Polyimide precursor composition, polyimide resin, wiring circuit board, and electronic device

Abstract

The polyimide precursor composition includes a polyamic acid, a photosensitive agent, and a development accelerator. The development accelerator is composed of parabens having a C1‒C4 hydrocarbon group, and the blending amount of the development accelerator per 100 parts by mass of the polyamic acid (solid content) is 5.0-30.0 parts by mass. Further, in the polyamic acid, the transmittance at a wavelength of 420 nm measured by a first transmittance measurement is 1.30% or less.

Description

Polyimide precursor composition, polyimide resin, wiring circuit board, and electronic device

[0001] The present invention relates to a polyimide precursor composition, a polyimide resin, a wiring circuit board, and an electronic device.

[0002] BACKGROUND ART Conventionally, a laminate in which a metal substrate, an insulating layer, a wiring layer, and a coating layer are laminated has been known as a wired circuit board used in an electronic device.

[0003] As a material for the insulating layer and the covering layer used in such a wired circuit board, for example, a polyimide precursor composition is known (see, for example, Patent Document 1 below).

[0004] Specifically, Example 8 of Patent Document 1 discloses a polyimide precursor composition containing a polyamic acid that is a reaction product of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as an acid anhydride component, p-phenylenediamine (PPD) and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) as diamine components, 1-ethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-4-hydropyridine as a photosensitizer, and hexylparaben as a development accelerator.

[0005] International Publication No. 2023 / 021961 Pamphlet

[0006] However, since the polyamic acid contained in the polyimide precursor composition of Patent Document 1 has high transmittance, there is a risk of inspection failures occurring in product inspections carried out during the manufacturing process of electronic components such as wiring circuit boards that include an insulating layer (polyimide resin) formed from such a polyimide precursor composition. Product inspection is a process for detecting defects in the product (electronic component) (e.g., foreign matter in the insulating layer, dimensional defects in the insulating layer, shape defects in the insulating layer, discoloration due to oxidation of the wiring layer (wiring pattern), breaks in the wiring layer (wiring pattern), and chips in the wiring layer (wiring pattern)). Inspection failures occur when such product defects are overlooked or when non-product defects are excessively detected.

[0007] Furthermore, the polyimide resin formed from the polyimide precursor composition is required to have suitable patterning properties.

[0008] The present invention aims to provide a polyimide precursor composition, a polyimide resin, a wiring circuit board, and an electronic device that suppress the occurrence of inspection defects and have appropriate patterning properties.

[0009] The term "appropriate patterning ability" means that the cross-sectional shape of the polyimide resin formed from the polyimide precursor composition is such that the sides are not excessively constricted and are not excessively inclined. Preferably, the cross-sectional shape of the polyimide resin formed from the polyimide precursor composition is substantially rectangular.

[0010] The present invention [1] provides a polyimide precursor composition comprising a polyamic acid, a photosensitizer, and a development accelerator, wherein the development accelerator is a paraben having a hydrocarbon group containing 1 to 4 carbon atoms, and the amount of the development accelerator blended is 5.0 parts by mass or more and 30.0 parts by mass or less per 100 parts by mass of the polyamic acid (solid content), and the polyamic acid has a transmittance of 1.30% or less at a wavelength of 420 nm as measured by the first transmittance measurement described below. (First Transmittance Measurement) The polyamic acid is coated on a polyethylene terephthalate film so that the thickness after drying is 20 μm. The coated polyamic acid is dried at 165° C. for 3 minutes to obtain a coating film of the polyamic acid. The transmittance of the coating film at a wavelength of 420 nm is measured using a spectrophotometer.

[0011] The present invention [2] includes the polyimide precursor composition according to the above [1], wherein the polyamic acid has a transmittance of 1.00% or less at a wavelength of 420 nm as measured by the second transmittance measurement described below. (Second Transmittance Measurement) The polyamic acid is coated on a copper alloy so that the thickness after curing is 20 μm. The coated polyamic acid is heated at 360° C. for 4 hours to cure it, thereby obtaining a polyamic acid film. The transmittance of the film at a wavelength of 420 nm is measured using a spectrophotometer.

[0012] The present invention [3] includes the polyimide precursor composition according to the above [1] or [2], in which the amount of the development accelerator blended is less than 20.0 parts by mass per 100 parts by mass of the polyamic acid (solid content).

[0013] The present invention [4] includes the polyimide precursor composition according to any one of the above [1] to [3], in which the amount of the development accelerator blended is more than 10.0 parts by mass per 100 parts by mass of the polyamic acid (solid content).

[0014] The present invention [5] includes the polyimide precursor composition according to any one of the above [1] to [4], wherein the development accelerator comprises butylparaben.

[0015] The present invention [6] includes a polyimide resin that is a cured product of the polyimide precursor composition according to any one of the above [1] to [5].

[0016] The present invention [7] includes a printed circuit board containing the polyimide resin described in the above [6].

[0017] The present invention [8] includes an electronic device including the wired circuit board described in [7] above.

[0018] The polyimide precursor composition of the present invention comprises a polyamic acid, a photosensitizer, and a development accelerator, the development accelerator being a paraben having a hydrocarbon group containing 1 to 4 carbon atoms, the amount of the development accelerator being 5.0 parts by mass or more and 30.0 parts by mass or less per 100 parts by mass of the polyamic acid (solid content), and the polyamic acid exhibits a transmittance of 1.30% or less at a wavelength of 420 nm as measured in a first transmittance measurement. Therefore, the occurrence of inspection defects is suppressed, and the composition has suitable patterning properties.

[0019] The polyimide resin of the present invention is formed from the polyimide precursor composition of the present invention, and therefore, the occurrence of inspection defects is suppressed and further, the polyimide resin has appropriate patterning properties.

[0020] The wired circuit board of the present invention contains the polyimide resin of the present invention. Therefore, the occurrence of inspection defects can be suppressed. Furthermore, the wired circuit board has appropriate patterning properties, thereby improving reliability.

[0021] The electronic device of the present invention includes the wired circuit board of the present invention. Therefore, the occurrence of inspection defects can be suppressed. Furthermore, the reliability is improved by having appropriate patterning properties.

[0022] Figures 1A to 1C show an example of a method for producing a wired circuit board of the present invention. Figure 1A shows a step of forming an insulating layer, and Figures 1B and 1C show a step of forming a wiring layer. Figures 2D and 2E show an example of a method for producing a wired circuit board of the present invention, following Figure 1C. Figures 2D and 2E show a step of forming a coating layer.

