agent that dissolves the metal used for the protective layer (PL) should be used. For this purpose, it is preferable to use an etching agent that dissolves the protective layer (PL) but does not dissolve the first metal layer (M1). Etching the metal of the protective layer (PL) but not the first metal layer (M1) means using an etching agent in which the difference in dissolution rates between the metal forming the protective layer (PL) and the metal constituting the first metal layer (M1) is five times or more compared to the etching agent used.

[0068] In the method for manufacturing a printed circuit board of the present invention, step 6 is a step of forming a pattern resist corresponding to a circuit pattern on the first metal layer (M1). Since the method for manufacturing a printed circuit board of the present invention uses a method called a semi-additive process, the pattern resist is formed on the parts of the first metal layer (M1) where circuits are not required. In the method for manufacturing a printed circuit board of the present invention, commercially available liquid resists and dry film resists can be suitably used as the resist for forming a pattern on the first metal layer (M1). The method for forming the pattern resist on the first metal layer (M1) can be selected appropriately according to the conditions used conventionally on copper films, and in the case of commercially available materials, processing can be carried out in accordance with the recommended method published in the technical manual.

[0069] In the method for manufacturing a printed circuit board of the present invention, step 7 is a step of forming a conductor layer (M2) of a circuit pattern inside the via and on the first metal layer (M1). The conductor layer (M2) is the part that will become the circuit pattern and pad portion of the printed circuit board manufactured in the present invention. The material constituting the conductor layer (M2) is preferably a metal, and there are no restrictions as long as it is a metal that can transmit electrical signals, but from the viewpoint of conductivity, material cost and versatility, copper is preferred. As a method for forming the conductor layer (M2) inside the via and on the first metal layer (M1), it is preferable to form it by electroplating using the first metal layer (M1) as an electrode, and in particular, it is recommended to form it by electroplating copper. In step 7, the conductor layer (M2) of the circuit pattern is formed on the first metal layer (M1) using the first metal layer (M1) as a conductive seed. This plating step is a method called a semi-additive process, in which a circuit pattern is formed by plating the resist-free portion formed in the circuit-unnecessary portion of the first metal layer (M1) in step 6.

[0070] In the method for manufacturing a printed circuit board of the present invention, step 8 is a step of peeling off the pattern resist. For the peeling method, any known and conventional method can be appropriately selected and used, but for example, it is acceptable to process it in accordance with the recommended method published in the product technical manual of the resist.

[0071] In the method for manufacturing a printed circuit board of the present invention, step 9 is a step of removing the first metal layer (UM1) of the non-circuit portion. The first metal layer (UM1) of the non-circuit portion is present in the portion from which the pattern resist has been peeled off. As a method for removing the first metal layer (UM1) of the non-circuit portion, it is preferable to chemically dissolve and remove the first metal layer (UM1) using a liquid that dissolves the metal forming the first metal layer (UM1).

[0072] When the same metal is used for the first metal layer (M1) and the conductor layer (M2), the thickness of the first metal layer (M1) is thinner than that of the conductor layer (M2). As a result, the first metal layer (M1) is dissolved and removed first, leaving the conductor layer (M2) behind, thus forming the circuit pattern. In this process, as the first metal layer (UM1) of the parts not used for the circuit is removed, a portion of the conductor layer (M2) that forms the circuit pattern is also etched, causing the circuit pattern to become thinner or narrower. To avoid this phenomenon, in the method for manufacturing printed circuit boards of the present invention, it is preferable that the metals constituting the first metal layer (M1) and the conductor layer (M2) are different metals. Specifically, it is preferable that the first metal layer (M1) is silver and the conductor layer (M2) is copper.

[0073] When the first metal layer (M1) is silver and the conductive layer (M2) is copper, the etching solutions described in, for example, Japanese Patents 06836734 and 07211571 can be suitably used as the chemical solution for removing the first metal layer (UM1) in the parts where the circuit is not needed.

[0074] By using the printed circuit board manufacturing method of the present invention described above, it is possible to manufacture printed circuit boards that maintain small via diameters and ensure sufficient adhesion between the insulating substrate and the conductor layer without roughening the surface of the insulating substrate. Therefore, by utilizing the present invention, high-performance substrates such as data center and server substrates, antenna substrates, and semiconductor package substrates that require high-density mounting and high-speed communication can be efficiently manufactured, thus making a significant contribution to the field of electronics mounting and offering high industrial applicability. [Examples]

[0075] The present invention will be described in detail below with reference to examples. However, the present invention is not limited in any way by the following examples.

