JP2008024883A - Polyimide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyimide film exhibiting excellent resistance to repeated flexing and resistance to repeated twisting. <P>SOLUTION: A polyimide film having excellent resistance to repeated flexing and resistance to repeated twisting is obtained by coating on a support a polyamide acid of a benzoxazole structure-containing polyimide precursor, drying, and performing imidation treatment by using a process for tensile deformation between the crystallization starting temperature obtained by using high output X-ray diffraction and the 90% imidation-attaining temperature obtained from IR measurement. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polyimide film having high rigidity and extremely high heat resistance, which is suitable as a base material for electronic components that can withstand bending in one direction and twisting in a random direction.

Polyimide film has excellent heat resistance, electrical properties, mechanical properties, dimensional stability, etc., so flexible printed wiring boards (FPC), carrier tapes for tape automated bonding (TAB), It is used in a wide range of fields such as various electronic materials including base materials for semiconductor mounting, industrial equipment, and high-performance parts such as aircraft.
In particular, in circuit boards and semiconductor package base materials associated with high-density mounting in recent years, it has become mainstream to use an insulating resin having a low dielectric constant as an interlayer insulating film in order to increase the speed of signal transmission. . A polyimide film is one of the typical insulating materials.
Usually, a polyimide film is bonded to a copper foil using an adhesive, or processed into a laminate (a polyimide film with a copper foil) composed of a film layer and a copper foil by vapor deposition, plating, sputtering, or casting. In other words, it is used as a base film of a flexible printed multilayer circuit board.

  As portable devices have become smaller and lighter in recent years, attempts have been made to reduce the size by folding or overlapping members having electronic circuits. Of course, a flexible printed wiring board using a conventional polyimide film as a base material has been frequently used for folding portions of compact portable devices. In order to cope with the more frequent folding method, bending direction, and folding with a high degree of freedom in the twisting direction, a substrate with excellent twist-flexibility characteristics is required. In the present situation, no satisfactory material has been obtained.

In order to cope with such a problem, a so-called polyimide benzoxazole film is proposed which is made of polyimide having a benzoxazole ring in the main chain and has high heat resistance and rigidity and little dimensional change due to temperature (see Patent Documents 1 to 3). . However, high twist resistance has not been reached to a level that satisfies the requirements regarding reliability, and its improvement has been strongly desired.
JP-A-6-56992 Japanese National Patent Publication No. 11-504369 Japanese National Patent Publication No. 11-505184

  It is an object of the present invention to provide a polyimide film that is suitable as a base material for electronic components that can withstand the use of bending in one direction and twisting in a random direction, has high rigidity, and has extremely high heat resistance. And

  In view of such a situation, the present inventors have intensively studied, and as a result, the crystal size in the c-axis direction and the crystal disorder in the c-axis direction, which are higher-order structure parameters of the polyimide film, fall within a specific range, and thus are not repeated in the past. It has been found that a polyimide film resistant to bending and repeated twisting can be obtained. Here, the resistance to repeated bending and twisting is to the polyimide film itself and the conductor layer used together with the polyimide film. The present inventors have further found that the characteristics can be evaluated by the frequency of the number of pinholes generated in the polyimide film by repeated bending and repeated twisting as a method for evaluating resistance to repeated bending and repeated twisting.

That is, this invention is based on the following structure.
1. A polyimide film, wherein the crystal size in the c-axis direction is 2 nm or more and 30 nm or less, and the crystal disorder in the c-axis direction is 1% or more and 15% or less.
2. 2. The polyimide film as described in 1 above, wherein the polyimide film is a polyimide film having a benzoxazole structure.
3. 2. The polyimide film as described in 1 above, wherein the crystal size in the c-axis direction is from 5 nm to 20 nm, and the crystal disorder in the c-axis direction is from 1.5% to 10%.
4). 3. The polyimide film according to 1 or 2 above, wherein the crystal size in the c-axis direction is 8 nm or more and 15 nm or less, and the crystal disorder in the c-axis direction is 2% or more and 5% or less.
5. 4. The polyimide film according to any one of 1 to 3, wherein the number of pinholes generated in a twist bending test using a gel bot tester is 0 or more and 3 or less.

  According to the present invention, the resistance to repeated bending and twisting is greatly improved by keeping the crystal size and crystal disorder of a polyimide film having a benzoxazole structure having a high elastic modulus and high heat resistance within a specific range. can do. Of course, a polyimide film having a benzoxazole structure is suitable for a high-density, high-fine wiring board material by taking advantage of its high elasticity and high heat resistance. In addition, by improving resistance to repeated twisting and bending at high levels, electronic boards and wiring for compact and lightweight handheld devices, portable devices, wearable devices, etc. that require compact folding and storing capacity and high degree of freedom of deformation. It can be widely used as a substrate, a cable material, an antenna material, a feeding material, a copper-clad substrate (FPC) for flexible printed wiring, a carrier tape for tape automated bonding (TAB), a chip-on-film (COF), and the like.

