JP2664246B2 - Printed circuit board manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a circuit on a printed circuit board, and more particularly to a method for forming a circuit on a printed circuit board suitable for forming high-density and fine circuits.

[Conventional technology]

Conventionally, high-density printed boards, such as double-sided printed boards and multilayer printed boards, use a copper-clad laminate as a starting material. The main method was to get it. However, this method is not suitable for high-density and fine circuit formation due to the use of electrolytic copper plating with large thickness variations and the circuit accuracy depending on both the etching resist formation accuracy and copper etching accuracy. It is. Therefore, various circuit forming methods suitable for high density and miniaturization have been provided. One of them is a pattern chemical copper plating method. This involves using a copper-clad laminate, masking the area other than the area where the circuit is to be formed with a photosensitive plating resist, then selectively performing chemical copper plating only on the area where the circuit is to be formed, and then removing the plating resist. This is a method of forming a circuit by etching and removing a portion other than the portion where the resist is removed, that is, the portion other than the portion where the circuit is to be formed. However, this method has a problem in that the plating resist is easily peeled off during plating, and good circuit formation cannot be performed. This problem is remarkable in chemical copper plating where there is almost no variation in plating thickness, and in many cases, there is not much problem in electrolytic copper plating. That is, while the plating speed of the electrolytic copper plating is high and the plating is completed in a short time, the plating speed of the chemical copper plating is low, so that a long plating is required, and the peeling proceeds. For example, to perform 30μm chemical copper plating
It takes 10 to 30 hours and takes more than 10 times longer than copper plating. As described above, since the plating is performed for a long time, the plating resist is damaged. For example, a chemical copper plating solution permeates through the interface between the plating resist and the base or through the resist film, and at the interface with the base, the hydroxyl ion 2H ₂ O + O ₂ + 4e → 4OH ^- ... (1) is generated, it is said that to destroy the interface. In addition, since the chemical copper plating solution is highly alkaline at around pH 12, it is considered that interface destruction between the plating resist and the base is likely to occur.

In order to solve such problems, the above-mentioned reference IBM Journal of Research and Development; 2
As described in Volume 9, No. 1, pages 27-36 (1985), the surface of a copper-clad laminate is polished and smoothed with pumice stone, and then this surface is treated with benzotriazole or the like. There has been proposed a method of masking a portion other than a circuit planned portion with a photosensitive plating resist. Also, when using electrolytic copper plating instead of chemical copper plating, see Japanese Patent Publication No. 50-91.
As described in Japanese Patent Publication No. 77, there is provided a method of adding benzotriazole or the like to a photosensitive plating resist. As a result, the problem that the plating resist peels off from the base has been greatly improved.

[Problems to be solved by the invention]

However, the prior art does not provide a sufficient description of the adverse effect on chemical copper plating when benzotriazole is applied. For example, when the applied amount is increased, there has been a problem that the plating speed is reduced locally or over the whole, or the physical properties of the plating film are reduced.

This is presumably because benzotriazole was dissolved in the chemical copper plating solution. When such a phenomenon occurs, sufficient reliability cannot be obtained, and in some cases, circuit formation itself becomes impossible. It is thought that proper control of the concentration of benzotriazole in the resist and the underlying surface is indispensable to control so that this problem does not occur. Was difficult.

An object of the present invention is to provide a pattern chemical copper plating method capable of forming a fine circuit. Specifically, it is an object of the present invention to provide a method suitable for forming a fine circuit in which a plating resist is sufficiently adhered to an underlying metal layer, does not peel off during plating, and does not adversely affect plating characteristics. is there.

[Means for solving the problem]

The above object is achieved by providing a second metal layer on the surface of a copper layer provided on an insulating plate, and then forming a resist at a required location, and then performing a pattern chemical copper plating process. Copper plating with standard hydrogen electrode (below
This is achieved by plating at a potential nobler than -550 mV with respect to NHE).

[Action]

In the pattern chemical copper plating, we investigated the phenomenon that the plating resist was peeled off, and found that the plating resist did not completely adhere to the base, and the chemical copper plating liquid infiltrated into the gap. It was presumed to be related to the chemical copper plating reaction occurring in the gap. In the present invention, in consideration of this point, the standard hydrogen electrode is set to -55.
It has been found that chemical copper plating at a potential nobler than 0 mV is effective from the viewpoint of preventing peeling of the plating resist, and that a good pattern can be formed. Although the obvious reason is unknown, if the plating reaction potential is sufficiently low, it is expected that the oxide on the surface of the second metal is reduced and the plating resist interface is destroyed. If the plating reaction potential is more noble, such a reduction reaction does not occur and is not destroyed. Nickel particularly effective as a second metal layer,
It has been found that when zinc, tin, and chromium are used, the object of the present invention can be substantially achieved if the plating reaction potential is noble than about -550 mV with respect to a standard hydrogen electrode.

