JP7492880B2 - Polyimide precursor composition - Google Patents

Description

The present invention relates to a polyimide precursor composition.

In the manufacture of wired circuit boards, polyimide, for example, is used as a material for forming an insulating layer. For example, in a wired circuit board having a metal substrate as a supporting substrate, a polyimide layer is formed on the metal substrate as a base insulating layer, and then a wiring pattern is formed on the polyimide layer. The polyimide layer is formed by photolithography, for example, as follows.

First, a varnish (polyimide precursor composition) containing polyamic acid as a polyimide precursor and a photosensitive agent is applied onto a substrate to form a coating film. Next, the coating film is dried to form an insulating film. Next, the insulating film is irradiated with ultraviolet light through a photomask (exposure process). The photomask has, for example, openings with a shape corresponding to the pattern shape of the polyimide layer. Next, the insulating film is heated (post-exposure heating process). In this process, imidization of polyamic acid proceeds in the exposed parts of the insulating film to form polyimide. Next, the insulating film is developed (development process). Specifically, the unexposed parts of the insulating film are dissolved and removed with a developer. Next, the insulating film remaining on the substrate is cured by heating (heat curing process).

For example, in the manner described above, a polyimide layer (polyimide film pattern) having a predetermined pattern shape is formed on a substrate. Technology relating to the formation of such a polyimide layer is described, for example, in Patent Document 1 below.

JP 2010-55110 A

The substrate of a printed circuit board is required to be thin enough to suit the application. The thinner the substrate, the greater the effect that the rigidity of the polyimide film pattern has on the rigidity of the printed circuit board. Therefore, from the perspective of controlling the rigidity of the printed circuit board, the polyimide film pattern must be formed with good dimensional precision. The thinner the substrate in the printed circuit board, the greater the requirement.

The present invention provides a polyimide precursor composition suitable for forming polyimide film patterns with high dimensional accuracy.

The present invention [1] includes a polyimide precursor composition that contains a polyamic acid, a photosensitizer, an imide acrylate compound, and an amine compound, and the content of the amine compound is 4.5 parts by mass or less per 100 parts by mass of the imide acrylate compound.

The present invention [2] includes the polyimide precursor composition described in [1] above, in which the content of the amine compound is 0.01 mass% or more.

The present invention [3] includes the polyimide precursor composition according to [1] or [2] above, in which the content of the amine compound is 0.33 mass% or less.

The present invention [4] includes the polyimide precursor composition according to any one of [1] to [3] above, in which the amine compound is a tertiary amine compound.

As described above, the polyimide precursor composition of the present invention contains an amine compound in addition to the polyamic acid, photosensitizer, and imide acrylate compound, and the content of the amine compound is 4.5 parts by mass or less per 100 parts by mass of the imide acrylate compound. Therefore, the polyimide precursor composition of the present invention is suitable for forming a polyimide film pattern with good dimensional accuracy by a photolithography method.

FIG. 1 shows an example of a method for forming a polyimide film pattern using the polyimide precursor composition of the present invention, in which FIG. 1A shows a coating process, FIG. 1B shows a drying process after coating, FIG. 1C shows an exposure process, FIG. 1D shows a development process, and FIG. 1E shows a heat curing process.

The polyimide precursor composition according to one embodiment of the present invention contains a polyamic acid, a photosensitizer, an imide acrylate compound, an amine compound, and an organic solvent. The polyimide precursor composition is a composition capable of forming a polyimide film pattern by a photolithography method.

Polyamic acid is a polyimide precursor, a reaction product of tetracarboxylic dianhydride and diamine. In polyamic acid, adjacent amide groups and carboxyl groups in the repeating unit react (imidization reaction) to form a closed ring structure containing imide groups, thereby forming a polyimide resin. The imidization reaction occurs, for example, by heating.

Examples of tetracarboxylic dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, and 2,3,5-tricarboxycyclopentylacetic dianhydride.

Examples of diamines include aromatic diamines. Examples of aromatic diamines include p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminophenylmethane, 4,4'-diaminodiphenyl sulfone, 1,4-diaminobenzene, 2,5-diaminotoluene, and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl.

The polyamic acid preferably contains a first structural unit represented by the following general formula (1) and a second structural unit represented by the following general formula (2): In general formula (1), _R1 is an alkyl group having 1 to 3 carbon atoms, m is 0 or a positive integer of 4 or less, and n is a positive integer of 4 or less.

The polyamic acid containing the first structural unit and the second structural unit can be obtained by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydride with at least two types of diamines in an organic solvent.