[0023] 1. Polyimide Precursor Composition The polyimide precursor composition of the present invention contains a polyamic acid, a photosensitizer, and a development accelerator. The polyimide precursor composition can be patterned by photolithography and becomes a polyimide resin by heating.

[0024] <Polyamic Acid> Polyamic acid is a polyimide precursor, for example, a reaction product of an acid dianhydride component and a diamine component. In polyamic acid, adjacent amide groups and carboxyl groups in the repeating unit react (imidization reaction) to form an imide group-containing closed ring structure, thereby forming a polyimide resin. The imidization reaction proceeds, for example, by heating.

[0025] [Acid Dianhydride Component] The acid dianhydride component is not particularly limited as long as the polyamic acid reaction product has a transmittance at a wavelength of 420 nm measured in the first transmittance measurement described below that satisfies a predetermined range. Examples of the acid dianhydride component include tetracarboxylic acid dianhydrides. Examples of the tetracarboxylic acid dianhydrides include aliphatic tetracarboxylic acid dianhydrides and aromatic tetracarboxylic acid dianhydrides. Preferably, aromatic tetracarboxylic acid dianhydrides are used.

[0026] Examples of the aliphatic tetracarboxylic dianhydride include cyclopentanetetracarboxylic dianhydride and tricarboxycyclopentylacetic dianhydride.

[0027] Examples of aromatic tetracarboxylic dianhydrides include benzenetetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, biphenylsulfonetetracarboxylic dianhydride, and naphthalenetetracarboxylic dianhydride.

[0028] Examples of benzenetetracarboxylic dianhydrides include benzene-1,2,4,5-tetracarboxylic dianhydride (also known as pyromellitic dianhydride). Examples of benzophenone tetracarboxylic dianhydrides include 3,3'-4,4'-benzophenone tetracarboxylic dianhydride. Examples of biphenyl tetracarboxylic dianhydrides include 3,3'-4,4'-biphenyl tetracarboxylic dianhydride, 2,2'-3,3'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl tetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride. Examples of biphenyl sulfone tetracarboxylic dianhydrides include 3,3',4,4'-biphenyl sulfone tetracarboxylic dianhydride. Examples of naphthalenetetracarboxylic dianhydrides include 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,4,5-naphthalenetetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride.

[0029] The acid dianhydride component may be used alone or in combination of two or more kinds.

[0030] From the viewpoint of mechanical strength, the acid dianhydride component preferably comprises a tetracarboxylic dianhydride. More preferably, it comprises an aromatic tetracarboxylic dianhydride. Even more preferably, it comprises biphenyltetracarboxylic dianhydride. Particularly preferably, it comprises 3,3'-4,4'-biphenyltetracarboxylic dianhydride. 3,3'-4,4'-biphenyltetracarboxylic dianhydride is sometimes abbreviated as BPDA.

[0031] [Diamine Component] The diamine component is not particularly limited as long as the polyamic acid reaction product has a transmittance at a wavelength of 420 nm measured in the first transmittance measurement described below that falls within a predetermined range. Examples of the diamine component include aromatic diamines and aliphatic diamines. Preferably, aromatic diamines are used.

[0032] Examples of aromatic diamines include aromatic diamines having a single aromatic ring and aromatic diamines having multiple aromatic rings.

[0033] Examples of aromatic diamines having a single aromatic ring include phenylenediamine and its derivatives, and xylylenediamine. Phenylenediamine is preferred from the viewpoint of increasing the planarity of the reaction product, polyamic acid.

[0034] In the polyamic acid reaction product, when the planarity is increased, the transmittance at a wavelength of 420 nm measured in the first transmittance measurement described below can be prevented from becoming excessively high. In other words, if the diamine component contains phenylenediamine, the transmittance at a wavelength of 420 nm measured in the first transmittance measurement described below can be adjusted to fall within a predetermined range, thereby preventing inspection defects.

[0035] Examples of phenylenediamines include o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine. Preferably, p-phenylenediamine is used. p-Phenylenediamine is sometimes abbreviated as PDA.

[0036] Examples of the phenylenediamine derivatives include those in which an alkyl group is bonded to phenylenediamine, such as 4-methyl-1,2-phenylenediamine, 4-methyl-1,3-phenylenediamine, 4,5-dimethyl-1,2-phenylenediamine, 2,5-dimethyl-1,4-phenylenediamine, and 2,4,6-trimethyl-1,3-phenylenediamine.

[0037] Xylylenediamines include, for example, m-xylylenediamine and o-xylylenediamine.

[0038] Examples of aromatic diamines having multiple aromatic rings include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminophenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, and 3,3'-diaminodiphenylmethane. Examples of suitable diaminodiphenyl ethers include 4,4'-diaminodiphenyl ether, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane, 4,4'-diaminobenzophenone, benzidine, 3,3'-dimethylbenzidine (o-tolidine), 2,2'-dimethylbenzidine (m-tolidine), 3,3'-dimethoxybenzidine, and 2,2'-dimethoxybenzidine. In order to enhance the planarity of the polyamic acid reaction product, 4,4'-diaminodiphenyl ether and m-tolidine are preferred. 4,4'-Diaminodiphenyl ether is sometimes abbreviated as ODA. Furthermore, m-tolidine is sometimes abbreviated as m-TD.

[0039] In the polyamic acid reaction product, when the planarity is increased, the transmittance at a wavelength of 420 nm measured in the first transmittance measurement can be prevented from becoming excessively high. In other words, if the diamine component contains 4,4'-diaminodiphenyl ether and / or m-tolidine, the transmittance at a wavelength of 420 nm measured in the first transmittance measurement described below can be adjusted to fall within a predetermined range, thereby preventing inspection defects.

[0040] An example of an aromatic diamine having multiple aromatic rings is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, in which the methyl groups of m-tolidine are substituted with trifluoromethyl. However, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl has high three-dimensionality (low planarity), and the polyamic acid, which is the reaction product, also has high three-dimensionality. Therefore, the polyamic acid, which is the reaction product, may have an excessively high transmittance at a wavelength of 420 nm, as measured in the first transmittance measurement described below.

[0041] Examples of aliphatic diamines include hexamethylenediamine, 1,8-diaminooctane, 1,12-diaminododecane, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane.

[0042] The diamine component may be used alone or in combination of two or more. Preferably, two or more are used in combination. More preferably, an aromatic diamine having a single aromatic ring and an aromatic diamine having multiple aromatic rings are used in combination.

[0043] The diamine component includes, for example, an aromatic diamine. Preferably, it includes an aromatic diamine having a single aromatic ring and an aromatic diamine having multiple aromatic rings. Preferably, it includes p-phenylenediamine and 4,4'-diaminodiphenyl ether and / or m-tolidine. More preferably, it consists of p-phenylenediamine and 4,4'-diaminodiphenyl ether, or p-phenylenediamine and m-tolidine.

