JPH0352238B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a printed wiring board by a semi-additive method, and particularly to a method for manufacturing a printed wiring board with excellent circuit accuracy and through-hole reliability.

[Technical background of the invention and its problems] Conventionally, printed wiring boards are made of copper-clad laminates,
A resist pattern is printed using photoresist, ink resist, etc. on the part that will become the circuit pattern, and after this is cured, the exposed parts that are not printed are etched using an aqueous solution of ferric chloride or cupric chloride. The etched oil method, in which circuits are formed by removing the metal, was the mainstream.

In the etched oil method, 70% of the copper foil used as the material is
~80% of the board is removed by etching, which increases the cost of the board, and since the through-holes are connected using electrolytic copper plating, the copper foil on the front and back of the board is 70 to 80 microns thick due to plating. Processing takes a long time, causing phenomena such as undercuts and overhangs.
There are still problems, such as not being suitable for manufacturing printed wiring boards with high circuit precision.

In recent years, a semi-additive method has been rapidly developed in which only the necessary circuits are formed by chemical plating and electroplating in order to overcome the drawbacks of the etched oil method and respond to the fine patterning of circuits, cost reduction, and resource saving. . In the semi-day tape method, a thermosetting butadiene adhesive made of a mixture of acrylonitrile rubber and a novolac type phenolic resin, a resol type phenolic resin, or an epoxy resin is applied onto a laminate having through holes, and the adhesive is heated and cured. After forming an adhesive layer, making the adhesive layer hydrophilic and activating it, and further forming a chemical copper plating layer on the entire surface including the inner wall of the through hole, plating is applied to the entire surface except for the inner wall of the hole and the predetermined circuit pattern. Coat the resist. Next, electrolytic copper plating is applied to form an electrolytic copper plating layer on the inner wall of the hole and a predetermined circuit pattern, and then the resist is peeled off and the exposed chemical copper plating layer is dissolved and removed with an etching solution such as ammonium persulfate to form a printed wiring board. This is a method of manufacturing.

However, in the semi-additive method, an electrolytic copper plating layer made of the same material as the chemical copper plating layer is formed, so when the chemical copper plating layer is etched with ammonium persulfate, etc., the electrolytic copper plating layer is also etched. . Moreover, the inner wall of the through-hole that is electroplated has a lower degree of etching than the circuit pattern because the etching liquid drains more slowly than the circuit pattern that is similarly electroplated.
~5 times. In particular, the etching solution tends to accumulate in the corner areas of the through holes, and depending on the etching conditions, the electrolytic copper plating layer and the chemical copper plating layer in the corner areas may all be etched while etching a chemical copper plating layer of only 1 to 3 microns. , may cause wire breakage. Although it is a semi-additive method that theoretically enables fine patterning, there are still many drawbacks in the actual process.

[Object of the Invention] An object of the present invention is to solve the problems of the above-mentioned semi-additive method and to provide a method for manufacturing a printed wiring board with excellent circuit pattern precision and through-hole reliability.

[Summary of the Invention] In order to achieve the above object, the present invention forms a protective layer that does not dissolve or is difficult to dissolve in an etching solution on the surface of the electrolytic copper plating layer, and that the protective layer is easily dissolved in a subsequent process. Focusing on finding a process that would allow for peeling, they conducted extensive research. As a result, by treatment with an aqueous alkali metal sulfide salt solution, it was possible to obtain a sulfide layer that was difficult to dissolve in an etching solution but could be easily dissolved and removed in an alkali cyanide aqueous solution. By forming this sulfide layer, etching of the electrolytic copper plating layer on the inner wall of the through hole and the circuit pattern is prevented, and a method for manufacturing a printed wiring board with good circuit pattern accuracy and extremely high through hole reliability has been discovered.

