JPH0412608B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical Field of the Invention The present invention relates to a conductive copper paste composition for high temperature baking used for forming electrodes of electronic components such as ceramic capacitors. (b) Background of the technology Generally, silver powder is used as the electrode material for ceramic capacitors, and silver paste is applied by brush painting, spraying, penetration, screen printing, etc.
A method of baking at 850℃ is used. However, in response to the soaring price and large fluctuations in silver prices, silver-saving measures were first taken, including the use of secondary additives such as metal oxides such as bismuth oxide, increased amounts of glass powder, and silver-plated nickel. Various attempts have been made, such as the addition of copper and ceramic particles, but the lower limit for the firing thickness of the silver electrode is 2 to 2.5 μm as silver, and 2 to 2.5 mg/cm ² as the amount of silver, and as a silver paste for screen printing. A drop in silver content below 40-45% is extremely dangerous in terms of product reliability. It is a well-known fact that the inherent properties of silver, such as migration and the drawback that it is easily eaten by solder, make it extremely effective to use copper electrodes that are inexpensive and have electrical conductivity close to that of silver. Problems when baking copper electrodes onto dielectric ceramics in a non-oxidizing nitrogen atmosphere include the fact that copper is easily oxidized, and the dielectric ceramics are deoxidized by reducing substances generated from organic matter, causing the dielectric ceramics to become semiconducting. This results in deterioration of insulation resistance, and in extreme cases, conduction, and generally it is difficult to obtain an electrode comparable to a silver electrode due to an increase in dielectric loss. (c) Prior art and problems The copper paste compositions currently on the market are mainly used as conductors in thick film ICs, and the first problem is that their prices are extremely high, far exceeding the price of silver pastes. It's on. In terms of characteristics, it is intended for use as a thick film IC conductor coated on an alumina substrate, so when applied to conductive ceramics for ceramic capacitors, silver electrodes are less effective in terms of capacitance and dielectric loss. You can't get anything equivalent to . Therefore,
First of all, the development of a copper paste that is significantly cheaper than silver paste and comparable in properties to silver paste is of great significance. In particular, the basic fine copper powder can be obtained at a price 3 to 4 times the current copper price of 380 yen/Kg, but the electrolytic copper powder has a complex dendritic shape, and the crushed copper fine powder has no fatty acids. It is a flaky powder containing The former has poor vehicle wettability and is difficult to prepare paint using a three-roll mill. especially,
This is all the more unfavorable for the purpose of reducing the amount of resin in the vehicle as much as possible. The latter had good wettability and dispersibility, but the flow of the roll-milled paint was extremely poor, making it unsuitable as a screen printing paste. In addition, a copper paste made from dendritic electrolytic copper powder has a lower capacitance and significantly lower tensile strength than a silver paste having the same frit composition, so it cannot be used. In addition, methods for producing fine copper powder include atomization in an inert gas and electron beam heating under high vacuum, but these methods are difficult to manufacture due to production equipment, particle size control, and cost. It is difficult to obtain copper powder suitable for ceramic capacitors. In addition, as a technique related to conductive copper paste compositions, for example, Japanese Patent Application Laid-open Nos. 58-105595 and 58-79837
