JP2015042718A - Porous polyimide film manufacturing method, porous polyimide film, composite film, wiring board, and multilayer wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous polyimide film which achieves a low dielectric constant while suppressing increase in the production cost, maintains mechanical characteristics by forming relatively small pores, and is suitably applicable as a substrate for an FPC or the like.SOLUTION: A production method of a porous polyimide film includes: a coating film formation step of forming a coating film by applying a coating liquid comprising a polar solvent, a polyimide precursor having a fluorine atom, and a compound that forms an amphoteric ion by complexing of carbon dioxide; a phase separation step of separating a phase of the polar solvent in the coating film by supplying carbon dioxide under pressure; a pore formation step of forming a plurality of pores in the coating film by vaporizing the polar solvent; and a heating step of imidizing the polyimide precursor by heating the coating film. The compound is a photocurable resin precursor having an amino group. The method preferably includes a step of curing the photocurable resin precursor by irradiating the coating film with light between the phase separation step and the pore formation step.

Description

  The present invention relates to a method for producing a porous polyimide film, a porous polyimide film, a composite film, a wiring board, and a multilayer wiring board.

  Since a portable information terminal such as a mobile phone is required to be thin, light, and easy to carry, the volume that can accommodate electronic components in the terminal is limited. Therefore, a flexible printed wiring board (FPC) that can be used by being folded may be used for mounting wiring and electronic components. In FPC, conductor wiring is formed on the surface of a flexible substrate. As a base material, a polyimide resin excellent in heat resistance, solvent resistance and insulation reliability is widely used.

  On the other hand, current portable information terminals are capable of high-speed and large-capacity communication. In such high-speed and large-capacity communication, a high-frequency signal flows through an electronic circuit on a substrate. When a high-frequency signal flows through an electronic circuit, transmission loss becomes a problem because the signal attenuates in proportion to the frequency. Therefore, it is desired that the FPC base material has a low dielectric constant and dielectric loss.

  As a technique for lowering the dielectric constant of a polyimide resin film used as a base material, it has been proposed to form a porous film (see, for example, JP 2012-007161 A). The porous polyimide film described in this publication is prepared by a method including the following steps (1) to (6).

(1) Step of forming a coating film by applying a resin solution containing a polar solvent, a polyimide precursor, and a photocurable resin precursor such as an acrylic monomer having a tertiary amino group on a substrate (2) Polar solvent A step of pre-drying to evaporate a part of the film from the coating film (3) A step of generating droplets of polar solvent in the coating film by dissolving carbon dioxide in the coating film under high pressure (4) Irradiation with ultraviolet rays A step of curing the photocurable resin precursor and fixing the shape of the droplets with the photocurable resin (5) a step of forming voids in the coating film by evaporating the droplets (6) The process of imidizing the polyimide precursor by heating the coating and vaporizing the photocurable resin

JP 2012-007161 A

  However, the polyimide resin precursor has a relatively low compatibility with other resins and precursors thereof, such as a photocurable resin precursor. Therefore, the polyimide precursor and the photocurable resin precursor are phase-separated, and the photocurable resin precursor is easily aggregated. As a result, the composite of the photocurable resin precursor and carbon dioxide also easily aggregates, so that the polar solvent droplets tend to aggregate to increase the pores. Depending on the application, there are concerns that the mechanical properties may decrease when the pores become large, and that the continuous pores are likely to be formed and that the unevenness of the wall surface when the through-holes are drilled in the polyimide resin film becomes large. It becomes. Moreover, there is a tendency that the position variation of the characteristics of the polyimide resin film becomes large.

  The polyimide resin precursor has a limit in solubility in a polar solvent, and it is possible to increase solubility by lowering the molecular weight, but there is a problem that mechanical properties and the like are lowered. When the content of the polar solvent in the material solution is large, when carbon dioxide is supplied in the step (3), it becomes difficult for the carbon dioxide and the tertiary amino group to form a complex. In order to avoid such an inconvenience, it is necessary to increase the supply amount of carbon dioxide, and this leads to an increase in production cost in combination with an increase in the use amount of the polar solvent.

  The present invention has been made on the basis of the above-mentioned circumstances, enables a reduction in dielectric constant while suppressing an increase in manufacturing cost, maintains mechanical characteristics by forming relatively small holes, and achieves FPC. An object of the present invention is to provide a porous polyimide film that can be suitably applied as an interlayer insulating film of a multilayer substrate or a multilayer wiring board.

The present invention
A coating film forming step of forming a coating film by applying a coating solution containing a polar solvent, a polyimide precursor having a fluorine atom, and a compound that forms amphoteric ions by complexing carbon dioxide;
A phase separation step of phase-separating the polar solvent in the coating film by supplying carbon dioxide under pressure;
A hole forming step of forming a plurality of holes in the coating film by evaporation of the polar solvent;
And a heating step of imidizing the polyimide precursor by heating the coating film.

Another invention is
It is the porous polyimide film manufactured by the manufacturing method of the said porous polyimide film.

Another invention is
A composite film in which a conductor film is formed on the surface of a substrate,
The base material is formed of the porous polyimide film.

Another invention is
A wiring board having a conductor pattern formed on the surface of a substrate,
The base material is formed of the porous polyimide film.

Another invention is
A multilayer wiring board provided with an interlayer insulating film,
The interlayer insulating film is formed of the porous polyimide film.

  According to the method for producing a porous polyimide film of the present invention, the mechanical characteristics are maintained by reducing the diameter of the pores while suppressing an increase in cost, and a porous polyimide film having a low dielectric constant is easily and reliably produced. it can. Therefore, the porous polyimide film of the present invention is suitably used for an FPC base material, an interlayer insulating film of a multilayer wiring board, and the like.

