JP6665990B2 - Base material for high-frequency printed wiring board, high-frequency printed wiring board, method for manufacturing base material for high-frequency printed wiring board, and method for manufacturing high-frequency printed wiring board - Google Patents

Description

  The present invention relates to a base material for a high-frequency printed wiring board, a high-frequency printed wiring board, a method for manufacturing a base material for a high-frequency printed wiring board, and a method for manufacturing a high-frequency printed wiring board.

  In recent years, as electronic devices have become smaller and lighter, there has been an increasing demand for smaller printed wiring boards used in these electronic devices. From such a point, a polyimide film which is excellent in insulation, flexibility, heat resistance and the like and can promote thinning is adopted as a base film of a printed wiring board today (see JP-A-2008-235346). ).

  On the other hand, the amount of information communication has been increasing today, and in order to respond to this, communication in high frequency ranges such as microwaves and millimeter waves has become popular in devices such as IC cards and portable communication terminals. Therefore, there is a need for a high-frequency printed wiring board having a small transmission loss when used in a high-frequency region.

  The transmission loss αd satisfies the following relationship (Equation (1)) with the frequency f, the relative dielectric constant εr of the dielectric layer, and the dielectric loss tangent tanδ.

  In particular, the high-frequency current flows on the surface of the conductor due to the skin effect. For this reason, as the dielectric layer (base film) used in the high-frequency printed wiring board, it is particularly required to reduce the transmission loss αd by reducing the relative dielectric constant εr and to suppress the loss due to the skin effect. ing.

JP 2008-235346 A

  However, the polyimide used as a main component of the base film of the conventional printed wiring board has a relatively large relative dielectric constant εr, and thus cannot sufficiently reduce the transmission loss αd.

  The present invention has been made based on the above-described circumstances, and a base for a high-frequency printed wiring board and a high-frequency printed wiring, which can reduce transmission loss and suppress loss due to a skin effect to improve high-frequency characteristics. It is an object of the present invention to provide a method for manufacturing a board, a base material for a high-frequency printed wiring board, and a method for manufacturing a high-frequency printed wiring board.

  A base material for a high-frequency printed wiring board according to one embodiment of the present invention, which has been made to solve the above-described problem, includes a dielectric layer containing a fluororesin as a main component and one surface side of which has been modified, And a seed layer laminated on one surface of the base material, wherein a main component of the seed layer is a metal, and an average thickness of the seed layer is 2 μm or less.

  A high-frequency printed wiring board according to another embodiment of the present invention made in order to solve the above problem has a dielectric layer containing fluorine resin as a main component and one surface side of which has been modified, A printed wiring board comprising a conductive pattern laminated on one surface, and formed using the base material for a high-frequency printed wiring board.

  A method for manufacturing a base material for a high-frequency printed wiring board according to another aspect of the present invention made in order to solve the above-described problem includes a step of modifying one surface side of a film containing a fluororesin as a main component, Forming a seed layer on one surface of the film after the modification step, wherein the main component of the seed layer is a metal, and the average thickness of the seed layer is 2 μm or less.

  A method for manufacturing a high-frequency printed wiring board according to another embodiment of the present invention made to solve the above-mentioned problem includes a dielectric layer containing a fluororesin as a main component and having one surface side modified, A method for manufacturing a printed wiring board, comprising: a conductive pattern laminated on one surface of a body layer, comprising: the dielectric layer; and a seed layer laminated on one surface of the dielectric layer. The main component of the layer is a metal, and the seed layer is formed using a base material for a high-frequency printed wiring board having an average thickness of 2 μm or less.

  ADVANTAGE OF THE INVENTION The base material for high-frequency printed wiring boards and the high-frequency printed wiring board of the present invention can reduce transmission loss and suppress loss due to a skin effect to improve high-frequency characteristics. Further, the method for manufacturing a base material for a high-frequency printed wiring board and the method for manufacturing a high-frequency printed wiring board according to the present invention provide a base material for a high-frequency printed wiring board and a high-frequency printed wiring that can reduce transmission loss and improve high-frequency characteristics. The plate can be manufactured easily and reliably.

It is a typical fragmentary sectional view showing the substrate for high frequency printed wiring boards concerning one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a modification step of the method for manufacturing the base material for a high-frequency printed wiring board in FIG. FIG. 2 is a schematic cross-sectional view illustrating a seed layer forming step of the method for manufacturing the base material for a high-frequency printed wiring board in FIG. 1. FIG. 2 is a schematic cross-sectional view illustrating a base layer laminating step of the method for manufacturing the base material for a high-frequency printed wiring board in FIG. 1. It is a typical fragmentary sectional view showing the substrate for high frequency printed wiring boards concerning a second embodiment of the present invention. FIG. 4 is a schematic partial cross-sectional view showing a high-frequency printed wiring board using the high-frequency printed wiring board base material of FIG. 3. FIG. 5 is a schematic cross-sectional view illustrating a resist pattern forming step of the method for manufacturing the high-frequency printed wiring board in FIG. 4. FIG. 5 is a schematic sectional view illustrating a second plating layer laminating step of the method for manufacturing the high-frequency printed wiring board in FIG. 4. FIG. 5 is a schematic cross-sectional view illustrating an etching step of the method for manufacturing the high-frequency printed wiring board in FIG. 4.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  A base material for a high-frequency printed wiring board according to one embodiment of the present invention includes a dielectric layer containing fluorine resin as a main component, one surface of which is modified, and a seed layer laminated on one surface of the dielectric layer. A main component of the seed layer is a metal, and the average thickness of the seed layer is 2 μm or less.

  In the base material for a high-frequency printed wiring board, since the dielectric layer is mainly composed of a fluororesin, the dielectric layer has a small relative dielectric constant, thereby reducing transmission loss. Further, in the base material for a high-frequency printed wiring board, since the one surface side of the dielectric layer is modified, the seed layer is easily brought into close contact with the one surface side. In particular, the base material for a high-frequency printed wiring board has such a property that one surface of the dielectric layer is modified so as to prevent the one surface from being roughened and to improve the adhesion to the seed layer. Can be increased. Therefore, the base material for a high-frequency printed wiring board suppresses the roughening of the contact surface between the seed layer and the dielectric layer, thereby preventing the propagation distance of the high-frequency characteristic signal from becoming long, thereby increasing the skin effect. Loss can be suppressed. In addition, since the high-frequency printed wiring board base material has an average thickness of the seed layer within the above range, even when miniaturization is required, plating can be formed to a certain thickness on one surface of the seed layer. it can. Accordingly, the base material for a high-frequency printed wiring board can reduce transmission loss and improve high-frequency characteristics.

  Preferably, the metal is copper or a copper alloy. As described above, since the metal is copper or a copper alloy, conductivity can be improved while suppressing costs.

  The seed layer is preferably made of a sintered body of metal particles, and the average particle diameter of the metal particles is preferably 1 nm or more and 500 nm or less. As described above, the seed layer is formed of a sintered body of metal particles, and the average particle diameter of the metal particles is in the above range, so that expensive vacuum equipment necessary for physical vapor deposition such as sputtering is required. Without this, a dense and substantially uniform sintered body can be accurately formed on one surface side of the dielectric layer.

  Further, the seed layer may be made of an electroless plating metal. Even if the seed layer is made of an electroless plating metal, the seed layer is formed on one surface side of the dielectric layer without requiring expensive vacuum equipment required for physical vapor deposition such as sputtering. Can be.

  The average thickness of the seed layer is preferably from 10 nm to 1 μm. By setting the average thickness of the seed layer in the above range, plating can be formed to a certain thickness while maintaining conductivity.

  The arithmetic average roughness Ra of the other surface of the seed layer is preferably 2 μm or less. As described above, when the arithmetic average roughness Ra of the other surface of the seed layer is within the above range, it is possible to prevent the propagation distance of the high-frequency characteristic signal from becoming long, and to further suppress the loss due to the skin effect. it can.

  It is preferable to provide a plating layer on one surface side of the seed layer. As described above, by providing the plating layer on one surface side of the sheet layer, the peel strength between the seed layer and the dielectric layer is improved, and the conductivity is improved.

