JP2014028966A - Polyimide film and copper-clad laminate having the same as substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film that is excellent in dimensional stability, and that is suitable to a substrate of a fine pitch circuit, especially to a COF(Chip on Film) in which wiring is performed in a film width direction by a narrow pitch; and a copper-clad laminate having the same as a substrate.SOLUTION: A polyimide film is characterized in that a coefficient of thermal expansion αMD in a machine transportation direction (MD) of the film is 3-10 ppm/°C, and a coefficient of thermal expansion αTD in a crosswise direction (TD) of the film is 10-20 ppm/°C, and moreover a copper-clad laminate is characterized in that the polyimide film is included as a substrate, and a copper having a thickness of 1-10 μm is formed on the polymide film.

Description

  The present invention is a polyimide film suitable for COF (Chip on Film), which is excellent in dimensional stability and finely wired in a fine pitch circuit substrate, particularly in a film width direction, and a copper-clad laminate based thereon It is about.

  As flexible printed circuit boards and semiconductor packages become highly fine, the requirements for polyimide films used in them have increased. For example, dimensional changes and curling due to bonding with metal are reduced, and handling is high. As a physical property of a polyimide film, a film having a thermal expansion coefficient comparable to that of a metal and a high elastic modulus and a film with small dimensional change due to water absorption are required, and a polyimide film corresponding to the film has been developed. .

  For example, examples of polyimide films using paraphenylenediamine to increase the elastic modulus are known (Patent Documents 1, 2, and 3). In addition, examples of polyimide films using biphenyltetracarboxylic dianhydride in addition to paraphenylenediamine to reduce dimensional change due to water absorption while maintaining high elasticity are known (Patent Documents 4 and 5).

  Furthermore, in order to suppress dimensional changes in the bonding process with the metal, the thermal expansion coefficient in the machine transport direction (hereinafter referred to as MD) of the film is set to be smaller than the thermal expansion coefficient in the width direction of the film (hereinafter referred to as TD). An example of a polyimide film having anisotropy is described. In the FPC process, a lamination method is generally used in which bonding with metal is performed by heating with roll-to-roll, and the film MD in this process is stretched due to tension, while TD is shrunk. The purpose is to cancel the phenomenon that occurs (Patent Document 6).

  By the way, in recent years, a two-layer type (a copper layer is directly formed on a polyimide film) that does not use an adhesive has been adopted as a copper-clad laminate in response to miniaturization of wiring. There are a method of forming a copper layer by plating on a film and a method of imidizing after casting a polyamic acid on a copper foil, but none of them is a thermocompression bonding process such as a lamination method. It is no longer necessary to make the thermal expansion coefficient of MD smaller than TD. Furthermore, in COF applications where the mainstream is a two-layer type, a pattern that is wired at a narrow pitch is common to the TD of the film, and conversely, the thermal expansion coefficient of TD. If it is large, the dimensional change between wirings becomes large during chip mounting bonding, and it is difficult to meet the demand for fine pitch. To cope with this, it is ideal to make the thermal expansion coefficient of the film as small as approximating that of silicon. There is a problem that distortion occurs.

JP-A-60-210629 JP-A 64-16832 JP-A-1-131241 JP 59-164328 A JP-A-61-111359 JP-A-4-25434

  The present invention has been made as a result of studying the solution of the above-described problems in the prior art as an object, and for COF that can reduce the dimensional change of the film TD while maintaining a thermal expansion coefficient approximate to that of a metal. The object of the present invention is to provide a polyimide film suitable for a fine pitch circuit substrate such as a copper-clad laminate.

In order to achieve the above-mentioned goal, the polyimide film of the present invention has a thermal expansion coefficient α _{MD of 10} to 20 ppm / ° C. in the machine transport direction (MD) of the film and a thermal expansion coefficient α _TD of 3 in the width direction (TD). -10 ppm / ° C, preferably α _MD is 14 to 18 ppm / ° C, and α _TD is 3 to 7 ppm / ° C.

Furthermore, the polyimide film of the present invention preferably has the following (1) to (5).
(1) The tensile modulus of elasticity in the machine transport direction (MD) and the width direction (TD) of the film are both 4.0 GPa or more.
(2) The 200 ° C. heat shrinkage in the machine transport direction (MD) and the width direction (TD) of the film are both 0.05% or less.
(3) Particles mainly composed of inorganic particles having a particle diameter of 0.07 to 2.0 μm are uniformly dispersed in the film at a ratio of 0.03 to 0.30% by weight per film resin weight, and on the surface Fine protrusions are formed.
(4) The average particle size of particles mainly composed of inorganic particles is 0.10 μm or more and 0.90 μm or less, preferably 0.10 μm or more and 0.30 μm or less.
(5) The number of protrusions formed by particles mainly composed of inorganic particles is 1 × 10 ³ to 1 × 10 ⁸ per 1 mm ² .

