JPH05243727A - Manufacture of circuit board - Google Patents

Abstract

PURPOSE:To provide the manufacture of a circuit board, in which a circuit board being high in the reliability and durability of electric connection can be obtained by a simple method, in the manufacture of the circuit board having a through hole. CONSTITUTION:A manufacture of circuit board which comprises providing an insulating substrate 1 with a through hole 2, filling the through hole with a hardenable conductive material giving a hardening body having electrical conductivity and hardening the material, thereafter smoothly grinding a surface constituted by the insulating substrate and the hardening body 3 of the hardenable conductive material, then giving electroless plating (and electrolytic plating) to the smoothed hardening body and insulating substrate surface to form a conductive layer 4 and thereafter forming a wiring pattern through a method for performing etching, etc.

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 having a through hole, by which a circuit board having high reliability and durability of electrical connection can be obtained by a simple method.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of circuit boards, formation of through holes for electrically connecting circuits formed on both surfaces of the board generally has a conductive layer formed by laminating copper foils on both surfaces. The insulating substrate is formed by a method in which a through hole is formed by drilling or punching and the through hole is subjected to electroless plating / electroplating, or a curable conductive composition typified by a silver paste is filled. However, in the above method, burrs are generated in the conductive layer around the through hole, and particularly in the later step of forming a wiring pattern,
There is a problem that the reliability around the through hole is reduced. In order to solve the above problem, a method has been proposed in which a through hole is provided without forming a conductive layer on both surfaces of an insulating substrate and a circuit board having a through hole is manufactured. In this method, electroless plating and electroplating are performed on the through holes formed in the insulating substrate to form conductive layers on both surfaces of the insulating substrate, simultaneously forming through holes, and forming a wiring pattern in the conductive layers. ..

[0003]

However, in the method of forming the conductive layer and the through hole after forming the through hole in the insulating substrate, it is formed as the first conductive layer formed in the insulating substrate. The conductive layer by electroless plating is
Due to poor durability against heat history, it was necessary to provide subsequent electroplating with a thickness of several tens of μm. In general, since electroplating is not uniform in thickness, it causes unevenness in the thickness of a conductive layer formed by electroplating on the substrate surface, and a good fine pattern can be formed in forming a wiring pattern. In addition to having the problem of difficulty, the obtained circuit board still had room for improvement in terms of durability against heat history.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems in a method of forming a wiring pattern including a through hole after forming a through hole in an insulating substrate. As a result, it has been found that the strain of the interface that contacts the surface of the insulating substrate having the through hole is extremely large in the through hole and the strain of the interface on the surface of the substrate is small. Then, the through hole of the insulating substrate is filled with a conductive resin to ensure the conduction, and the surface composed of the insulating substrate and the curable conductive material is ground smoothly to obtain the smoothed curable material. It has been found that by forming a wiring pattern on the surface of an insulating substrate containing a conductive substance, it is possible to obtain a highly reliable circuit board having excellent durability against heat history, and completed the present invention.

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

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-
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 (bismaleimide-triazine) resin resin laminated substrate, composite resin Examples thereof include synthetic resin substrates such as substrates, flexible substrates such as polyimide resins and polyester resins, and ceramic substrates. In particular, in the manufacturing method of the present invention, since the curable conductive material is filled and cured before forming the wiring pattern, the volatile component in the substrate is often diffused by the heating during the curing. Even when using, the method of the present invention can be applied without causing swelling of the wiring pattern or the conductive layer before the formation of the wiring pattern.

First, a through hole for a through hole is provided on the insulating substrate. The diameter of the through hole is not particularly limited as long as it can be filled with the curable conductive material. Generally, 0.2 mm or more, preferably
It is preferable to select from 0.3 to 2 mm.

As a method of forming the through holes for the through holes, known means similar to those for manufacturing a usual circuit board such as drilling, punching, laser processing, etc. are used without particular limitation.

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,
It is possible to use a known curable conductive substance which is made into a paste by mixing a conductive filler 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. Among these curable conductive substances, a substance that gives a cured body that is not substantially dissolved by an etching solution used for etching for forming a circuit pattern described later may be selected and 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. Specifically, the conductive filler 150 is added to 100 parts by volume of the thermosetting resin.
~ 2000 parts by volume.

