JPH05110247A - Manufacture of board for flexible printed wiring - Google Patents

Abstract

PURPOSE:To improve the adhesive properties of a polyimide film and a metallic layer by executing low-temperature plasma treatment to the surface of the polyimide film, to which alkali treatment is conducted previously, and forming the metallic layer through a wet type plating method. CONSTITUTION:Alkali treatment is performed as the pretreatment of the surface of a polyimide film first, and it is favorable that the surface of the polyimide film is dipped and treated into an aqueous solution such as sodium hydroxide, potassium hydroxide, etc., in pH 8 or more at a liquid temperature of 5-80 deg.C. The previously alkali-treated polyimide film is introduced into a low-temperature plasma treater, glow discharge is conducted and the low-temperature plasma of an inorganic gas is generated, and the surface is plasma-treated continuously. A thin metallic layer is formed onto the surface through an electroless plating method as one kind of a wet type plating method, and a metallic layer is formed through an electroplating method. Accordingly, the excellent adhesiveness of the polyimide film and the metallic layer are acquired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a flexible printed wiring board, which comprises directly forming a metal layer on the surface of a polyimide film.

[0002]

2. Description of the Related Art In recent years, the electronics field has been remarkably developed, and in particular, miniaturization of electronic devices for communication, consumer use, etc.
The demand for these performances has become more and more advanced as the weight and density have been increased. The flexible printed wiring board that meets such requirements has flexibility and can withstand repeated bending, and therefore can be mounted in a narrow space at a high density in three dimensions. Its applications are expanding as composite parts with connector functions.

Recently, high heat resistance is demanded for this flexible printed wiring board, and in order to satisfy these requirements, a two-layer type flexible body consisting only of a polyimide resin layer and a metal layer without using an adhesive is provided. A printed wiring board has been proposed (see Japanese Patent Publication No. 61-45511). There are two methods for manufacturing this substrate: a method of forming a polyimide resin layer on a metal foil and a method of forming a metal layer on a polyimide film. In the former case, it is common to cast a polyimide precursor on a metal foil and heat-cure it to form a polyimide layer.
The substrate obtained by this method has sufficient heat resistance, but 1) if a thin metal foil is used, wrinkles will form in the metal foil when the polyimide hardens.
Since it hardens at 00-400 ℃, the metal foil deteriorates. As a result, when a circuit is formed on the substrate, a circuit defect due to wrinkles, a bending defect due to oxidation of the metal foil, and the like occur.

In the latter case, it is common to form a metal layer on the surface of the polyimide film by electroless plating, electrolytic plating, sputtering, ion plating, vapor deposition, etc., and a substrate obtained by this method is sufficient. Although it is possible to obtain heat resistance, since the adhesion between the polyimide film and the metal layer is low, there remains a problem in terms of reliability, and improvement in this adhesion has been particularly required. In addition, in order to improve this adhesiveness, it has been proposed to subject the surface of the polyimide film to sandblasting and alkali treatment as pretreatment (see Japanese Patent Application Laid-Open No. 3-6382), but the strength of the film becomes weaker with sandblasting. In addition, there is a problem that foreign matter (blasting agent such as SiC) is mixed into the film, which causes troubles such as disconnection and contact of the circuit in the circuit processing process.

Further, only by the alkali treatment, it is expected that the anchor effect due to the unevenness of the polyimide film surface and the adhesion to the metal layer due to -OH, -COOH, etc. due to the hydrolysis of the polyimide will still be sufficient with the metal layer. At present, the adhesiveness is not obtained.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above problems and improve the adhesiveness between a polyimide film and a metal layer, and has excellent adhesion between the polyimide film and the metal layer. An object of the present invention is to provide a flexible printed wiring board having properties.

[0007]

Means for Solving the Problems The inventors of the present invention have diligently studied a pretreatment method for a polyimide film in order to solve the above problems, and as a result, the present invention has been achieved. A method for manufacturing a flexible printed wiring board is characterized in that the surface of the polyimide film is subjected to a low temperature plasma treatment, and a metal layer is further formed by a wet plating method.

The present invention will be described in detail below. As the polyimide film used in the present invention, the thickness is usually 12.5.
The thickness is in the range of up to 125 μm, but an appropriate thickness is used if necessary. The composition of the polyimide resin includes aliphatic, aliphatic-aromatic and aromatic polyimide resins, and the aromatic polyimide resin is preferable from the viewpoint of heat resistance and the like.