  The copper clad laminate of the present invention is characterized in that a polyimide film having any one of the above is used as a base material, and copper having a thickness of 1 to 10 μm is formed thereon.

  The polyimide film of the present invention can keep the thermal expansion coefficient in this direction low by advancing the orientation of the film to TD, and the thermal expansion coefficient of MD has a value close to that of metal, and further heat shrinkage. The rate is low and a high tensile elastic modulus is maintained.

  In producing the polyimide film of the present invention, first, an aromatic diamine component and an acid anhydride component are polymerized in an organic solvent to obtain a polyamic acid solution.

  Specific examples of the aromatic diamines include paraphenylenediamine, metaphenylenediamine, benzidine, paraxylylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfone, 3,3′-dimethyl-4,4′-diaminodiphenylmethane, 1,5-diaminonaphthalene, 3,3′-dimethoxybenzidine, 1,4-bis (3methyl-5 Aminophenyl) benzene and amide-forming derivatives thereof. Among them, the amount of diamine such as paraphenylenediamine, benzidine, 3,4'-diaminodiphenyl ether, which has an effect of increasing the tensile modulus of the film, is adjusted, and the finally obtained polyimide film has a tensile modulus of 4. It is preferable for the fine pitch substrate to be 0 GPa or more.

  Specific examples of the acid anhydride component include pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3 ′, 3,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid, 2,3,6,7-naphthalenedicarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) ether, pyridine-2,3,5,6-tetracarboxylic And acid anhydrides such as acids and their amide-forming derivatives.

  In the present invention, specific examples of the organic solvent used for forming the polyamic acid solution include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, 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 and N-vinyl-2-pyrrolidone, phenol, o-, Examples thereof include phenolic solvents such as m- or p-cresol, xylenol, halogenated phenol and catechol, or aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone, and these may be used alone or as a mixture. It is desirable to use But further xylene, the use of aromatic hydrocarbons such as toluene are also possible.

The polymerization method may be carried out by any known method, for example: (1) First, the aromatic diamine component is added to the solvent first, and then the aromatic tetracarboxylic acid component is added to the equivalent amount of the aromatic diamine component. To polymerize.

  (2) A method in which the total amount of the aromatic tetracarboxylic acid component is first put in a solvent, and then the aromatic diamine component is added in an amount equivalent to the aromatic tetracarboxylic acid component for polymerization.

  (3) After one aromatic diamine compound is put in a solvent, the aromatic tetracarboxylic acid compound is mixed at a ratio of 95 to 105 mol% with respect to the reaction components, and then mixed for the other time. A method in which an aromatic diamine compound is added, and then an aromatic tetracarboxylic acid compound is added and polymerized so that the total aromatic diamine component and the total aromatic tetracarboxylic acid component are approximately equivalent.

  (4) After putting the aromatic tetracarboxylic acid compound in the solvent, the aromatic tetracarboxylic acid compound is mixed for a time required for the reaction at a ratio of 95 to 105 mol% of one aromatic diamine compound with respect to the reaction component, and then the aromatic tetracarboxylic acid compound is mixed. A method of polymerizing by adding a carboxylic acid compound and then adding the other aromatic diamine compound so that the total aromatic diamine component and the total aromatic tetracarboxylic acid component are approximately equivalent.

  (5) A polyamic acid solution (A) is prepared by reacting one aromatic diamine component and an aromatic tetracarboxylic acid in a solvent so that either one becomes excessive, and the other aromatic diamine in another solvent. The polyamic acid solution (B) is prepared by reacting the component and the aromatic tetracarboxylic acid so that either one becomes excessive. A method of mixing the polyamic acid solutions (A) and (B) thus obtained to complete the polymerization. At this time, when adjusting the polyamic acid solution (A), if the aromatic diamine component is excessive, the polyamic acid solution (B) contains excessive aromatic tetracarboxylic acid component, and the polyamic acid solution (A) contains aromatic tetracarboxylic acid. When the acid component is excessive, the polyamic acid solution (B) makes the aromatic diamine component excessive, and the polyamic acid solutions (A) and (B) are combined to form the wholly aromatic diamine component and wholly aromatic compound used in these reactions. A method of adjusting the tetracarboxylic acid component to be approximately equivalent.