[0044] When the diamine component contains an aromatic diamine having a single aromatic ring (for example, p-phenylenediamine), the content (molar fraction) of the aromatic diamine having a single aromatic ring in the diamine component is, for example, 10 mol% or more, preferably 30 mol% or more, more preferably 50 mol% or more, even more preferably 60 mol% or more, and for example, 99 mol% or less, preferably 95 mol% or less, more preferably 90 mol% or less, even more preferably 85 mol% or less.

[0045] When the diamine component contains an aromatic diamine having multiple aromatic rings (e.g., 4,4'-diaminodiphenyl ether, m-tolidine), the content (molar fraction) of the aromatic diamine having multiple aromatic rings in the diamine component is, for example, 1 mol% or more, preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, and for example, 90 mol% or less, preferably 70 mol% or less, more preferably 50 mol% or less, even more preferably 40 mol% or less.

[0046] The polyamic acid is obtained by reacting an acid dianhydride component and a diamine component in an organic solvent. Specifically, the polyamic acid is obtained by reacting an acid dianhydride component containing 3,3',4,4'-biphenyltetracarboxylic dianhydride with a diamine component containing p-phenylenediamine and 4,4'-diaminodiphenyl ether and / or m-tolidine in an organic solvent.

[0047] The reaction temperature of the acid dianhydride component and the diamine component is, for example, 10° C. to 150° C., and the reaction time is, for example, 6 hours to 24 hours. Furthermore, the acid dianhydride component and the diamine component are reacted, for example, under atmospheric pressure.

[0048] The acid dianhydride component and the diamine component are selected from the molar amount of the acid anhydride group (—CO—O—CO—) of the acid dianhydride component and the molar amount of the amino group (—NH ２ ) are mixed in an amount equivalent to the molar amount of the hydroxybenzoate.

[0049] As described above, the polyamic acid is obtained as a solution. The organic solvent is not particularly limited, and examples thereof include known organic solvents, and preferred examples include the organic solvents described below.

[0050] The solids concentration of the polyamic acid solution is, for example, 1 mass % or more, preferably 3 mass % or more, and for example, 60 mass % or less, preferably 50 mass % or less.

[0051] The polyamic acid includes, for example, a first structural unit represented by the following formula (1). Preferably, the polyamic acid includes a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2) or (3). More specifically, if the acid dianhydride component includes 3,3'-4,4'-biphenyltetracarboxylic dianhydride and the diamine component includes p-phenylenediamine, the polyamic acid includes a first structural unit represented by the following formula (1). Furthermore, if the acid dianhydride component includes 3,3'-4,4'-biphenyltetracarboxylic dianhydride and the diamine component includes 4,4'-diaminodiphenyl ether, the polyamic acid includes a second structural unit represented by the following formula (2). Furthermore, if the acid dianhydride component includes 3,3'-4,4'-biphenyltetracarboxylic dianhydride and the diamine component includes m-tolidine, the polyamic acid includes a second structural unit represented by the following formula (3).

[0052]

[0053]

[0054]

[0055] The content of the polyamic acid (solid content) in the polyimide precursor composition (solid content) is, for example, 50% by mass to 95% by mass, preferably 55% by mass to 90% by mass, more preferably 60% by mass to 85% by mass, even more preferably 65% ​​by mass to 85% by mass, and particularly preferably 70% by mass to 85% by mass.

[0056] The content of polyamic acid (solid content) in the polyimide precursor composition (solid content) is, for example, 50 mass% or more, preferably 55 mass% or more, more preferably 60 mass% or more, even more preferably 65 mass% or more, and particularly preferably 70 mass% or more, and for example, 95 mass% or less, preferably 90 mass% or less, more preferably 85 mass% or less.

[0057] When the content of polyamic acid (solid content) in the polyimide precursor composition (solid content) is within the above range, the content of the development accelerator can be adjusted to an appropriate range, and appropriate patterning properties can be obtained.

[0058] In the polyamic acid, the transmittance at a wavelength of 420 nm measured by the first transmittance measurement described below is 1.30% or less, preferably 1.25% or less, more preferably 1.20% or less, even more preferably 1.15% or less, and for example, 0.1% or more.

[0059] (First Transmittance Measurement) Polyamic acid is coated onto a polyethylene terephthalate film so that the thickness after drying is 20 μm. The coated polyamic acid is dried at 165° C. for 3 minutes to obtain a polyamic acid coating film. The transmittance of the polyamic acid coating film at a wavelength of 420 nm is measured using a spectrophotometer.

[0060] In the first transmittance measurement, the transmittance at a wavelength of 420 nm is measured after peeling the polyamic acid coating film from the polyethylene terephthalate film.

[0061] The transmittance at a wavelength of 420 nm measured in the first transmittance measurement is a parameter used in the inspection process. Therefore, if the transmittance at a wavelength of 420 nm measured in the first transmittance measurement is equal to or less than the upper limit, the occurrence of inspection defects can be suppressed.

[0062] The transmittance at a wavelength of 420 nm measured in the first transmittance measurement varies depending on the structure of the polyamic acid. Specifically, if the polyamic acid has high flatness, the transmittance at a wavelength of 420 nm measured in the first transmittance measurement can be prevented from becoming excessively high.

[0063] Details of the first transmittance measurement will be described in Examples below.

[0064] In the polyamic acid, the transmittance at a wavelength of 420 nm measured by the second transmittance measurement described below is, for example, 1.50% or less, preferably 1.20% or less, more preferably 1.00% or less, even more preferably 0.80% or less, and for example, 0.1% or more.

[0065] (Second Transmittance Measurement) Polyamic acid is coated onto a copper alloy so that the thickness after curing is 20 μm. The coated polyamic acid is heated at 360° C. for 4 hours to be cured, thereby obtaining a polyamic acid film. The transmittance of the polyamic acid film at a wavelength of 420 nm is measured using a spectrophotometer.

[0066] In the first transmittance measurement, the transmittance at a wavelength of 420 nm is measured after forming a polyamic acid film on the copper alloy and then removing the copper alloy with an etching solution or the like.

[0067] The transmittance at a wavelength of 420 nm measured in the second transmittance measurement is a parameter used in the inspection process. Therefore, if the transmittance at a wavelength of 420 nm measured in the second transmittance measurement is equal to or less than the upper limit, the occurrence of inspection defects can be suppressed.