That is, in the present invention, an adhesive-attached laminate having through holes is hydrophilized and activated, a chemical copper plating layer is formed on the entire surface including the inner walls of the through holes, and then a chemical copper plating layer is formed on the entire surface including the inner walls of the through holes and the circuit pattern. After coating the surface of the copper plating layer with a resist pattern of plating resist, further forming an electrolytic copper plating layer on the inner wall of the through hole and the surface of the circuit pattern, the entire board is treated with an aqueous solution of alkali metal sulfide to remove the electrolytic copper plating. After forming a sulfide layer on the layer surface, the resist pattern is peeled off and the exposed chemical copper plating layer is dissolved and removed with an aqueous ammonium persulfate solution, and then treated with an alkali cyanide aqueous solution to dissolve the sulfide layer. This is a method for producing a printed wiring board, which is characterized by removing the printed wiring board.

The present invention will be explained in more detail.

First, a laminate with an adhesive layer on its surface as a base for plating, that is, an adhesive-coated laminate is made.

A laminate of paper phenol base material, paper epoxy base material, or glass epoxy base material is coated with an adhesive consisting of, for example, acrylonitrile rubber and a novolac type or resol type phenol resin or/and epoxy resin, if necessary. A resin containing powdered silica and a zirconium compound is coated and transferred, and the adhesive-attached prepreg is simultaneously molded to obtain an adhesive-attached laminate. Through-holes were formed in this laminate by pressing, etc., and then chromic acid was added to increase the adhesion strength between the adhesive layer and the chemical copper plating layer.
Hydrophilic treatment is performed using sulfuric acid, dichromic acid-sulfuric acid, chromic acid-boronic acid, etc., and then activated using a commonly used activation treatment solution containing stannous chloride, palladium chloride, and hydrochloric acid. Perform processing.

Chemical copper plating is applied to the entire surface of an adhesive-coated laminate having through-holes that has been subjected to hydrophilization and activation treatment to form a chemical copper plating layer with a thickness of usually 3 to 5 μm. Next, a resist pattern of plating resist is formed on the surface of the chemical copper plating layer except for the inner wall of the through hole and the necessary circuit pattern. This is for electrolytic copper plating of the inner wall of the through hole and the circuit pattern, and is performed by screen printing or the like.

Next, an electrolytic copper plating layer is formed on the inner wall of the through hole and the circuit pattern portion which are not covered with the plating resist. As the electrolytic copper plating bath, a copper pyrophosphate bath, a sulfuric acid bath, etc. are used, and the copper pyrophosphate bath provides good plating coverage and dense electrolytic copper, and also has good through-hole reliability. The entire substrate on which the electrolytic copper plating layer is formed on the inner walls of the through holes and the circuit pattern is treated with an aqueous solution of alkali metal sulfide to form a sulfide layer on the electrolytic copper plating. The first point of the present invention is to use an aqueous sulfurized alkali metal salt solution as the sulfiding solution. Examples of alkali metal sulfide salts include potassium sulfide, sodium sulfide, calcium sulfide, lithium sulfide, magnesium sulfide, barium sulfide, and the like, which are used as an aqueous solution. Further, a substance having a buffering effect such as ammonium chloride may be added as necessary. The mixing ratio is potassium persulfate 3-20g/ammonium chloride 5-100g/
It is preferable to do so. A common treatment method is immersion, and immersion for about 5 minutes at room temperature is usually sufficient. Next, peel off the plating resist film,
The exposed chemical copper plating layer is dissolved and removed with an aqueous ammonium persulfate solution. The second point of the present invention is that the sulfide layer formed with the aqueous alkali metal sulfide salt solution is removed by treatment with a dilute aqueous alkali cyanide solution.

As the alkali cyanide, potassium cyanide, sodium cyanide, etc. are used, and the treatment is carried out by spraying or dipping.

Other general treatment operations, such as neutralization treatment after hydrophilic treatment and hydrochloric acid treatment before activation treatment, etc., do not impair the effects of the present invention.

Through the above steps, it is possible to provide a method for manufacturing a printed wiring board with excellent circuit accuracy and through-hole reliability.

