JPH02251197A - Manufacture of high-density printed circuit board - Google Patents

Abstract

PURPOSE:To manufacture a high density printed circuit board having through- holes having small diameters and wirings among pins of high density with excellent reliability by improving the surface of a circuit pattern so as to enhance the adhesion of a resist at the time of electroless copper plating and the circuit pattern. CONSTITUTION:A photoresist 7 resisting an electroless copper plating liquid is formed onto a copper-clad laminated board 1 from the upper section of a circuit pattern 5. The surface of the circuit pattern 5 is improved for enhancing the adhesion of the circuit pattern 5 and the photoresist 7 at that time. The surface is improved in such a manner that only the surface of the circuit pattern (a copper wiring) 5 is oxidized chemically and roughened, and only copper oxide is melted and removed selectively through chemical treatment using an acid or an electroless copper plating solution. Accordingly, a high-density printed circuit board can be manufactured with excellent reliability.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention (first invention and second invention) relates to a method for manufacturing a high-density printed circuit board, particularly a process of selectively plating only the inner surfaces of through poles. The present invention relates to a method of manufacturing the circuit board having the same.

[Conventional technology]

When applying copper plating to the inner surface of the through-hole of a multilayer board,
Conventionally, perforated copper-clad laminates were plated and nucleated.
A method has been used in which a thin layer of electroless copper plating is applied to obtain electrical continuity, and then plating is performed to a desired thickness by electroplating.

In this method, as the mounting density increases, the through-hole diameter becomes smaller, and as the number of laminated layers increases and the plate thickness increases, the electroplating becomes thicker near the opening of the through-hole.
The problem was that it became thinner as it went deeper. However, this problem was resolved by using electroless copper plating.

However, with this electroless copper plating, the same thickness of copper deposited on the inner surface of the through hole is deposited on the surface, which increases the amount of etching required to form a circuit pattern.
Not only does etching take time, but pattern grain size may be reduced due to side etching or undercutting. For this reason, electroless copper plating is not suitable for manufacturing high-density printed circuit boards.

Therefore, several proposals have been made to solve these problems.

For example, Japanese Patent Application Laid-Open No. 48-8063 proposes a method in which pattern etching is performed after forming through holes, followed by plating nucleation treatment, followed by applying a plating-resistant solder resist and performing electroless plating. There is.

Furthermore, Japanese Patent Application Laid-open No. 48-8062 discloses that a perforated copper-clad laminate is subjected to plating nucleation treatment, pattern etching is then applied, a plating-resistant solder resist is applied, and then electroless copper plating is performed. A method is proposed.

Furthermore, JP-A-61-70790 discloses that a hole-drilled copper-clad laminate is subjected to plating nucleation treatment, electroless copper plating is applied to a thickness thinner than the desired thickness inside the through-hole, and pattern etching is performed to ensure durability. A method has been proposed in which after applying a plating solder resist, at least the inner surface of the through hole is electrolessly plated to a desired thickness.

[Problem to be solved by the invention]

However, these proposals also have the following problems.

That is, the method disclosed in JP-A-48-8063 improves the accuracy of the copper wiring pattern, but since the plating core metal particles remain on the surface of the base material, migration occurs and the insulation between the circuit patterns decreases. .

Furthermore, in the method disclosed in Japanese Patent Application Laid-Open No. 48-8062, plating nuclei may be detached during various processing steps, or the function thereof may be deteriorated.

Furthermore, JP-A-48-8062 and JP-A-61-7
In the method of Publication No. 0790, since the solder resist is supplied as ink, masking when electroless copper plating is performed on necessary parts is performed by screen printing. However, there are limits to the accuracy of this screen printing. Therefore, this method cannot cope with an increase in the number of small-diameter through poles or wiring between bins, and it is difficult to manufacture a high-density printed circuit board.