The filling of the above-mentioned curable conductive material into the through holes of the insulating substrate is such that the curable conductive material fills the entire space of the through holes and is slightly below both surfaces of the conductive layer, specifically, 0.1.
The method is not particularly limited as long as it is a method of filling so as to protrude by not less than mm, preferably 0.1 to 2 mm. A typical filling method of a 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 an 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, an electron beam curing oven, or the like. 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 of the insulating substrate and the cured body of the curable conductive material smoothly. That is,
By such grinding, in the later step of forming the wiring pattern, it is possible to accurately form the pattern using the etching resist and the plating resist. Therefore, the through hole can be conducted without forming a land around the through hole, and a fine pattern can be formed extremely advantageously. As a method for smoothly grinding the surface composed of the insulating substrate 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 insulating layer including the through hole portion. The method for forming the wiring pattern is not particularly limited. The following method can be given as a typical wiring pattern forming method.

That is, (A) a method of performing electroless plating on the smoothed surface to form a conductive layer, and then etching the conductive layer to form a wiring pattern, (B)
In the method of (A), after forming a conductive layer by electroless plating, further forming a conductive layer by electroplating,
(C) A method of forming a wiring pattern by electroless plating after forming a plating resist layer on the smoothed surface,
(D) After forming a thin conductive layer on the smoothed surface by electroless plating, a plating resist layer for providing a wiring pattern is formed on the surface of the conductive layer, and the surface is electroplated.
After removing the plating resist, the conductive layer under the plating resist layer is etched to form a wiring pattern.

By forming the wiring pattern on the smoothed surface as described above, the electrical connection between the through hole and the wiring pattern can be surely made. Further, since the wiring pattern formed by plating is formed only on the surface in which distortion is small with respect to the heat history, durability of the obtained circuit board against the heat history can be remarkably improved.

In the above method A, the method of forming the conductive layer by electroless plating is performed by electroless plating the entire surface of the insulating layer including the through holes.

During electroless plating, the surface of the substrate is
Generally, a catalyst activation treatment is performed. For the catalyst activation treatment, a known method is used without particular limitation. Generally, a palladium-based catalyst,
A general method is to apply an adhesive composed of a thermosetting resin such as an epoxy resin, rubber, and a filler to a substrate by a dipping method, a curtain coating method, a printing method, or the like.

As a material for the electroless plating layer, a known conductive metal is used without any particular limitation. Generally, copper used as a material for a curable conductive substance that gives a cured product having the above-mentioned conductivity. It is preferable to select the same material as the conductive metal such as. The thickness of the plating layer is not particularly limited, but if it is excessively thick, etching becomes difficult and unevenness in the thickness of the plating is caused to some extent. Therefore, it is preferably 100 μm or less, preferably 50 μm or less, and the reliability of the through hole In order to secure the property, the thickness is preferably 5 μm or more, more preferably 10 μm or more. The formation of the conductive layer,
Since the conductive layer is formed by electroless plating with little thickness unevenness, it is easy to form a fine pattern. The electroless plating may be carried out by a known method without particular limitation.

The above method B is a method of electroplating the surface of the electroless plating layer in order to improve the durability of the electroless plating layer formed in the method A. As such an electroplating method, a known method capable of forming a conductive layer of copper, gold, nickel or the like is adopted without particular limitation. In addition, if the thickness of the conductive layer formed by electroplating is too large, unevenness in the plating thickness will be manifested, which makes it difficult to form a fine pattern in the etching step for forming the circuit pattern as described above. Become. Therefore, the thickness of the conductive layer formed by such electroplating is preferably 50 μm or less, and more preferably 25 μm or less.

Further, as a method of forming a wiring pattern on the surface of the conductive layer including the through holes formed by the above methods A and B, a method of forming an etching pattern with an etching resist and performing etching is It is common. 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, in an etching method represented by a tenting method, a positive pattern is formed by a solder peeling method, SES
In the etching method represented by the method, a negative pattern may be adopted. As the etching solution used for the above-mentioned etching, known ones can be used without particular limitation. For example, ferric chloride etching solution, cupric chloride etching solution, ammonium persulfate etching solution, sodium persulfate etching solution, potassium persulfate etching solution, hydrogen peroxide / sulfuric acid etching solution, and alkaline with ammonium sulfate complex ion as the main component. An etching solution such as an etching solution may be used.