It is a process flow figure of the manufacturing method of the porous polyimide membrane concerning the present invention. It is a schematic diagram which shows an example of the processing apparatus used for the said manufacturing method. It is typical sectional drawing of the chamber of the processing apparatus of FIG. It is a typical perspective view for demonstrating the coating-film formation process in the said manufacturing method. It is the figure which showed typically the state of the coating film after a coating-film formation process. It is typical sectional drawing for demonstrating the preliminary drying process in the said manufacturing method. It is typical sectional drawing for demonstrating the preliminary hardening process in the said manufacturing method. It is typical sectional drawing for demonstrating the phase-separation process in the said manufacturing method. It is the figure which showed typically the state of the coating film after a phase-separation process. It is typical sectional drawing for demonstrating the ultraviolet irradiation process in the said manufacturing method. It is the figure which showed typically the state of the coating film after an ultraviolet irradiation process. It is the figure which showed typically the state of the coating film after an ultraviolet irradiation process. It is typical sectional drawing for demonstrating the void | hole formation process in the said manufacturing method. It is the figure which showed typically the state of the coating film after a void | hole formation process. It is typical sectional drawing for demonstrating the heating process in the said manufacturing method. It is the figure which showed typically the state of the coating film after a heating process.

[Description of Embodiment of the Present Invention]
The present invention made to solve the above problems
A coating film that forms a coating film by applying a coating solution containing a polar solvent, a polyimide precursor having a fluorine atom, and a compound that forms amphoteric ions by complexing carbon dioxide (hereinafter also simply referred to as “compound”). Forming process;
A phase separation step of phase-separating the polar solvent in the coating film by supplying carbon dioxide under pressure;
A hole forming step of forming a plurality of holes in the coating film by evaporation of the polar solvent;
And a heating step of imidizing the polyimide precursor by heating the coating film.

  According to the said manufacturing method, what has a fluorine atom as a polyimide precursor is contained in the coating liquid used in a coating-film formation process. A polyimide precursor having a fluorine atom is more compatible with other resins and its precursor than a polyimide precursor having no fluorine atom. Therefore, it can suppress that a polyimide precursor, other resin, and its precursor phase-separate, and can suppress appropriately the aggregation of the zwitterion formed by a carbon dioxide complex. As a result, it is possible to suppress an increase in the diameter of the polar solvent phase-separated in the coating film, and thus it is possible to reduce the diameter of the pores in the porous polyimide film. As a result, the dielectric constant of the porous polyimide film can be reduced while maintaining the mechanical characteristics. In addition, polyimides having fluorine atoms have a low molar polarizability and a large free volume (void formed between polymer chains). Therefore, in this respect as well, the dielectric constant is lower than that of polyimides having no fluorine atoms. Rate can be achieved. As described above, in this manufacturing method, it is possible to reduce the dielectric constant of the porous polyimide film, and to provide a porous polyimide film that can be suitably used as a substrate such as FPC, an interlayer insulating film of a multilayer wiring board, and the like. Is possible.

  Furthermore, a polyimide precursor having a fluorine atom has higher solubility in a polar solvent than a polyimide precursor having no fluorine atom. Therefore, the usage-amount of a polar solvent when dissolving the target quantity of a polyimide precursor in a polar solvent can be reduced. Moreover, since the usage-amount of a polar solvent can be reduced, a carbon dioxide can be effectively compounded and an amphoteric ion can be produced | generated appropriately. Therefore, the supply amount of carbon dioxide in the phase separation process may be reduced as compared with the case where a polyimide precursor having no fluorine atom is used. Thus, in the said manufacturing method, the raise of manufacturing cost can be suppressed by reducing the usage-amount of a polar solvent and a carbon dioxide.

The compound is a photocurable resin precursor having an amino group,
It is good to include the process of hardening the said photocurable resin precursor by the light irradiation with respect to the said coating film between the said phase-separation process and the said void | hole formation process.

  By including such a step, the shape of the polar solvent phase-separated in the phase separation step is fixed by the curing of the photocurable resin precursor. Therefore, a plurality of holes can be appropriately formed when the polar solvent is evaporated in the hole forming step, and deformation of the holes can be suppressed. As a result, since a high porosity can be realized, it is possible to provide a porous polyimide film in which a low dielectric constant is appropriately achieved. Moreover, there is a possibility that the increase in pore diameter due to coalescence of the separated polar solvents can be suppressed.

  Between the said coating-film formation process and the said phase-separation process, it is good to include the preliminary-curing process which irradiates light to the said photocurable resin precursor, and hardens a part of said photocurable resin precursor.

  By including such a pre-curing step, a part of the photo-curable resin precursor is cured, so that a phase separation structure with a polar solvent is easily formed, and this phase separation state can be appropriately maintained.

  As the photocurable resin precursor, N- (3-dimethylaminopropyl) methacrylamide, 2- (diethylamino) ethyl methacrylate, or N- (3-dimethylaminopropyl) acrylamide is preferable. By using these photocurable resin precursors, when carbon dioxide is supplied under pressure in the phase separation step, amphoteric ions can be appropriately formed with this carbon dioxide. Therefore, as a result of appropriate phase separation of the polar solvent, it is possible to appropriately reduce the dielectric constant by forming pores.

  It is good to include the preliminary drying process performed between the said coating-film formation process and the said phase-separation process, and evaporating a part of said polar solvent.

  By including such a preliminary drying step, the amount of the polar solvent contained in the coating film can be controlled, so that the amount and size of the pores formed in the polyimide film can be controlled to some extent. Moreover, since the polyimide precursor which has a fluorine atom has high solubility with respect to a polar solvent, it can reduce the quantity of a polar solvent required in order to dissolve a polyimide precursor. Therefore, when it is necessary to make the amount of the polar solvent contained in the coating film a target amount, the preliminary drying time can be shortened compared with the case where a polyimide precursor having no fluorine atom is used. As a result, it may be possible to suppress the non-uniform distribution of the solvent in the thickness direction and the increase in the pore diameter due to coalescence of the pores due to the long predrying time.

Yet another aspect of the present invention made to solve the above problems is as follows.
It is the porous polyimide film manufactured by the manufacturing method of the said porous polyimide film.

  Since the porous polyimide film is manufactured by the method for manufacturing the porous polyimide film, the dielectric constant is appropriately reduced while suppressing an increase in manufacturing cost and a decrease in mechanical characteristics. . Therefore, the porous polyimide film can be suitably used as a base material such as FPC, an interlayer insulating film of a multilayer wiring board, a separation film or a heat insulating film of a mixture.

