JP2008143032A - Manufacturing method of flexible copper clad laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a copper clad laminated body which has a high adhesive force between a conducting body and an insulating body, is excellent in electromigration resistance, can perform a micro-machining in a pitch of 30 μm or less, and is excellent in flex resistance. <P>SOLUTION: In the manufacturing method of the flexible copper clad laminate where a polyimide resin layer is formed on one side surface of a copper foil layer, when an analysis measurement is performed by a secondary ion mass analysis (SIMS) as the copper foil, the manufacturing method comprises a step which prepares an electrolytic copper foil where a carbon peak intensity is 4.0 or less with respect to a copper peak intensity of 50.0, the thickness is within a range of 5 μm-35 μm and an average crystal grain diameter of the copper foil before heat treatment is less than 2 μm, a step where a polyimide precursor resin solution is applied on the prepared copper foil and the polyimide resin layer is formed by performing drying and curing through the heat treatment at 300-400°C, and a step for removing the copper foil thickness of 10-90% by chemically polishing the copper foil layer surface not contacting with the polyimide resin layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

    The present invention relates to a method for producing a flexible copper-clad laminate (hereinafter sometimes abbreviated as a copper-clad laminate) used in electronic equipment, and more specifically, fine circuit processing is possible and excellent bending characteristics. The present invention relates to a method for manufacturing a flexible copper clad laminate.

    Flexible copper-clad laminates are widely used in electronic devices that require flexibility, flexibility, and high-density mounting of movable parts and hinges in hard disks. In recent years, further downsizing and sophistication of the device has progressed, and copper-clad laminates have been folded and stored in narrow spaces, and the bending angle of the device itself has become sharper. The supply of copper-clad laminates has become essential.

    Against this background, it is known to reduce the thickness of the copper foil as a means for improving the flexibility of the copper foil. In this case, the strain generated on the outer periphery of the bent portion during bending is reduced, and the flexibility is improved. However, simply thinning the copper-clad laminate has limitations due to design limitations. .

    Moreover, the rolled copper foil is known as a copper foil excellent in flexibility. As a method for producing a rolled copper foil, electrolytic copper is cast into an ingot, and rolling and annealing are repeated to form a foil. The copper foil produced by this method has a high elongation rate and a smooth surface, so that it is difficult to crack and has excellent folding resistance. However, the rolled copper foil is expensive, and it is difficult to produce a copper foil having a width of 1 m or more due to mechanical restrictions during production. So far, rolled copper foil has been reported to be applied to flexible copper-clad laminates as a copper foil with excellent flexibility. For example, Japanese Patent Publication No. 2000-256765 (Patent Document 1) discloses the use of a rolled copper foil having a large crystal grain size in order to obtain a copper-clad laminate having high bending resistance. However, such a rolled copper foil is soft, and a thin copper foil having a thickness of 35 μm or less tends to be deformed by handling at the time of manufacturing a laminated board. JP-A-8-296082 (Patent Document 2) shows an electrolytic copper foil with good recrystallization, and JP-A-8-283886 (Patent Document 3) has improved bending characteristics. An electrolytic copper foil for a flexible wiring board is shown. However, for example, in a method for producing a copper clad laminate by a casting method in which a solution-like polyimide precursor resin is applied and heat treatment for drying and thermosetting (imidization) is performed, the heat treatment step is performed at 300 ° C. It takes more heat. When heat treatment is performed at such a high temperature, the copper foil is completely annealed, and does not stretch and becomes brittle. In addition, there is a problem that the transportability is deteriorated because the copper foil is wrinkled by heat shrinkage.

JP 2000-256765 A JP-A-8-296082 JP-A-8-283886

    It is an object of the present invention to provide a laminated sheet that improves handling in the production of laminated sheets, can be processed into fine wires of 30 μm or less, and has excellent bending resistance.

    As a result of various studies, the present inventors have found that the above problems can be solved by using an electrolytic copper foil having specific characteristics, laminating a polyimide resin layer on the copper foil, and then passing through a specific process. The headline and the present invention were completed.