The at least two types of diamines include a diamine for the first structural unit (first diamine) and a diamine for the second structural unit (second diamine).

The first diamine may be an aromatic diamine. Examples of the aromatic ring contained in the aromatic diamine include benzene, biphenyl, triphenyl, terphenyl, toluene, xylene, and tolidine. As the first diamine, p-phenylenediamine is preferably used. That is, in general formula (1), m is preferably 0 and n is preferably 1.

The second diamine used is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl.

From the viewpoint of suppressing the thermal expansion coefficient of the polyimide film formed from the polyimide precursor composition, the molar ratio (a1/a2) of the first diamine (a1) to the second diamine (a2) is preferably 0.25 or more, more preferably 0.5 or more, and even more preferably 1 or more. From the viewpoint of suppressing the hygroscopic expansion coefficient of the polyimide film formed from the polyimide precursor composition, the molar ratio (a1/a2) is preferably 10 or less, more preferably 7.5 or less, and even more preferably 5 or less.

The content of polyamic acid in the polyimide precursor composition is preferably 5% by mass or more, more preferably 8% by mass or more. The content of polyamic acid in the polyimide precursor composition is preferably 30% by mass or less, more preferably 25% by mass or less. These configurations regarding the polyamic acid content are suitable for ensuring a good viscosity of the polyimide precursor composition.

The photosensitizer is a component that promotes imidization of polyamic acid contained in a portion (exposed portion) irradiated with light in the exposure step of the photolithography method (the portion where imidization of polyamic acid is promoted has a reduced solubility in a developer used in a development step following the exposure step). As the photosensitizer, a pyridine-based photosensitizer is preferably used. As the pyridine-based photosensitizer, for example, a compound (1,4-dihydropyridine derivative) represented by the following general formula (3) is used. In the general formula (3), R ₂ , R ₃ , R ₄ , and R ₅ are each a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and may be the same as or different from each other. In the general formula (3), Ar is an allyl group having a nitro group at the ortho position.

In general formula (3), _R2 is preferably a hydrogen atom or a methyl group. _R3 is preferably a hydrogen atom or a methyl group. _R4 is preferably a methyl group or an ethyl group. _R5 is preferably a methyl group or an ethyl group. _R6 is preferably a methyl group or an ethyl group. Ar is preferably a 2-nitrophenyl group.

Specific examples of pyridine-based photosensitizers include 1-ethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-1,4-dihydropyridine, 1-methyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-1,4-dihydropyridine, 1-propyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-1,4-dihydropyridine, and 1-propyl-3,5-diethoxycarbonyl-4-(2-nitrophenyl)-1,4-dihydropyridine. As the pyridine-based photosensitizer, 1-ethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-1,4-dihydropyridine represented by the following formula (4) is preferably used.

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

The content of the pyridine-based photosensitizer in the polyimide precursor composition is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, per 100 parts by mass of polyamic acid. Such a configuration is preferable from the viewpoint of ensuring the above-mentioned effect of reducing the solubility of the exposed portion in the developer in the polyimide precursor composition. The amount of the pyridine-based photosensitizer is preferably 70 parts by mass or less, more preferably 55 parts by mass or less, per 100 parts by mass of polyamic acid. Such a configuration is preferable from the viewpoint of suppressing precipitation of solids during storage of the polyimide precursor composition. In addition, the configuration is preferable from the viewpoint of suppressing a decrease in the thickness of the polyimide film pattern formed in the heat curing process after the development process of the photolithography method.

The imide acrylate compound is a component that promotes dissolution of the portion to be removed (the portion not exposed in the exposure step) in a developer in the development step of a photolithography method. Examples of the imide acrylate compound include compounds represented by the following general formula (5). In general formula (5), _R7 is a hydrogen atom or a methyl group, and _R8 is a divalent hydrocarbon group having 2 or more carbon atoms.

As the imide acrylate compound, N-acryloyloxyethylhexahydrophthalimide represented by the following formula (6) is preferably used: In general formula (5), R ₇ is preferably a hydrogen atom, and R ₈ is preferably an ethylene group.

Examples of imide acrylate compounds include N-acryloyloxyethyl-1,2,3,6-tetrahydrophthalimide and N-acryloyloxyethyl-3,4,5,6-tetrahydrophthalimide.

The amount of the imide acrylate compound is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of polyamic acid. Such a configuration is preferable from the viewpoint of ensuring the above-mentioned dissolution promotion effect in the development step in the photolithography method. The amount of the imide acrylate compound is preferably 110 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less, per 100 parts by mass of polyamic acid. Such a configuration is preferable from the viewpoint of suppressing a decrease in the thickness of the polyimide film pattern formed in the heat curing step after the development step in the photolithography method.