[Examples of the Invention] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 40 parts by weight of acrylonitrile rubber, 20 parts by weight of resol type phenolic resin, 20 parts by weight of bisphenol type epoxy resin, 10 parts by weight of fine powder silica, and 10 parts by weight of curing agent were added to a paper epoxy laminate (EPL manufactured by our company) with methyl ethyl ketone. - A chemical plating adhesive dissolved in a toluene mixed solvent was applied using a dip method, air-dried, and then thermally cured at 160°C for 40 minutes to form an adhesive layer with a thickness of about 30 microns. Next, after drilling through-holes at predetermined locations in the adhesive layered laminate, the adhesive layer was treated to make it hydrophilic with a chromic acid-sulfuric acid mixture, activated in a conventional manner, and then chemically treated. A chemical copper plating layer of 2.0 μm was formed on the entire surface including the inner wall of the through hole by immersing it in a copper plating solution. Thereafter, a plating resist was applied to the entire surface of the chemical copper plating layer except for the inner walls of the through holes and a predetermined circuit pattern. Next, it was activated with a 5% aqueous sulfuric acid solution and subjected to electrolytic copper plating treatment to form an electrolytic copper plating layer on the inner wall of the through hole and the circuit pattern. Next, it was immersed in an aqueous solution containing 15 g of potassium sulfide and 50 g of ammonium chloride at room temperature for 5 minutes to obtain a black sulfide layer on the electrolytic copper plating layer. Next, the plating resist was peeled off using methylene chloride, and then the exposed chemical copper plating layer was dissolved and removed by immersion in a 20% ammonium persulfate solution.

During this period, no change occurred in the sulfide layer of the electrolytic copper plating layer. Next, the sulfide layer on the surface of the electroplated layer was dissolved and removed by immersion treatment in a 10% potassium cyanide aqueous solution for several seconds to obtain a printed wiring board.

The thickness of the electrolytic copper plating layer on the inner wall of the through hole and the circuit pattern in the obtained printed wiring board was compared with the state of the electrolytic copper plating layer before the etching process. No variation was observed in the copper plating thickness between the inner wall and the circuit pattern. As shown in FIGS. 1 and 2, the copper plating layer was deposited with high accuracy.

Comparative Example A laminate with adhesive for chemical plating was made in the same manner as in the example, and subjected to drilling, hydrophilization, activation, chemical copper plating, resist coating, electrolytic copper plating, and then resist coating without sulfurization. After peeling off, the chemical copper plating layer is dissolved and removed using ammonium persulfate.
A printed wiring board was obtained. The precision of the copper plating layer obtained was not good as shown in FIGS. 3 and 4.

[Effects of the Invention] As explained above, according to the present invention, when etching the exposed chemical copper plating layer portion that is a non-circuit pattern portion, etching of the inner wall of the through hole and the electrolytic silver plating layer of the circuit pattern can be prevented, and the circuit pattern can be improved. It is possible to provide a method for manufacturing a printed wiring board with good precision and extremely high through-hole reliability.

[Brief explanation of drawings]

1 and 2 respectively show a cross-sectional view of a printed wiring board and a cross-sectional view of a circuit pattern according to the present invention,
FIG. 3 and FIG. 4 respectively show a cross-sectional view of a printed wiring board and a circuit pattern of a comparative example. 1...Substrate, 2...Copper plating layer.

Claims (1)

[Claims] 1 After hydrophilizing and activating an adhesive-attached laminate with through holes and forming a chemical copper plating layer on the entire surface including the inner walls of the through holes, a layer of chemical copper plating is applied to the surface of the chemical copper plating layer excluding the inner walls of the through holes and the circuit pattern. Cover the resist pattern of the metal resist,
Further, the entire substrate formed by forming an electrolytic copper plating layer on the inner wall of the through hole and the surface of the circuit pattern is treated with an aqueous alkali metal sulfide salt solution to form a sulfide layer on the surface of the electrolytic copper plating layer, and then the resist pattern is A method for producing a printed wiring board, which comprises removing the exposed chemical copper plating layer by dissolving it in an aqueous ammonium persulfate solution, and then treating it with an alkali cyanide aqueous solution to dissolve and remove the sulfide layer.