JPH1116419A - Electrically conductive paste and manufacture of ceramic multilayer substrate using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically conductive paste capable of forming a low electric resistance fine wiring, and also a method for manufacturing a ceramic multilayer substrate using this. SOLUTION: This method is achieved mainly with copper and copper oxide, and their desirable ratio for an electrically conductive paste is 90:10 to 30:70, and with this paste a prescribed pattern is formed on a green sheet including an inorganic composition, and after the necessary number of sheets are laminated, they are heated in a oxidation atmosphere. Then the wiring pattern is reduced by heating in a reduction atmosphere, and backed in an inert or reduction atmosphere to manufacture the ceramic multilayer substrate.

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 conductive paste and a ceramic multilayer substrate using the same, and more particularly, to a method for producing a ceramic substrate and a package which are often used as a multilayer wiring substrate for mounting electronic components. About.

[0002]

2. Description of the Related Art In recent years, ceramics have been increasingly used as a substrate material in multi-layer wiring boards on which highly integrated LSIs and various electronic components are mounted, in order to satisfy requirements such as miniaturization and high reliability. I have. Among them, alumina has advantages such as high strength, and therefore, the proportion of alumina in the ceramics for the substrate material is large. However, on the other hand, the firing temperature of the alumina is very high, around 1550 ° C.,
It is necessary to use W, Mo or the like having a high melting point as the wiring of the inner layer. However, these metals have a drawback that they have a high electric resistance, and the wiring formed thereby has a high electric resistance. Due to these problems, the operating frequency of the LSI has been remarkably increased.

In order to solve such a problem, a metal conductor having a low melting point and low electric resistance such as Ag, AgPd, Cu, Au, etc., and a metal conductor which can be fired at a low temperature at which the metal conductor can be used as an inner layer conductor are available. Research and development of ceramic materials was conducted. In particular, various studies have been made on copper-based conductors because of their advantages such as low cost and low diffusion of conductor components into the substrate.

[0004] However, compared with the case where copper wiring is formed on a sintered substrate of alumina or the like, a very advanced technique is required to form copper wiring by a simultaneous firing method with a green sheet. Usually, to simultaneously fire ceramic and conductor, paste containing conductor is printed on green sheet of ceramics, and this is laminated to an appropriate thickness and heated in the atmosphere, so that the laminate and paste Removal of organic matter and sintering of ceramics and conductors. Heating in an oxidizing atmosphere is indispensable to remove organic substances in the ceramic molded body, but when copper is heated in an oxidizing atmosphere, it is oxidized and it is difficult to form a low-resistance conductor. Various ideas have been devised.

In order to solve the above problem, for example,
In the method disclosed in JP-A-20914, a paste is prepared using cupric oxide as a main raw material, and thereby a pattern is formed on a green sheet. After heating this multilayer body in an oxidizing atmosphere to remove organic substances, reduce cupric oxide,
Fire in a nitrogen atmosphere. According to this method, it is possible to remove organic substances from the molded body and to form copper wiring. However, since volume shrinkage occurs at the stage of reducing cupric oxide to copper, it is difficult to form a dense copper wiring in the fired body, and there is a problem that the wiring is thin or disconnected, and particularly a fine wiring Could not be formed.

According to Japanese Patent Application Laid-Open No. 2-267990, a multilayer is formed by forming a pattern on a green sheet with a paste having a weight ratio of cupric oxide to copper in the range of 40:60 to 95: 5. A method is disclosed in which an organic substance is removed by heating the material in a neutral atmosphere composed of nitrogen and water vapor, and thereafter, the copper oxide is reduced and then fired in a neutral atmosphere. According to this method, by reducing the proportion of cupric oxide, the volume shrinkage at the reduction stage can be reduced, so that a relatively dense wiring can be formed. However, in this method, it is necessary to remove organic substances in a neutral atmosphere in order to suppress oxidation of copper. As a result, the removal of organic substances in the compact is incomplete, and low-molecular organic substances and carbon remain in the compact, so that the sintering of the ceramic compact tends to be incomplete, and various characteristics such as the strength of the substrate are reduced. There was a problem of lowering.

[0007]

As is apparent from the above problem, in order to manufacture a ceramic multilayer body having copper as an inner layer, it is necessary to control the expansion and contraction of the wiring during the manufacturing process to reduce the thinning and disconnection of the wiring. It is necessary to establish a method for forming a dense conductor. At the same time, it is necessary to completely remove the organic matter in order to prevent a reduction in various properties such as the strength of the fired body. Therefore, an object of the present invention is to control the expansion and contraction of the conductive paste in the process of manufacturing a ceramic multilayer body having a conductive pattern formed inside or on the surface, and at the same time to completely remove organic substances in the substrate, thereby achieving low resistance and high density. An object of the present invention is to provide a conductive paste capable of forming a complicated wiring and a method for manufacturing a ceramic multilayer substrate using the same.

[0008]

In order to produce a ceramic multilayer substrate which simultaneously solves the above-mentioned problems, it is necessary to control the expansion and contraction of the conductive paste in the process of manufacturing a ceramic multilayer body having a conductive pattern formed inside or on the surface. At the same time, it is necessary to completely remove organic substances from the substrate.
It is also important that these materials can be integrated by co-firing and that they can be planarized.

