JPH04359585A - Board for flexible printed circuit and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent damage of a surface of a polyimide film by forming the film of four layers of a protective plastic film, the polyimide film, a thermosetting adhesive layer and a metal foil. CONSTITUTION:After both side surfaces of a polyimide film and one side surface of a protective plastic film are activated by a low temperature plasma of inorganic gas, the activated surfaces of the polyimide film and the plastic film are thermally press-bonded. Then, after the other activated surface of the polyimide film is coated with heat-curing agent, a metal foil is press-bonded to be laminated. Thus, contact with rolls in a later circuit forming step, etc., wear, scratch, pressing damage, etc., at the time of handling, and damage of the surface of the polyimide film can be prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed circuit board with a protective film made of a polyimide film which has no scratches on the film surface and has good performance, and a method for producing the same.

0002

BACKGROUND OF THE INVENTION In recent years, as electronic products have become lighter, thinner, and more highly functional, demand for printed circuit boards has increased, and the range of use for flexible printed circuits has expanded, and the demand for flexible printed circuits has been increasing. Recently, as printed circuits have become more sophisticated, have finer patterns, and become thinner, appearance problems such as small scratches on the product surface have also arisen, and improvements are being demanded.

[0003] In particular, flexible printed circuit boards (hereinafter referred to as
The base film of FPC (abbreviated as FPC) may be scratched or damaged due to contact with the hard surface of equipment or careless handling.
It is easy to get abrasion scratches, etc., which not only impairs the appearance of the FPC, but also used in fields that require high flexibility, especially in applications such as FDDs, HDDs, and printers where bending is repeated over a long period of time. When the scratched surface of the base film is repeatedly bent, cracks may expand and lead to material failure.

[0004]Furthermore, FPC has recently become a cause of scratches.
The manufacturing process is becoming more and more complicated due to performance improvement, multilayering, compounding, miniaturization, etc., and the following are specific processes where scratches occur. 1) Substrate manufacturing process: (1) Process of manufacturing a substrate using a laminator: Scratches are likely to occur due to contact with various rolls. (2) Cure process, slitting process, packaging process: There is a lot of contact with rolls during handling. 2) Circuit creation process: (1) Surface preparation and cleaning process: Scratches occur due to polishing and handling. (2) Circuit printing process: There is a lot of handling and contact with various rolls in each process such as screen printing, dry film (photosensitive film) lamination, exposure, and development. (3) Etching process: In each process such as etching, cleaning, drying, etc., there is contact with various rolls and there is a lot of handling. 3) Circuit protection process using a coverlay film or cover coat material: Contact with various rolls and a lot of handling during processes such as temporarily pressing the coverlay film and the substrate, curing the adhesive, washing and drying, etc. 4) FPC outer mold processing and inspection process: There is contact with various rolls and a lot of handling during processes such as punching with a mold, adhesion of backing material, dimensional inspection, and performance inspection.

[0005]

[Problem to be solved by the invention] As mentioned above, FP
The base film of C is prone to scratches and abrasion marks due to contact with the hard surfaces of devices and carelessness during handling.When used for applications such as FDDs, HDDs, or printers, the scratched surface of the base film may Repeated bending may cause cracks to expand, leading to material failure. Furthermore, throughout the entire process of FPC manufacturing 1) to 4), there is a lot of contact with rolls in various devices, and there is a significant amount of handling. For this reason, FPC
The surface of the film may be abraded, scratched, dented or pressed by foreign objects, etc., and if left as is, it may lead to material destruction after it is mounted on a device. The present invention aims to eliminate these drawbacks and provide an intact FPC that retains its original performance.

[0006]

[Means for Solving the Problems] The present inventors have conducted intensive research to solve the above problems, and as a result, they have arrived at the present invention. A flexible printed circuit board comprising four layers: - thermosetting adhesive layer - metal foil. When manufacturing the flexible printed circuit board, both sides of the polyimide film and one side of the protective plastic film are activated in advance with low-temperature plasma of inorganic gas, and then each activation-treated side of the polyimide film and the protective plastic film is activated. A method for producing a flexible printed circuit board, which comprises heat-compression bonding the polyimide film, then applying a thermosetting adhesive to the other activated surface of the polyimide film, and then pressure-bonding and laminating the polyimide film with a metal foil. By using the flexible printed circuit board manufactured from the polyimide film with a protective film according to the present invention, it is possible to avoid contact with rolls during the subsequent circuit manufacturing process, wear and scratches during handling, etc.
The occurrence of press scratches, etc. is significantly reduced, which in turn prevents material destruction after the flexible printed circuit is mounted on equipment, leading to long-term stable operation of the equipment.