[0068] The transmittance at a wavelength of 420 nm measured in the second transmittance measurement varies depending on the structure of the polyamic acid. Specifically, if the polyamic acid has high flatness, the transmittance at a wavelength of 420 nm measured in the second transmittance measurement can be prevented from becoming excessively high.

[0069] The second transmittance measurement will be described in detail in the Examples section below.

[0070] <Photosensitizer> The photosensitizer is a component that promotes imidization of polyamic acid in a portion irradiated with light (exposed portion) in the exposure step of the photolithography method (the portion in which imidization of polyamic acid is promoted has reduced solubility in the developer used in the development step that follows the exposure step).

[0071] Examples of the photosensitizer include pyridine-based photosensitizers.

[0072] Examples of pyridine-based photosensitizers include compounds (1,4-dihydropyridine derivatives) represented by the following general formula (4): In general formula (4), R1, R2, R3, R4, and R5 each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and may be the same or different from one another. Also, in general formula (4), Ar represents an aryl group having a nitro group at the ortho position.

[0073]

[0074] In general formula (4), R1 is, for example, a hydrogen atom or a methyl group. R2 is, for example, a hydrogen atom or a methyl group. R3 is, for example, a methyl group or an ethyl group. R4 is, for example, a methyl group or an ethyl group. R5 is, for example, a methyl group or an ethyl group. Ar is, for example, a 2-nitrophenyl group.

[0075] Examples of pyridine-based photosensitizers represented by general formula (4) include 1-ethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-4-hydropyridine, 1-methyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-4-hydropyridine, 1-propyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-4-hydropyridine, and 1-propyl-3,5-diethoxycarbonyl-4-(2-nitrophenyl)-4-hydropyridine.

[0076] A preferred example of the pyridine-based photosensitizer is 1-ethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-4-hydropyridine represented by the following formula (5).

[0077]

[0078] Pyridine-based photosensitizers (1,4-dihydropyridine derivatives) can be obtained, for example, by reacting a substituted benzaldehyde with a twice-fold molar amount of alkylpropiolate (propargylic acid alkyl ester) and a specific primary amine in glacial acetic acid under reflux (Khim. Geterotsikl. Soed., pp. 1067-1071, 1982).

[0079] The content of the photosensitizer in the polyimide precursor composition (solid content) is, for example, 1.0 mass% or more, preferably 3.0 mass% or more, more preferably 5.0 mass% or more, even more preferably 7.0 mass% or more, and for example, 30 mass% or less, preferably 20 mass% or less, more preferably 15 mass% or less, even more preferably 10 mass% or less, and particularly preferably 9.0 mass% or less.

[0080] When the content of the photosensitizer in the polyimide precursor composition (solid content) is equal to or greater than the lower limit, the solubility of the exposed portion in the developer can be sufficiently reduced. When the content of the photosensitizer in the polyimide precursor composition (solid content) is equal to or less than the upper limit, precipitation of the solid content can be suppressed during storage of the polyimide precursor composition. Furthermore, reduction in the thickness of the polyimide resin formed in the heat curing step after the development step of the photolithography method can be suppressed.

[0081] The amount of the photosensitizer blended relative to 100 parts by mass of polyamic acid (solid content) is, for example, 3.0 parts by mass or more, preferably 5.0 parts by mass or more, more preferably 7.0 parts by mass or more, even more preferably 9.0 parts by mass or more, and for example, 30 parts by mass or less, preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less.

[0082] <Development Accelerator> The development accelerator accelerates the dissolution of the portion that has not been irradiated with light in the exposure step of the photolithography method (unexposed portion) in the developer in the development step.

[0083] The development accelerator is composed of parabens (paraoxybenzoic acid esters) having a hydrocarbon group having 1 to 4 carbon atoms, as represented by the following general formula (6): In other words, in general formula (6), R6 is a hydrocarbon group having 1 to 4 carbon atoms.

[0084]

[0085] Examples of parabens having a hydrocarbon group having 1 to 4 carbon atoms include methyl-4-hydroxybenzoate (methylparaben), ethyl-4-hydroxybenzoate (ethylparaben), propyl-4-hydroxybenzoate (propylparaben), isopropyl-4-hydroxybenzoate (isopropylparaben), butyl-4-hydroxybenzoate (butylparaben), and isobutyl-4-hydroxybenzoate (isobutylparaben). Preferred is butylparaben, which is represented by the following formula (7):

[0086]

[0087] The development accelerator can improve compatibility in the polyimide precursor composition by using a paraben having a hydrocarbon group containing 1 to 4 carbon atoms among parabens. Furthermore, when the development accelerator contains a paraben having a hydrocarbon group containing 1 to 4 carbon atoms, excessive inclination of the sides (excessively large inclination angle) in the cross-sectional shape of the polyimide resin formed from the polyimide precursor composition can be suppressed, and a polyimide resin having appropriate patterning properties can be formed.

[0088] Furthermore, since parabens having a hydrocarbon group containing 1 to 4 carbon atoms as development accelerators have an ester bond, when a basic developer is used in the development step, the ester bond of the parabens having a hydrocarbon group containing 1 to 4 carbon atoms is hydrolyzed by the basic developer to produce an alcohol and a carboxylic acid. This increases hydrophilicity, making it easier for the basic developer to penetrate into the polyamic acid. This improves the penetration of the basic developer into the polyamic acid, allowing unexposed areas to be more reliably removed in the development step. As a result, the formed polyimide resin has appropriate patterning properties.

[0089] The development accelerators may be used alone or in combination of two or more.

[0090] The development accelerator comprises a paraben having a hydrocarbon group having 1 to 4 carbon atoms, preferably butylparaben.

[0091] The content of the development accelerator in the polyimide precursor composition (solid content) is, for example, 1% by mass to 50% by mass, preferably 3% by mass to 40% by mass, more preferably 5% by mass to 30% by mass, even more preferably 7% by mass to 25% by mass, particularly preferably 8% by mass to 20% by mass, and most preferably 10% by mass to 15% by mass.

[0092] The content of the development accelerator in the polyimide precursor composition (solid content) is, for example, 1% by mass or more, preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, particularly preferably 8% by mass or more, and most preferably 10% by mass or more, and for example, 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, particularly preferably 20% by mass or less, and most preferably 15% by mass or less.

[0093] When the content of the development accelerator in the polyimide precursor composition (solid content) is equal to or less than the above upper limit, excessive narrowing of the lateral portions in the cross-sectional shape of the polyimide resin formed from the polyimide precursor composition can be suppressed, and a polyimide resin having appropriate patterning properties can be formed.

