JP2001151916A - Film for flexible print wiring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film for flexible print wiring exhibiting very firm adhesion between a polyimide film as a substrate and a copper thin film and formation of a fine pattern by etching. SOLUTION: The film for flexible print wiring is obtained by subjecting at least one side of the polyimide film containing 0.01-2 wt.%, based on the film, of aluminum oxide or silicon dioxide in the film to a plasma treatment, forming thereon a copper thin film having a film thickness of 50-5,000 nm by an ion-plating method by a pressure gradient type discharge and further forming on the copper thin film a film of copper by an electrolytic plating method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for flexible printed wiring used in an electronic circuit of a portable device such as a portable telephone, a PDA (Personal Digital Assistant), and a notebook personal computer.

[0002]

2. Description of the Related Art At present, flexible copper-clad laminates used for portable electronic devices are mainly made of a material obtained by bonding a copper foil to the surface of a polyimide or polyester film with an adhesive. 2. Description of the Related Art In recent years, portable electronic devices have been reduced in size, weight, and function, and electronic circuits inside the electronic devices have been increased in density. In such a situation, a fine pattern with a line width of 40 μm or less is required, and the need for bare chip mounting is increasing. In a film in which copper foil is bonded to a conventional plastic film, measures such as improving the heat resistance of the adhesive and making the copper foil thinner have been taken.
It is not sufficient for weight reduction and high functionality, and there are problems such as a decrease in dimensional accuracy and a decrease in electrical characteristics due to the adhesive.

Further, in a method of forming a fine pattern by thinning a copper foil (thickness: 10 μm or less), it is difficult to handle in a process of bonding with a substrate film, and there is a problem of generation of wrinkles during handling. There is also a method of electrodepositing a thin copper foil with an aluminum support that adopts a special process, bonding it to the substrate film, and removing the aluminum support by etching etc. before printing the circuit pattern, but very much There is also a problem that the process is complicated and the manufacturing cost is high.

As a countermeasure, a method of forming a copper film directly on a substrate film by a vacuum deposition method, a sputtering method, an ion plating method, or a copper plating method has been studied.
However, it takes time to achieve the required thickness of 5 to 10 μm, and the adhesion strength is not sufficient. Further, a method of forming a copper film on a substrate film by a vapor deposition / plating method has been studied. However, since an acid treatment is performed at the time of plating, there is a problem that an underlying vapor deposited film is peeled off. In addition, Tokubo Sho 5
JP-A-7-33718 proposes that a metal such as nickel, cobalt, palladium or the like can be further vapor-deposited and then copper can be further vapor-deposited to improve the adhesion. When left at rest, there is a problem such as peeling off at the interface between the copper vapor deposition film and the copper plating film. Japanese Patent Application Laid-Open No. 8-330728 proposes that chromium, a chromium alloy, or the like is vapor-deposited on a polyimide film containing tin at 0.02 to 1% by weight of the film, and then copper is vapor-deposited thereon. However, there is a problem that the addition of conductive tin to the polyimide film lowers the insulating property, requires an anchor deposition layer for copper deposition, and lowers the etching efficiency.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and comprises subjecting a polyimide film containing aluminum oxide or silicon dioxide to plasma treatment under predetermined conditions. After forming a copper thin film on it by ion plating and then depositing a copper film by electrolytic plating, the adhesion is very strong and a flexible printed wiring film that can be fine-patterned by etching Is to provide.

[Means for Solving the Problems]

[0006] The flexible printed wiring film of the present invention has solved the above-mentioned problems by the following technical items. (1) A film for flexible printed wiring in which a copper thin film having a thickness of 50 nm to 5000 nm is formed on at least one side of a polyimide film, and copper is formed on the copper thin film by an electrolytic plating method. Aluminum oxide or silicon dioxide in 0.0
1 to 2% by weight of a flexible printed wiring film.

(2) The copper thin film layer is a copper thin film continuously formed by an ion plating method using a pressure gradient discharge after performing a plasma treatment on at least one surface of a polyimide film. Has an X-ray relative intensity ratio of 0.3 at a crystal lattice plane index of <200> / <111>.
7. The flexible printed wiring film according to the above (1), wherein the thickness is 7 to 0.46.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polyimide film used in the present invention includes Kapton (Toray DuPont), Upilex (Ube Industries, Ltd.), Apical (Kanebuchi Chemical Industry)
Films available on the market as trade names such as Co., Ltd. can be effectively used. Usually, it is obtained by reacting an aromatic tetrabasic acid and an aromatic diamine in a polar solvent to form a polyamic acid film and thermally or chemically dehydrating imidization.