That is, the present invention relates to a method for producing a copper clad laminate in which a polyimide resin layer is formed on one surface of a copper foil layer. When the copper foil is analyzed and measured by secondary ion mass spectrometry (SIMS), a copper peak The carbon peak intensity is 4.0 or less with respect to the intensity 50.0, and the thickness is 5 μm to
A step of preparing an electrolytic copper foil within the range of 35 μm and having an average crystal grain size of the copper foil before heat treatment of less than 2 μm, and applying a polyimide precursor resin solution on the prepared copper foil, followed by A step of drying and curing by heat treatment to form a polyimide resin layer, and a step of chemically polishing the copper foil layer surface not in contact with the polyimide resin layer to remove 10 to 90% of the copper foil thickness. It is a manufacturing method of the flexible copper clad laminated board characterized by the above-mentioned.

Satisfying one or more of the following in the method for producing a flexible copper-clad laminate gives a more excellent flexible copper-clad laminate.
1) The heat treatment includes a step of holding in a temperature range of 300 to 400 ° C. for 3 minutes to 40 minutes.
2) The average crystal grain size of the copper foil after the heat treatment is in the range of 2 to 7 μm.
3) Chemical polishing is performed with an etching solution containing hydrogen peroxide at a concentration of 0.5 to 10% by weight and sulfuric acid at a concentration of 0.5 to 15% by weight.
4) The surface roughness Rz of the copper foil layer after chemical polishing is 2.5 μm or less.

    Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

The manufacturing method of the flexible copper clad laminated board of this invention has the following process.
a) When the copper foil is analyzed and measured by secondary ion mass spectrometry (SIMS), the carbon peak intensity is 4.0 or less with respect to the copper peak intensity of 50.0, and the thickness is within the range of 5 μm to 35 μm. Preparing an electrolytic copper foil in which the average crystal grain size of the copper foil before heat treatment is less than 2 μm;
b) a step of applying a polyimide precursor resin solution on the prepared copper foil, followed by drying and curing by heat treatment to form a polyimide resin layer;
c) A step of chemically polishing the copper foil layer surface not in contact with the polyimide resin layer to remove 10 to 90% of the copper foil thickness.

    The copper clad laminate of the present invention is composed of a copper foil and a polyimide resin layer. In addition, since copper foil forms a copper foil layer or a conductor layer in a copper clad laminate, it is also referred to as a copper foil layer or a conductor layer. Also, since the physical properties of copper foil change due to heat treatment in step b) above, if it is necessary to distinguish between the copper foil before and after heat treatment, the copper foil before heat treatment and after heat treatment respectively. Called copper foil.

    As the copper foil prepared in step a), an electrolytic copper foil is used. The electrolytic copper foil can be produced by a known method and can be obtained by electrolysis from an electrolytic solution mainly composed of copper sulfate. However, as a characteristic of the copper foil before the heat treatment, when the component is measured by secondary ion mass spectrometry (SIMS), the carbon peak intensity is 4.0 or less with respect to the copper peak intensity 50.0, And the average crystal grain size must be less than 2 μm.

    The average crystal grain size of the copper foil defined in the present invention is obtained by preparing a copper foil sample, subjecting the copper foil surface to physical polishing, and further etching with an acidic corrosive solution, which is then measured using an ultra-deep shape measurement microscope. Is a value measured in accordance with ASTM particle size measurement (ASTM E112) by the cutting method. Such an electrolytic copper foil can be selected by performing the above measurement on a commercially available electrolytic copper foil. For example, there are HL foil manufactured by Nippon Electrolytic Co., Ltd. and WS foil manufactured by Furukawa Circuit Foil Co., Ltd. Component measurement by secondary ion mass spectrometry (SIMS) depends on the conditions described later.

