JPH0567874A - Manufacture of circuit board - Google Patents

Abstract

PURPOSE:To make it possible to form a highly reliable through hole by a method wherein after a hardening conductive material is filled and hardened in the through hole in an insulating substrate having a conductive layer on either surface thereof, the surface constituted of the conductive layer and a hardened material consisting of the hardening conductive material of the insulating substrate is ground smoothly and a wiring pattern is formed. CONSTITUTION:A hardening conductive material 4 is hardened and thereafter, the surface constituted of a conductive layer 2 and a hardened material consisting of the material 47 of an insulating substrate is ground smoothly. Whereby, in a wiring pattern formation process which is the following process, the formation of a pattern using an etching resist and an etching can be secured efficiently performed. As a result, continuity of a through hole 3 can be hardly forming a land on the periphery of the hole 3. Thereby, the highly reliable hole 3 can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for manufacturing a circuit board. More specifically, it is a method of manufacturing a circuit board that can reliably connect the surrounding wiring pattern to the through hole without substantially providing a land portion around the through hole.

[0002]

2. Description of the Related Art Conventionally, conductive through holes have been formed in a circuit board by (a) forming through holes in an insulating substrate having conductive layers on both sides by drilling, and chemically plating or electroplating the through holes. Or (b) forming through-holes for through holes by drilling on an insulating substrate having conductive layers on both sides, etching the conductive layers, and then,
A general method is to form a through hole by filling the through hole with a curable conductive material typified by a copper paste / silver paste and curing it by a screen printing method or a pin insertion method.

[0003]

The formation of the conductive through holes by the above method (a) has been performed for a long time and is the mainstream of the current circuit board manufacturing method. However, in such a method, it is necessary to perform plating twice or more in order to improve the reliability of the through hole portion, which is not necessarily an advantageous method in terms of cost. In addition, since electroplating is performed a plurality of times on the entire surface of the circuit board, the thickness of the conductive layer becomes nonuniform, and variations may occur during etching for pattern formation. Therefore, it also has a drawback that it is difficult to deal with fine patterns.

Further, the method (b) is characterized in that the manufacturing process is short because there is no need for chemical plating or electric plating in the through holes for through holes. However, when the curable conductive material is filled in the through holes by screen printing, it is necessary to perform printing a plurality of times. Therefore, the land diameter formed around the through holes for through holes should be large in consideration of printing accuracy. Need to collect. Further, when the through hole is filled with the curable conductive material by the pin insertion method, it is necessary to make the through hole for through hole large enough to allow the pin to be inserted. Therefore, these methods are also difficult to deal with a circuit board having a fine pattern.

[0005]

As a result of intensive studies to solve the above problems, the inventors of the present invention formed through holes for through holes in an insulating substrate having conductive layers on both sides, and After the curable conductive substance is filled and cured, the surface formed by the conductive layer and the curable conductive substance is ground smoothly, and then a wiring pattern is formed on the smoothed surface to form a through hole. Need not be plated, and
With almost no land around the through hole,
They have found that a highly reliable conductive through hole can be formed, and completed the present invention.

That is, according to the present invention, through holes for through holes are provided in an insulating substrate having conductive layers on both sides, and a curable conductive substance that gives a cured product having conductivity is filled in the through holes and cured. After that, the surface formed by the conductive layer and the cured body of the curable conductive material is smoothly ground, and then a wiring pattern is formed, which is a method for manufacturing a circuit board.

In the present invention, the insulating substrate is not particularly limited, and those having known materials and structures can be used without limitation. Typical examples are paper base material-phenolic resin laminated board, paper base material-epoxy resin laminated board, paper base material-
Synthetic resin substrate such as polyester resin laminated substrate, glass substrate-epoxy resin laminated substrate, paper substrate-Teflon resin laminated substrate, glass substrate-polyimide resin laminated substrate, glass substrate-BT resin laminated substrate, composite resin substrate In addition, a flexible substrate made of polyimide resin, polyester resin, or the like, a metal-based insulating substrate obtained by insulating a metal plate made of aluminum, iron, stainless steel, or the like with epoxy resin or the like, a ceramics substrate, or the like. In the present invention, the insulating substrate has conductive layers on both sides. The material of the conductive layer is not particularly limited. Examples of typical materials include copper and nickel. Further, the thickness of the copper electrode layer is not particularly limited, but generally 5 to 7
0 μm is suitable.