  The average diameter of the holes is preferably 0.01 μm or more and 20 μm or less. As described above, when the average diameter of the holes is in the above range, it is possible to suppress the deterioration of the mechanical characteristics, the generation of continuous holes, and the occurrence of the position variation of the film characteristics while reducing the dielectric constant. Moreover, when the through-hole is formed in the said porous polyimide film by suppressing formation of the continuous void | hole, it is suppressed that the unevenness | corrugation of the inner surface of this through-hole becomes large. For this reason, it is possible to appropriately cope with a use in which the unevenness of the inner surface of the through hole becomes a problem.

  The porosity of the porous polyimide film is preferably 1% or more and 60% or less. Thus, by setting the porosity to the above range, both reduction in dielectric constant and mechanical characteristics can be appropriately achieved. Therefore, the said porous polyimide film can be used conveniently as base materials, such as FPC, the interlayer insulation film of a multilayer wiring board, etc.

Yet another aspect of the present invention made to solve the above problems is as follows.
A composite film in which a conductor film is formed on the surface of a substrate,
The composite film is characterized in that the base material is formed from the porous polyimide film.

  In the composite film, since the base material is formed from the porous polyimide film, a low dielectric constant of the base material is appropriately achieved. Therefore, the composite film can be suitably used as a composite film for producing an FPC for high-frequency signals.

Yet another aspect of the present invention made to solve the above problems is as follows.
A wiring board having a conductor pattern formed on the surface of a substrate,
The wiring board is characterized in that the base material is formed from the porous polyimide film.

  In the wiring board, since the base material is formed of the porous polyimide film, the base material is appropriately reduced in dielectric constant. Therefore, the wiring board can be suitably used as a wiring board for high-frequency signals.

Yet another aspect of the present invention made to solve the above problems is as follows.
A multilayer wiring board provided with an interlayer insulating film,
A multilayer wiring board, wherein the interlayer insulating film is formed of the porous polyimide film.

  In the multilayer wiring board, since the interlayer insulating film is formed of the porous polyimide film, the dielectric constant of the interlayer insulating film is appropriately reduced. Therefore, the multilayer wiring board can be suitably used as a multilayer wiring board for high-frequency signals.

[Details of the embodiment of the present invention]
A method for producing a porous polyimide film, a porous polyimide film, a composite film, a wiring board and a multilayer wiring board according to embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes are included within the meaning and range equivalent to the claim.

[Method for producing porous polyimide film]
As shown in FIG. 1, the method for producing the porous polyimide film includes a coating film forming process, a preliminary drying process, a preliminary curing process, a phase separation process, an ultraviolet irradiation process, a pore forming process, and a heating process. These steps can be performed using one or more devices. The preliminary drying step and the preliminary curing step can be omitted. Further, the preliminary curing step and the ultraviolet irradiation step are necessary only when a curable resin precursor such as a photocurable resin precursor described later is contained as a compound that is combined with carbon dioxide contained in the coating liquid. is there.

Here, an example of the processing apparatus used in the manufacturing method is shown in FIG. The processing apparatus 1 in FIG. 2 includes a CO ₂ cylinder 2, a UV light generator 3, and a chamber 4.

The CO ₂ cylinder 2 holds CO ₂ supplied into the chamber 4. The CO ₂ cylinder 2 is connected to the chamber 4 via a pipe 44.

  The UV light generation device 3 generates UV light to be irradiated in the ultraviolet irradiation process.

  The chamber 4 defines a space for performing various processes. As shown in FIG. 3, the chamber 4 is provided with a light projection window 41 on the upper wall 40, pipes 44 and 45 are connected to the side walls 42 and 43, and the hot plate 6 is accommodated therein.

  The light projection window 41 is a part for projecting the UV light generated in the UV light generation device 3 into the chamber 4. The light projection window 41 is not particularly limited as long as it can transmit UV light and has an appropriate strength. For example, a quartz glass plate is used.

Pipe 44 is for introducing the CO ₂ from the CO ₂ cylinder 2 into the chamber 4. The pipe 45 is for discharging CO ₂ in the chamber 4. Valves 46 and 47 are provided in the pipes 44 and 45. The valve 46 is for selecting a state in which CO ₂ is supplied into the chamber 4 and a state in which the valve ₂ is not supplied, and adjusts the supply pressure of CO _{2 to} the chamber 4 (internal pressure in the chamber 4). . The valve 47 is for selecting a state in which CO ₂ is discharged from the chamber 4 and a state in which it is not discharged, and adjusts the internal pressure of the chamber 4.

  The hot plate 6 includes a stage 60 and a heater 61. The stage 60 is a portion on which the substrate to be coated 51 on which the coating film 50 is formed is disposed. The stage 60 is made of a material having high thermal conductivity, such as aluminum or iron. The heater 61 is for heating the stage 60, and various known ones can be used, and a resistance heater is preferably used.

[Coating film forming process]
As shown in FIG. 4, the coating film forming step is performed by applying a coating liquid on the substrate 51 to be coated to form a coating film 50. This coating film forming step may be performed in the processing apparatus 1 or may be performed in an apparatus different from the processing apparatus 1.

<Coating substrate>
The coated substrate 51 is not particularly limited as long as it is not deteriorated by ultraviolet irradiation and does not deform at the heating temperature in the heating process. For example, it is made of metal, glass, resin, ceramics. Things can be used.

  When the metal coated substrate 51 is used, for example, copper, aluminum, or the like formed in a plate shape or a foil shape is used. In particular, when a metal foil such as a copper foil is used as the substrate 51 to be coated, when a porous polyimide film is formed on the substrate 51 to be coated, the metal foil is formed on the porous polyimide film. Therefore, the metal foil can be used as it is as a composite film without peeling off. Since this composite film has a conductive material such as copper foil formed on an insulating base material of a porous polyimide film, it can be used as a wiring board by forming a conductor pattern by etching the conductor. .

  In addition, when the porous polyimide film is peeled off after the porous polyimide film is formed on the substrate 51 to be coated, a known release agent is applied on the substrate 51 to be coated. The film 50 may be formed.

