JPH06125172A - Circuit board with plated throughhole and its manufacture - Google Patents

Abstract

PURPOSE:To inexpensively form a throughhole on a circuit board through a simplified process by forming a layer containing a conductive metal sulfide on the wall of the throughhole, and then, a metallic layer on the formed layer by electroplating. CONSTITUTION:A layer containing a conductive metal sulfide is formed on at least the wall of a throughhole of a board by using a disperse system containing metal sulfide. Then a metallic layer is formed on the layer containing metal sulfide by electroplating by using the layer containing metal sulfide as a cathode. Therefore, a throughhole can be inexpensively formed through a simplified process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a circuit board such as a printed wiring board or a ceramics board used in electronic equipment.

[0002]

2. Description of the Related Art A double-sided printed wiring board in which an electric circuit is formed on both sides of an insulating plate to conduct electricity through through holes, and a conductor layer is provided not only on the surface of the insulating substrate but also inside thereof, and through holes are formed between the conductor layers. The multilayer wiring board that is electrically connected with is used most widely in electronic devices. These through holes are usually connected by through hole plating.

As the through hole plating method, there are a subtractive method, a full additive method, a part additive method and the like. That is, there is an electroless plating method, or a combined process consisting of electroless plating and electroplating,
The process is appropriately selected and used from the viewpoints of the degree of miniaturization of the pattern of the formed circuit, the diameter of the through hole, the insulating material, and the manufacturing cost.

In general, the mainstream process is to electrolessly plate a substrate perforated with a drill, and then perform electroplating. This method is also subdivided into various methods from the viewpoints of the fineness of the pattern, the through hole diameter, and the manufacturing cost. Typical examples of the manufacturing process of this through-hole substrate include a tenting method, a photo ED method, and a pattern plating method.

A brief description of each method is as follows. First, the tenting method will be described. A double-sided copper clad laminate is drilled and panel plated. A dry film is applied and image processing is performed to form an etching resist. Etching is performed to form a circuit. By removing the etching resist and forming a solder resist or the like, a through hole substrate is obtained.

Next, the photo ED method will be described. A double-sided copper clad laminate is drilled and panel plated. A resist is formed on both sides and the inside of the through holes by using the electrodeposition method, and image processing is performed to form an etching resist.
Etching is performed to form a circuit. By removing the etching resist and forming a solder resist or the like, a through hole substrate is obtained.

Further, the pattern plating method will be described. A double-sided copper clad laminate is drilled and panel plated. Apply a dry film and process the image. Pattern plating is performed, and then etching resist plating is performed. After that, etching is performed to form a circuit. By removing the etching resist and forming a solder resist or the like, a through hole substrate is obtained.

All of the above methods have a panel plating step after drilling. Panel plating is to make electrical connection by conducting through-hole plating between conductor layers. This process is electroplating following through electroless plating on the through-hole part, or electroless plating called an additive method. It consists of plating thickening method.

[Problems to be Solved by the Invention]

Electroless plating includes EDTA, bipyridyl,
Using chelating agents such as cyanide compounds, palladium, tin, catalysts, harmful substances such as formalin, expensive resources, etc.
In addition, it is difficult to meet the demands of resource saving, no pollution, simplification of process control, reduction of the number of processes, shortening of process time, etc., such as long reaction time and use of a large amount of washing water to obtain a high quality plating film. there were.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and is intended to electrically connect conductors through a through hole of a through hole printed wiring board as a circuit board. And a new through-hole printed wiring board by the improved method.

According to the present invention, a conductive metal sulfide-containing layer is provided on at least a hole-punched surface (inner wall of a through hole) of a perforated substrate, and thereafter, the sulfide-containing layer is used as a cathode to form an electric field on the sulfide-containing layer. It is characterized in that a metal layer is provided by a plating method to electrically connect through holes.

As the substrate, an organic or inorganic insulator or a composite material thereof is used.

As the organic insulator, epoxy resin, fluororesin, polyimide resin, phenol resin or the like is used. Inorganic insulators include short glass fibers, woven glass cloth, and ceramics. A glass / epoxy base material such as FR-4, CEM-3 or CEM-1 is used as the composite material.

A single-sided or double-sided copper-clad substrate obtained by laminating a copper foil of 10 to 60 μm on one side or both sides of a substrate material, or a multilayer board in which these are used as an inner layer or an outer layer and combined with a prepreg is used.