    As a means of controlling the bending characteristics of the electrolytic copper foil, it is important to control two factors including the carbon component contained in the copper foil and the average crystal grain size. It has been known for a long time that the physical properties of metal crystals depend on the purity of the material, and in particular, the components contained in copper crystals themselves have a large effect as lattice defects. As the copper foil repeatedly undergoes plastic deformation, the lattice defects of the carbon component gradually increase, and a so-called work hardening phenomenon occurs in which the periphery of the lattice defects is no longer a complete crystal. Fracture due to fatigue occurs. For this reason, the carbon component of the prepared copper foil needs to be within the above range. The carbon component in the copper foil is preferably 2 or less, more preferably 0.1 to 1.0 as the carbon peak strength. Also, when the average crystal grain size is 2 μm or more, the copper foil itself becomes soft and easily deformed by the handling during the production of the laminate, so the average crystal grain size of the prepared copper foil must be within the above range. is there. The average crystal grain size of the copper foil before the heat treatment is preferably 0.5 μm or more and less than 2 μm, and more preferably in the range of 1.0 to 1.5 μm. Further, when subjected to heat treatment, the average crystal grain size tends to increase, but the average crystal grain size of the copper foil after the heat treatment is preferably in the range of 2 to 7 μm, preferably 2.5 to 5 μm. The amount of carbon component in the copper foil does not substantially change before and after the heat treatment.

    The thickness of the copper foil used is in the range of 5 to 35 μm, preferably in the range of 9 to 25 μm, and more preferably in the range of 12 to 18 μm. When the thickness of the copper foil exceeds 35 μm, it takes time to reduce the thickness by chemical polishing. Further, if the thickness of the copper foil is less than 5 μm, it is difficult to adjust the tension during the production of the laminate.

    In step b), a polyimide precursor resin solution is applied on the prepared copper foil, and a polyimide resin layer is formed by subsequent heat treatment.

    The polyimide resin and its precursor resin can be produced by reacting a known diamine and an acid anhydride in the presence of a solvent. Examples of the diamine used include 4,4′-diaminodiphenyl ether, 2′-methoxy-4,4′-diaminobenzanilide, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis ( 4-Aminophenoxy) benzene, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxy-4 4,4'-diaminobiphenyl, 4,4'-diaminobenzanilide and the like. Examples of the acid anhydride include pyromellitic anhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic acid diacid, and the like. Anhydrides and 4,4'-oxydiphthalic anhydride are mentioned. Diamine and an acid anhydride can also use 1 type (s) or 2 or more types.

    In addition, this reaction is preferably carried out in an organic solvent, and such an organic solvent is not particularly limited. Specifically, dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethyl is used. Examples include acetamide, N-methyl-2-pyrrolidone, hexamethylformamide, phenol, cresol, and γ-butyrolactone, and these can be used alone or in combination. Further, the amount of such organic solvent used is not particularly limited, but the amount used is such that the concentration of the precursor resin (polyamic acid) solution obtained by the polymerization reaction is about 5 to 30% by weight. It is preferable to use it after adjusting.

    The method for applying the polyimide precursor resin solution is not particularly limited, and the polyimide precursor resin solution can be applied with a coater such as a comma, die, knife, or lip. In this coating step, it is preferable that the polymerized precursor resin solution has a viscosity in the range of 500 to 35,000 cps.

    The applied polyimide precursor resin layer is dried and cured (imidized) in the subsequent heat treatment step. In this case, the heat treatment can be performed in a temperature range of 100 to 400 ° C. for about 10 to 40 minutes. In the present invention, after the solvent is dried at 160 ° C. or less, the bending characteristics of the copper foil are controlled. In order to achieve this, it is preferable to hold for at least 3 to 40 minutes in the temperature range of 300 to 400 ° C. A more preferable holding condition is 5 to 30 minutes in a temperature range of 310 to 390 ° C, and more preferably 7 to 20 minutes in a temperature range of 320 to 380 ° C. By setting the holding conditions in the heat treatment within the above range, the bending characteristics as a copper clad laminate can be improved.

    Here, the polyimide resin layer of the copper clad laminate may be formed of only a single layer or may be formed of a plurality of layers. In the case where a plurality of polyimide resin layers are used, other polyimide precursor resins can be sequentially applied and formed on polyimide precursor resin layers made of different components. When the polyimide resin layer is composed of three or more layers, the polyimide resin having the same configuration may be used twice or more.

