JPH0818171A - Flexible printed circuit board - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] To provide a flexible printed circuit board with a protective film, which is useful for the production of a polyimide film-based thin flexible printed circuit board and has good processability and peelability. [Structure] On one side of a polyimide film, a copper foil is laminated via a heat-resistant adhesive on the other side of the one-sided copper foil laminated film,
A flexible printed circuit board, which is formed by laminating a protective plastic film with a peelable adhesive, and a single-sided copper foil laminated film having a thickness of less than 60 μm,
A substrate for a flexible printed circuit, which is formed by laminating a protective plastic film with a peelable adhesive whose adhesive strength is reduced by irradiation with ultraviolet rays.

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, which is used for thin polyimide film type flexible printed circuit boards and the like and has good workability and peelability.

[0002]

2. Description of the Related Art In recent years, the demand for printed circuit boards has increased as electronic products have become lighter, thinner, and have higher performance, and in particular, flexible printed circuit boards (hereinafter abbreviated as FPC).
The range of its use has expanded, and its demand is increasing.
In recent years, as printed circuit boards have become more sophisticated, finer, smaller, and thinner, flexible printed circuit boards have become thinner. Therefore, there are wrinkles, scratches, breaks, etc., and circuit processing is impossible, or the yield is extremely poor, and processing problems occur, and there is a demand for improvement. The circuit fabrication process has recently become more complicated due to performance improvement, multilayering, compounding, miniaturization, etc. of FPC, and a continuous roll-to-roll manufacturing process is often used to improve productivity. The stress on the base film is increasing. In particular, if the base film is thin, it may be wrinkled, scratched, stretched under excessive tension, or even torn in the manufacturing process.

The following concrete steps can be considered as steps for producing defects such as wrinkles and scratches. 1) Cutting process of base film: Scratches are easily caused by a cutter, slitter or the like in a process of slitting into a required width and length. 2) Circuit manufacturing process: a) Surface adjustment process of the base film surface: Failure occurs due to cleaning, polishing, handling, etc. b)
Circuit printing process: There are many handling points in contact with various rolls in each process such as screen printing, photosensitive dry film lamination, exposure and development. c) Etching process: In each process such as etching, cleaning, and drying, there are many handling points in contact with various rolls. 3) Circuit protection process with cover lay film or cover coat material: Contact with various rolls in each process such as temporary pressing of cover lay film and base film, curing of adhesive, washing and drying, and many handling points . 4) FPC outer shape processing, inspection process: There are many handling points that come into contact with various rolls in processes such as punching with a die, adhesion and dimensional inspection of backing material, and performance inspection.

[0004]

[Problems to be Solved by the Invention] As described above, F
The base film of the substrate that makes up the PC goes through many processes
Processed to FPC. In particular, when the base film is thin, wrinkles, scratches and the like are likely to occur during handling and in the above-mentioned various steps, which leads to a decrease in product performance and a decrease in product yield. The present invention eliminates such drawbacks and protects the original FPC performance.
The present invention is intended to efficiently provide a flexible printed circuit board.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above problems, and as a result, have reached the present invention. The gist of the invention is a polyimide film (base film of a substrate). On the other side of the one-sided copper foil laminated film, which is obtained by laminating a copper foil on one side via a heat resistant adhesive,
A flexible printed circuit board characterized by being laminated with a peelable protective plastic film with an adhesive, more specifically, a single-sided copper foil laminated film having a thickness of 60 μm or less, and an adhesive strength reduced by UV irradiation. A flexible printed circuit board is formed by laminating a protective plastic film with a peelable adhesive.

Hereinafter, the present invention will be described in detail. First, the heat-resistant polyimide film, which is the base film of the flexible printed circuit board of the present invention, may be a commercially available product and has a thickness of
25 μm or less (25, 20, 15, 12.5, 10 μm, etc.) Width 500 to 10
16mm is common. Copper foil has a thickness of 35 μm or less (35, 30,
25, 18, 12, 10 μm, etc.) rolled and electrolytic copper foils are used. A copper foil is laminated on this base film via an adhesive.The thermosetting type heat-resistant adhesive used here requires high adhesiveness and heat resistance to withstand the use of solder etc. , Epoxy resin, NBR / phenolic resin, phenol / butyral resin, epoxy /
NBR resin, epoxy / phenolic resin, epoxy /
Nylon-based resin, epoxy / polyester-based resin, epoxy / acrylic-based resin, polyamide / epoxyphenol-based resin, polyimide-based resin, acrylic-based resin, silicone-based resin, etc. are exemplified, and the thickness of the adhesive during lamination is solid resin. It is preferably 4 to 30 μm in minutes.