It is also possible to use a photosensitive resist as a sulter resist, but the resistance of the resist to plating solutions is poor, and the plating solution can enter the interface between the copper and the resist, causing corrosion of the wiring. Therefore, a highly reliable printed circuit board cannot be obtained.

This invention (first invention and second invention) was made by focusing on such conventional problems, and it is possible to improve the adhesion between the resist and copper wiring (circuit pattern) during electroless copper plating. Therefore, an object of the present invention is to provide a method for manufacturing a high-density printed circuit board having small-diameter through holes and high-density wiring between pins with high reliability.

[Failure to solve the problem]

The method for manufacturing a high-density printed circuit board according to the first invention includes the following nine steps. Each step will be explained with reference to FIGS. 1 to 9 which schematically show them.

(1) A step of drilling through holes 2 in the copper-clad laminate 1 that has undergone inner layer processing, as shown in FIG.

(2) The step of applying activation treatment for electroless copper plating to the copper-clad laminate with through holes 2, that is, the laminate 1 is subjected to treatments such as degreasing, oxide film removal, and roughening. After that, as shown in Figure 2, plating nucleus 3 (usually palladium)
The process of imparting.

(3) After the activation treatment, electroless copper plating is applied to the surface of the copper-clad laminate l to a thickness thinner than a predetermined thickness (usually about 1 to 5 μm), and as shown in Figure 3, the first electroless copper plating is applied. Step of forming steel plating layer 4.

(4) Etching (
A step of forming a circuit pattern 5 as shown in FIG. 4 by a tenting method, a soldering method, etc.

(5) A fifth layer is formed on the surface of the circuit pattern 5 by chemical oxidation.
As shown in the figure, a step of forming an oxide film 6.

(6) A step of dissolving and removing the oxide film formed on the surface of the circuit pattern 5 by chemical treatment using acid or electroless copper plating solution, as shown in FIG.

(7) A step of attaching a photoresist 7 resistant to electroless copper plating solution to the copper-clad laminate 1 from above the circuit pattern 5, as shown in FIG.

(8) Expose the photoresist 7 using photolithography technology,
This is followed by a step of developing and forming a resist pattern 8 as shown in FIG.

(9) At least the inner surface of the through hole 2 is subjected to electroless copper plating as shown in FIG. 9, and a second electroless copper plating layer 9 ( 15 μm or more) from the viewpoint of reliability, and forming an electroless copper plating layer 10 with a predetermined thickness in both layers 4 and 9.

Note that the photoresist 7 used for masking during electroless copper plating used in steps (7) to (9) is used as a solder mask. The photoresist 7 needs to have resistance to electroless copper plating solution.

The most important steps in the first invention are steps (5) to (7).

That is, when attaching photoresist 7 that is resistant to electroless copper plating solution, this is a series of steps in which the surface of circuit pattern 5 is modified in order to improve the adhesion between circuit pattern 5 and the photoresist. The surface modification referred to here involves chemically oxidizing only the surface of the circuit pattern (copper wiring) 5 to roughen it, and then selectively removing only the copper oxide through chemical treatment using acid or electroless copper plating solution. This is done by dissolving and removing it.

Chemicals used for chemical oxidation include those consisting of sodium hypochlorite, sodium hydroxide, sodium phosphate, etc., and those consisting of copper acetate, copper sulfate, barium sulfide, ammonium chloride, etc., which are commonly used for blackening treatment. Those known as reagents can be mentioned.

Sulfuric acid is used as a treatment solution to dissolve and remove the oxide film.

Examples include hydrochloric acid, nitric acid, chromic acid, formic acid, and acetic acid, with sulfuric acid, hydrochloric acid, nitric acid, and the like being particularly preferred. These acids are used as 0.5-20% by volume aqueous solutions. As another treatment liquid, an electroless copper plating liquid can be used.

Although any electroless copper plating solution may be used, it is preferable to use the electroless copper plating solution used in step (9).