The present invention will be explained in detail below. First, the polyimide film used in the present invention may be a commercially available one, and has a thickness of 12.5 μm to 125 μm and a width of 500 to 1016 m.
m is common. The plastic film for protecting the polyimide film is preferably one that can withstand heat, chemicals, etc. in the board manufacturing process and circuit manufacturing process, and specific examples include polyester film, polypropylene film, TPX film (polymethylpentene), PPS film, and EVA film. etc. This protective film goes through board production, printed circuit production, actual size processing, and is finally removed just before or after mounting on the device is completed, so it maintains its adhesive properties until this stage, and after the purpose is achieved. It is necessary that it can be easily peeled off. Therefore, it is not necessary to have the adhesiveness to the extent that it is press-bonded through an adhesive, and it is preferable that the adhesiveness is such that it can be bonded by thermocompression bonding. However, it would be a problem if even some parts of the film peeled off during the long process, so in the present invention, the surfaces of the polyimide film and the protective film are activated with low-temperature plasma and then bonded by thermocompression, thereby achieving a balance between adhesiveness and peelability. solved.

This method of activating the film surface using low-temperature plasma involves passing the polyimide film and protective plastic film through a low-temperature plasma processing device that can reduce the pressure, creating an inorganic gas atmosphere inside the device, and increasing the pressure to 0.00.
A low-temperature plasma of inorganic gas is generated by applying direct current or alternating current of about 0.1 to 10 KV between the electrodes while maintaining the voltage at 1 to 10 Torr, preferably 0.01 to 1 Torr, and causing a glow discharge. The surface of the polyimide film is continuously plasma-treated while moving the polyimide film. The treatment time is preferably approximately 0.1 to 10 seconds. Inorganic gases used include inert gases such as helium, neon, and argon, oxygen, nitrogen, carbon monoxide, and air.

[0009] As a thermocompression bonding method for a low-temperature plasma-treated polyimide film and a protective film, it is sufficient to continuously press them using a heated thermal roll, and the temperature of the heating roll varies depending on the protective film used, but is 80 to 200°C.
The line pressure is preferably 5 to 30 kg/cm, and the line speed is 1 to 10 m/min.

Next, a method for manufacturing a flexible printed circuit board will be described. A metal foil is attached to the polyimide film with a protective film produced as described above via an adhesive. The thermosetting heat-resistant adhesive used here is one that laminates a heat-resistant polyimide film and metal foil, and requires high adhesiveness and heat resistance to withstand use with soldering, etc. is epoxy resin, N
BR-phenol resin, phenol-butyral resin, epoxy-NBR resin, epoxy-phenol resin, epoxy-nylon resin, epoxy-polyester resin, epoxy-acrylic resin, polyamide-epoxyphenol resin, polyimide Examples include resins such as acrylic resins, acrylic resins, and silicone resins, and the thickness of the adhesive during lamination is preferably 5 to 30 μm based on resin solid content.

[0011] Metal foils include copper foil, aluminum foil, iron foil, nickel foil, etc., but copper foil is good for printed circuits, and rolled and electrolytic copper foils with a thickness of 18 to 70 μm are preferred. used.

[0012] The method of laminating the polyimide film with a protective film and the metal foil is carried out in accordance with a conventional method, in which a thermosetting adhesive is applied to the polyimide film using a roll coater or the like, and the solvent is evaporated and removed using an in-line dryer to form a semi-cured adhesive. condition, and is continuously thermocompressed with metal foil using a heated thermo roll. Temperature is 60~150℃, linear pressure 5~
30 Kg/cm and line speed of 1 to 10 m/min are standard. The thus laminated flexible printed circuit board is further heated and cured in a curing oven at 80 to 200° C. for one to several tens of hours in order to complete the heat curing of the adhesive and improve the physical properties of the substrate.

[0013]

[Examples] Hereinafter, embodiments of the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto. (Evaluation method of flexible printed circuit board) 1) FPC
Surface flaw inspection: Measurement sample 240 x 240 mm
is inspected with a 20x magnifying glass to check for streaky scratches with a width of 0.05 mm or more, press scratches with a diameter of 0.10 mm or more, scratches, etc., and calculate the number of scratches. (Evaluation symbol) ◎: 0 to 2 pieces (there are almost no scratches). ○: 2 to 5 pieces. △: 6 to 10 pieces.
×: 10 or more pieces. 2) Mold releasability of the protective film: Cut the polyimide film with the protective film to a width of 20 mm, and
Peel off the protective film at a speed of 0 mm/min.

