JPH087644A - High temperature baking complying noble metal powder and conductor paste - Google Patents

Abstract

PURPOSE:To provide new high temperature baking complying noble metal powder which is formed by simultaneous baking of green ceramics and thick film conductor paste or is obtained by forming a thick film conductor on ordinary ceramics and by which a structural defect of an electronic part, a heater or the like can be prevented. CONSTITUTION:A surface of noble metal powder is covered with a compound of metal and organic acid, and next, heat treatment is performed in an inert atmosphere. Thereby, even by high temperature baking, oxidation is hardly caused, and abnormal grain growth is also hardly caused. Thereby, since conductor paste manufactured by using this high temperature baking complying noble metal powder coincides in a difference in a shrinkage factor with a ceramic board or the like at baking time, a structural defect such as separation or a crack is not caused. Since it is excellent in providing a very dense electrode film, an electronic part can be easily downsized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive powder which can be used as a thick film conductor of an electronic circuit and a conductive material for heaters and various electrodes of electronic parts, and a conductive paste using these. is there.

[0002]

2. Description of the Prior Art Pastes for precious metal thick film conductors are generally H
It is used for thick film conductors of IC circuits, electrodes for laminated ceramic capacitors, ceramic heaters, and various other electronic parts.

The conductor paste is formed by dispersing conductive powder, and if necessary, inorganic additives (inorganic binder, filler, etc.), glass frit and the like in an organic vehicle. The conductive powder used in such a conductive paste includes Ag,
Pd, Au, Pt and their alloys are used.

The conductor paste is printed on the ceramic substrate and the ceramic green sheet by a method such as screen printing, and is fired at a temperature that does not impair the characteristics of the respective conductive powders to satisfy various characteristics as a conductive film. Will be things.

In recent years, there has been an increasing demand for miniaturization of circuits and components, and in particular, electronic components have been developed into chips. Therefore, the conductor paste is required to have the same characteristics as the conventional ones even if the area is reduced and the thick film is thinned.

Further, the development of low-temperature fired ceramics has progressed along with the chip formation of electronic parts and the like, and it has become necessary to fire the ceramic paste at a temperature higher than the conventional firing range of the conductor paste. When the conventional conductor paste is used as it is and the firing temperature is raised, the pores in the electrode film increase, causing foaming, peeling, abnormal shrinkage,
Defects such as structural defects such as evaporation of electrodes occurred.

Therefore, if Ag is used, Ag / Pd alloy is used, and for Pd, Pt, etc., an inorganic additive (sintering inhibitor alumina, zirconia, silica or other ceramics) is added. , Which corresponded to high temperature firing.

In addition, various attempts have been made to suppress the volume expansion of the noble metal powder in response to high temperature firing.
For example, in JP-A-63-216204, silicon, aluminum, manganese, cobalt,
It describes a conductive powder coated with hydroxides of nickel, zinc and lead, a conductive paste containing the conductive powder, a glass powder and an organic vehicle as main components.

Further, JP-A-4-43504 discloses an electrode paste prepared by dispersing and kneading a palladium powder whose surface is coated with an oxide of silicon, aluminum, magnesium and cobalt in an organic vehicle. There is.

Japanese Unexamined Patent Publication No. 4-206612 discloses palladium powder, silicon, aluminum, magnesium, lead,
It is described that, regarding a conductor paste in which a metal alkoxide such as calcium and zinc and a metal chelate compound are dispersed in an organic vehicle, it is preferable that the metal alkoxide and the metal chelate compound be used by coating the surface of palladium powder.

[0011]

However, the use of Ag / Pd instead of Ag results in high cost and further increase in resistance value. In addition, the use of inorganic additives has problems such as an increase in resistance value and deterioration of solderability.

Further, Japanese Patent Laid-Open No. 63-216204,
JP-A-4-43504 and JP-A-4-20661
The conductor paste described in Japanese Patent Publication No. 2 has the effect of suppressing the oversintering of the treated noble metal powder more effectively than the untreated one, but it cannot be said that the effect is still sufficient. It has not been possible to completely prevent structural defects such as generation of pores and peeling.

Therefore, the present invention is excellent in the effect of suppressing oversintering,
A novel high temperature firing compatible precious metal powder for preventing structural defects of electronic parts, heaters, etc., which is obtained by simultaneous firing of green ceramic and thick film conductor paste or obtained by forming a thick film conductor on ordinary ceramics. The purpose is to provide a conductor paste. Further, it is an object of the present invention to provide an electrode film or the like that is as dense as possible by providing the product of the present invention, and to further miniaturize the electronic component.

