JPH0561796B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a high-density printed circuit board, particularly a method for manufacturing the same circuit board that includes a step of selectively plating only the inner surfaces of through holes. It is related to.

[Conventional technology]

When applying copper plating to the inner surface of a through-hole in a multilayer board, conventionally, a hole-drilled copper-clad laminate is subjected to plating nucleation treatment, and a thin layer of electroless copper plating is applied to obtain electrical continuity. , a method of plating to a desired thickness by electroplating has been used.

In this method, as the mounting density increases, the through-hole diameter decreases, and as the number of laminated layers increases and the board thickness increases, the electroplating thickness becomes thicker near the opening of the through-hole and thinner as it goes deeper. There was a problem. However, this problem could be solved 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 the circuit pattern, making etching time-consuming. In addition, pattern accuracy may be lowered due to sand etching or undercutting.
For this reason, electroless copper plating has been unsuitable for manufacturing high-density printed circuit boards.

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

For example, in Japanese Patent Application Laid-Open No. 48-8063, pattern etching is performed after making a through hole.
A method has been proposed in which a plating nucleation treatment is then applied, and then a plating-resistant solder resist is applied to perform electroless plating.

In addition, Japanese Patent Application Laid-open No. 48-8062 discloses that a perforated copper-clad laminate is subjected to plating nuclear treatment, pattern etched, and then coated with a plating-resistant solder resist, and then electroless copper plated. A method for performing this has been proposed.

Furthermore, JP-A No. 61-70790 discloses that a perforated 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-holes, and pattern etching is performed. A method has been proposed in which after applying a plating-resistant 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.

In other words, although the method disclosed in JP-A-48-8063 improves the accuracy of copper wiring patterns, the plating nuclear metal particles remain on the surface of the base material, which causes migration and reduces the insulation between circuit patterns. do.

Furthermore, in the method disclosed in Japanese Patent Application Laid-open No. 48-8062, plating nuclei may be detached during various processing steps, or their functionality may deteriorate.

Furthermore, JP-A-48-8062 and JP-A-61-
In the method of Publication No. 70790, 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, in this method,
It is difficult to manufacture high-density printed circuit boards because it cannot accommodate small-diameter through holes and an increase in the number of wires between pins.

This invention was made by focusing on such conventional problems, and it is a photoresist that is resistant to electroless plating solution and is made of a specific composition as a masking resist when performing electroless copper plating. death,
Furthermore, by using this in the form of a dry photosensitive element, a method for manufacturing the same circuit board is provided, which makes it possible to easily manufacture a high-density printed circuit board having small-diameter through holes and high-density wiring between pins. The purpose is to

[Means to solve the problem]

The method for manufacturing a high-density printed circuit board according to the present invention includes the following seven steps. Each step will be explained with reference to FIGS. 1 to 7 which schematically show them.

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

(2) a step of applying activation treatment for electroless copper plating to the copper-clad laminate 1 with the through holes 2 formed therein;
That is, after the laminate 1 is subjected to treatments such as degreasing, oxide film removal, and roughening, plating nuclei 3 (usually palladium) are applied as shown in FIG.

(3) Electroless copper plating is applied to the surface of the activated copper clad laminate 1 to a thickness thinner than a predetermined thickness (usually about 1 to 5 μm), as shown in Figure 3. Step of forming copper plating layer 4.

(4) A circuit pattern 5 is formed on the surface of the thin electroless copper plating layer 4 by etching (tenting method, soldering method, etc.) as shown in FIG.
The process of forming.

(5) A step of attaching a photoresist 6 resistant to electroless copper plating solution to the copper-clad laminate 1 from above the circuit pattern 5, as shown in FIG.

(6) A step of exposing the photoresist 6 using photolithographic technology and then developing it to form a resist pattern 7 as shown in FIG.