In the present invention, since there is no need to apply a treating agent such as benzotriazole to the metal surface, there is no problem that the quality of the plated film is degraded or the plated circuit is chipped.

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

In the present invention, the second metal layer 3 is provided on the copper 2 layer on the insulating plate 1, but in order to sufficiently achieve the object of the present invention, the surface of the copper 2 is sufficiently roughened before the formation of the second metal layer 3. (A). As a roughening method, a method of immersing in an aqueous solution of cupric chloride, an aqueous solution of ammonium persulfate, or the like for roughening is possible. Next, an oxide film layer is formed to form finer irregularities. Here, an alkaline zincate aqueous solution or the like can be used. Further, the oxide film layer is treated electrically or with a solution containing a reducing agent such as dimethylamine borane. By such a treatment, a good roughened surface can be obtained. Subsequently, the second metal layer 3 is formed on the roughened copper 2. (B) The second metal layer 3 is preferably made of a metal having a low potential. For example, nickel, zinc, tin, chromium and the like can be mentioned. These metals can be formed by electroplating, chemical plating, or the like. Next, portions other than the circuit forming portion are masked with the plating resist 4. (C)
A commercially available photosensitive resist can be used as the plating resist 4. For example, DuPont's Liston Film R-1220, T
-168, Laminar GSI of Thiokol Dynachem, and Huotek SR-3200 of Hitachi Chemical Co., Ltd. These plating resists 4 are of a film type, and are laminated on the surface of the substrate by a photo roll or the like. In the present invention, a liquid type can be applied in addition to the film type. In order to form a resist 4 at a required portion of the substrate surface, it can be achieved by performing ordinary exposure and phenomenon. Subsequently, copper plating is performed on a desired circuit formation portion. Here, it is desirable to remove the second metal layer 3 exposed at the circuit formation portion. (D) Since the copper plating is excellent, the chemical copper plating 5 for thickening which gives the film quality is suitable. (E) The pattern chemical copper plating 5 makes the plating reaction potential nobleer than -550 mV with respect to the standard hydrogen electrode, but as a method of shifting the plating reaction potential noblely, increasing the copper ion concentration, reducing Methods include lowering the agent concentration and pH. Further, there is a method of adding a sulfate ion or a formate ion, which is a plating reaction product, or other various ions. Other methods include increasing the dissolved oxygen concentration and adding a formalin oxidation reaction inhibitor or a copper ion reduction reaction accelerator.

By this method, after good pattern plating in which the peeling of the plating resist 4 does not substantially occur, an etching resist is formed by solder plating 6 by an ordinary method (F), and then the plating resist 4 is formed. After removing (G), the portion of the second metal layer 3 and the copper layer 2 covered with the plating resist 4 is removed by etching. (H) Eventually, the six soldered layers are removed, and (I) the circuit pattern of the printed board can be formed.

〔Example〕

 The present invention will be specifically described with reference to examples.

<Example 1> Process: 1.6 mm thick double-sided copper-clad glass epoxy laminate (copper foil thickness
(18 μm) with a 0.4 mm diameter drill. After the surface was polished with a brush, the inside of the hole was washed with high-pressure water. Next, the surface was soft-etched with an aqueous solution of ammonium persulfate, and then pickled. Subsequently, it was activated by immersion in a catalyst for chemical copper plating (sensitizer HS101B manufactured by Hitachi Chemical Co., Ltd.). Next, after pickling, it was immersed in a chemical copper plating solution having the following composition at 70 ° C. for 2 hours to form a chemical copper plating layer having a thickness of about 6 μm.

Step 2: After step 1, the surface was pickled and lightly roughened with an aqueous solution of ammonium persulfate (200 g /). Next, the resultant was treated with a liquid having the following composition at 70 ° C. for 2 minutes to form an oxide film layer having fine irregularities.

Further, the oxide film was reduced with a treatment solution having the following composition.

In addition, after thoroughly washing the surface by washing with water,
Were plated in 4 minutes matte electric nickel solution at 05A / dm ^2. After washing and drying, a photosensitive dry film, Liston 1220 manufactured by DuPont, was laminated by a hot roll heated to 110 ° C. Further, by performing an exposure phenomenon, a resist was formed on portions other than the circuit forming portion. Next, it was aged by heating at 140 ° C. for 1 hour.

Step 3: Next, the substrate was immersed in an aqueous solution of ammonium persulfate (200 g /), and the nickel plating layer exposed on the surface was removed by etching with copper. After pickling and washing with water,
It was immersed in a chemical copper plating solution having the following composition at 72 ° C., and a patterning chemical copper plating having a thickness of about 30 μm was performed at a plating reaction potential of −550 to −550 mV _vs. NHE.

