JPS5816624B2 - Printed wiring manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing printed wiring, particularly perforated double-sided printed wiring.

Conventionally, in order to meet the demands for higher density and higher reliability of circuits, copper foils with less side etching, that is, copper foils whose thickness has been reduced from 35 .mu.m to 18 .mu.m, have appeared.

As a further improvement, the following method is used in which a copper foil of about 5 or 8 microns is folded onto an aluminum foil.

That is, as a known method for manufacturing double-sided printed wiring with holes, a copper conductive film using aluminum foil as a carrier is bonded to both sides of an insulating substrate, holes are formed by punching, and then the aluminum foil is peeled off or melted. After that, there is a method of forming a conductive film on the inner surface of the hole by electroless plating the pot, or by electroplating after electroless plating to thicken the conductive film.

Thereafter, necessary circuits are etched on both sides of the board to form printed wiring.

This conventional aluminum foil carrier has a thickness of, for example, about 50 microns, and a 5-8 micron copper conductive film is usually electrolytically formed on this carrier, and the surface of the copper film is bonded to an insulating substrate.

In this conventional method, copper and aluminum are both metals, and must be adhered fairly firmly for intermediate processing.

Therefore, subsequent peeling of the aluminum is not easy, and when mechanically peeled off, the aluminum carrier has no tensile strength and is easily broken.

For this reason, it is difficult to reduce the thickness of the copper film and the thickness of the aluminum carrier, and the conventional method has the disadvantage that the peeling process cannot be performed quickly.

Aluminum carriers are soft and not very strong, so they are difficult to handle, and there is a risk of breakage.Furthermore, high tension cannot be applied during the bonding process to the substrate, making it easy to wrinkle and crack, making it difficult to process quickly. .

In addition, instead of the mechanical peeling described above, a method of removing the aluminum carrier by chemical treatment is also known, but in this case too, great care is required so as not to corrode the copper film, which is a conductive film, and it is not possible to remove the aluminum carrier quickly. Furthermore, it is difficult to reduce the thickness of the copper film, which is a conductive film, considering the risk of corrosion, and there are drawbacks such as the need to treat wastewater containing aluminum ions generated when removing aluminum. have

The present invention aims to eliminate these drawbacks of the conventional methods and provides a novel printed wiring manufacturing method.

That is, in the printed wiring manufacturing method of the present invention, a conductive metal film is formed on one surface of a carrier made of an organic film, the metal surface of the carrier is adhered to one or both sides of an insulating substrate, and holes are formed. The process consists of electroless plating of a conductive metal after removal of the metal.

The present invention will be explained in detail below.

The organic film having a conductive metal film used in the present invention can be manufactured by a known method or preferably by the novel method described below.

That is, this organic film includes polyester, nylon, polypropylene, polyethylene, polyethylene terephthalate, polyimide, polyvinyl chloride, rubber,
Synthetic rubber or other known organic films can be used as long as they have the strength to serve as a carrier for the metal film, and do not necessarily have to have insulation properties.

On the surface of this organic film, a primary metal layer such as copper, nickel, tin, etc. with good adhesion and conductivity is applied either alone or as an alloy.
It can also be formed into a single layer or multiple layers by vapor deposition or chemical deposition,
A conductive metal film is electrochemically deposited as a secondary metal layer on this primary metal layer.

Here, the thickness of the organic film can be appropriately selected in relation to the above-mentioned strength, and is also determined based on the necessity for protecting the metal film.

The secondary metal layer may be of a sufficient extent to permit electrochemical deposition of a conductive metal thereon, preferably having a diameter of 0, oi or more, preferably 0.1 to 0.2 .mu..

The secondary metal layer is formed by electroplating the same or different metal as the primary metal alone or as an alloy such as an alloy of copper and one or more of tin, nickel, and zinc in a single step or in multiple steps. Form a deposit.

At this time, it is also possible to form the lower layer of the secondary metal layer slowly and then quickly form the upper layer.

According to this method, the thickness of the secondary metal layer can be freely selected, and a film as an electrical conductor can be formed in the range of about 1 to 100 microns.

For purposes of the present invention, conductive metal films having a thickness of about 1 to 10 microns are particularly preferred, and such thin films are advantageously obtained by this method.

Further, the most preferable material for the secondary metal layer (the main portion of the conductive metal film) is copper.