(7) Electroless copper plating is performed on at least the inner surface of the through hole 2 as shown in FIG. 7, and a second electroless copper plating layer 8 is formed on the first electroless copper plating layer 4. (15 μm or more from the viewpoint of reliability), and forming an electroless copper plating layer 9 of a predetermined thickness on both layers 4 and 8.

Note that the photoresist 6 used for masking during electroless copper plating used in steps (5) to (7) is used as a solder mask.

The photoresist 6 used in this 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.

Photoresists that can be used in this invention include:
For example, those composed of the following components (a) to (e) can be mentioned. That is, (a) General formula (In the formula, k is 1 or 2, l is 1 or 2, m is 1
or 2, P ₁ to (5-k) are hydrogen atoms or methyl groups, Q ₁ to (4-l) are hydrogen atoms or methyl groups, R ₁ to (5-m) are hydrogen atoms or methyl groups,
n is an integer of 0 to 20) and a (meth)acrylic acid monoester of a dihydric alcohol. and 10 to 60 parts of polyurethane poly(meth)acrylate having two or more urethane bonds, (b) 5 to 45 parts of bisphenol type epoxy (meth)acrylate, (c) 20 to 60 parts of a linear polymer compound, and (d) 1 to 10 parts of a polymerization initiator that generates free radicals upon irradiation with light, and (e) a colorant, an adhesion improver, and a thermal polymerization stabilizer added as necessary ( A photoresist in which the total amount of a) + (b) + (c) is 100 parts can be mentioned. This photoresist has particularly good alkali resistance, making it possible to carry out the present invention.

Regarding the above photoresist, please refer to Japanese Unexamined Patent Publication No.
It is explained in detail in the -105240 publication.

The above-mentioned photoresist can be applied as a liquid resist, but since the liquid resist enters the inside of the through hole 2 during application, it is difficult to completely remove it by development. In particular, this is not possible for small-diameter through holes 2 of 0.3 mm or less. Therefore, when applying it as a liquid resist, it must be processed through complicated process steps, such as resist application by a hole-filling method. Therefore, this method is not preferred from the point of view of efficient printed circuit manufacturing.

However, this problem can be avoided by drying the liquid resist to form a film and laminating the film. This is because if the film is laminated, there is no fear that the resist will enter the through hole 2, and it can be completely removed by development.

Therefore, in the present invention, it is preferable to use the photoresist having the above composition in the form of a dry photosensitive element.

If the photosensitive element is processed using a vacuum laminator, air will not be trapped between the wires, so that it can be mounted on the laminate 1 with good wire coverage.

[Effect]

In this invention, a photoresist with high alkali resistance for electroless copper plating is composed of the above composition, and is used in the form of a dry photosensitive element, which is then exposed to light using photolithography technology.
Since patterning for masking is performed by development, and since the first electroless copper plating layer is thin, pattern formation by etching is easy, so it is possible to create small-diameter through holes and high-density wiring between pins. , and therefore high-density printed circuit boards can be easily created.

〔Example〕

Examples of the present invention will be described below.

Example 1 (1) Synthesis of polyurethane polyacrylate As a polyvalent aromatic isocyanate represented by general formula (1), 450 g of Millionate MR-400 (manufactured by Nippon Polyurethane Industry Co., Ltd.), 400 g of 2-hydroxyethyl acrylate, and methyl ethyl ketone were used.
400g of the above were placed in flask 2, 1.9g of zinc octylate was added thereto, and the mixture was reacted at 60°C for 8 hours. At this time, the reaction was carried out while blowing air at a flow rate of 1 ml/min to prevent polymerization. NCO was measured using a conventional method, and 0.2
The reaction was determined to have ended when the following values were reached. The polyurethane polyacrylate obtained contained 70% by weight solids.