No. 57-123877, etc. (d) Purpose of the Invention The present invention has been made to solve the problems of the conventional art, and its purpose is to reduce the electrostatic charge exhibited by silver electrodes in the process of applying copper electrodes to dielectric ceramics. It is an object of the present invention to provide a conductive copper paste composition capable of manufacturing copper electrode ceramic capacitors having the same level of capacitance, insulation resistance, dielectric loss, adhesive strength, etc. (E) Structure of the Invention In order to achieve the above object, the conductive copper paste composition according to the present invention comprises spherical copper powder having an average particle size of 0.3 to 2 μm, and ethyl cellulose and methyl-butyl methacrylate copolymer. A vehicle containing the mixture, and an oxygen releasing agent for firing in a neutral nitrogen atmosphere, which is a mixture of silver oxide and at least one metal oxide such as cobalt trioxide, vanadium pentoxide, and antimony pentoxide. . (F) Embodiments of the Invention When copper electrodes are applied to dielectric ceramics by firing in a neutral nitrogen atmosphere, the factors that cause defects are aldehyde residues and monoxide generated by thermal decomposition of organic compounds in an oxygen-deficient atmosphere. As mentioned above, this is caused by oxygen being taken away from the dielectric ceramic by reducing substances such as carbon. In order to prevent these negative effects, it is necessary to use the minimum amount of resin, especially ethyl cellulose, when preparing copper paste, and to evaporate regardless of the presence of oxygen due to depolymerization, sublimation, etc., and to discharge it from the firing furnace system. A resin like this is desirable. As a result of investigating the heating residues of various resins and organic compounds in a neutral nitrogen atmosphere, we found that among the acrylic resins that are said to be easily depolymerized, methyl-butyl methacrylate (Rohm and Haas), trade name: Acryloid B −66) is excellent;
As a result of combined use with ethyl cellulose, it became possible to reduce the amount of ethyl cellulose added to 0.5 to 1.5% by weight based on the copper powder. Figure 1 shows the results of thermal analysis of ethyl cellulose (trade name: ECN-200, manufactured by Hercules) conducted in a neutral nitrogen atmosphere. In Figure 1, a shows the weight loss curve of ethyl cellulose when heated in air, and b shows the weight loss curve of ethyl cellulose when heated in nitrogen gas (O ₂ 1 ppm). . According to FIG. 1, the residual amount of thermal decomposition at 900°C in nitrogen is about 10%. this
In order to remove CO ₂ gas from the system, an inorganic compound that generates oxygen through thermal decomposition, a so-called oxygen dispenser, is effective. Examples include oxides such as cerium, cobalt, chromium, and praseodymium. was found to be effective. That is, to give one example, silver oxide releases oxygen at around 400℃, where ethyl cellulose decomposes, and itself becomes silver.
Alloyed with copper and stabilized at high temperatures. Cobalt trioxide (cobalt black) releases oxygen over a temperature range of 700 to 900°C, forms CoO, fuses with glass, and stabilizes it. By releasing active oxygen over such a wide temperature range, the remaining ethyl cellulose was efficiently removed. As a result, as shown in Table 3 of Example E, which will be described later, a copper paste with dielectric loss and tensile strength comparable to that of a silver electrode could be obtained, and was rather superior. Hereinafter, the present invention will be further explained in detail by showing specific examples related to the present invention. First, a detailed explanation of the production of spherical copper fine powder,
The particle control method will be specifically explained. In the present invention, it is a prerequisite that the spherical copper particle size be structured and controlled over a range of 0.1 to 2 μm by chemical reduction from an inexpensive copper salt such as copper sulfate or copper nitrate. In the process of adding 2.5 mol of sodium hydroxide aqueous solution to a 1 mol of copper sulfate aqueous solution and reducing the black copper oxide produced with hytrazine hydrate to obtain copper powder,
Table 1 shows the relationship between the reduction temperature and the particle size of the produced copper powder. The grain size was expressed as the average of 50 grains from a scanning electron microscope (SEM) photograph.

