JPH05339084A - Production of copper metallized ceramic substrate - Google Patents

Abstract

PURPOSE:To provide the process for production of the copper metallized ceramic substrate which does not generate 'blister' of copper films by heating and has the copper films featuring excellent electrical characteristics. CONSTITUTION:This process for production of the copper metallized ceramic substrate consists in forming the first copper film of a porous structure having communicated spacings on a ceramic substrate by electroless plating, then forming the second copper film on this first copper film by electroplating. The above-mentioned copper film is formed of the porous structure having the communicated spacings and the substrate is heated under a reduced pressure after the formation of the second copper film and is then heated in a nitrogen atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a copper metallized ceramic substrate used for producing a ceramic wiring board, in which a copper film is formed on the surface of the ceramic substrate.

[0002]

2. Description of the Related Art In order to manufacture a ceramic wiring board, a so-called thick film method has been conventionally used in which a metal paste is printed on the surface of a ceramic substrate by using a screen printer to obtain a conductor layer. However, the circuit formed by this thick film method has a drawback that the circuit accuracy is poor and the electric conductivity is poor due to the influence of the mesh of screen printing, and the thick film method has a limit in producing a fine circuit. It was

In order to cope with the high precision and miniaturization of circuits in recent years, as a conductor forming method other than the thick film method, a method of directly forming copper on a ceramic substrate by electroless plating has been proposed. Copper obtained by the electroless plating method has electrical characteristics close to that of electrolytic copper and can form a circuit by a photographic method, so that it has an advantage of realizing high precision and miniaturization of a circuit. However, when a ceramic wiring board is manufactured using a copper film obtained by electroless plating, the copper film "blisters" (local peeling) due to heating such as baking of a thick film resistor after circuit formation. There is a problem that occurs. The cause of this "blister" is that the nucleating solution and plating solution components are contained in the interface between the ceramic and the copper film or in the copper film at the initial stage of deposition, and these components become gas when heated and cause volume expansion. It is thought to be because. As a method to prevent "blister" of the copper film due to this heating,
Japanese Unexamined Patent Publication (Kokai) No. 1-164786 proposes that the internal structure of the conductor layer be a structure having a gap necessary for releasing the internal gas generated during heat treatment.

The formation of a copper film by the electroless plating method has a problem that the deposition rate is slow, and the formation of a copper film by the electrolytic plating method has an advantage that the deposition rate is fast. In order to obtain a thick copper film, after forming a copper film of the minimum necessary thickness by electroless plating,
From there, a method of forming a copper film to a desired thickness by electrolytic plating has been proposed.

[0005]

A copper metallized ceramic manufactured by forming a copper film having a minimum required thickness by an electroless plating method and then forming a copper film on the copper film to a desired thickness by an electrolytic plating method. In the substrate, since the copper film obtained by electrolytic plating is generally dense, the internal structure of the copper film formed by electroless plating has a structure with a gap necessary to escape the internal gas generated during heat treatment. Even in this case, the internal gas generated during the heat treatment cannot escape to the outside of the copper film obtained by electrolytic plating, which causes a problem that the copper film "blisters" due to heating. In addition, there is a problem that the electric characteristics of the copper film formed by the electroless plating method having a structure having a gap are poor.

The present invention is intended to solve the above-mentioned drawbacks of the prior art, and is a copper metallized ceramic having a copper film which is free from the "blister" of the copper film due to heating and excellent in electrical characteristics. An object is to provide a method for manufacturing a substrate.

[0007]

According to the present invention, a first copper film having a porous structure having a communicating gap is formed on a ceramic substrate by electroless plating, and an electrolytic film is formed on the first copper film. In a method of manufacturing a copper metallized ceramic substrate in which a second copper film is formed by plating, a porous structure having a gap through which the second copper film communicates,
The method for producing a copper metallized ceramic substrate is characterized by heating under reduced pressure and then heating in a nitrogen atmosphere after forming the copper film.

The present invention will be described in detail below. The material of the ceramic substrate used in the present invention includes, for example, oxide-based ceramics such as alumina, forsterite, zirconia, mullite, cordierite, titania, barium titanate, and calcium titanate, carbide-based ceramics, and nitride-based ceramics. There are ceramics.

In the present invention, although not particularly limited, the surface of the ceramic substrate is preferably subjected to a roughening treatment in order to strengthen the adhesion with the first copper film. Note that, as the method of this surface roughening treatment, there are a mechanical surface roughening treatment using sandblasting and a chemical surface roughening treatment using a treatment agent such as hot phosphoric acid.