As an example, the polyimide film of the present invention is obtained by a method generally called a casting film forming method using a polyamic acid obtained by reacting an aromatic diamine and an aromatic tetracarboxylic acid anhydride as a precursor. Can do.
The polyimide film in the present invention preferably has a benzoxazole structure.
Benzene used in polyimide benzoxazole mainly composed of polyimide benzoxazole obtained by reacting aromatic diamines having a benzoxazole structure and aromatic tetracarboxylic anhydrides that can be particularly preferably used in the present invention. Examples of aromatic diamines having an oxazole structure include the following compounds.

Among these, amino (aminophenyl) benzoxazole isomers are preferable from the viewpoint of ease of synthesis. Here, “each isomer” refers to each isomer in which two amino groups of amino (aminophenyl) benzoxazole are determined according to the coordination position (eg, the above “formula 1” to “formula 4”). Each compound described in the above. These diamines may be used alone or in combination of two or more.
In the present invention, it is preferable to use 70 mol% or more of the aromatic diamine having the benzoxazole structure.

The present invention is not limited to the above items, and the following aromatic diamines may be used. Preferably, the diamines do not have the benzoxazole structure exemplified below as long as the total aromatic diamine is less than 30 mol%. Is a polyimide film using one or two or more in combination.
Examples of such diamines include 4,4′-bis (3-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, and bis [4- (3-aminophenoxy) phenyl]. Sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine,

3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfide, 3,3′-diaminodiphenyl sulfoxide, 3,4′-diaminodiphenyl sulfoxide 4,4′-diaminodiphenyl sulfoxide, 3,3′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminobenzophenone, 3,4′- Diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, bis [4- (4-aminophenoxy) phenyl] methane, 1 , 1-Bi [4- (4-aminophenoxy) phenyl] ethane, 1,2-bis [4- (4-aminophenoxy) phenyl] ethane, 1,1-bis [4- (4-aminophenoxy) phenyl] propane, 1 , 2-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl ]propane,

1,1-bis [4- (4-aminophenoxy) phenyl] butane, 1,3-bis [4- (4-aminophenoxy) phenyl] butane, 1,4-bis [4- (4-aminophenoxy) Phenyl] butane, 2,2-bis [4- (4-aminophenoxy) phenyl] butane, 2,3-bis [4- (4-aminophenoxy) phenyl] butane, 2- [4- (4-aminophenoxy) Phenyl] -2- [4- (4-aminophenoxy) -3-methylphenyl] propane, 2,2-bis [4- (4-aminophenoxy) -3-methylphenyl] propane, 2- [4- ( 4-aminophenoxy) phenyl] -2- [4- (4-aminophenoxy) -3,5-dimethylphenyl] propane, 2,2-bis [4- (4-aminophenoxy) -3,5-dimethylphen Le] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane,

1,4-bis (3-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) ) Biphenyl, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfoxide, bis [4- ( 4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 1,3-bis [4- (4-aminophenoxy) ) Benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (3 Aminophenoxy) benzoyl] benzene, 4,4′-bis [(3-aminophenoxy) benzoyl] benzene, 1,1-bis [4- (3-aminophenoxy) phenyl] propane, 1,3-bis [4- (3-aminophenoxy) phenyl] propane, 3,4'-diaminodiphenyl sulfide,

2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, bis [4- (3-aminophenoxy) phenyl] methane, 1,1 -Bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bis [4- (3-aminophenoxy) phenyl] ethane, bis [4- (3-aminophenoxy) phenyl] sulfoxide, 4,4 '-Bis [3- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [3- (3-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-α) , Α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, bis 4- {4- (4-aminophenoxy) phenoxy} phenyl] sulfone, 1,4-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-trifluoromethylphenoxy) -α, α-dimethylbenzyl] benzene, 1,3 -Bis [4- (4-amino-6-fluorophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-methylphenoxy) -α, α-dimethylbenzyl Benzene, 1,3-bis [4- (4-amino-6-cyanophenoxy) -α, α-dimethylbenzyl] benzene,