  The polymerization method is not limited to these, and other known methods may be used.

  The polyamic acid solution thus obtained contains a solid content of 5 to 40% by weight, preferably 10 to 30% by weight, and its viscosity is 10 to 2000 Pa · s as measured by a Brookfield viscometer, preferably 100-1000 Pa · s is preferably used for stable liquid feeding. Moreover, the polyamic acid in the organic solvent solution may be partially imidized.

  Next, the manufacturing method of the polyimide film of this invention is demonstrated.

  As a method for forming a polyimide film, a polyamic acid solution is cast into a film and thermally decyclized and desolvated to obtain a polyimide film, and a polyamic acid solution is mixed with a cyclization catalyst and a dehydrating agent. The method of obtaining a polyimide film by preparing a gel film by decyclizing it and heating it to remove the solvent is preferable, but the latter is preferable because the thermal expansion coefficient of the obtained polyimide film can be kept low. .

  In addition, this polyamic acid solution is used to obtain chemically slippery organic fillers such as titanium oxide, fine silica, calcium carbonate, calcium phosphate, calcium hydrogen phosphate, and polyimide filler as necessary to obtain the slipperiness of the film. An inorganic filler can be contained. Among these, fine protrusions are formed by uniformly dispersing fine silica having a particle diameter of 0.07 to 2.0 μm in the film at a ratio of 0.03 to 0.30% by weight per film resin weight. preferable. A particle diameter in the range of 0.07 to 2.0 μm is preferable because inspection of the polyimide film by an automatic optical inspection system can be applied without problems. When the addition amount exceeds 0.30% by weight, a decrease in mechanical strength is observed, and when it is 0.03% by weight or less, sufficient slipperiness effect is not observed, which is not preferable. The average particle diameter is preferably 0.10 μm or more and 0.90 μm or less, and more preferably 0.10 μm or more and 0.30 μm or less. An average particle size of 0.10 μm or less is not preferable because the slipperiness effect of the film is lowered, and an average particle size of 0.90 μm or more is not preferable because it exists as locally large particles.

  The polyamic acid solution can contain a cyclization catalyst (imidization catalyst), a dehydrating agent, a gelation retarder, and the like.

  Specific examples of the cyclization catalyst used in the present invention include aliphatic tertiary amines such as trimethylamine and triethylenediamine, aromatic tertiary amines such as dimethylaniline, and heterocyclic rings such as isoquinoline, pyridine and betapicoline. Although a tertiary amine etc. are mentioned, it is preferable to use at least 1 sort (s) of amine chosen from a heterocyclic tertiary amine.

  Specific examples of the dehydrating agent used in the present invention include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride, Acetic anhydride and / or benzoic anhydride are preferred.

  As a method for producing a polyimide film from a polyamic acid solution, a polyamic acid solution containing a cyclization catalyst and a dehydrating agent is cast on a support from a base with a slit and formed into a film, and an imide is formed on the support. The gel film is partially advanced to form a gel film having self-supporting properties, and then peeled off from the support, heat-dried / imidized, and subjected to heat treatment.

  The polyamic acid solution is formed into a film shape through a slit-shaped die, cast on a heated support, undergoes a thermal ring-closing reaction on the support, and is supported as a gel film having self-supporting properties. It is peeled from the body.

  The support is a metal rotating drum or endless belt, and its temperature is controlled by a liquid or gaseous heat medium and / or by radiant heat from an electric heater or the like.

  The gel film is heated to 30 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 causes a ring-closing reaction to volatilize the free organic solvent or the like. By drying the part, it becomes self-supporting and is peeled off from the support.

The gel film peeled off from the support is usually stretched in the running direction while regulating the running speed with a rotating roll. The draw ratio (MDX) in the machine conveying direction is 1.01 to 1.9 times, preferably 1.05 to 1.6 times, more preferably 1.05 to 1.4 times at a temperature of 140 ° C. or less. To be implemented. The gel film stretched in the conveying direction is introduced into a tenter device, and both ends in the width direction are gripped by the tenter clip, and stretched in the width method while running with the tenter clip. At this time, the stretching ratio in the width direction (TD) is set higher than the stretching ratio in the machine conveyance direction (MD) of the film. Specifically, the stretching ratio in the width direction is 1.1 to 1.1 of the stretching ratio in the machine conveyance direction. By setting the film to 1.5 times, it is possible to obtain a film in which the thermal expansion coefficient of the film TD is kept low while maintaining the thermal expansion coefficient close to that of a metal in the film MD, that is, the film MD that has been well oriented. Within these ranges, the stretching ratio of both is adjusted so that the thermal expansion coefficient α _TD of the film MD is 3 to 10 ppm / ° C., and the thermal expansion coefficient α _MD of the film TD is 10 to 20 ppm / ° C. The α _TD is preferably 3 to 7 ppm / ° C., and the α _MD is more preferably 14 to 18 ppm / ° C.

