JP7109946B2 - polyimide film - Google Patents

Description

The present invention relates to polyimide films.

As electronic devices become smaller, lighter, and more functional, printed wiring boards on which electronic components such as ICs and LSIs are mounted are required to have higher density wiring in a smaller space. A COF (Chip On Film) method has been developed and put into practical use, in which a chip is directly mounted on a flexible wiring board.
In recent years, this trend has become particularly noticeable in the mounting of ICs that drive displays such as liquid crystal televisions, notebook computers, and smartphones. In order to achieve this, progress has been made in improving mounting methods such as finer wiring and double-sided COF in which wiring is provided on both sides.

The copper-clad laminate used for COF employs a two-layer type in which a copper layer is directly formed on a polyimide film and no adhesive is used, which is capable of coping with miniaturization of wiring. There are two methods for this: a method of forming a copper layer on a film by sputtering and plating, and a method of casting polyamic acid on a copper foil and then imidizing it. A two-layer copper-clad laminate made by a sputtering/plating method has become mainstream.

The fine wiring of the COF substrate is formed by providing a photoresist layer on the surface of the copper layer of the copper-clad laminate, exposing and developing the photoresist layer to form a desired pattern, and using this pattern as a masking material, A method of selectively etching a copper layer (subtractive method) is used. However, with this method, it is difficult to reduce the wiring pitch [for example, smaller than 25 μm (for example, line width 12 μm, space width 13 μm)], and it is becoming difficult to deal with some state-of-the-art models.

In recent years, as an alternative method, a substrate metal layer is formed on the surface of an insulating substrate, a photoresist layer is provided on the surface of this substrate metal layer, a desired pattern is formed on the photoresist layer, and the exposed substrate is exposed. A method (semi-additive method) of forming a wiring pattern by electrolytically depositing a conductive metal on a material metal layer has attracted attention. According to this method, a small wiring pitch (for example, 20 μm or less) can be formed, and higher density mounting becomes possible.

Along with these technical trends, the requirements for characteristics and quality of polyimide films used for two-layer copper-clad laminates are becoming more and more sophisticated. For example, after a COF is mounted on an IC or panel, it is folded compactly and mounted on an electronic device. It became so.
In order to cope with these problems, for example, a metal base layer made of a nickel alloy is formed on the surface of a polyimide film without an adhesive, and a wiring having a laminated structure including a copper layer on the surface of the metal base layer is formed by a semi-additive method. A proposal has been made to specify the crystal orientation of a copper layer in a method for manufacturing a flexible wiring board (Patent Document 1).

Japanese Unexamined Patent Application Publication No. 2014-159608

An object of the present invention is to provide a novel polyimide film.

As described above, various studies have been made on the COF, but the inventors have found that there is room for further study and improvement.
For example, in a double-sided COF in which wiring is provided on both sides, the wiring on the inner surface of the bend has a smaller bending angle than the wiring on the outer surface. In order to cope with this, it is not enough to improve the copper layer as in Patent Document 1, and it is considered that the polyimide film also needs to be improved.

In addition, as the wiring becomes finer, the quality of the surface of the copper layer and the quality of the surface of the polyimide film are required to be higher. In addition, the copper-clad laminate used for wiring formation in the semi-additive method has a copper layer thickness less than one-third (1 to 3 μm) of the copper-clad laminate used in the conventional subtractive method. Since a plate is often used, higher quality is required for the surface of the polyimide film.

From this point of view, the inventors have attempted various studies, but have found it extremely difficult to achieve sufficient performance. For example, attempts have been made to smooth the surface of a polyimide film, but simply doing such an attempt will not only make the film less slippery, making it easier to handle, but also make it easier to transport and wind the film. Occasionally, scratches and wrinkles tend to occur, and in some cases, the surface quality of the film deteriorates.

Under such circumstances, the present inventors have made extensive research, and as a result, in a polyimide film containing inorganic particles, by focusing on both sides of the film and adjusting the protrusion ratio etc. on both sides, a polyimide film with excellent handleability and , and found that a polyimide film suitable for double-sided COF and the like can be obtained, and after repeated further studies, the present invention was completed.

That is, the present invention relates to the following inventions and the like.
[1]
A polyimide film containing inorganic particles, wherein the ratio of projections with a height of 0.8 μm or more on one side a of the film is A/100 cm ² , and the projections with a height of 0.8 μm or more on the other side b of the film A polyimide film in which both A and B are 10 or less (for example, polyimide film for double-sided COF), where B is the ratio of B per 100 cm ² .
[2]
A polyimide film containing inorganic particles, wherein the ratio of projections with a height of 0.8 μm or more on one side a of the film is A/100 cm ² , and the projections with a height of 0.8 μm or more on the other side b of the film A polyimide film in which the absolute value of the difference between A and B is 2 or more (for example, a polyimide film for double-sided COF), where the ratio of B is B/100 cm ² .
[3]
The polyimide film according to [1] or [2], wherein A and/or B are two or more.
[4]
The polyimide according to any one of [1] to [3], which has a surface roughness Ra of 0.01 to 0.05 μm and a surface roughness Rz of 0.05 to 0.6 μm on both sides a and b. the film.
[5]
The polyimide film according to any one of [1] to [4], which has a coefficient of thermal expansion in the MD direction of 4 to 10 ppm/°C and a coefficient of thermal expansion in the TD direction of 0 to 8 ppm/°C.
[6]
The polyimide film according to any one of [1] to [5], which has a tensile modulus of elasticity of 5 to 10 GPa and/or a loop stiffness of 10 to 75 mN/cm.
[7]
The polyimide film according to any one of [1] to [6], comprising a polyimide containing an aromatic diamine component containing paraphenylenediamine and an acid anhydride component as a polymerization component.
[8]
The polyimide film according to any one of [1] to [7], wherein the inorganic particles have an average particle size of 0.05 to 0.5 μm.
[9]
A metal laminate (especially a double-sided copper-clad laminate) using the polyimide film according to any one of [1] to [8].
[10]
A metal laminate (especially a double-sided copper-clad laminate) according to [9], wherein the copper thickness is 1 to 3 μm.
[11]
A substrate for double-sided COF using the metal laminate (especially double-sided copper-clad laminate) according to [9] or [10].
[12]
A method for producing a double-sided COF substrate by a semi-additive method using the metal laminate (especially double-sided copper-clad laminate) according to [9] or [10].

