JPS5952557B2 - Manufacturing method for printed wiring boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a printed wiring board, and more particularly, to a method for manufacturing a printed wiring board in which a circuit is formed in a circuit forming process that includes at least electroless plating. The present invention provides a method for manufacturing a printed wiring board in which an insulating substrate containing a catalyst is chemically etched and strong adhesion is obtained with the deposited electroless plating layer.

In recent years, as a method for manufacturing printed wiring boards, a method (additive method) in which a circuit is formed in a circuit forming step that includes at least electroless plating has become widely used.

This additive method involves chemically etching the insulating substrate and then coating the area other than where the circuit will be formed with electroless plating resist, or coating the area of the insulating substrate with electroless plating resist other than the area where the circuit will be formed. There is a method in which a circuit is formed by post-chemical etching and immersion in an electroless plating solution (full additive method), and a method in which an insulating substrate is chemically etched and immersed in an electroless plating solution to form an electroless plating layer on the entire surface of the board. After that, the area other than the area where the circuit will be formed is coated with electroplating resist, the circuit area is thickly plated by electroplating, the resist is peeled off, and the electroless plating layer other than the circuit area is removed by quick etching ( Semi-additive method) is being used.

In both of these methods, electroless plating is applied after chemically etching the insulating substrate. In this case, an electroless plating catalyst is applied in advance to the synthetic resin layer of the insulating substrate, at least in the part where the circuit will be formed. It is effective and reasonable to include it. That is, the electroless plating catalyst is preliminarily contained throughout the insulating substrate, only in the surface layer of the insulating substrate, and further only in the portion of the insulating substrate where the circuit is formed.

In order to deposit electroless plating, the galvanic plating catalyst must be exposed in an active state on the surface of the synthetic resin, but when contained in the synthetic resin layer, the catalyst particles are usually wrapped and surrounded by the synthetic resin. and is not in an active state.

An effective way to expose the plating catalyst is to etch the surface of the synthetic resin with a chemical etching solution.This process also creates a roughened surface that allows the deposited plating to firmly adhere to the synthetic resin layer. It is also important.

Oxidizing acid solutions are generally used as chemical etchants to roughen the surface as a pre-treatment for electroless plating, and sulfuric acid monosulfate-based etchants etch the synthetic resin layer to create an uneven and roughened shape on the surface. It is known.

However, although this system produces a good roughened shape, it not only exposes the plating catalyst in the synthetic resin, but also dissolves or inactivates it, which significantly impedes the precipitation of electroless plating, or On the other hand, the surface of the synthetic resin layer that forms the conductive circuit is easily oxidized and roughened and uneven. For example, diene-based synthetic rubber is contained in the synthetic resin in an amount of 50% by weight or more. In the case of a diene-based synthetic rubber-phenol resin adhesive, etc., it is also possible to use a taromtohydroborfluoric acid-based etching solution without using a chromic acid monosulfuric acid-based etching solution.

However, a substrate having a synthetic resin layer containing a large amount of diene-based synthetic rubber is undesirable because it lowers the electrical properties, heat resistance, or surface hardness of the printed wiring board, resulting in practical limitations. A chromic acid monobofluoric acid-based etchant does not damage the exposed plating catalyst in the synthetic resin, but as the required performance of printed wiring boards becomes more sophisticated, the content of diene-based synthetic rubber in the substrate synthetic resin is reduced. It is desirable to include it or not include it.

The present invention has been made in view of the above points.The present invention is made by chemically etching an insulating substrate containing an electroless plating catalyst at least in a portion where a circuit is to be formed, and forming a circuit in a circuit forming process including at least electroless plating. In the method for manufacturing printed wiring boards, after an insulating substrate is chemically etched with a chromic acid or sulfuric acid-based etching solution,... It is characterized by chemical etching using a chromic acid-hydroboric acid based etching solution.

That is, the present invention involves chemically etching an insulating substrate synthetic resin layer containing an electroless plating catalyst with a chromium sulfuric acid-based etching solution in a chemical etching process to create a surface roughness suitable for plating, and then chemically etching the insulating substrate synthetic resin layer containing an electroless plating catalyst with a chromium sulfuric acid-based etching solution. By chemically etching with a hydrogen acid-based etching solution, a roughened uneven shape suitable for electroless plating is formed without impairing the catalytic action of the replating catalyst, and printing with excellent adhesive strength for plating conductive circuits. It is possible to manufacture wiring boards in multiple sizes.

This method is particularly effective when the synthetic resin layer has a low content of diene-based synthetic rubber or a high content of thermosetting resin, that is, when printed wiring boards with high electrical properties, high heat resistance, and high surface hardness are required. be. As the plating catalyst contained in the synthetic resin of the insulating substrate, palladium or a palladium compound, or a mixture in which tin or a tin compound is used in combination with the palladium or palladium compound can be used.

In this case, the required catalyst content in the synthetic resin is 0.00
6% by weight or more and 10% by weight or less, preferably 0.02-2
It can be used in a range of % by weight, but since the amount used is very small, it can be used after being kneaded and dispersed in a synthetic resin using an organic solvent or adsorbed onto an inorganic filler. . As the chromic acid monosulfate-based etching solution, an aqueous solution of sulfuric acid and a chromium compound such as potassium dichromate, sodium dichromate, or chromic anhydride can be used, but hydrochloric acid or phosphoric acid can also be used in combination. Chromic acid-
As the hydroborofluoride-based etching solution, an aqueous solution of the above-mentioned chromium compound and hydroborofluoric acid can be used, and both can be used after being heated to 80° C. or lower. When chemically etching the synthetic resin layer, if parts other than those forming conductive circuits are to be covered with electroless plating resist, the plating resist should be applied to the necessary parts before that step, that is, after etching the entire synthetic resin layer of the insulating substrate. Alternatively, the synthetic resin layer of the conductive circuit forming portion may be etched after being coated with a plating resist.

