JPH0692762A - Production of metallized ceramic substrate - Google Patents

Abstract

PURPOSE:To efficiently produce a metallized ceramic substrate capable of avoiding partial swelling of the metal film by heating in a process after its production. CONSTITUTION:A metal film is formed on the surface of a ceramic substrate by electroless plating, the surface of the metal film is slightly etched and the substrate is heated in an inert gaseous 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 metallized ceramic substrate used for producing a ceramic wiring board or the like.

[0002]

2. Description of the Related Art Generally, a ceramic wiring board uses a so-called thick film method in which a conductive circuit is formed by printing a conductive paste on a surface of a ceramic substrate in a predetermined pattern using a screen printing machine. ing. However, in the case of the thick film method, it is difficult to control the film thickness of the conductor circuit, the electrical characteristics and mechanical characteristics of the obtained conductor circuit are not sufficient, and the precision is not so good that it is difficult to miniaturize the circuit. There is a problem of

Therefore, the use of a metallized ceramic substrate in which the precision and miniaturization of the conductor circuit can be achieved, that is, a ceramic substrate in which a metal film is formed on the surface of the ceramic substrate by an electroless plating method has been studied and put to practical use. Has been done. In the case of a metallized ceramic substrate, a conductor circuit having a predetermined pattern can be formed by using a photographic method capable of highly precise fine patterning, and the resistance value is also low because the conductor circuit is made of metal. .

However, in the above metallized ceramic substrate, the adhesion between the metal film and the ceramic substrate (adhesive strength)
Is not enough. When a wiring board is manufactured using a metallized ceramic substrate, heat treatment is performed for various purposes in processes such as circuit formation and electronic component mounting.However, during these heat treatments, blisters ( Local peeling) occurs, and the adhesion state between the metal film and the ceramic substrate becomes poor.

The blisters formed on the metal film are due to the fact that nucleating solution, plating solution components, etc. are taken into the interface and the metal film at the initial stage of deposition during the process of depositing and growing the metal film by the electroless plating method. ing. The taken-in plating liquid components and the like cannot be removed when they are gasified by the subsequent heat treatment, causing volume expansion and blistering. As a measure for preventing the blistering of the metal film, JP-A-1-164 is known.
Japanese Patent No. 786 proposes that the metal film has a crystal structure with a gap through which gas can escape. However, this measure is not practical.

This is because the metal film has a crystal structure with a gap through which gas can escape, and heat treatment is performed to diffuse the liquid component through the gap. However, the heat treatment requires a gentle temperature rise. Therefore, it takes a very long time to raise the temperature (long time such as 2 hours), and the productivity is low. It is considered that this is because the gap between the metal films is not wide enough to rapidly raise the temperature. If you do not perform sufficient heat treatment, it will not be possible to reliably suppress the occurrence of blisters,
There is no way to shorten the heating time.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention is a metallized ceramic substrate capable of avoiding a part of the metal film from bulging due to a heat treatment in a post-process performed after the production of the metallized ceramic substrate. It is an object of the present invention to provide a method capable of efficiently producing

[0008]

In order to solve the above problems, in the method for manufacturing a metallized ceramic substrate according to the present invention, a metal film is formed on the surface of the ceramic substrate by electroless plating, and the surface of the metal film is formed. On the other hand, after performing a shallow etching process, heat treatment is performed in an inert gas atmosphere in an inert gas atmosphere.

The present invention will be specifically described below. As the material of the ceramic substrate itself used in the present invention, oxide-based ceramics such as alumina, forsterite, zirconia, cordierite, titania, barium titanate, and calcium titanate are mainly used. Carbide-based ceramics, nitride-based ceramics such as aluminum nitride may be used, or a plurality of types of ceramics may be used in combination.

The ceramic substrate is preferably preliminarily subjected to a roughening treatment for exerting an anchor effect so that the adhesion of the conductor layer on the surface is enhanced, but it may be omitted. Examples of the surface roughening treatment include mechanical surface roughening treatment using sandblasting and the like, and chemical surface roughening treatment by etching with a surface roughening agent. The roughening treatment agent,
Examples include solutions of phosphoric acid, boric acid, HF, alkali metal compounds, and melts.

When the metal film is formed by electroless plating, it is preferable to perform nucleation on the surface of the ceramic substrate as an activation treatment. As the nucleating method, for example, when the nucleating agent is Pd, there are a sensitizing-activating method, a catalyst-acceleration method, and the like, but the kind and applying method of the nucleating agent are not limited to these examples. Any material that contributes to the deposition of the electroless plated film may be used.

The electroless plating solution used in the present invention includes, for example, copper sulfate, EDTA, and HCHO as basic components, and if necessary, NaOH (for pH adjustment) and a stabilizer that suppresses decomposition of the plating solution. Examples of the added electroless copper plating solution include, but needless to say, the present invention is not limited to these. Of course, in the present invention, the electroless plating is not limited to electroless copper plating, and may be other electroless plating such as electroless nickel plating or electroless chrome plating.

