JPS63199491A - Manufacture of flexible printed wiring board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention relates to a method for manufacturing a flexible printed wiring board, and more specifically, a method for producing a flexible printed wiring board, in which a conductor circuit is created on one or both sides of a flexible insulating base film. The present invention relates to a method suitable for manufacturing a flexible printed wiring board.

<Conventional technology> Compared to ordinary electric wires and rigid boards, flexible printed wiring boards can be smaller and lighter, have simpler wiring layouts, simplify wiring work, and improve circuit characteristics and reliability. Therefore, it is widely used for the internal wiring of electronic desktop calculators, telephones, and cameras, and the wiring panels of automobiles.

``1. In the production of flexible printed wiring boards, 1 ounce (approximately 35 μff1) copper foil or 1/2 ounce copper foil is laminated on one or both sides of a flexible insulating base film via an adhesive, A circuit board is created by creating a circuit pattern on this copper foil by etching, etc., and usually, the necessary places on the surface of the circuit board are
The conductor circuit is protected by laminating a resin film to form a film overlay or by applying a thermosetting liquid resin (ink) to form an overcoat.

<Problems to be Solved by the Invention> Incidentally, in recent years, as the demand and use of flexible printed wiring boards has expanded, the characteristics required of the printed wiring boards have become extremely strict. There is an increasingly strong demand for miniaturization, and there is also a strong demand for thinning of the overall thickness.

Here, in order to miniaturize the conductor circuit, it is necessary to use advanced etching technology and to reduce the thickness of the metal conductor that is the part to be etched. There are limits to how thin metal can be made. In other words, if the thickness of the copper foil is too thin, wrinkles, cracks, etc. will easily occur in the copper foil when it is laminated to an insulating base film. It has been extremely difficult to accurately form metal conductors with a diameter of 10μ0 or less.

This point was also a factor that made it impossible to reduce the overall thickness of the flexible printed wiring board.

Furthermore, since the surface of a circuit board exhibits an uneven surface due to conductor circuits, in order to completely fill in the recesses on the circuit board surface with a film overlay without any gaps, the thickness of the adhesive layer of the film overlay must be smaller than the thickness of the conductor metal. It is also necessary to increase the thickness of the flexible printed wiring board, making it even more difficult to reduce the overall thickness of the flexible printed wiring board. Furthermore, when forming an overcoat, it is difficult to uniformly coat the uneven surface of the circuit board with liquid resin. Problems arise in that "fading" or "repelling" occurs, or pinholes due to voids or the like become apparent, resulting in the layer not functioning as an insulating layer.

<Purpose of the invention> This invention was made in view of the problems mentioned above.
It is possible to form thin conductive metal, and
It is an object of the present invention to provide a method for manufacturing a flexible printed wiring board, which can obtain a circuit board with a flat surface, and can also achieve finer conductor circuits and thinner overall thickness.

Means for Solving the Problems> In order to achieve the above object, the method for manufacturing the flexible printed wiring board of this invention involves vapor vaporizing a metal conductor onto an insulating base film through an adhesive layer. At the same time or after this vapor phase deposition, a circuit pattern is created to form a circuit board, and the circuit board is pressurized to embed metal conductors in the adhesive layer to flatten the surface, and then a resin film or liquid resin is formed. is coated on the surface.

Effects> According to the method for manufacturing a flexible printed wiring board having the configuration described in 1-, since the metal conductor is vapor-deposited on the insulating base film, it is possible to easily form a thin metal conductor. Moreover, since the circuit board on which the circuit pattern has been created is pressurized and the metal conductor is embedded in the adhesive layer to flatten the surface, the surface can be thinly and uniformly coated with a resin film or liquid resin. be able to.

<Example> Embodiments will be described in detail below with reference to the accompanying drawings showing examples.

FIG. 1A shows an insulating base film (1) used in the method of manufacturing a flexible printed wiring board of the present invention. , an adhesive layer (2) made of a thermosetting adhesive is formed. The adhesive layer (2) may be epoxy-based, acrylic-based,
It is preferable to use a phenol-based adhesive that exhibits a stable semi-cured state (so-called B-stage state) at room temperature, and that is not deteriorated by etching liquids, resist stripping liquids, etc.

Then, as shown in Figure B, a metal conductor (3) such as copper is vapor-deposited on the insulating base film (1) via the adhesive layer (2). As this vapor deposition method, conventionally known thin film forming techniques such as vacuum evaporation method, sputtering method, cluster ion beam method, etc. can be applied, but in any case, the insulating base film (1)
It is preferable that the temperature can be set in a low temperature range from room temperature to about 100°C. By such vapor phase deposition method, 10μ
(2) A metal conductor (3) having the following thickness can be easily formed. Moreover, the adhesive layer (2) can dramatically improve the adhesion between the insulating base film (1) and the metal conductor (3).

Next, after creating a circuit pattern on the metal conductor (3) by etching to obtain a circuit board (P) (see C in the same figure),
The circuit board (P) is heated and pressed using a heat press, a heat roller, etc., and the metal conductor (3) is embedded in the adhesive layer (2) to make the surface of the circuit board (P) flat, and the adhesive layer (2) is cured (see the same figure).

The heating temperature and pressure in the heating and pressing step are appropriately set in a range that allows the adhesive layer (2) to flow, depending on the type of adhesive constituting the adhesive layer (2). .

