TWI394659B - Method for making high anti-flexion flexible copper clad laminate board - Google Patents

Description

Method for manufacturing high buckling flexible copper clad laminate

The present invention relates to a method for producing a flexible copper-clad laminate (hereinafter simply referred to as a copper-clad laminate) for use in an electronic device, and more particularly to a high-flexibility flexible copper-clad laminate excellent in high buckling characteristics. The manufacturing method of the board.

The flexible copper clad laminate is widely used in electronic devices that require flexural or soft, high-density assembly, such as a movable portion of a hard disk or a hinge portion of a mobile phone. In recent years, as the size and height of the device have progressed, the copper-clad laminate has been bent and stored in a narrow space, and the bending angle of the copper-clad laminate itself has become an acute angle. The supply of copper sheets with higher buckling is indispensable.

Based on this background, a method of improving the buckling property of a copper foil is known as a method of thinning the thickness of a copper foil. At this time, the deformation generated around the periphery of the bent portion at the time of buckling is reduced to improve the buckling property. However, only the copper clad laminate is thinned, which is limited by reasons such as design regulations.

A rolled copper foil is known as a copper foil excellent in buckling property. In the method for producing a rolled copper foil, electrical copper is cast into an ingot, and rolling and annealing are repeated to form a foil. The copper foil produced by this method is not easy to crack and excellent in folding resistance due to high elongation and smooth surface. However, the rolled copper foil is expensive, and it is difficult to manufacture a copper foil having a width of 1 m or more due to mechanical limitations at the time of manufacture. Further, it is difficult to stably produce a rolled copper foil having a small thickness, and since it is thin, the buckling property is improved, and it is necessary to perform a half-etching treatment or the like.

Further, the copper foil which is relatively easy to perform thickness adjustment at a low price is an electrolytic copper foil. In the electrolytic copper foil production method, first, a large cylindrical cathode having a diameter of 2 to 3 m, which is called a drum, is sunk in a half in an electrolytic solution containing copper sulfate as a main component, and an anode is provided so as to surround it. The copper is electrolyzed on the drum, and is rotated, and the deposited copper is sequentially peeled off to be produced. However, in general, since the impurities such as additives are present in the electrolytic solution, the crystal grain size of the precipitated copper is fine. When the crystal grain size is small, the elongation of the copper foil is low, and the grain boundary of the crystal is the starting point of cracking, so that the buckling property is remarkably inferior to that of the copper-clad laminate using the rolled copper foil.

Here, Patent Document 1 discloses an electrolytic copper foil having a good recrystallization property, and Patent Document 2 discloses an electrolytic copper foil for a flexible wiring board having improved buckling characteristics. However, in the method for producing a copper-clad laminate in which a solution-like polyimide precursor resin is coated on a copper foil, and a casting method is used for heat treatment for drying and heat hardening, the heat treatment step is heat of 300 ° C or higher. . In the high-temperature heat treatment in this manner, the copper foil is completely annealed, and the elongation disappears and becomes brittle. Further, there is also a problem that the transportability is deteriorated due to crease caused by thermal contraction of the copper foil.

(Patent Document 1) Japanese Laid-Open Patent Publication No. Hei 8-296082 (Patent Document 2)

An object of the present invention is to provide a method for stably producing a high-flexibility copper-clad laminate in a method for producing a copper-clad-coated polyimide precursor resin solution and performing heat treatment to obtain a copper-clad laminate.

As a result of various studies, the inventors have found that the use of an electrolytic copper foil having specific characteristics, the coating of the polyimide film on the copper foil, and the heat treatment under specific conditions can solve the above problems. invention.

That is, the present invention is a method for producing a high-flexibility flexible copper-clad laminate, which is obtained by coating a surface of a copper foil with a polyimide film of a polyimide precursor, followed by drying and hardening by a heat treatment step to produce a copper foil and a polyamide. In the method of copper-clad laminate of an imide resin layer, it is characterized in that an electrolytic copper foil is used as a copper foil, and in the above heat treatment step, it is maintained at a temperature range of 300 to 450 ° C for 3 to 40 minutes to make the copper foil described above. The average crystal grain size is grown to 2 to 8 times before the heat treatment step.