  A high-frequency printed wiring board according to one embodiment of the present invention includes a dielectric layer containing fluororesin as a main component, a modified surface on one surface side, and a conductive pattern laminated on one surface of the dielectric layer. A printed wiring board comprising the high-frequency printed wiring board base material.

  Since the high-frequency printed wiring board is formed using the base material for a high-frequency printed wiring board, transmission loss can be reduced and high-frequency characteristics can be improved.

  The high-frequency printed wiring board is preferably formed by a semi-additive method. Since the high-frequency printed wiring board has one surface side of the dielectric layer that has been modified, plating can be formed to a certain thickness on one surface side of the seed layer. It can be formed reliably. Further, by forming the conductive pattern by a semi-additive method, the cross section of the conductive pattern can be easily formed into a desired shape. Thereby, the cross-sectional area of the conductive pattern can be increased to improve the transmission characteristics.

  The lower base in the cross-sectional shape of the conductive pattern is defined as one side, and the average value of the area ratio of the cross section of the conductive pattern to a rectangle whose length adjacent to this side is equal to the average thickness of the conductive pattern is 0.9 or more. preferable. As described above, by setting the average value of the area ratio of the cross section of the conductive pattern to the above range, the cross sectional area of the conductive pattern can be made sufficiently large and the transmission characteristics can be sufficiently improved.

  A method for manufacturing a substrate for a high-frequency printed wiring board according to one embodiment of the present invention includes a step of modifying one surface side of a film containing a fluororesin as a main component, and one surface of the film after the modification step. Forming a seed layer on the substrate, wherein the main component of the seed layer is a metal, and the average thickness of the seed layer is 2 μm or less.

  In the method of manufacturing the base material for a high-frequency printed wiring board, one surface of a film containing a fluororesin as a main component is modified, and a seed layer is formed on the surface on which the modification treatment is performed. The adhesion between the film and the seed layer can be enhanced while preventing the one surface from being roughened. Further, in the method of manufacturing the base material for a high-frequency printed wiring board, since the average thickness of the seed layer is in the above range, even when miniaturization is required, plating is formed to a certain thickness on one surface of the seed layer. be able to. Therefore, the method for manufacturing a base material for a high-frequency printed wiring board can easily and reliably manufacture a base material for a printed wiring board that can reduce transmission loss and improve high-frequency characteristics.

  The seed layer forming step may include a step of applying an ink in which metal particles are dispersed in a solvent to one surface of the film, and a step of baking the ink applied to one surface of the film. The average particle diameter of the metal particles is preferably from 1 nm to 500 nm. As described above, in the seed layer forming step, the ink containing the metal particles having an average particle diameter in the above range is applied to one surface of the film, and the applied ink is baked to perform sputtering or the like. A dense and substantially uniform sintered body can be accurately formed on one surface side of the film without using expensive vacuum equipment required for physical vapor deposition.

  According to one embodiment of the present invention, there is provided a method for manufacturing a high-frequency printed wiring board, including a dielectric layer containing fluorine resin as a main component, one surface of which is modified, and a conductive layer laminated on one surface of the dielectric layer. A method of manufacturing a printed wiring board comprising a pattern, comprising: a dielectric layer; and a seed layer laminated on one surface of the dielectric layer, wherein a main component of the seed layer is a metal; It is formed using a high-frequency printed wiring board having an average layer thickness of 2 μm or less.

  Since the method for manufacturing a high-frequency printed wiring board uses the base material for a high-frequency printed wiring board as described above, it is possible to easily and reliably manufacture a high-frequency printed wiring board that can reduce transmission loss and improve high-frequency characteristics. it can.

  In the present invention, the “average particle diameter” means the one represented by the center diameter D50 of the volume particle size distribution in the dispersion. The average particle size can be measured with a particle size distribution measuring device (for example, Microtrac particle size distribution analyzer “UPA-150EX” manufactured by Nikkiso Co., Ltd.). The “arithmetic mean roughness Ra” means a value measured at a cutoff value (λc) of 2.5 mm and an evaluation length (l) of 12.5 mm according to JIS-B-0601: 2001. The “main component” refers to a component having the largest content, for example, a component having a content of 50% by mass or more. "Lower bottom" means the side of the conductive pattern on the dielectric layer side. The “average thickness” refers to the distance between the average line of the interface on the front surface and the average line of the interface on the back surface within the measured length in a cross section cut in the thickness direction of the object. Here, the “average line” is a virtual line drawn along the interface, and the total area of the peaks (the total area above the virtual line) and the total of the valleys defined by the interface and this virtual line are defined. A line whose area (total area below the imaginary line) is equal.

[Details of Embodiment of the Present Invention]
Hereinafter, a high-frequency printed wiring board base material, a high-frequency printed wiring board, a method for manufacturing a high-frequency printed wiring board base material, and a method for manufacturing a high-frequency printed wiring board according to an embodiment of the present invention will be described with reference to the drawings.

[First embodiment]
<Substrate for high frequency printed wiring board>
The base material 1 for a high-frequency printed wiring board in FIG. 1 includes a dielectric layer 2, a seed layer 3, and a base layer 4. The high-frequency printed wiring board substrate 1 has flexibility and is used as a substrate of a flexible printed wiring board.

(Dielectric layer)
The dielectric layer 2 contains a fluororesin as a main component. Here, “fluororesin” means that at least one of the hydrogen atoms bonded to the carbon atoms constituting the repeating unit of the polymer chain is a fluorine atom or an organic group having a fluorine atom (hereinafter, also referred to as a “fluorine atom-containing group”). ). The fluorine atom-containing group is a group in which at least one hydrogen atom in a linear or branched organic group is substituted with a fluorine atom, and examples thereof include a fluoroalkyl group, a fluoroalkoxy group, and a fluoropolyether group. .

  The “fluoroalkyl group” means an alkyl group in which at least one hydrogen atom has been replaced by a fluorine atom, and examples thereof include a “perfluoroalkyl group”. Specific fluoroalkyl groups include, for example, a group in which all hydrogen atoms of an alkyl group are substituted with fluorine atoms, a group in which hydrogen atoms other than one hydrogen atom at the terminal of an alkyl group are substituted with fluorine atoms, and the like. Can be

  The “fluoroalkoxy group” means an alkoxy group in which at least one hydrogen atom has been replaced by a fluorine atom, and examples thereof include a “perfluoroalkoxy group”. Specific examples of the fluoroalkoxy group include a group in which all hydrogen atoms of an alkoxy group are substituted with fluorine atoms, a group in which a hydrogen atom other than one hydrogen atom at the terminal of the alkoxy group is substituted with a fluorine atom, and the like. Can be

  The “fluoropolyether group” is a monovalent group having an oxyalkylene unit as a repeating unit and having an alkyl group or a hydrogen atom at a terminal, and at least one of the alkylene oxide chain and the terminal alkyl group. It means a monovalent group in which a hydrogen atom is substituted by a fluorine atom. Examples of the fluoropolyether group include a “perfluoropolyether group” having a plurality of perfluoroalkylene oxide chains as a repeating unit.

  Examples of the fluororesin that is the main component of the dielectric layer 2 include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). ), Tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinyl fluoride (PVF) And a thermoplastic fluororesin (THV) formed by three kinds of monomers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride, and a fluoroelastomer. Further, a mixture or a copolymer containing these compounds can also be used as the fluororesin.

  Among them, the fluororesin used as the main component of the dielectric layer 2 includes tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE), and combinations thereof. Since these fluororesins are materials having a low relative dielectric constant, transmission loss can be further suppressed by using these fluororesins as a main component of the dielectric layer 2.

  The dielectric layer 2 may be an optional component such as an engineering plastic, a flame retardant, a flame retardant aid, a pigment, an antioxidant, a reflection imparting agent, a hiding agent, a lubricant, a processing stabilizer, a plasticizer, a foaming agent, and a reinforcing agent. Material can be included. In this case, the upper limit of the content of the optional component in the dielectric layer 2 is preferably 50% by mass, more preferably 40% by mass, and still more preferably 30% by mass.

  The engineering plastic can be selected from known ones according to the characteristics required of the dielectric layer 2, and typically, an aromatic polyether ketone can be used.

