JP4443977B2 - Flexible copper clad laminate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a flexible copper-clad laminate, and more particularly to a flexible copper-clad laminate excellent in bending resistance.

Japanese Patent Laid-Open No. 2001-58203 Japanese Patent No. 3009383

  Flexible copper-clad laminates are widely used in electronic devices that require flexibility, flexibility, and high-density mounting. In recent years, with the increase in the memory capacity of devices, wiring pitches have been narrowed and high-density mounting has progressed, and the required level of mechanical properties for laminated boards has become higher. Electrolytic copper foil is generally considered good for the narrow pitch of flexible copper clad laminates because of the characteristics derived from the copper foil manufacturing method. On the other hand, in recent high-density mounting, the number of bent portions when the laminated plate is folded and stored in a housing has increased, and the bending angle has become smaller. Therefore, when it is rigid and has high tensile strength and low ductility like conventional electrolytic copper foil, the flexible copper-clad laminate produced by the copper foil is prone to wire breakage due to ductile fatigue of the copper foil. Therefore, there are many cases where electrical reliability cannot be obtained.

  According to Patent Document 1, the strength (I) of the (200) plane obtained by X-ray diffraction of the rolled surface after annealing to obtain a recrystallized structure was obtained by X-ray diffraction of fine powder copper ( It is described that the copper foil has high flexibility with respect to the strength (I0) of the (200) plane, and that high flexibility is exhibited by controlling the crystal structure. ing. According to Patent Document 2, in order to obtain the crystal structure of Patent Document 1, annealing immediately before the final cold rolling is performed under the condition that the average grain size of recrystallized grains obtained by this annealing is 5 to 20 μm. And the degree of rolling in the next final cold rolling is described as 90% or more.

  In addition, the conventional electrolytic copper foil does not change its tensile strength and rigidity even after annealing by heat treatment, and its annealing effect is small. Therefore, focusing on the bending resistance of the molded product, the tensile strength of the copper foil is suppressed before the heat treatment. In this case, it was difficult to adjust the tension during the production of the flexible copper-clad laminate, which was a factor in reducing productivity.

  From such a background, until now, in order to achieve both ductility, bending resistance, and fine pattern properties, the physical properties have been compensated by reducing the thickness of the copper foil and increasing the flexibility of the entire laminate. However, because this technology is restricted by the design of copper-clad laminates, the development of flexible copper-clad laminates that satisfy the above-mentioned ductility, bending resistance and fine patternability is desired without adjusting the thickness of the copper foil. It was.

  The present invention is a flexible copper-clad laminate that is easy to handle during the manufacture of copper-clad laminates without reducing the thickness of the copper foil, has high flexibility after molding, has good bendability, and has a long stress relaxation effect. The purpose is to provide a board.

  As a result of intensive studies, the present inventors have found that the above-described problems can be solved by using a specific copper foil for the flexible copper-clad laminate, and have completed the present invention.

That is, the present invention provides a copper clad laminate in which a copper foil layer is formed on one or both sides of a polyimide resin layer through a heat treatment step, and the elastic modulus of the copper foil layer before heat treatment is 50 to 80 GPa, A flexible copper-clad laminate characterized by the ratio (p2 / p3) of the elastic modulus (p3) between the previous elastic modulus (p2) and after heat treatment at 300 ° C. or higher being 3.5 to 5.5. is there.
In the flexible copper-clad laminate of the present invention, the copper foil layer preferably has a thickness of 12 to 18 μm and the resin layer has a thickness of 15 to 25 μm.