A novel polyimide film can be obtained in the present invention. In particular, the present invention can provide a polyimide film that is well balanced among dimensional stability, bending properties, and surface smoothness on both sides of the film.

Such a polyimide film is suitable for COF (Chip On Film), for example. In particular, it can be suitably used for a fine-pitch circuit board such as a double-sided COF having wiring on both sides for the purpose of high-density mounting, and a semiconductor package.

1 is a cross-sectional view of a copper-clad laminate using a polyimide film as a base material; FIG. FIG. 2 is a cross-sectional view and a surface view of a COF substrate for dimension evaluation in which a copper wiring circuit pattern is formed on a polyimide film; FIG. 10 is a diagram showing a cycle of folding the COF substrate for dimension evaluation and returning it to its original state; FIG. 4 is a cross-sectional view after the glass is pressure-bonded to the COF substrate for dimension evaluation.

[Polyimide film]
In the polyimide film of the present invention, the ratio of specific projections is adjusted on both sides of the film.

First, in the first aspect, in the polyimide film, the ratio of protrusions with a height of 0.8 μm or more on one side a of the film is A/100 cm ² (A per 100 cm ² ), and on the other side b of the film When the ratio of protrusions with a height of 0.8 μm or more is B/100 cm ² (B per 100 cm ² ), each of A and B is 20 or less (for example, 18 or less), preferably 15 or less. (eg, 12 or less), more preferably 10 or less (eg, 9 or less, 8 or less).

Although the lower limit values of the projection ratios A and B are not particularly limited, they may each be 0 or a finite value (1, 2, etc.), for example.

In this way, by suppressing the ratio of specific protrusions on both sides of the film, defects such as pinholes can be efficiently suppressed. Therefore, such a film tends to improve the yield, and is suitable as a film or the like for providing a metal layer such as copper on both sides. According to the study of the present inventors, unexpectedly, among protrusions, there seems to be a high correlation between protrusions of 0.8 μm or more and defects such as pinholes.

In the second aspect of the present invention, in the polyimide film, the absolute value of the difference between A and B is 1 or more, preferably 2 or more (for example, 3 or more).
The upper limit of the absolute value of the difference between A and B is not particularly limited, but is, for example, 30, 25, 20, 18, 16, 14, 12, 10, 9, 8, 7, 6, etc. good too.

In this way, by biasing the ratio of specific protrusions on both sides of the film, it is easy to ensure sufficient slipperiness between the surface a and the surface b of the film. In some cases, it is easy to efficiently obtain a film with excellent handleability. In addition, perhaps in connection with such excellent handleability, the film is less likely to be scratched or wrinkled, and wiring can be efficiently formed on the film (facilitating the formation of wiring at a high yield).

The polyimide film of the present invention may satisfy at least one aspect of the first aspect and the second aspect, more preferably both aspects.

In the first aspect and/or the second aspect, at least one of A and B (A and/or B) is a finite value [eg, 1 or more, preferably 2 or more (eg, 2 to 10 , 2 to 8, 3 to 7, etc.]. By intentionally forming protrusions on at least one of the surfaces, it is easy to obtain a film having an excellent balance between good wiring formation and handleability.

The polyimide film of the present invention may have a predetermined surface roughness. For example, Ra (center line average roughness) of the polyimide film may be, for example, about 0.01 to 0.05 μm, 0.01 to 0.04 μm. Further, Rz (10-point average roughness) of the polyimide film may be 0.05 to 0.6 μm, preferably 0.1 to 0.5 μm.

In addition, such surface roughness may be satisfied on either one of the surfaces a and b of the film, or may be satisfied on the surfaces a and b.

According to a polyimide film having such a surface roughness (especially a polyimide film that satisfies the combination of such surface roughness and the first and / or second aspect), the copper layer etc. come off (pin Holes) are less likely to occur, making it easier to improve the yield. In addition, during film processing and production of copper-clad laminates, it is easy to ensure sufficient film slipperiness. It seems to be easy to hold down, and it is easy to obtain a good film.

The polyimide film of the present invention may have a specific coefficient of thermal expansion. For example, the coefficient of thermal expansion of the polyimide film is about 4 to 10 ppm/°C, preferably 3.5 to 9 ppm/°C, more preferably about 3 to 8 ppm/°C in the MD direction (machine direction, machine direction, machine direction). and may be about 0 to 8 ppm/°C, preferably 0 to 6 ppm/°C, more preferably 0.5 to 5 ppm/°C in the TD direction (width direction, lateral direction, perpendicular direction). .