  This aromatic polyether ketone has a structure in which benzene rings are bonded at the para position and benzene rings are connected to each other by a rigid ketone bond (—C (＝ O) —) or a flexible ether bond (—O—). Is a thermoplastic resin. Examples of the aromatic polyether ketone include polyether ether ketone (PEEK) having an ether bond, a benzene ring, an ether bond, a benzene ring, a ketone bond, and a benzene ring having a structural unit arranged in this order, an ether bond, a benzene ring. , A polyether ketone (PEK) having a structural unit in which a ketone bond and a benzene ring are arranged in this order. Above all, PEEK is preferred as the aromatic polyether ketone. Such an aromatic polyether ketone is excellent in wear resistance, heat resistance, insulation, workability, and the like.

  As the aromatic polyether ketone such as PEEK, a commercially available product can be used. For example, a single-grade aromatic polyether ketone that is commercially available may be used, and a plurality of grades of aromatic polyether ketone may be used. A ketone may be used in combination, or a modified aromatic polyether ketone may be used.

  As the flame retardant, various known flame retardants can be used, and examples thereof include a halogen flame retardant such as a bromine flame retardant and a chlorine flame retardant.

  As the flame retardant aid, various known ones can be used, and examples thereof include antimony trioxide.

  As the pigment, various known pigments can be used, and examples thereof include titanium oxide.

  As the antioxidant, various known antioxidants can be used, and examples thereof include a phenolic antioxidant.

  As the reflection imparting agent, various known agents can be used, and examples thereof include titanium oxide.

  The reinforcing material is not particularly limited as long as it has a smaller coefficient of linear expansion than the dielectric layer 2. However, it has insulation properties, heat resistance that does not melt and flow at the melting point of the fluororesin, and is equivalent to that of the fluororesin. It is desirable to have the above tensile strength and corrosion resistance. As such a reinforcing material, for example, a glass cloth formed of glass in a cloth shape, a fluororesin-containing glass cloth in which such a glass cloth is impregnated with a fluororesin, metal, ceramics, polytetrafluoroethylene, polyetheretherketone , Polyimide, resin cloth containing heat-resistant fibers formed of aramid, etc., polytetrafluoroethylene, liquid crystal polymer, polyimide, polyamideimide, polybenzimidazole, polyetheretherketone, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl It can be composed of a heat-resistant film containing a vinyl ether copolymer, a thermosetting resin, a crosslinked resin, or the like as a main component. The resin cloth and the heat-resistant film preferably have a melting point (or heat deformation temperature) higher than the thermocompression bonding temperature in the step of forming the modified layers 5a and 5b described later. The weaving method of the resin cloth is preferably plain weave to make the dielectric layer 2 thin, but twill weave and satin weave are preferable to make the dielectric layer 2 bendable. In addition, a known weaving method can be applied.

  Further, the dielectric layer 2 may have a hollow structure. In this case, since the dielectric constant of the dielectric layer 2 can be reduced, transmission loss can be more effectively suppressed.

  The lower limit of the average thickness of the dielectric layer 2 is preferably 3 μm, more preferably 6 μm. On the other hand, the upper limit of the average thickness of the dielectric layer 2 is preferably 1 mm, more preferably 0.5 mm, further preferably 0.1 mm, and particularly preferably 55 μm. If the average thickness of the dielectric layer 2 is less than the above lower limit, the strength of the dielectric layer 2 may be insufficient. Conversely, if the average thickness of the dielectric layer 2 exceeds the above upper limit, application to electronic devices that require flexibility may be difficult.

  As a minimum of relative permittivity of dielectric layer 2, 1.2 is preferred, 1.4 is more preferred, and 1.6 is still more preferred. On the other hand, the upper limit of the relative permittivity of the dielectric layer 2 is preferably 2.7, more preferably 2.5, and still more preferably 2.3. When the relative dielectric constant of the dielectric layer 2 is less than the above lower limit, it is difficult to secure the dimensional stability of the dielectric layer 2. In particular, when the non-dielectric constant is reduced by foaming, the elastic modulus is too low, which makes processing and transport difficult and may increase the cost. On the other hand, when the relative dielectric constant of the dielectric layer 2 exceeds the above upper limit, the dielectric loss tangent may increase and transmission loss may not be sufficiently reduced, and sufficient transmission speed may not be obtained.

(Modified layer)
The dielectric layer 2 is modified on both sides. Specifically, the dielectric layer 2 has the modified layers 5a and 5b on one surface side and the other surface side. The modified layers 5a and 5b include a siloxane bond (Si-O-Si) and a hydrophilic functional group. The modified layers 5a and 5b are formed by, for example, a modifier (silane coupling agent) having a hydrophilic functional group and generating a siloxane bond bonded to a fluororesin which is a main component of the dielectric layer 2. It is formed. In this case, in the modified layers 5a and 5b, for example, a hydrophilic functional group is bonded to a Si atom constituting a siloxane bond. Here, the bond between the fluororesin and the modifier may be composed of only a covalent bond or may include a covalent bond and a hydrogen bond.

In the modified layers 5a and 5b, a Si atom constituting a siloxane bond (hereinafter, this atom is also referred to as a “siloxane bond Si atom”) is, for example, at least one of an N atom, a C atom, an O atom, and an S atom. It is covalently bonded to C atoms of the dielectric layer 2 through one atom. Specifically, Si atom of the siloxane bond, for example -O -, - S -, - S-S -, - (CH 2) n -, - NH -, - (CH 2) n -NH -, - It bonds to C atoms of the dielectric layer 2 through an atomic group such as (CH ₂ ) _n —O— (CH ₂ ) _m — (n and m are integers of 1 or more).

  Examples of the hydrophilic functional group include a hydroxyl group, a carboxy group, a carbonyl group, an amino group, an amide group, a sulfide group, a sulfonyl group, a sulfo group, a sulfonyldioxy group, an epoxy group, a methacryl group, a mercapto group, and a combination thereof. preferable. Among these, a hydrophilic functional group containing an N atom and a hydrophilic functional group containing an S atom are more preferable. These hydrophilic functional groups improve the adhesion of the surface of the dielectric layer 2.

  Further, the modified layers 5a and 5b may include two or more of these hydrophilic functional groups. By imparting hydrophilic functional groups having different properties to the modified layers 5a and 5b, the reactivity of the surface of the dielectric layer 2 can be varied. These hydrophilic functional groups can be bonded directly to the Si atom that is a component of the siloxane bond, or via one or more C atoms.

  As a modifier for forming the modified layers 5a and 5b having the above characteristics, a silane coupling agent having a hydrophilic functional group in a molecule is preferable, and among them, a silane coupling agent having a hydrolyzable silicon-containing functional group is preferable. Those are more preferred. Such a silane coupling agent chemically bonds to the fluororesin constituting the dielectric layer 2. The chemical bond between the silane coupling agent and the fluororesin of the dielectric layer 2 may be composed of only a covalent bond or may include a covalent bond and a hydrogen bond. Here, the “hydrolyzable silicon-containing functional group” refers to a group capable of forming a silanol group (Si—OH) by hydrolysis.

  The upper limit of the contact angle of the surfaces of the modified layers 5a and 5b with pure water is preferably 90 °, more preferably 80 °, and even more preferably 70 °. By setting the contact angle of the surfaces of the modified layers 5a and 5b with pure water to the above upper limit or less, the adhesion can be further improved. On the other hand, the lower limit of the contact angle of the surfaces of the modified layers 5a and 5b with pure water is not particularly limited. The contact angle can be controlled, for example, by adjusting the type and amount of the hydrophilic functional group. The “contact angle with pure water” is a value of a contact angle measured by a static drop method according to JIS-R-3257 (1999).