    Whether the polyimide resin layer is a single layer or a plurality of layers, a low thermal expansion polyimide resin layer having a thermal expansion coefficient of less than 30 ppm / K, preferably in the range of 5 ppm / K to 25 ppm / K. It is preferable to have. A thermoplastic polyimide resin having a glass transition temperature of 400 ° C. or lower, preferably 250 to 380 ° C., more preferably 300 to 350 ° C. on one or both surfaces of the low thermal expansion polyimide resin layer. It is preferable to provide a layer.

    Here, as the low thermal expansion polyimide resin, a structural unit represented by the following general formula (1) is preferably used as a main structural unit.

但し、Ar₁は式（２）又は式（３）で表される４価の芳香族基を示し、Ar₃は式（４） 又は式（５）で表される２価の芳香族基を示し、qは構成単位の存在モル比を示し、 ０.１〜１.０の範囲である。

However, Ar < ₁ > shows the tetravalent aromatic group represented by Formula (2) or Formula (3), and Ar < ₃ > represents the divalent aromatic group represented by Formula (4) or Formula (5). Q represents the molar ratio of the constituent units and is in the range of 0.1 to 1.0.

但し、R₁は独立に炭素数１〜６の１価の炭化水素基又はアルコキシ基を示し、X及 びYは独立に、単結合又は炭素数１〜１５の２価の炭化水素基、O、S、CO、SO、SO₂若し くはCONHから選ばれる２価の基を示し、nは独立に０〜４の整数を示す。

Provided that R ₁ independently represents a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, and X and Y independently represent a single bond or a divalent hydrocarbon group having 1 to 15 carbon atoms, O , S, CO, SO, SO _{2 or} a divalent group selected from CONH, and n independently represents an integer of 0 to 4.

    A thermoplastic polyimide resin can also be obtained by using one or more known diamines and known acid anhydrides in appropriate combination. The thermoplastic polyimide resin layer preferably has a glass transition temperature of 400 ° C. or less, more preferably 250 to 380 ° C., and still more preferably 300 to 350 ° C., and a thermal expansion coefficient of 30 ppm / K. The above is preferable. Here, the thermal expansion coefficient refers to a value of an average linear thermal expansion coefficient of 100 ° C. to 250 ° C. measured using a thermomechanical analyzer, and the glass transition temperature is measured by a dynamic viscoelasticity measuring apparatus. The peak value of loss modulus.

    The total thickness of the polyimide resin layer is preferably in the range of 15 to 50 μm, and more preferably in the range of 20 to 40 μm. When the polyimide resin layer is composed of a low thermal expansion polyimide resin layer and a thermoplastic polyimide resin layer, the total thickness is 1/2 or more, preferably 2/3 to 9/10 is a low thermal expansion polyimide resin layer. It is good to comprise. Further, from the viewpoint of heat resistance and dimensional stability, the thickness of one layer of the thermoplastic polyimide resin layer is preferably 5 μm or less, more preferably in the range of 1 to 4 μm.

    Advantageously, the thermal expansion coefficient of the entire polyimide resin layer should be less than 30 ppm / K, preferably in the range of 5-25 ppm / K. Moreover, it is good to heat-process so that the average crystal grain diameter of the copper foil after heat processing may become in the range of 2 micrometers-7 micrometers, Preferably it is 3-6 micrometers.