[0076] <Preparation Example 1: Preparation of Silver Coating Solution (1) for First Metal Layer Formation> Under a nitrogen atmosphere, a mixture containing 20 parts by mass of methoxypolyethylene glycol (number average molecular weight 2,000), 8.0 parts by mass of pyridine, and 20 ml of chloroform was mixed with a chloroform solution (30 ml) containing 9.6 parts by mass of p-toluenesulfonic acid chloride, which was then added dropwise for 30 minutes while stirring on ice. The mixture was then stirred at a bath temperature of 40°C for 4 hours, and 50 ml of chloroform was mixed in. Next, the obtained product was washed with 100 ml of 5% by mass aqueous hydrochloric acid solution, then with 100 ml of saturated sodium bicarbonate aqueous solution, then with 100 ml of saturated saline solution, dried with anhydrous magnesium sulfate, filtered, concentrated under reduced pressure, washed several times with hexane, filtered, and dried under reduced pressure at 80°C to obtain methoxypolyethylene glycol having p-toluenesulfonyloxy groups. 5.39 parts by mass of methoxypolyethylene glycol having a p-toluenesulfonyloxy group, 20 parts by mass of polyethyleneimine (manufactured by Aldrich, molecular weight 25,000), 0.07 parts by mass of potassium carbonate, and 100 ml of N,N-dimethylacetamide were mixed and stirred at 100°C for 6 hours under a nitrogen atmosphere. Next, 300 ml of a mixed solution of ethyl acetate and hexane (volume ratio of ethyl acetate / hexane = 1 / 2) was added, and after vigorous stirring at room temperature, the solid product was filtered. The solid was washed with 100 ml of a mixed solution of ethyl acetate and hexane (volume ratio of ethyl acetate / hexane = 1 / 2), and then dried under reduced pressure to obtain a compound in which polyethylene glycol was bonded to polyethyleneimine. A 138.8-part aqueous solution containing 0.592 parts by mass of the compound in which polyethylene glycol was bonded to the obtained polyethyleneimine was mixed with 10 parts by mass of silver oxide and stirred at 25°C for 30 minutes. Next, 46 parts by mass of dimethylethanolamine was gradually added while stirring, and the mixture was stirred at 25°C for 30 minutes. Subsequently, 15.2 parts by mass of a 10% by mass aqueous solution of ascorbic acid was gradually added while stirring, and stirring was continued for 20 hours to obtain a silver dispersion. A mixed solvent of 200 ml of isopropyl alcohol and 200 ml of hexane was added to the obtained silver dispersion and stirred for 2 minutes, followed by centrifugal concentration at 3000 rpm for 5 minutes. After removing the supernatant, a mixed solvent of 50 ml of isopropyl alcohol and 50 ml of hexane was added to the precipitate and stirred for 2 minutes, followed by centrifugal concentration at 2000 rpm for 10 minutes. After removing the supernatant, 20 parts by mass of water were added to the precipitate and stirred for 2 minutes to remove the organic solvent under reduced pressure. After adding 10 parts by mass of water and stirring to disperse, the dispersion was frozen in a -40°C refrigerator overnight, and then treated in a freeze-dryer (FDU-2200, manufactured by Tokyo Rikakikai Co., Ltd.) for 24 hours to obtain silver particles containing a dispersant with basic nitrogen atom-containing groups, consisting of grayish-green metallic flake-like lumps. The obtained silver particle powder containing a dispersant having a basic nitrogen atom group was dispersed in a mixed solvent of 45 parts by mass of ethanol and 55 parts by mass of ion-exchanged water to prepare a 5% by mass coating solution (1) for forming the first metal layer. The obtained silver particles were heated in an electric furnace at 500°C for 1 hour, and the proportion of the dispersant was calculated from the ash content, confirming that it was 5% by mass relative to 100% by mass of silver solids.