Further, it is preferable that the modified layers 5a and 5b have the following etching resistance. That is, the etching treatment in which iron chloride is contained, the specific gravity is 1.33 g / cm ³ , and the concentration of free hydrochloric acid is 0.2 mol / L (temperature: 45 ° C.) is immersed in an etching solution for 2 minutes. Therefore, it is preferable that the modified layers 5a and 5b are not removed. Here, “the modified layers 5a and 5b are not removed” means that the hydrophilicity is not lost, and the contact angle with pure water in the portion where the modified layers 5a and 5b are provided exceeds 90 °. Indicates no. If the modified layers 5a and 5b have the above etching resistance, an etchant may enter between the conductive pattern and the dielectric layer 2 when forming the conductive pattern using the base material 1 for a high-frequency printed wiring board. Therefore, the adhesion between the conductive pattern and the dielectric layer 2 can be favorably maintained. The etching resistance can be imparted to the modified layers 5a and 5b by using, for example, a preferable silane coupling agent described later. It should be noted that the etching process may cause patchy microscopic portions in the region where the modified layers 5a and 5b are formed, but when the entire region has hydrophilicity, such a state is not satisfied. It is assumed that hydrophilicity is maintained.

  Further, it is preferable that the modified layers 5a and 5b have etching resistance to an etching solution containing copper chloride. When the modified layers 5a and 5b have the etching resistance to the above-mentioned iron chloride-containing etching solution, the modified layers 5a and 5b have the same etching resistance to the etching solution containing copper chloride as described above. That has been confirmed.

  The lower limit of the average thickness of the modified layers 5a and 5b is preferably 10 nm, more preferably 20 nm. The upper limit of the average thickness of the modified layers 5a and 5b is preferably 400 nm, more preferably 200 nm. By setting the average thickness of the modified layers 5a and 5b to be equal to or more than the above lower limit, the adhesion can be further improved. On the other hand, when the average thickness of the modified layers 5a and 5b exceeds the upper limit, the high-frequency characteristics may be insufficient due to the influence of dielectric loss caused by the modified layers 5a and 5b. Therefore, by setting the average thickness of the modified layers 5a and 5b within the above range, the function of suppressing the transmission loss and the function of improving the adhesion can be exhibited in a well-balanced manner. The average thickness of the modified layers 5a and 5b can be measured by, for example, an electron microscope.

  The upper limit of the content of the modified layers 5a and 5b in the dielectric layer 2 is preferably 10% by mass, more preferably 5% by mass, and still more preferably 1% by mass. When the content is equal to or less than the upper limit, the function of suppressing transmission loss and the function of improving adhesion can be exhibited in a well-balanced manner. The lower limit of the content is not particularly limited as long as the adhesion can be improved.

(Seed layer)
The seed layer 3 is laminated on one surface of the dielectric layer 2. Specifically, the seed layer 3 is laminated on one surface of the modified layer 5a of the dielectric layer 2. The seed layer 3 is a metal layer for plating for forming plating on one surface side. The seed layer 3 contains a metal as a main component. Specifically, the seed layer 3 is composed of a sintered body of metal particles.

  The metal is not particularly limited as long as it has a certain conductivity, but from the viewpoint of improving the adhesion between the dielectric layer 2 and the seed layer 3, a metal oxide based on the metal or the metal It is preferred that a group derived from an oxide and a metal hydroxide based on the metal or a group derived from the metal hydroxide be generated, for example, copper, nickel, aluminum, gold, silver, palladium, and chromium. Or alloys of these and the like. Among them, copper or a copper alloy that can increase conductivity and adhesion to the dielectric layer 2 while suppressing cost is preferable.

  The lower limit of the average particle diameter of the metal particles is preferably 1 nm, more preferably 30 nm. On the other hand, the upper limit of the average particle diameter of the metal particles is preferably 500 nm, more preferably 100 nm. If the average particle diameter of the metal particles is less than the lower limit, the dispersibility and stability of the metal particles in the ink may be reduced in forming the seed layer 3. It may be difficult to form a dense and uniform sintered body on the surface. Conversely, when the average particle diameter of the metal particles exceeds the upper limit, the metal particles may be likely to precipitate in the ink, or the density of the metal particles may not be easily uniform when the ink is applied. is there.

  The lower limit of the average thickness of the seed layer 3 is preferably 10 nm, more preferably 50 nm, and still more preferably 100 nm. On the other hand, the upper limit of the average thickness of the seed layer 3 is 2 μm, preferably 1.5 μm, more preferably 1 μm, and particularly preferably 500 nm. If the average thickness of the seed layer 3 is less than the above lower limit, a cut may occur in the seed layer 3 in a plan view and the conductivity may be reduced. Conversely, if the average thickness of the seed layer 3 exceeds the above upper limit, the time required for plating may be long, and the productivity may be reduced. On the other hand, when the average thickness of the seed layer 3 is in the above range, the plating can be formed to a certain thickness while maintaining the conductivity.

  The upper limit of the arithmetic average roughness Ra of the other surface of the seed layer 3 is preferably 2 μm, more preferably 1 μm, and still more preferably 0.5 μm. If the arithmetic average roughness Ra of the other surface of the seed layer 3 exceeds the upper limit, the propagation distance of the high-frequency characteristic signal becomes longer, and the loss due to the skin effect may increase. Note that the lower limit of the arithmetic average roughness Ra of the other surface of the seed layer 3 is not particularly limited, and may be, for example, 0.001 μm.

(Base layer)
The base layer 4 is a ground layer provided over the entire other surface of the dielectric layer 2. The base layer 4 contains a metal as a main component. The main components of the base layer 4 include, for example, copper, silver, gold, stainless steel, iron, aluminum, nickel, and alloys thereof. Among them, copper or a copper alloy that can improve conductivity while suppressing the production cost is preferable.

  The lower limit of the average thickness of the base layer 4 is preferably 1 μm, more preferably 10 μm. On the other hand, the upper limit of the average thickness of the base layer 4 is preferably 2000 μm, more preferably 300 μm. If the average thickness of the base layer 4 is less than the lower limit, sufficient conductivity may not be obtained, and the strength may be insufficient, so that the dielectric layer 2 may not be properly laminated on one surface of the base layer 4. Conversely, if the average thickness of the base layer 4 exceeds the above upper limit, the cost increases and the base material 1 for a high-frequency printed wiring board may be unnecessarily thick.

<Production method of base material for high frequency printed wiring board>
Next, a method for manufacturing the base material 1 for a high-frequency printed wiring board will be described with reference to FIGS. 2A to 2C.

  The method for producing the base material for a high-frequency printed wiring board includes a step of modifying both sides of a film 2a containing a fluororesin as a main component (hereinafter, also simply referred to as a "fluororesin film 2a"), and a step of modifying this step. The method includes a step of forming the seed layer 3 on one surface of the film after the step, and a step of laminating the base layer 4 on the other surface of the film after the modification step. In the following, a case where the base layer lamination is performed after the seed layer formation step will be described. However, the base layer lamination step may be performed before the seed layer formation step.

<Reforming process>
In the modification step, as shown in FIG. 2A, both surfaces of the fluororesin film 2a are modified. Specifically, the modified layers 5a and 5b are formed on both surfaces of the fluororesin film 2a. In the reforming step, for example, a primer material containing the above-mentioned silane coupling agent as a modifier, an alcohol, and water is laminated on both surfaces of the fluororesin film 2a, and the alcohol of the primer material is removed by drying. By this modification step, both surfaces of the fluororesin film 2a are modified, so that the dielectric layer 2 is formed.

  As a minimum of content of a silane coupling agent in the whole primer material, 0.1 mass% is preferred and 0.5 mass% is more preferred. Further, the upper limit of the content of the silane coupling agent in the entire primer material is preferably 5% by mass, and more preferably 3% by mass. When the content of the silane coupling agent is equal to or more than the above lower limit, the adhesion can be further improved. On the other hand, when the content of the silane coupling agent exceeds the above upper limit, aggregation of the silane coupling agent occurs, which may make it difficult to form a primer material film having a uniform thickness.

  Examples of the alcohol contained in the primer material include methanol, ethanol, n-propanol, n-butanol, t-butanol, and isopropyl alcohol. One or more selected from these alcohol groups can be used as the alcohol.

  The water contained in the primer material is a substance that hydrolyzes the silane coupling agent, and a small amount is sufficient. For example, water is set to 0.01 part by mass or more and 0.1 part by mass or less based on 100 parts by mass of alcohol. . As the water, water existing in the air or water as an impurity contained in alcohol may be used.