In the present invention, the surface of the polyimide film is pre-treated with an alkali, but this is for effectively activating the surface by the following low-temperature plasma treatment, and the thickness of the modified layer at this time. Is preferably 0.05 to 2 μm, more preferably 0.1 to 1 μm. If it is less than 0.05 μm, the anchor effect is difficult to obtain, and the adhesiveness between the polyimide film and the metal layer is not improved, and if it exceeds 2 μm, the physical properties such as tensile strength, tear propagation resistance and elastic modulus of the film are deteriorated. Resulting in. As the alkali treatment method, it is preferable to perform immersion treatment in an aqueous solution of sodium hydroxide, potassium hydroxide or the like having a pH of 8 or more and a liquid temperature of 5 to 80 ° C. for 1 to 600 seconds. These conditions are appropriately determined depending on the polyimide resin composition and the like.

The greatest feature of the present invention is that the alkali treatment and the low temperature plasma treatment are combined as a pretreatment of the surface of the polyimide film. The low temperature plasma treatment to be carried out after the alkali treatment is to put a polyimide film which has been alkali treated in advance in a low temperature plasma treatment apparatus capable of reducing pressure,
The inside of the equipment is made an atmosphere of inorganic gas and the pressure is 0.001 to 10 Tor
While maintaining at r, preferably 0.01 to 1 Torr, a low temperature plasma of inorganic gas is generated by applying a direct current or an alternating current of about 0.1 to 10 KV between the electrodes and glow discharge to generate a low temperature plasma of the inorganic gas. The plasma treatment is continuously performed, but the plasma treatment time is preferably set to about 0.1 to 100 seconds. As the inorganic gas, an inert gas such as helium, neon, or argon, and oxygen, nitrogen, carbon monoxide, carbon dioxide, ammonia, or air are used, but these are not limited to one kind, and two or more kinds may be mixed. It is also optional to use. By performing this low-temperature plasma treatment, the surface of the polyimide film having the irregularities formed by the alkali treatment is activated, and the adhesiveness with the metal layer is improved.

Next, a metal layer is formed on the surface of the polyimide film which has been subjected to the alkali and low temperature plasma pretreatment by a wet plating method. First, a thin metal layer is formed by an electroless plating method which is one of the wet plating methods.
The thickness of the metal layer at this time is preferably 0.01 to 1 μm, and more preferably 0.05 to 0.5 μm. If it is less than 0.01 μm, uneven plating will occur on the metal layer, and when performing electroless plating on the electroless plated metal layer in the next step, problems such as uneven thickness of the metal layer and pinhole layer will occur, which is not preferable. If the thickness exceeds 1 μm, the time required for electroless plating becomes long, the manufacturing efficiency deteriorates, and the internal stress of the metal layer lowers the adhesiveness and heat resistance.

Next, a metal layer is formed on the polyimide film with the thin metal layer by electrolytic plating. The thickness of the metal layer at this time is appropriately determined depending on workability and application, but the thickness of the metal layer is preferably 2 to 35 μm as the sum of the thickness of the electroless plating metal layer and the thickness of the electrolytic plating metal layer, and further 5 -18 μm is preferable. If the thickness is less than 2 μm, the metal layer is thin, so that the circuit is broken at the time of forming the circuit, or the circuit has a small cross-sectional area, resulting in insufficient electrical capacity. If the thickness exceeds 35 μm, the time required for electrolytic plating becomes long, the manufacturing efficiency deteriorates, and it becomes impossible to cope with the formation of high density in which the line width and the line interval of the circuit are reduced due to the miniaturization of the wiring board. In addition,
These electroless plating and electrolytic plating may be conventional methods and are not particularly limited. Examples of the plating metal include chromium, nickel, copper and the like, but it is preferable to use copper from the viewpoint of electric resistance and workability.