The amine compound is a component that controls the developability of the developer in the development process. The amine compound is a compound that contains an amine nitrogen atom other than the nitrogen atom of an imide group or the nitrogen atom of an amide group.

Examples of the amine compounds include primary amine compounds, secondary amine compounds, and tertiary amine compounds. Examples of the primary amine compounds include ethanolamine, 3-aminobenzoic acid, 4-aminobenzoic acid, 1-aminoanthracene, and 1-aminoanthraquinone. Examples of the secondary amine compounds include diethanolamine, N-methylaniline, diphenylamine, N,N-dimethylethylenediamine, 1-(methylamino)anthraquinone, and 9-(methylaminoethyl)anthracene. Examples of the tertiary amine compounds include aliphatic tertiary amine compounds and nitrogen-containing heterocyclic compounds. Examples of the aliphatic tertiary amine compounds include trioctylamine and tridodecylamine. Examples of the nitrogen-containing heterocyclic compounds include imidazoles and pyridines. Examples of imidazoles include imidazole, N-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 1-benzyl-2-methylimidazole. Examples of pyridines include pyridine, methylpyridine, dimethylpyridine, propylpyridine, and 4-dimethylaminopyridine. These amine compounds may be used alone or in combination of two or more. As the amine compound, a tertiary amine compound is preferably used, and an aliphatic tertiary amine compound is more preferably used.

From the viewpoint of suppressing the volatilization of the amine compound in the heating process prior to the development step in the manufacturing process of the printed circuit board, the boiling point of the amine compound is preferably higher than the heating temperature in the heating process. Specifically, the boiling point of the amine compound is preferably 160°C or higher, more preferably 175°C or higher, and even more preferably 180°C or higher (the boiling point is the value at 1 atmospheric pressure).

The content of the amine compound in the polyimide precursor composition is 4.5 parts by mass or less, preferably 4.2 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3.5 parts by mass or less, and particularly preferably 3 parts by mass or less, relative to 100 parts by mass of the imide acrylate compound. The content of the amine compound is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, and particularly preferably 0.4 parts by mass or more, relative to 100 parts by mass of the imide acrylate compound. These configurations regarding the content of the amine compound are suitable for forming a polyimide film pattern with good dimensional accuracy from the polyimide precursor composition.

The content of the amine compound in the polyimide precursor composition is preferably 0.01% by mass or more, more preferably 0.025% by mass or more, and is preferably 0.33% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.25% by mass or less. This configuration regarding the content of the amine compound is preferable from the viewpoint of forming a polyimide film pattern with good dimensional accuracy from the polyimide precursor composition.

The content of the amine compound in the polyimide precursor composition is preferably 0.1 parts by mass or more, more preferably 0.25 parts by mass or more, and preferably 3.3 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass of polyamic acid. This configuration regarding the content of the amine compound is suitable for forming a polyimide film pattern with good dimensional accuracy from the polyimide precursor composition.

The organic solvent in the polyimide precursor composition may be, for example, an aprotic polar solvent. Examples of the aprotic polar solvent include N-methyl-2-pyrrolidone, dimethylacetamide, dimethylsulfoxide, dimethylformamide, and hexamethylphosphoramide. The content of the organic solvent in the polyimide precursor composition is, for example, 150 parts by mass or more and, for example, 2000 parts by mass or less, per 100 parts by mass of polyamic acid.

The polyimide precursor composition may contain other components. Examples of other components include a photosensitizer that increases the photosensitivity of the polyimide precursor composition.

Examples of photosensitizers include 3,3'-carbonylbis(7-N,N-dimethoxy)coumarin, 3-benzoylcoumarin, 3-benzoyl-7-N,N-methoxycoumarin, and benzalacetophenone. The amount of photosensitizer is, for example, 0.05 parts by mass or more and, for example, 20 parts by mass or less, per 100 parts by mass of polyamic acid.

The polyimide precursor composition can be prepared by mixing a polyamic acid, a photosensitizer, an imide acrylate compound, an amine compound, and other components added as necessary in an organic solvent. Specifically, the polyimide precursor composition can be prepared by blending a photosensitizer, an imide acrylate compound, an amine compound, and other components as necessary into a polyamic acid-containing solution obtained by reacting a tetracarboxylic dianhydride with a diamine in an organic solvent.

The polyimide precursor composition can be used to form a polyimide film pattern, for example, as follows:

First, as shown in FIG. 1A, a polyimide precursor composition is applied onto a substrate S to form a coating film 10A (coating process). Examples of substrates S include aluminum plates, stainless steel plates, copper plates, and silicon wafers.