According to the present invention, when an electrolytic copper foil having excellent copper foil transportability is used in the production of a copper clad laminate, the crystal grain size of the copper foil is controlled in the subsequent heat treatment step, whereby a flexible coating having good buckling characteristics can be produced. Copper laminate.

(Best form of implementing the invention)

Hereinafter, preferred embodiments of the present invention will be described in detail.

The copper clad laminate of the present invention comprises a copper foil and a polyimide resin layer. The copper foil may be provided only on one side of the polyimide layer or on both sides.

The copper foil used must be an electrolytic copper foil, and the preferred average crystal grain size before the heat treatment step of coating the polyimide precursor resin solution ranges from 0.5 to 2 μm, more preferably from 1.0 to 1.5 μm. The electrolytic copper foil can be produced by a known method, and an electrolytic solution containing copper sulfate as a main component is deposited by electrolysis. However, it is necessary to use it to recrystallize under a predetermined heat treatment condition, and the average crystal grain size is 2 to 8 times that before the heat treatment due to the heat treatment. The average crystal grain size of the copper foil defined in the present invention is a copper foil sample prepared before and after the heat treatment, and the surface of the copper foil is physically polished, and then etched using an acidic etching solution to measure the microscope in an ultra-depth shape. The measured value was measured according to ASTM particle size (ASTM E112) by a cutting method at a magnification of 2000 times. The electrolytic copper foil used in the present invention can be subjected to the above heat treatment in a commercially available electrolytic copper foil, and the change in the average crystal grain size can be measured to select an electrolytic copper foil suitable for the present invention. Specifically, it is preferred that the average crystal grain size before the heat treatment is selected to be in the range of 0.5 to 2 μm, and the average crystal grain size after the heat treatment is 2 to 8 times before the heat treatment, and the electrolytic copper foil satisfying the conditions has Japanese electrolysis. HL foil manufactured by the company or WS foil manufactured by Furukawa Circuit Foil.

When the average crystal grain size is less than twice that before the heat treatment, the crystal grain size of the copper foil before the heat treatment is large, the copper foil itself is soft and the transportability is poor, or the crystal grain size before the heat treatment is small, but the copper foil crystal after the heat treatment is crystallized. The particle size hardly grows, and as a result, a copper-clad laminate having high flexibility cannot be obtained. Further, when the average crystal grain size exceeds 8 times before the heat treatment, the crystal grain size after the heat treatment becomes extremely large, so that the copper foil is extremely soft and the conveyability is deteriorated. Further, since the crystal does not grow uniformly, the stress concentrates on the boundary, and cracks are likely to occur, and the buckling property is lowered.

When the average crystal grain size before the heat treatment step is less than 0.5 μm, the ratio of the buckling property is small even if the crystal is grown by 2 to 8 times after the heat treatment, and the transportability of the copper foil before the heat treatment is poor, and the recrystallization is likely to occur. When the crystal grain size after the film is too large, it is not preferable for the above reasons.

The electrolytic copper foil is preferably used by any one of surface treatments subjected to roughening treatment or electroplating treatment, or both.

The preferred thickness of the copper foil is in the range of 8 to 35 μm, particularly preferably in the range of 9 to 18 μm. When the thickness of the copper foil is less than 8 μm, it is difficult to adjust the tension at the time of manufacture of the copper clad laminate. On the other hand, when it exceeds 35 μm, the buckling property of the copper clad laminate is poor.

Next, the polyimine resin layer constituting the insulating layer of the copper clad laminate will be described. The polyimine resin layer is conventionally produced by polymerizing a diamine and an acid anhydride in the presence of a solvent.

The diamine to be used may, for example, be 4,4'-diaminodiphenyl ether, 2'-methoxy-4,4'-diaminobenzimidamide, 1,4-anthracene (4-amine). Phenoxy group) benzene, 1,3-anthracene (4-aminophenoxy)benzene, 2,2'-indole [4-(4-aminophenoxy)phenyl]propane, 2,2' - dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 4,4'-diaminobenzimidamide, and the like. The acid anhydride may, for example, be pyromellitic acid anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylphosphonium tetracarboxylic acid Anhydride, 4,4'-hydroxydicarboxylic anhydride. The diamine and the acid anhydride may be used alone or in combination of two or more.

