JPS624389A - Flexible circuit 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 [Technical Field of the Invention] The present invention relates to a flexible circuit board in which a conductive circuit is formed on an insulating film.

[Technical background of the invention]

In general, flexible circuit boards having coil-shaped conductor circuits are attracting attention from the viewpoint of improving the performance of thin coils such as thin micro motors and pickup heads of convex disc players.

By the way, examples of thin coils can be seen in JP-A No. 57-37898 (thick film fine pattern) and JP-A 56-78342 (printed circuit), but they involve photo-etching and complicated plating processes. .

That is, the conventional thin coil, claw, and flexible circuit board for a big-up head are constructed as shown in FIG. As shown in the figure, an insulating film 1 such as a 4-limide film has a conductor 2 made of steel with a joint of 130 ttm @ 100 μm and a thickness of 75 μm, and a coil circuit 3-1.3-2 is installed on both sides of the insulating film. .3-3.3-4 is formed. This coil circuit 3-1.3-2.3-3゜3-4 is energized from the electrode 4-1.4-2, and the through hole 5-1゜5-2.5 connects the coil circuits on both sides. −
3.5-4 are provided in series, respectively.

Next, a conventional manufacturing method will be explained with reference to FIG.

The base film 6, such as a /Liimide film, emerges from a relatively thick material with copper thin film electrodes adhered to both sides. The through hole 7 is a small hole made by press processing etc.
It has through-hole markings. This through-hole plating is a series of complex methods in which after surface treatments such as roughening and catalyst application, the entire surface is plated with copper to a thickness of 0.5 to 1 μm using chemical plating. Next, after through-hole plating, a coil circuit of arbitrary dimensions is photoetched using a photomask. The cross section of the conductor 8-1゜8-2 is a part of the copper foil 9-1.9-2゜9-3 has a chemical steel plating film I on its surface.
O-2,10-2°10-3, and electrical steel plating 11-1°11-2.11-3 is applied to a thickness of about 30 μm. Next, a cover film 13-1.13-2 such as a polyimide film is bonded via an adhesive 12-1.12-2,
Complete the flexible circuit board.

If necessary, solder, gold plating, etc. are applied to the electrodes 4-1, 4-2 (on which a double-sided liquid film 15 with release paper 14 is attached), and processed to facilitate assembly.

[Problems with background technology]

In the above conventional example, the gap between the conductors forming the coil circuit is smaller than the thickness due to the manufacturing method. For example, there are many complicated processes such as chemical plating processes and photoetching processes, and the occupancy rate of the conductor tends to be low because of large dimensional variations in these processes. For this reason, the performance of the thin coil has been degraded.

[Purpose of the invention]

An object of the present invention is to provide a flexible circuit board that reduces the number of steps that tend to cause dimensional variations and increases the occupancy rate of coil conductors.

[Summary of the invention]

The present invention is a flexible circuit board in which a conductive pattern is formed on a master substrate by electrodeposition and then transferred to an insulating film.

[Embodiments of the invention]

The flexible circuit board of the present invention is constructed as shown in FIG.
It is formed by transferring a conductor pattern consisting of 8-2 and 18-3. In this case, the insulating film 19 is made of a polyimide film or the like, or the electrodeposited metal 1B-1, 18-
2°18-3 is made of copper, gold, silver, etc. In addition, 2
0-1.20-2.20-3 are traces of conductor turns formed on the electrodeposited master substrate.

Next, a method for manufacturing the flexible circuit board will be described with reference to FIG.

First, as shown in Figure (a), a thin film electrode 11-1, 11-2 of a predetermined shape is formed by photo-etching on one side of a flat leather conductor substrate 16 made of glass or the like using vapor-deposited chromium or the like.
．． 17-3 is formed to form a master substrate for electrodeposition.

In this case, the dimensions and shape are arbitrarily designed depending on the function of the circuit, such as the conductor such as a coil and the connection portion of multilayer wiring.

In order to increase the occupancy rate of the coil conductor, some of the thin film electrodes 17-1, 17-2 have a pitch of about 130 μm1, for example.
A fine pattern with a width of about 20 μm and a thickness of about 0.1 μm is good.

Next K, same figure (b) As shown in K, the thin film electrode 17-1.17-2゜17-3
Electrodeposited metal 1B-1 about 50#I thick on top.

Form 18-2.18-3. In this case, electrodeposited metal 1
B-1, 18-2, and 18-3 are not economical steels, but the same results can be obtained by using gold, chain, etc., which have good electrical conductivity, or by combining them with multiple layers.