[0013]

EXAMPLES The embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto. (Example 1) A 25 μm thick Kapton film (trade name of polyimide film manufactured by Toray-Dupont Co., Ltd.) was alkali-treated for 60 seconds at 50 ° C. in a 20 wt% sodium hydroxide aqueous solution to obtain a modified layer of about 0.2 μm. It was This film 120
After drying at 30 ° C. for 30 minutes, low temperature plasma treatment was performed.
At this time, the plasma processing time is 0.1V or less vacuum, the oxygen flow rate is 2.0L / min, the applied voltage is 2KW and the frequency is 110K.
Input 30 KW power in Hz. In the plasma generator, four electrodes were arranged in a cylindrical shape, and the film was moved along the outside of the electrode at a distance of 40 mm outside the electrode at a speed of 10 m / min for about 25 seconds. Then, this polyimide film was subjected to electroless copper plating to obtain a 0.05 μm copper layer.
Further, a copper layer having a total thickness of 18 μm was obtained by electrolytic copper plating. For electroless copper plating, HS202B (Hitachi Kasei sensitizer), AD
P201 (Hitachi Kasei adhesion promoter), CUST201 (Hitachi Kasei electroless copper plating solution), electrolytic copper plating Cubelite
TH (Ebara Eugelite copper sulfate plating solution) was used under standard conditions. The characteristics of the flexible printed wiring board thus obtained are shown in Table 1.

Example 2 A Kapton film having a thickness of 25 μm (described above) was treated at 70 ° C. with a 20% by weight aqueous sodium hydroxide solution.
Alkaline treatment was performed for 60 seconds to obtain a modified layer of about 0.5 μm. Subsequent processing under the same conditions as in Example 1 was carried out to obtain a flexible printed wiring board, the characteristics of which are shown in Table 1.

Example 3 A Kapton film having a thickness of 25 μm (described above) was treated at 70 ° C. with a 20 wt% sodium hydroxide aqueous solution.
Alkali treatment was performed for 120 seconds to obtain a modified layer of about 0.9 μm. Then, the substrate was processed under the same conditions as in Example 1 to obtain a flexible printed wiring board. This characteristic is shown in Table 1.

Example 4 A substrate for flexible printed wiring was obtained by the same conditions as in Example 1, except that the plasma processing rate was changed from 10 m / min to 30 m / min.
This characteristic is shown in Table 1.

(Example 5) A substrate for flexible printed wiring was obtained by the same process as in Example 1, except that the plasma treatment gas was changed from oxygen to nitrogen. This characteristic is shown in Table 1.

Example 6 A substrate for flexible printed wiring was obtained by the same treatment as in Example 1, except that the thickness of the electroless copper plating was changed from 0.05 μm to 0.5 μm. This characteristic is shown in Table 1.

Comparative Example 1 A substrate for flexible printed wiring was obtained by treating under the same conditions as in Example 1 except that the Kapton film (described above) was not subjected to alkali treatment. This property is shown in Table 1, but sufficient adhesive strength was not obtained.

(Comparative Example 2) A Kapton film having a thickness of 25 mm (described above) was treated with a 20% by weight aqueous sodium hydroxide solution at 30 ° C.
The treatment was performed for a second to obtain a modified layer of about 0.02 μm. A flexible printed wiring board was obtained under the same conditions as in Example 1 below. This characteristic is shown in Table 1. Since the thickness of the alkali-modified layer was thin, sufficient adhesive strength could not be obtained.

Comparative Example 3 A substrate for flexible printed wiring was obtained under the same conditions as in Example 1 except that the Kapton film (described above) was not subjected to the low temperature plasma treatment. This property is shown in Table 1, but sufficient adhesive strength was not obtained.

(Comparative Example 4) A flexible printed wiring board was obtained under the same conditions as in Example 1 except that the copper layer 0.05 μm formed by electroless plating was changed to 2.0 μm. This characteristic is shown in Table 1. Neither adhesive strength nor heat resistance was satisfactory.

The methods for measuring the physical properties of the flexible printed wiring boards used in the above Examples and Comparative Examples are as follows. 1. Peel strength: Conforms to JIS C 6481. A circuit with a width of 1 mm is formed on the board, and this is peeled from the copper side in the 90 ° direction at a speed of 50 mm / min. 2. Solder heat resistance: Complies with JIS C 6481. Float a 25 mm square sample on the flow solder for 30 seconds and visually check for blister and peeling. Evaluation of Table 1: ◯: No abnormality. ×: There are blisters and peeling.

[0024]

[Table 1]

[0025]

Industrial Applicability According to the present invention, it is possible to provide a flexible printed wiring board having excellent adhesion between a polyimide film and a metal layer, and its industrial utility value is extremely high.

Claims (1)

[Claims] 1. A method for manufacturing a substrate for flexible printed wiring, which comprises subjecting a polyimide film surface which has been previously subjected to an alkali treatment to a low temperature plasma treatment, and further forming a metal layer by a wet plating method.