<Application method>
The method for applying the coating liquid to the substrate 51 to be coated is not particularly limited. For example, a bar coating method, a spin coating method, a dip coating method, a blade coating method, a spray method, a relief printing method, an intaglio printing method, Examples thereof include a lithographic printing method, a dispensing method, and an ink jet method. Among these, the bar coating method and the spin coating method are preferable.

<Coating liquid>
The coating liquid contains a polyimide precursor having a fluorine atom (hereinafter also referred to as “fluorine-containing polyimide precursor”), a compound that is complexed with carbon dioxide, and a polar solvent. In the range which does not inhibit, other arbitrary components may be included. As shown in the conceptual diagram of FIG. 5, the coating film formed by the coating liquid is in a state in which a compound that combines with carbon dioxide and a polar solvent are dispersed in a matrix of a fluorine-containing polyimide precursor. Conceivable. In FIG. 5, the example using the photocurable resin precursor which has the tertiary amino group mentioned later as a compound complexed with a carbon dioxide is shown.

(Fluorine-containing polyimide precursor)
As the fluorine-containing polyimide precursor, polyamic acid having fluorine atoms (hereinafter also referred to as “fluorine-containing polyamic acid”) is used. As such a fluorine-containing polyamic acid, for example, at least one hydrogen atom bonded to the carbon atom in the repeating unit is substituted with a fluorine atom or an organic group having a fluorine atom (hereinafter also referred to as “fluorine-containing group”). Things. 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 is substituted with a fluorine atom, and includes a “perfluoroalkyl group”. Specifically, a “fluoroalkyl group” is a group in which all hydrogen atoms of an alkyl group are substituted with fluorine atoms, and all hydrogen atoms other than one hydrogen atom at the end of the alkyl group are substituted with fluorine atoms. Group and the like.

  The “fluoroalkoxy group” means an alkoxy group in which at least one hydrogen atom is substituted with a fluorine atom, and includes a “perfluoroalkoxy group”. Specifically, a “fluoroalkoxy group” is a group in which all hydrogen atoms of an alkoxy group are substituted with fluorine atoms, and all hydrogen atoms other than one hydrogen atom at the end of the alkoxy group are substituted with fluorine atoms. Group and the like.

  The “fluoropolyether group” is a monovalent group having a plurality of alkylene oxide chains as a repeating unit and having an alkyl group or a hydrogen atom at the terminal, and the alkylene oxide chain and / or the terminal alkyl group or A monovalent group having a group in which at least one hydrogen atom in a hydrogen atom is substituted with a fluorine atom. “Fluoropolyether group” includes “perfluoropolyether group” having a plurality of perfluoroalkylene oxide chains as repeating units.

  The polyamic acid is obtained from, for example, a tetracarboxylic dianhydride and a diamine, and a fluorine-containing polyamic acid having a fluorine atom as at least one of the tetracarboxylic dianhydride and the diamine is used.

  Examples of the tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and 2,3,3 ′, 4′-biphenyltetracarboxylic acid. Dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 4,4′-oxydiphthalic dianhydride 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxy) Phenyl) propane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (3,4 -Dicarboxypheny ) Methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,2-bis (4- (4-aminophenoxy) phenyl) propane, 1,2,5,6-naphthalenetetracarboxylic dianhydride 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 3,3 ′, 4,4′-tetraphenylsilanetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, cyclobutane-1,2 3,4-tetracarboxylic dianhydride, and the like. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  As tetracarboxylic dianhydride which has a fluorine atom, what is represented by a following formula is preferable.

  Examples of the diamine include 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 2,4′-diaminodiphenyl ether, 2,2′-diaminodiphenyl ether, 4,4 ′. -Diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,4'-diaminodiphenylmethane, 2,2'-diaminodiphenylmethane, diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3, 4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,4'-diaminodiphenyl sulfone, 2,2'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 3,4'-dia Nodiphenyl sulfide, 3,3′-diaminodiphenyl sulfide, 2,4′-diaminodiphenyl sulfide, 2,2′-diaminodiphenyl sulfide, paraphenylenediamine, metaphenylenediamine, p-xylylenediamine, m-xylylenediamine O-tolidine, o-tolidine sulfone, 2,2′-dimethyl-4,4′-diaminobiphenyl, 2,2′-bistrifluoromethyl-4,4′-diaminobiphenyl, 4,4′-methylene-bis -(2,6-diethylaniline), 4,4'-methylene-bis- (2,6-diisopropylaniline), 2,4-diaminomesitylene, 1,5-diaminonaphthalene, 4,4'-benzophenonediamine, Bis- {4- (4′-aminophenoxy) phenyl} sulfone, 1,1, , 3,3,3-hexafluoro-2,2-bis (4-aminophenyl) propane, 2,2-bis {4- (4′-aminophenoxy) phenyl} propane, 3,3′-dimethyl-4 , 4′-diaminodiphenylmethane, 3,3 ′, 5,5′-tetramethyl-4,4′-diaminodiphenylmethane, bis {4- (3′-aminophenoxy) phenyl} sulfone, 2,2-bis (4 -Aminophenyl) propane, 1,4-diaminocyclohexane and the like. These diamines may be used alone or in combination of two or more.

  As the diamine having a fluorine atom, those represented by the following formula are preferred.

  Content of a fluorine-containing polyimide precursor is 50 mass% or more and 90 mass% or less in the total solid component in the said coating liquid, for example, Preferably they are 60 mass% or more and 85 mass% or less. By setting the content of the fluorine-containing polyimide precursor in the above range, pores can be appropriately formed.

(Compound compounded with carbon dioxide)
This compound forms zwitterions with carbon dioxide supplied in the phase separation step. Such a compound is not particularly limited as long as it can be complexed with carbon dioxide and can generate an amphoteric ion. For example, a compound having an amino group or the like can be exemplified, and a compound having a tertiary amino group is particularly preferable. preferable. Furthermore, in order to fix the shape of the polar solvent phase formed in the phase separation step, a photocurable resin precursor is preferable.