<Seed layer forming step>
In the seed layer forming step, as shown in FIG. 2B, the seed layer 3 is formed on one surface of the dielectric layer 2 formed by modifying the fluororesin film 2a. The seed layer forming step includes a coating step and a firing step.

(Coating process)
In the coating step, an ink in which metal particles are dispersed in a solvent is coated on one surface of the dielectric layer 2. Hereinafter, the coating step will be described in detail.

(Metal particles)
The metal particles dispersed in the ink can be produced by a high-temperature treatment method, a liquid phase reduction method, a gas phase method, or the like. Among them, according to the liquid phase reduction method, the production cost can be further reduced, and the particle diameter of the metal particles can be easily made uniform by stirring in an aqueous solution. The metal particles are manufactured by the high-temperature treatment method, the liquid-phase reduction method, the gas-phase method, or the like, so that the average particle diameter is adjusted to 1 nm or more and 500 nm or less as described above.

In order to produce the metal particles by a liquid phase reduction method, for example, a water-soluble metal compound and a dispersant that are the source of metal ions forming the metal particles are dissolved in water, and a reducing agent is added. The reduction reaction of the metal ions may be performed for a certain period of time. In the case of the liquid phase reduction method, the produced metal particles have a uniform spherical or granular shape and can be made into fine particles. For example, in the case of copper, copper (II) nitrate (Cu (NO ₃ ) ₂ ) or copper (II) sulfate pentahydrate (CuSO ₄ .5H ₂ O) and the like. Silver (I) nitrate in the case of silver addition (AgNO _3), silver methanesulfonate _(CH 3 _SO 3 Ag) or the like, in the case of gold tetrachloroaurate (III) acid tetrahydrate (HAuCl ₄ · _4H 2 O) In the case of nickel, nickel (II) chloride hexahydrate (NiCl ₂ .6H ₂ O), nickel nitrate (II) hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) and the like can be mentioned. As for other metal particles, water-soluble compounds such as chlorides, nitric acid compounds, and sulfuric acid compounds can be used.

  As the reducing agent, various reducing agents capable of reducing and precipitating metal ions in a liquid phase (aqueous solution) reaction system can be used. Examples of the reducing agent include sodium borohydride, sodium hypophosphite, hydrazine, transition metal ions such as trivalent titanium ion and divalent cobalt ion, ascorbic acid, reducing sugars such as glucose and fructose, Examples include polyhydric alcohols such as ethylene glycol and glycerin. Above all, a trivalent titanium ion is preferable as the reducing agent. The liquid phase reduction method using trivalent titanium ions as a reducing agent is referred to as a titanium redox method. In the titanium redox method, metal ions are reduced by redox action when trivalent titanium ions are oxidized to tetravalent, and metal particles are precipitated. Since the metal particles obtained by the titanium redox method have small and uniform particle diameters, the metal particles are more densely packed, and the coating film can be formed into a more dense film.

  In order to adjust the particle diameter of the metal particles, adjust the types and mixing ratios of the metal compound, the dispersant and the reducing agent, and adjust the stirring speed, temperature, time, pH, etc., when the metal compound is subjected to the reduction reaction. I just need. The lower limit of the pH of the reaction system is preferably 7, and the upper limit of the pH of the reaction system is preferably 13. By setting the pH of the reaction system within the above range, metal particles having a fine particle diameter can be obtained. At this time, the pH of the reaction system can be easily adjusted to the above range by using the pH adjuster. As the pH adjuster, a common acid or alkali such as hydrochloric acid, sulfuric acid, nitric acid, sodium hydroxide, sodium carbonate, and ammonia can be used. Particularly, in order to prevent deterioration of peripheral members, an alkali metal or alkaline earth is used. Nitric acid and ammonia which do not contain impurities such as metals, halogens, sulfur, phosphorus and boron are preferred.

The lower limit of the average particle diameter of the metal particles is preferably 1 nm, more preferably 10 nm,
30 nm is more preferred. In addition, the upper limit of the average particle diameter of the metal particles is preferably 500 nm, more preferably 300 nm, and still more preferably 100 nm. If the average particle size of the metal particles is less than the above lower limit, the dispersibility and stability of the metal particles in the ink may be reduced. On the other hand, when the average particle diameter of the metal particles exceeds the above upper limit, the metal particles may be easily precipitated, and the density of the metal particles may be non-uniform when the ink is applied.

  As a minimum of content rate of metal particles in ink, 5 mass% is preferred, 10 mass% is more preferred, and 20 mass% is still more preferred. Further, the upper limit of the content ratio of the metal particles in the ink is preferably 50% by mass, more preferably 40% by mass, and still more preferably 30% by mass. By setting the content ratio of the metal particles to the lower limit or more, the coating film can be formed into a denser film. On the other hand, when the content ratio of the metal particles exceeds the above upper limit, the film thickness of the coating film may be non-uniform.

(Other components)
The ink may contain a dispersant other than the metal particles. The dispersant is not particularly limited, and various dispersants capable of favorably dispersing metal particles can be used. The lower limit of the molecular weight of the dispersant is preferably 2,000, and the upper limit of the molecular weight of the dispersant is preferably 30,000. By using a dispersant having a molecular weight in the above range, the metal particles can be dispersed well in the ink, and the film quality of the coating film can be made dense and free from defects. When the molecular weight of the dispersant is less than the lower limit, the effect of preventing aggregation of the metal particles and maintaining the dispersion may not be sufficiently obtained. On the other hand, when the molecular weight of the dispersant exceeds the above upper limit, the bulk of the dispersant is too large, and during sintering of the coating film, sintering of the metal particles may be inhibited to cause voids. If the bulk of the dispersant is too large, the denseness of the coating film may be reduced, or the decomposition residue of the dispersant may lower the conductivity.

  The dispersant preferably does not contain sulfur, phosphorus, boron, halogen and alkali from the viewpoint of preventing deterioration of peripheral members. Preferred dispersants are those having a molecular weight in the above range, such as amine-based polymer dispersants such as polyethyleneimine and polyvinylpyrrolidone, and polyacrylic acid and hydrocarbon-based high-molecular weight compounds having a carboxy group in the molecule such as carboxymethylcellulose. Molecular dispersants, poval (polyvinyl alcohol), styrene-maleic acid copolymers, olefin-maleic acid copolymers, copolymers having a polar group such as a copolymer having a polyethyleneimine moiety and a polyethylene oxide moiety in one molecule. Molecular dispersants and the like can be mentioned.

  The dispersant may be incorporated in the ink in the form of a solution dissolved in water or a water-soluble organic solvent. When a dispersant is added to the ink, the lower limit of the content of the dispersant is preferably 1 part by mass with respect to 100 parts by mass of metal particles. Further, the upper limit of the content ratio of the dispersant is preferably 60 parts by mass with respect to 100 parts by mass of the metal particles. When the content of the dispersant is less than the lower limit, the effect of preventing metal particles from agglomerating may be insufficient. On the other hand, when the content ratio of the dispersant exceeds the upper limit, there is a possibility that an excess dispersant inhibits the sintering of the metal particles at the time of firing the coating film to generate voids, and the decomposition residue of the dispersant is reduced. It may remain as an impurity and lower the conductivity.

  As the dispersion medium in the ink, for example, water can be used. When water is used as the dispersion medium, the lower limit of the water content is preferably 20 parts by mass with respect to 100 parts by mass of the metal particles. The upper limit of the water content is preferably 1,900 parts by mass with respect to 100 parts by mass of metal particles. Water serving as a dispersion medium plays a role of, for example, sufficiently swelling the dispersant and dispersing the metal particles surrounded by the dispersant satisfactorily. The swelling effect may be insufficient. On the other hand, when the content of the water exceeds the upper limit, the content of the metal particles in the ink decreases, and there is a possibility that a good sintered body 3 having a required thickness and density cannot be formed.

