JPS6347249B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-temperature firing type conductive paint useful as an internal electrode of a ceramic multilayer capacitor. In general, the manufacturing method of multilayer capacitors is to produce an unfired dielectric formed using a dielectric composition in which ceramic dielectric powder such as a composite perovskite compound containing titanium oxide, barium titanate, and lead is uniformly dispersed in an organic vehicle. An electrode layer is formed by screen printing a conductive paint consisting of a conductive powder and an organic vehicle on the body sheet, and then a desired number of unfired dielectric sheets having electrode layers made in the same manner are applied. Finally, a dielectric sheet with no electrodes printed on it is stacked and compressed, or the dielectric composition and conductive paint are alternately screen printed and dried to form a dielectric layer and an internal electrode layer. An unfired laminate having alternating
External electrodes are attached to the sides of the integrated laminate to complete the process. Conventionally, metals such as platinum, palladium, silver, gold, Nilkel, copper, etc., which can withstand high-temperature baking, and their oxides have been used as conductive powder for high-temperature baking type conductive paints for internal electrodes. Organic vehicles include resin components such as ethyl cellulose, nitrocellulose, rosin, and polyterpene resin, and terpineol,
A mixture of organic solvents such as butyl carbitol, butyl cellosolve, kerosene, etc., with optionally added plasticizers such as diethyl phthalate, dibutyl phthalate, wax, etc., is used. In recent years, with the demand for smaller size and higher performance of electronic devices, there has been a demand for multilayer capacitors that are smaller and larger in capacity. For this reason, research has been conducted to further reduce the thickness of both the dielectric layer and the electrode layer while maintaining good performance. In addition, in order to obtain a high-performance multilayer capacitor that can be used in a high frequency range, the electrical resistance of the internal electrodes is further increased, for example, by 2×
It is required to reduce the resistance to 10 ^-5 Ω-cm or less. However, with conventional high-temperature firing type conductive paints, the fired electrode layer has a mesh-like structure with many voids, and the surface is rough and uneven.
The specific resistance is high, and therefore a considerable film thickness is required to reduce the specific resistance. Also, if you try to reduce the film thickness, the porosity will also increase, making the resistivity even higher.
As a result, the dielectric loss becomes large, and eventually the capacitor becomes unusable due to breakage or a drop in the withstand voltage of the capacitor.
There was a limit to making the internal electrode thinner and lowering the specific resistance. As a result of various studies, the present inventors have completed a high temperature firing type conductive paint that can meet the above requirements by blending special ingredients into a composition consisting of conductive powder and an organic vehicle. That is, the present invention is a high-temperature firing type conductive paint for internal electrodes of multilayer capacitors, which is characterized by containing an organic phosphate ester in addition to conductive powder and an organic vehicle. The organic phosphoric acid ester used in the present invention is one that completely decomposes and scatters when fired, such as allyl esters such as triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, trimethyl phosphate, triethyl phosphate, These include alkyl esters such as tributyl phosphate and tri(2-ethylhexyl) phosphate, and alkyl diallyl esters such as octyl diphenyl phosphate. Two or more of these compounds may be used in combination. By blending these organic phosphate esters, an extremely thin and dense electrode layer with good sinterability is formed, resulting in a resistivity value that is far superior to conventional ones.
In addition to being sufficiently durable for high frequency use, it is also possible to further reduce the thickness of the electrode without sacrificing properties such as dielectric loss characteristics. For example, while conventionally the practical limit was 4 to 5 μm at most, the present invention allows the thickness to be reduced to about 1 μm. Firstly, in the process of baking conductive paint, with conventional paints, after the paint film dries, the resin component in the vehicle rapidly decomposes and scatters around 300 to 400℃, and as a result, when observing the fired film, In contrast, in the present invention, the decomposition rate of the resin was slow due to the addition of the above-mentioned additives. This is because the electrode layer gradually contracts in the thickness direction and comes into close contact with the dielectric layer, resulting in an extremely small porosity.Secondly, the sinterability of the conductive powder is very good. Conceivable. Considering that in the past, when baking conductive paints, we used materials that were as easy to decompose as possible in order to completely decompose and remove the resin used, it would have been unexpected to slow down the decomposition rate. This was elucidated for the first time by the present inventors. The reason why the sinterability of the powder improves is not clear, but it is probably due to the improvement in the dispersibility of the conductive powder in the paint due to the addition of the organic phosphate ester, and the decomposition process of the organic phosphate ester during firing. This is thought to be related to a direct effect on the sintering of the conductive powder. In addition, since the additives of the present invention are ultimately burned out during baking,
Unlike the case of using metal oxides, etc., there is also the advantage that the performance of the multilayer capacitor will not deteriorate even if a large amount is added. As the resin component of the organic vehicle of the present invention, conventionally used resins such as ethyl cellulose, nitrocellulose, and polyterpene resin can be used, but good results can be obtained from any of them. In particular, relatively flame-retardant resins or mixtures of these and oils and fats are used. When it is included, a more uniform and dense electrode layer is formed due to the synergistic effect with the organic phosphate ester, so it is preferable. As this flame-retardant resin, rosin, phenolic resin, maleic acid resin, melamine resin, urea resin, alkyd resin, and modified resins thereof can be used, and as the oil and fat, non-drying oil such as olive oil and castor oil, soybean oil can be used. ,
Semi-drying oils such as cottonseed oil are preferred. Other components of the vehicle, ie, solvents, plasticizers, etc., may be those commonly used and are appropriately blended depending on the required coating suitability. The total amount of organic phosphate ester and organic vehicle used in the paint is 20 parts by weight per 100 parts by weight of conductive powder.
~150 parts by weight. Although the organic phosphate ester is effective even when added in small amounts, it is practically preferable to add 5 parts by weight or more to 100 parts by weight of the conductive powder. Even if a large amount is blended, there is no problem as long as it is within the range that can form a paint. As the conductive powder, high melting point metals such as platinum,
One or more of palladium, silver, gold, nickel, copper, and oxides and alloys thereof are used. Furthermore, it does not depart from the scope of the present invention to include additives such as metal oxides, which are often added to improve the characteristics of capacitors. Next, the present invention will be explained with reference to Examples. Although the case where palladium is used as the conductive powder has been described here, the same effect can be obtained using other conductive powders. Example 1 Palladium powder 100 parts by weight Tricresyl phosphate 10 Ethyl cellulose 9 Terpineol 51 Dibutyl phthalate 8 The above components were kneaded in a roll mill to obtain a high temperature firing type conductive paint. Examples 2 to 13, Comparative Examples 1 to 2 High temperature firing type conductive paints having the compositions shown in Table 1 were obtained in the same manner as in Example 1. Examples 7 to 9 are examples in which triphenyl phosphate or tri(2-ethylhexyl) phosphate was used instead of tricresyl phosphate, and Comparative Examples 1 to 2 are examples in which no organic phosphorus compound was blended. The high-temperature firing conductive paint of each example and comparative example was screen printed on an alumina substrate, dried at 150°C for 3 hours, then heated at a rate of 250°C/1 hour, and baked at a peak temperature of 1350°C for 3 hours. did. The thickness and specific resistance of the fired film were measured, and the results are shown in Table 1. still,
The dry film thickness was approximately 8 μm in each case.