Next, as shown in FIG.
18-2. An insulating film 19 fixed to 18-3 is formed.

Next, as shown in FIG. 4(d), a transfer process begins, which can be accomplished by mechanically peeling off the insulating film 19.

In this way, the desired flexible circuit board 24 is obtained.

The nonconductor substrate 16 with the thin film electrodes 12-1.17-2.17-3 remaining can be used for transfer many times as a master for electroforming.

The above method involves making the thickness of the insulating film 19 extremely thin and depositing metal 1B-1゜18-2.18-
3 can be made thicker, and when applied to a thin coil, it is useful for improving the performance of the coil circuit.

The flexible circuit board of the present invention thus produced can also be assembled by laminating separately produced circuit boards. FIG. 3 shows this embodiment, in which a first flexible circuit board 24-1 and a second flexible circuit board 24-2 are pasted together with an adhesive layer 21 interposed therebetween. In particular, when the electrodeposited metal surfaces face each other, the electrodeposited metal surface side has a groove 20-1. Therefore, as shown in the figure, an extremely thin adhesive layer (insulating thin film) 21 can be obtained.

When the conductors of the first and second flexible circuit boards are electrically connected to each other for multilayer wiring, as shown in FIG. The thin film 21 can be destroyed and welded.

Further, in the flexible circuit board of the present invention, as in the prior art, if necessary, a double-sided adhesive film 24 with a release paper 23 may be attached, or the electrodes of the current-carrying parts may be soldered or plated.

Other examples of electroforming master substrates are shown in Figure 5 (
As shown in a) and (b), in the figure, 25 is a glass substrate, 26 is a 100XOCr layer with a thickness, 27 is a Pd layer with a thickness of 500X, 28 is an Au layer with a thickness of 1 μm, 29
is a Cr layer with a thickness of 5001, and 30 is a 5io2 layer with a thickness of 1 μm.
Layer 31 is a Ti layer with a thickness of 10,001 mm. The 5tO2 layer 30 has a predetermined circuit IJ? Metal is electrodeposited on the Cr layer 29 having a smooth metal surface exposed from the turn opening 35 which serves as a mask during electrodeposition. According to these electroforming masters, since a highly conductive current-carrying layer made of Au, Pd, Cu, etc. is used below the Cr layer 29, even parts far from the current-carrying part can receive the same uniform current as near parts. You can get the desired thickness.

Therefore, the flexible circuit board made using this
For example, the thickness of the coil conductor can be made uniform, miniaturization, and the space factor of the conductor can be increased.

In addition, with regard to the transfer of electrodeposited metal, the method is not limited to the above-mentioned embodiments, but it is also possible to laminate an insulating film on which an adhesive layer is formed to an electroforming master substrate on which an electrodeposited metal is formed, and then peel off the insulating film. It can also be done by

〔Effect of the invention〕

According to the present invention, the occupancy rate of the conductor in the obtained coil circuit can be increased by about 5% compared to the conventional method, heat generation during operation is reduced, and stable coil characteristics can be obtained. Further, according to the present invention, it is possible to eliminate complicated processes that tend to cause dimensional variations in minute parts such as coil circuits.

Note that the scope of application of this invention is not limited to the above embodiments,
It is clear that it is useful as a thin motor coil or a small flexible circuit board. In particular, for fine conductor circuits, it is possible to eliminate disconnections and sheet defects that occur during repeated photoetching and chemical plating.
This is essential for miniaturization and thinning.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a flexible circuit board according to an embodiment of the present invention, and FIGS. 2(a) to (d) are schematic cross-sections showing a method for manufacturing a flexible circuit board according to an embodiment of the present invention. Figures 3 and 4 are views showing examples of the use of the flexible circuit board of the present invention, and Figures 5(a) and 5(b) are cross-sectional views showing examples of the electroforming master used in the manufacturing method of the present invention. 6 is a schematic plan view showing a flexible circuit board with a coil circuit used in a pickup head of a compact disc player, and FIG. 7 is a flexible circuit board manufactured using conventional techniques including photoetching and chemical plating processes. FIG. 16... Nonconductor substrate, 27-J, 27-2°11-3
... Thin film electrode, 1B-1, 18-2゜18-3...
Electrodeposited metal, 19...Insulator, 20-1°20-2.2
0-3... Concave groove, 21... Insulating thin film. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 5 Figure 6 Figure 1!7

Claims (1)

[Claims] A flexible circuit board made by electrodepositing metal in a predetermined pattern on a master board and transferring it to an insulating film.