3,3′-diamino-4,4′-diphenoxybenzophenone, 4,4′-diamino-5,5′-diphenoxybenzophenone, 3,4′-diamino-4,5′-diphenoxybenzophenone, 3, 3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3 '-Diamino-4,4'-dibiphenoxybenzophenone, 4,4'-diamino-5,5'-dibiphenoxybenzophenone, 3,4'-diamino-4,5'-dibiphenoxybenzophenone, 3,3'- Diamino-4-biphenoxybenzophenone, 4,4′-diamino-5-biphenoxybenzophenone, 3,4 -Diamino-4-biphenoxybenzophenone, 3,4'-diamino-5'-biphenoxybenzophenone, 1,3-bis (3-amino-4-phenoxybenzoyl) benzene, 1,4-bis (3-amino- 4-phenoxybenzoyl) benzene, 1,3-bis (4-amino-5-phenoxybenzoyl) benzene, 1,4-bis (4-amino-5-phenoxybenzoyl) benzene, 1,3-bis (3-amino) -4-biphenoxybenzoyl) benzene, 1,4-bis (3-amino-4-biphenoxybenzoyl) benzene, 1,3-bis (4-amino-5-biphenoxybenzoyl) benzene, 1,4-bis (4-Amino-5-biphenoxybenzoyl) benzene, 2,6-bis [4- (4-amino-α, α-dimethylbenzyl) pheno Si] A part or all of the hydrogen atoms on the aromatic ring in the benzonitrile and the aromatic diamine are halogen atoms, alkyl groups having 1 to 3 carbon atoms or alkoxyl groups, cyano groups, or alkyl groups or alkoxyl group hydrogen atoms. Examples thereof include aromatic diamines substituted with a halogenated alkyl group having 1 to 3 carbon atoms, partially or entirely substituted with halogen atoms, or alkoxyl groups.

  The aromatic tetracarboxylic acids used in the present invention are, for example, aromatic tetracarboxylic anhydrides. Specific examples of the aromatic tetracarboxylic acid anhydrides include the following.

These tetracarboxylic dianhydrides may be used alone or in combination of two or more.
In the present invention, one or two or more non-aromatic tetracarboxylic dianhydrides exemplified below may be used in combination as long as they are less than 30 mol% of the total tetracarboxylic dianhydrides. Examples of such tetracarboxylic acid anhydrides include butane-1,2,3,4-tetracarboxylic dianhydride, pentane-1,2,4,5-tetracarboxylic dianhydride, and cyclobutanetetracarboxylic acid. Acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, cyclohexane-1,2,4,5-tetracarboxylic dianhydride, cyclohex-1-ene-2,3 5,6-tetracarboxylic dianhydride, 3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohexane-3 -(1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride 1-ethylcyclohexane -(1,2), 3,4-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane- 1- (2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ′, 4′-tetracarboxylic dianhydride,

Bicyclo [2.2.1] heptane-2,3,5,6-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1 , 3-Dipropylcyclohexane-1- (2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ′, 4′-tetracarboxylic dianhydride, bicyclo [2.2.1] Heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] Oct-7-ene-2,3,5,6-tetracarboxylic dianhydride and the like. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  The solvent used when the polyamic acid is obtained by reacting (polymerizing) the aromatic diamine and the aromatic tetracarboxylic acid (anhydride) dissolves both the monomer as a raw material and the polyamic acid to be produced. Although it will not specifically limit if it is a thing, A polar organic solvent is preferable, for example, N-methyl- 2-pyrrolidone, N-acetyl- 2-pyrrolidone, N, N- dimethylformamide, N, N- diethylformamide, N, N -Dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoric amide, ethyl cellosolve acetate, diethylene glycol dimethyl ether, sulfolane, halogenated phenols and the like. These solvents can be used alone or in combination. The amount of the solvent used may be an amount sufficient to dissolve the monomer as a raw material. As a specific amount used, the mass of the monomer in the solution in which the monomer is dissolved is usually 5 to 40% by mass, The amount is preferably 10 to 30% by mass.

The polymerization reaction conditions for obtaining the polyamic acid may be conventionally known conditions. As a specific example, stirring and / or continuous in an organic solvent at a temperature range of 0 to 80 ° C. for 10 minutes to 30 hours. Mixing may be mentioned. If necessary, the polymerization reaction may be divided or the temperature may be increased or decreased. In this case, the order of adding both monomers is not particularly limited, but it is preferable to add aromatic tetracarboxylic acid anhydrides to the solution of aromatic diamines. The mass of the polyamic acid in the polyamic acid solution obtained by the polymerization reaction is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, and the viscosity of the solution is measured with a Brookfield viscometer (25 ° C.). From the viewpoint of the stability of liquid feeding, it is preferably 10 to 2000 Pa · s, and more preferably 100 to 1000 Pa · s. The reduced viscosity (ηsp / C) of the polyamic acid in the present invention is not particularly limited, but is preferably 3.0 dl / g or more, and more preferably 4.0 dl / g or more.
Vacuum defoaming during the polymerization reaction is effective for producing a high-quality polyamic acid organic solvent solution. Moreover, you may perform superposition | polymerization by adding a small amount of terminal blockers to aromatic diamines before a polymerization reaction. Examples of the end capping agent include compounds having a carbon-carbon double bond such as maleic anhydride. The amount of maleic anhydride used is preferably 0.001 to 1.0 mol per mol of aromatic diamine.