By setting the coefficient of thermal expansion to such a range, poor bonding is less likely to occur when mounted on a semiconductor or glass panel, and the film is more suitable for use in fine-pitch circuit boards, semiconductor packages, and the like.

The polyimide film of the present invention preferably has a tensile modulus of 5 GPa or more (eg, 5 to 10 GPa), more preferably 6 to 8 GPa in MD and 7 to 10 GPa in TD. Such tensile modulus may be sufficient in the MD and/or TD of the film, particularly in both MD and TD.

The loop stiffness of the polyimide film of the present invention is preferably 10 to 75 mN/cm, more preferably 10 to 65 mN/cm.

The polyimide film of the present invention usually contains inorganic particles (or fillers). Such inorganic particles are not particularly limited, and examples thereof include titanium oxide, silica, calcium carbonate, calcium phosphate, and calcium hydrogen phosphate.

The average particle size of the inorganic particles may be, for example, 0.01 to 5 μm, preferably 0.02 to 2 μm (eg, 0.03 to 1 μm), and more preferably about 0.05 to 0.5 μm.
The average particle size of the inorganic particles was measured with a laser diffraction/scattering particle size distribution analyzer LA-920 manufactured by Horiba, Ltd. in a slurry state dispersed in DMAc (N,N-dimethylacetamide). In the particle size distribution, the median diameter is defined as the average particle diameter.

The content of the inorganic particles is not particularly limited as long as it does not interfere with the effects of the present invention. It may be 0.3 to 1.0% by mass.

(Method for producing polyimide and polyimide film)
A polyimide film (or a polyimide or polyamic acid constituting a polyimide film) usually has an aromatic diamine component and an acid anhydride component (tetracarboxylic acid component) as polymerization components. The polymerized component may contain other polymerized components as long as the main components are the aromatic diamine component and the acid anhydride component.
The production of the polyimide film is not particularly limited, but first, an aromatic diamine component and an acid anhydride component are polymerized in an organic solvent to obtain a polyamic acid (polyamic acid) solution.

The polyimide film of the present invention may suitably contain paraphenylenediamine as an aromatic diamine component. By using an aromatic diamine component containing paraphenylenediamine in this way, it is easy to efficiently obtain a polyimide film having the properties and physical properties described above.
The aromatic diamine component may contain things other than paraphenylenediamine. Specific examples of the aromatic diamine component other than paraphenylenediamine include metaphenylenediamine, benzidine, paraxylylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, and 4,4′. -diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,5-diaminonaphthalene, 3,3'-dimethoxybenzidine, 1,4-bis(3 -methyl-5-aminophenyl)benzene and their amide-forming derivatives. These may be used individually by 1 type, and may be used in mixture of 2 or more types.
As the aromatic diamine component, a combination of paraphenylenediamine and 4,4'-diaminodiphenyl ether and/or 3,4'-diaminodiphenyl ether is preferred. Among these, paraphenylenediamine and 3,4'-diaminodiphenyl ether, which have the effect of increasing the tensile modulus of the film, are adjusted to adjust the amount of the diamine component so that the resulting polyimide film has a tensile modulus of 5 GPa or more. It is preferable because the transportability is also improved.

Specific examples of the acid anhydride component include pyromellitic acid, 3,3′,4,4′-diphenyltetracarboxylic acid, 2,3′,3,4′-diphenyltetracarboxylic acid, 3,3′, 4,4'-benzophenonetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl) ether, pyridine-2,3,5,6-tetra Aromatic tetracarboxylic anhydride components such as carboxylic acids and amide-forming derivatives thereof can be mentioned, and pyromellitic dianhydride and 3,3′,4,4′-diphenyltetracarboxylic dianhydride are preferred. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

Among these, a particularly suitable combination of the aromatic diamine component and the acid anhydride component is one or more selected from the group consisting of paraphenylenediamine, 4,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl ether. A combination of an aromatic diamine component and one or more acid anhydride components selected from the group consisting of pyromellitic dianhydride and 3,3',4,4'-diphenyltetracarboxylic dianhydride. .