However, the liquid temperature of electroless copper plating used at this time is (
9) Electroless copper plating solution temperature 20-3
It is preferable to set the temperature as low as 0°C. If the liquid temperature is set to the same as in step (9), the dissolution efficiency of copper oxide will increase, but
Unnecessary parts may be electroless copper plated, reducing the reliability of the wiring. If the temperature is set to 20 to 30 degrees Celsius, such problems will not occur and copper oxide can be effectively dissolved.

The method for manufacturing a high-density printed circuit board according to the second invention includes the following eight steps. Each step will be explained with reference to FIGS. 10 to 17 which schematically show them.

(1) A step of drilling through holes 12 in the copper-clad laminate 11 that has undergone inner layer processing, as shown in FIG.

(2) A step of performing activation treatment for electroless copper plating on the copper-clad laminate 11 with the through holes 12, that is, the laminate 11 is subjected to treatments such as degreasing, oxide film removal, and roughening. After plating, as shown in FIG. 11, there is a step of applying plating nuclei 13 (usually palladium).

(3) After the activation treatment, electroless copper plating is applied to the surface of the copper-clad laminate 11 to a thickness thinner than a predetermined thickness (usually about 1 to 5 μm), and as shown in FIG. Step of forming copper plating layer 14.

(4) A step of forming a metal layer 15 other than copper, which has excellent adhesion with the resin layer, on the surface of this copper-clad laminate 11, as shown in FIG.

(5) A step of forming a circuit pattern 16 on the surface of this copper laminate 11 by etching (tenting method, soldering method, etc.) as shown in FIG.

(6) A step of attaching electroless copper plating and photoresist 17 resistant to dripping liquid to the copper-clad laminate 11 from above the circuit pattern 16, as shown in FIG.

(7) A step of exposing the photoresist 17 using photolithography and developing it to form a resist pattern 18 as shown in FIG. 16.

(8) Electroless copper plating is performed on at least the inner surface of the through hole 2, as shown in FIG. 17, and a second electroless copper plating layer 19 (15μ
m or more) and form an electroless copper plating layer 20 of a predetermined thickness with three layers 14, 15, and 19.

Note that the photoresist 17 used for masking during electroless copper plating used in steps (6) to (8) is a salter.
Used as a mask.

The photoresist 17 used in the second invention needs to have resistance to electroless copper plating solution. Generally known dry film resists for etching, photoresists for solder masks, etc. have insufficient alkali resistance and are difficult to use in the present invention.

The most important steps in the second invention are steps (4) to (6).

That is, when attaching the photoresist 17 that is resistant to electroless copper plating solution, this is a series of steps in which the surface of the circuit pattern is modified in order to improve the adhesion between the circuit pattern and the resist. The surface modification referred to here is performed by forming a metal layer other than copper, which has excellent adhesion to the resin layer 15, on the surface of the circuit pattern (copper wiring). The metal layer 15 is preferably formed by a plating method such as chromium plating or cobalt-molybdenum plating called chromate treatment.

[Effect]

In the first invention, since the surface of the circuit pattern 5 is roughened, the adhesion between the photoresist 7 and the circuit pattern 5 is improved, and the interface (bonding surface) between the photoresist 7 and the circuit pattern 5 is formed during electroless copper plating. Electroless copper plating can be performed reliably without the plating solution entering the surface.

In the second invention, since the metal layer 15 with excellent adhesion to the resin layer is formed on the surface of the circuit pattern, the adhesion between the photoresist 17 and the circuit pattern 16 is improved, and when electroless copper plating is performed, the photoresist 17 The plating solution does not enter the interface between the circuit pattern 16 and the circuit pattern 16. Therefore, electroless copper plating can be selectively performed only on necessary parts with high precision.

〔Example〕

A detailed description of the invention is provided below.

Examples 1 to 3 are examples of the first invention, and Comparative Examples 1 to 4
is shown for comparison with Examples 1 to 3. Examples 4 and 5 are second examples, and Comparative Examples 5 and 6 are shown for comparison with Examples 4 and 5.