  Examples of the photocurable resin precursor having a tertiary amino group include N- (3-dimethylaminopropyl) methacrylamide, 2- (diethylamino) ethyl methacrylate, N- (3-dimethylaminopropyl) acrylamide, and acrylic. Examples include 2- (diethylamino) ethyl acid, 2- (dimethylamino) ethyl methacrylate, 2- (dimethylamino) ethyl acrylate, and the like. Among these, N- (3-dimethylaminopropyl) methacrylamide, 2- (diethylamino) ethyl methacrylate, and N- [3- (dimethylamino) propyl] acrylamide are preferable.

  The content of the compound complexed with carbon dioxide is, for example, 10% by mass or more and 50% by mass or less, and preferably 15% by mass or more and 40% by mass or less in the total solid components. By setting the content of the compound to be complexed with carbon dioxide within the above range, the polar solvent can be appropriately phase-separated and pores can be appropriately formed.

  When using a photocurable resin precursor having a tertiary amino group as a compound to be combined with carbon dioxide, an auxiliary agent (initiator) for curing the photocurable resin precursor is included in the coating liquid. It is preferable. The initiator may be selected according to the type of the photocurable resin precursor, but when using the photocurable resin precursor exemplified above, for example, 1-hydroxycyclohexyl phenyl ketone, diphenyl (2, 4,6-trimethylbenzoyl) phosphine oxide (common name: Lucirin TPO) can be used. As 1-hydroxycyclohexyl phenyl ketone, “Irgacure 184” manufactured by BASF Japan Ltd. can be suitably used.

  The content of the initiator is, for example, 5 parts by mass or more and 35 parts by mass or less, preferably 10 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the photocurable resin precursor. By setting the content of the initiator in the above range, the photocurable resin precursor can be appropriately cured after the phase separation of the polar solvent, and thus it is possible to form pores with a stable shape.

(Polar solvent)
Examples of the polar solvent include low molecular weight solvents such as N, N-dimethylacetamide, N-methylpyrodoline, N, N-dimethylformamide and the like.

  In addition, the amphoteric ions formed by complexing with carbon dioxide are difficult to form when water is present. Therefore, it is preferable to use a dehydrated solvent having a low water content as the polar solvent. The water content in the polar solvent is, for example, 100 ppm or less, preferably 50 ppm or less, more preferably 30 ppm or less.

  The content of the polar solvent is appropriately determined depending on, for example, the viscosity of the target coating liquid, the solubility of the solid component in the polar solvent, whether or not to perform a preliminary drying step, and the like. The content of the polar solvent is usually 50 parts by mass or more and 400 parts by mass or less, and preferably 70 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the solid component in the coating liquid.

(Optional component)
The coating liquid may contain various known arbitrary components as long as the effects of the present invention are not impaired, such as not inhibiting the formation of pores. As an arbitrary component, a hardening accelerator, a viscosity modifier, a flame retardant, an organic and inorganic filler etc. are mentioned, for example.

[Pre-drying process]
The preliminary drying step is a step of evaporating a part of the polar solvent. As shown in FIG. 6, the substrate 51 to be coated on which a coating film is formed is placed on the stage 60 accommodated in the chamber 4 and heated by the hot plate 6. The preliminary drying step is performed so that the volume content of the fluorine-containing polyimide precursor and the compound complexed with carbon dioxide in the coating film is increased, in other words, the volume content of the polar solvent is decreased. . Therefore, the preliminary drying step can be omitted when the content of the polar solvent in the coating liquid is small.

  The drying conditions in the preliminary drying step, for example, the preliminary drying temperature and the preliminary drying time may be determined by the type of the polar solvent, the content of the polar solvent in the coating liquid, the amount of the polar solvent to be evaporated, and the like.

  The preliminary drying temperature is, for example, 30 ° C. or more and 100 ° C. or less. The preliminary drying time affects the porosity, pore size, etc. in the fluorine-containing polyimide film, and the longer the preliminary drying time, the smaller the porosity and pore diameter tend to be. From this point of view, an optimal time can be selected as the preliminary drying time according to the purpose. The preliminary drying time is, for example, 30 seconds or more and 8,000 seconds or less.

[Precuring process]
The pre-curing step is a step necessary only when a curable resin precursor such as a photo-curable resin precursor is contained as a compound to be combined with carbon dioxide to be contained in the coating liquid as described above, and can be omitted. It is. Further, the preliminary curing step can be performed simultaneously with the preliminary drying step, or may be performed prior to the preliminary drying step.

  This pre-curing step is a step of irradiating a photocurable resin precursor with light such as UV light to cure (polymerize) a part of the photocurable resin precursor. As shown in FIG. 7, the preliminary curing step is generated in the UV light generation device 3 (see FIG. 2) via the projection window 41 on the coating film 50 on the substrate 51 to be coated placed on the hot plate 6. It is performed by irradiating the UV light. The light irradiation conditions in the preliminary curing step are, for example, the types of curable resin precursors and initiators, their contents, the types of polar solvents, the contents of polar solvents, the degree of curing to be achieved (degree of polymerization), and the coating liquid. It is determined appropriately according to the viscosity of the liquid.

In the case where an ultraviolet curable resin precursor is contained in the coating liquid as a photocurable resin precursor and the UV curing resin precursor is irradiated with UV light to perform a preliminary curing step, the irradiation wavelength, irradiation intensity, and irradiation of the UV light are performed. The time is, for example, 200 nm to 400 nm, 100 mW / cm ^{2 to} 500 mW / cm ² , 10 seconds to 300 seconds, respectively. Moreover, the wavelength of UV light is suitably selected according to the kind of photocurable resin precursor to be used.

[Phase separation process]
The phase separation step is performed by supplying carbon dioxide under pressure. This phase separation step is performed in order to separate the polar solvent that becomes pores in the polyimide resin precursor. As shown in FIGS. 2 and 8, the phase separation step is performed by supplying carbon dioxide from the CO ₂ cylinder 2 through the pipe 44 into the chamber 4. The carbon dioxide is dissolved in the applied solution by the pressurized supply of carbon dioxide. Carbon dioxide forms a complex with a compound such as a photocurable resin precursor and becomes zwitterions. This zwitterion causes the polar solvent to phase separate. That is, as shown in FIG. 9, many zwitterions exist around the phase-separated polar solvent.