Further, in the above method C, a known method can be used without particular limitation for forming the plating resist layer formed in the portion excluding the wiring pattern. As a specific example, a method using a dry film, a resist ink, or the like can be used without particular limitation, and may be appropriately selected depending on the fineness of the wiring pattern. A wiring pattern is formed on the surface of the insulating layer including the through hole portion excluding the plating resist layer. The wiring pattern is generally formed by electroless plating. The catalyst activation treatment described above is performed during electroless plating. For electroless plating, the plating method in the above method A is adopted without particular limitation. Further, the thickness of the plated layer formed is not particularly limited, but is preferably such that the reliability of the through hole due to plating is improved and the uneven thickness of the plated layer does not occur. To give a concrete example, 100
It is preferably 5 μm or less, and more preferably 5 μm or more in consideration of improvement in reliability of through holes. Particularly preferably, 5 to 5
It is 0 μm.

In the above method D, the thin conductive layer formed by electroless plating may have a thickness such that the next electroplating is carried out, and generally 0.2 to 1 μm.
A thickness of m is preferred. Further, in the above method, the method shown in the above method A is adopted without particular limitation as the method of electroless plating, formation of a plating resist layer, electrolytic plating and etching.

In the method of the present invention, after forming a wiring pattern by the above-mentioned method, an insulating layer is formed on the wiring pattern, and then a second wiring pattern is formed to manufacture a multilayer circuit board. It is possible.

The method for forming the insulating layer is not particularly limited, and known methods can be adopted without limitation. Generally, a method using a curable insulating resin in various forms such as a dry film, a liquid resist, a combined use of a dry film and a liquid resist is adopted. When a dry film is used for forming the insulating layer by the above method, the thickness accuracy of the insulating resin layer is good,
Since the back surfaces can be formed at the same time, the insulating layer can be formed more efficiently and with high accuracy. As a method of forming the insulating layer, a printing method, a photography method, or the like may be appropriately adopted depending on the fineness.

The method for forming the second wiring pattern on the insulating layer is also not particularly limited, but after forming a conductive layer of 5 to 35 μm by the electrolytic plating and / or electroless plating, Generally, a wiring pattern is formed in the same manner as the pattern forming method described above.

[0027]

According to the method of the present invention, it is possible to obtain a highly reliable circuit board having excellent durability against heat history.
Further, since the conductive layer is formed on the smoothed surface on the through hole portion, it is possible to perform pattern formation and etching with an etching resist with high precision, and as a result, especially the land is substantially formed around the through hole portion. The wiring pattern can be formed without providing the wiring, and the wiring density can be increased. Further, since the circuit board obtained by the present invention can mount components directly on the through holes by soldering or the like, it is extremely useful in manufacturing a circuit board having a higher wiring density. Further, in the present invention, the second wiring pattern may be formed on the wiring pattern formed on the insulating substrate via the insulating layer to obtain a further densified circuit board.

[0028]

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

Example 1 A curable conductive material which gives a cured product having conductivity was prepared by the following method, and a circuit board was manufactured. That is, the average particle size is 6.8 μm and the tap density is 2.99 g / cm.
³ , dendritic electrolytic copper powder with a specific surface area of 4200 cm ² / g, linoleic acid to the copper powder surface, 0.25 × 10 ^-5 mmol
/ Cm ² and compounded in a mortar for 15 minutes under a nitrogen atmosphere. The pretreated copper powder thus obtained was used with respect to 100 parts by weight of a binder of neopentyl glycol glycidyl ether (epoxy equivalent = 150) / novolac type phenol resin (hydroxy equivalent = 105) = 74/26 (weight ratio). 456 parts by weight, and further, 2.8 parts by weight of 2-ethyl-4-methylimidazole was added to 100 parts by weight of the binder, followed by kneading with a three-roll mill for 30 minutes to prepare a curable conductive composition ( Copper paste).