The base film and the copper foil are adhered to each other in a conventional manner by applying a thermosetting adhesive to a heat-resistant polyimide film with a roll coater or the like and using an in-line dryer at 50 to 150 ° C. to remove a solvent (toluene, MEK, etc.). The organic solvent) is evaporated and removed to a semi-cured state, and thermocompression bonding is continuously performed with the copper foil by a heated heating roll. Temperature is 60-1
Standards are 50 ° C, linear pressure 5 to 30 kg / cm 2, and line speed 1 to 10 m / min. This laminated film has a temperature of 80-200 ℃ in order to complete the thermosetting of the adhesive and improve the physical properties of the substrate.
And heat-cured in a curing oven for 1 to several tens of hours to obtain a single-sided copper foil laminated film. In the present invention, the single-sided copper foil laminated film produced as described above preferably has a thickness of 60 μm or less. At present, when the thickness exceeds 60 μm, the base film is elastic even without using a protective film such as that of the present invention, which will be described later, and no problem occurs in the current manufacturing technology. Specifically, the base film is 25 μm or less, preferably 8 to 25 μm, the copper foil is 35 μm or less, preferably 8 to 35 μm, the thickness of the heat resistant adhesive is 5 to 20 μm, and the total thickness of the laminated product is 60 μm or less 20 μm
The above range is suitable as the single-sided copper foil laminated film for a flexible printed circuit board of the present invention.

The greatest feature of the present invention is that a peelable adhesive is used to prevent external damage such as wrinkles, scratches, and tears in the above-mentioned various steps until the single-sided copper foil laminated film becomes a flexible printed circuit board as a final product. The agent-attached protective film is laminated on the bare surface of the base film of the single-sided copper foil laminated film to protect the bare surface of the single-sided copper foil laminated film, and to be strong enough to withstand machining. Since this protective film undergoes steps such as printed circuit production, FPC punching, etc. when manufacturing the substrate, and is finally removed before mounting on electrical / electronic equipment, it maintains the necessary adhesiveness up to this stage. However, it is necessary that it can be easily peeled off after the purpose is achieved, and in general, a polyester film having a thickness of 20 to 100 μm coated with a peelable pressure-sensitive adhesive is preferable. The coating thickness of this peelable adhesive is preferably 5 to 50 μm, and 5 μm
If it is less than 50 μm, the adhesive force is too weak to protect the base film, and if it exceeds 50 μm, it is too thick to sufficiently exhibit the adhesive force and it is uneconomical.

[0009] The adhesive is peelable, has a strong adhesive force in the initial stage, and is firmly adhered to the base film (heat-resistant polyimide film) of the thin-film type single-sided copper foil laminated film. The adhesive strength must be protected so that it does not come off and the adhesive strength in this case is 150
~ 800g / 25mm required, preferably 200-600g / 25mm
Is. If the adhesive strength is less than 150 g / 25 mm, the protective film will easily peel off during handling, and the protective film will peel off before the circuit is formed. If it exceeds 800 g / 25 mm, the adhesive force will be too strong and the protective film cannot be removed from the FPC because the desired adhesive force will not be obtained even if it is irradiated with the ultraviolet rays described below. Further, it is necessary to be able to easily peel off after the circuit is manufactured, and the peeling force after the circuit is manufactured is 50 g / 25 mm or less, preferably 30 g / 25 mm or less, and more preferably 5 to 30 g / 25 mm. If the adhesiveness is strong, it is difficult to remove it from the surface of the base film, and even if it is removed, the base film will be wrinkled and cannot be mounted on an electronic device. In order to satisfy these two contradictory conditions, specifically, a so-called UV-curable acrylic polymer type pressure-sensitive adhesive whose adhesive strength is significantly reduced by ultraviolet irradiation or the like is suitable, for example, adhesive tape Adwill manufactured by Lintec Co., Ltd. D series etc. are suitable. This adhesive tape is suitable for the present invention because it can have an adhesive force of 150 g / 25 mm or more and a peeling force of 30 g / 25 mm or less by the ultraviolet treatment described later.

As a method for laminating the base film of the above-mentioned one-sided copper foil laminated film and the protective film with a peelable pressure-sensitive adhesive, it suffices to continuously press-bond with a heated heat roll,
The heating roll temperature varies depending on the protective film used, but it is preferably room temperature to 100 ° C, and the pressure is 5 to 30 kg / cm in linear pressure.
The line speed should be 1-10m / min. Through the above steps, the single-sided copper foil laminated film in which the protective film with the release adhesive is laminated, that is, the flexible printed circuit board of the present invention is completed. In the process of mounting on an electric / electronic device, since the adhesive strength is too strong to peel off the protective film as it is, an ultraviolet treatment is applied to reduce the adhesive strength. This UV treatment is carried out by irradiating the bare surface of the peelable adhesive protective film of the substrate with a UV lamp of 30 to 200 W from a distance of 5 to 20 cm and passing the adhesive in about 1 to 10 seconds. Adhesive strength of 50g / 25mm or less,
It can be easily peeled off continuously. If the electric power of ultraviolet rays is too low, the adhesive strength will not decrease so much, and if it is too high, the effect will be weak and uneconomical.