  An organic solvent can be added to the ink as needed for viscosity adjustment, vapor pressure adjustment, and the like. As such an organic solvent, various organic solvents that are water-soluble can be used. Specific examples thereof 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 and other esters; glycol ethers such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether;

  When an organic solvent is added to the ink, the lower limit of the content ratio of the organic solvent is preferably 30 parts by mass with respect to 100 parts by mass of metal particles. The upper limit of the content ratio of the organic solvent is preferably 900 parts by mass with respect to 100 parts by mass of the metal particles. When the content ratio of the organic solvent is less than the above lower limit, the effects of adjusting the viscosity of the ink and adjusting the vapor pressure may not be sufficiently obtained. On the other hand, when the content ratio of the organic solvent exceeds the above upper limit, for example, the swelling effect of the dispersant by water becomes insufficient, and there is a possibility that metal particles may aggregate in the ink.

  In the case of producing metal particles by a liquid phase reduction method, the metal particles precipitated in a reaction system of a liquid phase (aqueous solution) are once formed into a powder form through steps such as filtration, washing, drying, and crushing. Can be used to prepare an ink. In this case, an ink containing metal particles can be obtained by mixing powdered metal particles, a dispersion medium such as water, and, if necessary, a dispersant, an organic solvent, and the like at a predetermined ratio. At this time, it is preferable to prepare an ink using a liquid phase (aqueous solution) in which metal particles are precipitated as a starting material. Specifically, the liquid phase (aqueous solution) containing the precipitated metal particles is subjected to a treatment such as ultrafiltration, centrifugation, washing, and electrodialysis to remove impurities, and if necessary, is concentrated to remove water. . Alternatively, conversely, after adding water to adjust the concentration of the metal particles, an ink containing the metal particles is prepared by further mixing an organic solvent at a predetermined ratio as needed. According to this method, generation of coarse and irregular particles due to aggregation of metal particles during drying can be prevented, and a dense and uniform seed layer 3 can be easily formed.

(Ink application method)
Examples of a method of applying the ink in which the metal particles are dispersed to one surface of the dielectric layer 2 include a spin coating method, a spray coating method, a bar coating method, a die coating method, a slit coating method, a roll coating method, and a dip coating method. Can be used. Alternatively, ink may be applied to only a part of one surface of the dielectric layer 2 by screen printing, a dispenser, or the like. After the application of the ink, a coating film is formed, for example, by drying at room temperature.

(Firing process)
In the firing step, the coated ink is fired. Specifically, in the baking step, a coating film formed from the ink applied to one surface of the dielectric layer 2 is dried and then heat-treated. In this firing step, the metal particles are sintered together to form a sintered body, and the sintered body is fixed to one surface of the dielectric layer 2. Thereby, a seed layer 3 having an average thickness of 2 μm or less is formed on one surface of the dielectric layer 2. The dispersant and other organic substances that can be contained in the ink are volatilized or decomposed by firing. Further, in the vicinity of the interface between the seed layer 3 and the dielectric layer 2, the metal particles are oxidized by firing, so that the generation of metal hydroxide based on the metal particles and the group derived from the metal hydroxide is suppressed. A metal oxide based on metal particles and a group derived from the metal oxide (hereinafter collectively referred to as “metal oxide or the like”) are generated. The metal oxide or the like generated near the interface between the seed layer 3 and the dielectric layer 2 is strongly bonded to the fluororesin constituting the dielectric layer 2, so that the adhesion between the seed layer 3 and the dielectric layer 2 is small. Strength increases.

  The baking is preferably performed in an atmosphere containing a certain amount of oxygen in order to promote oxidation of metal particles near the interface between the seed layer 3 and the dielectric layer 2. In this case, the lower limit of the oxygen concentration in the firing atmosphere is preferably 1 ppm by volume, more preferably 10 ppm by volume. Further, the upper limit of the oxygen concentration is preferably 10,000 ppm by volume, more preferably 1,000 ppm by volume. If the oxygen concentration is less than the lower limit, the amount of metal oxide or the like generated in the vicinity of the interface between the seed layer 3 and the dielectric layer 2 is reduced, and the adhesion between the dielectric layer 2 and the seed layer 3 is reduced. There is a possibility that it cannot be improved. On the other hand, if the oxygen concentration exceeds the upper limit, the conductivity of the seed layer 3 may be reduced due to excessive oxidation of the metal particles.

  The drying can be performed, for example, at room temperature.

  As a minimum of the above-mentioned heat treatment temperature, 100 ° C is preferred and 150 ° C is more preferred. On the other hand, the upper limit of the temperature of the heat treatment is preferably 400 ° C, more preferably 350 ° C. When the heat treatment temperature is lower than the lower limit, the amount of metal oxide or the like generated near the interface between the seed layer 3 and the dielectric layer 2 is reduced, and the adhesion between the dielectric layer 2 and the seed layer 3 is reduced. There is a possibility that it cannot be improved. On the other hand, when the heat treatment temperature exceeds the upper limit, the dielectric layer 2 may be deformed. The heat treatment time is not particularly limited, but may be, for example, in a range from 30 minutes to 600 minutes.

<Base layer lamination process>
In the base layer laminating step, the base layer 4 is laminated on the other surface of the dielectric layer 2 as shown in FIG. 2C. In the base layer laminating step, for example, a metal foil constituting the base layer 4 is thermocompression-bonded to the dielectric layer 2. This thermocompression bonding is preferably performed under reduced pressure in order to prevent bubbles or voids from being formed between the base layer 4 and the dielectric layer 2. Further, in order to suppress oxidation of the base layer 4, it is preferable to perform the treatment under low oxygen conditions (for example, in a nitrogen atmosphere).

<Advantages>
In the base material 1 for a high-frequency printed wiring board, since the dielectric layer 2 is mainly composed of a fluororesin, the dielectric constant of the dielectric layer 2 is small, so that transmission loss can be reduced. In addition, since the high-frequency printed wiring board base material 1 is modified on one surface side of the dielectric layer 2, the seed layer 3 is easily brought into close contact with the one surface side. In particular, the base material 1 for a high-frequency printed wiring board is formed by modifying the surface of one side of the dielectric layer 2 so as to prevent the surface of the dielectric layer 2 from being roughened. Can be improved in adhesion. Therefore, the base material 1 for a high-frequency printed wiring board suppresses the roughening of the contact surface between the seed layer 3 and the dielectric layer 2 to prevent the propagation distance of the high-frequency characteristic signal from becoming longer. Loss due to the skin effect can be suppressed. Further, in the base material 1 for a high-frequency printed wiring board, since the average thickness of the seed layer 3 is in the above range, even when miniaturization is required, plating is formed to a certain thickness on one surface of the seed layer 3. be able to. Therefore, the base material 1 for a high-frequency printed wiring board can reduce transmission loss and improve high-frequency characteristics.

  Therefore, the method for manufacturing a base material for a high-frequency printed wiring board can easily and reliably manufacture a base material for a printed wiring board that can reduce transmission loss and improve high-frequency characteristics.

  In the method for producing a base material for a high-frequency printed wiring board, the seed layer forming step is performed by applying the ink containing metal particles having an average particle diameter in the above range to one surface of the film, and then applying the ink. Since the ink is fired, a dense and substantially uniform sintered body can be accurately formed on one surface side of the dielectric layer 2 without using expensive vacuum equipment necessary for physical vapor deposition such as sputtering. .

[Second embodiment]
<Substrate for high frequency printed wiring board>
The high frequency printed wiring board base material 11 of FIG. 3 is formed using the high frequency printed wiring board base material 1 of FIG. The high-frequency printed wiring board 11 of FIG. 3 includes a dielectric layer 2, a seed layer 3, a base layer 4, and a plating layer (first plating layer 12). The high-frequency printed wiring board 11 is a flexible printed wiring board having flexibility. The dielectric layer 2, the seed layer 3, and the base layer 4 are the same as those of the high-frequency printed wiring board substrate 1 of FIG.

(First plating layer)
The first plating layer 12 is laminated on one surface of the seed layer 3. The plating metal forming the first plating layer 12 enters not only the outer surface of the seed layer 3 but also the inside of the seed layer 3 (the gap between the metal particles forming the seed layer 3). If a void remains in the seed layer 3, the void portion serves as a fracture starting point, and the seed layer 3 is easily peeled off from the dielectric layer 2. In this void portion, the metal constituting the first plating layer 12 is removed. The filling prevents the dielectric layer 2 from peeling off. In addition, the conductivity of the first plating layer 12 is improved by filling the voids of the metal particles forming the seed layer 3 with the metal of the first plating layer 12. The plating method for forming the first plating layer 12 is not particularly limited, and may be electroless plating or electroplating. However, the gap between the metal particles forming the seed layer 3 can be more accurately determined. It is preferable to use electroless plating which can easily and surely increase the peel strength of the seed layer 3 and the dielectric layer 2 by filling.