As the electroless plating used in the present invention, for example, copper sulfate, EDTA, and HCHO are used as a plating solution as a basic component, and if necessary, a pH adjusting NaOH or a stabilizer for suppressing decomposition of the plating solution is used. There is a method of using the added plating solution. Then, the first of the porous structure having a communicating gap formed by this electroless plating
The copper film is a copper film having gaps that serve as air holes between crystal grains grown on a ceramic substrate, and the amount of stabilizer added such as sodium cyanide in the electroless plating, the pH value,
Alternatively, such a structure can be obtained by selecting electroless plating conditions such as the concentration of a plating solution component such as Cu or HCHO. The size of the gap communicating with the first copper film is not particularly limited as long as it is large enough to allow the internal gas generated during the heat treatment to escape. The thickness of the first copper film is not particularly limited as long as it does not cause a problem in forming the second copper film on the first copper film by electrolytic plating.

A feature of the present invention is that after the formation of the first copper film,
A second copper film having a porous structure having a void communicating with the first copper film is formed by electrolytic plating, and then heating under reduced pressure and then heating in a nitrogen atmosphere are performed. .. The method for forming the second copper film having a porous structure having the communicating gaps by electrolytic plating is not particularly limited, but, for example, normal electrolysis using a plating solution containing copper sulfate or the like as a main component. In plating, a method of increasing the current density may be used without using an additive called a brightening agent. In the case of copper sulfate plating, the conditions for obtaining a copper film having a porous structure having a communicating gap were examined, and it was found that the plating solution contained 40 to 50 g / l of copper sulfate and contained 97% sulfuric acid. 1
It has a composition containing 90 to 200 g / l and no brightener added, and a current density of 3 to 4 A / dm ^2.
It has been found that is preferable for obtaining a copper film having a porous structure.

In the heating under reduced pressure of the present invention, the liquid component contained in the interface between the ceramic substrate and the first copper film or in the first copper film is heated as a gas, and the second copper film is heated. I am aiming to escape to the outside. The heating conditions under this reduced pressure are 400 to 800 ° C. under a reduced pressure of 750 mmHg or less.
It is desirable to heat in the range of 10 to 30 minutes. Regarding the degree of reduced pressure, when the degree of reduced pressure is higher than 750 mmHg, the contained liquid components are not sufficiently removed, so that there is a problem that the prevention of blistering is insufficient. On the other hand, 75
It is not necessary to particularly limit the limit value for the degree of reduced pressure of 0 mmHg or less, and the condition may be determined from the viewpoint of the performance and productivity of the device. Further, if the heating temperature is 400 ° C. or lower, or if the heating and holding time is 10 minutes or shorter, the contained liquid components are not sufficiently removed, so that there is a problem that the prevention of blistering is insufficient. Also, the heating temperature is 80
When the temperature is 0 ° C or higher, the copper film itself is densified by heating at a stage where the contained liquid components are not sufficiently removed, and the contained liquid components are not sufficiently removed. There is a problem that the prevention of occurrence of is insufficient.

Then, heating in a nitrogen atmosphere after heating under reduced pressure densifies the first copper film by electroless plating and the second copper film by electrolytic plating to form a copper film to be a conductor layer. The aim is to improve the electrical characteristics, and the heating atmosphere is preferably a nitrogen atmosphere from the viewpoint of preventing copper oxidation,
As the heating condition, it is desirable to heat for 90 minutes or more in the range of 800 to 1000 ° C. Because 1000
When the temperature exceeds ℃, since the melting point of copper is 1053 ℃, there is a risk of copper melting, and heating at less than 800 ℃ or less than 90 minutes, the effect of improving the electrical characteristics of the copper film is not remarkable. is there.

As described above, according to the manufacturing method of the present invention, there is a problem that "blister" (local peeling) occurs in the copper film due to heating such as baking of the thick film resistor after forming the circuit. It is possible to manufacture a copper metallized ceramic substrate having a copper film that does not occur and has excellent electrical characteristics.

[0015]

The first copper film formed by electroless plating and the second copper film formed by electrolytic plating according to the present invention have a porous structure having a communicating gap. Acts as a passage for releasing the contained liquid component, which causes "blister" (local peeling) of the copper film in the process of manufacturing the ceramic wiring board, as a gas to the outside. Further, the heating under reduced pressure after the formation of the second copper film serves to release the contained liquid component as a gas by heating to the outside of the second copper film. Then, the heating in the nitrogen atmosphere after the heating under the reduced pressure densifies the first copper film and the second copper film having the porous structure to improve the electrical characteristics of the entire copper film. Work.

[0016]

EXAMPLES The present invention will be described below with reference to examples. Needless to say, the present invention is not limited to the following examples.

Example 100 mm square manufactured by Matsushita Electric Works, Ltd. (product number: CM7000),
The surface of the 0.8 mm thick alumina substrate was treated with hot phosphoric acid.
Surface is roughened, and then this alumina substrate is made into PdCl.₂Melting
Nucleation is performed by immersing in liquid and attaching Pd nuclei to the substrate surface.
It was. A liquid composition of sulfuric acid was added to this nucleated alumina substrate.
Copper 10g / l, EDTA / 2Na / 2H ₂O30g /
1, formalin 50ml / l, sodium cyanide 5m
Electroless solution with g / l, liquid temperature 60 ℃, pH 12.4
Plating with plating solution, thickness of 5μm as the first copper film
Form a porous copper film with open spaces
I made it.