Specific examples of the electroless plating solution include copper sulfate: 10 g / liter, EDTA · 2Na · 2H ₂ O:
30 g / liter, formalin: 50 ml / liter,
Sodium cyanide 5 mg / liter, liquid temperature 60 ° C, p
An example of the electroless copper plating solution is H12.4. In the case of the present invention, the metal film formed by electroless plating preferably has a porous structure. In the case of a porous structure, there are permeable gaps between the crystal grains that compose the metal film on the surface of the ceramic substrate, and the composition of the electroless plating solution, that is, the amount of stabilizer added such as sodium cyanide and the pH value. Alternatively, the metal film having a porous structure can be formed by selecting the plating conditions such as the concentration of the plating liquid component such as Cu or HCHO. For example, the electroless copper plating solution described above can form a copper film having a porous structure. Further, the thickness of the metal film is not limited to a particular thickness. It suffices that the thickness be such that the subsequent etching process does not make it thinner than necessary.

In the present invention, the surface of the metal film formed by electroless plating is lightly etched. By this etching process, the crystal grains of the metal film are selectively etched to form gaps, or the existing gaps are widened to allow sufficient ventilation. The result is a shape with sufficient ventilation holes between the crystal grains. Etching process is 3μm
It is preferable to perform the etching at a rate of not more than / minute. This is because it is easy to realize an appropriate etching that can selectively remove between the crystal grains. If the etching rate is more than 3 μm / min, the etching action is too strong, and it is difficult to selectively remove the space between crystal grains. However,
If the etching rate is too slow, it takes time. Therefore, it is appropriate to perform the etching at a rate of about 0.1 μm / min or more. The etching depth of this etching treatment is preferably 0.3 μm or more. 0.3 μm
If it is less than the range, it is difficult to form a sufficient gap between crystal grains.

The contact between the metal film and the etching solution is
The immersion method and the immersion stirring method are preferable, and selective etching between crystal grains tends to be difficult by the spray injection method. Suitable etching chemicals for performing etching at an etching rate of 3 μm / min or less include ammonium persulfate, sodium persulfate, sulfuric acid-hydrogen peroxide system and the like.

After the etching treatment, heat treatment is performed in an inert gas atmosphere. This heat treatment is performed in order to gasify and diffuse the intake liquid component that causes blistering, and at the same time close the gap formed by the etching process to densify and prevent the liquid component from being newly taken in. . Further, the heat treatment in the inert gas atmosphere can avoid the inconvenience such as the oxidation of the metal film.

This heat treatment is preferably carried out at a temperature in the range of 800 to 1000 ° C. for 10 minutes or longer. 1
If the temperature exceeds 000 ° C, copper may melt (melting point of copper: 1053 ° C), and if the temperature is lower than 800 ° C, the metal film is insufficiently densified and a liquid component is newly taken in in a subsequent circuit forming step or the like. Because there is a fear. Further, if the heating time is less than 10 minutes, it tends to be difficult to realize sufficient densification in an appropriate temperature range. The time for raising the temperature to the above heating temperature is not particularly limited, and the temperature can be raised in a short time (for example, 30 minutes) according to the heating ability of the heating device.

After that, a metal film may be laminated on the metal film formed by electroless plating by electrolytic plating. The metallized ceramic substrate thus obtained is subjected to patterning treatment or the like to finish it into a ceramic wiring board.

[0019]

In the method for producing a metallized ceramic substrate of the present invention, a sufficient gap is formed by etching treatment between crystal grains of a metal film formed by electroless plating, and then the liquid component taken in by heat treatment is gasified. At the same time as dissipating, the metal film is densified. As a result, the taken-in liquid component is not removed and remains, and no new liquid component is taken in in the subsequent step.

That is, the metal film formed by electroless plating is
As shown in FIG. 3, it has a structure in which crystal grains of about 5 μm are connected, and the etching treatment causes a gap of 3 μm or less between the crystal grains as shown in FIG. At the same time as the gasified liquid component is diffused during the heat treatment, the heat treatment finally results in a dense structure with closed gaps (recrystallized) as shown in FIG. .

In addition, in the case of the present invention, since a process requiring a particularly long time is not required, the metallized ceramic substrate can be efficiently manufactured. When the etching process is performed at an etching rate of 3 μm / min or less, proper etching between crystal grains of the metal film can be easily realized. When the heat treatment is performed at a temperature in the range of 800 to 1000 ° C. for a heating time of 10 minutes or more, the removal of the liquid component and the densification are more sufficiently performed while avoiding damage to the metal film.

[0022]

Embodiments of the present invention will be described below. Of course,
The present invention is not limited to the embodiments described below. - Example 1 - length × width: after performing graining by hot phosphoric acid to the surface of the alumina substrate having a thickness of 0.8mm at 10 cm × 10 cm (Matsushita Electric Works Co., product No. CM7000), the PdCl ₂ solution Nucleation was performed by immersing the substrate to attach Pd nuclei to the surface of the substrate.