(Examples 1 to 5) Thickness: 25 μm, Width: 5
Both sides of a 08 mm polyimide film and a polypropylene film with a thickness of 50 μm and a width of 510 mm as a protective film, TPX film (polymethylpentene),
Each side of the polyester film was subjected to plasma treatment at a speed of 30 m/min using a continuous low temperature plasma treatment apparatus. Processing conditions are vacuum level 0.1 torr and oxygen 1.0 L/
The device was supplied with an applied voltage of 2 KV, 110 KHz, and an input of 30 KW. Four electrodes were arranged in a cylindrical shape, and the film was moved along the outer periphery of the electrodes at a distance of 40 mm outside the electrodes for processing. Next, the polyimide film and the protective film were thermocompression bonded using a heating roll with a diameter of 250 mm and a length of 600 m and a silicone rubber roll. The conditions were as follows: temperature shown in Table 1, linear pressure 20 kg/cm, 3 m
The low-temperature plasma-treated surfaces were heat-pressed together at a line speed of /min and wound into a roll. Next, an epoxy/NBR adhesive was applied to the low-temperature plasma-treated surface of the polyimide film with a protective film to a thickness of 18 mm after drying.
After coating with a roll coater to a thickness of 35 μm and removing the solvent through an in-line dryer to make the adhesive semi-hardened, apply a layer of electrolytic copper foil of 35 μm and heated roll temperature.
It was heat-pressed at 120° C., a line pressure of 20 kg/cm, and a line speed of 3 m/min, and wound up into a roll. This was further cured in a curing oven at 80°C for 5 hours. 12
The material was cured by heating at 0° C. for 5 hours to produce a flexible printed circuit board.

Next, first (flaws on the substrate surface) were measured. 1) The surface scratches were inspected and the mold releasability of the protective film was measured using the above-mentioned inspection method using the substrate as it was, and the results are shown in Table 1. 2) A test FPC circuit was produced using the following method, and then the protective film was removed and a surface scratch inspection on the polyimide film surface was performed. (Flaws in the FPC manufacturing process) 1) The FPC board manufactured as described above was slit into rolls of 50 m with a width of 240 mm using a slitter. 2) Wet-level the copper foil surface with a polisher at a speed of 1 m/min, wash with water, and dry. 3) Adhere the dry film to the substrate at 120° C. and at a speed of 1 m/min. 4) A parallel pattern with a line width of 0.2 mm and a line spacing of 0.2 mm is exposed using a photographic method. 5) Processing, resist removal, etching and water washing were carried out roll-to-roll at a speed of 0.5 m/min. 6) Next, cut it to 240 x 240 mm. 7) Coverlay film CA335 (Shin-Etsu Chemical Co., Ltd.
Co., Ltd. product name) is 240 x 240 mm, and 6
) is press-molded under the following conditions. Temperature 160
°C, pressure 50 kg/cm for 2 hours and 30 minutes. The protective film of the FPC sample prepared in this way was removed and an inspection for scratches on the surface of the polyimide film was conducted, and the results are shown in Table 1.

[0016]

[Table 1]

(Comparative Example 1) Polyimide film and epoxy/N were used without using the protective film in Example 1.
A flexible printed circuit board was produced by laminating electrolytic copper foil in the same manner using a BR adhesive.

(Comparative Examples 2 to 5) Flexible printed circuit boards were prepared in the same manner as in Example 1, except that a protective film that was not subjected to plasma treatment was used. Comparative Examples 1 to 5 were also inspected for scratches on the substrate surface and scratches in the FPC manufacturing process in the same manner as in Example 1, and the results are shown in Table 1.

[0019]

According to the present invention, a protective plastic film is attached to a polyimide film as a base film by thermocompression bonding and then processed into a flexible printed circuit board. It is possible to prevent the occurrence of scratches on the surface of the polyimide film, contributing to improving the bending resistance of the flexible printed circuit after it is mounted on equipment, and has extremely high industrial value.

Claims (2)

[Claims] 1. A flexible printed circuit board comprising four layers: a protective plastic film, a polyimide film, a thermosetting adhesive layer, and a metal foil. 2. When manufacturing the flexible printed circuit board according to claim 1, after activating both sides of the polyimide film and one side of the protective plastic film with low-temperature plasma of an inorganic gas, the polyimide film and the A flexible printed circuit characterized in that each activated surface of a protective plastic film is bonded by thermocompression, then a thermosetting adhesive is applied to the other activated surface of the polyimide film, and then laminated with metal foil by pressure bonding. method for manufacturing substrates for