  The film dried in the drying zone is heated for 15 seconds to 10 minutes with hot air, an infrared heater or the like. Next, heat treatment is performed at a temperature of 250 to 500 ° C. for 15 seconds to 20 minutes with hot air and / or an electric heater.

  Moreover, although the running speed is adjusted to adjust the thickness of the polyimide film, the thickness of the polyimide film is preferably 3 to 250 μm. If it is thinner or thicker than this, the film-forming property of the film is remarkably deteriorated.

  The polyimide film thus obtained is preferably further annealed at a temperature of 200 to 500 ° C. By doing so, thermal relaxation of the film occurs and the heat shrinkage rate can be kept small. In the manufacturing method of the polyimide film of the present invention, since the orientation to the film TD is strong, the heat shrinkage rate in this direction tends to be high, but the heat shrinkage rate at 200 ° C. is reduced by the thermal relaxation from the annealing treatment. Since both MD and TD of the film can be suppressed to 0.05% or less, the dimensional accuracy is further improved, which is preferable. Specifically, the film is run in a furnace at 200 to 500 ° C. under low tension, and annealing treatment is performed. The time during which the film stays in the furnace is the processing time, but it is controlled by changing the running speed, and the processing time is preferably 30 seconds to 5 minutes. If it is shorter than this, heat is not sufficiently transmitted to the film, and if it is longer, it becomes overheated and the flatness is impaired. The film tension during running is preferably 10 to 50 N / m, more preferably 20 to 30 N / m. When the tension is lower than this range, the running property of the film is deteriorated, and when the tension is high, the heat shrinkage rate in the running direction of the obtained film is increased, which is not preferable.

  Moreover, in order to give adhesiveness to the obtained polyimide film, the film surface may be subjected to electrical treatment such as corona treatment or plasma treatment or physical treatment such as blast treatment.

  Regarding the copper formation method, there is a method of directly forming copper on the polyimide film by sputtering or plating, and a method of bonding a copper foil on the polyimide film via an adhesive, but the former can control the copper thickness, Further, it is advantageous in terms of dimensional stability, and is preferable because of its high reliability in terms of electrical characteristics.

  The polyimide film thus obtained and the copper-clad laminate based on the polyimide film can keep the thermal expansion coefficient in this direction low by advancing the orientation of the film to TD, and the heat of MD The expansion coefficient has a value close to that of a metal, has a low heat shrinkage rate, and maintains a high tensile elastic modulus. Therefore, a fine pitch circuit substrate, particularly a COF (Chip) wired at a narrow pitch on a TD of a film. on Film).

  Hereinafter, the present invention will be described specifically by way of examples.

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

  Moreover, each characteristic in an Example was evaluated with the following method.

(1) Thermal expansion coefficient TMA-50 manufactured by Shimadzu Corporation was used, and measurement was performed under the conditions of a measurement temperature range: 50 to 200 ° C and a rate of temperature increase: 10 ° C / min.

(2) A film having a heat shrinkage of 20 cm × 20 cm was prepared, and the film size (L1) after being left in a room adjusted to 25 ° C. and 60% RH for 2 days was measured, followed by heating at 200 ° C. for 60 minutes. Thereafter, the film size (L2) was measured after being left in a room adjusted to 25 ° C. and 60% RH for 2 days, and evaluated by the following formula calculation.
Heat shrinkage rate = − (L2−L1) / L1 × 100

(3) Tensile elastic modulus RTM-250 manufactured by A & D was used, and the tensile modulus was measured under the condition of 100 mm / min.

(4) Particle size distribution A sample dispersed in a polar solvent was measured using SALD-2000J manufactured by Shimadzu Corporation.

(5) Number of protrusions Using an ultra-high resolution field emission scanning electron microscope (UHR-FE-SEM) S-5000 manufactured by Hitachi, the film surface was 10,000 times magnified, and the protrusions were counted. In addition, Pt was coated as SEM pretreatment.