Examples of the solvent include dimethylacetamide, N-methylpyrrolidone, 2-butanone, diglyme, and xylene. These may be used alone or in combination of two or more.

In the present invention, the polyimine resin layer is formed by directly coating a copper foil in a precursor state. In the coating step, the viscosity of the precursor resin solution before polymerization is preferably in the range of 500 to 35,000 cps. The coated polyimine precursor resin layer continues to dry and harden in a heat treatment step. The heat treatment conditions at this time may be carried out in a temperature range of 100 to 400 ° C for about 10 to 40 minutes. However, in the present invention, after drying the solvent at 160 ° C or lower, the copper foil must be recrystallized at least 300. Heat treatment was carried out at 450 ° C for 3 to 40 minutes. The heat treatment is preferably carried out at a temperature of from 350 to 400 ° C for a range of from 5 to 20 minutes. When the heat treatment conditions are not within the above range, the control of the crystal grain size of the copper foil in the heat treatment step is not appropriate, and a copper-clad laminate having high flexibility cannot be obtained.

The polyimide layer may be formed of only a single layer or a plurality of layers. When the polyimine resin layer is a plurality of layers, it can be formed by sequentially coating other polyimide precursor resin precursors on the polyimide film precursor layer formed of different constituent components. When the polyimine resin layer includes three or more layers, the polyimine resin having the same structure may be used twice or more.

When the polyimine resin layer is in the case of a single layer or a plurality of layers, it preferably has a coefficient of thermal expansion of less than 30 × 10 ^{- 6} /K, advantageously from 5 × 10 ^{- 6} /K to 25 × 10 ^- A low thermal expansion polyimine resin layer in the range of ⁶ / K. Therefore, it is preferable to provide a thermoplastic polyimide polyimide resin layer having a glass transition temperature of 350 ° C or less, preferably 250 to 350 ° C on either or both sides of the low thermal expansion polyimide resin layer.

Here, the low thermal expansion polyimine resin is preferably a constituent unit mainly composed of a structural unit represented by the following general formula (1).

However, Ar ₁ represents a tetravalent aromatic group represented by the formula (2) or the formula (3), Ar ₂ represents a divalent aromatic group represented by the formula (4), and R ₁ independently represents a carbon number of 1 to 6. a monovalent hydrocarbon group or alkoxy group, X and Y independently represent a single bond or a divalent hydrocarbon group having 1 to 15 carbon atoms, a divalent group selected from O, S, CO, SO ₂ or CONH, and n independently represents 0 to An integer of 4. The main constituent unit means preferably 60 mol%, more preferably 80 mol%, of the constituent unit. Thus, the above structural unit may be present in a single polymer or as a structural unit of the copolymer.

The thermoplastic polyimine resin layer may be used by suitably combining one or more kinds of conventional diamines with a conventional acid anhydride. The thermoplastic polyimine resin layer preferably has a glass transition temperature of 350 ° C or less, preferably 250 to 350 ° C, and a thermal expansion coefficient of 30 × 10 ^{- 6} /K or more. Further, in the present invention, the glass transition temperature is in the above range, and the coefficient of thermal expansion is less than 30 × 10 ^{- 6} /K, which is contained in the low thermal expansion polyimine resin layer. The coefficient of thermal expansion as defined in the present invention refers to the value of the average coefficient of thermal expansion measured from a thermomechanical analyzer at 100 ° C to 250 ° C; the glass transition temperature refers to the loss modulus of elasticity measured by a dynamic viscoelasticity measuring device. The peak.

The thickness of the polyimide resin layer is preferably in the range of 15 to 50 μm. When the polyimine 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, and advantageously 2/3 to 9/10 may be It is composed of a low thermal expansion polyimide resin layer. Further, the thermoplastic polyimide polyimide resin layer has a thickness of 5 μm or less, preferably 1 to 4 μm, from the viewpoint of heat resistance and dimensional stability. When the thermoplastic polyimide layer is provided on both sides of the low thermal expansion polyimide resin layer, the total thickness is twice the aforementioned value.