  The supply pressure of carbon dioxide in the phase separation step is, for example, 2 MPa or more and 10 MPa or less, preferably 4 MPa or more and 6.5 MPa or less. The supply time of carbon dioxide is, for example, 30 seconds to 500 seconds, preferably 75 seconds to 200 seconds. If the supply pressure and supply time (supply amount) of carbon dioxide are less than the lower limit, the polar solvent may not be properly phase separated. On the other hand, even if the supply pressure of carbon dioxide and the supply time (supply amount) exceed the above upper limits, it is not possible to achieve porosity sufficient for the increase in pressure and supply amount, which may be disadvantageous in manufacturing cost. There is.

[Ultraviolet irradiation process]
An ultraviolet irradiation process is a process performed when the said coating liquid contains a photocurable resin precursor as a compound complexed with a carbon dioxide. As shown in FIG. 10, the ultraviolet irradiation process is performed in the same manner as the ultraviolet curing process, although the ultraviolet irradiation conditions are different. By this ultraviolet irradiation process, the polar solvent can be enclosed by curing the photocurable resin precursor as shown in FIG. More conceptually, as shown in FIG. 12, the polar solvent is phase-separated in the polyimide resin precursor, and the photocurable resin surrounds the polar solvent.

What is necessary is just to determine the ultraviolet irradiation conditions in an ultraviolet irradiation process according to the kind of photocurable resin and initiator to be used, content of these, etc. Ultraviolet irradiation intensity is, for example 100 mW / cm ² or more 500 mW / cm ² or less, preferably 150 mW / cm ² or more 300 mW / cm ² or less. The ultraviolet irradiation time is, for example, 10 seconds to 300 seconds, preferably 30 seconds to 100 seconds.

[Hole formation process]
The hole forming step is a step of forming a plurality of holes by evaporating the polar solvent. As shown in FIG. 13, the pore forming step is a part where the polar solvent is present by phase separation as shown in FIG. 14 by heating the coating film 50 by the hot plate 6 and evaporating the polar solvent. Holes are formed in At this time, by closing the valve 46 while opening the valve 47 (see FIG. 2), it is preferable to stop the supply of carbon dioxide while keeping the pressure in the chamber 4 at normal pressure. In addition, a void | hole formation process can also be abbreviate | omitted by performing simultaneously with the heating process mentioned later.

  When the photocurable resin precursor is used as the compound to be complexed with carbon dioxide, the heating in the pore formation step is preferably performed at a temperature lower than the boiling point of the polar solvent. The heating temperature and heating time in this pore formation step are determined according to the type of polar solvent used, the content of the polar solvent, the type of compound complexed with carbon dioxide, etc. Hereinafter, it is set to 60 seconds or more and 3600 seconds or less.

[Heating process]
The heating step is a step of curing by imidizing the fluorine-containing polyimide resin precursor. As shown in FIG. 15, this heating step is performed by heating the coating film 50 with the hot plate 6 as in the preheating step and the hole forming step. By performing the heating process, a fluorine-containing polyimide film having a plurality of pores is formed as shown in FIG. 16. In this process, a compound that is complexed with carbon dioxide such as a photocurable resin precursor is simultaneously evaporated. It is preferable to do so. As a result of curing of the polyimide precursor, a porous polyimide film having a large number of pores formed in the polyimide resin is obtained.

  What is necessary is just to determine the heating conditions in a heating process according to the kind of polyimide resin precursor and an electron pair donating compound. The heating temperature is at least the imidization temperature of the polyimide resin precursor, for example, 130 ° C. or higher and 350 ° C. or lower, preferably 150 ° C. or higher and 250 ° C. or lower. The heating time is, for example, 600 seconds or more and 7,200 seconds or less, preferably 1,800 seconds or more and 3,600 seconds or less.

  In addition, when the pore formation process (evaporation of polar solvent) is performed simultaneously in the heating process, if there is a large gap between the curing temperature of the polyimide resin precursor and the boiling point of the polar solvent, the heating temperature in the heating process is stepwise. Alternatively, the temperature may be increased continuously and gradually. By performing such heating, the evaporation of the polar solvent and the curing of the polyimide resin precursor can be appropriately performed.

<Advantages>
According to the said manufacturing method, what has a fluorine atom as a polyimide precursor is contained in the coating liquid used in a coating-film formation process. A polyimide precursor having a fluorine atom is more compatible with other resins and its precursor than a polyimide precursor having no fluorine atom. Therefore, it can suppress that a polyimide precursor, other resin, and its precursor phase-separate, and can suppress appropriately the aggregation of the zwitterion formed by a carbon dioxide complex. As a result, it is possible to suppress an increase in the diameter of the polar solvent phase-separated in the coating film, and thus it is possible to reduce the diameter of the pores in the porous polyimide film. As a result, the dielectric constant of the porous polyimide film can be reduced while maintaining the mechanical characteristics. In addition, polyimides having fluorine atoms have a low molar polarizability and a large free volume (void formed between polymer chains). Therefore, in this respect as well, the dielectric constant is lower than that of polyimides having no fluorine atoms. Rate can be achieved. As described above, in this manufacturing method, it is possible to reduce the dielectric constant of the porous polyimide film, and to provide a porous polyimide film that can be suitably used as a substrate such as FPC, an interlayer insulating film of a multilayer wiring board, and the like. Is possible.

  Furthermore, a polyimide precursor having a fluorine atom has higher solubility in a polar solvent than a polyimide precursor having no fluorine atom. Therefore, the usage-amount of a polar solvent when dissolving the target quantity of a polyimide precursor in a polar solvent can be reduced. Moreover, since the usage-amount of a polar solvent can be reduced, a carbon dioxide can be effectively compounded and an amphoteric ion can be produced | generated appropriately. Therefore, the supply amount of carbon dioxide in the phase separation process may be reduced as compared with the case where a polyimide precursor having no fluorine atom is used. Thus, in the said manufacturing method, the raise of manufacturing cost can be suppressed by reducing the usage-amount of a polar solvent and a carbon dioxide.