(2) Synthesis of bisphenol type epoxy acrylate Epicote 828 (manufactured by Yuka Ciel Co., Ltd., epoxy equivalent: 190) 570 g (3 equivalents) and acrylic acid 201
g (2.8 mol) into flask 1, and 0.77 g (0.1 mol) of methoxyphenol as a polymerization inhibitor.
weight%), benzyldimethylamine 3.9g (0.5
% by weight) and reacted at 90°C for 6 hours.
After that, the acid value was measured by the usual method, and the value was 1.
The end point was defined as:

(3) Preparation of photosensitive element Urethane acrylate from (1) above (solid content is 60%
(24 parts)) 40 parts Epoxy acrylate of (2) above 25 parts Methyl methacrylate, butyl methacrylate, methacrylic acid (weight ratio: 80/18/2 copolymer, molecular weight approximately 150,000 40 parts 2-ethylanthraquinone 4.5 Part p-methoxyphenol 0.1 part Methyl ethyl ketone 45 parts A solution of the photosensitive resin composition having the above composition was prepared.

This resin solution was applied onto a polyethylene terephthalate film with a thickness of 25 μm, and dried at room temperature for 20 minutes, at 70°C for 10 minutes, and at 100°C for 5 minutes. Got the sex element.

(4) Fabrication of printed circuit board Through holes and component holes were formed in a glass epoxy copper clad laminate with a board thickness of 1.6 mm and a copper foil thickness of 18 μm. Next, after performing a catalyst treatment for electroless plating, an electroless copper plating bath (PH
The substrate was immersed for 2 hours at 12.5°C and 60°C, and a copper film of approximately 3 μm was applied to the entire surface.

Then, an etching resist was applied to form a wiring pattern.

The photosensitive element obtained in (3) above was laminated on this substrate using a vacuum laminator. After lamination, it was exposed using a negative mask and then heated at 80℃.
After heating for 10 minutes, spray development was performed using 1,1,1-trichloroethane (20°C,
80 seconds). After development, it was dried at 80° C. for 5 minutes and irradiated with 2.5 J/cm ² using a high-pressure mercury lamp (80 W/cm). Thereafter, heat treatment was performed at 150° C. for 30 minutes to form a protective film.

Next, electroless copper plating bath (PH12.0, 60℃)
The board was immersed in water for 12 hours, and copper plating with a thickness of approximately 20 μm was applied to the through holes and component holes. After electroless plating treatment, thoroughly rinse with water and heat to 80℃.
The film was dried at 130° C. for 10 minutes, and then heated at 130° C. for 60 minutes. During this series of electroless plating processes, the protective film does not deteriorate, blister, or peel.
It showed sufficient resistance.

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.
The photoresist was also stable, with no cracks or peeling observed, and it was found that it could be used satisfactorily as a solder mask.

Example 2 (1) Synthesis of bisphenol type epoxy acrylate Epicote 5050 (manufactured by Yuka Ciel Co., Ltd., brominated epoxy resin, epoxy equivalent: 390) 390 g
(1 equivalent), 67 g (0.94 equivalent) of acrylic acid, and 460 g of methyl ethyl ketone were placed in flask 1, and methoxyphenol was added as a polymerization inhibitor.
Adding 0.45g and 2.2g of imidazole, Example 1
Epoxy acrylate was obtained in the same manner as above. The product contained approximately 50% solids by weight.

(2) Preparation of photosensitive element Urethane acrylate of Example 1 (solid part is 40
66 parts epoxy acrylate of (1) above (solid part is 15
30 parts Methyl methacrylate/methyl acrylate copolymer (weight ratio 80/20/, molecular weight approx. 150,000) 40 parts 2-ethylanthraquinone 5 parts p-methoxyphenol 0.1 part Phthalocyanine green 0.4 part Benzotriazole 0.1 40 parts methyl ethyl ketone A solution of the photosensitive resin composition having the above composition was prepared.

This resin solution was applied onto a polyethylene terephthalate film with a thickness of 25 μm, and dried at room temperature for 20 minutes, at 70°C for 10 minutes, and at 100°C for 5 minutes. Got the sex element.