Then, a coating layer (4) made of a film overlay or an overcoat is formed on a predetermined portion of the surface of the planarized circuit board (P) to obtain a flexible printed wiring board (see E of the same figure). At this time, since the surface of the circuit board (P) is finished flat, the film overlay or overcoat can be formed easily and with high precision, and the thickness of the coating layer (4) can also be reduced. can be achieved. In addition, as the above-mentioned film overlay, films such as polyester film, polyimide film, etc., polyimide-based, epoxy-based, polyester-based,
It is formed by superposing the adhesive layer on the circuit board (P) via an adhesive layer made of a thermosetting adhesive such as phenol-butyral adhesive, and then heating and curing the adhesive layer. Also,
As the overcoat, a method is adopted in which a thermosetting resin paint made of liquid resin such as epoxy or urethane is applied and cured by heating.

The method for manufacturing a flexible printed wiring board of the present invention is not limited to the above embodiments, but includes, for example, an adhesive layer (2
) with a hot melt adhesive such as polyester, and the circuit pattern is formed using a mask method using a metal conductor (3
), and forming conductor circuits on both sides of the insulating base film (1) can be made in various ways without changing the gist of the invention.

Specific Example 1 A copper conductor with a thickness of 3 μm was formed by sputtering on a polyimide film provided with an adhesive layer made of a thermosetting adhesive, and a dry film with a thickness of 25 μm (trade name Liston; DuPont Co., Ltd.) was applied to the copper conductor. laminate the
A circuit pattern with a line width and line spacing of 25μ was exposed to UV light, developed with 1, ], 1-1 liquid ethane, and then immersed in an etching solution (cupric chloride) to form a copper conductor. At the same time as etching, the etching resist was peeled off using methylene chloride to obtain a circuit board.

Next, the above circuit board was heat-pressed using a heat press at a heating temperature of 160°C and a pressure of 25 kg/cut for 60 minutes to obtain a circuit board with a flat surface, and then a 3-fold thick adhesive layer was applied. Press bond the film overlay with (heating temperature 180°C, pressure 25 kg/c
a, 60 minutes of pressurization), a flexible printed wiring board was obtained.

The flexible printed wiring board obtained in this way has
It was confirmed that there were no defects such as voids. Furthermore, it was confirmed that the solder heat resistance required for film overlays was an extremely good value of 300°C.

Specific Example 2 After obtaining a circuit board with a flattened surface in the same manner as in Specific Example 1, epoxy resin ink was applied to the surface of this circuit board by screen printing (the coating thickness was 3 μm) and oven cured at 120° C. for 2 hours to form an overcoat.

It was confirmed that the thus obtained flexible printed wiring board had a uniform overcoat, was free from defects such as voids, and exhibited solder heat resistance at 300°C.

Comparative Example 1 A copper conductor with a thickness of 3 μm was formed by sputtering on a polyimide film provided with an adhesive layer made of a thermosetting adhesive, and this was heated at 160° C. by heat pressing.
The adhesive layer was cured without embedding the metal conductor in the adhesive layer by thermocompression bonding for 60 minutes at a pressure of +-Okg/cm. Then, a 25 μm thick dry film (trade name: Liston) was applied to the copper conductor -1-〇-.
DuPont) was laminated, and a circuit pattern with a line width and line pitch of 25 μm was exposed to UV light.
．． ．． 1.1-) After development with dichloroethane, the copper conductor was etched by dipping in an etching solution (cupric chloride) and the etching resist was removed with methylene chloride to obtain a circuit board. Next, the above circuit board is
As in Example 1, a film overlay having an adhesive layer with a thickness of 3μ0 was press-bonded (heating temperature 180°).
C1 pressurization pressure 25 kg/oa, 60 minutes), a flexible printed wiring board was obtained.

As shown in FIG. 2, the flexible printed wiring board thus obtained has voids (5) involved in a considerable portion of the circuit edges, and has a soldering heat resistance of 22.
It was confirmed that the temperature was 0° C. or lower, which was lower than that of Specific Example 1.

Comparative Example 2 After obtaining a circuit board in the same manner as in Comparative Example 1, an epoxy resin ink was applied to the surface of the circuit board by screen printing (with a coating thickness of 3 μO).
l), oven curing was performed at 120° C. for 2 hours to form an overcoat.

As shown in Figure 3, the flexible printed wiring board obtained in this way has an unevenly formed overcoat, has many defects such as voids, and has poor soldering heat resistance below 220°C. , which was confirmed to be lower than that of Specific Example 2.

<Effects of the Invention> As described in 2 below, according to the method for manufacturing a flexible printed wiring board of the present invention, the metal conductor is vapor-deposited onto the insulating base film via the adhesive layer, so the thickness can be reduced. A thin metal conductor can be easily and uniformly formed with good adhesion, and the metal conductor is embedded in the adhesive layer to flatten the surface of the circuit board, making it easy to apply a film overlay or overcoat. It has the unique effect of being able to be formed uniformly and thinly, resulting in miniaturization of the conductor circuit and reduction in overall thickness.

[Brief explanation of the drawing]

FIGS. 1A to 1E are process diagrams sequentially showing a method for manufacturing a flexible printed wiring board according to the present invention, and FIGS. 2 and 3 are enlarged sectional views of main parts showing a comparative example. (1)...Insulating base film, (2)...Adhesive layer, (3)...Metal conductor, (4)...Coating layer, (P
)...Circuit board. Patent applicant: Sumitomo Electric Industries, Ltd. Figure 1

Claims (1)

[Claims] 1. A metal conductor is vapor-deposited on an insulating base film via an adhesive layer, a circuit pattern is created at the same time or after this vapor-phase vapor deposition to form a circuit board, and the circuit board is pressurized. A method for manufacturing a flexible printed wiring board, which comprises embedding a metal conductor in an adhesive layer to flatten the surface, and then coating the surface with a resin film or liquid resin.