JPS6387797A - Method of forming conductive circuit on substrate - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a method of forming a conductive circuit on a substrate such as a printed circuit board using copper foil, and in particular to a method of effectively using a newly developed copper conductive paste with good metal plating properties. When forming at least two layers of conductive circuits that are electrically connected to one side of the substrate, the outer periphery of the electrode portion of the 211th conductive circuit is formed in a waveform, and the inner side of the electrode portion of the first layer conductive circuit is and apply copper conductive paste so as to span the outside,
The present invention relates to a method of forming a conductive circuit in which the conductivity is improved by increasing the cross-sectional area of the conductive path through metal plating, and the adhesion strength of the second layer conductive circuit is increased.

Prior Art Conventionally, in printed circuit boards using fI foil, when the conductive circuit formed there becomes complex beyond a certain level, it becomes necessary to electrically connect one part of the conductive circuit to another part. With the conventional technology, it was not possible to industrially form two or more layers of conductive circuits on one side of a printed circuit board, so if there is such a need, both sides of the printed I board can be used. There was no other way than to use a so-called double-sided through-hole board in which the formed copper foil etched circuit was electrically connected using through-holes.

However, with this double-sided through-hole board, it is necessary to paste W4'4 on both sides of the board, perform etching processing, and perform a large number of holes using an NC device, etc., resulting in high material and manufacturing costs. The drawback was that it took a long time and production was poor.

Therefore, in order to improve the drawbacks of the conventional method described above,
It is desired to establish a technology for industrially forming two or more layers of conductive circuits on one side of a printed circuit board, but for this purpose, it is necessary to develop an inexpensive copper conductive paste with good conductivity and metal plating properties, especially copper plating properties. It was needed. However, this copper conductive paste requires heating to harden the paste, but due to its characteristics, copper is extremely susceptible to oxidation, contrary to precious metals such as silver, so this heating causes the copper powder in the paste to oxidize. It has been considered difficult to put it into practical use because it oxidizes, increases electrical resistance, and deteriorates solderability. In addition, when metal plating is applied to heat-cured copper conductive paste, the surface is usually used as a catalyst.
This method requires a step of activating the copper powder using a binder, exposing the copper powder particles from the resin layer as a binder, and creating a so-called plating nucleus, which has the drawback of requiring a large number of man-hours.

In addition, in order to form two or more layers of conductive circuits on one side, in Utility Model Publication No. 55-42460, highly insulating resist polybutadiene is used for the insulating coating layer, and 20% phenol resin, for example, is used for the base circuit covered with the copper coating. , copper powder 63% and solvent 17%
%, the adhesive paste is thickened to a thickness of 20 μm by electroless plating, and a copper coating is applied. At present, there are no examples of this being implemented industrially.

The applicant of the present application has been conducting research for many years in order to develop a copper conductive paste that can eliminate all of the above-mentioned drawbacks, and has finally completed this and succeeded in commercializing it. It is made by adding a small amount of special additives such as anthracene in addition to copper powder and synthetic resin.
020, ACP-030, and ACP-007P. ACP-020
The fl conductive paste has 80% by weight of copper powder and 20% by weight of synthetic resin as main components, and has extremely good conductivity, but its soldering properties are somewhat poor. ACP-0
The copper conductive paste No. 30 mainly contains 85% by weight of copper powder and 15% by weight of synthetic resin, and has good solderability although its conductivity is slightly inferior to that of ACP-020. Also ACP
-007P copper conductive paste is this ACP-030
It has been improved to allow metal plating, such as copper chemical plating, to be applied on the cured coating film without a catalyst, and it has extremely excellent metal plating properties.

Therefore, the applicant of this application used the newly developed copper conductive paste with good metal plating properties, applied it to the first layer conductive circuit that can be metal plated, cured it by heating, and applied metal plating on top of it. For example, Japanese Patent Application No. 60-216041 discloses a method of forming a second layer conductive circuit connected to a first layer conductive circuit by using a method of forming a conductive circuit of at least 2N on one side of the substrate.
It was proposed in the application of .

In these conventional techniques, as shown in FIGS. 5 and 6, a first layer conductive circuit CI made of a copper foil 2 formed on a substrate l is formed by etching, and then
A plating-resistant resist 3 is applied by printing to the substrate l, leaving the parts 2a and 2b where it is necessary to electrically connect the layer conductive circuit CI and the second layer conductive circuit Ct, and the part where no connection is necessary and the first layer Surface 1a of substrate 1 without conductive circuit C1
is coated with a plating-resistant resist 3 (not shown in FIG. 5 as the plating-resistant resist 3 is transparent).

