JPH0118035B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for forming a conductive thin film on a ceramic surface. [Prior Art and Problems to be Solved by the Invention] Forming a metal film on the surface of ceramics is an important technique indispensable for forming conductor portions of ceramic multilayer wiring boards. CVD is a method for forming a film on the surface of ceramics.
There are other methods such as PVD and PVD, but they can only form small thicknesses. Furthermore, Japanese Patent Application Laid-Open No. 1320225/1983 discloses a method for bonding metal to ceramics. In this method, a metallic member is heated in a reactive atmosphere at a temperature below the eutectic temperature of the metal to form a eutectic, and the formed eutectic wets the ceramic and bonds the ceramic and metal when cooled. This is what I did. Oxygen is used as a reactive gas in the reactive atmosphere used. However, since this method uses an oxidizing atmosphere, there is a drawback that the surface of the conductor portion is oxidized and the solder cannot be wetted. Further, JP-A-55-90478 discloses a method of bonding a ceramic molded body to a metal. This method involves contacting copper or copper sulfide with a ceramic molded body (oxide-based, nitride-based, carbide-based, boride-based, glass, etc.) in an oxidizing atmosphere (air, oxygen, mixed gas of air and oxygen, inert It is bonded by heating with a mixture of gas and oxygen). However, this method also has the drawback that the conductor portions are severely oxidized, resulting in poor solder wetting and making soldering almost impossible. There is also a method of metallizing the ceramic surface using a metallizing paste. By the way, metallizing pastes that are generally used for electrical purposes have good electrical properties when baked onto the surface of ceramics to form a film, and also have high bonding strength with ceramics, as well as the ability to bond with conductors or other materials. Good wettability of the solder is required when bonding with a metallic connector. However, conventional metallization pastes contain oxide-based glass components, and during the metallization process, the glass components contained in the paste are melted, and this melt blends well with the ceramic surface, resulting in a good Achieves high bonding strength. However, in the case of materials such as silicon carbide ceramics, which have low reactivity with oxide glass, the glass components contained in the paste do not easily react with the ceramics, and on the contrary, many bubbles are generated, making it difficult to combine easily. Can not. Particularly when forming a film using a Cu paste containing Cu as a main component, the bonding strength and solderability vary significantly depending on the type of heating atmosphere. That is, when heated in air or in an oxygen atmosphere, although the bonding strength becomes high, there is a problem in that the Cu powder in the paste becomes severely oxidized and wetting with solder becomes significantly poor. On the other hand, if the atmosphere is heated in a reducing atmosphere (e.g. hydrogen gas, mixed gas of nitrogen gas and hydrogen, etc.) or an inert gas atmosphere (e.g. nitrogen gas, argon gas), vacuum, etc. to prevent Cu oxidation, the solder Although favorable results can be obtained in terms of wettability, there is a problem in that adhesive strength is reduced. An object of the present invention is to solve the above-mentioned problems of the prior art, to make it possible to bake a conductive paste even on ceramics that have low reactivity with oxides, such as silicon carbide, and to make it possible to bake a conductive paste onto ceramics such as silicon carbide. It is an object of the present invention to provide a method for forming a conductive film on the surface of non-oxide ceramics, which has extremely high bonding strength, prevents oxidation of the film, and has good wettability with solder. [Means for Solving the Problems] The method of the present invention provides a
A seed or two or more metal powders, a P compound, Bi,
A paste containing one or more types of Ge is applied to the surface of non-oxide ceramics and heated in an inert gas atmosphere containing water vapor. [Function] That is, when heated in such an inert gas atmosphere containing water vapor, the water vapor in the humidified inert gas atmosphere decomposes and oxidizes the surface of the non-oxide ceramic during heating and firing of the paste. In addition, part of the metal powder or conductive metal compound powder, P compound, Bi, and Ge in the paste is oxidized, and a reaction layer of these oxides is formed at the interface between the ceramic and the paste, which improves the compatibility between the ceramic and the conductive film. This improves the bonding strength and improves the bonding strength. In addition, the oxidizing effect of this inert gas atmosphere containing water vapor is not strong, and the degree of oxidation of the film as a whole is low, and the oxides of P compounds, Bi, and Ge also sink to the ceramic side, forming a conductive layer. The proportion of oxide on the film surface side is lowered, and the solder wettability of the conductive film surface is also ensured sufficiently. The paste used in the present invention contains metal powder as a main component and one or more of P compounds, Bi, and Ge as secondary metals. This metal powder includes Cu, Ag, and Pd.
and one or more types of Ni. Moreover, LaB ₆ can be mentioned as a conductive metal compound. A paste containing Cu as a main component includes, for example, Cu powder and a P compound (e.g.
A slurry-like paste containing powders of Bi or Ge (Cu-P alloy, B-P alloy, Fe-P alloy, etc.) and dispersed in an organic base material can be used. As the organic material base material, various well-known materials can be used, such as a butyl carbitol solution containing ethyl cellulose. The temperature at which ceramics coated with such a paste is heated does not need to be raised to the ceramic sintering temperature; in short, it may be any temperature at which the metal powder in the paste is baked.
Pastes containing Cu are heated at a temperature of 700 to 1050°C, preferably 850 to 1000°C. Since the heating temperature is thus low, the added metal is properly metallized on the ceramic surface without completely melting, and since the ceramic undergoes little thermal deformation, sufficient dimensional accuracy of the conductive film can be ensured. The atmosphere at this time is an inert gas atmosphere containing water vapor. Inert gases include nitrogen,
