JPS6387795A - 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 electrode portions of the second layer conductive circuits are placed inside the electrode portions of the first layer conductive circuits. Moreover, by applying the copper conductive paste in a ring shape with a hollow part formed in the center, the total length of the thick end surface connected to the first layer conductive circuit of the metal plating plated on the copper conductive paste is increased. The present invention relates to a method of forming a conductive circuit in which conductivity is improved by increasing the cross-sectional area of a conductive path by metal plating.

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

However, according to this double-sided through-hole board, copper foil is pasted on both sides of the board, etching processing is performed, and N
Since a large number of holes must be drilled using a C device or the like, material costs and manufacturing costs are high, and productivity is 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, in order to apply metal plating to heat-cured copper conductive paste, the surface is usually activated using a catalyst to expose the copper powder particles from the resin layer as a binder, thereby forming the so-called plating core. It had the drawback of requiring a manufacturing process and requiring a large number of man-hours.

In addition, in order to form two or more layers of conductive circuits on one side, in Japanese Utility Model Publication No. 55-42460, highly insulating resist polybutadiene is used for the insulating coating layer, and 20% phenol resin 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. ■Made by Asahi Chemical Research Institute! Ii1 conductive paste ACP
-020, ACP-030 and ACP-007P. ACP-02
The copper conductive paste designated ACP-0 is mainly composed of 80% by weight of copper powder and 20% by weight of synthetic resin, and has extremely good conductivity, but its soldering properties are somewhat poor.
The copper conductive paste No. 30 mainly contains 85% by weight of copper powder and 15% by weight of synthetic resin, and has good soldering properties although its conductivity is slightly inferior to that of ACP-020. Also AC
The copper conductive paste P-007P is this ACP-03
This is an improved version of 0, which allows metal plating, such as copper chemical plating, to be applied on the cured coating film without a catalyst, and has extremely excellent metal plating properties.

Therefore, the applicant of the present 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 4 on top of it. A method of forming at least two layers of conductive circuits on one side of a substrate by forming a second layer conductive circuit connected to the first layer conductive circuit by applying
It was proposed in the application of . In these conventional techniques, as shown in FIGS. 6 and 7, a first layer conductive circuit C4 made of copper foil 2, etc. formed on a substrate 1 is formed by etching, and then the first layer conductive circuit C4 is formed by etching. C.

A plating resist 3 is applied to the substrate 1d by printing, leaving the parts 2a and 2b where it is necessary to electrically connect the circuit and the second layer conductive circuit Ct. The surface 1a of the substrate 1 that is not covered is covered with a plating-resistant resist 3 (not shown in FIG. 6 because 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 resist 3 is not applied, and after being heated and cured and cleaned, as shown in FIG. Copper chemical plating, which is an example of metal plating, is applied to the conductive paste 4 to form a copper plating N5, and a second layer conductive circuit Ct is formed by the copper plating layer 5 and the copper conductive paste 4. , at least two layers of electrically connected conductive circuits CI+C are formed in a stacked state.

However, in the above conventional technology, the first layer conductive circuit C,
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 6.
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 N5 to the electrode portion 2d is determined by the total area of the thick end surface 5a (shown in a dotted pattern in FIG. 6) that is in direct contact with the electrode portion 2d of the copper plating layer 5. It is determined by the size of the cross-sectional area of the conductive path, and the second
Layer conductive circuit C! The adhesion strength is determined by the area of the electrode portion 4d of the second layer conductive circuit C2, the total length of the outer periphery 48, etc.

For this reason, the shape of the electrode portion 4d of the second layer conductive circuit Ct as shown in FIG. 6 has the disadvantage that good conductivity and large adhesion strength cannot be obtained.