    In the step b), a laminate in which a polyimide resin layer is provided on the copper foil is obtained. Therefore, in step c), the copper foil surface not in contact with the insulating layer is chemically polished with an etching solution to remove a part of the copper foil and reduce the thickness of the copper foil. A stretched laminate. As the etching solution, an etching solution containing 0.5 to 10% by weight of hydrogen peroxide and 0.5 to 15% by weight of sulfuric acid is preferable. The removal of the copper foil may remove 10 to 90%, preferably 20 to 75%, more preferably 40 to 70% of the copper foil thickness. The thickness of the copper foil is 3 to 18 μm, preferably 5 to 12 μm. When the thickness of the copper foil is larger than 18 μm, not only the bending resistance is lowered, but also fine processing in the circuit becomes difficult. When the copper foil thickness is less than 3 μm, the electromigration resistance of the circuit is poor. The surface roughness (Rz) of the copper foil on the chemically polished surface after chemical polishing is a 10-point average roughness of 2.5 μm or less, preferably 1.5 μm or less, and more preferably 1.0 μm or less. More preferably, it is good to set it as 0.5-1.0 micrometer or less. When the surface roughness of the copper foil is larger than 2.5 μm, it becomes difficult to finely process the circuit.

    Moreover, the surface roughness of the polyimide resin layer side of the copper foil is not particularly limited, but in particular, the flexible copper-clad laminate is applied to applications with a fine circuit width of 15 to 40 μm pitch (for example, FPC). In this case, the surface roughness (Rz) on the polyimide resin layer side is preferably 1.5 μm or less, more preferably in the range of 0.1 to 1.5 μm, and still more preferably in the range of 0.5 to 1.0 μm.

    The copper clad laminate produced according to the present invention is a single-sided copper clad laminate having a copper foil layer on one side of a polyimide resin layer. From the copper clad laminate produced according to the present invention, a double-sided copper clad laminate having a copper foil layer on both sides can also be obtained. The double-sided copper-clad laminate can be manufactured, for example, by preparing the above-mentioned two sets of copper-clad laminates, facing the resin layer side-by-side, and press-bonding with a hot press. In this case, a method of thermocompression bonding with a polyimide film interposed therebetween is also preferable. In addition, when press-bonding by hot pressing, when receiving heat equal to or higher than that of the heat treatment, the total time of heat treatment and hot pressing should be within the above range.

    Based on electrolytic copper foil with reduced impurities and excellent flexibility, it has high adhesion between conductors and insulators, excellent electromigration resistance, fine processing of 30μm pitch or less, and high bending resistance. An excellent copper clad laminate is obtained. As a result, it can be effectively used as a COF application for flexible printed circuit boards. In addition, by using electrolytic copper foil with higher conductivity than rolled copper foil, the electrical resistance in the fine circuit can be kept low.

    Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In the following examples, unless otherwise specified, various evaluations are as follows.

1) Measurement of carbon component by secondary ion mass spectrometry (SIMS) The copper-clad laminate obtained in each Example and Comparative Example was used as primary ions on the coated surface side of the copper foil using IMS-4F manufactured by CAMECA. , Cs + is irradiated at an intensity of 14.5 KeV and 50 nA in a region of 100 μm ² , and copper and carbon secondary ions (negative ions) emitted from the region are 1 second each within a measurement range of 60 μmφ. The intensity was measured one by one.

2) Measurement of crystal grain size of copper foil The prepared copper foil was observed at a magnification of 2,000 times with an ultra-deep shape measurement microscope VK8500 manufactured by Keyence Corporation, and ASTM particle size measurement by a cutting method (ASTM E112 ) Was used to determine the average crystal grain size. Moreover, about the copper foil of the copper clad laminated board obtained by each Example and the comparative example, after performing physical grinding | polishing to these copper foil surfaces, it etched using acidic corrosive liquid, and this was set as above. Similarly, the average crystal grain size was determined.

3) MIT bending test method The bending test sample was obtained by processing a copper-clad laminate for each bending test and providing a 15 μm epoxy adhesive layer on a 12 μm thick polyimide film on the surface on which the circuit was formed. A commercially available cover material was obtained by thermocompression bonding using a high-temperature vacuum press machine under conditions of a pressure of 40 kgf / cm ^{2 and} a temperature of 160 ° C. for 60 minutes so that the circuit forming surface and the adhesive layer face each other. In the following, this is called a test piece.
Using the MIT bending test apparatus manufactured by Toyo Seiki Seisakusho, bending was repeated under the following conditions, and the number of times until the test piece was disconnected was determined as the number of bendings.
Specimen width: 9 mm, Specimen length: 90 mm, Circuit width / Insulation width = 150 μm / 200 μm, Specimen sampling direction: Specimen sample length is parallel to the machine direction, bending radius r2 = 0. The test was performed under the conditions of 8 mm, vibration stroke = 20 mm, vibration speed: 1500 times / minute, weight of weight 250 g, bending angle = 90 ± 2 °.

