JPH0217697A - Manufacture of high-density printed circuit board - Google Patents

Abstract

PURPOSE:To manufacture a high-density printed circuit board extremely easily by using a photo-resist having resistance against an electroless copper plating solution as a masking resist at the time of electroless copper plating. CONSTITUTION:A high-density printed circuit board is manufactured through the following six processes. A through-hole is bored to a copper-clad laminated board 1. Activation treatment for electroless copper plating is executed. Circuit patterns 4 are formed by employing an etching resist. The etching resist is removed, and a photo-resist 5 having resistance against an electroless copper plating solution is mounted. The photo-resist 5 is exposed and developed and a resist pattern 6 is shaped. The internal surface of the through-hole 2 is electroless copper-plated in specified thickness, thus forming a plating layer 7. The photo-resist 5 mainly comprises three kinds of 10-60 pts. polyurethane polyacrylate, 5-45 pts. bisphenol type epoxy acrylate and a 20-60 pts. linear polymer compound and has excellent alkali resistance. The density of small- diameter through-holes and wirings among pins can be increased.

Description

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

[Conventional technology]

When applying copper plating to the inner surface of the through-hole of a multilayer board,
Conventionally, plating core treatment was applied to perforated copper-clad laminates.
A method has been used in which electroless copper plating is performed thinly 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 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 a circuit pattern.
Not only does etching take time, but pattern accuracy may be reduced due to side etching or undercuts.

For this reason, electroless copper plating is not suitable for manufacturing high-density printed nameplates.

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 making through holes, followed by plating nucleation treatment, and then applying a plating-resistant solder resist to perform 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, Japanese Patent Application Laid-open 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-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.

In other words, the method disclosed in JP-A-48-8063 improves the precision 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. do.

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

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 portions is performed by screen printing. However, there are limits to the accuracy of this screen printing. Therefore, this method cannot cope with small-diameter through holes and an increase in the number of wires between pins, making it difficult to produce a high-density printed circuit board.

This invention was made by focusing on these conventional problems, and by using a photoresist that is resistant to electroless plating solution as a masking resist when performing electroless copper plating, small-diameter through holes and It is an object of the present invention to provide a method for manufacturing a high-density printed circuit board that can easily manufacture a high-density printed circuit board having high-density wiring between pins.

[Means to solve the problem]

The method for manufacturing a high-density printed circuit board according to the present invention includes the following six steps. Each step will be explained with reference to FIGS. 1 to 6 which schematically show them.

(1) Step of drilling through-holes 2 in the copper-clad laminate l that has been subjected to inner layer processing, as shown in Fig. 1.

(2) A step of applying activation treatment for electroless copper plating to the copper-clad laminate 1 with through holes 2 drilled, that is, the same laminate 1 is subjected to treatments such as degreasing, oxide film removal, and roughening. After that, as shown in FIG. 2, there is a step of applying plating nuclei 3 (usually palladium).

(3) A step of forming a circuit pattern 4 on the surface of the activated copper-clad laminate 1 using an etching resist, as shown in FIG. 3.

(4) After removing the etching resist, as shown in FIG. 4, a step of attaching a photoresist 5 that is resistant to electroless copper plating solution.

(5) Expose the photoresist 5 using photolithography technology,
This is followed by a step of developing and forming a resist pattern 6 as shown in FIG.

(6) At least on the inner surface of the through hole 2, as shown in FIG. 6, perform electroless copper plating to a predetermined thickness to form an electroless copper plating layer 7 (thickness is 15 μm or more from the viewpoint of reliability). Process.

Note that the photoresist 5 used for masking during electroless copper plating used in steps (4) to (6) is used as a solder mask.

The photoresist 5 used in this invention needs to have resistance to electroless copper plating solution.

Generally known dry film resists for etching, potresists for solder masks, etc. have insufficient alkali resistance and are difficult to use in the present invention.