(Example 1) (1) Synthesis of bisphenol-type epoxy acrylate Epicote 828 (manufactured by Yuka Shell Co., Ltd., epoxy equivalent: 19
0) 570 g (3 equivalents) and 201 g acrylic acid (
2.8 mol) was placed in a 1 fl flask, and 0.77 g (0.1% by weight) of methoxyphenol was added as a polymerization inhibitor.
, benzyldimethylamine 3.9g (0.5wt h1%)
was added and reacted at 90°C for 6 hours. Thereafter, the acid value was measured by a conventional method, and when the value became 1 or less, it was considered as the end point.

(2) Preparation of photosensitive element First, a solution of a photosensitive resin composition having the following composition was prepared.

Bisphenol type epoxy acrylate synthesized in (1) above: 30 parts pentaerythritol triacrylate 20 parts Methyl methacrylate/methyl acrylate/styrene (weight ratio 70:10:20 copolymer, molecular weight approx. 100,000)
・・・・・・ 45 parts benzophenone
・・・・・・ 4.8 parts Michler ketone
・・・・・・ 0.2 parts P-methoxyphenol ・
...-,0,2 parts methyl ethyl ketone ...
... 50 parts, and then the obtained solution was made into a layer with a thickness of 25 μm.
The photosensitive resin composition was coated on a polyethylene terephthalate film and dried at room temperature for 20 minutes, at 70° C. for 10 minutes, and at 100° C. for 5 minutes to obtain a photosensitive element having a layer thickness of about 70 μm.

(3) Fabrication of printed circuit board Thickness of substrate 1.6111111. Through holes and component holes were formed in a glass epoxy copper clad laminate made of copper foil with a thickness of 18 μm. Next, after performing a catalyst treatment for electroless plating, an electroless copper plating bath (pH 12, 5, 60°C
) for 1 hour, and a 2 μm thick copper film was applied to the entire surface.

An etching resist was applied to the obtained substrate, and a circuit pattern was formed on the surface thereof.

This substrate was placed in a chemical oxidation treatment solution with the following composition at 90°C.
The circuit pattern was immersed in water for 2 minutes to form an oxide film on the circuit pattern.

Sodium hypochlorite 31 g/It Sodium hydroxide 15 g/, Q Sodium phosphate
12g/fi Next, the substrate on which the oxide film was formed was immersed in 5% by volume sulfuric acid at room temperature for 2 minutes to remove the black oxide film formed on the surface, thoroughly washed with water, and dried at 80°C for 30 minutes. I did it.

The photosensitive element obtained in (2) was vacuum laminated on this substrate, exposed to light, annealed at 80° C. for 10 minutes, and then spray developed using 1,1,1-trichloroethane.

After development, dry at 80℃ for 5 minutes and irradiate with ultraviolet light (2.5J/
cm2) and heating at 150° C. for 30 minutes to form a protective film on the substrate.

Next, the substrate was immersed in an electroless copper plating bath (pH 12, 0° C., 60° C.) for 16 hours, and the through holes and component holes were plated with copper to a thickness of about 30 μm. After plating, wash thoroughly with water, dry at 80°C for 10 minutes, and then dry at 130°C for 12 minutes.
Heat treatment was performed for 0 minutes.

During this −= series of electroless plating treatments, the protective film deteriorates,
No blistering or peeling occurred, and no plating solution entered between the resist and the circuit pattern.

In addition, the through-holes of the printed circuit board manufactured through the above process have good plating, and no problems occur in appearance or solder tests (260°C, 10 seconds, 5 cycles or more). There wasn't.

(Example 2) An electroless copper plating solution was used to remove the oxide film in Example 1. That is, a substrate with an oxide film formed on a circuit pattern is immersed in an electroless copper plating solution adjusted to pH 12, 5, and 40°C for 5 minutes while sufficiently vibrating to remove the oxide film and thoroughly remove the oxide film. It was washed with water and dried at 80°C for 30 minutes.