Purpose The present invention has been made to eliminate the drawbacks of the prior art described above, and its purpose is to provide an electrode portion of the second layer conductive circuit inside the electrode portion of the first layer conductive circuit. Copper conductive paste is applied in a ring shape so that the entire outer periphery is contained and the center is hollow, and the thick end surface of the metal plating is applied to the first layer on the outer periphery and inner periphery of the electrode part of the second N conductive circuit. The purpose is to improve the conductivity of the second layer conductive circuit and increase its adhesion strength by increasing the cross-sectional area of the conductive path formed by metal plating connected to the 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. 1st JH! A method of forming at least two layers of conductive circuits on one side of the substrate by applying metal plating to the electric circuit and the copper conductive paste to form a second layer conductive circuit electrically connected to the first N conductive circuit. , Applying the copper conductive paste in a ring shape so that the entire outer periphery of the electrode portion of the second layer conductive circuit is contained inside the electrode portion of the first layer conductive circuit, and a hollow portion is formed in the center. The present invention is characterized in that thick end faces of the metal plating are connected to the first N conductive circuit on the outer and inner peripheries of the electrode portion, thereby increasing the cross-sectional area of the conductive path formed by the metal plating.

The present invention will be explained below based on the embodiments shown in the drawings. In the method of forming a conductive circuit on a substrate according to the present invention, as in the conventional method, first, as shown in FIG. A first layer conductive circuit CI made of copper foil 12 etc. is formed by etching, and then portions 12a and 12b are left where it is necessary to electrically connect the first layer conductive circuit C and the second layer conductive circuit C2. A plating resist 1 is applied to the substrate 11.
3 is applied by printing, and the surface 1"1a of the substrate 11 where no connection is necessary and where the first layer conductive circuit C3 does not exist is covered with a plating-resistant resist 13.Then, the plating-resistant resist 13 is left uncoated. A copper conductive paste 14 with good metal plating properties is applied to the part by screen printing, cured by heating, and cleaned. As shown in FIG. Plating is applied to form a copper plating layer 15, and the second layer conductive circuit C2 is formed by the copper plating layer 15 and the copper conductive paste 14.
, and at least two layers of electrically connected conductive circuits C1C2 are formed on one side of the substrate 11 in a laminated state.

In the present invention, in the above method, the outer periphery 14el of the electrode portion 14d of the second layer conductive circuit C2 is entirely contained within the inner side 12f of the electrode portion 12d of the first layer conductive circuit CI, and the center thereof is hollow. Apply the copper conductive paste 14 in a ring shape so as to form the electrode portion 14C.
Copper plating layer 15 at outer periphery 14e and inner periphery 14f of d
The thick end surface 15a of is connected to the first layer conductive circuit C1,
The cross-sectional area of the conductive path by the copper plating layer 15 is increased.

In FIG. 1, the plating-resistant resist 13 is omitted because it is transparent, and is part of the thick end surface 15a of the copper plating layer 15 formed covering the copper conductive paste 14 of the second layer conductive circuit Ct. , the part indicated by the dotted pattern in FIG.
It is formed in a ring shape on the electrode portion 12d, and the portion of the thick end face 15a indicated by the dotted pattern is formed in a double ring shape, which is better than the conventional example shown in FIG. The cross-sectional area of the conductive path is more than twice as large. In addition, a plating resist 13 is applied to the hollow part 14C.
As shown in FIG. 3, a copper plating layer 15 is formed entirely in the hollow part, and the first layer conductive circuit C is not coated.
, the adhesion strength of the copper plating layer to the copper plating layer is increased, and the conductivity is also improved.

In this way, the thick end surface 15 of the copper plating layer 15 is coated on the outer periphery 14e and the inner periphery 14f of the electrode portion 14d of the copper conductive paste 14.
As shown in FIG.
It is necessary to leave a gap 16 for the thickness of the copper plating layer on the outer periphery 14e of d, and not to coat the hollow part 14c.

In the above description, the first layer conductive circuit C7 is the copper foil 1.
2 has been described as being formed by etching, but this is not limited to the etching method. Copper conductive paste 14 used in the present invention is applied to substrate 11 and cured by heating, and then copper plating is applied to the entire surface. It is clear that a conductive circuit using a metal other than a copper plate may also be used.