The blending ratio of paraphenylenediamine in the aromatic diamine component is to obtain the thermal expansion coefficient in the above range, to give the film an appropriate strength, to prevent poor running performance, etc., relative to the total amount of the aromatic diamine component. may be selected from the range of 15 mol% or more (e.g., 18 mol% or more), usually 20 mol% or more (e.g., 25 mol% or more), preferably 30 mol% or more (e.g., 31 mol% or more) , 32 mol % or more), preferably 33 mol % or more, more preferably 35 mol % or more.
The upper limit of the proportion of paraphenylenediamine in the aromatic diamine component may be, for example, 100 mol %, especially less than 100 mol % [for example, 99 mol %, 95 mol %, 90 mol %, 80 mol %, 70 mol %, 60 mol % or less (eg, 60 mol %, 55 mol %, 52 mol %, 50 mol %, 48 mol %, 45 mol %, etc.)].
Typically, the ratio of the paraphenylenediamine component in the aromatic diamine component is 15 to 80 mol% (eg, 18 to 75 mol%), 20 to 75 mol% (eg, 25 to 70 mol %), 30 to 65 mol % (eg, 32 to 60 mol %, 30 to 55 mol % (eg, 32 to 50 mol %)).
Further, when the aromatic diamine component contains 4,4'-diaminodiphenyl ether and/or 3,4'-diaminodiphenyl ether (especially 4,4'-diaminodiphenyl ether), 4,4'-diamino in the aromatic diamine component The ratio of diphenyl ether and/or 3,4'-diaminodiphenyl ether may be selected from the range of, for example, 85 mol% or less (eg, 82 mol% or less), preferably 80%, based on the total amount of the aromatic diamine component. mol% or less (e.g., 78 mol% or less), more preferably 75 mol% or less (e.g., 73 mol% or less), and 70 mol% or less (e.g., 68 mol% or less, 65 mol% or less) good too.
The lower limit of the ratio of 4,4'-diaminodiphenyl ether and/or 3,4'-diaminodiphenyl ether (particularly 4,4'-diaminodiphenyl ether) in the aromatic diamine component is not particularly limited, and is, for example, 1 mol%, It may be 5 mol %, 10 mol %, 15 mol %, 20 mol %, 30 mol %, 40 mol %, 45 mol %, 50 mol %, 52 mol %, 55 mol %, 60 mol % and the like.
Typically, the ratio of 4,4'-diaminodiphenyl ether and/or 3,4'-diaminodiphenyl ether (especially 4,4'-diaminodiphenyl ether) in the aromatic diamine component is 20-85 mol% (eg, 22-82 mol%), 25-80 mol% (eg, 30-78 mol%), 35-75 mol% (eg, 38-72 mol%), 40-70 mol% (eg, 45 to 70 mol %), 50 to 68 mol %, and the like.
The blending ratio (molar ratio) in the acid anhydride component is not particularly limited as long as it does not interfere with the effects of the present invention. Examples include 3,3',4,4'-diphenyltetracarboxylic dianhydride. In this case, the content of 3,3′,4,4′-diphenyltetracarboxylic dianhydride is preferably 15 mol % or more (eg, 18 mol % or more) relative to the total amount of the acid anhydride component, and 20 mol. % or more is more preferable, and 25 mol % or more is even more preferable.
The upper limit of the ratio of 3,3',4,4'-diphenyltetracarboxylic dianhydride in the acid anhydride component may be 100 mol%, particularly less than 100 mol% (e.g., 99 mol%, 95 mol%, 90 mol%, 85 mol%, 80 mol%, 70 mol%, 60 mol%, 50 mol%, 45 mol%, 42 mol%, 40 mol%, 38 mol%, 35 mol%, 33 mol %, etc.).
Typically, the proportion of 3,3',4,4'-diphenyltetracarboxylic dianhydride in the acid anhydride component is 15 to 85 mol% (for example, 18 to 70 mol %), 18 to 60 mol % (eg, 18 to 50 mol %), 20 to 40 mol %.
When the acid anhydride component contains pyromellitic dianhydride, the proportion of pyromellitic dianhydride is, for example, 15 mol% or more (e.g., 20 mol% or more) relative to the total acid anhydride component, preferably may be about 25 mol% or more (e.g., 30 mol% or more), more preferably about 35 mol% or more (e.g., 40 mol% or more), and may be about 45 mol% or more (e.g., 48 mol% or more, 50 mol% % or more, 55 mol % or more, 58 mol % or more, 60 mol % or more, 62 mol % or more, etc.).
The upper limit of the proportion of pyromellitic dianhydride in the acid anhydride component is not particularly limited, and may be, for example, 100 mol%, particularly less than 100 mol% (e.g., 95 mol%, 90 mol%, 85 mol %, 80 mol %, 82 mol %, 75 mol %, 72 mol %, etc.).
Typically, the proportion of pyromellitic dianhydride in the acid anhydride component is 10 to 95 mol% (for example, 12 to 90 mol%), 15 to 85 mol% ( 20 to 82 mol %), 30 to 85 mol % (eg, 40 to 82 mol %), 50 to 80 mol % (eg, 60 to 80 mol %).
By using such a polyamic acid composed of an aromatic diamine component and an acid anhydride component as a raw material (precursor) for a polyimide film, the thermal expansion coefficient of the polyimide film is changed to the machine conveying direction (MD) of the film, It is preferable because it can be easily adjusted within the above range in both the width direction (TD).

Further, in the present invention, specific examples of the organic solvent used for forming the polyamic acid solution include sulfoxide solvents such as dimethylsulfoxide and diethylsulfoxide, N,N-dimethylformamide, N,N-diethylformamide, and the like. formamide solvents, N,N-dimethylacetamide, acetamide solvents such as N,N-diethylacetamide, pyrrolidone solvents such as N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, phenol, o-, Examples include phenolic solvents such as m- or p-cresol, xylenol, halogenated phenols and catechol, and aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone, which may be used alone or in combination of two or more. is preferably used as a mixture, but aromatic hydrocarbons such as xylene and toluene can also be used.