[0014]

As a result of intensive studies conducted by the present inventors in accordance with the above object, the above structural defects of electronic parts are found to be caused by vigorous growth of particles of noble metal powder in high temperature firing, and a ceramic substrate. It is thought that this is caused by the difference in the shrinkage rate between and. Then, even when a conventional conductor paste material was used, further research was conducted in order to prevent the above-mentioned defects from occurring. By closely coating the surface of the noble metal powder with another metal compound, these problems The present invention has been completed by finding that the above can be solved.

That is, according to the present invention, the surface of a noble metal powder is coated with a compound of a metal and an organic acid (hereinafter referred to as "organic acid metal salt"), and then heat treatment is carried out in an inert atmosphere, which corresponds to high temperature firing. It provides precious metal powder. It is presumed that the noble metal powder for high temperature calcination of the present invention obtained after the heat treatment has the organic compound portion removed by the heat treatment, and that ultrafine metal particles are deposited and coated on the surface of the noble metal powder.

The metal constituting the organic acid metal salt coated in the first step is preferably selected from at least one of aluminum, calcium, titanium, yttrium and zirconium, and the organic compound portion is naphthenic acid,
It is preferable to select at least one or more from abietic acid, octylic acid, and ethylhexanoic acid.

The preferable coating amount of the organic acid metal salt is 0.01 to 5% by weight in terms of the oxide of the metal with respect to the noble metal powder. In addition, the heat treatment after the coating with the organic acid metal salt in the first step is preferably performed within the range of 350 ° C to 700 ° C.

Further, the present invention provides a conductor paste prepared by dispersing the above-mentioned high temperature calcination noble metal powder in an organic vehicle, wherein the high temperature calcination noble metal powder is blended in an amount of 35 to 85% by weight based on the total weight of the paste. Is preferably provided.

[0019]

The conductor paste of the present invention reduces the exposed surface area of the noble metal by coating the surface of the noble metal powder with another metal compound during the firing process of the paste.
The reaction between the noble metal powder and oxygen in the atmosphere is suppressed. Therefore, by dispersing the noble metal powder for high temperature firing in the organic vehicle, a thick film conductor paste capable of preventing various structural defects can be obtained.

That is, in circuits, electrodes, heaters, etc. manufactured using the noble metal powder for high temperature firing of the present invention, abnormal grain growth of noble metal particles due to the high temperature of the firing base is suppressed, and green ceramics (including green sheet), etc. Since the substrate and the conductor paste of the present invention are contracted with each other, structural defects such as foaming, peeling from the sheet, and evaporation of the contracting electrode can be prevented.

The excellent effect of suppressing sintering as in the present invention is a characteristic obtained only by heat-treating noble metal powder coated with an organic acid metal salt in an inert atmosphere, and when heat-treating in air. It is significantly superior to the sintering suppression effect obtained in. At this time, the details of the reason for this are unknown, but the organic acid metal salt-coated noble metal powder is considered to be one in which the organic substance was removed by heat treatment and was coated with the precipitated metal particles. It is presumed that it is much finer than when it is heat-treated.

As described above, there are some documents disclosing the technique of coating the surface of a noble metal powder such as palladium powder with another metal compound as described in the present application. Are different.

First, in Japanese Patent Laid-Open No. 216204/1988, the metal hydroxide itself coated with the noble metal powder reacts with the glass melted during the firing process of the paste and is gradually burned off to the substrate side together with the glass ( JP-A-63-216204, No. 3
(Refer to the second column to the sixth column in the right column on the upper side of the page). With the burnout of the metal hydroxide, the grain growth suppressing effect also decreases, so that structural defects cannot be completely prevented. On the other hand, in the conductor paste of the present invention, the coating material of the noble metal powder compatible with high temperature firing is not burned off even when the paste is fired, abnormal grain growth of the noble metal powder is almost completely suppressed, and no structural defect occurs.