Then, a copper conductive paste 4 with good metal plating properties is applied by screen printing to the remaining areas where the plating-resistant resist 3 is not applied, cured by heating, and cleaned.
As shown in FIG. 6, chemical plating of copper, which is an example of metal plating, is applied to the copper conductive paste 4 to form a copper plating layer 5, and the copper plating layer 5 and the copper conductive paste 4 form a second layer conductive circuit. Ct, and electrically connected conductive circuits c, , C2 of at least 2N are formed on one side of the substrate 1 in a laminated state.

However, in the above conventional technology, the first layer conductive circuit C3
Copper conductive paste 4 applied to electrode portion 2d of copper foil 2 of
No particular consideration was given to the shape of , as shown in Figure 5.
For example, the coating was applied to a simple rod shape with an arcuate end 4a. On the other hand, the conductivity of the copper plating layer 5 to the electrode portion 2d is determined by the total area of the thick end surface 5a that is in direct contact with the electrode portion 2d of the copper plating layer 5, that is, the cross-sectional area of the conductive path (
The adhesion strength of the second layer conductive circuit C2 is determined by the area of the electrode portion 4d of the second layer conductive circuit C8, the total length of the outer circumference 4e, etc. determined by

For this reason, the shape of the electrode portion 4d of the second layer conductive circuit C2 as shown in FIG. 5 has the disadvantage that good conductivity and large adhesion strength cannot be obtained.

Purpose The present invention has been made in order to eliminate the drawbacks of the prior art described above, and its purpose is to form a conductive circuit of at least 2N electrically connected to one side of a substrate. , the outer periphery of the electrode portion of the second layer conductive circuit is formed into a wave shape, and a copper conductive paste is applied so that the electrode portion is located on the inside and outside of the electrode portion of the first layer conductive circuit. The objective is to increase the cross-sectional area of the conductive path by plating to improve conductivity. Another purpose is to increase the adhesion strength of the second layer conductive circuit.

Structure In short, the present invention forms a first layer conductive circuit that can be metal-plated on a substrate, applies a copper conductive paste with good metal plating properties to the electrode portion of the first layer conductive circuit, and heats and hardens the paste. Metal plating is applied to the first layer conductive circuit and the copper conductive paste to form a 211th conductive circuit electrically connected to the first layer conductive circuit, thereby forming at least two layers of conductive circuits on one side of the substrate. In the method, the electrical paste is applied so that the outer periphery of the electrode portion of the second layer conductive circuit is formed in a wave shape and is located on the inside and outside of the electrode portion of the first layer conductive circuit, and A thick end face of the metal plating is connected to the first layer conductive circuit at a part of the outer periphery of the electrode portion of the second layer conductive circuit to form a conductive path by the metal plating, and a conductive path is formed by the metal plating. Another part of the electrode portion is located outside the electrode portion of the first layer conductive circuit and is in close contact with the substrate.

In the method of forming a conductive circuit on a substrate according to the present invention, as in the conventional example, first, as shown in FIG.
A first layer conductive circuit C3 made of a copper foil 32 etc. formed on the substrate is formed by etching, and then the first layer conductive circuit C and the second layer conductive circuit C2 are required to be electrically connected. A plating-resistant resist 33 is applied by printing to the substrate 31, leaving only the parts 32a and 32b, and the parts unnecessary for connection and the first J! ! The surface 31a of the group vi, 31 where the conductive circuit C, does not exist is coated with a plating-resistant resist 33. Then, a W4 conductive paste 34 with good metal plating properties is applied by screen printing to the remaining areas where the plating-resistant resist 33 is not applied, cured by heating, and cleaned. As shown in FIG. Copper chemical plating, which is an example of metal plating, is applied to the conductive paste 34 to form copper plating N35, and a second layer conductive circuit Ct is formed by the liquid-heated plating layer 35 and the copper conductive paste 34. , at least two electrically connected conductive circuits ClIC, are formed in a stacked state.

In the present invention, in the method described above, the outer periphery 34e of the electrode portion 34d of the second layer conductive circuit C2 is formed in a wave shape, and the inner periphery 34e of the electrode portion 32d of the first layer conductive circuit C8 is
Copper conductive paste 34 is applied so as to be located across 2f and outside 32g, and the thick end surface 35a of the copper plating layer 35 becomes the first layer conductive in a part of the outer periphery 34e of the electrode portion 34d of the second layer conductive circuit C2. A conductive path formed by copper plating is formed by being connected to the circuit C0, and another part of the electrode portion 34d of the second layer conductive circuit C2 is the 111th conductive circuit C.