As the plating-resistant resist 13, 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. To explain other conditions, the copper conductive paste 14 is, for example, ■ Copper conductive paste ACP- manufactured by Asahi Chemical Research Institute.
Apply OQ7P by screen printing and apply at a temperature of 150
Cure for 30 to 60 minutes. Furthermore, to explain the plating pretreatment for forming the copper plating layer 15, this plating pretreatment includes, for example, sodium hydroxide (Na
The surface is washed with a 4 to 5% by weight aqueous solution of hydrochloric acid (HCI) for several minutes, and the surface is treated with a 5 to 10% by weight aqueous solution of hydrochloric acid (HCI) for several minutes. Through this surface treatment, the copper conductive paste 14
A large number of copper powder particles appear between the binders on the surface of the steel, and nuclei for copper plating are easily formed. Therefore, catalyst treatment as in ordinary electroless copper plating is not necessary.

Next, to explain chemical copper plating, the substrate 11 is immersed in a chemical copper plating bath, and chemical copper plating is applied to the surface of the copper conductive paste 14 as shown in FIG. 3, resulting in the formation of a copper plating layer 15. In this chemical copper plating bath, the pH is 13 to 13, the temperature is 65 to 75° C., and the thickness of the copper plating layer 15 is 5 μm or more. The plating rate in this case is 1.5 to 3 μm/hour.

As shown in FIGS. 1 and 3, the copper plating layer 15
An overcoat (not shown) (for example, Asahi Chemical Research Institute plating resistant resist CR-2001) is applied to the surface of the substrate 11 on which the oxide is formed, and then heated and cured.
A substrate 11 on which N conductive circuits C, , C, are formed is completed.

In the above embodiment, the metal plating applied to the copper conductive base 14 was described 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. be. Further, in the above embodiment, two layers of conductive circuit Cr are provided on one side of the substrate 11.
Although the description has been made to form Cz, it is clear that three or more layers of conductive circuits can be formed by repeating the above steps on an overcoat.

Next, in the first embodiment of the present invention shown in FIGS. 1 to 3, the outer periphery 14 of the electrode portion 14d of the second layer conductive circuit C2 is
e and the inner circumference 14f are circular, whereas in the second embodiment shown in FIG.
The outer periphery 14e is similarly formed in a circular shape, but the inner periphery 14f is formed in the shape of a cross connected by circular arcs.
The length of the thick end face 15a of the copper plating layer 15 is longer than that of the first embodiment shown in FIG.
5, the cross-sectional area of the conductive path is made larger, and the adhesion strength to the first layer conductive circuit CI is further improved.

Next, a third embodiment shown in FIG. 5 will be described. In this embodiment, the outer periphery 14e and the inner periphery 14f of the electrode portion 14d of the second layer conductive circuit C2 formed over the first layer conductive circuit CI are , are connected by circular arcs to form a continuous waveform, and the outer periphery 14e and the inner periphery 14 are smaller than the first embodiment.
The total length of the thick end surface 15a of the copper plating layer 15 at f is made longer, so that the cross-sectional area of the conductive path by the copper plating layer 15 is further increased.

Furthermore, by forming the outer periphery 14e and the inner periphery 14f in a waveform in this way, the adhesion strength of the second layer conductive circuit C to the first layer conductive circuit C is also greatly improved.

Next, the copper conductive paste 14 and the plating-resistant resist 13 used in the present invention will be explained in detail.

First, as an example of the copper conductive paste 14, a copper conductive paste with good copper plating property called ACP-007P manufactured by Asahi Chemical Research Institute will be described. In general, copper is a metal that is easily oxidized, and in powder form in particular, it is more easily oxidized due to its large surface area.Therefore, unlike noble metal pastes that use non-oxidizing noble metal powder, it is possible to remove the oxide film on copper particles and prevent re-oxidation. It is necessary to design a paste composition.In order to design a copper conductive paste that is easy to perform 0W4 chemical plating and has high adhesion to the base material, its constituent components, copper powder,
The important points are the selection of materials such as binders, special additives for oxidation prevention (for example, anthracene, anthracenecarboxylic acid, anthrazine, and anthranilic acid are effective), dispersants, and solvents, and appropriate dispersion crosstalk technology.