  As the metal used for the electroless plating, copper, nickel, silver, or the like having good conductivity can be used. However, when the main component of the seed layer 3 is copper or a copper alloy, adhesion to the seed layer 3 is considered. Then, it is preferable to use copper or nickel. When a metal other than nickel is used for the electroless plating, it is preferable to use a plating solution containing nickel or a nickel compound in addition to the plating metal.

  The procedure of the electroless plating is not particularly limited, and includes, for example, a cleaning step, a rinsing step, an acid treatment step, a rinsing step, a pre-dip step, an activator step, a rinsing step, a reduction step, a rinsing step, and other known means. May be used for electroless plating.

  The metal used for the electroplating is not particularly limited, and may be the same metal as the metal used for the electroless plating. Also, the procedure of the electroplating is not particularly limited, and may be appropriately selected from known electroplating baths and plating conditions.

  The lower limit of the average thickness of the first plating layer 12 is preferably 0.2 μm, more preferably 0.3 μm. On the other hand, the upper limit of the average thickness of the first plating layer 12 is preferably 1 μm, more preferably 0.5 μm. If the average thickness of the first plating layer 12 is less than the lower limit, the metal forming the first plating layer 12 may not be sufficiently filled in the voids in the seed layer 3. Conversely, when the average thickness of the first plating layer 12 exceeds the above upper limit, the time required for electroless plating is lengthened, and the productivity may be reduced.

<Advantages>
Since the base material 11 for a high-frequency printed wiring board has the first plating layer 12, the gap between the metal particles forming the seed layer 3 is filled with the metal by plating. Therefore, the printed wiring board base material 11 can improve the peel strength between the seed layer 3 and the dielectric layer 2 and can also enhance the conductivity.

<High frequency printed wiring board>
The high-frequency printed wiring board 21 of FIG. 4 is formed using the high-frequency printed wiring board base material 11 of FIG. The high-frequency printed wiring board 21 includes the dielectric layer 2, the base layer 4, and the conductive pattern 22. The high-frequency printed wiring board 21 is a flexible printed wiring board having flexibility. The method of forming the high-frequency printed wiring board 21 is not particularly limited, and any of a semi-additive method and a subtractive method can be used. However, in order to make the cross section of the conductive pattern 22 a desired shape, it is preferable to use the semi-additive method. Hereinafter, a case where the high-frequency printed wiring board 21 is formed by a semi-additive method will be described. Note that the dielectric layer 2 and the base layer 4 are the same as the base material for the high-frequency printed wiring board in FIG.

(Conductive pattern)
The conductive pattern 22 is laminated on one surface of the dielectric layer 2. The conductive pattern 22 is formed by a so-called semi-additive method in which electroplating and etching are performed on the seed layer 3 and the first plating layer 12 of the base material 11 for a high-frequency printed wiring board in FIG. The procedure of electroplating is not particularly limited, and may be appropriately selected, for example, from known electroplating baths and plating conditions.

  The thickness of the conductive pattern 22 is set in accordance with what kind of printed circuit is to be produced, and is not particularly limited. For example, the lower limit of the average thickness of the conductive pattern 22 is preferably 1 μm, and more preferably 2 μm. Further, the upper limit of the average thickness of the conductive pattern 22 is preferably 100 μm, more preferably 50 μm. If the average thickness of the conductive pattern 22 is less than the above lower limit, the conductive pattern 22 may be easily damaged. On the other hand, when the average thickness of the conductive pattern 22 exceeds the upper limit, it may be difficult to make the high-frequency printed wiring board 21 thinner.

  The lower bottom and the upper bottom of the conductive pattern 22 are disposed substantially in parallel. Here, “substantially parallel” refers to a range in which the angle between the lower base and the upper base is 0 ° ± 10 °, and preferably a range of 0 ° ± 5 °. The “upper bottom” is a side facing the lower bottom.

  The lower limit of the average value of the length ratio of the upper base to the lower base in the cross-sectional shape of the conductive pattern 22 is preferably 0.9, and more preferably 0.95. If the average value of the length ratio is less than the lower limit, the cross-sectional area of the conductive pattern 22 may not be sufficiently large, and the transmission characteristics may not be sufficiently improved. In addition, the upper limit of the average value of the length ratio can be set to 1. In addition, it is preferable that the above-mentioned length ratio satisfies the above-mentioned range at least in the wiring portion included in the conductive pattern 22. Here, in the case where one surface of the conductive pattern 22 is curved in the thickness direction, the “upper bottom” is replaced by a virtual straight line at a position 9/10 of the average thickness from the lower bottom of the conductive pattern 22. Is also possible. Further, the “cross section of the conductive pattern” means a cross section having a minimum area, for example, a cross section in a plane perpendicular to the axial direction of the conductive pattern.

  The cross-sectional shape of the conductive pattern 22 is substantially rectangular. Specifically, the lower base in the cross-sectional shape of the conductive pattern 22 is defined as one side, and the length of the side adjacent to this side is equal to the average thickness of the conductive pattern 22. As a minimum, 0.9 is preferred and 0.95 is more preferred. If the average value of the cross-sectional area ratio is less than the lower limit, the cross-sectional area of the conductive pattern 22 may not be sufficiently large, and the transmission characteristics may not be sufficiently improved. In addition, the upper limit of the average value of the area ratio of the cross section can be set to 1. It is preferable that the area ratio satisfies the above range at least in a wiring portion included in the conductive pattern 22.

  The cross-sectional shape of the conductive pattern 22 can be adjusted, for example, by controlling the cross-sectional shape of a non-laminated region of the resist pattern described later.

<Production method of high frequency printed wiring board>
Next, a method for manufacturing the high-frequency printed wiring board will be described with reference to FIGS. 5A to 5C. Here, a method of forming the high-frequency printed wiring board by a semi-additive method will be described.

  The method for manufacturing the high-frequency printed wiring board includes a dielectric layer 2 containing fluororesin as a main component, one surface of which is modified, and a conductive pattern 22 laminated on one surface of the dielectric layer 2. It is used as a method for manufacturing the high-frequency printed wiring board 21. The high-frequency printed wiring board is manufactured by a semi-additive method using the above-described base material 11 for a high-frequency printed wiring board. The method for manufacturing a high-frequency printed wiring board includes a conductive pattern forming step.

<Conductive pattern forming step>
As shown in FIGS. 5A to 5C, the conductive pattern forming step includes forming a resist pattern Y on one surface of the first plating layer 12 and plating the surface of the first plating layer 12 exposed from the resist pattern Y. And a step of laminating the second plating layer 23, stripping the resist pattern Y, and etching the seed layer 3 and the first plating layer 12 using the second plating layer 23 as a mask.

(Resist pattern formation step)
In the resist pattern forming step, a resist pattern Y is formed on one surface of the first plating layer 12 as shown in FIG. 5A. Specifically, a resist film is laminated on one surface of the first plating layer 12, and then exposed and developed to form a resist pattern Y having a predetermined pattern. Examples of the method of laminating the resist film include a method of applying a resist composition on one surface of the first plating layer 12, a method of laminating a dry film photoresist on one surface of the first plating layer 12, and the like. Can be Exposure and development conditions of the resist film can be appropriately adjusted depending on the resist composition used and the like.

(Second plating layer lamination process)
In the second plating layer laminating step, as shown in FIG. 5B, electroplating is performed to form the second plating layer 23 in the non-laminated region of the resist pattern Y.

(Resist pattern stripping process)
In the resist pattern stripping step, the resist pattern Y is stripped from the first plating layer 12. Specifically, the resist pattern Y is stripped using a stripper. As the stripping solution, known ones can be used, for example, an alkaline aqueous solution such as sodium hydroxide and potassium hydroxide, an organic acid solution such as alkylbenzene sulfonic acid, and a polar solvent with an organic amine such as ethanolamine. A mixed solution is exemplified.