(6) Friction coefficient (Static friction coefficient)
It measured according to JIS K-7125. That is, using a slip coefficient measuring apparatus SlipTester (manufactured by Technonez Co., Ltd.), the film processing surfaces are overlapped, a 200 g weight is placed thereon, one of the films is fixed, and the other is pulled at 100 mm / min. The coefficient of friction was measured.

(7) Dimensional change rate and curl before and after solder bath treatment of the film formed with copper wiring and (i) Copper layer formation A nickel / chromium alloy (nickel / chromium) on a 35 mm wide (TD) × 120 mm wide (MD) film Chromium = 95/5) was sputtered to form a 0.03 μm thick nickel / chrome layer. Next, copper was sputtered on the nickel / chromium alloy layer to form a 0.1 μm thick copper layer. Using the formed copper layer as an electrode, electrolytic plating was performed using a copper sulfate plating solution (copper sulfate pentahydrate 200 g, sulfuric acid 100 g, hydrochloric acid 0.10 ml, Nippon Reonal copper sulfate plating additive 17 ml, water 1000 l). Finally, a copper layer having a thickness of 8 μm was formed.

(Ii) Photoresist pattern formation On the obtained 8 μm thick copper layer, Clariant Japan photoresist AZP4620 was applied at 1000 rpm × 5 seconds + 1600 rpm × 30 seconds with a spin coater (Mikasa 1H-360S). Then, it was dried in an oven at 105 ° C. for 20 minutes to remove the solvent in the photoresist. The formed photoresist layer was 9 μm thick.

  Next, the formed photoresist layer was exposed using a photomask. A photomask in which 50 lines with a pitch of 100 μm (wiring width 55 μm / wiring interval 45 μm) are formed side by side in the TD direction was used. The exposure amount was 400 mJ / cm2.

  After the exposure, an aqueous solution of AZ400K / water = 90/10 (weight ratio) was prepared using a photoresist developer AZ400K manufactured by Clariant Japan, and this formulation solution was immersed in 25 ° C. for 4 minutes and subjected to rocking development. A photoresist was formed in a 100 μm pitch wiring shape.

(Iii) Copper etching After forming a photoresist in a wiring shape, using a 35 wt% aqueous iron chloride solution as a copper etching solution, etching is performed while showering the copper etching solution from a spray nozzle at 40 ° C. for 2 minutes to obtain a copper layer. Was patterned at a pitch of 100 μm (wiring width 50 μm / wiring interval 50 μm). After copper etching, it was immersed in 25 ° C. × 5 minutes × twice and washed with rocking water, and then naturally dried.

(Iv) Photoresist removal After forming the copper wiring, using a 2.5 wt% aqueous solution of sodium hydroxide, immersion + rocking peeling was performed at 25 ° C for 3 minutes to dissolve and remove the photoresist. After removing the photoresist, it was immersed at 25 ° C. for 5 minutes × twice and washed with rocking water, and then naturally dried.

(V) Tin plating After the removal of the photoresist, electroless tin plating was performed by dipping at 25 ° C. for 2 minutes using an electroless tin plating solution LT34 manufactured by Shipley Far East. After electroless tin plating, it was dipped at 25 ° C. for 5 minutes × twice and washed with rocking water, and then naturally dried.

(Vi) Dimensional change rate and curl measurement After tin plating, the dimension in the TD direction was measured (L3). Next, it was immersed in a 250 ° C. solder bath for 30 seconds, and after the immersion, the dimension in the TD direction was measured again (L4). The dimensional change rate before and after the treatment with the solder bath was determined by the following formula.
Dimensional change rate (%) = (L4−L3) / L3 × 100

  As for curling, the sample was allowed to stand in a flat place after the treatment with the solder bath, and the amount of warping from the floor of the end of the sample was evaluated as “curl”.

[Example 1]
In a 500 ml separable flask, 239.1 g of DMAc was placed, and 4.53 g (0.042 mol) of PPD, 21.53 g (0.108 mol) of 4,4′-ODA, 8.79 g (0.030 mol) of BPDA, PMDA26 0.06 g (0.119 mol) was added, reacted at room temperature and normal pressure for 1 hour, and stirred until uniform to obtain a polyamic acid solution.

  Subsequently, 0.03% by weight of N, N-dimethylacetamide slurry of silica having an average particle diameter of less than 0.08 μm and an average diameter of 0.30 μm excluded from 2 μm or more was added to the polyamic acid solution per resin weight, and sufficiently stirred. Dispersed.