Furthermore, known manufacturing methods for the organic film having the above-mentioned conductive metal film include vapor deposition, chemical plating, etc.
If a thick metal film is required, one formed by adhering metal foil can also be used.

The present invention will be explained in more detail below using the drawings.

The metal-coated film obtained as described above is then adhered to one or both sides of an insulating substrate.

Here, the insulating substrate is made of phenol resin, epoxy resin, vinyl chloride, polyester resin, or other known electrically insulating materials.

In the figure, the metal surface of the metal film-coated film is well adhered to one surface of the insulating substrate 1, or to both surfaces for double-sided printed wiring, by a known method.

When bonded on both sides, a cross section as shown in FIG. 1 is obtained.

Here, the metal film 2 is protected by being sandwiched between the film 3 and the substrate 1 in a sandwich-like manner.

Therefore, the next hole 4 can be easily formed by pressing during the processing process without damaging the metal film 2 (FIG. 2).

In particular, the metal film (2) on the bottom surface of the substrate is easily damaged in the press hole-opening process, and the bottom opening of the hole (4) may fray or curl up irregularly if there is no film. Therefore, it can be maintained forcibly by the protective effect of the film.

Damage to the metal film caused by hard foreign objects on the work surface can be eliminated by selecting the film thickness and strength.

This film 3 is then removed.

This removal is carried out by a mechanical method, or by dissolution using a solvent that selectively dissolves only the film without corroding the insulating substrate or metal film.

The adhesion force between this organic film and the metal film is not as strong as the adhesion force between aluminum and copper as in the conventional method.
Moreover, since this organic film has higher tensile strength and greater flexibility than aluminum foil, it can be quickly and easily mechanically peeled off.

FIG. 3 shows an end view of this film 3 after removal.

In this case, it goes without saying that the adhesion between the metal film 2 and the insulating substrate 1 needs to be stronger than the adhesion between the metal film 2 and the film 3.

Further, after the above steps, a conductive metal layer 5 is formed on the inner surface of the hole 4 as shown in FIG.

A known method for this purpose may be a known electroless plating method (chemical plating method).

In this case, since the metal film 2 is formed around the opening periphery of the hole 4, the metal film deposited on the inner surface of the hole 4, where no metal film is present, transfers its adhesion force to the metal film 2 around the opening periphery of the hole 4. It is reinforced by a conductive metal layer 5 deposited on the surface.

The conductive metal layer 5 can be formed into a single layer or multiple layers using conductive metals such as copper, nickel, and tin, or an alloy thereof, alone or as an alloy.

At this time, the conductive metal layer 5 is naturally deposited on the surface of the metal film 2 on the substrate surface, but if necessary, areas other than the periphery of the opening can be masked to prevent excessive deposition.

According to the present invention, the thickness of the metal film 2 on the surface can be 1 to 10 microns, preferably 3 to 8 microns.

As the electroless plating method, for example, a chemical plating method in which metal is deposited from a metal salt solution is applied.

After the above treatment, the metal films 2 and 5 on the surface of the insulating substrate are etched to obtain the desired printed wiring.

At this time, the thickness of the metal film to be etched is 1 to 10μ if masked before electroless plating of the conductive metal layer, and 20 to 30μ even without masking, which can be extremely thin, so side etching does not occur during etching. In this way, precision etching becomes possible.

As described in detail above, the present invention provides a new and effective manufacturing method for double-sided printed wiring with holes, and also makes it possible to manufacture printed wiring with thinner and more precise printed wiring circuits than conventional methods. It has the advantage of

[Brief explanation of the drawing]

1 to 4 sequentially show the manufacturing process of an embodiment of the present invention. FIG. 1 shows a cross-sectional view of an insulating substrate with metal-coated films adhered to both sides. FIG. 2 shows an end view of the insulating substrate after hole drilling, FIG. 3 shows the state after film removal, and FIG. 4 shows the state after electroless plating. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... Conductive metal film, 3... Organic film, 4... Hole,
5... Conductive metal layer.

Claims (1)

[Claims] 1 A conductive metal film is formed on one surface of a carrier made of an organic film, the metal surface of the carrier is adhered to one or both sides of an insulating substrate, holes are processed, and after the film is removed, a conductive metal film is formed. A method for manufacturing printed wiring characterized by electroless plating.