[0094] The amount of the development accelerator blended relative to 100 parts by mass of the polyamic acid (solid content) is, for example, 5.0 parts by mass to 30.0 parts by mass, preferably 7.5 parts by mass to 25.0 parts by mass, more preferably 10.0 parts by mass to 23.0 parts by mass, even more preferably 12.5 parts by mass to 20.0 parts by mass, and particularly preferably 15.0 parts by mass to 18.0 parts by mass.

[0095] The amount of the development accelerator to be blended per 100 parts by mass of polyamic acid (solid content) is 5.0 parts by mass or more, preferably 7.5 parts by mass or more, more preferably 10.0 parts by mass or more, even more preferably more than 10.0 parts by mass, particularly preferably 12.5 parts by mass or more, and most preferably 15.0 parts by mass or more. The amount of the development accelerator to be blended per 100 parts by mass of polyamic acid (solid content) is 30.0 parts by mass or less, preferably 25.0 parts by mass or less, more preferably 23.0 parts by mass or less, even more preferably 20.0 parts by mass or less, particularly preferably less than 20.0 parts by mass, and most preferably 18.0 parts by mass or less.

[0096] When the blending amount of the development accelerator per 100 parts by mass of the polyamic acid (solid content) is equal to or greater than the above lower limit, the difference in development speed between the exposed and unexposed areas can be sufficiently ensured, thereby ensuring patterning properties. Also, when the blending amount of the development accelerator per 100 parts by mass of the polyamic acid (solid content) is equal to or less than the above upper limit, excellent compatibility can be achieved, and development contrast can be improved.

[0097] The amount of the development accelerator blended relative to 100 parts by mass of the photosensitizer is, for example, 30 parts by mass to 400 parts by mass, preferably 50 parts by mass to 350 parts by mass, more preferably 80 parts by mass to 320 parts by mass, and even more preferably 100 parts by mass to 300 parts by mass.

[0098] The amount of the development accelerator blended relative to 100 parts by mass of the photosensitizer is, for example, 30 parts by mass or more, preferably 50 parts by mass or more, more preferably 80 parts by mass or more, and even more preferably 100 parts by mass or more, and for example, 400 parts by mass or less, preferably 350 parts by mass or less, more preferably 320 parts by mass or less, and even more preferably 300 parts by mass or less.

[0099] <Other Components> The polyimide precursor composition may contain other components. Preferably, it does not contain other components. Examples of other components include a photosensitizer.

[0100] Examples of photosensitizers include 3,3'-carbonylbis(7-N,N-dimethoxy)coumarin, 3-benzoylcoumarin, 3-benzoyl-7-N,N-methoxycoumarin, and benzalacetophenone.

[0101] The amount of the photosensitizer blended relative to 100 parts by mass of the polyamic acid (solid content) is, for example, 0.05 to 20 parts by mass.

[0102] <Method for Preparing Polyimide Precursor Composition> The polyimide precursor composition can be prepared, for example, by mixing a polyamic acid, a photosensitizer, a development accelerator, and other components added as needed. The polyimide precursor composition can be prepared as a diluted solution (varnish) of the polyimide precursor composition by mixing a solution of the polyamic acid, a photosensitizer, a development accelerator, and other components added as needed, or by mixing a polyamic acid, a photosensitizer, a development accelerator, and other components added as needed in an organic solvent. Specifically, the diluted solution (varnish) of the polyimide precursor composition can be prepared by blending a photosensitizer, a development accelerator, and other components added as needed with a solution of the polyamic acid obtained by reacting a tetracarboxylic dianhydride with a diamine component in an organic solvent.

[0103] Examples of the organic solvent include aprotic polar solvents, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide, dimethylformamide, and hexamethylphosphoramide.

[0104] The amount of the organic solvent to be blended relative to 100 parts by mass of the polyamic acid (solid content) is, for example, 150 to 2000 parts by mass.

[0105] The content of polyamic acid (solid content) in the diluted solution (varnish) of the polyimide precursor composition is, from the viewpoint of ensuring a favorable viscosity of the polyimide precursor composition, for example, 5% by mass or more, preferably 7.5% by mass or more, and more preferably 10% by mass or more, and for example, 20% by mass or less, preferably 17% by mass or less, and more preferably 15% by mass or less.

[0106] The content of the photosensitizer in the diluted solution (varnish) of the polyimide precursor composition is, for example, 0.1 mass% or more, preferably 0.2 mass% or more, more preferably 0.5 mass% or more, even more preferably 0.7 mass% or more, and particularly preferably 1.0 mass% or more, and for example, 20 mass% or less, preferably 15 mass% or less, more preferably 10 mass% or less, even more preferably 7 mass% or less, and particularly preferably 5 mass% or less.

[0107] When the content of the photosensitizer in the diluted solution (varnish) of the polyimide precursor composition is equal to or greater than the lower limit, the imidization of the polyamic acid by heating in the exposed area of ​​the polyimide precursor composition can be promoted, and the solubility of the exposed area in the developer can be reduced. When the content of the photosensitizer in the diluted solution (varnish) of the polyimide precursor composition is equal to or less than the upper limit, a reduction in the thickness of the polyimide resin pattern can be suppressed during the heating step.

[0108] The content of the development accelerator in the diluted solution (varnish) of the polyimide precursor composition is, for example, 0.1 mass % or more, preferably 0.5 mass % or more, more preferably 0.7 mass % or more, even more preferably 1.0 mass % or more, and for example, 25 mass % or less, preferably 20 mass % or less, more preferably 15 mass % or less, even more preferably 10 mass % or less, and particularly preferably 5 mass % or less.

[0109] When the content of the development accelerator in the diluted solution (varnish) of the polyimide precursor composition is equal to or greater than the lower limit, the difference in development speed between the exposed and unexposed areas can be sufficiently ensured, thereby ensuring patternability. When the content of the development accelerator in the diluted solution (varnish) of the polyimide precursor composition is equal to or less than the upper limit, sufficient compatibility can be ensured, thereby improving development contrast.

[0110] The polyimide precursor composition (or varnish) forms a polyimide resin by heat curing.

[0111] 2. Polyimide Resin The polyimide resin is a cured product of the polyimide precursor composition. Specifically, the polyimide resin can be formed by heating and curing the polyimide precursor composition (or varnish). The heating temperature is, for example, 300°C to 450°C.

[0112] The polyimide resin is used, for example, as an insulating layer or a covering layer of a printed circuit board, which will be described later.

[0113] 3. Wired Circuit Board The wired circuit board includes, for example, a base material, an insulating layer, a wiring layer, and a covering layer in this order in the thickness direction. The covering layer is disposed so as to cover the wiring layer. At least one layer selected from the group consisting of the insulating layer and the covering layer contains a polyimide resin that is a cured product of the polyimide precursor composition described above.