The polymerization method may be carried out by any known method. For example, (1) the total amount of the aromatic diamine component is first placed in a solvent, and then the acid anhydride component is added in an amount equivalent (equimolar) to the total amount of the aromatic diamine component. A method of polymerizing in addition to
(2) A method in which the entire amount of the acid anhydride component is first put into a solvent, and then the aromatic diamine component is added so as to be equivalent to the acid anhydride component for polymerization.
(3) One aromatic diamine component (a1) is put into a solvent, and then one acid anhydride component (b1) is mixed at a ratio of 95 to 105 mol % with respect to the reaction components for the time required for the reaction. After that, the other aromatic diamine component (a2) is added, and then the other acid anhydride component (b2) is added so that the total aromatic diamine component and the total acid anhydride component are approximately equivalent. A method of adding and polymerizing.
(4) After putting one acid anhydride component (b1) into a solvent, one aromatic diamine component (a1) is mixed at a ratio of 95 to 105 mol% with respect to the reaction components for the time required for the reaction. After that, the other acid anhydride component (b2) is added, and then the other aromatic diamine component (a2) is added so that the total aromatic diamine component and the total acid anhydride component are approximately equivalent. to polymerize.
(5) One aromatic diamine component and an acid anhydride component are reacted in a solvent so that one of them is excessive to prepare a polyamic acid solution (A), and the other aromatic diamine component is reacted in another solvent. and an acid anhydride component are reacted so that one of them becomes excessive to prepare a polyamic acid solution (B). A method in which the polyamic acid solutions (A) and (B) thus obtained are mixed to complete the polymerization. At this time, when the aromatic diamine component is excessive when preparing the polyamic acid solution (A), the acid anhydride component is excessive in the polyamic acid solution (B), and the acid anhydride component is excessive in the polyamic acid solution (A). In the case of , the polyamic acid solution (B) contains an excess amount of the aromatic diamine component, the polyamic acid solutions (A) and (B) are mixed, and the total aromatic diamine component and the total acid anhydride component used in these reactions are Adjust so that it is approximately equal. The polymerization method is not limited to these, and other known methods may be used.

The polyamic acid solution thus obtained usually contains 5 to 40% by weight of solids, preferably 10 to 30% by weight of solids. Further, the viscosity is usually 10 to 2000 Pa·s as measured by a Brookfield viscometer, and preferably 100 to 1000 Pa·s for stable liquid transfer. Also, the polyamic acid in the organic solvent solution may be partially imidized.

Next, a method for producing a polyimide film will be described. As a method for forming a polyimide film, a method of casting a polyamic acid solution into a film and thermally decyclizing and desolvating it to obtain a polyimide film, and a method of mixing a cyclization catalyst and a dehydrating agent with a polyamic acid solution and chemically There is a method of obtaining a polyimide film by decyclization to form a gel film and removing the solvent by heating to obtain a polyimide film. preferable.

In the chemical decyclization method, first, the polyamic acid solution is prepared. In the present invention, the polyamic acid solution may generally contain inorganic particles as described above.

The polyamic acid solution used here may be a prepolymerized polyamic acid solution, or may be a polyamic acid solution that is sequentially polymerized when adding inorganic particles.

The polyamic acid solution may contain a cyclization catalyst (imidization catalyst), a dehydrating agent, a gelling retardant, and the like.

Cyclization catalysts include amines such as aliphatic tertiary amines (trimethylamine, triethylenediamine, etc.), aromatic tertiary amines (dimethylaniline, etc.), heterocyclic tertiary amines (e.g., isoquinoline, pyridine, β-picoline, etc.). These may be used individually by 1 type, and may be used in mixture of 2 or more types.

Dehydrating agents include acid anhydrides such as aliphatic carboxylic anhydrides (eg, acetic anhydride, propionic anhydride, butyric anhydride, etc.), aromatic carboxylic anhydrides (eg, benzoic anhydride, etc.), and the like. . These may be used individually by 1 type, and may be used in mixture of 2 or more types.
The gelation retardant is not particularly limited, and acetylacetone or the like can be used.

As a method for producing a polyimide film from a polyamic acid solution, a polyamic acid solution (in particular, a polyamic acid solution containing a cyclization catalyst and a dehydrating agent) is cast on a support to form a film, and the support is There is a method in which imidization is partially progressed on the body to form a self-supporting gel film, then the film is peeled off from the support, dried by heating/imidized, and heat-treated.

Examples of the support include a rotating drum and an endless belt made of metal, but there is no particular limitation as long as the material is uniform and the surface roughness can be controlled and managed.

The gel film is usually heated to 20 to 200° C., preferably 40 to 150° C. by receiving heat from the support and/or receiving heat from a heat source such as hot air or an electric heater, and undergoes a ring closure reaction, resulting in the liberated organic solvent and the like. By drying the volatiles, it becomes self-supporting and is released from the support.

The gel film peeled from the support may be stretched. As for the stretching treatment, the apparatus and method are not limited as long as the stretching in the machine direction (MD) and the stretching in the width direction (TD) can be combined at a predetermined ratio. The draw ratio for producing the film having the effects of the present invention is usually at a temperature of 200° C. or higher, and the MD is usually 1.05 to 1.9 times, preferably 1.1 to 1.6 times. , and more preferably 1.1 to 1.5 times. TD is usually 1.1 to 1.5 times the magnification X of MD, and may preferably be 1.2 to 1.45 times.

The film may be heat-treated at a temperature of 250 to 500° C. for 15 seconds to 30 minutes using hot air and/or an electric heater.

It is preferable to adjust the solid concentration, viscosity, and amount of polymer cast onto the support so that the thickness of the film is 5 to 75 μm, preferably 10 to 50 μm, more preferably 20 to 40 μm.