[Table] According to the SEM photograph, the copper powder according to the present invention
As shown in the figure, it is spherical, and its advantage is clear when compared with the electrolytic copper powder shown in Figure 3. still,
Figure 2 is a 10,000x SEM photograph of No. 3 copper powder.
Figure 3 is a 3000x SEM photograph of electrolytic copper powder.
The tapping density of these copper powders is No.2~
Regarding No. 5, it was 2.5 to 3.2 gr/cm ³ , and it was possible to produce a copper paste with good compatibility with the vehicle and good printing characteristics. In addition to copper sulfate, water-soluble copper salts such as copper nitrate, copper chloride, and copper acetate may be used as raw materials for producing copper powder. In addition to hydrazine hydrate, sodium borohydride, formalin, subpowder, etc. can be used as reducing agents.
There are problems with manufacturing costs, product purity, particle control, etc. In the present invention, the basis for setting the copper powder particle size to 0.3 to 2 μm was determined based on the degree of firing of the fired copper surface of the copper paste electrode prepared for each copper powder. That is, the second
As shown in the table, the quality of the copper surface gloss, color tone, and solderability were judged, and non-defective products were marked with a circle.

[Table] When the copper powder particle size is 0.1 μm or less, it becomes black and the tapping density becomes 2 or less, and the resulting copper paint also has poor fluidity. Moreover, the firing range is narrow,
At 500 to 600°C, sufficient characteristics as a copper electrode cannot be obtained. For particle size 0.3~2μm, 700℃~900℃
Appropriate sintering of copper powder was carried out over a period of 0.7
A good firing surface was obtained in the 800-900°C region for ~1.0 μm particles. In the copper powder reduction reaction of the present invention, the temperature at which spherical copper powder of 2 μm can be obtained is 85° C., which is the limit at which the reaction can proceed smoothly, and it is difficult to control the reaction temperature above that temperature.
In addition, as shown in Table 3, copper paste prepared using commercially available spherical particles of about 3 μm and dendritic electrolytic copper powder has inferior capacitance and tensile strength compared to copper powder paste of 0.3 to 0.7 μm. Very unsatisfactory results were obtained regarding strength. Therefore, in the present invention,
Spherical copper powder of 0.3 to 2 μm was specified, which is particularly useful from a practical point of view. The ethyl cellulose used for vehicle preparation is
Comparative Example By using a material with a high degree of polymerization, such as Hercules' product names: ECN-200 and ECT-200, it is possible to reduce the absolute amount of addition, which is 0.5 to 2.0% based on the weight of copper powder. However, no problems were observed in the preparation of the copper paste, especially in the three-roll drawing process. Of course, this was made possible by the combined use of methyl-butyl methacrylate copolymer (trade name: Acryloid B-66, manufactured by Rohm and Haas), which has good depolymerizability. In this way, in the present invention, the conductive copper fine powder is
A copper paste that mainly has good wettability with vehicles and has excellent printability and coating properties can be obtained by three-roll milling. Hereinafter, the content of the present invention will be specifically explained with reference to Examples. Example A Method for producing spherical copper powder with an average particle size of 0.3 μm: Add 15 pieces of water to 30 reaction vessels equipped with a stirrer, add 5 kg of copper sulfate pentahydrate, and stir to dissolve. When 5 kg of 40% sodium hydroxide aqueous solution is added to this, black cupric oxide is produced via blue copper hydroxide. Keeping the internal temperature at 40°C, drop a solution of hydrazine hydrate and water: 11, and finish the reduction by taking care to keep the reaction temperature at 44-46°C. The produced copper powder precipitate is filtered, washed and dried at 100-110°C in a hot air blast oven. As a result, 1.27 kg of spherical copper powder with an average particle size of 0.3 μm was produced.
Obtained. Example B Method for producing spherical copper powder with an average particle size of 0.7 μm: In Example A, by keeping the reduction reaction temperature at 64 to 66°C, the spherical copper powder with an average particle size of 0.7 μm was reduced to 1.27 μm.
Got Kg. Example C Method for producing spherical copper powder with an average particle size of 1 μm: In Example A, by keeping the reduction reaction temperature at 74 to 76°C, 1.27 kg of spherical copper powder with an average particle size of 1 μm was prepared.
Obtained. Example D Method for producing spherical copper powder with an average particle size of 2 μm: In Example A, by maintaining the reduction reaction temperature at 84 to 86°C, 1.27 kg of spherical copper powder with an average particle size of 2 μm was prepared.
Obtained. Example E The spherical copper powder obtained in Examples A to D and the commercially available
Copper paste prepared using 3 μm copper powder and electrolytic copper powder FCC-1110 (trade name, Fukuda Metal Foil & Powder Industries Co., Ltd.) was printed on a disk dielectric substrate with F characteristics, and the oxygen partial pressure was 1 ppm or less in a nitrogen atmosphere. Table 3 summarizes the results of baking at 900°C. The compositions of the copper pastes prepared and compared are shown below. Copper powder 80 parts by weight Gala powder-A 2.4 Cobalt oxide [Co ₂ O ₃ (cobalt black)]
0.4 〃 Silver oxide (Ag ₂ O) 1.2 〃 Ethyl cellulose 0.5 〃 Methyl-butyl methacrylate copolymer
1.5 〃 n-Butyl carbitol 14 〃 Total 100 〃 However, in the above composition, barium-manganese borosilicate glass is used as glass powder-A, and Hercules' trade name is used as ethyl cellulose:
ECN-200 was used, and Acryloid B-66 (trade name, manufactured by Rohm and Haas) was used as a methyl-butyl methacrylate copolymer. The above composition was sufficiently dispersed and homogenized using three rolls to obtain a paint having a viscosity of 250 to 300 poise. The application is
After drying at 110℃ for 10 minutes by screen printing method,
The copper electrode was baked through a belt-type nitrogen atmosphere furnace. The resulting copper electrode ceramic capacitor was immersed in a 6:4 eutectic solder bath at 250° C. for 3 seconds to apply solder and lead wires. At this time, ordinary rosin flux was used as the flux, and the solder wettability was good.