The aromatic tetrabasic acids include pyromellitic dianhydride, biphenyltetracarboxylic anhydride, benzophenonetetracarboxylic anhydride, oxydiphthalic anhydride, hydrofurandiphthalic anhydride and the like. Examples thereof include 4,4′-diaminodiphenyl ether, paraphenylenediamine, dimethylbenzidine, diaminodiphenylmethane, toluylenediamine,
3,3'-diaminobenzophenone, methoxydiaminobenzene, p, p-aminophenoxybenzene, p, m
-Aminophenoxybenzene, m, p-aminophenoxybenzene, m, m-aminophenoxybenzene and the like.

The polar solvent includes N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like. The film is formed by heating this solution while casting and removing the solvent to cause a ring closure dehydration reaction.
These series of steps are continuous and the ring closure is from low temperature to 400 ° C.
It is performed in a short time by passing through a furnace in several stages up to the above high temperature. The film may have an appropriate thickness as needed, and a film having a thickness of 25 μm to 125 μm is used. If necessary, at least one surface of the polyimide film may be subjected to a known anchor coating treatment.

In the present invention, aluminum oxide or silicon dioxide contained in a resin comprising an aromatic tetrabasic acid and an aromatic diamine has a particle size of 0.1 to 5 μm and 0.01 to 0.01 μm.
２2% by weight. Desirably, 0.1 to
A range of 1% by weight is preferred. If the content is less than 0.01% by weight, the adhesion is poor, which is not preferable. On the other hand, if it exceeds 2% by weight, the workability is poor, which is not preferable. The film formation is performed by adding aluminum oxide or silicon dioxide at the time of forming the polyimide film, or applying a solution containing aluminum oxide or silicon dioxide on at least one surface of the polyimide film after forming the polyimide film, thereby forming a solvent. Is carried out while removing the compound to cause a ring-closing dehydration reaction.

In the present invention, the surface of the above-mentioned polyimide film is subjected to plasma treatment. In the plasma treatment, an inorganic gas is introduced in a vacuum vessel under a reduced pressure atmosphere, a high-frequency voltage is applied to an internal electrode, and a plasma (ion, electron, excited molecule, radical, ultraviolet light, etc.) is generated by discharging. ) Is made to collide with the surface of the film. As a device for performing the surface treatment, a device provided with an inductively coupled electrode or a capacitively coupled electrode in a vacuum vessel and connected to a high frequency power supply via a matching box is preferable. This process may be performed by either a batch system or a continuous system.

In the present invention, the plasma treatment on the surface of the polyimide film is performed under a reduced pressure atmosphere of 0.01 to 5 Pa. When the atmospheric pressure is lower than 0.01 Pa,
The pressure tends to fluctuate due to the effect of degassing from the polyimide film, and if it exceeds 5 Pa, the discharge becomes unstable, which is not preferable. Discharge power is 0.1 to 10 W / c
It is generally within the range of m ² . Processing time is 1
About 600 seconds. As the high-frequency power supply, a power supply having a frequency of several hundred KHz to several tens MHz is usually used. For example, in practice, it is preferable to use a power supply of 13.56 MHz. Various gases can be used as the atmosphere gas for the plasma treatment, but argon, helium, oxygen, nitrogen, carbon dioxide, and the like are preferable.

In the present invention, as a method for forming a copper thin film, a physical vapor deposition method such as a vacuum deposition method, a sputtering method, and an ion plating method can be adopted. Among them, the ion plating method is most preferable because it is excellent in adhesion and crystallinity with the base film. In particular, since the copper thin film is also important for the adhesion to the substrate,
An ion plating method using a pressure gradient discharge method, in which an intermediate electrode is provided between the cathode and the anode and a pressure gradient is applied between the degree of vacuum on the cathode side and the degree of vacuum on the anode side, uses a copper thin film and a substrate. In addition to the extremely strong adhesion, the evaporation amount of the film-forming material is large, and the ionization efficiency is higher than conventional vacuum evaporation and sputtering methods. Since a film speed can be obtained, productivity is high, and a film can be formed at a low temperature.