A circuit board was manufactured according to the steps shown in FIG. That is, (a) the insulating substrate 1 has a thickness of 1.6.
mm glass base epoxy resin laminate,
(B) A through hole 3 having a diameter of 0.8 mm was created by drilling. (C) As the curable conductive material 4 in the through hole 3,
The copper paste prepared by the above method was filled by the screen printing method. The copper paste was cured for 20 minutes in a far infrared conveyor furnace whose temperature was controlled to a maximum temperature of 240 ° C. (D) Next, the 320th and 600th buffs were sequentially used to polish the surface of the cured copper paste from which the cured body protruded, and the surface of the insulating substrate containing the cured body was smoothed. (E) Next, a thick electroless copper plating layer 4 having a thickness of 15 μm was formed on the smoothed surface of the insulating substrate. (F) Next, a dry film (“Aquamer CF” 1.5 mil manufactured by Hercules Co., Ltd.) is laminated as an etching resist layer 6 on the electroless plated surface, and an exposure positive pattern (the pattern is exposed and connected to the through hole portion) ( The land portion is substantially absent). (G) After that, etching was performed with a cupric chloride etching solution, and (h) the etching resist layer was peeled off to form a wiring pattern.

The resistance value of the formed through hole is obtained by measuring the resistance between the wiring patterns connected to the through hole on the front and back sides, and the average value of 8.7 is measured for 64 holes.
The standard deviation of mΩ was 1.24 mΩ. A repeated thermal shock test was conducted at 20 ° C. for 15 seconds and 260 ° C. for 5 seconds. The average rate of change of the through-hole resistance value after 100 times of repetition was 3%, which was almost unchanged.

Example 2 A circuit board was manufactured according to the steps shown in FIG. That is, (a) a glass-based epoxy resin laminate having a thickness of 1.6 mm is used as the insulating substrate 1, and (b) a diameter of 0.8
The mm through hole 3 was created by drilling. (C) A copper paste prepared by the same method as in Example 1 was filled in the through holes 3 as the curable conductive material 4 by a screen printing method. The copper paste was cured for 20 minutes in a far infrared conveyor furnace whose temperature was controlled to a maximum temperature of 240 ° C. (D) Next 32
The surface of the cured copper paste from which the cured body was projected was polished by sequentially using the 0th and 600th buffs to smooth the surface of the insulating substrate containing the cured body. (E) Next, electroless copper plating was applied to the smoothed insulating substrate surface to a thickness of 0.3 μm. (F) Further, a copper plating layer having a thickness of 15 μm was formed on the electroless plated surface by electroplating. (G)
Next, a dry film (“Aquamar C” manufactured by Hercules Co., Ltd.) is formed as an etching resist layer 6 on the electroplated surface.
F "1.5 mil) was laminated and exposed to form an etching positive pattern (substantially free of lands) connected to the through holes. (H) After that, etching was performed with a cupric chloride etching solution, and (i) the etching resist layer was peeled off to form a wiring pattern.

The resistance value of the formed through hole is obtained by measuring the resistance between the wiring patterns connected to the through hole on the front and back sides, and the average value of 8.8 is measured for 64 holes.
The standard deviation of mΩ was 1.30 mΩ. A repeated thermal shock test was conducted at 20 ° C. for 15 seconds and 260 ° C. for 5 seconds. The average value of the change rate of the through-hole resistance value after the number of repetitions of 100 times was 2%, and there was almost no change.

Example 3 A circuit board was manufactured according to the steps shown in FIG. That is, (a) a glass-based epoxy resin laminate having a thickness of 1.6 mm is used as the insulating substrate 1, (b) diameter, 0.
An 8 mm through hole 2 was created by drilling. (C)
As the curable conductive material 3, the through hole 2 was filled with the copper paste prepared by the above method by a screen printing method.
The copper paste was cured for 20 minutes in a far infrared conveyor furnace whose temperature was controlled to a maximum temperature of 240 ° C. (D) Next, the 320th and 600th buffs were sequentially used to polish the surface of the cured copper paste from which the cured body protruded, and the surface of the insulating substrate containing the cured body was smoothed. (E) Next, a plating resist 11 was applied to the smoothed insulating substrate surface by screen printing. (F) Next, a wiring pattern was formed by the thick electroless plating layer 6 having a thickness of 15 μm.

The resistance value of the formed through hole is obtained by measuring the resistance between the wiring patterns connected to the through hole on the front and back sides, and the measurement of 64 holes is performed, and the average value is 9.5.
The standard deviation of mΩ was 2.31 mΩ. 20 ° C for 15 seconds
A repeated thermal shock test was performed at 260 ° C. for 5 seconds. The average value of the change rate of the through-hole resistance value after 100 times of repetition was 5%, and there was almost no change.