After the completion of the plating, the substrate was thoroughly washed with water to complete the steps up to the pattern chemical copper plating.

<Example 2> In Example 1, the amount of copper sulfate (pentahydrate) in the pattern chemical copper plating solution in Step 3 was 15 g / formalin (37%).
And the reaction potential was -520 to -480 mV _vs N
The steps up to pattern chemical copper deposition were completed in exactly the same manner as in Example 1 except that HE was used.

<Example 3> Exactly the same as Example 1 except that the plating reaction potential was -500 mV _vs NHE by adding 30 g of sodium sulfate and 30 g / sodium formate to the chemical copper plating solution of step 3 in Example 1. The process up to the pattern chemical copper plating was completed by the method described above.

<Example 4> In step 2 of Example 1, a pattern was formed in the same manner as in Example 1 except that zinc plating was performed in a zinc oxide plating bath at 0.3 A / dm ² for 6 minutes instead of electric nickel plating. The process up to chemical copper plating was completed.

In step 2 of <Example 5> Example 1, pattern chemical electric nickel plated 0.3 A / dm ³ instead an electric sparrow with bath, except that the 6 minutes sparrow with Example 1 and exactly the same manner The process up to copper plating was completed.

<Comparative Example 1> The chemical copper plating solution in Step 3 of Example 1 was adjusted to have a copper sulfate (pentahydrate) content of 5 g / pH 12.9 and a plating reaction potential of -630 to -580 mVB _vs NHE. Except for this, the steps up to the pattern chemical copper plating were completed in the same manner as in Example 1.

<Comparative Example 2> In the chemical copper plating solution in Step 3 of Example 1, the amount of copper sulfate (pentahydrate) was 3.5 g /, and the plating reaction potential was −6.
The process up to pattern chemical copper plating was completed in the same manner as in Example 1 except that the voltage was set to 50 to -600 mV _vs NHE.

<Comparative Example 3> The process up to pattern chemical copper plating was performed in exactly the same manner as in Comparative Example 1 except that the electric nickel plating in Comparative Example 1 was replaced with electric zinc plating (0.3 A / dm ² , 6 minutes). Completed.

<Comparative Example 4> The process up to pattern chemical copper plating was performed in exactly the same manner as in Comparative Example 1 except that the electric nickel plating in Comparative Example 1 was replaced with electric zinc plating (0.3 A / dm ² , 6 minutes). Completed.

As a result of observing peeling and blistering of the plating resist in Examples 1 to 5 described above, the occurrence thereof was very small, and there was no problem in pattern formation. On the other hand, in Comparative Examples 1 to 3, peeling and swelling of the attached resist were recognized, and when soldering was performed in the next step, soldering was attached to the area where the resist was peeled off. Inconvenience occurred in circuit formation.

〔The invention's effect〕

According to the present invention, since local peeling and blistering of the plating resist can be substantially prevented, there is a great effect in forming a fine pattern.

[Brief description of the drawings]

FIG. 1 is a sectional view of a printed wiring board manufacturing process according to one embodiment of the present invention. 1 ... insulating plate, 2 ... copper, 3 ... second metal layer, 4 ... plating resist, 5 ... chemical copper plating, 6 ... solder plating.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ryoji Toba 1st Horiyamashita, Hadano City, Kanagawa Prefecture Inside Hitachi, Ltd. Kanagawa Plant (72) Inventor Motoyo Wajima 1st Horiyamashita, Hadano City, Kanagawa Prefecture Hitachi, Ltd. Inside the Kanagawa Plant (72) Inventor Masashi Miyazaki 1 Horiyamashita, Hadano City, Kanagawa Prefecture Inside the Kanagawa Plant, Hitachi, Ltd. (56) References JP-A-60-96767 (JP, A) JP-A 64-13794 (JP, A)

Claims (3)

(57) [Claims] 1. A method for manufacturing a printed circuit board, comprising: providing a second metal layer on a surface of a copper layer provided on an insulating plate, forming a plating resist at a required portion, and then performing pattern chemical copper plating. Pattern chemical copper plating -55 with respect to standard hydrogen electrode
A method for manufacturing a printed circuit board, comprising: plating at a potential nobler than 0 mV. 2. The method according to claim 1, wherein said bimetallic layer is selected from the group consisting of nickel, zinc, tin, and chromium.
A method for manufacturing a printed circuit board comprising at least one or an alloy thereof. 3. The method according to claim 2, wherein prior to forming the second metal layer, the surface of the copper layer is roughened, an oxide film layer is formed on the surface, and fine irregularities are formed. And then reducing the oxide layer on the surface.