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

Hereinafter, the flexible copper clad laminate of the present invention will be further described.
The copper foil which comprises a copper clad laminated board can use the rolled copper foil, the electrolytic copper foil, etc. which were manufactured by the well-known method. The copper foil used in the present invention needs to have an elastic modulus of 50 to 80 GPa before the heat treatment of the copper foil layer. If the elastic modulus is lower than 50 GPa, deformation tends to occur during the production of the flexible copper-clad laminate, and if it is too low, it may break. When the elastic modulus exceeds 80 GPa, the rigidity increases, the relaxation of the tensile stress during the production of the flexible copper-clad laminate decreases, and plastic deformation is likely to occur. Moreover, this copper foil needs to have a ratio (p2 / p3) of an elastic modulus (p2) before heat treatment and an elastic modulus (p3) after heat treatment at 300 ° C. or higher of 3.5 to 5.5. It is. If the elastic modulus ratio is lower than 3.5, only a flexible copper-clad laminate with poor flexibility can be obtained.

  The flexible copper-clad laminate of the present invention is produced by a production process having a heat treatment step of the flexible copper-clad laminate using the copper foil exhibiting the above elastic modulus and elastic modulus ratio. The heat treatment temperature in the heat treatment step is 300 ° C. or higher, preferably 300 to 450 ° C. If the heat treatment temperature is lower than 300 ° C., it is speculated that the copper foil is not sufficiently recrystallized, and the elastic modulus may not be changed, which is not preferable. On the other hand, when it exceeds 450 ° C., the copper foil is deteriorated due to oxidation or the like, and the polyimide resin used in the flexible copper clad laminate may be decomposed, which is not preferable. The heat treatment time at a temperature of 300 ° C. or higher is arbitrary, but is preferably 5 to 40 minutes. It is advantageous that the heat treatment step also serves as a heat treatment step performed for drying and imidization of the polyimide or its precursor applied to the copper foil.

  The thickness of the copper foil used is 8 to 35 μm, preferably 12 to 18 μm. If the copper foil thickness is less than 8 μm, it is difficult to adjust the tension during production of the flexible copper-clad laminate, and if it exceeds 35 μm, the flexibility of the flexible copper-clad laminate is inferior, which is not preferable. Further, the roughness of the copper foil is a smooth surface, Rz = 0.5 to 1.5 μm, Ra = 0.05 to 0.25 μm, and the rough surface is Rz = 0.5 to 1.5 μm, Ra = 0. 0.05 to 0.30 μm. By using a copper foil having a roughness in this range, a copper-clad laminate capable of forming a fine circuit pattern is obtained. In particular, since the roughness of the rough surface affects the fine pattern property during circuit processing, it is preferable to use a copper foil having a Ra of 0.05 to 0.27.

  As a specific example of the copper foil satisfying the above elastic modulus, elastic modulus ratio, and thickness, there can be mentioned BHY-HA foil manufactured by Nikko Metal Co., Ltd.

Next, the polyimide resin layer of the copper clad laminate will be described.
This polyimide resin layer can be formed by heat-treating a polyimide precursor resin (polyamic acid) obtained by reacting a known diamine and acid anhydride in the presence of a solvent.

  Examples of the diamine used in the polyamic acid 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 dianhydride, 4,4′-oxydiphthalic anhydride and the like. Each of the diamine and acid anhydride may be used alone or in combination of two or more.

  Examples of the solvent include dimethylacetamide, n-methylpyrrolidinone, 2-butanone, diglyme, xylene and the like. One kind may be used, or two or more kinds may be used in combination.

  The polyimide resin layer is preferably formed by directly applying a polyimide precursor on the copper foil layer in a solution state, and the resin viscosity of the precursor is preferably 500 to 35000 cps. The applied precursor resin liquid is dried and imidized by performing a heat treatment, and the heat treatment conditions are preferably a temperature of 100 to 400 ° C. and a treatment time of about 20 to 40 minutes. The polyimide resin layer may be composed of only a single layer or may be formed of a plurality of layers. In the case of forming a plurality of polyimide resin layers, it can be formed by sequentially applying other polyimide resins on a polyimide resin layer 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.