[0114] The shape of the substrate may be, for example, a film (including a sheet) having a predetermined thickness, or a plate.

[0115] Examples of the substrate include a silicon wafer, a ceramic sheet (ceramic plate), and a metal sheet (metal plate). Examples of the metal include aluminum, stainless steel, and copper.

[0116] The thickness of the substrate is, for example, 5 μm to 300 μm, preferably 10 μm to 200 μm, and more preferably 15 μm to 150 μm.

[0117] Examples of the material for the insulating layer include a polyimide resin that is a cured product of the polyimide precursor composition. When the material for the covering layer described below is a polyimide resin that is a cured product of the polyimide precursor composition, the material for the insulating layer may be a known material that is commonly used for wiring circuit boards.

[0118] The thickness of the insulating layer is, for example, 1 μm to 50 μm, or preferably 5 μm to 30 μm.

[0119] Examples of materials for the wiring layer include metals. Preferably, chromium and copper are used. More preferably, copper is used. The materials for the wiring layer may be used alone or in combination of two or more. Preferably, chromium and copper are used in combination.

[0120] The thickness of the wiring layer is, for example, 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 30 μm.

[0121] Examples of the material for the covering layer include a polyimide resin that is a cured product of the polyimide precursor composition. When the material for the insulating layer is a polyimide resin that is a cured product of the polyimide precursor composition, the material for the covering layer may be a known material that is commonly used for wiring circuit boards.

[0122] The thickness of the coating layer is, for example, 1 μm to 50 μm, or preferably 5 μm to 30 μm.

[0123] Next, a method for forming a wired circuit board 1 using the above polyimide precursor composition will be described with reference to FIGS. 1A to 1C and 2D to 2E.

[0124] As shown in FIG. 1A, an insulating layer is formed on a substrate S (insulating layer forming step). Specifically, an insulating layer material (for example, a diluted solution (varnish) of the polyimide precursor composition) is applied to form an insulating layer coating. The insulating layer coating is then dried. After drying, the coating is irradiated with ultraviolet light (exposure). After the ultraviolet irradiation, the coating is heated to harden the coating, thereby forming an insulating layer 10.

[0125] Examples of the application method include spin coating and screen printing.

[0126] The drying temperature is, for example, 100° C. to 200° C. The drying time is, for example, 1 minute to 15 minutes.

[0127] The wavelength of the irradiated ultraviolet light is, for example, 300 nm to 450 nm. The cumulative irradiation amount of the ultraviolet light is, for example, 100 mJ / cm. ２ ~1000mJ / cm ２ is.

[0128] The heating temperature is, for example, 300° C. to 450° C. The heating time is, for example, 1 hour to 10 hours.

[0129] Next, as shown in Figures 1B and 1C, a conductor pattern 20 (wiring layer) is formed by a semi-additive method (wiring layer formation process). Specifically, as shown in Figure 1B, a wiring layer material made of metal is first laminated on the insulating layer 10 as a base by sputter deposition to form a metal layer 21. Next, a plating resist 30 having a reverse pattern shape to the predetermined wiring pattern is formed using a dry film resist. Thereafter, copper plating 22 is used to form the conductor pattern 20 (wiring layer) that will become the predetermined wiring pattern in the parts of the metal layer 21 where the plating resist is not formed.

[0130] Thereafter, as shown in FIG. 1C, the plating resist 30 is removed by chemical etching, and the metal layer 21 in the area where the plating resist was formed is also removed by chemical etching.

[0131] 2D and 2E, a coating layer 40 is formed on the conductive pattern 20 (coating layer forming step). Specifically, a coating layer material (e.g., a diluted solution (varnish) of the polyimide precursor composition) is first applied to form a coating layer film. The coating layer film is then dried.

[0132] The application method, drying temperature, and drying time are, for example, the same as those described in the insulating layer forming step above.

[0133] The coating layer film has a thickness of, for example, 1 μm or more, preferably 10 μm or more, and for example, 50 μm or less, preferably 40 μm or less.

[0134] 2D, the coating layer is irradiated with ultraviolet light through a photomask M. The photomask M has openings Ma corresponding to the pattern shape of the conductor pattern 20 (wiring layer).

[0135] The wavelength of the irradiated ultraviolet light and the cumulative irradiation amount of the ultraviolet light are, for example, the same as those described in the insulating layer forming step above.

[0136] The ultraviolet irradiation through the photomask M generates exposed portions 41 and unexposed portions 42 in the coating layer film. After the ultraviolet irradiation, the coating layer film 40A may be preheated.

[0137] The preheating temperature is, for example, 100° C. to 300° C. The preheating time is, for example, 1 minute to 30 minutes.

[0138] Next, as shown in Figure 2E, the coating layer film is developed. Specifically, the unexposed portions 42 of the coating layer film are dissolved and removed by a developer. After development, the exposed portions 41 are heated. As a result, a polyimide resin is formed in the exposed portions 41 of the coating layer film, forming the coating layer 40.

[0139] The developer may be, for example, a basic developer. Examples of the basic developer include an inorganic alkaline solution and an organic alkaline solution. Examples of the inorganic alkaline solution include an aqueous solution of sodium hydroxide and an aqueous solution of potassium hydroxide. Examples of the organic alkaline solution include an aqueous solution of tetramethylammonium hydroxide (TMAH) and a TMAH / equinene (a mixed solvent mainly composed of ethanol) solution. A TMAH / equinene solution is preferred.

[0140] Examples of the developing method include a dipping method, a spray method, and a puddle method.

[0141] The heating temperature and heating time are, for example, the same as those described in the insulating layer forming step above.

[0142] In this manner, a laminate consisting of the insulating layer 10, the conductor pattern 20 (wiring layer) having a predetermined pattern shape, and the covering layer 40 covering the conductor pattern 20 (wiring layer) is formed on the substrate S. This results in a wired circuit board 1. An example of such a wired circuit board is a suspension board with a circuit for a hard disk drive.

[0143] The wired circuit board 1 may include a metal underlayer (e.g., a nickel layer or a chromium layer) between the conductive pattern 20 and the covering layer 40. The metal underlayer improves adhesion between the conductive pattern 20 and the covering layer 40.

[0144] 4. Electronic Device An electronic device includes the above-described printed circuit board.

[0145] Examples of electronic devices include notebook personal computers and smartphones.