  The polyimide film of the present invention is a polyimide precursor having a self-supporting property by applying a polyamic acid solution obtained by solution polymerization of the above-mentioned diamines and tetracarboxylic acid anhydrides in a solution and drying on the support. After the film is formed, it is obtained by an imidization reaction by a chemical method or heating.

It is preferable to select and carry out the drying conditions and high-temperature imidation conditions for the green film that is the precursor of the polyimide film. Examples of the drying conditions for obtaining the green film include N, N-dimethylacetamide. When using as a solvent, a drying temperature becomes like this. Preferably it is 70-130 degreeC, More preferably, it is 80-125 degreeC, More preferably, it is 85-120 degreeC. When this drying temperature is higher than 130 ° C., the molecular weight is lowered, and the green film tends to be brittle. In addition, imidization partially proceeds during the production of the green film, and it becomes difficult to obtain desired physical properties during the imidization process. On the other hand, when the temperature is lower than 70 ° C., the drying time becomes long, the molecular weight tends to decrease, and the handling property tends to be poor due to insufficient drying. Further, the drying time is preferably 5 to 90 minutes, more preferably 15 to 80 minutes, although it depends on the drying temperature. When the drying time is longer than 90 minutes, the molecular weight is lowered and the film tends to be fragile. When the drying time is shorter than 5 minutes, the handling property tends to be poor due to insufficient drying.
A conventionally known drying apparatus can be applied, and examples thereof include hot air, hot nitrogen, far infrared rays, and high frequency induction heating.

  The polyimide film of the present invention has a crystal size in the c-axis direction of 2 nm to 30 nm, preferably 5 nm to 20 nm, more preferably 8 nm to 15 nm, and crystal disorder in the c-axis direction is 1% to 15%. , Preferably 1.5% to 10%, more preferably 2% to 5%. Hereinafter, a method for producing a polyimide film having such characteristics will be described in detail. The polyimide film of the present invention has a predetermined c-axis by causing crystal growth in the c-axis direction under an appropriate tensile stress in the process of thermal imidization treatment of a green film, particularly in the process of imidization reaction. Crystal size in the direction and crystal disorder in the c-axis direction can be realized. Specifically, a c-axis crystal growth start temperature and an imidization reaction temperature at which an imidization rate of 90% in a method for measuring an intermediate structure described later are obtained, and 1. each of two directions orthogonal to each other in these temperature ranges. This can be realized by applying a tensile deformation of 01 to 1.2 times to the film. As an example, the processes (I) and (II) can be shown. In the chemical method, an imidizing agent is allowed to act on the green film, and the c-axis crystal growth start time and the reaction time at which the imidization rate is 90% or more are obtained by an evaluation method described later. It can be realized by giving the film a tensile deformation of 1.01 to 1.2 times in each of the two directions.

[Process I] (1) A green film is tensilely deformed 1.01 to 1.2 times in the longitudinal direction of the film in a temperature range of 25 ° C. to 50 ° C. (2) Grip both ends of the green film that has been pulled and deformed with clips or pin tenters. (3) In the temperature range from 50 ° C. to 150 ° C., the film width is adjusted to such an extent that no sag is generated according to the relaxation and shrinkage of the film. (4) In the temperature range from 150 ° C. to 280 ° C., the film is subjected to tensile deformation in the film width direction by 1.01 to 1.25 times. (5) In the temperature range of 280 ° C. to 520 ° C., the grip is continued to such an extent that the film does not sag in the range of 0.99 to 1.02. (6) Cool to room temperature.

[Process II] (1) Grip both ends of the green film with clips or pin tenters. (2) In the temperature range from 50 ° C. to 150 ° C., the film width is adjusted to such an extent that no sagging occurs according to the relaxation and shrinkage of the film. (3) In the temperature range of 150 ° C. to 280 ° C., the tensile deformation is performed 1.01 to 1.25 times in two directions perpendicular to each other. (4) In the temperature range of 280 ° C. to 520 ° C., gripping is continued to such an extent that the film does not sag in the range of 0.99 to 1.02. (5) Cool to room temperature.
Although the thickness of a polyimide film is not specifically limited, Usually, it is 1-250 micrometers, Preferably it is 2-50 micrometers. Furthermore, when higher durability against repeated bending and repeated twisting is required, it is preferably 2 to 40 μm, more preferably 2 to 27 μm, still more preferably 2 to 15 μm, still more preferably 2 to 9 μm. This thickness can be easily controlled by the amount of the polyamic acid solution applied to the support and the concentration of the polyamic acid solution.