The copper-clad laminate produced by the present invention may be a single-sided copper-clad laminate having a copper foil layer on one side of the polyimide film, or a copper-clad laminate having a copper foil layer on both sides. For the two-sided copper-clad laminate, for example, two sets of copper-clad laminates can be prepared and manufactured by hot pressing and pressing on the resin side. In this case, it is preferred to apply a heat-pressing film to the polyimide film held therebetween.

(Example)

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited thereto. Further, in the following examples, it is not particularly limited, and various evaluations are as follows.

Average crystal size

Prepare a copper foil sample before and after the heat treatment, perform physical polishing on the surface of the copper foil, and then etch it with an acidic etching solution, and observe it at a magnification of 2000 times with an ultra-depth shape measuring microscope VK8500 manufactured by the company. The average crystal grain size was determined by a cutting method according to the method of ASTM particle size measurement (ASTM E112).

Buckling test

The evaluation was carried out according to the following IPC test method and MIT test method. The buckling test sample is processed by a copper-clad laminate circuit for various buckling tests, and a 15 μm epoxy-based adhesive layer of a commercially available covering material is provided on a 12 μm-thick polyimide film on the surface of the circuit. The circuit formation surface and the adhesive layer were opposed to each other, and were obtained by hot pressing using a high-temperature vacuum presser under the conditions of a pressure of 40 kgf/cm ² , 160 ° C, and 60 minutes. Hereinafter, each of the buckling test samples is referred to as a test piece.

2-1) IPC buckling test method The IPC buckling test was carried out by an IPC buckling test apparatus manufactured by Shin-Etsu Machinery Co., Ltd. The buckling was repeated under the following conditions, and the number of times when the resistance value of the test piece exceeded the initial value of 5% was determined as the number of buckling times.

Test piece width: 8 mm, test piece length: 150 mm, loop width / insulation width = 150 μm / 200 μm, test piece take direction: take the test piece's long direction parallel to the mechanical direction, radius of curvature r1 = 1.25 mm, vibration stroke (stroke): 20 mm, vibration speed: Acceleration was generated at 1500 times/min.

2-2) MIT buckling test method The MIT buckling test was performed on a MIT buckling test apparatus manufactured by Toyo Seiki Seisakusho Co., Ltd. The number of times of the test piece line was obtained by repeating the buckling under the following conditions as the number of buckling times.

Test piece width: 9 mm, test piece length: 90 mm, loop width / insulation width = 150 μm / 200 μm, test piece take direction: take the test piece's long direction parallel to the mechanical direction, the yield radius r2 = 0.8 mm, vibration The test was carried out under the conditions of stroke: 20 mm, vibration speed: 1500 times/min, load weight = 250 g, and bending angle = 90 ± 2°.

Synthesis Example 1

In the reaction vessel, N,N-dimethylacetamide was fed. Dissolving 4,4'-diamino-2,2'-dimethylbiphenyl (DADMB) and 1,3-quinone (4-aminophenoxy)benzene (1, while stirring in the reaction vessel) 3-BAB) in the container. Next, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic anhydride (PMDA) were added. The total amount of monomer input was 15% by weight, and the molar ratio of each diamine was DADMB: 1,3-BAB was 90:10, and the molar ratio of each anhydride was BPDA:PMDA was 20:79. . Thereafter, stirring was continued for 3 hours, and the solution viscosity of the obtained polyimine precursor resin liquid a was measured to be 20,000 cps. Further, the polythenimine resin obtained in the synthesis example was measured to have a thermal expansion coefficient of 15 × 10 ^{- 6} /K.

Synthesis Example 2

In the reaction vessel, N,N-dimethylacetamide was fed. 2,2'-贰[4-(4-Aminophenoxy)phenyl]propane (BAPP) was dissolved in the vessel while stirring in the reaction vessel. Second, add BPDA and PMDA. The total amount of the monomers was 15% by weight, and the molar ratio of each of the anhydrides was 5:95 for BPDA:PMDA. Thereafter, stirring was continued for 3 hours, and the solution viscosity of the obtained polyimine precursor resin liquid b was measured to be 5000 cps. Further, the glass transition temperature of the polyimide resin obtained in the synthesis example was measured at 310 °C.