[Table] As is clear from Table 1, when the high temperature firing type conductive paint of the present invention is used, an extremely thin electrode film with excellent conductivity can be obtained. Although an alumina substrate was used in the experiment, the results showed exactly the same tendency even if an unfired ceramic sheet was used. Next, the high-temperature firing type conductive paints of Example 4 and Comparative Example 1 were screen printed on an alumina substrate with different film thicknesses, and fired under the same conditions as in the previous example. The relationship between the film thickness and specific resistance after firing was investigated for each, and is shown in FIG. As is clear from the figure, when the coating material of the present invention is used, an extremely good resistivity value is obtained even if the film thickness is reduced (curve A). Comparative example 1
Conventional paints are unusable when the diameter is less than 3 μm.
Even where the film thickness is large, the specific resistance value is higher than that of the present invention (curve B). This indicates that the fired film has many voids and is not dense.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between fired film thickness and specific resistance when using the present invention and the conventional high-temperature-baked conductive paint, where curve A is for the present invention paint and curve B is for the conventional paint. This is the case.

Claims (1)

[Claims] 1. A high-temperature firing type conductive paint for internal electrodes of multilayer capacitors, comprising conductive powder, an organic vehicle, and a phosphate ester. 2. The organic vehicle contains at least one or more of rosin, phenolic resin, maleic acid resin, melamine resin, urea resin, alkyd resin, and mixtures of these with oils and fats.
A high temperature firing type conductive paint for internal electrodes of a multilayer capacitor according to claim 1.