[Measurement method of film structure during film formation]
Using a four-continuous heating furnace designed so that the temperature can be changed sequentially, the intermediate structure of the film when the temperature is changed is evaluated by X-ray diffraction measurement and IR measurement. As a measurement sample, a green film that has been coated and dried is used, and the sample is cut into a circle with a diameter of 7 mm. The circular sample is set in a sample holder provided at the tip of the sample rod, and the circular sample is gripped from directly above so that film shrinkage caused by solvent evaporation accompanying temperature change is performed. The sample bar was set in place. Within the temperature range from room temperature to 500 ° C., the processing temperature of the four consecutive heating furnaces is changed and arranged, and the heating furnace is sequentially moved while the sample rod is fixed, so that the above two measurements are performed individually. . Specifically, the film is held for 3 minutes in each heating step and then sent to the next furnace to perform time-resolved X-ray diffraction measurement or IR measurement while performing imidization reaction treatment.

[Method of evaluating temperature at the start of c-axis crystal growth]
The crystal size in the c-axis direction is measured using an X-ray diffraction method. A high-brightness X-ray source is used as the X-ray source, and the measurement film is set so that the angle formed by the X-ray source direction and the film surface is vertical, and X-ray diffraction measurement is performed by the transmission method. The X-ray diffraction measurement conditions are shown below.
[X-ray diffraction measurement conditions]
Green film thickness: IF equivalent to 38 μm X-ray irradiation time; 1 second Data transfer time; 5 seconds The X-ray diffraction pattern is, for example, HAMATATU PHOTOTONICS K. et al. K. Recording is performed using a CCD camera (X-Ray Image Intensifier (V5445P MOD) and Dual Mode Cooled CCD CAMERA (C4880)). The recorded image data is transferred to a personal computer, and after the equatorial and azimuth data are cut out, the apparent crystal size (D ₀₀₁ ) is calculated from the half-value width of the peak on the (001) plane as Calculation is performed using the following Sherler equation [Equation 1].

[Formula 1] D ₀₀₁ (Å) = 0.9 · λ / β · cos θ
λ: X-ray wavelength (0.7293mm)
β: Peak width at half peak of (001) plane
θ ＝ Bragg angle

The rise start time observed when _D001 is plotted against the residence time in the furnace is obtained, and the temperature corresponding to the rise start time is determined from the temperature profile as the c axis crystal growth start temperature.
A synchrotron is preferable as the high-intensity X-ray source. As an X-ray source, an X-ray brightness of 10 ¹⁵ photons / (s · mm ² · (mrad) ² · 0.1% bandwidth) or more, more preferably 10 ¹⁸ photons / (s · mm ² · (mrad) It is preferable to use an X-ray source having an X-ray luminance of ² · 0.1% bandwidth. In the following embodiment of the present invention, the large synchrotron radiation facility SPring8 is used as an X-ray source, and a BL40B2 hatch is used. X-rays taken out through the bending magnet were monochromatized through a monochromator ((111) plane of silicon crystal), and then the shape of the X-ray beam was shaped using a confocal mirror.

[Evaluation method of imidation reaction temperature for 90% imidization ratio]
Infrared light is taken out of the IR apparatus through a reflecting mirror, and the above-described four-continuous heating furnace is set between the detector and the imidization reaction tracking. The operation method of the 4-continuous heating furnace conformed to the X-ray diffraction method. The IR measurement conditions are shown below.
[IR measurement conditions]
Green film thickness: IF equivalent to 10 μm Device name used: FT-IR FTS-60A / 896 manufactured by BIO-RAD Resolution: 2 cm ⁻¹
Measurement wave number range: 650-8000 cm ⁻¹
Sensitivity; 1
Detection time: 1.05 sec.

Using the following formula (2), an imidation relative value IMx at each residence time is obtained, and a graph in which the imidation relative value with respect to the residence time is plotted is created. Note that λ ₁₇₇₈ is the absorbance at the imide specific wavelength ₁₇₇₈ cm ⁻¹ (near), and λ ₁₄₇₈ is the absorbance of the measurement surface near the aromatic ring specific wavelength ₁₄₇₈ cm ⁻¹ .

[Formula 2] IMx = λ ₁₇₇₈ / λ ₁₄₇₈

  When the imidation relative value IMx at the final imidation reaction temperature of 400 ° C. or higher is defined as an imidization rate of 100%, an imidization relative value that gives an imidization rate of 90% is obtained, and the relative value, the graph, and the temperature profile The imidation reaction temperature at which an imidization rate of 90% was obtained.