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 over time.

In order to meet these demands, the above-mentioned copper conductive paste is made of a highly pure electrolytic copper powder that contains a large amount of dendritic powder precipitated by electrolysis, and a porous sponge made by reducing metal oxides. Fine powder, etc. is used. 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, the above ■Asashi Kagaku Institute Steel Conductive Paste ACP-
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 (3X3ts”) is 3
．． 0 kg or more.

Further, details regarding the constituent components and conductive properties of the above W4 conductive paste can be found in Japanese Unexamined Patent Publication No. 55-6 filed by the present applicant.
609 (Japanese Unexamined Patent Publication No. 56-103260) and patent application No. 60-
216041, 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, and 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 Log 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 and shape are green and ink-like, the adhesion (cross cut) is 100/100 (copper foil surface), the surface hardness (using Empi) is 8H or more, and the solvent resistance (in trichlorethylene). ) for 15 seconds or more, soldering heat resistance (
260℃) is 5 cycles or more, surface insulation resistance value is 5X1
0"Ω or more, volume resistance value is 1 x 10'4Ω-■, withstand voltage (15μm) is 3.5 kV or more, dielectric loss tangent (IMHz
) is 0.03 or less.

Effects As described above, the present invention applies the copper conductive paste so that the entire outer periphery of the electrode portion of the second layer conductive circuit fits inside the electrode portion of the first layer conductive circuit, and there is a hollow part in the center. It was applied in a ring shape, and the thick end faces of the metal plating were connected to the first N conductive circuit at the outer and inner peripheries of the electrode portions of the second layer conductive circuit to increase the cross-sectional area of the conductive path by the metal plating. The effect of improving the conductivity of the layer conductive circuit and increasing its adhesion strength 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. A partial plan view of the board; Figure 2 is a vertical cross-sectional view taken along arrows -■ in Figure 1 showing a state where copper conductive paste has been applied; -M longitudinal cross-sectional view, 4th
FIG. 5 is a partial plan view similar to FIG. 1 according to a second embodiment of the present invention, FIG. 5 is a partial plan view similar to FIG. 1 according to a third embodiment of the present invention, and FIGS. The figures relate to a conventional example, and Fig. 6 is a partial plan view similar to Fig. 1, and Fig. 7 is a partial plan view of Fig. 6.
It is a sectional view along the arrow line. 11 is a substrate, 12 is a copper foil forming the first layer conductive circuit, 1
2d is an electrode part, 12f is an inner side, 14 is a copper conductive paste, 14c is a hollow part, 14d is an electrode part, 14e is an outer periphery,
15 is a copper plating layer which is an example of metal plating, 15a is a thick end face, CI is a first layer conductive circuit, and C1 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 of forming the copper conductive paste, the copper conductive paste is arranged so that the entire outer periphery of the electrode portion of the second layer conductive circuit fits inside the electrode portion of the first layer conductive circuit, and the center thereof is hollow. is coated in a ring shape, and thick end surfaces of the metal plating are connected to the first layer conductive circuit at the outer and inner peripheries of the electrode portion to increase the cross-sectional area of the conductive path by the metal plating. A method of forming conductive circuits on a substrate. 2. The method for forming a conductive circuit on a substrate according to claim 1, wherein the metal plating is chemical copper plating. 3 The outer periphery and inner periphery of the electrode portion of the second layer conductive circuit are:
Claim 1 characterized in that the shape is circular.
A method for forming a conductive circuit on a substrate as described in Section 1. 4. The method of forming a conductive circuit on a substrate according to claim 1, wherein the inner periphery of the electrode portion of the second layer conductive circuit is formed in a cross shape connected by circular arcs. 5 The outer periphery and inner periphery of the electrode portion of the second layer conductive circuit are:
2. The method of forming a conductive circuit on a substrate according to claim 1, wherein the conductive circuit is formed into a continuous waveform connected by circular arcs.