  Thereafter, the polyamic acid solution was cooled at −5 ° C., and then 15% by weight of acetic anhydride and 15% by weight of β-picoline were mixed with 100% by weight of the polyamic acid solution to imidize the polyamic acid.

The polyimide polymer thus obtained was cast on a rotary drum at 90 ° C. for 30 seconds, and then the obtained gel film was stretched 1.1 times in the running direction while heating at 100 ° C. for 5 minutes. Next, both end portions in the width direction were held and stretched 1.5 times in the width direction while heating at 270 ° C. for 2 minutes, and then heated at 380 ° C. for 5 minutes to obtain a 38 μm-thick polyimide film. This polyimide film was annealed for 1 minute in a furnace set at 220 ° C. under a tension of 20 N / m, and then evaluated for each characteristic.
Thermal expansion coefficient of the film _MD α MD: 15.8ppm / ℃
Thermal expansion coefficient of the film _TD α TD: 4.8ppm / ℃
200 ° C. heat shrinkage (MD): 0.02%
200 ° C. heat shrinkage (TD): 0.02%
Tensile modulus (MD): 6.0 GPa
Tensile modulus (TD): 6.6 GPa
Silica addition amount: 0.03% by weight
Particle size distribution: 0.08 to 2.0 μm
Average particle diameter: 0.30 μm
Number of protrusions: 3.2 × 10 ⁵ / mm ²
Dimensional change rate: 0.02%
Curl: 2.5mm
Friction coefficient: 0.90

[Examples 2 to 15]
In the same procedure as in Example 1, the raw materials and ratios of the aromatic diamine component and the aromatic tetracarboxylic acid component, the addition amount of silica, and the average particle diameter were reacted as shown in Tables 1, 2, and 3, respectively. After obtaining the solution, the stretching ratios in the transverse direction and the longitudinal direction were as shown in Tables 1, 2 and 3, and the characteristics of the polyimide film obtained by the same operation as in Example 1 were evaluated. The results are shown in.

  * The molar ratio in the table indicates mol% in the wholly aromatic diamine component and mol% in the wholly aromatic tetracarboxylic acid component, respectively.

[Comparative Examples 1-4]
In the same procedure as in Example 1, after obtaining a polyamic acid solution in the proportions shown in Table 4, the amount of aromatic diamine component and aromatic tetracarboxylic acid component, the amount of silica added, and the average particle diameter, the transverse direction and the longitudinal direction were obtained. The properties of the polyimide film obtained in the same manner as in Example 1 were evaluated as shown in Table 4, and the results are shown in Table 4.

  * The molar ratio in the table indicates mol% in the wholly aromatic diamine component and mol% in the wholly aromatic tetracarboxylic acid component, respectively.

  The polyimide film of the present invention can be suitably used for a fine pitch circuit substrate, particularly for COF (Chip on Film) wired in a narrow pitch on the TD of the film.

Claims (9)

A polyimide film characterized by having a thermal expansion coefficient α _{MD in} the machine transport direction (MD) of the film in the range of 10 to 20 ppm / ° C. and a thermal expansion coefficient α _{TD in} the width direction (TD) of 3 to 10 ppm / ° C. A polyimide film having a thermal expansion coefficient α _MD of 14 to 18 ppm / ° C. in a machine transport direction (MD) of the film and a thermal expansion coefficient α _{TD of 3} to 7 ppm / ° C. in a width direction (TD).   The polyimide film according to claim 1 or 2, wherein the tensile modulus of elasticity in the machine transport direction (MD) and the width direction (TD) of the film is both 4.0 GPa or more.   The polyimide film according to any one of claims 1 to 3, wherein both the 200 ° C heat shrinkage in the machine conveyance direction (MD) and the width direction (TD) of the film are 0.05% or less.   Inorganic particles having a particle diameter of 0.07 to 2.0 μm are uniformly dispersed in the film at a ratio of 0.03 to 0.30% by weight per film resin weight, and fine protrusions are formed on the surface. The polyimide film according to claim 1, wherein:   6. The polyimide film according to claim 5, wherein the average particle diameter of the inorganic particles is 0.10 μm or more and 0.90 μm or less.   6. The polyimide film according to claim 5, wherein the average particle size of the inorganic particles is 0.10 μm or more and 0.30 μm or less. ^8. The polyimide film according to claim 5, wherein the number of protrusions formed by the inorganic particles is 1 × 10 ³ to 1 × 10 ⁸ per 1 mm ² .   A copper-clad laminate, wherein the polyimide film according to claim 1 is used as a base material, and copper having a thickness of 1 to 10 μm is formed thereon.