JPH01154590A - Forming method for circuit - Google Patents

Abstract

PURPOSE:To simplify manufacturing steps without undercut of a circuit of an additive method and to reduce its cost by coating and drying a mold releasable sheet with an adhesive in which photosensitive metal oxide is dispersed in solution made of synthetic rubber, superposing it, integrating them by heating and pressurizing, isolating the sheet, chemically roughening it, then adhering specific metal ions to an adhesive layer, selectively exposing it and dipping it in an electroless plating solution. CONSTITUTION:Fine particle powder of photosensitive metal oxide, synthetic rubber, curable resin, phosphorus fatty material and inorganic filler are dispersed in organic solvent thereby to form an adhesive solution, coats a releasable sheet and is dried. Then, the sheet is superposed with prepreg with the adhesive face disposed inside, and integrated by heating and pressurizing. Thereafter, the sheet is isolated and removed, the adhesive layer is oxidized to be roughened, dipped and dried in metal ionic solution which shows catalytic activity for electroless plating by reduction, and then pattern-exposed, thereby forming a catalyst particle layer. Then, it is washed with water, and dipped in the electroless plating solution, thereby forming a circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a circuit forming method that is excellent in forming fine patterns.

[Prior art]

Conventionally, the mainstream method for manufacturing printed wiring boards has been the etched foil method, in which circuits are formed by dissolving and removing unnecessary copper foil from portions of a copper-clad laminate other than those corresponding to circuits.

In recent years, printed wiring boards have become more dense and lower in cost, but the etched foil method has problems such as undercutting of circuits due to etching and complicated manufacturing processes. For this reason, efforts have been made to increase density by pattern plating, use of ultra-thin copper foil, etc., and to reduce costs by streamlining the manufacturing process, but it is believed that each has its limits.

On the other hand, the additive method in which a circuit is formed by electroless plating of an insulating group 'Gt' has the advantage that in principle there is no circuit undercut, the manufacturing process is simple, and costs can be reduced. However, the process is not fully established, and it has drawbacks such as low line accuracy and low reliability of insulation between circuits.

(Objective of the Invention) The present invention has the advantage that there is no undercut in the circuit of the additive method, the manufacturing process is simple, and costs can be reduced. In addition, the present invention has excellent line accuracy and reliability of insulation between circuits. The present invention was completed as a result of research to develop a circuit formation method with excellent performance.

[Structure of the invention]

In the present invention, an adhesive made by uniformly dispersing fine particles of photosensitive metal oxide in a solution consisting of synthetic rubber, a curable resin, and a phospholipid is applied onto a releasable sheet and dried, and this sheet and prepreg are bonded together. The sheets are stacked with the adhesive-coated side on the inside and integrated by heating and pressurizing.The obtained adhesive-coated insulating substrate is peeled off from the releasable sheet, chemically roughened, and exposed to light. Metal ions that are catalytically active for electroless plating are attached to the adhesive layer using a photosensitive metal oxide, and a metal particle layer that is catalytically active for electroless plating is formed by selective exposure. This invention relates to a circuit forming method characterized by forming a circuit by immersing it in an electrolytic plating solution.

Next, the present invention will be specifically explained in order of manufacturing steps.

The base material of the insulating substrate is paper, glass woven fabric, glass non-woven fabric, etc. The resin solution for impregnation is phenol resin, melamine resin, etc.
Thermosetting resins such as epoxy resins can be used.

In this case, photosensitive metal oxide fine particles that enable through-hole formation can be added to the impregnating resin solution, if necessary. The base material is impregnated with the resin solution and dried to produce a prepreg.

The adhesive that improves the adhesion between the insulating substrate and the plated metal is mainly composed of fine particle powder of photosensitive metal oxide, synthetic rubber, curable resin, phospholipid, and inorganic filler.

Photosensitive metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide have properties as n-type semiconductors, and their surfaces become reductive when exposed to ultraviolet rays, so they can be reduced like palladium ions. This makes it possible to form a circuit by using metal ions that are catalytically active for electroless plating. In particular, titanium oxide has strong reducing properties and is most suitable for this method.