First, as shown in FIG. 1B, the coating film 10A is dried by heating to form an insulating film 10B on the substrate S (post-coating drying process). The drying temperature is, for example, 160° C. or higher and, for example, 200° C. or lower. The drying time is, for example, 1 minute or higher and, for example, 15 minutes or lower. The thickness of the insulating film 10B is, for example, 1 μm or higher and, for example, 50 μm or lower.

Next, as shown in FIG. 1C, the insulating film 10B is irradiated with ultraviolet light through a photomask M (exposure step). The photomask M has an opening Ma having a shape corresponding to the pattern shape of the polyimide film to be formed. The wavelength of the irradiated ultraviolet light is, for example, 300 nm or more and, for example, 450 nm or less. The cumulative dose of the ultraviolet light is, for example, 100 mJ/ ^cm2 or more and, for example, 1000 mJ/ ^cm2 or less. In this step, an exposed portion 11 and an unexposed portion 12 are generated in the insulating film 10B. After this step, the insulating film 10B may be heated.

Next, as shown in FIG. 1D, the insulating film 10B is developed (developing step). Specifically, the unexposed portion 12 of the insulating film 10B is dissolved and removed by the developer. As the developer, for example, an alkaline aqueous solution is used. As the alkaline aqueous solution, for example, an inorganic alkaline aqueous solution and an organic alkaline aqueous solution are used. As the inorganic alkaline aqueous solution, for example, an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution are used. As the organic alkaline aqueous solution, for example, an aqueous solution of tetramethylammonium hydroxide is used. As the developing method, for example, an immersion method, a spray method, and a paddle method are used.

Next, as shown in FIG. 1E, the insulating film 10B remaining on the substrate S is cured by heating to form a polyimide film pattern 10C (heat curing process). The heating temperature is, for example, 300° C. or higher and, for example, 450° C. or lower. The heating time is, for example, 1 hour or higher and, for example, 10 hours or lower.

For example, in the manner described above, a polyimide layer (polyimide film pattern 10C) having a predetermined pattern shape is formed on the substrate S. Such a method for forming a polyimide film pattern can be used, for example, in the manufacturing process of a wiring circuit board. An example of a wiring circuit board is a suspension board with a circuit that is assembled into a hard disk drive.

As described above, the polyimide precursor composition of this embodiment contains an amine compound in addition to the polyamic acid, photosensitizer, and imide acrylate compound, and the content of the amine compound is 4.5 parts by mass or less, preferably 4.2 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3.5 parts by mass or less, and particularly preferably 3 parts by mass or less, per 100 parts by mass of the imide acrylate compound. Such a polyimide precursor composition is suitable for forming a polyimide film pattern with good dimensional accuracy by a photolithography method. Specific examples are shown in the following examples and comparative examples.

The present invention will be specifically described below with reference to examples. The present invention is not limited to the examples. In addition, the specific numerical values of the compounding amounts (contents), physical property values, parameters, etc. described below 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") of the corresponding compounding amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Form for carrying out the invention."

Example 1
First, polyamic acid was synthesized. Specifically, in a 1000 mL four-neck flask, a solution containing 94.15 g (320 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 27.68 g (256 mmol) of p-phenylenediamine (PPD), 20.50 g (64 mmol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), and 874 g of N-methyl-2-pyrrolidone (NMP) was stirred at room temperature (25°C) for 50 hours (synthesis of polyamic acid). As a result, an NMP solution containing polyamic acid was obtained. The synthesized polyamic acid contains the above-mentioned first structural unit and second structural unit. In this polyamic acid, m in the above general formula (1) representing the first structural unit is 0, and n in the general formula (1) is 1. The proportion of the second structural unit in this polyamic acid is 20 mol %.

Next, the NMP solution containing polyamic acid, a photosensitizer, an imide acrylate compound, and an amine compound were mixed to prepare a photosensitive polyimide precursor composition. The photosensitizer was 1-ethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)-1,4-dihydropyridine represented by the above formula (4). The imide acrylate compound was N-acryloyloxyethylhexahydrophthalimide (Aronix M140 manufactured by Toagosei Co., Ltd.) represented by the above formula (6). The amine compound was tridodecylamine (TDA, boiling point 220°C [0.03 mmHg]). In preparing the polyimide precursor composition, the amount of the photosensitizer was 14 parts by mass, the amount of the imide acrylate compound was 52 parts by mass, and the amount of the amine compound was 0.47 parts by mass relative to 100 parts by mass of polyamic acid. In the prepared polyimide precursor composition, the content of the amine compound is 0.06% by mass, and the content R of the amine compound per 100 parts by mass of the imide acrylate compound is 0.8 parts by mass.