Other steps were carried out in accordance with Example 1 to produce a printed circuit board. The effect was similar to that of Example 1.

(Example 3) As the plating resist in Example 1.2, Photec SR, -3000 (manufactured by Hitachi Chemical) was used to produce a printed circuit board according to the procedure of Examples 1 and 2.

After plating, the printed circuit board was inspected in detail, but no peeling of the resist or infiltration of the plating solution between the resist and the circuit pattern occurred. I ran a solder test on this circuit board and no problems occurred.

(Comparative Example 1) The oxide film removal step in Example 1.2 was omitted, a resist was laminated, and electroless copper plating was performed in the same manner as in Example 1 to produce a substrate.

In this method, the electroless copper plating solution penetrated into the bonding surface between the resist and the circuit pattern, causing discoloration of the circuit pattern.

(Comparative Example 2) Instead of roughening the circuit pattern surface by chemical oxidation performed in Example 1.2, the circuit pattern surface was roughened by mechanical polishing, and a substrate was produced in the same manner as in Example 1. did.

In this method, peeling from the substrate was observed in some parts of the fine circuit pattern.

(Comparative Example 3) A substrate on which electroless copper plating was formed (before roughening the circuit pattern surface by chemical oxidation in Examples 1 and 2)
A resist was laminated on the substrate (as shown in FIG. 4), and Example 1,
A substrate was prepared by performing electroless copper plating in the same manner as in 2.

In this method, the plating solution entered the bonding surface between the resist and the circuit pattern, and the resist of the circuit pattern was peeled off when the cellophane tape was peeled off in the soldering heat resistance test.

(Comparative Example 4) After forming an oxide film on the circuit pattern in Example 2, a resist was immediately laminated, and electroless copper plating was performed in the same manner as in Example 2 to produce a substrate.

In this method, the electroless copper plating solution penetrated into the bonding surface between the resist and the circuit pattern, causing discoloration of the circuit pattern.

(Example 4) (1) Synthesis of bisphenol-type epoxy acrylate It was synthesized in the same manner as in Example 1.

(2) Preparation of photosensitive element It was produced in the same manner as in Example 1.

(3) Preparation of printed circuit board Through holes and component holes were formed in a glass epoxy copper clad laminate with a substrate thickness of 1.6 mm and a copper foil thickness of 18 μm. Next, after performing a catalyst treatment for electroless plating, the substrate was immersed in an electroless copper plating bath (pH 12, 5, 60° C.) for 1 hour to form a copper film of about 2 μm over the entire surface.

The entire surface of this substrate was plated with chromium to a thickness of about 1 μm at a current density of 50 A/dm 2 using a chromium plating bath having the composition shown below.

Chromic anhydride 250 g/l sulfuric acid
2. 5 g/It was then thoroughly washed with water, and an etching resist was applied to form a circuit pattern by a conventional method.

The photosensitive element obtained in (2) above was laminated on this substrate using a vacuum laminator. After laminating, it was exposed to light using a negative mask, and then heated at 80°C for 10 minutes.
Spray development was performed using 1,1.1-trichloroethane (20° C., 80 seconds). After development, dry at 80°C for 5 minutes, and use a high pressure mercury lamp (sow/cm) to
It was irradiated with J/cm2. Thereafter, heat treatment was performed at 150° C. for 30 minutes to form a protective film.

Next, the substrate was immersed in an electroless copper plating bath (pH 12, 0, 60° C.) for 12 hours, and copper plating with a thickness of about 20 μm was applied to the through holes and component holes. After electroless plating treatment, after thoroughly rinsing with water, drying at 80℃ for 10 minutes,
Further, heat treatment was performed at 130° C. for 60 minutes.