Next, in order to obtain a film thickness required for the circuit, the liquid composition was 40 g / copper sulfate on the substrate on which the first copper film was formed.
1, 97% sulfuric acid 190g / l, sodium chloride 0.1g
/ L, without adding a brightening agent, using an electrolytic plating solution consisting of a liquid temperature of 25 ° C., electrolytic plating is performed under the conditions of a cathode current density of 4 A / dm ² , and a second copper film having a thickness of 30 μm is connected. A copper film having a porous structure having a gap to be formed was formed. Next, the substrate on which the first copper film and the second copper film are formed is heated at 500 ° C. for 30 minutes in an electric furnace depressurized to 10 mmHg, and the first interface at the interface between the ceramic and the copper film or at the initial stage of deposition The liquid component contained in the copper film was discharged as a gas to the outside of the substrate. Next, this substrate was heated at 900 ° C. for 90 minutes in an electric furnace in a nitrogen atmosphere to densify the first copper film and the second copper film to obtain a copper metallized ceramic substrate.

With respect to the copper metallized ceramic substrate thus obtained, the heat resistance and the volume resistivity of the copper film were evaluated. The heat resistance was 95% in the nitrogen atmosphere of the test piece.
It was heated at 0 ° C. for 10 minutes, and the surface of the test piece was observed to examine whether or not “swelling” occurred in the copper film. The volume resistivity of the copper film was measured according to JIS-C2525.
The results obtained are shown in Table 1.

COMPARATIVE EXAMPLE 1 Using the same alumina substrate as in the example, a copper film having a porous structure having a thickness of 5 μm and having a communicating gap was formed as the first copper film on the alumina substrate in the same manner as in the example. Forming,
Then, a second copper film having a porous structure having a thickness of 30 μm and having communicating gaps was formed on the first copper film.
The heat resistance and the volume resistivity of the copper film of the obtained copper metallized ceramic substrate were evaluated in the same manner as in the examples without heating under reduced pressure and heating in a nitrogen atmosphere. The results obtained are shown in Table 1.

Comparative Example 2 Using the same alumina substrate as in the example, a copper film having a porous structure having a thickness of 5 μm and having a communicating gap was formed as the first copper film on the alumina substrate in the same manner as in the example. Formed.

Next, in order to obtain the film thickness required for the circuit, the liquid composition was 75 g / copper sulfate on the substrate on which the first copper film was formed.
1, 97% sulfuric acid 190g / l, sodium chloride 0.1g
/ L, brightener (product name of Uemura Kogyo Co., Ltd. Sulcup AC-
90) Electrolytic plating was carried out at a cathode current density of 2 A / dm ² using an electrolytic plating solution consisting of 5 ml / l and a solution temperature of 25 ° C., and a second copper film having a thickness of 30 μm and a dense structure. A copper film was formed. Next, the heat resistance and the volume resistivity of the copper film of the obtained copper metallized ceramic substrate were evaluated in the same manner as in the examples without heating under reduced pressure and heating in a nitrogen atmosphere. The results obtained are shown in Table 1.
Shown in.

[0023]

[Table 1]

From the above results, the copper metallized ceramic substrate according to the manufacturing method of the present invention is a copper metallized ceramic substrate having a copper film which is excellent in electrical characteristics without causing "blister" of the copper film due to heating. It was confirmed.

[0025]

Since the copper metallized ceramic substrate produced by the production method of the present invention is produced as described above, no blistering occurs during the heat treatment in the post-processing of circuit formation, and the electrical characteristics are excellent. It becomes a copper metallized ceramic substrate having a copper film.

Claims (3)

[Claims] 1. A ceramic substrate is provided with a first copper film having a porous structure having a communicating space by electroless plating, and then a second copper film is formed on the first copper film by electrolytic plating.
In the method for producing a copper metallized ceramic substrate for forming a copper film, the second copper film has a gap communicating with it.
A method for producing a copper metallized ceramic substrate, which has a porous structure and is heated under reduced pressure and then heated in a nitrogen atmosphere after the formation of the second copper film. 2. The production of a copper metallized ceramic substrate according to claim 1, wherein the heating under reduced pressure is performed under reduced pressure of 750 mmHg or less at 400 to 800 ° C. for 10 to 30 minutes. Method. 3. The production of a copper metallized ceramic substrate according to claim 1, wherein the heating in a nitrogen atmosphere is performed in a nitrogen atmosphere in the range of 800 to 1000 ° C. for 90 minutes or more. Method.