[0077] <Preparation Example 2: Preparation of coating liquid (1) for forming resin layer (C)> 60 parts by mass of phenoxy resin 4250 (bisphenol A / bisphenol F mixed type manufactured by Mitsubishi Chemical Corporation, molecular weight 60,000, solid content 100% by mass), 33 parts by mass of aminotriazine novolac resin ("Phenolite LA-7052" manufactured by DIC Corporation, solid content 60% by mass), 17 parts by mass of epoxy resin ("EPICLON EXA-830CRP" manufactured by DIC Corporation; bisphenol F type epoxy resin, epoxy group equivalent 162 g / equivalent), 3 parts by mass of trimellitic anhydride, and 0.5 parts by mass of "TBZ" manufactured by Shikoku Chemicals, Inc. as a curing catalyst were mixed, diluted with cyclohexanone to a non-volatile content of 2% by mass, and uniformly mixed to obtain a coating liquid (1) for forming a resin layer (C).

[0078] <Preparation Example 3: Preparation of Laminate (F1)> The silver coating solution (1) for forming the first metal layer obtained in Adjustment Example 1 was applied to the surface of the release layer of the release film (TN-200, PET release film; 38 μm thick) that will serve as the protective layer (PL) using a desktop-type small coater (K ​​Print Coat Instruments, K Printing Profer), and dried at 150°C for 5 minutes to form a coating film mainly composed of silver that will serve as the first metal layer (M1), with a thickness of 0.1 μm after drying. Subsequently, the coating liquid (1) for forming the resin layer (C) obtained in adjustment example 2 was applied using a desktop miniature coater (RK Print Coat Instruments' "K Printing Profer") and dried at 180°C for 3 minutes to coat a layer corresponding to the resin layer (C) with a dried thickness of 0.3 μm. This formed a first metal layer (M1) and a resin layer (C) on the surface of the release film corresponding to the protective layer (PL), thereby obtaining a laminate (F1).

[0079] <Preparation Example 4: Preparation of Laminate (F2)> On the glossy surface (non-roughened surface) of copper foil (F2-WS copper foil manufactured by Furukawa Electric Co., Ltd.; 18 μm thick), the silver coating solution (1) for forming the first metal layer obtained in Adjustment Example 1 was applied using a desktop miniature coater (RK Print Coat Instruments Co., Ltd. "K Printing Profer"), and dried at 200°C for 5 minutes to coat a silver layer corresponding to the first metal layer (M1) with a dried thickness of 0.1 μm. Subsequently, the resin layer (C) forming coating liquid (1) obtained in adjustment example 2 was applied using a desktop miniature coater (RK Print Coat Instruments' "K Printing Profer") and dried at 180°C for 3 minutes to form a layer corresponding to the resin layer (C) with a dried thickness of 0.3 μm. This formed a first metal layer (M1) and a resin layer (C) on the surface of the copper foil corresponding to the protective layer (PL), and a laminate (F2) was obtained.

[0080] <Preparation Example 5: Preparation of Curable Resin Layer (B)> Three parts by mass of bisphenol-type epoxy resin ("ZX059" manufactured by Nippon Steel Chemical Co., Ltd., a 1:1 mixture of bisphenol A and bisphenol F, with an epoxy equivalent of approximately 169), three parts by mass of naphthalene-type epoxy resin ("HP-4032D" manufactured by DIC Corporation, with an epoxy equivalent of approximately 144), twelve parts by mass of crystalline bifunctional epoxy resin ("YX4000HK" manufactured by Mitsubishi Chemical Corporation, with an epoxy equivalent of approximately 185), nine parts by mass of dicyclopentadiene-type epoxy resin ("HP7200H" manufactured by DIC Corporation, with an epoxy equivalent of approximately 275), and ten parts by mass of phenoxy resin ("YX7200B35" manufactured by Mitsubishi Chemical Corporation, a MEK solution with a solid content of 35% by mass) were heated and dissolved in 30 parts by mass of solvent naphtha while stirring. After cooling to room temperature, 40 parts by mass of an active ester compound (DIC Corporation's "HPC-8000-65T," a toluene solution with approximately 223 active group equivalents and 65% by mass of nonvolatile content), 3 parts by mass of a curing accelerator (4-dimethylaminopyridine, a MEK solution with 5% by mass of solid content), and spherical silica (average particle size 0.25 μm, Admatex Corporation's "SO-C1," carbon content per unit surface area 0.36 mg / m²) surface-treated with a phenylaminosilane coupling agent (Shin-Etsu Chemical Co., Ltd.'s "KBM573") were added. 2 140 parts by mass of ) were mixed and uniformly dispersed in a high-speed rotary mixer to prepare a varnish for forming a curable resin layer (B). Next, the resin varnish was uniformly applied to the release surface of a release PET film (thickness 38 μm) so that the thickness of the curable resin layer (B) after drying would be 30 μm, and dried at 80-120°C (average 100°C) for 4 minutes to prepare a curable resin layer (B) on the release PET film.