The electrode portion 32d is located outside the electrode portion 32d so as to be in close contact with the substrate 31.

Further, in the first embodiment of the present invention shown in FIGS. 1 to 3, the electrode portion 34d of the second layer conductive circuit Ct is formed by forming the copper conductive paste 34 into a ring shape such that the center thereof is a hollow portion 34c. The thick end face 35 of the copper plating 1135 is coated on a part of the outer periphery 34e and the inner periphery 34f of the electrode portion 34d.
a is connected to the first layer conductive circuit CI to increase the cross-sectional area of the conductive path by copper plating. Also the second
The inner circumference 34f of the electrode portion 34d of the layer conductive circuit C2 is formed in a circular shape.

In FIG. 1, the plating-resistant resist 33 is omitted because it is transparent, and is part of the thick end surface 35a of the copper plating layer 35 formed covering the copper conductive paste 34 of the second layer conductive circuit Ct. , The portion shown in a dotted pattern in FIG. 1 is the first layer conductive circuit C.

This total area is such that the copper conductive paste 34 is formed circularly on the inner periphery 34f on the electrode portion 32d of the first layer conductive circuit CI, and is connected to the first layer on the outer periphery 34e. Electrode portion 32 of conductive circuit C.
Only the waveform portion located inside d forms a conductive path intermittently, and the thick end face 35 shown by this dotted pattern
The portion a is double formed with an outer periphery 346 and an inner periphery 34f, so that a considerably larger cross-sectional area of the conductive path can be obtained than in the conventional example shown in FIG. Further, the electrode portion 34d of the second layer conductive circuit C2 protruding to the outside 32g of the first layer conductive circuit C1 is extremely effective in increasing the adhesion strength. In addition, a plating resist 33 is applied to the hollow part 34C.
As shown in FIG. 3, copper plating]'i15 is formed on the entire surface of the hollow portion, forming the first layer conductive circuit C.

The structure is such that the adhesion strength of the liquid-warmed plating layer to the plating layer is increased and the conductivity is also improved. Further, a copper plating layer 35 is also formed on the inner side 32f of the electrode portion 32d of the first layer conductive circuit C3, so that the adhesion strength is further increased and the conductivity is also improved.

In the above description, the first layer conductive circuit C3 is formed by etching the W4 foil 32, but this is not limited to the etching method. It is obvious that the conductive circuit may be one in which the conductive circuit is coated on a substrate, heated and cured, and then subjected to chemical copper plating on the entire surface, or a conductive circuit using a metal other than copper.

As the plating-resistant resist 33, for example, ■ plating-resistant resist CR-2001 manufactured by Asahi Chemical Research Institute is applied.
For example, it is cured by heating at 150° C. for 30 minutes.

Regarding other conditions, the copper conductive paste 34 is, for example, ■Copper conductive paste A manufactured by Asahi Chemical Research Institute.
CP-OQ7P is applied by screen printing and cured by heating at a temperature of 150° C. for 30 to 60 minutes.

Further, to explain the plating pretreatment for forming the copper plating layer 35, this plating pretreatment includes, for example, washing with a 4 to 5% by weight aqueous solution of sodium hydroxide (NaOH) for several minutes, and washing with hydrochloric acid (IcI) 5 Surface treatment is performed for several minutes with a 10% by weight aqueous solution. Through this surface treatment, many particles of copper powder appear between the binders on the surface of the copper conductive paste 34, and nuclei for copper plating are easily formed. Therefore, catalyst treatment as in normal electroless plating is not necessary.

Next, to explain chemical copper plating, the substrate 31 is immersed in a chemical copper plating bath, and the surface of the W4 conductive paste 34 is coated with
As shown in FIG. 3, chemical copper plating is applied to form a copper plating layer 35. This chemical copper plating bath is used at a pH of 11 to 13 and a temperature of 65 to 75°C to form a copper plating layer 35. The thickness shall be 5 μm or more. The plating rate in this case is 1.5 to 3 microns per hour.

As shown in FIGS. 1 and 3, the copper plating layer 35
An overcoat (not shown) (e.g., plating-resistant resist CR-2001 manufactured by Asahi Chemical Research Institute) is applied to the surface of the substrate 31 on which the oxide is formed, and then cured by heating.
A substrate 31 on which N conductive circuits C+ and Ct are formed is completed.

In the above embodiment, the metal plating applied to the copper conductive paste 34 was explained as copper plating, but it is clear that this is not limited to copper plating, and noble metal plating such as silver plating or gold plating may be used. It is. Further, in the above embodiment, a two-layer conductive circuit C+ is provided on one side of the substrate 31.
, C2 was explained, but this can be done by repeating the above steps on the overcoat.
It is also clear that conductive circuits can be formed in more than one layer.