[0011]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Method of measuring physical properties of FPC) (1) Releasability of protective film: Cut the copper-clad laminated film with protective film into a width of 25 mm, and peel off the protective film in the 180 ° direction at a speed of 50 mm / min. (2) Inspection of wrinkles and scratches on the FPC surface: measurement sample 240 ×
The 240 mm was inspected with a magnifying glass of 20 times, the wrinkles and the disconnection of the wiring were inspected, and the number was obtained. Wrinkles: 100 sheets were inspected. Circuit break: 20 sheets were inspected. Evaluation symbol: Breakage point (sheet / sheet) in one sheet: ◎ ... 0, △: 3-5, ◯: 1-2, ×: 6.

(Examples 1 to 5) Thickness 12.5 μm, width 508 mm
Epoxy / NBR adhesive is applied to the polyimide film of No.1 by a roll coater so that the thickness after drying becomes 10 μm, the solvent (MEK) is removed through an in-line dryer, and the adhesive is semi-cured at 120 ° C. Then, the copper foil shown in Table 1 and heating roll temperature 120 ℃, linear pressure 20kg / cm, 3m / min
It was heated and pressed at a line speed of, and wound into a roll. This is further cured in an oven for curing at 80 ℃ for 5 hours, 12
It was heat-cured at 0 ° C. for 5 hours to prepare a single-sided copper foil laminated film. Next, on this bare polyimide film, a polyester film with a thickness of 50 μm was coated with a release adhesive (acrylic polymer) 15 μm as a protective film Adwill D-
Heated rolls (temperature 50
C., linear pressure 20 kg / cm.sup.2) at a line speed of 3 m / min, followed by thermocompression bonding and winding into a roll to obtain a flexible printed circuit board of the present invention.

Next, an FPC (flexible printed circuit board) was produced by sequentially performing the following steps. 1) The FPC board manufactured as described above is slit by a slitter with a width of 240 mm into a slit of 50 m. 2) Wet the copper foil surface with a polishing machine at a speed of 1 m / min, wash it with water and dry it. 3) Bond the photosensitive dry film to the substrate at 120 ° C. at a speed of 1 m / min. 4) Photographically print a parallel pattern with a line width of 0.2 mm and a line spacing of 0.5 mm. 5) Development, resist removal, etching and washing with water are carried out by a roll to roll at a speed of 0.5 m / min. 6) Next, the FPC sheet produced in this way is 240 x 240 mm.
It was cut into strips, irradiated with ultraviolet rays under the following conditions, the protective film was peeled off, and the physical properties of FPC were measured. Irradiation condition: High pressure mercury lamp ... 80W / cm, irradiation distance ... 10
cm, irradiation time ... 3 seconds.

(Comparative Examples 1 to 5) FPC was prepared in the same manner as in Example 1 except that a flexible printed circuit board without a protective film was used, and its physical properties were measured.
It was shown to.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

EFFECTS OF THE INVENTION According to the present invention, the workability useful for producing a thin flexible printed circuit board of polyimide film type,
It is possible to provide a flexible printed circuit board with a protective film having excellent peelability, and its industrial utility value is extremely high.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a flexible printed circuit board with a protective film with a peelable pressure-sensitive adhesive according to the present invention.

[Explanation of symbols]

 1 Single-sided copper foil laminated film 2 Protective film with release adhesive 3 Base film (heat resistant polyimide film) 4 Heat resistant adhesive 5 Copper foil 6 Protective film (polyester film) 7 Release adhesive

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B32B 27/00 M 8413-4F 27/36 8413-4F H05K 1/03 C 7511-4E 3/00 R

Claims (2)

[Claims] 1. A peelable protective plastic film with a pressure-sensitive adhesive is laminated on the other side of a single-sided copper foil laminated film in which a copper foil is laminated on one side of a polyimide film via a heat-resistant adhesive. Flexible printed circuit board. 2. A flexible printed circuit according to claim 1, which is formed by laminating a single-sided copper foil laminated film having a thickness of 60 μm or less and a peelable adhesive protective plastic film whose adhesive strength is reduced by UV irradiation. substrate.