(Etching process)
In the etching step, as shown in FIG. 5C, the seed layer 3 and the first plating layer 12 are etched using the second plating layer 23 as a mask. By this etching, a conductive pattern 22 is formed on one surface of the dielectric layer 2.

<Advantages>
Since the high-frequency printed wiring board 21 is formed using the high-frequency printed wiring board base material 11, transmission loss can be reduced and high-frequency characteristics can be improved.

  Since the high-frequency printed wiring board 21 is modified on one surface side of the dielectric layer 2, plating can be formed to a certain thickness on one surface side of the seed layer. And it can form reliably. Further, by forming the high-frequency printed wiring board 21 by a semi-additive method, the cross section of the conductive pattern 22 can be easily formed into a desired shape. Therefore, the high-frequency printed wiring board 21 can improve the transmission characteristics by increasing the sectional area of the conductive pattern 22.

  Since the method for manufacturing the high-frequency printed wiring board uses the base material 11 for the high-frequency printed wiring board, the high-frequency printed wiring board 21 capable of reducing transmission loss and improving high-frequency characteristics can be easily and reliably manufactured. .

  Since the method of manufacturing the high-frequency printed wiring board is formed by a semi-additive method, the cross section of the conductive pattern 22 can be easily formed into a desired shape. Therefore, the method for manufacturing a high-frequency printed wiring board can improve the transmission characteristics by increasing the cross-sectional area of the conductive pattern 22.

[Other Embodiments]
The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is not limited to the configuration of the above-described embodiment, but is indicated by the appended claims, and is intended to include all modifications within the scope and meaning equivalent to the appended claims. You.

  For example, the seed layer is not limited to a sintered body as long as the average thickness is 2 μm or less, and may be made of, for example, an electroless plated metal. When the seed layer is composed of an electroless plating metal, examples of the metal include copper, nickel, aluminum, gold, silver, palladium, chromium, and alloys thereof. Among them, copper or a copper alloy that can increase conductivity and adhesion to a dielectric layer while suppressing cost is preferable. Even when the seed layer is made of an electroless plating metal, the seed layer can be formed on one surface side of the dielectric layer without requiring expensive vacuum equipment required for physical vapor deposition such as sputtering. it can. When the seed layer is made of an electroless plating metal, the average thickness of the seed layer and the arithmetic average roughness Ra of the other surface can be the same as those of the seed layer 3 in FIG. The seed layer may be made of, for example, a copper foil or the like in addition to the sintered body and the electroless plated metal.

  Only the surface of the dielectric layer on which the seed layer is laminated may be modified. In addition, the dielectric layer does not necessarily need to be modified on the entire surface of one surface, and may be modified only on a portion necessary for forming a conductive pattern.

  The dielectric layer does not necessarily need to be modified by a silane coupling agent, and may be modified by, for example, injecting a plasma gas such as oxygen, nitrogen, hydrogen, argon, or ammonia onto the surface of the dielectric layer. Can also. In this plasma treatment, the plasma is brought into contact with the surface of the dielectric layer to etch the fluororesin on the outer surface of the dielectric layer, and oxygen or nitrogen atoms are added to the outer surface to modify the surface of the dielectric layer. Quality. This plasma treatment may be performed using plasma of an inert gas containing a compound having a hydrophilic group.

  The high-frequency printed wiring board substrate does not necessarily have to have the first plating layer on one surface side of the seed layer. The base material for a high-frequency printed wiring board may form a conductive pattern by, for example, directly laminating a second plating layer on one surface of the seed layer.

  The base material for a high-frequency printed wiring board does not necessarily need to be used as a substrate of a flexible printed wiring board, and may be used as a substrate of a rigid printed wiring board. Further, the base layer does not necessarily have to be laminated on the entire surface of the other surface of the dielectric layer, and a conductive pattern may be appropriately formed by etching or the like.

  The base material for a high-frequency printed wiring board does not necessarily need to include the base layer on the other surface of the dielectric layer. The base material for the high-frequency printed wiring board may be formed by laminating a base layer in, for example, an arbitrary manufacturing process of the high-frequency printed wiring board.

  As described above, the high-frequency printed wiring board base material and the high-frequency printed wiring board of the present invention can reduce transmission loss, suppress loss due to the skin effect, improve high-frequency characteristics, and use high frequency. It is suitably used for communication equipment and the like. Further, the method of manufacturing a base material for a high-frequency printed wiring board and the method of manufacturing a high-frequency printed wiring board of the present invention manufacture a base material for a high-frequency printed wiring board and a high-frequency printed wiring board suitable for a communication device or the like using a high frequency. Suitable for

DESCRIPTION OF SYMBOLS 1, 11 High frequency printed wiring board base material 2 Dielectric layer 2a Fluororesin film 3 Seed layer 4 Base layers 5a, 5b Modified layer 12 First plating layer 21 High frequency printed wiring board 22 Conductive pattern 23 Second plating layer Y Resist pattern

Claims (11)

A dielectric layer having a modified layer containing a siloxane bond and a hydrophilic functional group on at least one surface side, containing a fluororesin as a main component,
A seed layer laminated on one surface of the modified layer of the dielectric layer,
The main component of the seed layer is a metal,
Ri der average thickness 2μm or less of the seed layer,
A base material for a high-frequency printed wiring board, wherein the other surface of the seed layer has an arithmetic average roughness Ra of 2 μm or less .   The base material for a high-frequency printed wiring board according to claim 1, wherein the metal is copper or a copper alloy. The seed layer is composed of a sintered body of metal particles,
The base material for a high-frequency printed wiring board according to claim 1 or 2, wherein the metal particles have an average particle size of 1 nm or more and 500 nm or less.   The base material for a high-frequency printed wiring board according to claim 1 or 2, wherein the seed layer is made of an electroless plating metal.   The high-frequency printed wiring board substrate according to any one of claims 1 to 4, wherein an average thickness of the seed layer is 10 nm or more and 1 µm or less. The base material for a high-frequency printed wiring board according to any one of claims 1 to 5 , further comprising a plating layer on one surface side of the seed layer. A dielectric layer having a modified layer containing a siloxane bond and a hydrophilic functional group on at least one surface side, containing a fluororesin as a main component,
A conductive pattern including a seed layer laminated on one surface of the modified layer of the dielectric layer,
The main component of the seed layer is a metal,
Ri der average thickness 2μm or less of the seed layer,
A high-frequency printed wiring board having an arithmetic mean roughness Ra of the other surface of the seed layer of 2 μm or less . The bottom of the cross-sectional shape of the conductive pattern is defined as one side, and the average value of the area ratio of the cross section of the conductive pattern to a rectangle whose length adjacent to this side is equal to the average thickness of the conductive pattern is 0.9 or more. Item 8. A high-frequency printed wiring board according to item 7 . A step of forming a modified layer containing a siloxane bond and a hydrophilic functional group on at least one surface side of a film containing a fluororesin as a main component,
Forming a seed layer on one surface of the modified layer of the film after the modification step,
The main component of the seed layer is a metal,
Ri der average thickness 2μm or less of the seed layer,
A method for producing a base material for a high-frequency printed wiring board , wherein the arithmetic mean roughness Ra of the other surface of the seed layer is 2 μm or less . The seed layer forming step,
A step of applying an ink in which metal particles are dispersed in a solvent to one surface of the film,
Baking the ink applied to one surface of the film,
The method for producing a substrate for a high-frequency printed wiring board according to claim 9 , wherein the metal particles have an average particle diameter of 1 nm or more and 500 nm or less. A dielectric layer having a modified layer containing a siloxane bond and a hydrophilic functional group on at least one surface side, containing a fluororesin as a main component,
And a conductive pattern laminated on one surface of the dielectric layer, comprising:
And a seed layer laminated on one surface of the modified layer of the dielectric layer and the dielectric layer, the main component of the seed layer is a metal state, and are the mean thickness 2μm or less of the seed layer And a method for manufacturing a high-frequency printed wiring board formed by using a base material for a high-frequency printed wiring board in which the other surface of the seed layer has an arithmetic average roughness Ra of 2 μm or less .

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