[0146] (Effects) The polyimide precursor composition of the present invention comprises a polyamic acid, a photosensitizer, and a development accelerator, the development accelerator being comprised of a paraben having a hydrocarbon group containing 1 to 4 carbon atoms, the amount of the development accelerator blended per 100 parts by mass of the polyamic acid (solid content) being 5.0 parts by mass or more and 30.0 parts by mass or less, and the polyamic acid exhibits a transmittance of 1.3% or less at a wavelength of 420 nm as measured in the first transmittance measurement. Therefore, the occurrence of inspection defects is suppressed, and the composition has appropriate patterning properties.

[0147] The polyimide resin of the present invention is formed from the polyimide precursor composition of the present invention, and therefore, the occurrence of inspection defects is suppressed and further, the polyimide resin has appropriate patterning properties.

[0148] The wired circuit board of the present invention contains the polyimide resin of the present invention. Therefore, the occurrence of inspection defects can be suppressed. Furthermore, the wired circuit board has appropriate patterning properties, thereby improving reliability.

[0149] The electronic device of the present invention includes the wired circuit board of the present invention. Therefore, the occurrence of inspection defects can be suppressed. Furthermore, the reliability is improved by having appropriate patterning properties.

[0150] The present invention will be described in more detail below with reference to examples, comparative examples, and reference examples. It should be noted that the present invention is not limited to the examples, comparative examples, and reference examples. The specific numerical values ​​of the blending ratios (contents), physical properties, parameters, etc. used in the following description can be replaced with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than" or "exceeding") of the corresponding blending ratios (contents), physical properties, parameters, etc. described in the above-mentioned "Modes for Carrying Out the Invention."

[0151] <Details of Components> The trade names and abbreviations of the components used in each example and each comparative example are described in detail below.

[0152] BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PDA: p-phenylenediamine ODA: 4,4'-diaminodiphenyl ether m-TD: m-tolidine TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl NMP: N-methyl-2-pyrrolidone NKS-4: 1-ethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-4-hydropyridine BP: butylparaben HP: hexylparaben TMAH: tetramethylammonium hydroxide Equinene: mixed solvent with ethanol as the main ingredient

[0153] Preparation of Polyimide Precursor Composition Example 1 First, polyamic acid (A) was synthesized. Specifically, in a 5000 mL four-neck flask, a solution containing 415.69 g (1.413 mol) of BPDA, 129.87 g (1.201 mol) of PDA, 42.44 g (0.212 mol) of ODA, and 3612 g of NMP was stirred at room temperature (25°C) (synthesis of polyamic acid (A)). This resulted in an NMP solution containing polyamic acid (A). The synthesized polyamic acid (A) contained the first structural unit described above. The proportion of the first structural unit in this polyamic acid (A) was 85 mol%.

[0154] Next, an NMP solution containing polyamic acid (A), NKS-4 (photosensitizer), and BP (development accelerator) were mixed to prepare a varnish of a photosensitive polyimide precursor composition. In preparing the polyimide precursor composition, the blending ratio of the photosensitizer was 10 parts by mass and the blending amount of butylparaben was 10 parts by mass per 100 parts by mass of polyamic acid (A) (solid content). This resulted in a solution (varnish) of the polyimide precursor composition of Example 1.

[0155] Examples 2 to 4 As shown in Table 1, polyimide precursor compositions of Examples 2 to 4 were prepared in the same manner as the polyimide precursor composition of Example 1, except that the amount of butylparaben added was changed.

[0156] Example 5 A polyimide precursor composition of Example 5 was prepared in the same manner as in Example 1, except that polyamic acid (A) was changed to polyamic acid (B) as shown in Table 1. The preparation of polyamic acid (B) is described below.

[0157] In a 300 mL four-neck flask, a solution containing 29.42 g (100 mmol) of BPDA, 7.57 g (70 mmol) of PDA, 6.37 g (30 mmol) of m-TD, and 266 g of NMP was stirred under heating (80°C) (synthesis of polyamic acid (B)). This resulted in an NMP solution containing polyamic acid (B). The synthesized polyamic acid (B) contained the first structural unit described above. The proportion of the first structural unit in this polyamic acid (B) was 70 mol %.

[0158] Example 6 A polyimide precursor composition of Example 6 was prepared in the same manner as in Example 5, except that the amount of butylparaben added was changed as shown in Table 1.

[0159] Comparative Example 1 A polyimide precursor composition of Comparative Example 1 was prepared in the same manner as the polyimide precursor composition of Example 1, except that polyamic acid (A) was changed to polyamic acid (C) and the amount of butylparaben was changed as shown in Table 1. The preparation of polyamic acid (C) is described below.

[0160] In a 1000 mL four-neck flask, a solution containing 94.15 g (320 mmol) of BPDA, 27.68 g (256 mmol) of PDA, 20.50 g (64 mmol) of TFMB, and 874 g of NMP was stirred at room temperature (25°C) (synthesis of polyamic acid (C)). This resulted in an NMP solution containing polyamic acid (C). The synthesized polyamic acid (C) contained the first structural unit described above. The proportion of the first structural unit in this polyamic acid (C) was 80 mol%.

[0161] Comparative Examples 2 and 3 Polyimide precursor compositions of Comparative Examples 2 and 3 were prepared in the same manner as the polyimide precursor composition of Example 1, except that the blended amount of butylparaben was changed as shown in Table 1. In Comparative Example 2, butylparaben was not blended, and the blended amount of butylparaben was 0 parts by mass.

[0162] Comparative Example 4 A polyimide precursor composition of Comparative Example 4 was prepared in the same manner as in Example 5, except that the amount of butylparaben added was changed as shown in Table 1.

[0163] Comparative Example 5 A polyimide precursor composition of Comparative Example 5 was prepared in the same manner as the polyimide precursor composition of Example 1, except that hexylparaben was used instead of butylparaben and the amount of hexylparaben was changed as shown in Table 1. Note that the polyimide precursor composition of Comparative Example 5 could not be formed into a film in the evaluation of patterning ability described below due to poor compatibility. Therefore, the evaluation of patterning ability for Comparative Example 5 is indicated by "-".

[0164] <Evaluation> [Transmittance] The transmittance of the polyamic acids (polyamic acids (A), (B), and (C)) used in each Example and Comparative Example (before curing) was measured according to the first transmittance measurement method described below. The results are shown in Table 1.

[0165] (First Transmittance Measurement) Each polyamic acid was applied to a polyethylene terephthalate (PET) film by spin coating so that the thickness after drying was 20 μm. The applied polyamic acid was dried at 165° C. for 3 minutes to obtain a polyamic acid coating film. The polyamic acid coating film was peeled off from the PET film, and the transmittance of the polyamic acid coating film at a wavelength of 420 nm was measured using a spectrophotometer (product name: UV-Vis-NIR V670, manufactured by JASCO Corporation).