Example 1

An electrolytic copper foil 1 having a thickness of 12 μm (HL foil manufactured by Nippon Electrolysis Co., Ltd., average crystal grain size before heat treatment: 1.0 μm) was prepared. The polyimine precursor resin solution b obtained in Synthesis Example 2 was uniformly coated on the copper foil so as to have a thickness of about 2 μm after hardening, and then dried by heating at 130 ° C to remove the dissolved coal. Next, the polyimine imide resin precursor solution a prepared in Synthesis Example 1 was uniformly coated thereon by lamination in a manner of a thickness of about 20 μm after hardening, and dried by heating at 135 ° C to remove the solvent. Further, the polyimine resin precursor solution b was uniformly coated on the polyimine layer so as to have a thickness of about 3 μm after hardening, and dried by heating at 130 ° C to remove the solvent.

This laminate was then subjected to a heat treatment step of a stepwise temperature rise at 130 ° C to 380 ° C for 10 minutes to obtain a single-sided copper-clad laminate having a polyimide thickness of 25 μm. At this time, the maximum heating temperature was 380 ° C, and heat treatment was performed at this temperature for 6 minutes. Further, the average crystal grain size of the copper foil after the heat treatment was 6.3 μm. The single-sided copper-clad laminate was used to prepare a sample for the IPC buckling test and the MIT buckling test, and the buckling test was performed separately. As a result, the number of IPC buckling was 17,600 times at a buckling radius of 1.25 mm, and the number of MIT buckling tests was 4,700 times at a buckling radius of 0.8 mm.

Example 2

An electrolytic copper foil 2 having a thickness of 12 μm (WS foil manufactured by Furukawa Circuit Foil Co., Ltd., average crystal grain size before heat treatment: 1.1 μm) was prepared. Using this copper foil, a single-sided copper-clad laminate having a polyimide thickness of 25 μm was obtained in the same manner as in Example 1. Further, the average crystal grain size of the copper foil after the heat treatment was 3.3 μm. The IPC buckling frequency of the sample was 14,700 times at a buckling radius of 1.25 mm, and the number of MIT buckling tests was 3,900 times at a buckling radius of 0.8 mm.

Comparative example 1

An electrolytic copper foil 3 having a thickness of 12 μm (VLP foil manufactured by Mitsui Metals Co., Ltd., average crystal grain size before heat treatment: 1.2 μm) was prepared. Using this copper foil, a single-sided copper-clad laminate having a polyimide thickness of 25 μm was obtained in the same manner as in Example 1. Further, the average crystal grain size of the copper foil after the heat treatment was 1.3 μm. The IPC buckling number of the sample was 4100 times at a buckling radius of 1.25 mm, and the number of MIT buckling tests was 1100 times at a buckling radius of 0.8 mm.

Claims (3)

The invention relates to a method for manufacturing a high-flexibility flexible copper-clad laminate, which is coated with a polyimide film of a polyimide film on a surface of a copper foil, and then dried and hardened by a heat treatment step to produce a copper foil and a polyimide resin layer. In the method for copper-clad laminate, an electrolytic copper foil having an average crystal grain size of 0.5 to 2 μm is used as the copper foil, and in the above heat treatment step, the temperature is maintained at a temperature ranging from 350 to 400 ° C for 5 to 20 minutes. The average crystal grain size of the copper foil is grown to 2 to 8 times before the heat treatment step. The method for producing a high-flexibility flexible copper-clad laminate according to the first aspect of the invention, wherein the copper foil before the heat treatment step has an average crystal grain size of 1.0 to 1.5 μm. The method for producing a high-flexibility flexible copper-clad laminate according to claim 1 or 2, wherein the polyimine resin layer is pre-coated by using a plurality of polyimine precursor resin solutions. The cloth is coated with a polyimide resin precursor layer, and other polyimide precursor resin precursors are sequentially coated, followed by drying and hardening in a heat treatment step, and at least one layer has a thermal expansion coefficient of less than 30×10 ^-6 /K. The low thermal expansion polyimine resin layer and the thermoplastic polyimide polyimide resin layer having a glass transition temperature of at least 350 ° C.