It is preferable to further anneal the polyimide film thus obtained. By doing so, thermal relaxation of the film occurs, and the heat shrinkage rate can be kept small. The annealing temperature is not particularly limited, but is preferably 200° C. or higher and 500° C. or lower, more preferably 200° C. or higher and 370° C. or lower, and particularly preferably 210° C. or higher and 350° C. or lower. Thermal relaxation from the annealing treatment can keep the heat shrinkage rate at 200° C. within the above range, which is preferable because the dimensional accuracy is further improved.

In order to impart adhesiveness to the obtained polyimide film, the surface of the film may be subjected to electrical treatment such as corona treatment or plasma treatment or physical treatment such as blasting. It can be carried out according to a conventional method. The pressure of the atmosphere when performing plasma treatment is not particularly limited, but is usually in the range of 13.3 to 1330 kPa, preferably in the range of 13.3 to 133 kPa (100 to 1000 Torr), and 80.0 to 120 kPa (600 to 900 Torr). is more preferred.

The atmosphere in which the plasma treatment is performed contains at least 20 mol% of an inert gas, preferably 50 mol% or more, more preferably 80 mol% or more, and more preferably 90 mol% or more. Most preferred are those that The inert gas includes He, Ar, Kr, Xe, Ne, Rn, _N2 and mixtures of two or more thereof. A particularly preferred inert gas is Ar. Further, oxygen, air, carbon monoxide, carbon dioxide, carbon tetrachloride, chloroform, hydrogen, ammonia, tetrafluoromethane (carbon tetrafluoride), trichlorofluoroethane, trifluoromethane, etc. are mixed with the inert gas. You may Preferred mixed gas combinations used as the atmosphere for the plasma treatment of the present invention are argon/oxygen, argon/ammonia, argon/helium/oxygen, argon/carbon dioxide, argon/nitrogen/carbon dioxide, argon/helium/nitrogen, and argon. /helium/nitrogen/carbon dioxide, argon/helium, helium/air, argon/helium/monosilane, argon/helium/disilane, and the like.

The processing power density for plasma treatment is not particularly limited, but is preferably 200 W·min/m ² or more, more preferably 500 W·min/m ² or more, and most preferably 1000 W·min/m ² or more. The plasma irradiation time for plasma treatment is preferably 1 second to 10 minutes. By setting the plasma irradiation time within this range, the effect of the plasma treatment can be fully exhibited without deterioration of the film. The type of gas, gas pressure, and processing density for plasma processing are not limited to the above conditions, and plasma processing may be performed in the atmosphere.

As described above, the polyimide film of the present invention has specific characteristics and physical properties (such as a specific proportion of protrusions), but such aspects can be adjusted by appropriately selecting the above conditions. . For example, a specific proportion of projections on both sides of the film can be adjusted by selecting the average particle size and amount of inorganic particles added to the polyamic acid solution. In addition, since such a projection ratio may be affected by the viscosity of the polyamic acid solution, the surface roughness of the support on which the polyamic acid solution is cast, the film draw ratio after peeling from the support, etc., these factors should be considered. You may adjust a protrusion ratio by selecting. That is, in the present invention, the ratio of protrusions on both sides of the film is reduced by adjusting the average particle size of the inorganic particles, the amount added, the viscosity of the polyamic acid solution, the surface roughness of the support, the draw ratio of the film, etc., within a predetermined range. It makes it possible to adjust.

Since the polyimide film obtained in this way is excellent in dimensional stability, surface smoothness, bending characteristics, etc., as described later, COF (Chip On Film) wiring at a narrow pitch in the film width direction, particularly high density It can be suitably used for a fine-pitch circuit board such as a double-sided COF having wiring on both sides for the purpose of mounting, and a semiconductor package.

[Copper clad laminate]
The present invention also includes a copper-clad laminate using (provided with) the polyimide film of the present invention described above. In such a copper-clad laminate, a copper layer is formed on at least one side of a polyimide film, and in particular, a copper layer is formed on both sides of the polyimide film.
The method for producing such a copper-clad laminate is not particularly limited, and a conventionally known production method may be followed. For example, on at least one surface (especially both surfaces) of a polyimide film, a metal layer containing nickel chromium as a main component formed by a sputtering method is generally laminated with a layer containing copper as a main component by electroplating. target. The copper-clad laminate of the present invention can be obtained, for example, by providing a nickel-chromium alloy layer on both sides of a polyimide film and forming copper with a predetermined thickness (for example, a thickness of 1 to 3 μm) thereon by electroplating. .

The present invention also includes a substrate for double-sided COF using (provided with) the copper-clad laminate of the present invention described above. The double-sided COF substrate may be a copper-clad laminate provided with a wiring circuit.
The method for manufacturing such a double-sided COF substrate is not particularly limited, and a known method can be used, but in particular, it may be manufactured by a semi-additive method.
As a more specific method, the wiring circuit is patterned using the photolithography method, the resist layer is peeled off where the wiring is to be formed, the wiring is formed on the exposed thin copper layer by electrolytic copper plating, and then the resist layer is formed. , removing the thin copper layer and the underlying metal layer, forming tin of 0.1 to 0.5 μm on the wiring by electroless tin plating, and then laminating a solder resist on the required portion.