[0081] <Preparation Example 6: Preparation of Silver Etching Solution (1)> To 47.4 parts by mass of water, 2.6 parts by mass of acetic acid was added, and then 50 parts by mass of 35% by mass of hydrogen peroxide solution was added to prepare silver etching solution (1).

[0082] (Example 1) A core material (CCL-HL832NB, manufactured by Mitsubishi Gas Chemical Company, Inc., with copper foil laminated on both sides, base material thickness 0.1 mm, copper foil 12 μm) was prepared, and an inner layer circuit board (A) with a conductive pattern was fabricated. Then, the side of the PET film on which the curable resin layer (B) was fabricated, as prepared in Adjustment Example 5, was set on the conductive pattern side of the inner layer board, and bonded using a batch-type vacuum pressure laminator. The pressure was reduced to 13 hPa or less for 30 seconds, and then pressed at 100°C and 0.7 MPa for 30 seconds. After that, it was heated at 170°C for 15 minutes, and the release PET film was peeled off to laminate the curable resin layer (B) onto the inner layer circuit board (A). Next, the glossy side (non-roughened side) of a copper foil (F2-WS manufactured by Furukawa Electric Co., Ltd., 18 μm thick) was bonded onto the curable resin layer (B), and the two were heat-pressed together at 195°C for 90 minutes using a hand press ("Mini Test Press" manufactured by Toyo Seiki Seisakusho Co., Ltd.). Then, the copper foil was etched across its entire surface by immersion in a 40°C ferric chloride etching solution (40% by mass content) for 3 minutes, thereby obtaining a laminate in which the cured curable resin layer (B) was laminated on an inner layer circuit board (A). Subsequently, corona treatment was performed on the surface of the curable resin layer (B) of the laminate (using a corona surface modification evaluation device TEC-4AX manufactured by Kasuga Electric Co., Ltd., electrode-substrate distance 0.5 mm, 100 W). Then, the surface on which the resin layer (C) of the laminate (F1) obtained in adjustment example 3 was formed was bonded to the surface of the curable resin layer (B) of the laminate, and pressed with a hand press (Mini Test Press manufactured by Toyo Seiki Seisakusho Co., Ltd.) at 180°C for 1.5 minutes to obtain a laminate (L1') on an inner layer substrate (A) in the following order: curable resin layer (B), resin layer (C), first metal layer (M1) mainly composed of silver, and PET film as a protective layer (PL). Next, a CO2 laser was used to form non-penetrating holes with a diameter of 30 μm from the surface of the protective layer (PL) PET film, reaching the copper circuit metal portion (IM) of the inner circuit board (A) (the via tops on the surface of the curable resin layer (B) were 20 μm). Then, desmearing was performed using plasma treatment to remove the smear generated by the laser processing. Subsequently, carbon was deposited on the surface of the non-penetrating hole sidewalls of the substrate thus obtained using MacDermid's Black Hole Process (conditioning-carbon adsorption-etching), thereby obtaining electrical connections between the first metal layer (M1), the non-penetrating holes, and the circuit metal portion (IM) of the inner circuit board. After peeling off the protective layer (PL) PET film to expose the silver layer of the first metal layer (M1), a dry film resist (RY5125 manufactured by Resonaq Corporation) is laminated onto the silver first metal layer (M1) to form a resist pattern so that the first metal layer (M1) in the circuit pattern area is exposed, and with the first metal layer (M1) as the cathode side, the current density is 3A / dm 2 By performing electrolytic copper plating (Toplutina HV, manufactured by Okuno Pharmaceutical Co., Ltd.) for 30 minutes, a conductor layer (M2) of the circuit pattern was formed inside the non-through vias and on the first metal layer (M1). After stripping the pattern resist, the first metal layer (UM1) consisting of unwanted silver was removed using the silver etching agent prepared in Preparation Example 6 to obtain a printed circuit board.