Therefore, the present inventors have conducted intensive studies and studied the expansion and shrinkage behavior of copper and copper oxide when heated, under various atmospheres and in various temperature ranges. As a result of approaching the expansion and contraction behavior of ceramic materials, it has been found that the above objects can be achieved with the following combinations of materials and firing processes. First, copper and cuprous oxide are mainly used as raw materials of the conductive paste, and those having a ratio of 90:10 to 30:70 are used. This conductive paste is formed in a predetermined pattern on the surface of the green sheet containing the inorganic composition, and a necessary number of the pastes are laminated. Next, the laminate is heated in an oxidizing atmosphere to remove organic substances, further heated in a reducing atmosphere to reduce the wiring pattern, and then baked in an inert or reducing atmosphere to provide a flat and signal transmission. A ceramic multilayer substrate with excellent characteristics can be obtained.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The reason why the conductive paste is mainly made of copper and cuprous oxide as described in claim 1 is that expansion and shrinkage when heated in an oxidizing atmosphere and a reducing atmosphere by a combination of the two. It is because it can suppress. That is, copper is oxidized when heated in an oxidizing atmosphere and expands due to a decrease in specific gravity, and conversely when heated in a reducing atmosphere, contracts due to an increase in specific gravity. On the other hand, cuprous oxide shrinks by sintering when heated in an oxidizing atmosphere. Further, when heated in a reducing atmosphere, copper oxide is reduced to copper to increase the specific gravity, but the volume hardly changes because it is dense at the oxidation stage. Therefore, by combining copper and cuprous oxide, expansion and shrinkage can be suppressed, and generation of cracks and cracks due to stress applied to the ceramic substrate can be suppressed.

[0011] The ratio of copper to cuprous oxide in the conductive paste is set to 90:10 to 30:70, because when the copper ratio exceeds 90%, heating is performed in an oxidizing atmosphere. When the ratio of cuprous oxide exceeds 70%, when the substrate is heated in an oxidizing atmosphere, the shrinkage is large and the wiring cracks. The firing atmosphere is defined as described in claim 3 because heat treatment in an oxidizing atmosphere is required to remove organic substances contained in the substrate and the wiring. When the heat treatment is performed in a neutral atmosphere, the organic substance or carbon remains in the substrate, so that the firing density of the substrate decreases or the bending strength of the substrate decreases. In order to reduce the signal wiring layer oxidized in the process of removing organic substances to metal, it is necessary to perform heat treatment in a reducing atmosphere. Further, in order to sinter the reduced signal wiring layer without oxidizing, it is necessary to fire in an inert atmosphere such as N ₂ or Ar or in a reducing atmosphere.

Examples 1 to 4 and Comparative Examples 1 and 2 Green sheets were prepared from 55% by weight of anorthite-crystallized glass and 45% by weight of alumina as ceramic substrate materials. Next, 30 wt% of a vehicle was added to and mixed with a commercially available copper powder (average particle size of about 2 μm) and a cuprous oxide powder (average particle size of about 3 μm) to prepare a conductive paste. This conductive paste was printed on the surface of the green sheet in a predetermined pattern. Printing was performed by screen printing. Then, the green sheets are stacked so as to have a thickness of 2 mm, and are hot-pressed at 100 ° C. and 100 kgf.
/ Cm ² under pressure.

Thereafter, heat treatment is performed at 600 ° C. for 2 hours in the air, and reduction treatment is performed at 300 ° C. for 1 hour in an H ₂ —N ₂ atmosphere.
Firing was performed at 900 ° C. for 30 minutes in _two atmospheres to obtain a ceramic substrate. Table 1 shows the results. In Examples 1 to 4, which were within the range specified in the present invention, the wiring resistance was sufficiently low, and no cracks or cracks occurred on the substrate or the wiring. On the other hand, in Comparative Examples 1 and 2, which were outside the specified range of the present invention, cracks occurred in the substrate and the wiring.

[0014]

[Table 1]

Example 5 and Comparative Examples 3 to 5 A laminate having an inner layer of a conductive paste was prepared in the same manner as in Example 1, and baked under the conditions shown in Table 2. The conductive paste used was Cu: Cu ₂ O = 50: 50. Table 2 shows the results. In Example 5 manufactured under the conditions specified by the present invention, the wiring had sufficiently low resistivity, and no discoloration occurred on the substrate or the wiring.

On the other hand, in Comparative Example 3 fabricated under conditions outside the range specified in the present invention, a large amount of carbon remained in the substrate because the substrate was not heat-treated in an oxidizing atmosphere, and as a result, the substrate became gray and wiring Was discolored and the resistance was increased.
Comparative Example 4 produced under conditions outside the range specified in the present invention.
In No., the wiring was black because the reduction treatment was not performed, and the wiring was partially peeled off. Further, in Comparative Example 5 produced under conditions outside the range specified in the present invention, since firing was not performed in an inert atmosphere, the wiring exhibited a black color due to oxidation, and the wiring was partially peeled.

[0017]

[Table 2]

[0018]

According to the present invention, a Cu conductor having a low conductor resistance can be formed as an inner layer so that the signal transmission speed can be adapted to a high speed of an LSI or the like. A substrate is obtained.

Claims (3)

[Claims] 1. A conductive paste comprising mainly copper and cuprous oxide. 2. The conductive paste according to claim 1, wherein the ratio of copper to cuprous oxide in the conductive paste is 90:10 to 30:70. 3. A predetermined pattern is formed on a green sheet containing an inorganic composition by using a conductive paste mainly composed of copper and cuprous oxide, and after laminating a required number of such patterns,
Ceramics using a conductive paste characterized by removing organic matter by heating in an oxidizing atmosphere, reducing the wiring pattern by heating in a reducing atmosphere, and then firing in an inert or reducing atmosphere A method for manufacturing a multilayer substrate.