The present invention includes various combinations of the above configurations within the technical scope of the present invention as long as the effects of the present invention are exhibited.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

In the examples, PPD represents paraphenylenediamine, 4,4′-ODA represents 4,4′-diaminodiphenyl ether, PMDA represents pyromellitic dianhydride, and BPDA represents 3,3′,4 ,4′-diphenyltetracarboxylic dianhydride, and DMAc represents N,N-dimethylacetamide.

[Example 1]
(Preparation of polyimide film)
Prepare PPD (molecular weight 108.14), 4,4'-ODA (molecular weight 200.24), BPDA (molecular weight 294.22), PMDA (molecular weight 218.12) at a molar ratio of 35/65/30/70 Then, the mixture was made into a 20% by weight solution in DMAc and polymerized to obtain a polyamic acid solution of 3500 poise. To this, DMAc slurry of silica having an average particle size of 0.1 μm was added in an amount of 0.5% by weight based on the weight of the resin, and sufficiently stirred to disperse. Next, a 125 μm thick polyester film (Lumirror X43: manufactured by Toray Industries, Ra 0.2 μm) was placed on a glass plate as a support, and a polyamic acid solution was placed on the support and cast using an applicator. Subsequently, this was immersed in a mixed solution of acetic anhydride and β-picoline for 10 minutes to cause an imidization reaction, then the polyimide gel film was peeled off from the polyester film, and the gel film was manually stretched in the direction of the applicator (hereinafter referred to as MD ) and 1.40 times in the vertical direction (hereinafter referred to as TD), and fixed to a support frame. After drying by heating at 300° C. for 20 minutes and then at 400° C. for 5 minutes, the film was removed from the supporting frame to obtain a polyimide film having a thickness of 35 μm.

This film was evaluated for the following characteristics, and the results are shown in Table 1.
(1) Surface roughness Measured according to JIS B0601-1982 using a surface roughness measuring machine SE-3500 (manufactured by Kosaka Laboratory).
(2) Number of surface protrusions Using a laser microscope VK-9710 (manufactured by KEYENCE CORPORATION), protrusions on the film surface were observed in a field of view of 100 cm ² and the height was measured to count the number of protrusions of 0.8 µm or more.
The observation was performed by magnifying the measurement site by 10 times with an objective lens (200 times magnification on the monitor). In addition, the width of the observed protrusions was all 15 μm or more (there were no protrusions with a width of less than 15 μm), and when the protrusions had a plurality of protrusions, the height of the highest protrusion was Satoshi.
(3) Thermal expansion coefficient TMA-60 (manufactured by Shimadzu Corporation) was used, and the measurement temperature range was 50 to 200°C, and the heating rate was 10°C/min.
(4) Tensile modulus RTM-250 (manufactured by A&D) was used, and tensile speed was measured at 100 mm/min.
(5) Loop Stiffness Loop stiffness tester DA (manufactured by Toyo Seiki Seisakusho) was used to measure under the conditions of a sample width of 20 mm, a loop length of 50 mm, and a compression distance of 20 mm.
(6) Film Handleability The support surface and the non-support surface of the sample were superimposed and fixed on a slip tester (manufactured by Techno Needs Co., Ltd.), and the static friction coefficient and dynamic friction coefficient were measured at a load of 200 g and a measurement speed of 120 mm / min. It was measured. Table 1 shows the results.

(Creation of double-sided copper-clad laminate)
After forming a nickel chromium layer (Ni:Cr=80:20m, thickness 25 nm) and a copper layer (thickness 100 nm) by sputtering on the support surface of the polyimide film obtained above, similarly, the non-support surface A nickel-chromium layer and a copper layer were also formed on the substrate. Subsequently, a copper layer having a thickness of 2 μm was formed on both surfaces by electroplating using a copper sulfate plating solution.

The following items were evaluated for the obtained double-sided copper-clad laminate (FIG. 1). The results are listed in Table 1.

(7) Number of Pinholes After protecting the support surface of the double-sided copper-clad laminate with a cover film, etching was performed using a ferric chloride solution to remove the copper layer and nickel-chromium layer on the non-support surface. Subsequently, in a dark room, a fluorescent backlight was illuminated from the polyimide surface (non-support surface), and the number of light (pinholes) leaking to the copper surface (support surface) was visually counted in a field of view of 100 cm ² . rice field. The number of pinholes on the non-support surface was also evaluated in a similar manner.

(Creation of substrate for COF for evaluation)
Regarding the sample from which the copper layer and the nickel-chromium layer on the non-support surface of the double-sided copper-clad laminate obtained above were removed, the copper surface (support surface) was treated with Slucup ACL-067 manufactured by Uyemura & Co., Ltd. to 15% with water. After degreasing by immersing in the diluted solution at 30° C. for 30 seconds, a photoresist is laminated so that the dry thickness is 15 μm, and the evaluation pattern (line width 20 μm, space width 20 μm) shown in FIG. 2 is exposed and exposed. Developed. After that, a copper plating layer having a thickness of 8 μm was formed by a semi-additive method according to a conventional method, and a substrate for COF for evaluation was produced.
The obtained COF substrate was evaluated for the following items, and the results are shown in Table 1.

(8) Bendability The conductor side of the COF substrate was folded inward as shown in FIG. 3, and after applying a load of 1.0 kgf for 10 seconds, the COF substrate was returned to its original state. This cycle was repeated 5 to 30 times, during which the bent portions of the conductor were observed under a microscope, and the number of times until the conductor was broken was measured.