First, a through hole for a through hole is provided in the above-mentioned insulating substrate having conductive layers on both sides. The diameter of the through hole is not particularly limited and can be set arbitrarily. In particular, in the present invention, the diameter of the through hole is equal to or larger than a diameter capable of filling the curable conductive material, usually 0.3 mm or more, and preferably 0.3 to 2 mm.
You can also select more. Further, in the present invention, it is possible to surely establish conduction even with such a minute hole diameter, which is effective in forming a fine pattern described later. As a method of forming the through holes for the through holes, known methods similar to those for manufacturing a normal circuit board such as drilling, punching, and laser processing are used without particular limitation. In this case, in order to improve the reliability of the electrical connection between the cured body of the curable conductive material filled in the through hole and the conductive layer, an inclined surface is present in the cross section of the conductive layer located at both ends of the through hole. It is preferable to increase the contact area with the cured product. The method of forming an inclined surface in at least a part of the cross-section of the conductive layer in the above-mentioned through hole, after forming through-holes for through holes in the insulating substrate having a conductive layer on both sides, soft etching with a soft etching solution The conductive layer and the insulating substrate are formed by a method of forming the inclined surface or by a drill having a diameter slightly larger than that of the through hole before or after forming the through hole for the through hole in the insulating substrate having conductive layers on both sides. There is no particular limitation on the method of grinding the tape in a tapered shape, the method of forming an etching resist having a diameter slightly larger than that of the through hole around the through hole, and performing the etching to form the resist.

In the present invention, the through hole is filled with a curable conductive substance which gives a cured product having conductivity and is cured. The curable conductive material is gold, silver, copper, nickel,
A known curable conductive substance in the form of a paste can be used by mixing a conductive material such as lead or carbon and a crosslinkable thermosetting resin such as an epoxy resin or a phenol resin together with an organic solvent if necessary. Of these curable conductive materials, the etching liquid used for etching, for example, ferric chloride etching liquid, cupric chloride etching liquid, ammonium persulfate etching liquid, sodium persulfate etching liquid, potassium persulfate etching liquid. A material that gives a cured product that is not substantially dissolved by an etching solution such as a hydrogen peroxide / sulfuric acid etching solution or an alkaline etching solution containing ammonium sulfate complex ions as a main component is preferably used.

Further, the above-mentioned curable conductive material has an electric resistance after curing of 1 × in order to obtain good through-hole resistance.
It is preferable to select the conductive material and adjust the amount used so that it becomes 10 ⁻² Ω · cm or less.

The filling of the above-mentioned curable conductive substance into the through holes of the insulating substrate is such that the curable conductive substance fills the entire space of the through holes and is a little from both surfaces of the conductive layer, specifically, 0. 1m
There is no particular limitation as long as it is a method of filling it so as to protrude by m or more, preferably 0.1 to 2 mm. A typical filling method of the curable conductive material is, for example, a method of applying one or more times by a printing method, a method of press-fitting with a pair of front and back squeegees from both sides of the insulating substrate, a roll coater or a curtain coater. Means such as a method of filling in by the above method and scraping off the excess paint with a squeegee are preferably used.

The curable conductive material filled in the through-hole is cured by a known curing method such as a hot air oven, an infrared oven, a far infrared oven, an ultraviolet curing oven and an electron beam curing oven. What is suitable for curing may be appropriately selected and cured.

In the present invention, after the curable conductive material is cured, it is important to grind the surface formed by the conductive layer and the cured body of the curable conductive material smoothly. That is, by such grinding, it is possible to accurately form a pattern using an etching resist and to perform etching in the subsequent step of forming a wiring pattern. Therefore, the through hole can be conducted without forming a land around the through hole, and the wiring pattern can be formed extremely advantageously for forming the fine pattern. As a method for smoothly grinding the surface composed of the conductive layer and the curable conductive material, a method used for polishing an ordinary conductive layer such as slurry polishing, buff polishing, and scrub polishing is preferably used.

In the present invention, a wiring pattern is formed on the smoothed surface of the conductive layer including the through hole portion. As a method of forming the wiring pattern, a method of forming an etching pattern with an etching resist and performing etching is generally used. As the etching resist used here, a dry film, a resist ink, or the like is used without particular limitation, and it may be appropriately selected and used depending on the fineness of the pattern. Further, as the etching resist pattern, a positive pattern or a negative pattern may be appropriately adopted by the etching method. For example, a positive pattern may be adopted in an etching method typified by a tenting method, and a negative pattern may be adopted in a solder peeling method and an etching method typified by an SES method.