[Porous polyimide film]
The porous polyimide film of the present invention is obtained by the production method described above. The average diameter of the pores of the porous polyimide film is preferably 0.01 μm or more and 20 μm or less, more preferably 0.05 μm or more and 10 μm or less. When the average diameter of the pores exceeds 20 μm, there is a concern that the mechanical characteristics are deteriorated, continuous pores are easily formed, and unevenness of the wall surface when the through holes are drilled in the porous polyimide film is increased. This may be a problem depending on the application. Also, there is a tendency that the position variation of the characteristics of the porous polyimide film becomes large. On the other hand, when the average diameter of the pores is less than 0.01 μm, it is difficult to increase the porosity, and it is difficult to appropriately reduce the dielectric constant of the porous polyimide film.

  The porosity of the porous polyimide film is preferably 1% or more and 60% or less, and more preferably 20% or more and 50% or less. If the porosity exceeds 60%, the mechanical properties may be lowered depending on the pore diameter. On the other hand, if the porosity is less than 1%, the effect of reducing the dielectric constant of the porous polyimide film may be reduced.

  Thus, in the said porous polyimide film, coexistence of low dielectric constant and a mechanical characteristic can be aimed at by optimizing the average diameter and porosity of a void | hole. Similarly, it is possible to achieve both high heat insulation and mechanical characteristics, separation characteristics, permeation characteristics, and mechanical characteristics.

  The proportion of fluorine atoms in the polyimide film is, for example, 20 wt% or more and 60 wt% or less, preferably 30 wt% or more and 50 wt% or less. By setting the proportion of fluorine atoms within the above range, suitable characteristics can be obtained. In particular, in the case of a substrate material that requires a low dielectric constant and a low dielectric loss, it is possible to balance these characteristics with mechanical characteristics and thermal characteristics.

[Composite membrane]
The composite film of the present invention is obtained by forming a conductor film on the surface of a base material formed from the porous polyimide film having fluorine atoms. The composite film is used for forming a printed wiring board or a multilayer wiring board. The method for forming the conductor film is not particularly limited, and can be carried out by existing methods such as bonding with a conductor foil, formation of a liquid phase such as plating of a conductor metal, formation of a gas phase such as sputtering, and application of a conductor metal ink.

  In the composite film, since the base material is formed from the porous polyimide film, a low dielectric constant of the base material is appropriately achieved. Therefore, the composite film can be suitably used as a composite film for producing an FPC for high-frequency signals.

[Wiring board]
The wiring board of the present invention is obtained by forming a conductor pattern on the surface of a base material formed from the porous polyimide film having fluorine atoms. The conductor pattern is generally formed by etching the conductor of the composite film, but it can also be formed by partially plating a conductor metal on the porous polyimide film or by partially applying a conductor metal ink. It is.

  In the wiring board, since the base material is formed of the porous polyimide film, the base material is appropriately reduced in dielectric constant. Therefore, the wiring board can be suitably used as a wiring board for high-frequency signals.

[Multilayer wiring board]
The multilayer wiring board of the present invention includes an interlayer insulating film. This interlayer insulating film is an insulating film interposed between the layers of the multilayer wiring board. The interlayer insulating film is formed from the porous polyimide film having fluorine atoms.

  In the multilayer wiring board, since the interlayer insulating film is formed of the porous polyimide film, the dielectric constant of the interlayer insulating film is appropriately reduced. Therefore, the multilayer wiring board can be suitably used as a multilayer wiring board for high frequency signals.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Example 1]
<Formation of polyimide film>
(Synthesis of fluorine-containing polyimide precursor varnish)
68.5.17 g of N, N-dimethylacetamide (hereinafter referred to as “DMA”) is placed as a solvent in a 1 L flask equipped with a thermometer, a condenser tube, a calcium chloride packed tube, a stirrer, and a nitrogen blowing tube. Stir. To this, 131.88 g of 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl was added and completely dissolved while flowing 150 mL of nitrogen gas per minute from a nitrogen blowing tube. Thereafter, 182.95 g of 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride was added over 1 hour with stirring, and then heated at 80 ° C. with stirring for 2 hours. The solution was allowed to cool to obtain a polyimide precursor varnish.

(Coating liquid application process)
71.1% by mass of a previously synthesized polyimide precursor (polar solvent: fluorine-containing polyimide precursor = 70% by mass: 30% by mass) (hereinafter referred to as “FPI”), a photocurable resin precursor having an amino group 24.7% by mass of 2- (dimethylamino) ethyl methacrylate (hereinafter referred to as “DMA-EMA”) and 1-hydroxycyclohexyl phenyl ketone (“Irgacure 184” manufactured by BASF Japan Ltd.) (hereinafter “Irg-184”) as an initiator The coating liquid was obtained by mixing 4.2% by mass and stirring.

  This coating solution was applied onto a copper foil by a bar coating method to form a coating film. As the copper foil, a glossy surface of electrolytic copper foil having a thickness of 35 μm was used.

(Preliminary drying process)
The preliminary drying was performed for 150 seconds in a state where the copper foil on which the coating film was formed was placed on the hot plate 6 heated to 90 ° C.

(Phase separation process)
The phase separation step was performed by introducing carbon dioxide for 150 seconds at a pressure of 6.5 MPa while the hot plate 6 was heated to 40 ° C.

(UV irradiation process)
The ultraviolet irradiation process was performed by irradiating ultraviolet rays with an irradiation intensity of 187 mW / cm ² through the projection window 41 for 60 seconds while applying the pressure of carbon dioxide gas.

(Hole formation process)
The pore formation step was performed by evaporating the polar solvent 11 by gradually lowering the pressure in the chamber to normal pressure, removing the coating film from the chamber 4 and leaving it in the atmosphere.

(Heating process)
The heating process was performed by heat-treating at 110 ° C. for 60 minutes in a nitrogen atmosphere, and further heat-treating at 210 ° C. for 60 minutes to imidize the polyamic acid and vaporize the photocurable resin and the initiator. . As a result, a fluorine-containing porous polyimide film was obtained.

[Examples 2 to 5]
A fluorine-containing porous polyimide membrane was prepared in the same manner as in Example 1 except that the contents of the resin varnish, photocurable resin precursor and initiator, and the conditions of the drying step and the heat treatment step were as shown in Table 1. Formed.