[Examples 2 to 5 and Comparative Example 2]
Each of the polyimide precursor compositions of Examples 2 to 8 and Comparative Example 2 was prepared in the same manner as the polyimide precursor composition of Example 1 except for the content of the amine compound.

In the polyimide precursor composition of Example 2, the content of the amine compound is 0.12% by mass, and the content R of the amine compound relative to 100 parts by mass of the imide acrylate compound is 1.7 parts by mass. In the polyimide precursor composition of Example 3, the content of the amine compound is 0.2% by mass, and the content R is 2.8 parts by mass. In the polyimide precursor composition of Example 4, the content of the amine compound is 0.3% by mass, and the content R is 4.1 parts by mass. In the polyimide precursor composition of Example 5, the content of the amine compound is 0.02% by mass, and the content R is 0.3 parts by mass. In the polyimide precursor composition of Comparative Example 2, the content of the amine compound is 0.35% by mass, and the content R is 4.8 parts by mass.

[Examples 6 to 8]
Each of the polyimide precursor compositions of Examples 6 to 8 was prepared in the same manner as the polyimide precursor composition of Example 1, except for the following.

In the polyimide precursor composition of Example 6, trioctylamine (TOA, boiling point 365°C [760 mmHg]) is used as the amine compound, the content of the amine compound is 0.03 mass%, and the content R is 0.4 mass parts. In the polyimide precursor composition of Example 7, TOA is used as the amine compound, the content of the amine compound is 0.06 mass%, and the content R is 0.8 mass parts. In the polyimide precursor composition of Example 8, TOA is used as the amine compound, the content of the amine compound is 0.1 mass%, and the content R is 1.4 mass parts.

Comparative Example 1
A polyimide precursor composition of Comparative Example 1 was prepared in the same manner as in Example 1, except that no amine compound was used.

[Evaluation of dimensional accuracy]
The dimensional accuracy of the polyimide film patterns formed from the polyimide precursor compositions of Examples 1 to 8 and Comparative Examples 1 and 2 was examined as follows.

First, the polyimide precursor composition was applied onto a substrate (made of stainless steel) to form a coating film (coating process). A spin coater was used for coating. Next, the coating film was dried in a dryer at 165°C for 2 minutes (post-coating drying process). Next, the coating film was irradiated with ultraviolet light through a photomask by an ultraviolet irradiator (exposure process). The photomask has a plurality of openings. Each opening has a linear opening shape with a line width of 100 μm. The cumulative exposure dose of ultraviolet light was set to 200 mJ/ ^cm2 . Next, the film on the substrate was heated on a hot plate at 185°C for 2 minutes (post-exposure heating process). This caused the exposed portion of the film to harden. Next, a developer was applied to the film on the substrate by a spray method to remove the unexposed portion of the film (development process). As the developer, a water-ethanol solution of tetramethylammonium hydroxide (volume ratio of water to ethanol was 1:1) was used. This resulted in the formation of a polyimide film pattern (multiple linear polyimide films) on the substrate.

Next, the line width was measured at 10 random points on the polyimide film pattern. Next, the average line width was calculated as the finished width W' from the measured line width. Next, the ratio (%) of the difference between the finished width W' and the designed width W (= W' - W) to the designed width W was calculated. Then, with regard to the dimensional accuracy of the polyimide film pattern, a ratio of -5% or more and less than 7.5% was evaluated as "excellent", a ratio of -7.5% or more and less than -5% or 7.5% or more and less than 15% was evaluated as "good", and a ratio of less than -7.5% or more and 15% or more was evaluated as "unacceptable". The results are shown in Table 1.

S: Substrate 10A, Coating film 10B, Insulating film 10C, Polyimide film pattern 11, Exposed portion 12, Unexposed portion

Claims (4)

A polyamic acid,
A photosensitizer,
an imide acrylate compound;
An amine compound (excluding the photosensitizer) ,
A polyimide precursor composition, comprising the amine compound in an amount of 4.5 parts by mass or less based on 100 parts by mass of the imide acrylate compound. The polyimide precursor composition according to claim 1, wherein the content of the amine compound is 0.01% by mass or more. The polyimide precursor composition according to claim 1 or 2, wherein the content of the amine compound is 0.33 mass% or less. The polyimide precursor composition according to any one of claims 1 to 3, wherein the amine compound is a tertiary amine compound.

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