JPH03201592A - Manufacture of printed circuit board - Google Patents

Abstract

PURPOSE:To simply obtain a printed circuit board having excellent productivity by forming a through hole, then making plating catalyst adhere to the entire surface, and then removing the catalyst of the surface layer by physical polishing. CONSTITUTION:A hole 4 to become a through hole is opened at a metal foil- plated laminated board adhered with a metal foil 1 through an insulating board 2. The board is dipped in solution containing electroless plating catalyst 5 to apply the catalyst 5 to the entire surface including the hole. In order to remove the catalyst 5 adhered to the position except the inner wall of the hole 4, the surface of the foil 1 is polished. The inner wall of the hole 4 to become a through hole is protected, an etching resist 6 for protecting the foil 1 of the part to become a circuit is formed, the foil 1 of the part not becoming a circuit is removed by etching, and the resist 6 is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a printed wiring board having two or more circuit layers.

(Prior art) Printed wiring boards are manufactured using the subtract method, which involves removing unnecessary parts of the copper foil from a copper-clad laminate by etching;
The additive method, in which circuit conductors are formed on an insulating substrate by electroless plating at the required locations, and the partial additive method, in which conductors are partially formed using electroless plating, are known.
When manufacturing a printed wiring board having two or more circuit conductor layers, a method using electroless plating is also known for metallizing through holes connecting different conductor layers. ~ As a method of metallizing the inner wall of a through hole in such a manufacturing method, as disclosed in Japanese Patent Application Laid-open No. 61-252689, a resist is formed on the entire surface of an insulating substrate, and then a through hole is formed. A method is disclosed in JP-A-52-116866, in which a hole is made, a catalyst for electroless plating is attached to the entire surface including the inside of the hole, and the resist is peeled off, leaving the catalyst only in the hole that will become a through hole. As shown in Japanese Patent Laid-open No. 5, a method of forming a permanent solder resist with hydrophobicity on a portion of an insulating substrate that does not form a circuit, and preventing a catalyst from adhering to the resist surface where electroless plating is not necessary.
As disclosed in Japanese Patent No. 9400596, a circuit is formed by drilling holes to serve as through holes in a copper-clad laminate and etching away unnecessary portions of the copper foil on the copper-clad laminate.
A method of attaching an electroless plating catalyst to the entire surface including the inside of the hole, and then removing the catalyst other than the hole with a chemical;
As disclosed in Japanese Unexamined Patent Publication No. 60-187094, a circuit is formed by drilling holes to serve as through holes in a steel-clad laminate and etching away unnecessary parts of the W4 foil of the copper-clad laminate. There is a method of applying a conductive resin only to the inner wall surface of the through-hole, or a method of applying a catalyst for electroless plating to the entire copper-clad laminate in which through-holes are formed, as disclosed in JP-A No. 61-2386. After attaching the
A method is known in which a circuit is formed by etching unnecessary parts of the copper foil of a copper-clad laminate, and at the same time, a catalyst adhering to the parts to be etched is removed.

[Problem to be solved by the invention]

Problems with the conventional method will be explained below.

The method of applying the electroless plating catalyst only to the inside of the through-hole using the first resist increases the number of steps to form the resist, making it more complicated. Part of the conductor cannot be made thicker.

In the second method of using a permanent solder resist having hydrophobic properties, a highly wettable electroless plating catalyst is applied to the reconstituted solution into slight depressions such as scratches generated in the previous process on the surface of the solder resist. , metal deposited by electroless plating may form unnecessary circuits.

The method of attaching the catalyst to the third through-hole and after the circuit is formed completely removes any catalyst residue attached to the insulating substrate or adhesive surface in areas where there is no circuit conductor, even after subsequent polishing or chemical treatment. Since it is difficult to do so, insulation deterioration due to the residue occurs and reliability decreases.

The method of applying conductive resin only to the fourth hole wall is difficult to reliably apply to the hole wall, is complicated to apply, and is difficult to make the conductivity of the conductive resin equivalent to that of metal. This makes the connection unreliable.

The method for removing the fifth catalyst together with unnecessary conductors is as follows:
Since the catalyst does not remain between the circuit patterns, it does not cause insulation deterioration and the process is simple. However, since the catalyst is attached to the copper surface that forms the necessary circuit, it is difficult to use etching resist for forming the circuit. Adhesion with the copper foil decreases, etching accuracy decreases, and adhesion between the solder resist used for final finishing and the circuit copper foil also decreases, making it easy to peel off.

The present invention solves these problems and provides a method for manufacturing printed wiring boards that is simple and has excellent mass productivity.

