JP2002094217A - Method of manufacturing printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming an organic resist film high enough in strength to stand an etchant spray in an etching process. SOLUTION: An organic film 9 is selectively formed on the surface of a copper plating by the use of an alkyl benzimidazole solution, and the exposed part of the copper plating is etched, using the organic film 9 as an etching resist in a process of manufacturing a copper through-hole printed wiring board. All the surface of the copper plating 4 including the inner wall of a through-hole is subjected to a blacking treatment 5 before an organic film is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for forming a conductive pattern.

[0002]

2. Description of the Related Art A method of forming a conductor pattern of a printed wiring board having through holes is roughly classified into an additive method and a subtractive method. A method of attaching copper to a conductor pattern portion including a through hole is an additive method. There is a subtractive method in which both surfaces of the base material and the wall surfaces of the through holes are covered in advance with copper, and unnecessary copper is removed by etching or the like. Of these two types of manufacturing methods,
Except in special cases, the subtractive method is used exclusively.

Here, the subtractive method for removing unnecessary copper by etching generally uses a printed resin film, a photosensitive resin film, gold plating, and solder plating as an etching resist. The selection is based on the disadvantages. Gold-plated printed wiring boards
In soldering during the assembly of a printed wiring board, gold diffuses into the solder to make the solder brittle, and in recent years there has been a strong tendency to avoid etching resists by gold plating except in special cases. In addition, etching resists formed by solder plating occupied a large portion for some time, but in recent years, they have been used only when necessary after taking measures against pollution.

Accordingly, in recent years, there has been a trend toward a finished conductor pattern in which a copper surface without gold or solder overcoat plating is exposed, and among these, a manufacturing method using a photosensitive resin film as an etching resist has become widespread. ing.
Since this method protects the wall copper in the through-hole from the etching solution by a resin film stretched on both sides of the through-hole opening, it is well known as a tenting method, which is analogous to weathering with a tent.

[0005] In recent years, high speed and miniaturization of electronic devices have promoted the refinement and high density of conductive patterns as required specifications for printed wiring boards, and therefore it is necessary to design via lands as small as possible. . In order to design a small-diameter land exceeding the limit of the tenting method, a conventional method of removing a solder after forming a conductor pattern using solder plating as an etching resist, which is called a solder peeling method, is used. Had been manufactured. However, it is not advisable to use the solder that eventually peels, both in terms of environmental protection and cost.

As a substitute for the solder, 2-alkylbenzimidazole, 2-alkyl-benzimidazole which selectively forms an organic film on a copper surface,
Compounds such as 2-phenylbenzimidazole and 2-phenyl-alkylbenzimidazole are known (JP-A-3-235395).

FIG. 2 is a schematic sectional view showing a method of manufacturing a printed wiring board using an organic resist film formed by the treatment with the chemical substance as an etching resist. FIG. 2A shows a hole 13 for a through hole formed in a copper-clad laminate 11, and a plating copper 14 formed by electroless copper plating and electrolytic copper plating is applied to the hole wall 13 and the copper foils 12 on both surfaces. Affix photosensitive resin film 15,
This shows a state in which the exposure 17 is performed while the exposure positive film 16 is brought into close contact. FIG. 2B shows a state in which a developing step for cleaning and removing the unexposed portion of the photosensitive resin film 15 and a soft etching step for removing an oxide film on the exposed plated copper surface have been completed, and FIG. , Organic coating 18 of the chemical substance
FIG. 2 (d) shows a state in which the processing step and the washing / drying / heating step for curing have been completed, and FIG.
FIG. 2E shows the etching of the exposed portion copper, and FIG.
This shows a state where the organic coating 18 has been removed.

As described above, there is a “soft etching” step before the “organic coating processing step” in the manufacturing process. Two copper-clad laminates with negative circuits formed by photo
After immersing in a 0% aqueous sodium persulfate solution for 20 seconds and soft-etching the copper surface, immersing the copper-clad laminate in a 1% solution of 2-alkylbenzimidazole or 2-alkyl-alkylbenzimidazole, slowly Treated at a temperature of 50 ° C. for 3 minutes while moving. "a.

[0009]

However, the removal of the oxide film on the copper surface in the soft etching step before the formation of the coating lowers the reactivity of the formation of the coating, and the pressure of the spray of the etching solution is reduced in the subsequent etching step. It was found that the film could lose due to losing. The present invention has been made to solve the above problems, and has as its object to provide a manufacturing method for forming an organic resist film having sufficient strength to withstand spraying of an etching solution in an etching step.