The copper used in the present invention has a purity of 99.9%.
Of oxygen-free copper as an evaporation material. The thickness of the copper thin film is preferably from 50 nm to 5000 nm. More preferably, it is 100 nm to 1000 nm,
If the thickness is less than nm, the deposited film is dissolved and peeled off by the acid of the treatment liquid when the electrolytic plating thin film is formed. On the other hand, when the thickness is 5000 nm or more, the film formation time becomes long, the productivity is poor, and the substrate may be deformed and curled by heat.

It is known that when a copper film is formed by an ion plating method, crystallinity is developed depending on film forming conditions such as a deposition rate, a can roll temperature, a plasma beam current, and a bias voltage. When the film is formed by the method of the present invention, a film in which the ratio of the peak intensity of the crystal lattice plane index <200> to the peak intensity of the plane index <111> in the X-ray diffraction pattern is in the range of 0.37 to 0.46. Is generated.
If the relative strength ratio is less than 0.37, lifting and peeling are liable to occur when acid treatment is performed before copper plating. Also, 0.46
Is the relative strength of the bulk copper, and there was no problem with the acid treatment. In the present invention, as a method for performing copper plating, a chemical treatment such as solvent degreasing, alkali degreasing, or activation is performed, followed by washing with water and copper sulfate plating. Solvent degreasing is performed by immersing in a solvent such as trichlorethylene or vapor degreasing when the stain is severe. Alkaline degreasing is immersed in a liquid of 50 to 80 ° C composed of sodium hydroxide, sodium carbonate, sodium silicate and a surfactant. Activation is performed by immersion in hydrochloric acid or sulfuric acid at room temperature. The copper plating bath is
It is classified into a copper sulfate bath, a copper cyanide bath, a copper borofluoride bath, a copper pyrophosphate bath, and the like. The copper sulfate bath is widely used because of its low cost and easy management.

[0017]

EXAMPLES In the following Examples and Comparative Examples, parts mean parts by weight and% means% by weight unless otherwise specified.

The evaluation of the copper thin films obtained in Examples and Comparative Examples was performed as follows. a. Thickness The thickness of the copper vapor deposition film was measured from a cross-sectional photograph taken by a scanning electron microscope (S-510) manufactured by Hitachi, Ltd. b. X-Relative Intensity of Copper Thin Film Using a X-ray diffractometer (RINT2000) manufactured by Rigaku Corporation, peak intensity of crystal lattice plane index <200> existing in a scanning range of 2θ = 42 to 53 ° in an X-ray diffraction pattern. And the ratio of the peak intensities of the surface indices <111> are measured.

C. Chemical resistance of copper thin film A copper-deposited sample is immersed in trichlorethylene for 5 minutes, washed with water, and immersed in a 2N aqueous sodium hydroxide solution for 5 minutes. Then, it is washed with water, immersed in a 2N aqueous hydrochloric acid solution for 5 minutes, and then washed with water. After drying at 110 ° C. for 10 minutes, the copper thin film was subjected to a cross-cut method based on JIS K5400.
The cellophane tape was peeled off, and the state of adhesion was visually observed. As the evaluation method, in 100 squares of 1 mm square, those with no peeling were rated as ○, those with a peeled area of less than 35% were rated as △, and those with a peeled area of 35% or more were rated as x. d. Adhesion of Copper Plating Film A copper-plated sample was prepared at 121 ° C. under a pressure of 2 kg / cm ^2.
After standing for 24 hours in an autoclave of supersaturated water vapor, the surface of the copper film surface was observed. Thereafter, the substrate is immersed in a 2N hydrochloric acid aqueous solution for 5 minutes and then washed with water. After drying at 110 ° C for 10 minutes,
The copper film was subjected to cellophane tape peeling by a cross cut method based on JIS K5400, and the state of adhesion was visually observed. As the evaluation method, in 100 squares of 1 mm square, those with no peeling were rated as ○, those with a peeled area of less than 35% were rated as △, and those with a peeled area of 35% or more were rated as x.

