JPH02312295A - Manufacture of printed board - Google Patents

Abstract

PURPOSE:To prevent a plating resist from separating or swelling so as to enable the formation of a fine pattern by a method wherein a pattern chemical copper plating is executed at a certain potential specified to that of a reference hydrogen electrode. CONSTITUTION:A second metal layer 3 is provided onto a copper layer 2 on an insulating board 1, which is masked with a plating resist 4 excluding a circuit forming part, and a pattern chemical copper plating 5 is carried out onto the required circuit forming part. The pattern chemical copper plating 5 is executed at a plating reaction potential higher than the potential of a reference hydrogen electrode by -550mV. After plating, an etching resist is formed through solder plating 6, then the plating resist 4 is removed, the parts of the second metal layer 3 and the copper layer 2 covered with the plating resist 4 are removed through etching, the solder plating layer 6 is removed, and the circuit pattern of a printed board is formed. By this setup, a plating resist can be prevented from separating or swelling, and a fine pattern can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming a circuit on a printed board, and particularly to a method for forming a circuit on a printed board suitable for forming a high-density and fine circuit.

[Conventional technology]

Conventionally, high-density printed boards such as double-sided printed boards and multilayer printed boards are obtained by using copper-clad laminates as the starting material, forming through holes by panel electroplating, and then etching away the copper except for the two circuit parts. was the mainstream. However, this method is unsuitable for forming high-density, fine circuits because it uses electrolytic copper plating with large variations in thickness, and the accuracy of each circuit depends on both etching resist formation precision and copper etching precision. It is. Therefore, various circuit formation methods suitable for high density and miniaturization have been provided. One of them is patterned chemical copper plating. This involves using a copper-clad laminate, masking the area other than the area where the circuit is to be formed with photosensitive plating cyst, and then selectively applying chemical copper plating only to the area where the circuit is to be formed.
This is a method of forming a circuit by removing the plating resist and etching away the copper in the areas where the resist was removed, that is, in areas other than the areas where the circuit is to be formed. However, this method has the problem that the plating resist easily peels off during plating, making it impossible to form a good circuit.

This problem is noticeable in chemical copper plating, where there is almost no variation in plating thickness, and is often less of a problem in electrical steel plating. That is, whereas Ti electrolytic copper plating has a fast plating speed and completes plating in a short time, chemical copper plating has a slow plating speed and requires a long plating time, resulting in progressive peeling. For example, chemical copper plating of 30 μm takes 10 to 30 hours, which is more than ten times longer than electrical steel plating. As plating is carried out for a long period of time, the plating resist is damaged6.For example, the chemical copper plating solution seeps through the resist film, or at the interface between the plating resist and the base (1). Hydroxyl ion 2I4ZO10oz+4e-+408- ・=(
1) is generated and is said to destroy the interface. Also,
Since the chemical copper plating solution is highly alkaline with a pH of around 12, it is thought that the interface between the plating resist and the base is likely to break down.

In order to solve such problems, the above-mentioned document 18M Journal of Research and Development 82
Volume 29, Nα1, pages 27-36 (1985)
As described in , there is a method of polishing the surface of a copper-clad laminate with pumice to make it smooth, then treating this surface with benzotriazole, etc., and masking the area other than the planned circuit area with a photosensitive plating resist. Proposed. Furthermore, when electrolytic copper plating is used instead of chemical copper plating, a method is provided in which benzotriazole or the like is added to the photosensitive plating resist, as described in Japanese Patent Publication No. 50-9177. . As a result, the problem of the plating resist peeling off from the underlying layer has been significantly improved.

[Problem to be solved by the invention]

However, the prior art does not sufficiently describe the adverse effects on chemical copper plating when benzotriazole is applied. For example, increase the amount applied and increase the plating speed locally, or.

There was a problem in that the overall strength of the plating film deteriorated or the physical properties of the plating film deteriorated.

This is presumed to be because benzotriazole was dissolved into the chemical copper plating solution. When such a phenomenon occurs, there is a drawback that not only sufficient reliability cannot be obtained, but also that formation of two circuits itself becomes impossible in some cases. In order to prevent this problem from occurring, it is thought that appropriate concentration control of benzotriazole in the resist and on the underlying surface is essential, but since there are variations in other factors such as the surface condition, circuit formation was difficult in some respects.

An object of the present invention is to provide a patterned chemical copper plating method that allows formation of fine circuits. Specifically, the objective is to provide a method suitable for forming fine circuits in which the plating resist adheres sufficiently to the base metal layer, does not peel off during plating, and does not adversely affect the plating characteristics.

[Means to solve the problem]

The above purpose is to provide a second metal layer on the surface of a copper layer provided on an insulating board, then to form a plating resist in the required areas, and then to perform patterned chemical copper plating in a printed board manufacturing method. Standard hydrogen electrode (hereinafter N
This is achieved by plating at a potential lower than -550 mV vs. HE.