(3) Production of printed circuit board A printed circuit board was produced using the same board as in Example 1 and through the same steps. During this series of electroless plating treatments, the protective film did not deteriorate, blister, or peel, and exhibited sufficient resistance.

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.
The photoresist was also stable, with no cracks or peeling observed, and it was found that it could be used satisfactorily as a solder mask.

Comparative Example After forming through holes and component holes in a glass epoxy copper clad laminate with a substrate thickness of 1.6 mm and a copper foil thickness of 18 μm, and performing catalyst treatment for electroless copper plating, A copper film of approximately 3 μm was applied to the entire surface using the same plating solution. Then, a wiring pattern was formed according to a conventional method.

A solvent-developed dry film for etching was laminated on the obtained substrate using a vacuum laminator, and a masking pattern was prepared by a conventional method. Thereafter, in the same manner as in Example 1, irradiation in a high-pressure mercury furnace and heat treatment were performed to perform electroless copper plating.

After 4 to 6 hours, the substrate was pulled up and the copper deposition properties were examined, and although the copper deposition was good, the masking protective film was whitened. Furthermore, when electroless copper plating was continued, peeling of the protective film and seepage of the plating solution occurred. From this, it has become clear that photoresists for etching cannot be applied to this invention.

〔Effect of the invention〕

As described above, according to the present invention, a photoresist resistant to an electroless copper plating solution is composed of the above-mentioned specific composition and used as a masking resist when performing electroless copper plating. Because it is used in a dry photosensitive element state, and because the thickness of the first electroless copper plating layer is small, pattern formation by etching is less affected than by conventional methods. High-density printed circuit boards with high-density and high-density inter-bin wiring can be manufactured very easily.

[Brief explanation of drawings]

1 to 7 are cross-sectional views showing the method of manufacturing a high-density printed circuit board according to the present invention in order of steps. In the figure, 1 is a copper-clad laminate, 2 is a through hole, 3 is a plating core, 4 is a first electroless copper plating layer, 5 is a circuit pattern, 6 is a photoresist, 7 is a resist pattern, 8 is a second 9 represents an electroless copper plating layer having a predetermined thickness.

Claims (1)

[Claims] 1. A step of forming a through hole in a copper-clad laminate, a step of subjecting the laminate to activation treatment for electroless copper plating, and a step of applying electroless copper plating to the surface of the laminate. a step of forming a first electroless copper plating layer by applying a thinner than a predetermined thickness, a step of forming a circuit pattern on the surface of the laminate by etching, and a step of applying an electroless copper plating solution to the laminate. a step of applying a resistant photoresist, a step of forming a resist pattern on the laminate using a photolithography technique, and a step of applying a resist pattern to the laminate on the first electroless copper plating layer on the inner surface of at least the through hole of the laminate. applying electroless copper plating to form a second electroless copper plating layer;
forming an electroless copper plating layer with a predetermined thickness in both layers, and the photoresist has the following (a) to (e)
An alkali-resistant photoresist consisting of the following components and having a total of 100 parts of the components (a), (b), and (c), which is applied in the state of a dry photosensitive element. A method for manufacturing a high-density printed circuit, characterized by: (a) General formula (In the formula, k is 1 or 2, l is 1 or 2, m is 1
or 2, P ₁ to (5-k) are hydrogen atoms or methyl groups, Q ₁ to (4-l) are hydrogen atoms or methyl groups, R ₁ to (5-m) are hydrogen atoms or methyl groups,
n is an integer from 0 to 20) and a (meth)acrylic acid monoester of a dihydric alcohol. and 10 to 60 parts of polyurethane poly(meth)acrylate having two or more urethane bonds. (b) 5 to 45 parts of bisphenol type epoxy (meth)acrylate. (c) 20 to 60 parts of a linear polymer compound. (d) 1 to 10 parts of a polymerization initiator that generates free radicals upon photoirradiation. (e) Colorants, adhesion improvers, and thermal polymerization stabilizers added as necessary.