[Method of evaluating crystal size in c-axis direction and crystal disorder in c-axis direction]
The crystal size in the c-axis direction and the crystal disorder in the c-axis direction are measured using an X-ray diffraction method. Using the X-rays generated from the copper target of the rotating anti-cathode as the X-ray source, set the measurement film so that the angle between the X-ray source direction and the film surface is perpendicular, and use the scintillation counter as the detector and transmit The X-ray diffraction profile is measured by the method. The X-ray diffraction measurement conditions are shown below.
[X-ray diffraction measurement conditions]
Device used: RINT2500 Rigaku Corporation output: 40 kV, 200 mA
Attachment; Fiber sample table Slit size; Collimator: 1 mm, Vertical restriction slit: 2 °, Horizontal restriction slit: 1/2 °
Counting time: 4 seconds Step angle: 0.01 °
Gonio radius; 185mm

From the obtained X-ray diffraction profile, the integral width of the diffraction peak corresponding to the (00L) plane is evaluated. From the integral width (δs) _{0 of} this diffraction profile, the true crystal size (D) and the crystal disturbance g are calculated using the Hosmann equation [Equation 3] shown below.

[Formula 3] (δs) ₀ ² = (1 / D) ² + (πgm) ⁴ / c ²
Here, D is the true crystal size, m is the order, and c is the crystal lattice spacing.

When applying the Hozeman theory, a straight line is obtained by plotting the square of these integral widths against the fourth power of the respective diffraction orders, and the slope of this straight line (hereinafter referred to as the slope of the Hozeman plot) is obtained. . The degree of disorder (g) of the crystal lattice spacing is calculated by substituting into the following equation using the slope of this Hozeman plot. This equation is expressed by the slope of the Hozeman plot = (πg) ⁴ / c ² (see P395 in “X-ray diffraction of polymer” above).

Next, a printed wiring board base substrate using the above-described polyimide benzoxazole film will be described.
Here, the base substrate for a printed wiring board is a substantially flat substrate having a structure in which a metal layer is laminated on at least one surface of a polyimide film as an insulating plate. The metal layer to be laminated may be a metal layer for a circuit that is intended to form a circuit by processing such as etching or the like. It may be a metal layer used for the purpose. As the use of the base substrate for a printed wiring board, FPC, TAB carrier tape, and the like are preferable because the characteristics of the polyimide film of the present invention such that swelling and peeling under a high temperature environment are small can be utilized. The metal laminated on at least one surface of the polyimide film is not particularly limited, and preferably copper, aluminum, stainless steel, or the like.
The method of laminating is not particularly limited, and a method of attaching a metal plate to a polyimide film using an adhesive, a method of forming a film by applying a polyamic acid solution to the metal plate as a support and imidizing as described above A method of forming a metal layer on a polyimide film using a dry film forming method (vacuum coating technique) such as vapor deposition, sputtering, or ion plating, or a metal layer on a polyimide film by a wet plating method such as electroless plating or electroplating. The method of forming etc. are mentioned.
A metal layer can be laminated on at least one surface of the polyimide film by combining these methods alone or in combination.
An inorganic coating film such as a single metal or a metal oxide may be formed on the surface of the metal layer used in the present invention. Further, the surface of the metal layer may be subjected to treatment with a coupling agent (aminosilane, epoxysilane, etc.), sand plast treatment, hole treatment, corona treatment, plasma treatment, etching treatment, and the like. Similarly, the surface of the polyimide benzoxazole film may be subjected to honing treatment, corona treatment, plasma treatment, etching treatment, and the like.

[Repeated twist bending test using gel bot tester]
The MIT method and the IPC method have been used for the evaluation method of the bending characteristic generally performed in the flexible printed wiring board. However, these evaluation methods can only obtain information on the bending characteristic in one direction, It was not sufficient to evaluate twisting properties in random directions other than one direction. Therefore, an evaluation method using a gel bot tester (manufactured by Rigaku Kogyo Co., Ltd.) was employed in the twist resistance test of the polyimide film according to the present invention, in which “twist” was added in addition to bending in a random direction and place. . As conditions, a MIL-B131H sample piece of 112 inch × 8 inch is cylindrical with a diameter of 3 (1/2) inch, both ends are held, an initial gripping interval is 7 inch, and a stroke is 3 (1/2) inch. A reciprocating motion of this operation was performed 10 times at a speed of 40 times / min under the conditions of 23 ° C. and 65% relative humidity with a twist of 400 degrees. About what was cut out to the size of 100 mm x 100 mm from the film sample which performed the gelbo test 10 times, the number of the permeation | transmission locations of the ink was counted on the filter paper, and the number was used as the number of pinholes. A material having a small number of pinholes is a base material having high gelbo resistance, and is effective as a base material of the present invention.

  Examples of the present invention will be described below, but the present invention is not limited thereto. In addition, the evaluation method of the physical property in the following examples is as follows except for the above.

1. Reduced viscosity of polyamic acid (ηsp / C)
A solution dissolved in N-methyl-2-pyrrolidone so that the polymer concentration was 0.2 g / dl was measured at 30 ° C. using an Ubbelohde type viscosity tube.