Examples of photoresists that can be used in this invention include:
Examples include those composed of the following components (a) to (e). That is, (a) General formula (wherein is 1 or 2.l is 1 or 2.m is 1 or 2.
P1 to (5-k) are hydrogen atoms or methyl groups.

Qs ~ (4-1) ha hydrogen atom or methyl group, R, ~ (5
- m) is a hydrogen atom or a methyl group, n is an integer of 0 to 20)) and (meth)acrylic acid monoester of dihydric alcohol are reacted, and in one molecule 10 to 60 parts of a polyurethane (poly(meth)acrylate) having two or more (meth)acryloyl groups and two or more urethane bonds.

(b) Bisphenol type epoxy (meth)aclate 5
~45 parts, (C) 20 to 60 parts of a linear polymer compound, (d) 1 to 10 parts of a polymerization initiator that generates free radicals upon irradiation with light, and (e) optionally added. colorants, adhesion improvers,
A photoresist may be mentioned which is composed of a thermal polymerization stabilizer, and the total amount of (a) + (b) and (c) is 100 parts. This photoresist has particularly good alkali resistance,
Enables implementation of this invention.

The above-mentioned photoresist is described in detail in Japanese Patent Application No. 1987 (AP841 s 7) filed on the same day by the same inventor, Photosensitive Resin Composition and Photosensitive Element.

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 in the case of a small diameter through hole 2 of 0.3 square centimeters 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 holes 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 is used as a resist for electroless copper plating, and this is exposed and developed using photolithography technology to perform patterning for masking, so it is possible to create small-diameter through holes and wiring between bins. High densification is possible and therefore high density printed circuit boards can be easily produced.

〔Example〕

The present invention will be described in detail below.

Example 1 (1) Synthesis of polyurethane polyacrylate General formula (1
) as the polyvalent aromatic isocyanate, Millionate MR-400 (manufactured by Nippon Polyurethane Kogyo Co., Ltd.)
450 g and 2-hydroxyethyl acrylate 4
00 g and 400 g of methyl ethyl ketone were placed in a No. 24 flask, 1.9 g of zinc octylate was added thereto, and the mixture was reacted at 60° C. for 8 hours.

At this time, to prevent polymerization, air was added at 1 ml/min.
The reaction was carried out while blowing at a flow rate of . The NGO was measured by a conventional method, and the reaction was terminated when it became 0.2 or less. The obtained polyurethane polyacrylate was 7
It contained 0% solids by weight.

(2) Synthesis of bisphenol-type epoxy acrylate Epicote 828 (manufactured by Yuka Shell Co., Ltd., epoxy equivalent: 19
0 ) 570 g (3 equivalents) and 201 acrylic acid
g (28 mol) into a 1 liter flask, and 0.77 g (0.1% by weight) of methoxyphenol as a polymerization inhibitor.
, 3.9 g (0.5% by weight) of benzyldimethylamine were added, and the mixture was 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.

(3) Preparation of photosensitive element 40 parts of the urethane acrylate of (1) above (
Solid content: 60% (24 parts)) 25 parts of the epoxy acrylate from (2) above Methyl methacrylate/butyl methacrylate/methacrylic acid (weight ratio: 8o/1s/2 copolymer, molecular weight approximately 150,000 40 parts 2- Ethylanthraquinone 4.5 parts p
-Methoxyphenol 0.1 part Methyl ethyl ketone 45 parts A solution of a 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 then heated at room temperature for 20 minutes and at 70°C for 1 hour.
The photosensitive element was dried at 100'C for 5 minutes to obtain a photosensitive element having a photosensitive resin composition layer thickness of about 70 μm.

(4) 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 catalyst treatment for electroless plating,
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, then heated at 80°C for 10 minutes, and then spray developed using 1,1.1-)lichloroethane (20°C, 80 seconds). After development, heat at 80°C for 5
Dry for 2 minutes using a high pressure mercury lamp (soW/an). ．． It was irradiated with 5 J/ad. Thereafter, heat treatment was performed at 150° C. for 30 minutes to form a protective film.