[Means for Solving the Problems] The manufacturing method of the present invention is characterized by comprising the following steps, as shown in FIGS. 1(a) to (g).

A. Step of drilling a hole 4 to serve as a through hole in a metal foil-clad laminate in which a metal foil 1 is bonded to an insulating substrate 2 (see Fig. 1).
Shown in a). ).

B. Step of immersing the laminate in a solution containing the electroless plating catalyst 5 and applying the electroless plating catalyst 5 to the entire surface including the inside of the hole (as shown in FIG. 1(b)).

C1 A step of polishing the surface of the metal foil 1 in order to remove the electroless plating catalyst 5 attached to a portion other than the inner wall of the hole 4 that will become the through hole (as shown in FIG. 1(C)).

D. Etching resist 6 that protects the inner wall of the hole 4 that will become the through hole and protects the metal foil 1 that will become the circuit.
(shown in FIG. 1(d)), the step of etching away the portions of the metal foil 1 that will not form a circuit, and removing the etching resist 6 (shown in FIG. 1(e)).

E. Apply solder resist 7 that can withstand electroless plating solution and remains permanently, except around the holes 4 that will serve as through holes and in areas where thickness is required for circuits or where alignment accuracy is required. Forming process (Fig. 1 (
Shown in f).

).

F. A step of electroless plating only on the conductor exposed from the solder resist 7 and depositing the plating metal 8 in the through holes and in the places where thickness is required for the circuit or where it is necessary to ensure alignment accuracy (step (shown in Figure 1 (g)).

All materials used in the process of the present invention can be those used in conventional printed wiring boards.

That is, the insulating substrate 2 in step A includes a so-called rigid board such as a glass cloth-epoxy resin, an epoxy resin containing short glass fibers, a paper-epoxy resin, or a paper-phenol resin, a polyimide film, a polyester film, A flexible substrate such as a polyethylene film or a polytetrafluoroethylene film can be used, and as the metal M1, copper foil, aluminum foil, or the like can be used. For drilling, a drill, a mold, etc. can be used. .

The electroless plating catalyst 5 in step B includes palladium,
Materials selected from the group consisting of gold, platinum, copper, and salts thereof can be used, and combinations of materials selected from these groups can also be used.

In order to remove the electroless plating catalyst 5 that has adhered to areas other than the inner wall of the hole 4 that will become the through hole in step C, the surface of the metal foil 1 can be polished manually using a brush, sandpaper, etc. Although this can be done, it is preferable to use a rotary brush or the like in order to shorten the process time and make the work more uniform.

Etching resist 6 that protects the inner wall of hole 4, which will be a through hole in the process, and protects the metal foil l of the part that will become a circuit.
Any commonly used etching resist ink or photo-curable etching resist film that is commercially available can be used as the etching resist film. By the printing method using negative film,
The etching resist 6 can be formed into a desired shape and can chemically dissolve a specific metal. For example, in the case of copper, an aqueous solution of cupric chloride or ferric chloride is sprayed in a shower. The portions of the gold i-foil 1 that do not form a circuit can be removed by etching, and the etching resist 6 can be removed by dissolving the etching resist ink or by dissolving or decomposing the etching resist in the form of a film. You can use anything.

As the solder resist that can withstand the electroless plating solution in step E and remains permanently, any material can be used as long as it is not attacked by the electroless plating solution in a hardened state, and this is also the same as the etching resist mentioned above. It can be formed by a method similar to that of .

As the electroless plating in step F, any conventional plating can be used depending on the metal to be deposited.

In addition, if the shape in which the metal 8 is deposited is such that when it is made into a printed wiring board, electrical connections can be made all at once outside the printed wiring board, electrolytic plating may be used instead of electroless plating. You can also use

This plating metal is preferably copper, but it may also be a metal that has at least electrical conductivity, such as Ni or Au.

[Function] If the plating catalyst adheres to areas other than the through-holes of a printed wiring board, it will cause insulation deterioration and a decrease in the adhesion of etching resists and solder resists used for circuit shapes. This is a manufacturing method in which a plating catalyst is attached and then the surface layer of the plating catalyst is removed by physical polishing.Since there are no circuits formed and the surface is smooth, the catalyst can be easily removed.

In addition, even if the brush used for polishing penetrates into the through-hole to some extent and some of the catalyst inside the through-hole is removed, the inside of the through-hole within the reach of the brush bristles is close to the metal foil and does not originally contain catalyst. This is because the only required portion is the insulating layer portion 5 located inside the through hole.

Example 1 MCL-[-67, which is a double-sided copper-clad laminate, was mounted on an insulating substrate.
Using N (manufactured by Hitachi Chemical Co., Ltd., trade name) with a thickness of 1.6 mm, holes were made to become through holes using the punching method, and CUST, a solution containing a catalyst for electroless copper plating, was prepared.
201 (Hitachi Chemical Industries, Ltd.)