The present invention also provides a method of manufacturing a circuit board, characterized in that a plating layer is formed on the surface smoothed by the grinding in order to more reliably form the wiring pattern. To do.

That is, according to the present invention, through holes for through holes are provided in an insulating substrate having conductive layers on both sides, and a curable conductive substance that gives a cured body having conductivity is filled in the through holes and cured. After that, the surface formed by the conductive layer and the cured body of the curable conductive material is ground smoothly, and then a plating layer is formed on the smoothed surface and then a wiring pattern is formed. And a method for manufacturing a circuit board.

In the present invention, the material of the plating layer to be formed is not particularly limited to known conductive metals,
Generally, it is preferable to select the same material as the conductive metal such as copper used as the material of the conductive layer. The method for forming the plating layer is not limited, and known methods can be used without particular limitation. Generally, a chemical (electroless) plating method, an electroplating method and the like can be mentioned. The thickness of the plating layer is
The thickness is preferably such that the reliability of the through hole due to plating is improved and the thickness unevenness of the plating layer does not occur. Generally, from the viewpoint of preventing thickness unevenness, 50 μm or less,
Considering the improvement of the reliability of the through hole, 5 μm or more is preferable. Particularly preferably, it is 5 to 35 μm.

[0018]

According to the method of the present invention, a through hole having a highly reliable conduction is formed without performing chemical plating, electric plating or the like, and substantially without providing a land portion in the peripheral portion of the through hole. be able to. Further, in particular, in a circuit board obtained by a method of forming a plating layer on a smoothed surface, components can be directly mounted on the through holes by soldering, etc. Extremely useful.

[0019]

EXAMPLES Examples are shown below for specifically explaining the present invention, but the present invention is not limited to these examples.

Example 1 A circuit board was manufactured according to the steps shown in FIG. That is, (a) as the insulating substrate 1 having the conductive layers 2 on both sides,
Using a 1.6 mm thick glass-based epoxy resin copper-clad laminate, (b) diameter 0.3 mm, 0.4 mm, 0.5 mm, and 0.5 mm.
6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm through hole 3
Was created by drilling. After drilling, soft etching was performed to form an inclined surface A having the shape shown in FIG. 2 on the cross section of the conductive layer 2.

(C) A commercially available thermosetting silver paste (PS-Tokuriki Kaken Co., Ltd.) is used as the curable conductive material 4 in the through hole 3.
652) was filled by the screen printing method. The silver paste was dried and hardened in a hot air drying oven at 80 ° C. for 4 hours at 150 ° C. for 2 hours.

(D) Next, the surfaces of the hardened silver paste hardened material were polished by sequentially using No. 320 and No. 600 buffs to smooth the surface of the conductive layer containing the hardened material.

(E) Next, on the smoothed conductive layer surface,
A dry film ("Aquamer CF" 1.5 mil manufactured by Hercules Co., Ltd.) was laminated as the etching resist 5 and exposed to form an etching positive pattern (substantially no land portion) connected to the through hole portion.

(F) After that, etching was performed with a cupric chloride etching solution, and (g) the etching resist was peeled off to form a wiring pattern having wirings connected to the through holes.

The resistance value of the formed through hole is obtained by measuring the resistance between the wiring patterns which are connected to the through hole by the surface separation, and is 43 mΩ for the diameter of the through hole of 0.3 mm and 24 mΩ for the diameter of 0.4 mm, respectively. 15mΩ for 0.5mm, 11mΩ for 0.6mm, 8 for 0.7mm
mΩ, 6mΩ for 0.8mm, 5mΩ for 0.9mm,
It was 4 mΩ for 1.0 mm, and showed a good resistance value equivalent to that at the time of forming a through hole by conventional multi-step plating.
Then, a repeated thermal shock test was performed at -45 ° C for 30 minutes / 125 ° C for 30 minutes. After 1000 times of repetition, the through-hole resistance value hardly changed. Also, 3
After 000 times, there was almost no change in the through-hole resistance value.

Example 2 A circuit board was manufactured in the same manner as in Example 1 except that soft etching was not performed after drilling.