[0083] (Example 2) In the same manner as in Example 1, a laminate (L1') was obtained by laminating a curable resin layer (B), a resin layer (C), a first metal layer (M1) mainly composed of silver, and a PET film as a protective layer (PL) on an inner layer substrate (A) in the following order. Next, the PET film, which is the protective layer (PL), was peeled off to expose the first metal layer (M1) mainly composed of silver, which was used as a cathode and electrolytic copper plating (Dupont Copper Gleam ST-901 2A / dm 2A 1 μm thick copper plating film was formed by a 2-minute 30-second process. In this way, a laminate (L1') was obtained on the inner layer substrate (A) consisting of a curable resin layer (B), a resin layer (C), a first metal layer (M1) mainly composed of silver, and a copper plating film as a protective layer (PL). Next, a 20 μm diameter non-through hole was formed from the 1 μm thick copper surface of the protective layer (PL) using a UV laser, reaching the copper circuit metal part (IM) of the inner layer circuit board (A). Then, desmear was performed by plasma treatment to remove the smear generated by the laser processing. After that, carbon was deposited on the surface of the non-through hole sidewalls of the substrate with the non-through hole obtained in this way by MacDermid's Black Hole Process (conditioning - carbon adsorption treatment - etching), thereby obtaining electrical connections between the first metal layer (M1), the non-through hole, and the circuit part of the inner layer circuit board. The protective layer (PL), a copper layer, was removed by a micro-etching step in the black hole process, exposing the primary silver metal layer (M1). After forming a pattern resist on the primary silver metal layer (M1), a printed circuit board was obtained in the same manner as in Example 1.

[0084] (Example 3) Except for using a laminate (F2) made of copper foil prepared in Preparation Example 4 instead of the PET laminate (F1) used in Example 1, a laminate (L1') was obtained by laminating a curable resin layer (B), a resin layer (C), a first metal layer (M1), and a protective layer (PL) in that order on an inner layer circuit board (A) in the same manner as in Example 1. Next, the copper protective layer (PL) was etched from a thickness of 18 μm to a thickness of 1 μm by half-etching. After via formation with a UV laser, a printed circuit board was obtained in the same manner as in Example 2.

[0085] (Example 4) A core material (CCL-HL832NB, manufactured by Mitsubishi Gas Chemical Company, Inc., with copper foil laminated on both sides, base material thickness 0.1 mm, copper foil 12 μm) was prepared, and an inner layer circuit board (A) with a conductive pattern was fabricated. Then, the side of the PET film on which the curable resin layer (B) was fabricated, as prepared in Adjustment Example 5, was set on the conductive pattern side of the inner layer board, and bonded using a batch-type vacuum pressure laminator. The pressure was reduced to 13 hPa or less for 30 seconds, and then pressed at 100°C and 0.7 MPa for 30 seconds. After that, it was heated at 170°C for 15 minutes, and the release PET film was peeled off to laminate the curable resin layer (B) onto the inner layer circuit board (A). Subsequently, the surface of the laminate (F2) using the copper foil prepared in Preparation Example 4, on which the resin layer (C) was formed, was aligned with the surface of the curable resin layer (B) of the laminate, and it was heat-pressed using a vacuum hot press (Hot Press, manufactured by Japan Steel Works Ltd.) at 200°C, 4 MPa, and for 100 minutes to obtain a laminate (L1') on an inner layer substrate (A) in which the curable resin layer (B), resin layer (C), first metal layer (M1) mainly composed of silver, and copper foil as a protective layer (PL) were laminated in this order. From the step of half-etching the copper of the protective layer (PL) onward, a printed circuit board was obtained in the same manner as in Example 3.

[0086] (Examples 5-8) In Examples 1 to 4, printed circuit boards were obtained in the same manner as in Examples 1 to 4, except that the desmearing process was changed from dry desmearing to wet desmearing.

[0087] <Dry desmear treatment> The wet desmear treatment in Examples 1-4 was performed using a plasma with an 8 / 2 mixed gas of O2 / CF4 for 15 minutes.

[0088] <Wet desmear treatment - Condition 1> The wet desmear treatment in Examples 5-8 was performed using desmear treatment chemicals manufactured by Attec Japan. The treatment was carried out using the swelling agent "Swelling Dip Securigant P", the oxidizing agent "Concentrate Compact CP" (alkali permanganate solution), and the reducing agent "Reduction Solution Securigant P-500". The substrate having non-penetrating holes with via formation was immersed in the swelling agent solution at 60°C for 5 minutes to swell, then the smear was removed with the oxidizing agent solution at 80°C for 5 minutes, and then neutralized with the reducing agent solution at 40°C for 5 minutes.