Then, a 10 μm thick copper film was formed on the surface of the alumina substrate by electroless copper plating. For plating, copper sulfate: 10 g / liter, EDTA / 2Na / 2
H ₂ O: 30 g / liter, formalin: 50 ml / liter, sodium cyanide 5 mg / liter, liquid temperature 6
An electroless copper plating solution having a temperature of 0 ° C. and a pH of 12.4 was used.
The copper film had a porous structure.

After plating, the surface layer of the copper film was etched. Etching is 50 g / liter of sodium sulfate,
It was carried out by immersing the solution in sulfuric acid 10 ml / liter at a liquid temperature of 30 ° C. and an etching rate of 0.5 μm / min for 60 seconds. Then, the etched alumina substrate was heat-treated in a nitrogen atmosphere. The heat treatment was performed at 900 ° C. for 30 minutes using an electric furnace. The temperature rising time in the heat treatment is 30 minutes. Thus, a metallized ceramic substrate was obtained. The surface of the metal film of this metallized ceramic substrate was a dense film in which copper was recrystallized, as shown in FIG.

-Example 2-A copper film was formed on the surface of an alumina substrate in the same manner as in Example 1, and then the surface layer of the copper film was etched. Etching is performed with 35% hydrogen peroxide water 4.5 ml / liter, sulfuric acid 5 ml / liter, copper sulfate 15 g / liter and a liquid temperature of 3
30 at 0 ℃, etching rate 2μm / min
It was performed by dipping for a second.

Then, the etched alumina substrate was heat-treated in a nitrogen atmosphere. The heat treatment was performed at 900 ° C. for 60 minutes using an electric furnace. The temperature rising time in the heat treatment is 30 minutes. Thus, a metallized ceramic substrate was obtained. -Comparative Example 1-In the same manner as in Example 1, a copper film having a thickness of 10 µm was formed on the surface of the alumina substrate by electroless copper plating to obtain a metallized ceramic substrate.

The metallized ceramic substrates obtained in the examples and the comparative examples were examined for blisters on the copper film. No blisters were found in any of them. Further, with respect to the metallized ceramic substrates of Examples 1 and 2, it was examined whether or not liquid components would be re-introduced into the copper film in the circuit forming step to cause blistering. That is, a heat resistance test was conducted after 5 minutes of immersion in caustic soda having a concentration of 10%, which is used when removing the resist in the circuit forming step. The heat resistance test was conducted by testing the test piece in a nitrogen atmosphere at 9
Heating at 00 ° C for 10 minutes (however, heating time 30 minutes)
Then, it was examined whether blisters had occurred on the surface of the copper film, but no blisters were found in any of them.

A heat resistance test was conducted on the metallized ceramic substrate of Comparative Example 1. The heat resistance test is performed by heating the test piece in a nitrogen atmosphere at 900 ° C. for 10 minutes (however,
The temperature was raised for 30 minutes), and it was examined whether blisters were generated on the surface of the copper film, and blisters were found. From these test results, it is understood that blistering is less likely to occur in the metallized ceramic substrate of the present invention.

[0029]

According to the manufacturing method of the present invention, in the obtained metallized ceramic substrate, the liquid component is not taken in, and a new liquid component is also prevented from being taken in in the subsequent step, so that the metal film is prevented. Since no blistering occurs and a process that requires a long time is not required, the metallized ceramic substrate can be efficiently manufactured and the productivity is high.

When the etching treatment is performed at an etching rate of 3 μm / min or less, proper etching between crystal grains of the metal film can be easily realized, and the metallized ceramic substrate can be manufactured more stably. In addition, when the heat treatment is performed at a temperature in the range of 800 to 1000 ° C. for a heating time of 10 minutes or more, the removal of the liquid component and the densification are more sufficiently performed while avoiding the damage of the metal film, so that the blisters are more likely It is hard to occur.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a surface (metal structure) after etching treatment of a copper film by electroless copper plating.

FIG. 2 is an electron micrograph showing the surface (metal structure) of the metal film after the heat treatment by electroless copper plating.

[Fig. 3] Surface of copper film (metal structure) by electroless copper plating
It is an electron micrograph showing.

Claims (3)

[Claims] 1. A metallized ceramic in which a metal film is formed on the surface of a ceramic substrate by an electroless plating method, the surface of the metal film is shallowly etched, and then heat treatment is performed in an inert gas atmosphere. Substrate manufacturing method. 2. The method for producing a metallized ceramic substrate according to claim 1, wherein the etching treatment is performed at an etching rate of 3 μm / min or less. 3. The method for producing a metallized ceramic substrate according to claim 1, wherein the heat treatment is performed at a temperature in the range of 800 to 1000 ° C. for a heating time of 10 minutes or more.