[0166] Furthermore, the transmittance of the polyamic acids (polyamic acids (A), (B), and (C)) (after curing) of each of the Examples and Comparative Examples was measured according to the second transmittance measurement method described below. The results are shown in Table 1.

[0167] (Second Transmittance Measurement) Each polyamic acid was spin-coated onto a copper alloy to a thickness of 20 μm after curing. The coated polyamic acid was heated at 360° C. for 4 hours to cure. The copper alloy was then removed using an aqueous ferric chloride solution to obtain a polyamic acid film. The transmittance of the polyamic acid film at a wavelength of 420 nm was measured using a spectrophotometer.

[0168] [Patterning ability] (Tilt angle) A solution (varnish) of the polyimide precursor composition of each Example and each Comparative Example (except Comparative Example 5) was spin-coated onto a SUS foil (stainless steel foil) and heated at 165°C for 3 minutes to obtain a film with a thickness of approximately 20 µm. Half of this film was covered with SUS foil and exposed to an exposure dose of 200 mJ / cm using an exposure machine. ２After exposure to 1000 kJ / s, the film was heated at 185°C for 5 minutes to obtain a two-part patterned sample film approximately 20 μm thick. The film was then developed by several 2-second dip developments in a TMAH / echinene solution and rinsed with deionized water. The developed sample film was then cut in the thickness direction (vertical direction) using a microtome (Leica Biosystems). The CCD image was observed at 100x magnification using a CCD (OLYMPUS). The inclination angle (tilt angle) of the side edge of the developed sample film relative to the surface of the SUS foil was determined and evaluated according to the following criteria. The results are shown in Table 1. Note that if the inclination angle of the side edge of the developed sample film is small, the cross-sectional shape will be trapezoidal, which can cause problems such as wiring not being able to be arranged as designed. {Criteria} A: The inclination angle of the side edge surface of the sample film after development is 60° or more. B: The inclination angle of the side edge surface of the sample film after development is 30° or more and less than 60°. C: The inclination angle of the side edge surface of the sample film after development is less than 30°.

[0169] (Resist Residue) A solution (varnish) of the polyimide precursor composition of each Example and Comparative Example (except Comparative Example 5) was applied onto a 20 μm thick stainless steel foil (SUS304) so ​​that the thickness after curing would be 10 μm, to form an insulating layer coating. The insulating layer coating was then dried at 165° C. for 3 minutes. After drying, the coating was irradiated with ultraviolet light (wavelength 365 nm, 200 mJ / cm ２ ) and heated at 360°C for 4 hours to harden the insulating layer coating film, thereby forming an insulating layer.

[0170] Next, a metal layer consisting of a 30 nm-thick chromium thin film and a 70 nm-thick copper thin film was sequentially formed on the insulating layer as a base by sputter deposition. Next, a plating resist having a reverse pattern shape to the predetermined wiring pattern was formed using a dry film resist, and then a conductor pattern (wiring layer) having the predetermined wiring pattern was formed by electrolytic copper plating using a semi-additive method in the areas of the metal layer where the plating resist was not formed. The conductor pattern had a thickness of 14 μm, each wire of the conductor pattern had a width of 12 μm, and the spacing between wires was 12 μm. The plating resist was then removed by chemical etching, and the chromium thin film and copper thin film on which the plating resist had been formed were then removed by chemical etching.

[0171] After removing the plating resist, the amount of resist residue on the insulating layer side was confirmed by observing the CCD images at a magnification of 50x using a CCD (manufactured by Olympus Corporation). The presence or absence of residue was confirmed on 36 CCD images, and evaluated according to the following criteria. The results are shown in Table 1. Note that if a constriction occurs in the cross-sectional shape, resist will remain in the constricted portion, which may increase the amount of resist residue and lead to product defects. {Criteria} A: No resist residue was confirmed in any CCD images. B: Resist residue was confirmed in 1 or more but less than 10 CCD images. C: Resist residue was confirmed in 10 or more CCD images.

[0172]

[0173] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0174] The polyimide precursor composition and polyimide resin of the present invention are suitable for use in insulating layers and coating layers of wiring circuit boards used in electronic devices. The wiring circuit board of the present invention is also suitable for use as a circuit-equipped suspension board for hard disk drives. Furthermore, the electronic device of the present invention is also suitable for use as a notebook personal computer or a smartphone.

[0175] REFERENCE SIGNS LIST 1 Wired circuit board S Base material 10 Insulating layer 20 Conductor pattern (wiring layer) 21 Metal layer 22 Copper plating 30 Plating resist 40 Covering layer 41 Exposed portion 42 Unexposed portion

Claims

1. A polyimide precursor composition comprising a polyamic acid, a photosensitizer, and a development accelerator, wherein the development accelerator is a paraben having a hydrocarbon group containing 1 to 4 carbon atoms, the amount of the development accelerator blended per 100 parts by mass of the polyamic acid (solid content) is 5.0 parts by mass or more and 30.0 parts by mass or less, and the polyamic acid has a transmittance of 1.30% or less at a wavelength of 420 nm as measured by the first transmittance measurement described below. (First Transmittance Measurement) The polyamic acid is coated on a polyethylene terephthalate film so that the thickness after drying is 20 μm. The coated polyamic acid is dried at 165°C for 3 minutes to obtain a coating film of the polyamic acid. The transmittance of the coating film at a wavelength of 420 nm is measured using a spectrophotometer.

2. The polyimide precursor composition according to claim 1, wherein the polyamic acid has a transmittance of 1.00% or less at a wavelength of 420 nm as measured by the second transmittance measurement described below. (Second Transmittance Measurement) The polyamic acid is coated on a copper alloy so that the thickness after curing is 20 μm. The coated polyamic acid is heated at 360° C. for 4 hours to cure it, thereby obtaining a polyamic acid film. The transmittance of the film at a wavelength of 420 nm is measured using a spectrophotometer.

3. The polyimide precursor composition according to claim 1, wherein the amount of the development accelerator blended is less than 20.0 parts by mass per 100 parts by mass of the polyamic acid (solid content).

4. The polyimide precursor composition according to claim 1, wherein the amount of the development accelerator blended is more than 10.0 parts by mass per 100 parts by mass of the polyamic acid (solid content).

5. The polyimide precursor composition of claim 1, wherein the development accelerator comprises butylparaben.

6. A polyimide resin which is a cured product of the polyimide precursor composition according to any one of claims 1 to 5.

7. A printed circuit board comprising the polyimide resin according to claim 6.

8. An electronic device comprising the printed circuit board according to claim 7.

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