As the double-sided copper-clad substrate, a rigid plate having a thickness of 0.3 mm to 1.6 mm or a so-called flexible double-sided substrate having a thickness of 0.3 mm is used.

A copper-clad substrate is usually provided with through holes for electrical connection between the front and back or inner layers having a diameter of 0.2 mm to 1.2 mm by drilling or punching.

In the present invention, the conductive metal sulfide-containing layer is formed on at least the insulating material of the through hole.

Regarding the conductive metal sulfide, its properties and synthesis method are disclosed in JP-A-62-143306 and JP-A-61-215661 by the inventor of the present invention.
It is disclosed in JP-A-61-10008 and JP-A-64-18915.

In the present invention, since the conductive metal sulfide-containing layer is used as the base electrode for through-hole electroplating, the metal sulfide needs to have high conductivity. That is, the electrical conductivity of the metal sulfide is 10 ^-4 Scm ^-1 or more, preferably 10 ^-2 Scm ^-1 or more. As a metal capable of forming a sulfide having high electric conductivity, IUPAC
Elements of group numbers 4 to 12 in the periodic table of elements according to the Inorganic Chemistry Nomenclature Revised Edition (1989) are used.

Among these, copper sulfide, nickel sulfide,
Iron sulfide, cadmium sulfide, cobalt sulfide and chromium sulfide are preferable because they are inexpensive and relatively safe. Copper sulfide is particularly preferable because it has high electric conductivity and is inexpensive.

The metal sulfide is obtained by reacting a metal compound with a sulfur compound. As the metal compound, sulfates, nitrates, halides, organic acid salts, organic metal compounds and the like are used. In particular, halides, sulfates,
Nitrate and acetate are inexpensive and preferable for pollution control.

Examples of the sulfur compound include mercaptan, hydrogen sulfide, alkyl sulfide, thiosulfate, sodium sulfide, ammonium sulfide, thiourea, thiosulfate and sulfite.

As the reaction system, a reaction system using a sulfur compound such as hydrogen sulfide gas or sodium sulfide in a liquid phase reaction or a slurry reaction system is adopted. As the liquid phase, an organic solvent having a high solubility of water or a metal compound in the solvent, such as acetonitrile, dimethylformamide, dimethylforsulfoxide, etc., is appropriately selected. In particular, an aqueous solution is desirable, and as the sulfur compound, hydrogen sulfide gas, sodium sulfide, ammonium sulfide, thiosulfate, etc. are inexpensive and preferable in terms of pollution control.

The reaction temperature is -20 ° C to 300 ° C.

The reaction conditions of the metal compound and the sulfur compound in the present invention are not particularly limited, but the molar ratio of the metal compound and the sulfur compound is 1: 0.001 to 1:10.
The range of 00 is desirable. Particularly preferred is 1:
It is desirable that the range is 0.1 to 1:10.

In the present invention, a dispersion system containing fine particles of metal sulfide (also including a dispersion liquid in which a polymer compound is dissolved) is applied or attached to the inner wall of the through-hole, and the dispersion medium is removed to remove the dispersion medium. -It is characterized in that a metal sulfide layer is formed on the inner wall of the hole. The thickness of the metal sulfide layer is 0.0
3 μm to 50 μm is preferable. Particularly preferably 0.1
μm to 10 μm.

The above dispersion system is disclosed in JP-A-62-143306.
No. 61-215661 and 61-100.
08, JP-A-64-18915, and further JP-A-6-18
The description is given in JP-A-91005. An aqueous solution in which a metal sulfide is dispersed in water in a colloidal state has been conventionally known (see each item of metal sulfide published in “Kagaku Daijiten” published by Kyoritsu Shuppan, 1937). A dispersion liquid having a particle size of 1 μm or less is generally referred to as a sol or a colloid solution. A conductive metal sulfide particle having a particle size of 100 μm or less is dispersed in water or an organic solvent. The conductive layer is provided by adhering the dispersion system to at least the inner wall of the through-hole and removing the dispersion medium such as water or an organic solvent.

Generally, metal sulfides have low mechanical strength,
Difficult to obtain a film. On the other hand, a polymer compound is easy to obtain a film (film). Therefore, in the present invention, the soluble polymer compound is particularly preferably added to the sulfide dispersion liquid. As the polymer compound to be added, a hydrophilic substance is particularly preferably selected so that the subsequent electroplating will proceed smoothly.