  The flexible copper-clad laminate of the present invention can be produced by applying a polyimide resin on a copper foil as described above, but can also be produced by laminating one or more layers of polyimide film on a copper foil. . The flexible copper-clad laminate thus produced may be a single-sided copper-clad laminate having a copper foil layer only on one side, or a double-sided copper-clad laminate having a copper foil layer on both sides. Examples of the double-sided copper-clad laminate include a method of forming a single-sided copper-clad laminate and then crimping the copper foil layer by hot pressing, a method of sandwiching a polyimide film between two copper foil layers, and crimping by hot pressing.

  ADVANTAGE OF THE INVENTION According to this invention, the flexible circuit material of a flexible copper clad laminated board can be improved, and a flexible circuit material with high reliability can be provided at the time of use to the electric and electronic components used by bending.

Hereinafter, the present invention will be described in more detail with reference to examples.
In the following examples, various evaluations are based on the following unless otherwise specified.

[Measurement of elastic modulus]
Using a universal testing machine (STROGRAPH-R1) manufactured by Toyo Seiki Seisakusho Co., Ltd., measurement was performed in an environment of 23 ° C. and 50% RH.
[Evaluation of folding resistance]
A 200 μm wide line and space circuit is formed on a flexible copper-clad laminate with a test piece width of 8 mm and a test piece length of 150 mm, and CISV-1215 manufactured by Nikkan Kogyo Co., Ltd. is used as the cover material. A cover material was laminated, and an acceleration test was performed using an IPC bending tester manufactured by Shin-Etsu Engineering Co., Ltd. under conditions of curvature r: 1.25 mm, vibration stroke: 20 mm, vibration speed: 1500 times / minute. In this test, the number of times until the electrical resistance of the sample increased by 5% was obtained.

The polyimide precursor resin solution used in the examples was synthesized according to the following formulation.
Synthesis example 1
N, N-dimethylacetamide was added as a solvent to a reaction vessel capable of introducing a thermocouple, a stirrer and nitrogen. In this reaction vessel, 4,4′-diamino-2,2′-dimethylbiphenyl (DADMB) and 1,3-bis (4-aminophenoxy) benzene (DAB) were dissolved in the vessel with stirring. Next, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added. The total amount of monomers was 15 wt%, the molar ratio of each diamine (DADMB: BAB) was 90:10, and the molar ratio of each acid anhydride (BPDA: PMDA) was 20:79. Thereafter, stirring was continued for 3 hours, and the viscosity of the obtained polyimide precursor resin solution was 20000 cps.

Synthesis example 2
N, N-dimethylacetamide was added as a solvent to a reaction vessel capable of introducing a thermocouple, a stirrer and nitrogen. 2,2-bis [4- (4-aminophenoxy) phenyl] propane was dissolved in this reaction vessel with stirring. Next, BPDA and PMDA were added. The total amount of monomers charged was 15 wt%, and the molar ratio of each acid anhydride (BPDA: PMDA) was 4:69. Thereafter, stirring was continued for 3 hours, and the viscosity of the obtained polyimide precursor resin solution was 5000 cps.

Prepare BHY-HA foil manufactured by Nikko Metal Co., Ltd. as a copper foil, apply the polyimide precursor resin solution obtained in Synthesis Example 2 on this foil, dry it, and then obtain the polyimide precursor resin obtained in Synthesis Example 1. The solution was applied and dried, and the polyimide precursor resin solution obtained in Synthesis Example 2 was further applied and dried thereon to obtain a laminate in which the polyimide precursor resin layer was formed on the copper foil layer.
This laminate was put in an oven and heat-treated at 360 ° C. for 3 minutes to obtain a single-sided copper-clad laminate having a polyimide resin thickness of 25 μm. The elastic modulus of the copper foil before heat treatment was 62 GPa, the elastic modulus of the copper foil after heat treatment was 17 GPa, and the elastic modulus ratio was 3.6.
The folding resistance test result of the obtained flexible copper clad laminate was 55,000 folding resistance.