[Comparative Example 1]
In Example 2, the fluorine-containing polyimide film was formed by performing heat treatment without passing through the phase separation step, the ultraviolet irradiation step, and the pore formation step (Table 1).

[Comparative Example 2]
(Synthesis of polyimide precursor varnish not containing fluorine)
In a 1 L flask equipped with a thermometer, a condenser tube, a calcium chloride packed tube, a stirrer, and a nitrogen blowing tube, 861.63 g of DMA was added as a solvent and stirred. To this, 78.55 g of 4,4′-diaminodiphenyl ether was added and completely dissolved while flowing 150 mL of nitrogen gas from the nitrogen blowing tube per minute. Thereafter, 85.57 g of pyromellitic dianhydride was added with stirring over 1 hour, and then heated at 80 ° C. for 1 hour with stirring. The solution was allowed to cool to obtain a polyimide precursor varnish.

  A porous polyimide film containing no fluorine was obtained from the composition and process conditions shown in Table 1 using the obtained resin varnish.

Abbreviations in Table 1 are as follows.
FPI: polyimide precursor having fluorine PI: polyimide precursor DMA: N, N-dimethylacetamide DMA-EMA: 2- (dimethylamino) ethyl methacrylate DEA-EMA: 2- (diethylamino) ethyl methacrylate Irg-184: 1- Hydroxycyclohexyl phenyl ketone ("Irgacure 184"; manufactured by BASF Japan)
Lucirin TPO: Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide

<Evaluation>
The porous polyimide resins of Examples 1 to 5 and Comparative Examples 1 and 2 were evaluated for the pore formation state, porosity, pore diameter, and dielectric constant. The evaluation results are shown in Table 2.

(Hole formation state)
The vacancy formation state was confirmed by confirming the presence and extent of vacancy formation from a cross-sectional photograph taken with a scanning electron microscope (“JSM-6700F” manufactured by JEOL Ltd.). This hole formation state was evaluated according to the following criteria.

○: Homogeneous pores are observed Δ: Pore is observed but non-homogeneous (some parts do not have pores)
×: No pores are observed

(Porosity)
The porosity was calculated from the density measured by the dimensional method using the following formula.

    Porosity = [1− (density of porous polyimide film / density of non-porous polyimide film)] × 100

(Average diameter of holes)
The average diameter of the holes (hole diameter) was determined using image analysis software ("Image J" from National Institute of Health) from a cross-sectional photograph taken with a scanning electron microscope ("JSM-6700F" from JEOL Ltd.). It calculated using the following formula from the cross-sectional area of the holes calculated in the above.

    Hole diameter = (hole cross-sectional area / 3.141) ^ (1/2) × 2

(Dielectric constant)
The dielectric constant of the porous polyimide film was measured with a cavity resonator method dielectric constant measuring device (“KF604A” manufactured by Kanto Electronics Application Development Co., Ltd.).

  The dielectric constant of the porous fluorine-containing polyimide film is 2.23 to 2.72 (Examples 1 to 5), which is lower than the dielectric constant of 2.80 (Comparative Example 1) of the non-porous fluorine-containing polyimide film. doing. Moreover, the dielectric constant of the polyimide film made porous by using a resin varnish that does not contain fluorine as the resin varnish is 2.75 (Comparative Example 2), and low dielectric constant is obtained by containing fluorine as in Examples 1-5. It is also being streamlined.

  According to the method for producing a porous polyimide film of the present invention, the mechanical characteristics are maintained by reducing the diameter of the pores while suppressing an increase in cost, and a porous polyimide film having a low dielectric constant is easily and reliably produced. it can. Therefore, the porous polyimide film of the present invention is suitably used for an FPC base material, an interlayer insulating film of a multilayer wiring board, and the like.

1 processor 2 CO ₂ cylinder 3 UV generator 4 chamber 40 upper wall 41 projecting window 43 side walls 44, 45 pipe 47 valve 50 coating 51 coating film forming material 6 hotplate 60 stage 61 heater

Claims (11)

A coating film forming step of forming a coating film by applying a coating solution containing a polar solvent, a polyimide precursor having a fluorine atom, and a compound that forms amphoteric ions by complexing carbon dioxide;
A phase separation step of phase-separating the polar solvent in the coating film by supplying carbon dioxide under pressure;
A hole forming step of forming a plurality of holes in the coating film by evaporation of the polar solvent;
A heating step of imidizing the polyimide precursor by heating the coating film. The compound is a photocurable resin precursor having an amino group,
The manufacturing method of the porous polyimide film of Claim 1 including the process of hardening the said photocurable resin precursor by light irradiation with respect to the said coating film between the said phase-separation process and the said void | hole formation process.   The method according to claim 2, further comprising a preliminary curing step of irradiating the photocurable resin precursor with light between the coating film forming step and the phase separation step to cure a part of the photocurable resin precursor. The manufacturing method of the porous polyimide membrane of description.   4. The photocurable resin precursor is N- (3-dimethylaminopropyl) methacrylamide, 2- (diethylamino) ethyl methacrylate, or N- (3-dimethylaminopropyl) acrylamide. The manufacturing method of the porous polyimide membrane of description.   The porous polyimide film according to any one of claims 1 to 4, further comprising a preliminary drying step that is performed between the coating film forming step and the phase separation step and evaporates a part of the polar solvent. Manufacturing method.   The porous polyimide film manufactured by the manufacturing method of the porous polyimide film of any one of Claims 1-5.   The porous polyimide film according to claim 6, wherein the average diameter of the pores is 0.01 μm or more and 20 μm or less.   The porous polyimide film according to claim 6 or 7, wherein the porosity is 1% or more and 60% or less. A composite film in which a conductor film is formed on the surface of a substrate,
A composite film, wherein the substrate is formed from the porous polyimide film according to any one of claims 6 to 8. A wiring board having a conductor pattern formed on the surface of a substrate,
A wiring board, wherein the substrate is formed of the porous polyimide film according to any one of claims 6 to 8. A multilayer wiring board provided with an interlayer insulating film,
A multilayer wiring board, wherein the interlayer insulating film is formed from the porous polyimide film according to any one of claims 6 to 8.

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