Next, in the first embodiment of the present invention shown in FIGS. 1 to 3, the inner periphery 34 of the electrode portion 34d of the second layer conductive circuit c2 is
f is formed in a circular shape, but in the second embodiment shown in FIG. 4, the inner circumference 34f of the electrode portion 34d is formed in a corrugated shape connected by circular arcs, which is different from the first embodiment shown in FIG. The length of the thick end face 35a at the inner circumference 34f of the copper plating layer 35 is longer than in the case of the example, the cross-sectional area of the conductive path by the copper plating JW35 is made larger, and the adhesion strength to the first layer conductive circuit C1 is increased. has also improved. In FIG. 4, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted.

Next, the 1iiiI electric paste 34 and the plating-resistant resist 33 used in the present invention will be described in detail.

First, as an example of the copper conductive paste 34, a copper conductive paste with good copper plating property called ACP-007P manufactured by Asahi Chemical Research Institute will be explained. Generally, copper is a metal that is easily oxidized, and in particular, copper is more easily oxidized in powder form because it has a large surface area. Therefore, unlike noble metal pastes that use non-oxidizing noble metal powders, it is necessary to design a paste composition that can remove the oxide film on copper particles and prevent re-oxidation. In order to design a copper conductive paste that is easy to chemically plate steel and has high adhesion to the base material, the components such as copper powder, binder, and special additives for anti-oxidation (e.g., anthracene, anthracene carboxylic acid, anthrazine) , anthranilic acid is effective), the selection of materials such as dispersants and solvents, and appropriate dispersion and kneading techniques are important points.

Copper powder differs in particle shape and particle size depending on its manufacturing method.
The electrolytic method (a method in which copper is deposited in powder form by electrolysis) produces dendritic, highly pure powder, while the reduction method (a method in which copper is reduced with a reducing gas) produces spongy, porous fine particles. is provided. In order to form the above-described conductive circuit of the present invention, the copper conductive paste must have the following characteristics.

(1) Good screen printability and ability to form fine patterns.

(2) Excellent adhesion to the substrate.

(3) To withstand the high temperature alkaline bath of chemical copper plating.

(4) Good adhesion to copper plating.

(5) Stable printability can be obtained with little viscosity change due to aging.

The above to meet such demands! ! ILS electrolytic paste uses high-purity electrolytic copper powder, which contains many dendrites precipitated by electrolysis, and porous spongy fine powder made by reducing metal oxides. ing. Powders obtained by processing these copper powders into flakes (pulverized powders) are also used.

In order to increase the content of copper powder in the paste, it is necessary to mix particles with different particle sizes and shapes in a close-packed manner.

Next, regarding the binder in the copper conductive paste, the binder must act as a dispersion vehicle for a large amount of powder, as a strong adhesive to the substrate, and at the same time must be sufficiently resistant to the alkaline bath of chemical copper plating. It won't happen.

Therefore, the binder used is one containing an epoxy resin that has a high copper powder content, has very good adhesion to copper foils and glass epoxy substrates, and has very good plating deposition properties, and has very good adhesion to the plating film.

Next, apply CP- to the copper conductive paste made by Asahi Chemical Research Institute.
An example of the characteristics of the copper plating deposited on 007P is that the color tone and shape are reddish brown and paste-like, and the viscosity is 300 to 500 ps at 25 ° C.
The adhesion on the copper foil and the resin substrate both passed the tape test, the adhesion between the copper conductive paste and the plating after copper plating passed the tape test, and the solderability had a spread rate of 96% or more. So, the tensile strength (3 x 3 cranes 2) is 3.
0 kg or more.

Further, details regarding the constituent components and conductive properties of the above-mentioned copper conductive paste can be found in Japanese Patent Application No. 55-66 filed by the present applicant.
09 (Japanese Unexamined Patent Publication No. 56-103260) and patent application No. 60-2
16041, so the explanation will be omitted.

Next, to explain the plating-resistant resist, in the present invention, a plating-resistant resist called CR-2001 manufactured by Asahi Chemical Research Institute is used. If it is inconvenient to connect the second layer conductive circuit to the conductive circuit, a plating-resistant resist is coated on the first layer conductive circuit by a printing method.
In addition to having good insulation properties, it is also required to have particularly excellent alkali resistance. CR-2001 was developed as a plating resist that can withstand acidity for more than 4 hours at 70°C in an alkaline bath with a pH of 12, the same as the chemical copper plating bath.
This is a plating-resistant resist.