In this way, since the present method directly forms a pattern by irradiating light, it is possible to obtain a circuit with extremely excellent line precision.

The particle size of the photosensitive metal oxide powder is 0.1 to 10 μm, preferably 1 to 5 μm. If the particle size is 0.1μ or less,
The adhesion between the adhesive layer and the plated metal decreases, and when the surface is 10 μm or more, the line precision of the circuit decreases.

Further, it is preferable to prepare the adhesive so that the photosensitive metal oxide is contained in the solid content of the adhesive in an amount of 5 to 40% by weight, preferably 10 to 20% by weight. If the content is less than 5% by weight, the reducing power of the photosensitive metal oxide will be insufficient, and if it is more than 40% by weight, the adhesion between the adhesive layer and the plating metal and heat resistance will decrease.As a synthetic rubber, acrylonitrile is used. Ingredients 25-45
High weight percent acrylonitrile content NBR can be used.

Curable resins include phenolic resin, epoxy resin,
Thermosetting resins such as melamine resins and photocuring resins such as polymers of acrylic esters of polyhydric alcohols such as trimethylolpropane triacrylate and pentaerythritol triacrylate can be used.

The mixing ratio of these is 25 to 100 parts for phenol resin, 50 to 150 parts for epoxy resin, 20 to 40 parts for melamine resin, to 100 parts of NBR.
In addition, trimethylolpropaline lipid is used to make it easier to peel off the release sheet from the adhesive surface and to improve the heat resistance of the adhesive layer after creating an adhesive-attached insulating substrate by heating and pressing. , lecithin is preferred.

The blending amount can be selected within the range of 0.1 to 5% by weight based on the solid content of the adhesive, depending on the required degree of releasability.

Inorganic fillers include silicon dioxide, calcium carbonate,
Fine powder such as aluminum hydroxide can be used. The compounding ratio of these is 1 to 5% by weight in the case of silicon dioxide, 0.5 to 3% by weight in the case of calcium carbonate, and 0.5 to 3% by weight in the case of aluminum hydroxide, based on the total amount of the synthetic rubber and the curable resin. 1-5% camellia is good.

These inorganic fillers are effective in improving the heat resistance of the adhesive layer and the adhesion to the plated metal. An adhesive solution is prepared by dispersing or dissolving the photosensitive metal oxide fine particles, synthetic rubber, curable resin, phospholipid, and inorganic filler in an organic solvent such as acetone, MEK, or MIBK.

Next, an adhesive solution is applied to the releasable sheet and dried. As the release sheet, a metal tube, a plastic film, paper, etc. can be used, but a metal tube is preferable from the viewpoint of heat resistance in the drying process after applying the adhesive. In particular, aluminum foil is preferred from the viewpoint of cost. The drying process is for drying and removing the solvent in the adhesive using hot air and for advancing the thermal reaction of the adhesive to a certain degree. Adhesive application is done using a roll coater.
, bar coater, curtain flow coating, transfer using a squeeze roll, etc., followed by continuous drying using a hot air drying ratio.

The thickness of the adhesive layer is preferably 20 to 200 μm. Especially from 30~
A thickness of 120 μm is preferable from the viewpoint of adhesion between the adhesive layer and the plated metal and the coating work.

Next, the adhesive-coated releasable sheet is stacked on the prepreg with the adhesive side facing inside, and is integrated by heating and pressing to produce an insulating substrate with a photosensitive metal oxide-containing adhesive.

The adhesive layer thus formed has a uniform surface, little variation in thickness, and less contamination by foreign matter.

Next, the removable sheet is removed from the photosensitive metal oxide-containing adhesive-attached insulating substrate, and after drilling and drying if necessary, chromic acid/sulfuric acid is added to improve the adhesion strength with the plating metal. The adhesive layer is roughened by oxidation to form fine irregularities on the adhesive surface. Next, it is immersed in a metal ion solution that becomes catalytically active for electroless plating through reduction.
After drying, pattern exposure is performed to form a catalyst particle layer.

It is preferable to use ultraviolet light for exposure. The metal ion is preferably a palladium ion.