[0010]

According to a first aspect of the present invention, there is provided a method for manufacturing a printed wiring board, wherein an organic film is selectively formed on a copper surface by using a solution such as an alkylbenzimidazole system, and the organic film is exposed as an etching resist. In manufacturing a copper through-hole printed wiring board for etching copper, the entire surface of the copper plating surface including the through-hole walls is blackened before the organic film forming process.

According to the first aspect of the present invention, the reactivity of the alkylbenzimidazole-based solution to copper is better than the reactivity to the copper surface from which the oxide film has been removed. A durable and strong organic resist film can be formed.

[0012]

FIG. 1 is a schematic sectional view showing a method for manufacturing a printed wiring board according to an embodiment of the present invention. In various attempts to form an organic film on a copper surface using a solution containing 2-alkylbenzimidazole as a main component, 2-alkylbenzimidazole has better reactivity with copper oxide than a copper surface from which an oxide film has been removed. I knew it. The blackening treatment in the present invention is one embodiment for uniformly oxidizing the copper surface before forming the organic film. The manufacturing process of the present invention will be described with reference to FIG.

FIG. 1A shows a hole 3 for a through hole in a copper-clad laminate 1 and a plated copper 4 formed by electroless copper plating followed by electrolytic copper plating on the wall surface of the hole 3 and the entire surface of the copper foil 2. This shows a state where the blackening film 5 is formed on the surface of the plated copper 4 after the application. The blackening film 5 is formed by dipping in a solution of sodium hypochlorite and sodium hydroxide at about 70 ° C. for about 5 minutes. FIG. 1B shows a state in which a photosensitive resin film 6 is stuck on both surfaces, and a positive film 7 for exposure is brought into close contact with the photosensitive resin film 6 for exposure 8, and FIG. The state after development after removal is shown.

FIG. 1 (d) shows 2-
This is a state in which the organic coating 9 is formed with a solution containing alkylbenzimidazole as a main component. The organic coating 9 is formed by immersing it in a 1% solution of 2-alkylbenzimidazole and treating it at a temperature of 50 ° C. for 3 minutes while slowly moving the organic coating 9 in the same manner as in the example of the above-mentioned publication. FIG.
(E) shows the removal of the photosensitive resin film 6 and the drying and curing of the organic film 9 formed in the previous step. At this stage, the organic coating 9 has sufficient strength to protect copper remaining in the through hole and as a conductor pattern from the spray of the etching solution.

FIG. 1 (f) shows a state where the copper not covered by the organic film 9 is etched to form a conductor pattern, and FIG. 1 (g) shows a state where the organic film 9 is removed. At this stage, the inside of the through hole and the copper surface of the conductor pattern are in a blackened state, but a solder resist is applied as a post-process omitted in the drawing, and the surface is polished and the oxide film is removed as a pretreatment. Therefore, the blackened film is eliminated.

In the above embodiment, as a means for oxidizing the copper surface, a blackening treatment with a solution of sodium hypochlorite and sodium hydroxide was described. However, the same method can be applied to other methods for uniformly oxidizing the copper surface. The effect is obtained.

[0017]

According to the present invention, it is possible to selectively form a printed wiring board having micro vias or a printed wiring board having a large through-hole diameter with a copper through-hole, which cannot be worked by the tenting method, by selectively using a copper surface. Alkylbenzimidazole-based solutions that form an organic film by reacting with a can form a strong organic film with better reactivity on a blackened copper surface than on a copper surface without an oxide film, By spraying the etching solution, a good conductor pattern can be formed with good yield without damaging the organic film.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a method for manufacturing a printed wiring board according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a method for manufacturing a printed wiring board using an organic resist film formed by treatment with an alkylbenzimidazole-based solution as an etching resist.

[Explanation of symbols]

 Reference Signs List 1 copper-clad laminate 2 copper foil 3 through-hole 4 plated copper 5 blackened film 6 photosensitive resin film 7 exposure positive film 8 exposure 9 organic coating 11 copper-clad laminate 12 copper foil 13 through-hole ( Hole wall) 14 Plated copper 15 Photosensitive resin film 16 Positive film for exposure 17 Exposure 18 Organic coating

Claims (1)

[Claims] 1. A method of manufacturing a copper through-hole printed wiring board, wherein an organic film is selectively formed on a copper surface with an alkylbenzimidazole-based solution, and the exposed portion is etched using the organic film as an etching resist. A method for manufacturing a printed wiring board, comprising subjecting a copper plating surface including a through-hole wall to a blackening process before a film forming process.