2. Film thickness of polyimide film The thickness of the film was measured using a micrometer (Finereuf, Millitron 1254D).

3. Tensile modulus, tensile breaking strength and tensile breaking elongation of polyimide film The film after drying was cut into strips having a length of 100 mm and a width of 10 mm in the longitudinal direction (MD direction) and the width direction (TD direction), respectively, and used as test pieces. Using a tensile tester (Shimadzu Autograph (trade name) model name AG-5000A), the tensile modulus, tensile breaking strength and tensile breaking elongation were measured under the conditions of a tensile speed of 50 mm / min and a distance between chucks of 40 mm. It was measured.

4). Linear expansion coefficient (CTE) of polyimide film
For the polyimide film to be measured, the dimensional change rate in the MD direction and the TD direction is measured under the following conditions, respectively, and the dimensional change rate at intervals of 30 ° C. to 45 ° C., 45 ° C. to 60 ° C.,. The temperature was measured, this measurement was performed up to 300 ° C., and the average value of all measured values was calculated as CTE. The meanings of the MD direction and the TD direction are the same as in the measurement of “3.” above.
Device name: TMA4000S manufactured by MAC Science
Sample length; 20mm
Sample width: 2 mm
Temperature rise start temperature: 25 ° C
Temperature rising end temperature: 400 ° C
Temperature increase rate: 5 ° C / min
Atmosphere: Argon

5. Melting point and glass transition temperature of polyimide film Thermal data (melting point (melting peak temperature Tpm) and glass transition point (Tmg)) of the sample were determined under the following measurement conditions in accordance with JIS K7121.
Device name: DSC3100S manufactured by MAC Science
Pan ： Aluminum pan (non-airtight)
Sample mass: 4mg
Temperature rising start temperature: 30 ° C
Temperature increase rate: 20 ° C / min
Atmosphere: Argon

(Examples 1-2)
<Polymerization>
The inside of a reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod was purged with nitrogen, and then 300 parts by mass of 5-amino-2- (p-aminophenyl) benzoxazole (p-DAMBO) was charged. Next, 4400 parts by mass of N, N-dimethylacetamide was added and completely dissolved, and then 300 parts by mass of pyromellitic dianhydride was added and stirred at a reaction temperature of 25 ° C. for 17 hours. An acid solution was obtained. Ηsp / C of this product was 4.1 dl / g.
<Preparation of polyimide precursor film (green film)>
Subsequently, this polyamic acid solution was coated on a stainless steel belt using a T-die, dried under the processing conditions shown in Table 1, and the polyamic acid film which became self-supporting after drying was peeled off from the stainless steel belt to a thickness of 70 μm. A green film was obtained. The residual solvent amount of the green film at this time was 36%.
Using the obtained green film, the c-axis crystal growth start temperature and the 90% imidization ratio attainment temperature were determined in advance. The results are shown in Table 1. The following process conditions were determined based on the obtained c-axis crystal growth start temperature and the 90% imidization rate attainment temperature.
<Longitudinal stretching>
The obtained green film was longitudinally stretched at a magnification shown in Table 1 by using rolls having different rotational speeds at room temperature of 28 ° C.
<Heat treatment and transverse stretching>
The green film after longitudinal stretching is subjected to heat treatment and stretching under the conditions shown in Table 1 in a hot air processing machine having three heating zones in which the pin width can be arbitrarily changed, and then a 6-inch ABS resin core It was wound up on a roll.
The characteristic value of the obtained polyimide film was evaluated. The results are shown in Table 1.

The following processing was performed using the obtained polyimide film. The film was cut into a 50 cm × 200 cm square and fixed by being sandwiched between stainless steel frames having openings. Next, plasma treatment of the film surface was performed. The plasma treatment conditions were a xenon gas, a frequency of 13.56 MHz, an output of 100 W, a gas pressure of 0.8 Pa, a treatment temperature of 25 ° C., and a treatment time of 5 minutes. Next, using a nickel-chromium (3 mass%) alloy target under conditions of a frequency of 13.56 MHz, an output of 400 W, a gas pressure of 0.8 Pa, and a thickness of 10 mm / sec by RF sputtering in an argon atmosphere. An 80-mm nickel-chromium alloy film (underlayer) was formed, and then the temperature of the substrate was raised to 250 ° C., and copper was deposited at a rate of 100 k / sec to form a 0.3 μm thick copper thin film. The obtained copper thin film forming film is fixed to a plastic frame, and a copper sulfate plating bath is used to form a thick copper plating layer (thickening layer) having a thickness of 5 μm, followed by heat treatment at 300 ° C. for 10 minutes. The intended metallized polyimide film was obtained. Using the obtained metallized polyimide film, photoresist: FR-200, manufactured by Shipley Co., Ltd. was applied and dried, then contacted and exposed with a glass photomask, and further developed with a 1.2 mass% KOH aqueous solution. Next, etching is performed with a cupric chloride etching line containing HCl and hydrogen peroxide at a spray pressure of 40 ° C. and 2 kgf / cm ² to form a pattern with a minimum wiring pitch of 30 μm. Electroless tin plating was performed to a thickness of 5 μm, and then an annealing treatment at 125 ° C. for 1 hour was performed to produce a substrate made of each film.

