JPS61163691A - Formation for electric circuit of 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] [Technical Field] The present invention relates to a method for forming electric circuits on a printed wiring board using a semi-additive method. be. This semi-additive method, for example,
The process is shown in the figure. In other words, first of all, Figure 3 (
, ), an adhesive layer 8 is formed as necessary on the surface of an electrically insulating wiring board 1 made of a laminate or the like, and a third
As shown in Figure (b), the surface of the adhesive layer 8 is roughened by etching with a mixed acid and activated. The activation treatment can be performed by applying a colloidal palladium dispersion W11 or the like to adhere the palladium catalyst cores 9 to the surface of the adhesive layer 8.

Then, by electroless plating such as electroless copper plating, the surface of the wiring board 1 is coated with a thickness of 0.5 to 100% through the adhesive layer 8.
A thin metal scrap 2 of about 2 μm is formed as shown in FIG. 3(c). Electroless plating can be performed, for example, by immersion in a copper sulfate plating bath. After forming such a thin metal layer 2, a mask layer 3 is coated on the surface of the metal layer 2 by printing a Menki resist or dry film lamination, leaving an electric path pattern as shown in FIG. 3(d). After this, electroplating such as electrolytic copper plating is performed to form electric circuits 4 in a pattern shape on the surface of the metal layer 2 in the portions not covered with the mask layer 3, as shown in FIG. 3(e). Electrolytic plating can be performed, for example, by immersing the scrap metal 2 in a copper sulfate plating bath and applying electricity to it, and the plating metal is deposited only on the parts that are not covered with the mask layer 2 and are in contact with the plating bath. Therefore, the electric path 4 can be formed in the metal layer 2 in a pattern shape. Then, after dissolving and removing the mask Nj3 with a sodium hydroxide solution as shown in Figure 3 ('), it is lightly etched with an etching solution such as ammonium persulfate to remove the metal in the exposed part as shown in Figure 3 ([1]). This is to remove layer 2 by etching.

The problem with such a semi-additive method is that when the exposed metal layer 2 is etched away,
The metal of the electric circuit 4 is also affected by the etching solution on its surface.
If the required thickness of the electrical circuit 4 cannot be maintained, or if the electrical circuit 4 is formed in a particularly complicated pattern, ungrooved etching may occur, resulting in defects.

[Object of the Invention] The present invention has been made in view of the above points, and provides a method for forming electric circuits on a printed wiring board that can prevent electric circuits from being subjected to etching action during etching of a metal layer. The purpose is to provide

[Disclosure 1 of the Invention] However, the method for forming an electric path on a printed wiring board according to the present invention involves forming a thin metal layer 2 on the surface of a wiring board 1 by electroless plating, and then forming an electric path 4 on the surface of this metal layer 2. The mask layer 3 was coated in areas other than the areas covered by the mask layer 3, and then the metal layer 2 was energized to form an electric path 4 on the surface of the metal layer 2 by electroplating in the areas not covered by the mask layer 3, and the mask layer 3 was removed. Later, when the electric circuit 4 is formed by removing the portion of the metal layer 2 exposed by removing the mask N3 with an etching liquid, the surface of the electric circuit 4 is coated with a protective coating I! having etching liquid resistance. It is characterized in that the metal JvJ2 is etched in a state covered with i5, and the etching is performed in a state where the electric circuit 4 is protected with a protective skin 1II5.
In this way, the electric circuit 4 is prevented from being attacked by the etching solution, thereby achieving the above object,
The present invention will be explained in detail below with reference to Examples.

Fig. 1 shows an embodiment of the construction method of the present invention, and the operations up to forming the electric circuit 4 by electroplating are shown in Fig.
This can be carried out by the same operations as steps a) to (c). Then, as shown in Fig. 3(e), the electric circuit 4 is electroplated.
After forming, the surface of the electric circuit 4 is covered with a protective skin Bs as shown in FIG. 1(a).

The protective film 5 is formed so that it will not be attacked by the etching solution used when etching the thin metal FF12.For example, it is made of preflux, such as Glyco-T manufactured by Shikoku Fine Chemical Co., Ltd., which has excellent adhesion to the copper circuit 4. This can be formed by dipping. Further, the protective film 5 can be formed by an oxide film formed on the surface of the electric circuit 4 by baking or the like, or can be formed by an oxide film or a sulfide film formed on the surface of the electric circuit 4 by chemical treatment or the like. I can do it. After the surface of the electric circuit 4 is coated with the protective film 5 in this manner, the mask layer 3 is removed as shown in FIG. 1(b), and the mask layer 3 is etched as shown in FIG. 1(C). The portions of the metal layer 2 exposed by the removal are removed by etching. Protective skin 1 here
If the protective film 5 is formed by preflux treatment, an ammonium persulfate solution or an alkaline solution is used as the etching solution, and if the protective film 5 is formed of an oxide film or a sulfide film, an alkaline solution is used as the etching solution. Do it like this. The protective film 5 formed by the pre-7 fax process is not dissolved in ammonium persulfate or alkali, and the protective film 5 made of an oxide film or sulfide film is not dissolved in alkali. It is possible to perform etching removal processing. When an oxide film or a sulfide film is formed by chemicals, it is preferable to remove these films eventually. Further, even if an oxide film is formed by baking, it is finally removed if necessary. Since the protective film 5 formed by the pre-flux treatment can be easily removed by pickling, the work of forming the electric circuit can be carried out by a continuous method.

In addition, in the embodiment shown in FIG. 1, the preparation of the protective film 5 is shown in FIG.
) after creating circuit 4, but 13
After the process of removing the mask layer 3 in Figure (f), the process shown in Figure 2 (
The protective film 5 may be formed as shown in a), and then the metal layer 2 may be removed by etching as shown in FIG. 2(b).

[Effect of the Invention J As described above, in the present invention, the metal layer is etched with the surface of the electric circuit covered with a protective film that is resistant to etching liquid. It is possible to prevent etching of the metal layer without complicating the process (it is possible to prevent the electric circuit from being subjected to etching action, and in this way, the metal layer can be etched without the electric circuit being attacked). Since the etching process can be carried out, the metal layer can be sufficiently etched, and the insulation reliability between the electric circuits can be improved by preventing the metal layer from smearing.

[Brief explanation of the drawing]

FIGS. 1(aHb) and (c) are cross-sectional views showing some steps in one embodiment of the present invention, and FIGS. 2(a) and (b) are cross-sectional views showing some steps in another embodiment of the invention. Figures 3(a) to (g)
FIG. 2 is a cross-sectional view showing the steps of a semi-additive electric circuit forming method. 1 is a wiring board, 2 is a metal layer, 3 is a mask layer, 4 is an electric path,
5 is a protective film.

Claims (1)

[Claims] (1) After forming a thin metal layer on the surface of the wiring board by electroless plating, cover the surface of this metal layer with a mask layer except for the parts where electric circuits are to be formed, and then cover with the mask layer by applying electricity to the metal layer. Electrical paths are formed by electroplating on the surface of the metal layer in the areas that are not exposed, and after the mask layer is removed, the metal layer in the areas exposed by the removal of the mask layer is further removed using an etching solution to form an electric path. A method for forming an electric circuit on a printed wiring board, characterized in that the metal layer is etched while the surface of the electric circuit is coated with a protective film having resistance to an etching liquid.