Comparative Example 1
A flexible copper clad laminate was produced in the same manner as in Example 1 except that BHY-22BT foil manufactured by Nikko Metal Co., Ltd. was used as the copper foil.
The elastic modulus of the copper foil before heat treatment was 53 GPa, the elastic modulus of the copper foil after heat treatment was 23 GPa, and the elastic modulus ratio was 2.3.
The folding resistance test result of the obtained flexible copper-clad laminate was 1,500 folding resistance times.

Prepare BHY-HA foil manufactured by Nikko Metal Co., Ltd. as a copper foil, apply the polyimide precursor resin solution obtained in Synthesis Example 2 on this foil, dry it, and then obtain the polyimide precursor resin obtained in Synthesis Example 1. The solution was applied and dried, and the polyimide precursor resin solution obtained in Synthesis Example 2 was further applied and dried thereon to obtain a laminate in which the polyimide precursor resin layer was formed on the copper foil layer. This laminate was heat treated at 360 ° C. for 6 minutes to obtain a single-sided copper-clad laminate having a polyimide resin thickness of 25 μm.
The elastic modulus of the copper foil before heat treatment was 62 GPa, the elastic modulus of the copper foil after heat treatment was 16 GPa, and the elastic modulus ratio was 3.9.
The folding resistance test result of the obtained flexible copper clad laminate was 54,000 folding resistance.

Comparative Example 2
A flexible copper clad laminate was produced in the same manner as in Example 2 except that Nikko Metal Co., Ltd. HY-22BT foil was used as the copper foil.
The elastic modulus of the copper foil before heat treatment was 53 GPa, the elastic modulus of the copper foil after heat treatment was 21 GPa, and the elastic modulus ratio was 2.5.
The folding resistance test result of the obtained flexible copper clad laminate was 12,000 folding resistance.

Prepare Nikko Metal Co., Ltd. BHY-HA foil as a copper foil, apply the polyimide precursor resin solution obtained in Synthesis Example 2 on this foil, dry it, and then obtain the polyimide precursor resin solution obtained in Synthesis Example 1 Was applied and dried, and the polyimide precursor resin solution obtained in Synthesis Example 2 was further applied and dried thereon to obtain a laminate in which the polyimide precursor resin layer was formed on the copper foil layer. This laminate was heat-treated at 360 ° C. for 13 minutes to obtain a single-sided copper-clad laminate having a polyimide resin thickness of 25 μm.
The elastic modulus of the copper foil before heat treatment was 62 GPa, the elastic modulus of the copper foil after heat treatment was 15 GPa, and the elastic modulus ratio was 4.1.
The folding resistance test result of the obtained flexible copper clad laminate was 52,000 folding resistance.

Comparative Example 3
A flexible copper-clad laminate was produced in exactly the same manner as in Example 3 except that Nikko Metal Co., Ltd. BHY-22BT foil was used as the copper foil.
The elastic modulus of the copper foil before heat treatment was 53 GPa, the elastic modulus of the copper foil after heat treatment was 21 GPa, and the elastic modulus ratio was 2.5.
The folding resistance test result of the obtained flexible copper clad laminate was 12,000 folding resistance.

Claims (2)

In the copper-clad laminate copper foil layer on one or both sides of the polyimide resin layer is formed, and after the heat treatment step of the copper foil layer is heat-treated at 300 ° C. or higher, the copper foil used for the copper foil layer The elastic modulus before heat treatment is 50 to 80 GPa, and the ratio (p2 / p3) of the elastic modulus before heat treatment (p2) to the elastic modulus after heat treatment at 300 ° C. or higher (p3) is 3.5 to 5.5. A flexible copper clad laminate characterized by the above.
  The flexible copper clad laminate according to claim 1, wherein the copper foil layer has a thickness of 12 to 18 μm and the resin layer has a thickness of 15 to 25 μm.