(9) Dimensional stability Using the COF substrate for evaluation obtained above as an adherend (glass) with an anisotropic conductive film (ACF: product name, Hitachi Chemical Anisolm C5311), 180 ° C. × 10 seconds, 5 MPa (Fig. 4).

The external dimensions of 30 samples of circuit patterns for evaluation were measured before (L3) and after (L4) pressure bonding, and the standard deviation of elongation calculated by the following formula was measured.
Elongation rate (%) = {(L4-L3) / L3} x 100

[Example 2]
A polyimide film having a thickness of 38 μm was obtained in the same manner as in Example 1 except that the gel film was stretched 1.25 times in MD and 1.40 times in TD.

[Example 3]
A polyimide film having a thickness of 35 μm was obtained in the same manner as in Example 1, except that a DMAc slurry of silica having an average particle size of 0.4 μm was used.

[Example 4]
A polyimide film having a thickness of 25 μm was obtained in the same manner as in Example 3, except that the gel film was stretched 1.15 times in MD and 1.35 times in TD.

[Example 5]
PPD, 4,4′-ODA, BPDA, and PMDA were adjusted to a molar ratio of 20/80/35/65, and silica having an average particle size of 0.4 μm was used. A polyimide film with a thickness of 38 μm was obtained.

[Example 6]
A polyimide film having a thickness of 38 μm was obtained in the same manner as in Example 3, except that PPD, 4,4'-ODA, BPDA and PMDA were used in a molar ratio of 30/70/25/75.

[Example 7]
A polyimide film having a thickness of 25 μm was obtained in the same manner as in Example 5, except that calcium hydrogen phosphate having an average particle size of 1.0 μm was used.

[Example 8]
PPD and BPDA were mixed at a molar ratio of 1:1, and DMAc slurry of silica having an average particle size of 0.1 μm was added at 0.5% by weight per resin weight to prepare a polyamic acid solution. A polyimide film having a thickness of 38 μm was obtained in the same manner as in Example 4, except that a polyester film having a thickness of 125 μm (Lumirror S10: manufactured by Toray Industries, Inc., Ra 0.05 μm) was used as the support.

[Example 9]
A polyimide film having a thickness of 35 μm was obtained in the same manner as in Example 3, except that PPD, 4,4′-ODA, BPDA and PMDA were used in a molar ratio of 40/60/25/75.

[Example 10]
A polyimide film having a thickness of 35 μm was obtained in the same manner as in Example 3, except that PPD, 4,4'-ODA, BPDA and PMDA were used in a molar ratio of 45/55/35/65.

The properties of the polyimide films obtained in Examples 2 to 8, and the double-sided copper-clad laminates and evaluation COF substrates prepared in the same manner as in Example 1 using them were evaluated in the same manner as in Example 1. , Table 1 shows the results.

From the results in the above table, it can be said that the polyimide films of Examples are films excellent in surface smoothness, dimensional stability, bendability, and the like. In addition, it was confirmed that the film was excellent in balance of surface smoothness on both sides of the film, so that the film was easy to handle and could maintain high productivity.

The polyimide film of the present invention is excellent in dimensional stability, bending properties and the like. Moreover, in the present invention, a film having high surface quality on both sides can be obtained. Therefore, such a polyimide film of the present invention can be suitably used for fine-pitch circuit boards such as double-sided COF with wiring on both sides, and semiconductor packages, particularly for the purpose of high-density mounting.

Claims (12)

A polyimide film containing inorganic particles, wherein the ratio of projections with a height of 0.8 μm or more on one side a of the film is A/100 cm ² , and the projections with a height of 0.8 μm or more on the other side b of the film A polyimide film for double-sided COF, wherein each of A and B is 10 or less , and the absolute value of the difference between A and B is 2 or more , where B is the ratio of B per 100 cm ² . 2. The polyimide film according to claim 1 , wherein both A and B are 8 or less , and the absolute value of the difference between A and B is 3 or more. 3. The polyimide film according to claim 1, wherein A and/or B are two or more. The polyimide film according to any one of claims 1 to 3, having a surface roughness Ra of 0.01 to 0.05 µm and a surface roughness Rz of 0.05 to 0.6 µm on both sides a and b. The polyimide film according to any one of claims 1 to 4, which has a coefficient of thermal expansion of 4 to 10 ppm/°C in the MD direction and 0 to 8 ppm/°C in the TD direction. The polyimide film according to any one of claims 1 to 5, which has a tensile modulus of elasticity of 5 to 10 GPa and/or a loop stiffness of 10 to 75 mN/cm. 7. The polyimide film according to any one of claims 1 to 6, comprising a polyimide containing an aromatic diamine component containing paraphenylenediamine and an acid anhydride component as a polymerization component. The polyimide film according to any one of claims 1 to 7, wherein the inorganic particles have an average particle size of 0.05 to 0.5 µm. A double-sided copper-clad laminate using the polyimide film according to any one of claims 1 to 8. 10. The double-sided copper-clad laminate according to claim 9, wherein the copper thickness is 1-3 μm. A double-sided COF substrate using the double-sided copper-clad laminate according to claim 9 or 10. A method for producing a double-sided COF substrate by a semi-additive method using the double-sided copper-clad laminate according to claim 9 or 10.

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