The photosensitive metal oxide contained in the adhesive layer has properties as an n-type semiconductor, and its surface becomes reducible when irradiated with ultraviolet rays, making it possible to form a catalyst particle layer with palladium. Next, after washing with water to remove unreacted metal ions, it is immersed in an electroless plating solution such as electroless copper or electroless nickel to form a desired circuit.

According to this method, it is possible to form a circuit directly without using a resist as in the usual additive method, and it is also possible to form a circuit without the presence of insulation inhibiting substances such as palladium between the circuits. .

(Effects of the Invention) A printed wiring board having a circuit obtained by the present invention has the following features.

(1) An adhesive layer with a smooth surface, less variation in thickness, and less contamination of foreign matter is formed.

(2) Since the circuit is directly formed using photoreaction,
The circuit has excellent line accuracy.

(3) The manufacturing process is simple and cost-effective.

(4) Excellent insulation properties because there are no insulation-inhibiting substances between the circuits.

(Example〕 Hereinafter, the present invention will be explained in detail with reference to Examples.

NBR with a bound acrylonitrile content of 35% (Japan: f
11200 parts by weight of epoxy resin per 100 parts by weight of 8i epoxy 8 parts by weight EK 600 parts by weight The above resin mixture was stirred at 80'C for 3 hours (with a foot stand to obtain an adhesive solution). This adhesive solution was applied to aluminum foil with a thickness of 50 μm using a roll coating method and dried through continuous drying at 50 to 160° C. The adhesive film thickness was 100 μm.

This adhesive-coated aluminum foil was layered one by one on both sides of 8 pieces of epoxy resin-impregnated glass cloth with the adhesive side inside, and heated at 160℃ and 100KF! /ci for 120 minutes to integrate, thereby obtaining an insulating substrate with a photosensitive metal oxide-containing adhesive having a thickness of 1.6#.

Next, the aluminum foil was peeled off and 60'C chromic acid (15
0g/! ＞/Concentrated fiA acid (1 in 400ml aqueous solution)
The adhesive layer was immersed for 0 minutes to roughen the surface by oxidation, then immersed in warm water at 65° C. for 5 minutes, washed, and then dried.

Next, palladium chloride (1,59/I)/concentrated hydrochloric acid (
100 I/i) After immersing in an aqueous solution for 5 minutes, it was dried.

Next, films with the desired pattern were superimposed on both sides of the substrate and exposed for 2 minutes under a 125 to 1 high pressure mercury lamp.

Next, unreacted palladium ions in the non-exposed area were removed by washing with water for 2 minutes, and the plate was immersed in a plating solution at 60° C. having the following composition for 20 hours to obtain a copper circuit with a thickness of 35 μm.

20.03 mOl#l CuSO4・5HO K4 [Fe(CN) 6 ] 40m'j/f! E
DTA-4Na 0.08 mol/1(C
5H4N > 225my/1 HCHOO, 04mol#! PH12.5 (adjusted with NaOH)

Claims (2)

[Claims] (1) After chemically roughening an insulating substrate with an adhesive layer made by uniformly dispersing fine particles of photosensitive metal oxide in a solution consisting of synthetic rubber, curable resin, inorganic filler, and phospholipid, it is exposed to light. When the photosensitive metal oxide is used, metal ions that are catalytically active for electroless plating are attached to the adhesive layer, and selectively exposed to light to form a metal particle layer that is catalytically active for electroless plating. A circuit forming method characterized by forming a desired circuit by immersing it in an electroless plating solution. (2) An adhesive made by uniformly dispersing fine particles of photosensitive metal oxide in a solution consisting of synthetic rubber, curable resin, inorganic filler, and phospholipid; applied on a releasable sheet and dried;
This sheet and the prepreg are overlapped with the adhesive coated side of the sheet on the inside and integrated by heating and pressurizing.The releasable sheet is peeled off from the resulting adhesive-coated insulating substrate, chemically roughened, and then exposed to light. At this time, metal ions that are catalytically active for electroless plating are attached to the adhesive layer by the photosensitive metal oxide, and a metal particle layer that is catalytically active for electroless plating is formed by selective exposure. A circuit forming method characterized by forming a circuit by immersing the plate in an electroless plating solution.