[Function] When we investigated the phenomenon in which the plating resist peels off in patterned chemical copper plating, we found that it occurs because the plating resists 1 to 1 are not in complete contact with the base, and the chemical copper plating solution seeps into the gaps. It was assumed that this was related to the fact that a chemical copper plating reaction occurred in the gap. In the present invention, taking this point into consideration, we have developed a
It has been found that chemical copper plating at a potential higher than 50 mV is effective from the viewpoint of preventing peeling of the plating resist, and enables good pattern formation.

Although the exact reason for this is unknown, it is expected that if the plating reaction potential is sufficiently base, the oxide on the surface of the second metal layer will be reduced and the plating resist interface will be destroyed. If the plating reaction potential is more noble, such a reduction reaction will not occur and destruction will not occur. When using nickel, zinc, tin, and chromium, which are particularly effective as the ferric gold I'iII layer, a plating reaction potential of about -550 mV or more nobler than a standard hydrogen electrode will substantially accomplish the purpose of the present invention. I found out that it can be achieved.

In the present invention, there is no need to apply a treatment agent such as benzotriazole to the metal surface, so there are no problems such as deterioration of the quality of the plated film or chipping of the plated circuit.

Hereinafter, the manufacturing process of the present invention will be explained with reference to FIG.

In the present invention, the second metal layer 3 is provided on the second copper layer on the insulating plate 1, but in order to fully achieve the purpose of the present invention, the surface of the copper 2 is sufficiently roughened before forming the second metal layer 3. (A), it is possible to roughen the surface by immersing it in a cupric chloride aqueous solution, ammonium persulfate aqueous solution, etc. However, an alkaline chlorite aqueous solution or the like can be applied here. Furthermore, the oxide film layer can be electrically or
Treat with a solution containing a reducing agent such as dimethylamine borane. A good roughened surface can be obtained by such treatment. Subsequently, a second metal layer 3 is formed on the roughened copper 2. (B) A metal with a base potential is suitable for this second metal layer 3. for example.

Examples include nickel, zinc, tin, and chromium.

These metals can be formed by electroplating or chemical plating, etc. All parts other than the 0 and 1 circuit forming portions are masked with a plating resist 4. (C) A commercially available photosensitive resist can be used as the plating resist 4. Examples include Riston Film R-1220 and T-168 from DuPont, Laminar GSI from Thiokol Dynachem, and Fotec 5R-3200 from Hitachi Chemical. These plating resists 4 are of film type and are laminated onto the substrate surface using a hot roll or the like. Furthermore, in the present invention, liquid types can also be applied in addition to film types. In order to form the plating resists 1-4 at necessary locations on the substrate surface, this can be achieved by performing normal exposure and phenomena. Subsequently, patterned copper plating is performed on desired circuit forming portions. Here, it is desirable to remove the second metal layer 3 exposed in one circuit forming portion. (D) Thick chemical copper plating 5 is suitable for patterned copper plating, which provides excellent matte film quality. (E) In this patterned chemical copper plating 5, the plating reaction potential is made nobler than -550 mV with respect to the standard hydrogen electrode, but as a method of shifting the plating reaction potential to a nobler state, the copper ion concentration is increased. There are methods of lowering the reducing agent concentration and pH. Further, there are methods of adding sulfate ions, formate ions, which are plating reaction products, or various other ions. Other methods include increasing the dissolved oxygen concentration and adding a formalin oxidation reaction inhibitor or a copper ion reduction reaction promoter.

By this method, after plating a good pattern in which peeling of the plating resist 4 does not substantially occur,
Form an etching resist by solder plating 6F)
Then, after removing the plating resist 4 (G), the second metal layer 3 and the copper ribs 2 in the portions covered with the plating resist 4 are removed by etching. (F() Finally, the 6 layers of solder plating are removed, and (I) the circuit pattern of the printed board can be formed.

〔Example〕

The present invention will be specifically explained with reference to Examples.

<Example 1> Step 1: A hole was drilled with a 0.4 mm diameter drill in a double-sided copper-clad glass epoxy laminate (copper W3 thickness: 18 μm) having a thickness of L, 6Il+m. After polishing the surface with a brush, the inside of the hole was cleaned with high-pressure water. Next, the surface was soft etched using an aqueous ammonium persulfate solution.

Furthermore, it was pickled. Subsequently, the product was activated by immersing it in a catalyst for chemical copper plating (Sensitizer H8101B manufactured by Hitachi Chemical Co., Ltd.) Next, it was pickled and then immersed in a chemical copper plating solution with the following composition at 70°C for 2 hours. A chemical copper plating layer having a thickness of about 6 μm was formed by dipping.

Step 2: After completing Step 1, the surface was pickled and lightly roughened with an aqueous ammonium persulfate solution (200 g/Ω).

Next, a solution with the following composition was heated to 70°C.

The treatment was carried out for 2 minutes to form an oxide film layer with fine irregularities.