【table】

[Table] As shown in Table 3, pastes using copper powder No. 2 to No. 5 are comparable to conventional silver electrode products, proving the usefulness of the present invention. It was done. Commercially available copper powder with a particle size of 3 μm costs 70,000 yen/kg.
The price was the same as that of silver, and it was inferior in both capacitance and tensile strength. As mentioned above, in copper paste for screen printing, it is necessary to reduce the absolute amount of organic matter to the maximum due to the fate of firing in a nitrogen atmosphere.
A composition with a relatively large amount of metal is desirable. From the viewpoint of paint preparation, a metal content of about 80% is an appropriate point, and the amount of ethyl cellulose and resin is necessarily regulated, and the total amount is 1 to 4% by weight based on the copper powder. During firing at 900°C in a nitrogen atmosphere, about 10% of the ethyl cellulose remains as shown in Figure 1, so the oxygen necessary to burn it is mostly supplied from silver oxide and metal oxides. Of course, nitrogen gas also contains several ppm or less of oxygen, and experimentally it was found that an oxygen dispenser amount of 0.5 to 2.0% by weight relative to the copper powder was sufficiently effective. As a result of printing and baking in the same manner with the following copper paste composition, results similar to those shown in Table 3, such as capacitance, insulation resistance, and dielectric loss, were obtained, and they were inferior to silver electrode products. It was something that didn't exist. No. 3 Cu paste Copper powder No. 3 80 parts by weight Glass powder-B 0.8 〃 Silver oxide (Ag ₂ O) 1.0 〃 Antimony oxide 0.5 〃 Ethyl cellulose 0.4 〃 Methyl-butyl methacrylate copolymer
1.5 n-butylcarbitol 18 Total 100 However, in the above composition, using barium-calcium-borosilicate glass as glass powder-B,
As the ethyl cellulose, ECT-200 (trade name, manufactured by Hercules) was used, and as the methyl-butyl methacrylate copolymer, Acryloid B-66 (trade name, manufactured by Rohm and Haas) was used. No. 4 Cu paste Copper powder No. 4 80 parts by weight Glass powder-C 1.6 〃 Silver oxide (Ag ₂ O) 1.5 〃 Cobalt oxide [Co ₂ O ₃ (cobalt black)]
0.5 〃 Ethyl cellulose 0.6 〃 Methyl-butyl methacrylate copolymer
2.0 〃 n-Butyl Carbitol 13.8 〃 Total 100 〃 However, in the above composition, barium-bismuth borosilicate glass is used as glass powder-C, and Hercules' trade name as ethyl cellulose:
ECN-200 was used, and Acryloid B-66 (trade name, manufactured by Rohm and Haas) was used as a methyl-butyl methacrylate copolymer. In addition to the disk-shaped ceramic capacitors of the examples, copper electrode formation was also effective for cylindrical, wedge-shaped, and laminated chip capacitor terminal electrodes. Example FF Characteristic multilayer chip capacitor terminal electrode baked with copper paste using copper powder of No. 3 in Table 3 is compared with the conventional general terminal electrode of Ag80:Pd20 as shown in Table 4. As shown in Figure 2, no difference was observed in the amount of electrostatic dissolution or dielectric loss. When the cross section of the terminal electrode was observed after polishing, the palladium internal electrode was sufficiently diffused into the copper layer, and no voids were observed at the interface. In particular, it is extremely effective against solder erosion.
Although the second dipping was repeated three times, no visible damage was observed.

[Table] In the table, firing conditions: N ₂ :O ₂ (in the area outside firing
40ppm, 1ppm in the combustion zone, maximum at 900℃. ) Also, Ag
- Pd paste is fired at maximum temperature of 850℃ in air. (G) Effects of the Invention As described above, according to the present invention, it is possible to manufacture a copper electrode ceramic capacitor in which the capacitance, insulation resistance, dielectric loss, adhesive strength, etc. exhibited by the silver electrode are at the same level, and the cost is reduced. A conductive paste can be provided at low cost in place of silver.

[Brief explanation of drawings]

Fig. 1 is a graph showing the thermogravimetric analysis results of ethyl cellulose, Fig. 2 is a scanning electron microscope (SEM) photograph showing the particle size of spherical copper powder in an example of the present invention,
FIG. 3 is a scanning electron microscope (SEM) photograph showing the particle size of electrolytic copper powder. In the figure, a shows a weight loss curve of ethyl cellulose when heated in air, and b shows a weight loss curve of ethyl cellulose when heated in nitrogen gas (O ₂ 1 ppm).

Claims (1)

[Claims] 1. Spherical copper powder having an average particle size of 0.3 to 2 μm;
During firing in a neutral nitrogen atmosphere consisting of a vehicle containing a mixture of ethyl cellulose and methyl-butyl methacrylate copolymer, and a mixture of silver oxide and at least one metal oxide such as cobalt trioxide, vanadium pentoxide, and antimony pentoxide. A conductive copper paste composition comprising: an oxygen releasing agent; 2 The vehicle is characterized by containing a mixture of 0.5 to 1.5% by weight of ethyl cellulose and 0.5 to 2.5% by weight of methyl-butyl methacrylate copolymer based on spherical copper powder having an average particle size of 0.3 to 2 μm. A conductive copper paste composition according to claim 1. 3. The method according to claim 1, wherein the weight of the oxygen releasing agent during firing in a neutral nitrogen atmosphere is 0.5 to 2.0% by weight based on the spherical copper powder having an average particle size of 0.3 to 2 μm. Conductive copper paste composition.