After drying, the plated catalyst on the surface of the copper foil was removed using a polisher using a rotating nylon brush.

Next, as an etching resist, an ultraviolet-sensitive film Photec 887AP-25 (manufactured by Hitachi Chemical Co., Ltd., trade name) was laminated, and after baking and development of a circuit board, etching was performed with cupric chloride. The etching resist was removed using a 3% sodium carbonate solution to form a circuit pattern.

Next, Photek 5R-3000-2, an ultraviolet-sensitive film, was used as a solder resist for electroless plating.
2 (manufactured by Hitachi Kaei Kogyo Co., Ltd., trade name) using a vacuum laminator, baking, development, and after-curing were performed to form a solder resist.

Next, it was immersed for 9 hours in CC-4 plating solution (trade name, Hitachi Chemical Co., Ltd.), which is an electroless copper plating solution consisting of copper sulfate, formaldehyde, a complexing agent, caustic soda, soda cyanide, etc., to a thickness of 18 μm. Plated copper was deposited.

Example 2 Double-sided copper-clad laminate F-30νC225RC2 based on polyimide film developed for flexible use
1. Using CUST201, a solution containing a catalyst for electroless copper plating, a through-hole was drilled using an NC-controlled drill machine using CUST201, a solution containing a catalyst for electroless copper plating.
(Hitachi Chemical Industries, Ltd.

After drying, the plating catalyst on the surface of the copper foil was removed by a polisher using a rotating nylon brush.

Next, as an etching resist, an ultraviolet-sensitive film FOTECH 887AF-25 (manufactured by Hitachi Kakai Kogyo Co., Ltd., trade name) was laminated, and after the circuit pattern was printed and developed, it was etched with cupric chloride. The etching resist was removed using a 3% sodium carbonate solution to form a circuit pattern.

Next, FOTECH 5R-3000-2, an ultraviolet-sensitive film, was used as a solder resist for electroless plating.
2 (manufactured by Hitachi Kakogyo Co., Ltd., trade name) using a vacuum laminator, baking, development, and after-curing were performed to form a solder resist.

Next, it was immersed for 9 hours in CC-4 plating solution (trade name, Hitachi Chemical Co., Ltd.), which is an electroless copper plating solution consisting of copper sulfate, formaldehyde, a complexing agent, caustic soda, soda cyanide, etc. Plated copper with a thickness of 18 μm was deposited.

As a result of examining the adhesion of the etching resist and solder resist and the degree of insulation deterioration of the printed wiring board produced in this way, it was found that the results were almost the same as those obtained when no catalyst was used at all. I was able to confirm that this was not the case.

〔Effect of the invention〕

As described above, according to the present invention, the plating catalyst, which has a negative effect on adhesion and insulation performance, can be deposited only inside the through-hole, which is highly reliable, and also forms a resist for the electroless plating catalyst. 1. There is no difficult process such as applying conductive resin partially. We were able to provide an efficient manufacturing method.

[Brief explanation of drawings]

FIGS. 1(a) to 1(g) are cross-sectional views showing the manufacturing process of an embodiment of the present invention. 1. Metal foil 2. Insulating substrate 3, inner layer conductor 4. Hole 5 that becomes a through hole, plating catalyst 6. Etching resist 7, solder resist 8 Electroless plated metal old

Claims (1)

[Claims] 1. A method for manufacturing printed wiring boards that consists of the following steps. A. A process of drilling holes (4) to serve as through holes in a metal foil-clad laminate in which a metal foil (1) is bonded to an insulating substrate (1). B. A step of immersing the laminate in a solution containing an electroless plating catalyst (5) and applying the electroless plating catalyst (5) to the entire surface including the inside of the hole. C. A step of polishing the surface of the metal foil (1) in order to remove the electroless plating catalyst (5) that has adhered to areas other than the inner wall of the hole (4) that will become the through hole. D. Protecting the inner wall of the hole (4) serving as the through hole,
An etching resist (6) is formed to protect the metal foil (1) in the part that will become a circuit, and the metal foil (1) in the part that will not become a circuit is formed.
1) and removing the etching resist (6). E. The solder resist (7), which can withstand electroless plating solution and remains permanently, is inserted into the through-hole (4).
The process of forming the circuit by excluding areas where thickness is required or alignment accuracy is required. F. A step in which electroless plating is performed only on the conductor exposed from the solder resist (7), and plating metal (8) is deposited in the through holes and in areas where thickness is required for the circuit or where alignment accuracy is required. .