Specifically, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinyl alcohol,
Examples of the hydrophilic polymer compound include polyethylene oxide, polyvinyl pyridine, polyvinyl pyrrolidone, and polyethyleneimine. Molecular weight is 5000 to 3
It is, 000,000. If the molecular weight is too low, the sulfide layer swells during electroplating and is easily dissolved, which is not preferable. In addition, when the metal sulfide is prepared using a solvent other than water, a polymer compound soluble in the solvent may be used. For example, N, N-dimethylformamide (DMF)
When using dimethyl sulfoxide (DMSO) as a solvent, Chemistry of Materials
As shown in Volume 4, page 570 (1992),
Polyvinyl formal, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, etc. are used as the polymer compound.

The addition ratio (weight ratio) of the polymer to the metal sulfide is preferably 0.01 to 3 times that of the metal sulfide 1.

As the dispersion medium, in addition to water, DMF, DMS
Examples of organic solvents include O and toluene. Industrially, it is particularly preferable to use water as the dispersion medium because it is inexpensive, safe and non-polluting. Further, in order to improve the storage stability of the dispersion system, the surface of the metal sulfide may be chemically modified or a stabilizer may be added to the dispersion system. Further, the metal sulfide is mainly composed of metal and sulfur, but may partially contain an organic substance or an inorganic substance as exemplified in Japanese Patent Application No. 59-127413. Further, it may be a mixture with a salt such as sodium sulfate or ammonium chloride, which is formed when the metal sulfide is prepared.

The concentration of the metal sulfide in the dispersion is 0.1 to 2
0 wt% is preferable. If the concentration is too low, the conductivity required for plating cannot be obtained, and if the concentration is too high, the fluidity decreases and it becomes difficult to uniformly adhere to the inner wall of the small diameter through-hole.

In order to firmly attach the metal sulfide to the through holes of the printed circuit board, the perforated board is subjected to pretreatments such as degreasing cleaning, soft etching and oxidation treatment, if necessary. Examples of the degreasing cleaning include mechanical methods such as buffing, and washing with a jet water after rinsing with an aqueous surfactant solution. As the soft etching, dilute sodium hydroxide aqueous solution, dilute potassium hydroxide aqueous solution, sodium carbonate aqueous solution or the like is used when the substrate is glass / epoxy, and sodium-naphthalene is used when the substrate is polytetrafluoroethylene. A system organic solution is used. Even when the base material is ceramics, alkali or acid is selected. An example of the oxidation treatment is an aqueous mixed solution of potassium permanganate and caustic alkali.

Further, in order to promote adhesion of the metal sulfide to the through holes of the printed circuit board, at least the through holes are pretreated with a coupling agent such as iodine, polyethyleneimine or polyvinyl alcohol. Is preferred. As the pretreatment method, the printed board is immersed in a solution of the above coupling agent 0.005 to 1 mol / l (liter), preferably 0.01 to 0.5 mol / l for about 10 minutes and then washed with water. Is desirable. However, the present invention is naturally not limited by the presence or absence of this pretreatment.

After forming the conductive metal sulfide, a metal layer is provided thereon by electroplating. A known metal is used as the metal layer, but in particular, copper, nickel, gold, tin,
From the viewpoints of cost, fineness and reliability, it is preferable to select one of the lead / tin alloys according to the application of the substrate and the pattern forming method.

As a general-purpose printed circuit board, copper plating and lead / tin solder plating are particularly preferable.

Known methods can be easily applied to the metal electroplating. The thickness of the plating is controlled by the amount of electricity, but it is 0.1
It is from 70 μm to 70 μm, and normally 5 to 40 μm is suitable. For example, as the copper plating solution, a copper sulfate plating solution prepared by adding an appropriate amount of a brightening agent and chlorine ions to a copper sulfate sulfuric acid aqueous solution or a copper pyrophosphate plating solution prepared by adding an appropriate amount of a brightening agent to an aqueous solution of copper pyrophosphate-ammonia pyrophosphate is used. To be

The substrate to be plated has a cathode current density of 1 to 10 A.
/ Dm ² , the temperature is 20 to 60 ° C., and electrolytic copper plating is performed using a copper anode with stirring. Copper sulfate plating is preferable in terms of plating quality or pollution control.

In the case of solder plating, borofluoride first
An aqueous solution of tin, lead borofluoride and hydrofluoroboric acid is used as a plating bath.

In the manufacturing process of the through-hole plated printed circuit board according to the present invention, one embodiment is to perform electrolytic copper plating after depositing a metal sulfide on the entire copper clad board perforated with a drill. It is also possible to attach an organic resist film to a portion other than the portion punched by a drill to selectively attach a metal sulfide to the drilled portion, and selectively perform electroplating on the hole portion.