[0089] <Wet desmear treatment - Condition 2> The wet desmear treatment was performed in the same manner as in Condition 1, except that the immersion time in the oxidizing agent solution was changed from 5 minutes to 20 minutes.

[0090] (Comparative Example 1) Similar to Example 1, a core material (CCL-HL832NB, manufactured by Mitsubishi Gas Chemical Company, Inc., with copper foil laminated on both sides, substrate thickness 0.1 mm, copper foil 12 μm) was prepared, and an inner layer circuit board (A) with a conductive pattern was fabricated. Then, the side of the PET film on which the curable resin layer (B) was fabricated, as prepared in Adjustment Example 5, was set on the conductive pattern side of the inner layer board, and bonded using a batch-type vacuum pressure laminator. The pressure was reduced to 13 hPa or less for 30 seconds, and then pressed at 100°C and 0.7 MPa for 30 seconds. After that, it was heated at 170°C for 15 minutes, and the release PET film was peeled off to laminate the curable resin layer (B) onto the inner layer circuit board (A). Next, a CO2 laser was used to form non-through holes with a diameter of 30 μm from the surface of the curable resin layer (B), reaching the circuit metal part (IM) made of copper on the inner circuit board (A). Then, a desmear treatment was performed under the same conditions as in Example 1 to remove the smear generated by the laser processing and to roughen the surface of the curable resin layer (B). Next, a catalyst for electroless copper plating was applied to the surface of the curable resin layer (B), and then it was immersed in a Rochelle salt type electroless copper plating solution at 32°C for 15 minutes to form an electroless copper plating film of 0.6 μm. After drying at 150°C for 30 minutes and then acid washing, a dry film resist (RY5125, manufactured by Resonaq) was laminated onto the electroless copper plating layer to form a resist pattern so that the electroless copper plating layer of the circuit pattern area was exposed, and with the electroless copper plating layer as the cathode side, the current density was 3 A / dm 2 By performing electrolytic copper plating (Toplutina HV, manufactured by Okuno Pharmaceutical Co., Ltd.) for 30 minutes, copper conductor layers of the circuit pattern were formed in the vias of non-through holes and on the electroless copper plating layer. After stripping the pattern resist, the electroless copper plating layer in areas where the circuit was not needed was removed using a sulfuric acid / hydrogen peroxide etching agent to obtain a printed circuit board.

[0091] (Comparative Example 2) A printed circuit board was obtained in the same manner as in Comparative Example 1, except that the desmear treatment, which serves to remove smear generated by laser processing and roughen the surface of the curable resin layer (B), was changed from dry desmear to wet desmear under the same conditions as in Examples 5 to 8.

[0092] (Comparative Example 3) A printed circuit board was obtained in the same manner as in Comparative Example 1, except that the immersion time in the oxidizing agent solution for wet desmearing was changed from 5 minutes to 20 minutes.

[0093] <Method for evaluating the adhesion strength of the conductive layer (M2) on the curable resin layer (B)> In Examples 1-8 and Comparative Examples 1-3, copper stripe patterns with a thickness of 18 μm were obtained on the curable resin layer (B) in the same manner as in Examples 1-8 and Comparative Examples 1-3, except that a 3 mm wide stripe pattern was formed on the curable resin layer (B) instead of a circuit pattern. The strength of one stripe of this stripe pattern was evaluated by peeling it off at a speed of 50 mm / min in a 90° direction.

[0094] <Method for evaluating via size> The diameter of the via top before and after desmearing was evaluated using a scanning electron microscope (Keyence Real Surface Microscope VE-9800).

[0095] <Evaluation of via connectivity> Cross-sectional observation of the via portions of the printed circuit boards obtained in Examples 1-8 and Comparative Examples 1-3 was evaluated using a scanning electron microscope (Keyence Real Surface Microscope VE-9800). The evaluation items included whether there were any cavities in the via-filled copper plating, whether there were any gaps between the curable resin layer (B) forming the via and the copper-plated conductor layer (M2), and whether there was any residual smear at the interface between the inner copper layer and the filled copper-plated conductor layer (M2).

[0096] <Evaluation of circuit pattern width changes due to seed layer etching> In Examples 1-8 and Comparative Examples 1-3, the change in circuit pattern width of the printed circuit board before and after seed layer removal was evaluated using a scanning electron microscope (Keyence Real Surface Microscope VE-9800).

[0097] Table 1 summarizes the evaluation results for the above items for Examples 1-8 and Comparative Examples 1-3. Each item was rated as Excellent (◎), Good (○), Fair (△), or Poor (×).