4) Measurement of surface roughness of copper foil Using an ultra-deep shape measuring microscope (manufactured by KEYENCE, VK-8500), it was measured at a magnification of 2,000 and 140 μm in the length direction of the copper foil surface.

5) Measurement of glass transition temperature Using a viscoelasticity analyzer (RSA-II, manufactured by Rheometric Science Effy Co., Ltd.), the polyimide film obtained from the synthesis example was used as a 10 mm wide sample, and a 1 Hz vibration was applied from room temperature. The dynamic viscoelasticity when the temperature was raised to 400 ° C. at a rate of 10 ° C./min was measured to determine the glass transition temperature (maximum value of loss tangent (Tan δ)).

6) Measurement of the coefficient of thermal expansion The temperature of the polyimide film obtained in the synthesis example was raised to 250 ° C. with a thermomechanical analyzer (manufactured by Seiko Instruments Inc.) and held at that temperature for 10 minutes, and then 5 ° C./min. It cooled at the speed | rate and calculated | required the average thermal linear expansion coefficient from the dimensional change of the polyimide film from 240 degreeC to 100 degreeC.

Synthesis example 1
N, N-dimethylacetamide is placed in a reaction vessel. In this reaction vessel, 4,4′-diamino-2′-methoxybenzanilide (MABA) was dissolved in the vessel with stirring. Next, pyromellitic anhydride (PMDA) and 4,4′-diaminodiphenyl ether (DAPE) were added. The total amount of monomers was 15 wt%, and the molar ratio of each diamine was MABA: DAPE, 60:40. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a viscous polyimide precursor resin liquid a. Further, the polyimide precursor resin liquid a obtained in this synthesis example was used as a polyimide resin film, and the coefficient of thermal expansion was measured, and it was 15 ppm / K.

Synthesis example 2
N, N-dimethylacetamide is placed in a reaction vessel. In this reaction vessel, 2,2′bis [4- (4-aminophenoxy) phenyl] propane (BAPP) and 1,4-bis (4-aminophenoxy) benzene (TPE-Q) were stirred in the vessel. Dissolved. Next, BPDA and PMDA were added. The total amount of monomers introduced was 15 wt%, and the molar ratio of each diamine was BAPP: TPE-Q, 80:20. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a viscous polyimide precursor resin liquid b. Further, the polyimide precursor resin liquid b obtained in this synthesis example was converted into an imide and the glass transition temperature was measured.

In producing the copper-clad laminate, the following three types of copper foils were prepared. The carbon peak intensity is an intensity with respect to the copper peak intensity of 50.0 by SIMS. The polished surface side Rz is the surface roughness Rz on the side subjected to chemical polishing.
1) Copper foil 1: electrolytic copper foil, thickness 12 μm, carbon peak intensity 0.29, average crystal grain diameter 1.0 μm before heat treatment, insulating layer side Rz 0.6 μm, polished surface side Rz 0.7 μm
2) Copper foil 2: electrolytic copper foil, thickness 12 μm, carbon peak intensity 0.58, average crystal grain size before heat treatment 1.2 μm, insulating layer side Rz 1.3 μm, polished surface side Rz 0.9 μm
3) Copper foil 3: electrolytic copper foil, thickness 12 μm, carbon peak intensity 8.25, average crystal grain size before heat treatment 1.2 μm, insulating layer side Rz 0.8 μm, polished surface side Rz 1.7 μm, manufactured by Mitsui Kinzoku Co., Ltd. VLP foil

The following etching solutions were used for chemical polishing of the intermediate laminate.
Etching solution: Hydrogen peroxide / sulfuric acid based chemical polishing solution (sulfuric acid concentration 20 g / L, hydrogen peroxide concentration 80 g / L)