The resistance value of the formed through hole was measured in the same manner as in Example 1. As a result, the through hole diameter was 45 mΩ for 0.3 mm, 26 mΩ for 0.4 mm, 16 mΩ for 0.5 mm, and 13 mΩ for 0.6 mm. , 9 mm for 0.7 mm, 7 mΩ for 0.8 mm, 6 for 0.9 mm
It was 4 mΩ for mΩ and 1.0 mm. After that, -45
A repeated thermal shock test was performed at 30 ° C. for 30 minutes and 125 ° C. for 30 minutes. After 1000 times of repetition, the through-hole resistance value hardly changed.

Example 2 A circuit board was manufactured according to the steps shown in FIG. That is, (a) as the insulating substrate 1 having the conductive layers 2 on both sides,
Using a 1.6 mm thick glass-based epoxy resin copper-clad laminate, (b) diameter 0.3 mm, 0.4 mm, 0.5 mm, and 0.5 mm.
6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm through hole 3
Was created by drilling.

(C) A commercially available thermosetting silver paste (PS-Tokuriki Kaken Co., Ltd.) is used as the curable conductive material 4 in the through hole 3.
652) was filled by the screen printing method. The silver paste was dried and hardened in a hot air drying oven at 80 ° C. for 4 hours at 150 ° C. for 2 hours.

(D) Next, the surfaces of the hardened silver paste hardened bodies were polished by sequentially using No. 320 and No. 600 buffs to smooth the surface of the conductive layer containing the hardened bodies.

(E) Next, electroplating was performed on the smoothed conductive layer surface including the through hole portion. The plating bath is Kaparaside GS (trade name: Nippon Schering Co., Ltd.)
Using the company Ltd.), thickness at a current density of 2A / m ² 10
A μm plated layer 5 was formed.

(F) On the surface of the plating layer 5, a dry film (“Aquamar CF” 1.5 mil manufactured by Hercules Co., Ltd.) is laminated as an etching resist 6 and exposed to light to be connected to the through hole. A pattern (substantially free of lands) was formed.

(G) After that, etching was performed with a cupric chloride etching solution, and (h) the etching resist 6 was peeled off to form a wiring pattern having wirings connected to the through holes.

The resistance value of the formed through-hole is obtained by measuring the resistance between the wiring patterns connected to the through-hole by the surface separation. 14mΩ for 0.5mm, 10mΩ for 0.6mm, 8 for 0.7mm
mΩ, 6mΩ for 0.8mm, 5mΩ for 0.9mm,
It was 4 mΩ for 1.0 mm, and showed a good resistance value equivalent to that at the time of forming a through hole by conventional multi-stage plating. Then, a repeated thermal shock test was conducted at -45 ° C for 30 minutes / 125 ° C for 30 minutes. After 1000 times of repetition, the through-hole resistance value hardly changed. Also, after 3000 times, the through-hole resistance value hardly changed.

Further, as shown in FIG. 4, after covering the circuit with the solder resist 7, the electronic component 9 is directly mounted by the solder 8 on the through hole of the circuit board formed by the above method. It is possible to obtain a circuit board having a high wiring density.

[Brief description of drawings]

FIG. 1 is a process drawing showing a typical embodiment of the method of the present invention.

FIG. 2 is a cross-sectional view of a typical through hole in the method of the present invention.

FIG. 3 is a process chart showing a typical embodiment of the method of the present invention.

FIG. 4 is a cross-sectional view showing one mode of mounting electronic components on a circuit board obtained by the method of the present invention.

[Explanation of symbols]

 1 Insulating Substrate 2 Conductive Layer 3 Through Hole 4 Curable Conductive Material 5 Plating Layer 6 Etching Resist 7 Solder Resist 8 Solder 9 Electronic Parts

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Ito 1-1, Mikage-cho, Tokuyama-shi, Yamaguchi Prefecture Tokuyama Soda Stock Company

Claims (2)

[Claims] 1. A through hole for a through hole is provided in an insulating substrate having conductive layers on both sides, and a curable conductive substance that gives a cured product having conductivity is filled in the through hole and cured, and then the conductive substance is formed. A method for manufacturing a circuit board, comprising: smoothly grinding a surface formed by a layer and a cured body of a curable conductive material, and then forming a wiring pattern. 2. A through hole for a through hole is provided in an insulating substrate having a conductive layer on both sides, a curable conductive substance that gives a cured product having conductivity is filled in the through hole and cured, and then the conductive substance is formed. A circuit board, characterized in that a surface constituted by a layer and a cured body of a curable conductive material is ground smoothly, a plating layer is formed on the smoothed surface, and then a wiring pattern is formed. Method.