Example 4 A circuit board was manufactured according to the steps shown in FIG. That is, (a) a glass-based epoxy resin laminate having a thickness of 1.6 mm is used as the insulating substrate 1, and (b) the diameter is 0.
An 8 mm through hole 2 was created by drilling. (C)
A copper paste prepared by the same method as in Example 1 was filled in the through hole 2 as a curable conductive material 3 by a screen printing method. The copper paste was cured for 20 minutes in a far infrared conveyor furnace whose temperature was controlled to a maximum temperature of 240 ° C. (D) Next 3
The surface of the cured copper paste from which the cured body protruded was polished by sequentially using No. 20 and No. 600 buffs to smooth the surface of the insulating substrate containing the cured body. (E) Next, a thin electroless plating layer 12 was formed on the smoothed insulating substrate surface. (F) Next, a plating resist layer 11 corresponding to the wiring pattern was formed on the electroless plating layer. (G) Next, an electroplating layer 5 having a thickness of 15 μm was formed on the electroless plating surface. (H) After that, the plating resist was removed. (I) Finally, with a ferric chloride etching solution,
The thin electroless plating layer was etched to form a wiring pattern.

The resistance value of the formed through hole is obtained by measuring the resistance between the wiring patterns connected to the through hole on the front and back sides, and the average value of 11.
The standard deviation of 2 mΩ was 0.98 mΩ. A repeated thermal shock test was conducted at 20 ° C. for 15 seconds and 260 ° C. for 5 seconds. The average value of the change rate of the through hole resistance value after the number of repetitions of 100 times was 4%, and there was almost no change.

In the circuit board manufactured according to the present invention, as shown in FIG. 5, the electronic component 9 can be mounted on the through hole by the solder 8. Therefore, it is possible to reduce the distance between the through holes and increase the mounting density of components. In contrast, conventional through holes (Fig. 6)
Then, after the through hole is formed, the copper plated through hole 10
Therefore, the above mounting is difficult, and it is necessary to mount the electronic component at a position away from the through hole to the extent that solder is prevented from flowing out from the through hole in the through hole.
Moreover, it is necessary to provide a weir with the solder resist layer 7. Therefore, it is difficult to increase the mounting phase density.

Comparative Example 1 In Example 1, without filling the through holes for through holes with the curable conductive material, the insulating substrate was plated with electroless copper with a thickness of 0.3 μm, and then with copper by electroplating with a thickness of 15 μm. A circuit board was manufactured in the same manner except that a layer was provided and a conductive layer and a through hole were simultaneously formed.

The circuit board thus obtained was subjected to a repeated thermal shock test at 20 ° C. for 15 seconds and 260 ° C. for 5 seconds. After 100 repetitions, the through hole was completely broken.

[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 process drawing showing a typical embodiment of the method of the present invention.

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

FIG. 4 is a process drawing showing a typical embodiment of the method of the present invention.

FIG. 5 is a cross-sectional view at the time of mounting a typical surface mount component in the method of the present invention.

FIG. 6 is a cross-sectional view of a general circuit board when surface-mounted components are mounted.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Through hole 3 Curable conductive substance 4 Electroless plating layer 5 Electroplating layer 6 Etching resist layer 7 Solder resist layer 8 Solder 9 Electronic component 10 Copper plating through hole 11 Plating resist layer 12 Thin electroless plating layer

Front page continuation (72) Inventor Seiji Kato 1-1 Mikagecho, Tokuyama City, Yamaguchi Prefecture Tokuyama Soda Co., Ltd.

Claims (2)

[Claims] 1. A through hole for a through hole is provided in an insulating substrate,
After filling the through hole with a curable conductive material that gives a cured body having conductivity and curing the same, the surface formed by the insulating substrate and the cured body of the curable conductive material is ground smoothly, and then the smooth surface is smoothed. A method for manufacturing a circuit board, which comprises forming a wiring pattern on the surface of the printed circuit board. 2. The method for manufacturing a circuit board according to claim 1, wherein after forming a wiring pattern, an insulating layer is formed on the wiring pattern to form a second wiring pattern.