LCD driving semiconductor chips were face-down mounted on each film substrate. The bump is formed by electrolytic plating by opening an area formed by a photoresist. After formation, the photoresist is removed. This bump is connected to the electrode of the film substrate by a gold-tin eutectic bond. The connection condition in this case is that a load of 13 kgf is applied from the semiconductor chip side with a tool of 440 ° C. and held for 2 seconds.
Semiconductor chip mounting methods include not only gold-tin eutectic connection, but also gold-gold thermocompression bonding, ultrasonic connection, anisotropic conductive film, NCP, and the like. The connection method may be appropriately selected and used.
As other mounting components, chip resistors, capacitors, package ICs, coils, connectors, and the like are connected by soldering or the like to form a module type FPC. The obtained FPC is provided with a “twisted bent portion” having a length of 8 mm and a width of 1.6 mm, assuming folding and “twisting” after assembly. A terminal is taken out from both ends of a conductor line having a width of 150 μm that is conducted before and after the twisted bent portion, and while monitoring the conduction state, a curvature radius of 1.4 mm and a bending angle of 180 ° to −150 ° are provided in the portion. Evaluate the number of cycles until the conductor line breaks by repeatedly deforming it twice at a rate of one twist of 180 degrees in the direction of the FPC surface around the bent part (this combination is taken as one cycle). did. As a result, the FPC using the film of this example did not break even after 10,000 cycles were repeated.
(Example 2)
Similarly, polyimide films were prepared under the conditions shown in Table 1 and evaluated in the same manner as in Example 1. The results are shown in Table 1. Similar to Example 1, in the FPC using this film, the conductor pattern did not break even after 10,000 cycles of repeated bending and twisting.

(Example 3-5)
<Polymerization and film production example 2>
After the inside of the reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod was purged with nitrogen, 240 parts by mass of 5-amino-2- (p-aminophenyl) benzoxazole (p-DAMBO), 4,4′- 60 parts by weight of diaminodiphenyl ether was charged. Next, 4400 parts by mass of N, N-dimethylacetamide was added and completely dissolved, and then 300 parts by mass of pyromellitic dianhydride was added and stirred at a reaction temperature of 25 ° C. for 24 hours. A polyamic acid solution was obtained. Ηsp / C of this product was 4.0.
Using this polyamic acid solution, a polyimide film of Example 3 was obtained under the film forming conditions shown in Table 1. The characteristic value of the obtained polyimide film was evaluated. The results are shown in Table 1. Similarly, in the FPC using this film, the conductor pattern did not break even after 10,000 cycles of repeated bending and twisting.
Similarly, the films shown in Example 4 and Example 5 were obtained under the conditions described in Table 1. The evaluation results are shown in Table 1. In any film of any of the examples, the FPC obtained from such a film exhibited good repeated bending resistance and repeated twisting characteristics similar to those of Example 1.

(Comparative Examples 1 and 2)
A polyimide benzoxazole film was obtained and evaluated in the same manner as in Example 1 except that the temperature profile of the heat treatment was changed as shown in Table 2. The results are shown in Table 2.

  The pin width in the table is a numerical value representing the relative magnification when the pin width in the previous stage is 1.0.

  As described above, the polyimide film of the present invention has excellent repeated bending resistance and repeated twisting resistance, and exhibits high heat resistance, dimensional stability, high temperature and humidity resistance, and is highly foldable. It is useful as a flexible substrate material used for equipment that requires twisting freedom.

Claims (5)

  A polyimide film, wherein the crystal size in the c-axis direction is 2 nm or more and 30 nm or less, and the crystal disorder in the c-axis direction is 1% or more and 15% or less.   The polyimide film according to claim 1, wherein the polyimide film is a polyimide film having a benzoxazole structure.   The polyimide film according to claim 1, wherein the crystal size in the c-axis direction is 5 nm or more and 20 nm or less, and the crystal disorder in the c-axis direction is 1.5% or more and 10% or less.   The polyimide film according to claim 1 or 2, wherein the crystal size in the c-axis direction is 8 nm or more and 15 nm or less, and the crystal disorder in the c-axis direction is 2% or more and 5% or less.   The polyimide film according to claim 1, wherein the number of pinholes generated in a twist bending test using a gel bot tester is 0 or more and 3 or less.