Next, electroless copper plating bath (pH 12,0,80'C)
The substrate was immersed in water for 16 hours, and copper plating with a thickness of about 25 μm was applied to the through holes and component holes. After electroless plating, it was thoroughly washed with water, dried at 80°C for 10 minutes, and further heat-treated at 130°C for 60 minutes.

During this series of electroless plating processes, the protective film deteriorates.

No blistering or peeling occurred, and sufficient resistance was exhibited.

The through holes of the printed circuit board produced through the above steps were plated with good quality.

10 in a solder bath at 255-265°C as a solder heat resistance test.
Although it was immersed for a second, no peeling of the plating film occurred.

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

Example 2 (Synthesis of υ bisphenol type epoxy acrylate Epicoat 5050 (manufactured by Yuka Shell Co., Ltd., brominated epoxy resin, epoxy weight 1390) 390 g (1
), 67 g (0.94 equivalent jl) of acrylic acid and 460 g of methyl ethyl ketone were placed in 14 flasks.
Epoxy acrylate was obtained in the same manner as in Example 1 by adding 0.45 g of nonaxyphenol and 22 g of imidazole as a polymerization inhibitor. The product contained approximately 50% solids by weight.

(2) Preparation of photosensitive element Urethane acrylate of Example 1: 66 parts (solid part: 40 parts) Epoxy acrylate of (1) above: 30 parts (
Solid portion: 15 parts) Copolymer of methyl methacrylate and methyl acrylate (heavy weight ratio 1/20, molecular weight approximately 150,000) 40 parts 2-ethylanthraquinone 5 parts I)-methoxyphenol 0.1 part Phthalocyanine green
O-4-part benzotriazole
0.1 part methyl ethyl ketone
A solution of 40 parts of the photosensitive resin composition having the above composition was prepared.

This resin liquid was applied onto a polyethylene terephthalate film with a thickness of 25 μm, and then heated at 70C for 20 minutes at room temperature.
The photosensitive element was dried at 100° C. for 5 minutes to obtain a photosensitive element having a photosensitive resin composition layer thickness of about 70 μm.

(3) Preparation of printed circuit board A printed circuit board was prepared using the same substrate as in Example 1 and through the same steps. During a series of electroless plating treatments, the protective film did not deteriorate, blister, or peel off, and showed sufficient resistance.

The through holes of the printed circuit board produced through the above steps were plated with good quality.

10 in a solder bath at 255-265°C as a solder heat resistance test.
Although it was immersed for a second, no peeling of the plating film occurred.

The photoresist was also stable, with no cracking or peeling observed, and it was found to be suitable for use as a solder mask.

Through-holes and component holes were formed in a glass epoxy copper-clad laminate with a comparative example board thickness of 1.6 μm * copper foil thickness of 18 μm,
After performing a catalyst treatment for electroless copper plating, a wiring pattern was formed according to a conventional method.

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

- After 1 to 6 hours, the substrate was pulled up and the copper precipitation was examined, and although the copper precipitation was good, the masking protective film turned white. Furthermore, when electroless copper plating was continued,
Peeling of the protective film and penetration 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, □Free! can be used as a masking resist when performing electroless copper plating. Since a photoresist that is resistant to cast copper plating solution is used, high-density printed circuit boards with small-diameter through holes and high-density wiring between pins can be manufactured extremely easily.

[Brief explanation of the drawing]

1 to 6 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 circuit pattern, 5 is a photoresist, 6 is a resist pattern, and 7 is an electroless copper plating layer.

Claims (1)

[Claims] 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,
A process of forming a circuit pattern on the surface of the laminate by etching, a process of attaching a photoresist that is resistant to electroless copper plating solution to the laminate, and a process of forming a resist pattern on the laminate using photolithography. The process of
A method for manufacturing a high-density printed circuit board, comprising the step of applying electroless copper plating to at least the inner surface of the through hole of the laminate to form an electroless copper plating layer of a predetermined thickness.