The through-hole plated substrate obtained by electroplating the metal sulfide thus obtained is subsequently sent to the image forming step, for example, a resist by the photo ED method, a dry film resist by the tenting method or After the dry film resist or the like is formed by the pattern plating method, the photo E is formed by metal etching or pattern etching followed by metal etching.
A through-hole plated substrate by the D method, a through-hole plated substrate by tenting, and a through-hole plated substrate by the pattern plating method are obtained. Among these, the photo-ED method, which has been industrialized in recent years, is particularly preferable from the viewpoint of low cost and fineness.

[0042]

【Example】

Example 1 A glass / epoxy double-sided substrate (thickness: 1.6 mm, FR-
A substrate provided with a through hole having a diameter of 0.8 mm by drilling in 4) was used as a test piece.

This substrate was buffed, washed with water, degreased with a 4% aqueous sodium hydroxide solution, and washed with water.

On the other hand, an aqueous solution of copper sulfate and an aqueous solution of sodium sulfide were mixed and reacted at room temperature in the coexistence of polyvinyl alcohol having a molecular weight of 22000 to obtain a black hydrosol. The starting material concentration of the reaction system was 0.05 mol / l of copper sulfate, 0.05 mol / l of sodium sulfide, and 1 polyvinyl alcohol.
It was 2.5 g / l. A part of this hydrosol was sampled, dried on a glass plate, and the electrical conductivity was measured by the four-terminal method. As a result, it was 1.7 Scm ⁻¹ . In addition, the particle size of the black matter is 0.1 to 0.2 μm as a result of observation with an electron microscope.
Met.

By the way, it is well known that black conductive copper sulfide is produced in the reaction between a copper compound and sodium sulfide and the reaction between a copper compound such as copper sulfate and sodium thiosulfate under heating. Therefore, this black substance is considered to be copper sulfide. This 1 wt% copper sulfide aqueous colloidal solution was applied to the inner surface of the through hole of the substrate, and 10
It was dried at 0 ° C. for 5 minutes. After repeating this operation 3 times,
Conduction was obtained between both sides of the substrate.

Copper electroplating was performed on this substrate. High-purity copper sulfate for plating (CuSO ₄ , 5H ₂
O) 30 g / l, special grade sulfuric acid 250 g / l, chloride ion 2
5 ppm, additive 50 ml / l (Shipley Co., XP-8
A mixed solution consisting of 802) was used. When the printed board was used as a cathode and the plating was carried out for 30 minutes under stirring at a cathode current density of 1.5 A / dm ^{2 at} a temperature of 25 ° C., all the through holes were copper-plated. Subsequently, plating was carried out, and copper was plated in the through holes to a thickness of 30 μm. The copper plating in the through holes was firmly attached to the substrate.

INDUSTRIAL APPLICABILITY The present invention is simplified because a conductive metal sulfide-containing layer is formed on a through hole of a circuit board and a metal layer is formed on the conductive metal sulfide-containing layer by an electroplating method. Through-hole formation can be carried out at low cost.

Claims (5)

[Claims] 1. A method for providing a conductive metal layer on at least a through hole portion of a printed wiring board having a through hole on a double-sided board or a multi-layer board made of an insulating organic polymer, glass fiber and / or an insulating ceramics material, etc. A step of providing a conductive metal sulfide-containing layer by using a metal sulfide-containing dispersion system on at least the perforated surface of the substrate, and an electroplating method on the sulfide-containing layer using the conductive metal sulfide-containing layer as a cathode. And a step of providing a metal layer on the inner wall of the through hole. 2. The metal sulfide is selected from copper sulfide, nickel sulfide, cobalt sulfide, and iron sulfide, and the polymer substance coexists as a film-forming substance. For manufacturing through-hole plated circuit boards. 3. The method for manufacturing a through-hole plated circuit board according to claim 1, wherein the metal layer is copper, nickel, gold, tin, lead, or a lead / tin alloy. 4. A double-sided or multilayer through-hole plated circuit board having a conductive metal sulfide-containing layer formed by a metal sulfide-containing dispersion system in a through hole portion. 5. A metal plating layer made of any one of copper, nickel, tin, and lead / tin alloy is formed on the conductive metal sulfide-containing layer having a thickness of 0.03 μm to 50 μm. Double-sided or multi-layer through-hole plated circuit board.