Copper foil 1 was used as the copper foil. On the copper foil, the polyimide precursor resin solution b obtained in Synthesis Example 2 was uniformly applied so that the thickness after curing was about 2 μm, and then dried by heating at 130 ° C. to remove the solvent. Next, the polyimide precursor resin a prepared in Synthesis Example 1 so as to be laminated thereon was uniformly applied so as to have a thickness after curing of about 35 μm, and dried by heating at 135 ° C. to remove the solvent. Further, the polyimide precursor resin liquid b was uniformly applied onto the polyimide precursor resin layer so that the thickness after curing was about 3 μm, and the solvent was removed by heating and drying at 130 ° C.
This laminated body was then passed through a heat treatment step in which the temperature was raised stepwise from 130 ° C. to 380 ° C. over 10 minutes to obtain an intermediate laminated body having a polyimide resin layer thickness of 40 μm. At this time, the maximum heating temperature was 380 ° C., and heat treatment was performed at this temperature for 6 minutes. The total holding time in the temperature range of 300 ° C. to 380 ° C. is about 10 minutes. The average crystal grain size of the copper foil after the heat treatment was 4.0 μm.
The copper foil layer of the intermediate laminate was chemically polished with an etching solution to obtain a copper clad laminate A so that the copper foil layer became 8.0 μm. In the copper clad laminate A thus obtained, the surface roughness Rz on the chemical polishing surface side of the copper foil layer was 0.8 μm.

    The copper foil 2 was used as the copper foil, and an intermediate laminate having a polyimide resin layer thickness of 40 μm was obtained in the same manner as in Example 1. The copper foil layer of this intermediate laminate was subjected to chemical polishing in the same manner as in Example 1 to obtain a copper clad laminate B. The average crystal grain size of the copper foil of the obtained copper clad laminate B was 3.0 μm, and the surface roughness Rz on the chemically polished surface side was 0.6 μm.

Comparative Example 1
The copper foil 3 was used as the copper foil, and an intermediate laminate having a polyimide resin layer thickness of 40 μm was obtained in the same manner as in Example 1. The copper foil layer of this intermediate laminate was subjected to chemical polishing in the same manner as in Example 1 to obtain a copper clad laminate D. In addition, the average crystal grain size of the copper foil of the obtained copper-clad laminate D was 1.3 μm, and the surface roughness Rz of the copper foil layer on the chemically polished surface side was 1.0 μm.

    The above results are summarized in Table 1.

Claims (5)

In the method for producing a copper clad laminate in which a polyimide resin layer is formed on one surface of the copper foil layer,
When the copper foil is analyzed and measured by secondary ion mass spectrometry (SIMS), the carbon peak intensity is 4.0 or less with respect to the copper peak intensity 50.0, and the thickness is in the range of 5 μm to 35 μm. A step of preparing an electrolytic copper foil in which the average crystal grain size of the copper foil before heat treatment is less than 2 μm, and applying a polyimide precursor resin solution on the prepared copper foil, followed by drying and hardening by heat treatment Forming a polyimide resin layer,
And a step of chemically polishing a copper foil layer surface not in contact with the polyimide resin layer to remove the copper foil thickness of 10 to 90%.     The method for producing a flexible copper-clad laminate according to claim 1, wherein the heat treatment includes a step of holding for 3 to 40 minutes in a temperature range of 300 to 400 ° C.     The method for producing a flexible copper-clad laminate according to claim 1 or 2, wherein the average crystal grain size of the copper foil after heat treatment is in the range of 2 to 7 µm.     The chemical polishing is performed with an etching solution containing hydrogen peroxide at a concentration of 0.5 to 10% by weight and sulfuric acid at a concentration of 0.5 to 15% by weight. A method for producing a flexible copper-clad laminate.     The method for producing a flexible copper-clad laminate according to any one of claims 1 to 4, wherein the surface roughness Rz of the copper foil layer after chemical polishing is 2.5 µm or less.