Argon, helium, neon, or the like can be used, but nitrogen gas is particularly preferred. Further, the amount of water vapor added to such inert gas is preferably about 0.01 to 1.0% based on the inert gas,
The overall atmosphere is a weakly acidic atmosphere. Also,
In a hydrogen gas atmosphere containing water vapor, the weak oxidizing power of water vapor is hindered by the reducing power of hydrogen gas, resulting in a very weak oxidizing power in the atmosphere as a whole, and the added metal has a low affinity for oxygen. A sufficient amount of metal oxide cannot be obtained, and therefore sufficient strength between the ceramic and the conductive film cannot be expected. Various methods can be used to add water vapor to the inert gas, including a method of passing nitrogen gas into the heating furnace through a bubbler. At this time, the amount of moisture added to the inert gas can be adjusted by adjusting the heating temperature of the bubbler. The present invention is suitable for application to ceramics made of materials such as silicon carbide ceramics, in which a film cannot be easily formed with a paste containing conventional oxide glass powder. P compounds, Bi, and Ge easily become oxides when heated at low temperatures in a weakly oxidizing atmosphere, and therefore a conductive film can be easily formed on the surface of non-oxide ceramics. The present invention is not limited to silicon carbide ceramics, and it goes without saying that a film can be formed on the surface of various non-oxide ceramics. [Example] A film was formed on the surface of SiG ceramics using the paste shown in Table 1. A paste was prepared by adding 20% by weight of a butyl curbitol solution containing 6% by volume of ethyl cellulose to a mixed powder of each powder having the composition shown in Table 1 and Cu powder to form a slurry. The SiC ceramic molded body is made by hot pressing a mixture of SiC powder with 1% by weight of berium oxide in a reduced pressure atmosphere.The density ratio is 98% or more, and the thermal conductivity at room temperature is 0.6 cal/cm, sec, °C or more. , specific resistance is 10 ¹² Ωcm
The above molded body was used. The surface roughness of this molded body is set to ±3 μm, and after surface cleaning such as degreasing, the above-mentioned paste is screen printed on this surface, and the atmosphere is set to include H ₂ gas, N ₂ gas, Ar gas, and moisture.
Calcination was performed by turning on _N2 gas and holding each firing temperature for 15 minutes. Prior to firing, the paste was dried by holding the substrate at 120° C. for 10 minutes. The adhesive strength of the bonded metal thin film was determined by the method shown in Fig. 1, and the adhesive strength of the bonded metal thin film was determined by the method shown in Figure 1.
A metal thin film 2 of 20 μm is provided, and a weight of
Solder 3 with Ag2%, Sn62.5%, Pb35.2%, Sb0.3%
Copper foil 4 with a width of 1.5 mm and a thickness of 0.5 mm is bonded by
The peel strength (Kg/mm ² ) when pulled in the direction perpendicular to the arrow in the figure was determined. Furthermore, a solder wettability test was conducted by dipping the above-mentioned fired substrate into a solder bath for 2 to 3 seconds. Based on the appearance, a three-level evaluation was performed, with a very small solder adhesion area marked with an "x", a somewhat good one marked with a "△", and a good one marked with a "○". In the table, "touch" indicates adhesive strength, and the value is expressed in kg/mm ² unit. "Wet" indicates wettability to solder. _N2 gas atmosphere containing moisture is removed using a bubbler filled with water (dimensions
_N2 gas was passed through the bubbler at a rate of 1/min through a 80φ x 130mm tube, and the amount of water was determined by heating the water in the bubbler together with the container. Moisture content was measured by passing the water through the trap before entering the furnace through the bubbler and determining the increase in weight of the trap. As shown in Table 1, the atmosphere during firing was _H2 gas,
In the case of using Ar gas, adhesion could not be achieved because vitrification of the added metal and oxide of the paste was not formed. Also, it was not possible to conduct a solder wetness test. Even in the case of N ₂ gas, it is not possible to obtain a paste with sufficient adhesive strength and good solder wettability with each paste. Since none of the above gas atmospheres has any oxidizing power, the metal powder does not form metal oxides, and it is therefore expected that the ceramics and conductive film will be compatible with each other and the bonding strength will be increased. do not have. 0.02%, 0.2% moisture in _N2 gas
When fired in an atmosphere that contains moisture, the adhesion and solder wettability are excellent, especially when the firing temperature is 970°C rather than 870°C.
It was better at ℃. [Effect of the invention] As described above, according to the structure of the present invention, Cu, Ag,
One or more metal powders of Pd and Ni,
Non-oxide ceramics coated with a paste containing one or more of P compounds, Bi, and Ge are heated with water vapor.

【table】

A conductive film is formed on the ceramic surface by heating in an inert gas atmosphere containing [Table].Since this conductive film contains metal oxide, this conductive film has strong adhesive strength to the ceramic. Furthermore, since this conductive film does not contain an excessive amount of metal oxide, the wettability between this conductive film and solder is also extremely good. Further, since the heating temperature does not need to be as high as the ceramic sintering temperature, thermal deformation of the ceramic is small, and therefore, a ceramic having a conductive film with good dimensional accuracy can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a method for testing the peeling of a metallized layer. 1... SiC ceramic molded body, 2... Metal thin film, 3... Solder, 4... Copper foil.

Claims (1)

[Claims] 1. One or more metal powders of Cu, Ag, Pd, and Ni, and one or more of P compounds, Bi, and Ge.
A process of applying a paste containing at least one of the above-mentioned species to the surface of a non-oxide ceramic, and a process of heating the non-oxide ceramic coated with the paste in an inert gas atmosphere containing water vapor. A method of forming a conductive film on the surface of physical ceramics. 2. The method for forming a conductive film on the surface of non-oxide ceramics according to claim 1, wherein the non-oxide ceramics are SiC. 3. The inert gas is one or more of N ₂ , Ar, He, and Ne. Method of forming membranes.