During this series of electroless plating treatments, the protective film did not deteriorate, blister, or peel off, and exhibited sufficient resistance. Furthermore, the through holes of the printed circuit board produced through the above steps were well plated. As a solder heat resistance test, it was immersed in a solder bath at 255 to 265°C for 10 seconds, but no peeling of the plating film occurred.

(Example 5) Photec S was used as the plating resist in Example 4.
Example 4
A printed circuit board was fabricated using the following steps.

After plating, the printed circuit board was inspected in detail, but no peeling of the resist or infiltration of the plating solution between the resist and the circuit pattern occurred. I conducted a solder test on this circuit board and no problems occurred.

Comparative Example 5) A printed circuit board was produced in the same manner as in Example 4, except that the resist was laminated without performing the chromium plating in Example 4.

In this method, during electroless copper plating, the plating solution entered the interface (joint surface) between the resist and the circuit pattern, causing corrosion of the circuit pattern. Additionally, when peeling off cellophane tape during a solder heat resistance test, the resist on the circuit pattern peeled off.

(Comparative Example 6) Instead of forming a metal layer other than copper in Example 4, the surface of the circuit pattern was roughened by mechanical polishing, and a substrate was produced in the same manner as in Example 4.

In this method, some of the fine circuit patterns were observed to peel off from the substrate.

〔Effect of the invention〕

As described above, according to the present invention, the adhesion between the resist and the circuit pattern during electroless copper plating is improved, so that high-density printed circuits having small-diameter through holes and high-density inter-bin wiring can be fabricated. Boards can be manufactured reliably.

[Brief explanation of drawings]

1 to 9 are cross-sectional views showing the manufacturing process of a high-density printed circuit board according to the first invention in order of process, and FIGS. 10 to 17
The figures are cross-sectional views showing the manufacturing process of the high-density printed circuit board according to the second invention in order of process. In the figure, 1 and 11 are copper-clad laminates, 2.12 is a through hole, 3.13 is a plating core, 4.14 is the first electroless copper plating layer, 5.15 is a circuit pattern, and 6 is an oxide film. ,7
．． 17 is photoresist, 8.18 is resist pattern,
Reference numeral 9.19 indicates a second electroless copper plating layer, and reference numeral 10.20 indicates an electroless copper plating layer having a predetermined thickness.

Claims (2)

[Claims] (1) A process of forming through holes in a copper-clad laminate, a process of subjecting the laminate to activation treatment for electroless copper plating, and applying electroless copper plating to the surface of the laminate to a predetermined thickness. A step of applying a thin layer to form a first electroless copper plating layer, a step of forming a circuit pattern on the surface of the laminate by etching, a step of forming an oxide film on the surface of the circuit pattern by chemical oxidation, A step of dissolving and removing the oxide film by chemical treatment, a step of attaching a photoresist that is resistant to electroless copper plating solution to the laminate, a step of forming a resist pattern on the laminate using photolithography, A step of forming a second electroless copper plating layer on the first electroless copper plating layer on at least the inner surface of the through hole of the laminate, and forming an electroless copper plating layer of a predetermined thickness with both layers. A method for manufacturing a high-density printed circuit board, comprising: (2) A process of forming through holes in a copper-clad laminate, a process of subjecting the laminate to activation treatment for electroless copper plating, and applying electroless copper plating to the surface of the laminate to a predetermined thickness. A step of forming a first electroless copper plating layer by applying a thin layer, a step of forming a metal layer other than copper that has excellent adhesion with the resin layer on the surface of the laminate, and a step of forming a metal layer on the surface of the laminate. A step of etching the layer to form a circuit pattern, a step of attaching a photoresist that is resistant to electroless copper plating solution to the laminate, and a step of forming a resist pattern on the laminate using photolithography technology. , a second electroless copper plating layer is formed on the first electroless copper plating layer on at least the inner surface of the through hole of the laminate, and both plating layers and the metal layer have a predetermined thickness of electroless copper. A method for manufacturing a high-density printed circuit board, comprising the step of forming a plating layer.