Furthermore, the above oxide film was reduced with a treatment liquid having the following composition.

Furthermore, after thoroughly cleaning the surface by washing with water, 0.
It was plated with a matte electrolytic nickel plating solution at 0.05 A/dm for 4 minutes. After washing with water and drying, it was laminated with a photosensitive dry film, Riston 1220 manufactured by DuPont, using a hot roll heated to 110°C. Furthermore, by performing exposure and development, a plating resist was formed in areas other than the circuit forming area.

Next, it was heated and aged at 140° C. for 1 hour.

Step 3: Next, ammonium persulfate aqueous solution (200g/
Q), and the nickel plating layer exposed on the surface was etched and removed along with the copper. After pickling and washing with water, immerse in a chemical copper plating solution with the following composition at 72°C to obtain a plating reaction potential of -550 to -500 mV vs. NHE.
Patterned chemical copper plating with a thickness of approximately 30 μm was performed.

After plating was completed, the product was thoroughly washed with water and the process up to patterned chemical copper plating was completed.

<Example 2> In Example 1, the plating reaction was carried out by changing the amount of copper sulfate (pentahydration amount) in the patterned chemical copper plating solution in step 3 to 15 g/Q and the amount of formalin (37%) to 1.5 g/Q. The steps up to patterned chemical copper plating were completed in exactly the same manner as in Example 1, except that the potential was set to -520 to -480 mV vs. NHE.

<Example 3> Completely the same method as Example 1 except that 30 g/ρ of sodium sulfate and 30 g/ρ of sodium formate were added to the chemical copper plating solution in Step 3 of Example 1 to set the plating reaction potential to -500 mV vs NHE. 6 (Example 4) In step 2 of Example 1, acid zinc plating was performed at 0.3 A/d in place of electrolytic nickel plating.

The process up to patterned chemical copper plating was completed in exactly the same manner as in Example 1, except that zinc plating was carried out for 6 minutes.

<Example 5> In step 2 of Example 1, electrolytic nickel plating was performed at 0,3 A/drr instead of electrolytic nickel plating.
? .

The steps up to patterned chemical copper plating were completed in exactly the same manner as in Example 1, except that plating was carried out for 6 minutes.

<Comparative Example 1> The chemical copper plating solution in Step 3 of Example 1 was mixed with sulfuric acid @ (5
Hydrate) amount was 5 g/Q, pH 12,9, and the plating reaction potential was -630 to -580 mVBvsN.
The steps up to patterned chemical copper plating were completed in the same manner as in Example 1 except that HE was used.

<Comparative Example 2> The chemical copper plating solution in Step 3 of Example 1 was mixed with copper sulfate (5
The steps up to patterned chemical copper plating were completed in the same manner as in Example 1, except that the amount of hydrate was 3.5 g/12 and the plating reaction potential was -650 to -600 mV vs. NHE.

Comparative Example 3 Comparative Example 1 except that the electrolytic nickel plating in Comparative Example 1 was replaced with electrolytic zinc plating (0.3 A/drrr, 6 minutes)
The process up to patterned chemical copper plating was completed in exactly the same manner as above.

<Comparative Example 4> The process up to patterned chemical copper plating was completed in exactly the same manner as Comparative Example 1, except that the electrolytic nickel plating in Comparative Example 1 was replaced with electrolytic zinc plating (0.3 A/drrl', 6 minutes). did.

Regarding Examples 1 to 5 described above, the peeling and blistering of the plating resist was observed by vA, and as a result, the occurrence thereof was very slight, and there was no problem at all in pattern formation. On the other hand, in Comparative Examples 1 to 3, a lot of peeling and blistering of the plating resist was observed, and when solder plating was performed in the first step, solder plating was also attached to the places where the resist had peeled off, forming one circuit. An inconvenience arose.

〔Effect of the invention〕

According to the present invention, local peeling and blistering of the plating resist can be substantially prevented, which is highly effective in forming fine patterns.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a printed wiring board manufacturing process according to an embodiment of the present invention.

Claims (3)

[Claims] 1. A second metal layer is provided on the surface of the copper layer provided on the insulating plate,
Next, in a method for manufacturing a printed circuit board in which a plating resist is formed at necessary locations and then patterned chemical copper plating is performed, the patterned chemical copper plating is performed at a temperature of -5 with respect to a standard hydrogen electrode.
A method for manufacturing a printed circuit board, characterized by plating at a potential higher than 50 mV. 2. In claim 1, the bimetallic layer is made of nickel, zinc, tin, or chromium.
A method for manufacturing a printed circuit board, characterized in that it is made of at least one kind or an alloy thereof. 3. In claim 2, prior to forming the second metal layer, the surface of the copper layer is roughened, an oxide film layer is formed on the surface, fine irregularities are created, and then the surface is roughened. A method for manufacturing a printed circuit board, comprising reducing the oxide film layer.