In the latter case, it is preferable to use a hydrophobic resist that is not corroded by the etching solution. Example
1. An iron plate with predetermined through-holes for mounting parts is used in the core of the insulating board, and a synthetic resin layer for insulating the iron plate is made of epoxy resin and calcium carbonate as main components, and 15% by weight of diene-based synthetic rubber. Hereinafter, a powder coating (PC-10549 manufactured by Hitachi Chemical Co., Ltd.) containing a mixture of palladium chloride kneaded and dispersed in an epoxy resin solution as a catalyst for electroless plating was used to statically coat the iron plate. An insulating substrate was created by electro-coating and heat curing.

The pencil hardness (JISK54OO) of the surface of this substrate was 4H or higher. A thermosetting plating resist whose main component is epoxy resin is applied to the parts other than the circuit forming part of this board (4)
HGM-02BK (manufactured by Rikkasei Kogyo Co., Ltd.) was screen printed and cured by heating. Next, add 50 g of potassium dichromate, 50 g/l of chromic acid anhydride and 360 ml/l of concentrated sulfuric acid.
After immersion for 13 minutes at 40° ± 2°C in an etching solution consisting of an aqueous solution of
4 in an etching solution prepared by dissolving 11 in hydroborofluoric acid.
The sample was immersed at 0° C. for 7 minutes for etching, washed with water for neutralization, and then immersed in an electroless plating bath (4) CC4 bath manufactured by Rikkasei Kogyo Co., Ltd. for about 30 hours. A conductive circuit approximately 35 μm thick was formed. After washing with water and drying, the peel strength of the conductive circuit was measured based on JISC648l, and the results were 1.9 to 2.0 k.
It had a value of g/Cm. When observing the surface and cross section of the substrate synthetic resin after etching using a scanning electron microscope, it was found that approximately 1
A uniform uneven shape with a depth of 0 to 20 μm was formed. Comparative Example 1 The insulating substrate used in Example 1 was treated with only the etching solution of potassium dichromate, chromic anhydride, and concentrated sulfuric acid used in Example 1 at 40°C for 5 minutes.Those treated at 40°C for 20 minutes. , those treated at 50°C for 5 minutes and those treated at 50°C for 20 minutes were immersed in an electroless plating bath CC-14 bath.
No plating was deposited even after 0 and 50 hours. 1. Compared to Example 1, the surface and cross section of the synthetic resin after etching showed a uniform roughened shape with no particular difference other than slightly larger irregularities.

Example 2 As an insulating substrate, a laminated plate containing a plating catalyst (
4) Apply an adhesive (4) Ritsukasei Kogyo Co., Ltd. HA-04) containing a metal catalyst and containing a diene synthetic rubber-phenol resin as the main component to Ritsukasei Kogyo Co., Ltd. LP-147F) and dry. After curing, predetermined through holes were punched to create a substrate.

This adhesive-sided pencil. The hardness was about HB. Next, using an etching solution consisting of an aqueous solution of 15 g/1 potassium dichromate, 500 ml of concentrated sulfuric acid, and 15 ml of concentrated hydrochloric acid,
After etching by immersion at 0 ± 2°C for 10 minutes, the etching solution was prepared by dissolving 15 g of sodium dichromate and 5 g of chromic anhydride in 48% hydroborofluoric acid 11 at 40 ± 2°C.
It was immersed for a minute and etched, washed with water, neutralized, and then dried to remove water.

Next, portions other than the conductive circuit portion were coated with a hydrophobic ultraviolet curable resist by screen printing and cured, and then immersed in an electroless plating bath CC-4 for about 30 hours.

A conductive circuit approximately 35 μm thick was formed. The peel strength of the conductive circuit had a value of 2.0 to 2.1 kg/Cm. When the adhesive surface after etching was observed with a scanning electron microscope, it exhibited uniform unevenness with a depth of approximately 10 μm.

Reference Example 2 The insulating substrate used in Example 2 was electrolessly plated using only the etching solution consisting of potassium dichromate, concentrated sulfuric acid, and concentrated hydrochloric acid at 40°C for 10 minutes and at 40°C for 20 minutes. Although it was immersed in Bath CC-4, no plating was deposited even after 30 hours had passed.

The roughened uneven shape after etching was observed to be a uniform uneven shape similar to that seen in Example 1. As explained above, when forming a conductive circuit in a circuit formation process that includes at least electroless plating using an insulating substrate containing an electroless plating catalyst, a chromic acid monosulfuric acid-based etchant is used to synthesize the substrate. Although the resin layer was sufficiently etched, the plating catalytic effect was lost and the plating did not precipitate. By performing acid-based etching, it became possible to achieve the necessary and sufficient etching action and to deposit the plating.

Claims (1)

[Claims] 1. In a method of manufacturing a printed wiring board, in which an insulating substrate containing an electroless plating catalyst is chemically etched in at least a portion where a circuit is formed, and a circuit is formed in a circuit forming process including at least electroless plating, the insulating substrate is A method for manufacturing a printed wiring board, which comprises chemically etching with a chromic acid or monosulfuric acid based etchant, and then chemically etching with a chromic acid-fluoroboric acid based etchant.