This paste is similar to the copper conductive paste ACP-007P and has an epoxy resin as its main component, and is printed using a 180-mesh polyester screen and cured by heating at 150° C. for 30 minutes. A thick film of about 15 to 30 μm is preferable from the viewpoint of chemical resistance and voltage resistance. Its main characteristics are as follows.

In other words, it has strong adhesion to the base material and excellent adhesion to copper foil, and the cured film does not deteriorate even if immersed in alkali-resistant (pH 12) for a long time. It's safe. Further, the method of using this plating-resistant resist is that the coating method is screen printing, and the mixing ratio is 10 g of the hardening agent to 100 g of the main agent. The curing conditions include a temperature range of 150 to 200°C and a set time of 30 to 15 minutes.

The main characteristics are that the color tone and shape are green and ink-like, and the adhesion (cross cut) is 100/10100 (
foil surface), surface hardness (using Empi) of 8 layers or more, solvent resistance (in trichlorethylene) of 15 seconds or more, soldering heat resistance (260℃) of 5 cycles or more, surface insulation resistance value of 5X
10"Ω or more, volume resistance value is 1 x 10'4Ω-B, withstand voltage (15μm) is 3.5 kV or more, dielectric loss tangent (IMH)
z) is 0.03 or less.

Effects The present invention, when forming at least two layers of conductive circuit electrically connected to one side of a substrate as described above, forms the outer periphery of the electrode portion of the second layer conductive circuit in a wave shape, and Since the copper conductive paste is applied so that it is located across the inside and outside of the electrode part of the first layer conductive circuit, the cross-sectional area of the conductive path due to metal plating is increased, and the conductivity can be improved. There is. Moreover, the effect of significantly increasing the adhesion strength of the second layer conductive circuit can be obtained.

[Brief explanation of the drawing]

1 to 3 relate to the first embodiment of the present invention, and FIG. 1 shows a state in which copper plating, which is an example of metal plating, has been completed.A first layer conductive circuit and a second layer conductive circuit have been formed. 2 is a partial plan view of the board; FIG. 2 is a vertical sectional view taken along the nm arrow in FIG. 1 showing a state in which copper conductive paste has been applied; FIG. 3 is a partial plan view of the board in FIG. 4 is a partial plan view similar to FIG. 1 according to the second embodiment of the present invention, FIGS. 5 and 6 are related to the conventional example, and FIG.
A plan view similar to the figure, and FIG. 6 is a longitudinal sectional view taken along the line Vl--Vl in FIG. 5. 31 is a substrate, 32 is a copper foil forming the first layer conductive circuit, 3
2f is inside, 32g is outside, 34 is copper conductive paste, 3
4c is a hollow part, 34d is an electrode part, 34e is an outer periphery, 35
35a is a thick end face, CI is a first layer conductive circuit, and C2 is a second layer conductive circuit.

Claims (1)

[Claims] 1. A first layer conductive circuit that can be metal plated is formed on a substrate, and a copper conductive paste with good metal plating properties is applied to the electrode portion of the first layer conductive circuit and cured by heating, Metal plating is applied to the first layer conductive circuit and the copper conductive paste to form a second layer conductive circuit electrically connected to the first layer conductive circuit, so that at least two layers of conductive circuits are formed on one side of the substrate. In the method, the copper conductive paste is applied so that the outer periphery of the electrode portion of the second layer conductive circuit is formed in a wave shape and is located on the inside and outside of the electrode portion of the first layer conductive circuit. , a thick end face of the metal plating is connected to the first layer conductive circuit at a part of the outer periphery of the electrode portion of the second layer conductive circuit to form a conductive path by the metal plating; A method for forming a conductive circuit on a substrate, characterized in that another part of the electrode portion of the circuit is located outside the electrode portion of the first layer conductive circuit and is in close contact with the substrate. 2. The electrode part of the second layer conductive circuit is coated with the copper conductive paste in a ring shape so that the center thereof is hollow, and the thickness of the metal plating is applied on a part of the outer periphery and the inner periphery of the electrode part. 2. The method of forming a conductive circuit on a substrate according to claim 1, wherein the end face is connected to the first layer conductive circuit to increase the cross-sectional area of the conductive path formed by the metal plating. 3. The method of forming a conductive circuit on a substrate according to claim 2, wherein the inner periphery of the electrode portion of the second layer conductive circuit is formed in a circular shape. 4. The method for forming a conductive circuit on a substrate according to claim 2, wherein the inner periphery of the electrode portion of the second layer conductive circuit is connected by circular arcs to form a continuous waveform. . 5. The method for forming a conductive circuit on a substrate according to claim 1, wherein the metal plating is chemical copper plating.