[0098] In the present invention's method for manufacturing printed circuit boards, adhesion of the conductor layer (M2) formed in a later process to the curable resin layer (B) is ensured by laminating a first metal layer (M1) on the curable resin layer (B), or by laminating a resin layer (C) and the first metal layer (M1) on the curable resin layer (B). However, in the comparative examples, in order to sufficiently adhere the conductor layer (M2) to the curable resin layer (B), it is necessary to roughen the surface of the curable resin layer (B) at the same time as smear removal. In comparative examples 1 and 2, the desmear treatment conditions are mild, so adhesion cannot be ensured. On the other hand, in comparative example 3, the surface of the curable resin layer (B) is roughened by strengthening the desmear treatment conditions, thereby improving the adhesion strength. However, at the same time, the via diameter is widened, which presents a problem from the viewpoint of reducing via diameter.

[0099] <Evaluation of surface roughness of curable resin layer (B) by wet desmear treatment> The surface of the curable resin layer (B) after removing the protective layer (PL) and first metal layer (M1) of the printed circuit board manufactured in Example 1, and the surface of the curable resin layer (B) after the wet desmear treatment—conditions 1 and 2—in Comparative Examples 2 and 3 were observed using a scanning electron microscope (Keyence Real Surface Microscope VE-9800). Figure 19(a) shows the surface morphology of the curable resin layer (B) in Example 1, (b) shows the surface morphology of the curable resin layer (B) in Comparative Example 2, and (c) shows the surface morphology of the curable resin layer (B) in Comparative Example 3.

[0100] In Example 1, the surface roughness of the curable resin layer (B) was found to be reduced when desmearing was performed by plasma treatment because of the presence of a protective layer (PL). Similarly, in Comparative Example 2, the surface roughness of the curable resin layer (B) was reduced because wet desmearing was performed for a short time under conditions where a protective layer (PL) was absent. On the other hand, in Comparative Example 3, the surface roughness of the curable resin layer (C) was increased because wet desmearing was performed for a long time under conditions where a protective layer (PL) was absent.

[0101] [Table 1] [Explanation of symbols]

[0102] 1: Inner layer circuit board (A) 2: Circuit metal part (IM) of the inner layer circuit board 3: Curable resin layer (B) 4: First metal layer (M1) 5: Protective layer (PL) 6: Beer 7: Smear 8: Conductive 9: Pattern Resist 10: Conductor layer (M2) 11: Resin layer (C)

Claims

1. Step 1: Forming a laminate (L1) on an inner circuit board (A) by stacking a curable resin layer (B), a first metal layer (M1), and a protective layer (PL) in that order. Step 2 involves forming vias that connect to the circuit metal portion (IM) of the inner layer circuit board (A) from the protective layer (PL) side of the laminate (L1) through the protective layer (PL), the first metal layer (M1), and the curable resin layer (B). Step 3 is a desmearing process to remove the smear generated in step 2. Step 4: Conducting the via layer to form an electrical connection between the circuit metal part (IM) of the inner layer circuit board (A) and the first metal layer (M1). Step 5 involves removing the protective layer (PL) to expose the first metal layer (M1). Step 6: Forming a pattern resist corresponding to the circuit pattern on the first metal layer (M1). Step 7: Forming a conductor layer (M2) of the circuit pattern inside the via and on the first metal layer (M1). Step 8: Stripping off the pattern resist. Step 9: Remove the first metal layer (UM1) of the circuit-free portion. A method for manufacturing a printed wiring board, characterized by having the following features.

2. The method for manufacturing a printed wiring board according to claim 1, characterized in that a curable resin layer (B), a first metal layer (M1), and a protective layer (PL), which are laminated on the inner circuit board (A), are formed on both sides of the inner circuit board (A).

3. The method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that step 1 is a step 1' which manufactures a laminate (L1') in which a resin layer (C) is further present between the curable resin substrate (B) and the first metal layer (M1).

4. The method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the main component of the metal constituting the first metal layer (M1) is silver.

5. The method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the main component of the metal constituting the protective metal layer (PL) is copper.

6. A method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the main component of the metal constituting the first metal layer (M1) is silver, and the protective layer (PL) is a metal mainly composed of copper.

7. The method for manufacturing a printed circuit board according to claim 1 or 2, characterized in that the desmear treatment performed in step 3 is dry desmear.

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