Example 1 One side of a 50 μm-thick polyimide film containing 0.1% by weight of aluminum oxide in a film was vacuumed to 0.5 P
After performing the plasma treatment with oxygen at a, a copper thin film having a thickness of 100 nm was formed by an ion plating method using a pressure gradient discharge. The film formation conditions at that time were a vacuum of 4 × 10 ⁻² Pa, an evaporation rate of 25.0 nm / sec, a can roll temperature of 90 ° C., a discharge current of 200 A, and a discharge voltage of 60 V. The surface is treated with a 2N hydrochloric acid aqueous solution for 5 minutes, and then the thickness is 800 mm by electrolytic plating in a copper sulfate bath.
It was set to 0 nm. Table 1 shows the evaluation results.

Example 2 A film was formed in the same manner as in Example 1 except that the thickness of the copper thin film was changed to 1000 nm. Table 1 shows the evaluation results. Example 3 A film was formed in the same manner as in Example 1 except that aluminum oxide was changed to silicon dioxide. Table 1 shows the evaluation results.

Example 4 A film was formed in the same manner as in Example 1 except that the evaporation rate under the film forming conditions was 1.5 nm / sec. Table 1 shows the evaluation results. Comparative Example 1 A sample was obtained in the same manner as in Example 1 except that a polyimide film containing no aluminum oxide was used. Table 1 shows the evaluation results.

Comparative Example 2 A sample was obtained in the same manner as in Example 1 except that the polyimide film was not plasma-treated with oxygen. Table 1 shows the evaluation results. Comparative Example 3 A sample was obtained in the same manner as in Example 1 except that film formation by an ion plating method was performed by film formation by a vacuum evaporation method. Table 1 shows the evaluation results.

Comparative Example 4 A sample was obtained in the same manner as in Example 1 except that the thickness of the copper thin film formed by the ion plating method was changed to 40 nm. Table 1 shows the evaluation results.

[0025]

[Table 1]

As is evident from Table 1, in Comparative Examples 1, 2 and 3, the vapor-deposited copper thin films have poor chemical resistance. Particularly, the edge portion was lifted by immersion in hydrochloric acid. Comparative Example 4
Although there was no problem with the chemical resistance of the copper thin film, peeling occurred at the interface between the copper thin film and the copper plating film in the evaluation of adhesion after copper plating. In contrast to these comparative examples, Examples 1 to 4 of the present invention have good chemical resistance of the copper thin film and good adhesion of the copper plating film.
Fine pattern formation with a line width of 40 μm was possible by etching with an aqueous ferric chloride solution.

[0027]

The film for flexible printed wiring obtained by the present invention is obtained by subjecting at least one surface of a polyimide film containing 0.01 to 2% by weight of aluminum oxide or silicon dioxide to a plasma treatment, and applying a pressure gradient discharge to the surface. By an ion plating method, a copper thin film having an X-ray diffraction pattern plane index of <200> / <111> and an X-ray relative intensity ratio of 0.37 to 0.46 was formed to a thickness of 50 nm.
Forming at a thickness of up to 5000 nm has good adhesion to the polyimide film, enables formation of a fine pattern by etching, and is extremely useful in practice.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 79/08 C08L 79/08 Z H05K 1/03 610 H05K 1/03 610N 610R 670 670A 1/09 1 / 09 A 3/38 3/38 A F-term (reference) 4E351 AA04 BB01 BB32 BB33 CC02 CC03 CC21 DD04 4F006 AA39 AA55 AB73 BA07 CA08 DA00 DA01 EA03 4F100 AA19B AA19H AA20B AA20H AB17A AB17C AB17E AB33ABE66 BABBAC GB43 JK06 JL01 YY00B 4J002 CM041 DE146 DJ016 FD016 GF00 GQ00 GQ02 5E343 AA18 AA33 BB24 CC78 DD23 DD24 DD25 DD43 EE36 GG02 GG08

Claims (2)

[Claims] (1) at least one side of a polyimide film,
In a film for flexible printed wiring in which a copper thin film having a thickness of 50 nm to 5000 nm is formed and copper is formed on the copper thin film by an electrolytic plating method, aluminum oxide or silicon dioxide is added to the polyimide film in an amount of 0. A film for flexible printed wiring, characterized in that it is contained in an amount of from 0.01 to 2% by weight. 2. The copper thin film layer is a copper thin film continuously formed by an ion plating method using a pressure gradient discharge after performing a plasma treatment on at least one surface of a polyimide film. Crystal lattice plane index <2
00> / <111> X-ray relative intensity ratio of 0.37 to
2. The flexible printed wiring film according to claim 1, wherein the thickness is 0.46.