Further, in the method for coating the metal hydroxide of the above-mentioned publication, since the soluble salts of the above-mentioned metals are deposited and deposited as hydroxides on the surface of the noble metal powder by adjusting the pH, uniform coating is required. Is difficult (see page 3, lower column, left column, lines 3 to 11 of the same publication). However, since the noble metal powder for high temperature firing of the present invention starts by evaporating the solvent to coat the organic acid metal salt, the surface of the noble metal powder can be uniformly and tightly coated. Therefore, even if a paste of this is baked, pores do not occur,
Obtain an extremely dense phase.

Japanese Unexamined Patent Publication No. 4-206612 limits the applicable noble metal powder to palladium powder. Also,
This is a paste in which a metal alkoxide and a metal chelate compound are dispersed, and is inferior in the effect of suppressing oxidation as compared with the case of coating. It is also described that a precious metal powder is deposited and coated with a metal alkoxide and a metal chelate compound (see Example 6 described in JP-A-4-206612, page 4, upper part).

However, the heat treatment in this method is considered to be carried out in air because there is no particular description, and this point is different from the present invention. As described above, whether the heat treatment is performed in air or in an inert atmosphere greatly affects the sintering suppressing effect, and the heat treatment in air is inferior to the sintering suppressing effect. Abnormal grain growth cannot be completely prevented, and the occurrence of structural defects cannot be prevented. Also, the denseness of the electrode film remains unsatisfactory.

The precious metal powder to which Japanese Patent Laid-Open No. 4-43504 is also applied is limited to palladium powder. The metal oxide coating method is a method in which a colloidal solution of a metal oxide is added to a dispersion of palladium powder in water to adsorb and coat colloidal particles on the surface of the palladium powder.

On the other hand, the coating method of the present invention comprises dissolving the organic acid metal salt in a suitable solvent, dispersing the noble metal powder therein, and then evaporating and removing the solvent, as will be described in detail later. It coats the surface of the noble metal powder, and it is presumed that the coated particles of the present invention are denser and finer than the coating of colloidal particles in JP-A-4-43504.

Therefore, since the noble metal powder for high temperature firing of the present invention has an extremely large number of coating substances around the noble metal powder particles during paste firing, the effect of suppressing abnormal grain growth of the noble metal powder is great.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a noble metal powder for high temperature calcination of the present invention, Au, Ag, Pd, Pt or alloys thereof produced by well-known reduction precipitation method, gas phase reaction method, gas reduction method and the like are used. Precious metal powder is used as a raw material. The preferable particle size of this noble metal powder is 0.2 to 2.0 μm.

In the first stage of the precious metal powder for high temperature firing of the present invention, the surface of the precious metal powder is coated with an organic acid metal salt. The coating is performed by dispersing the precious metal powder in a solution of a predetermined amount of an organic acid metal salt dissolved in a suitable organic solvent, and evaporating the solvent while automatically stirring in a closed flask. The method is desirable, and the method using a rotary evaporator or the like is convenient also in the problem of treatment with a solvent or the like.

The organic acid metal salt is a compound of a metal and an organic acid, and the organic acid is preferably a carboxylic acid. For example, a compound of a metal selected from aluminum, calcium, titanium, yttrium, and zirconium with an organic acid such as naphthenic acid, abietic acid, octylic acid, and ethylhexanoic acid can be used. As described above, the organic acid metal salt is used by being dissolved in a suitable solvent that does not cause hydrolysis or ionization, for example, an organic solvent such as toluene or xylene, but it is not completely dissolved in the sol. It may be a shape.

The organic acid metal salt is preferably coated on the noble metal powder in an amount of about 0.01 to 5% by weight in terms of oxide. A more preferable coating amount is 0.1 to 5% by weight,
It is particularly preferably from 1 to 5% by weight, at which time structural defects hardly occur.

If it is less than 0.01%, the effect is small, and
Variations in sinterability occur. On the other hand, if it exceeds 5%, the effect of suppressing sintering (over-sintering) becomes excessive, the firing shrinkage becomes small, the shrinkage ratio with the substrate does not match, and it causes peeling and the like. Further, the resistance value increases and the covering effect cannot be obtained.

The noble metal powder coated with the organic acid metal salt thus obtained has a sufficient sintering suppressing effect. However, the powder that retains the organic compound has poor compatibility with the vehicle at the time of forming a paste, and may cause deterioration such as gelation. Therefore, when the coated powder is further heat-treated in an inert atmosphere, a noble metal powder excellent in all aspects such as the effect of suppressing sintering, dispersibility at the time of forming a paste, and printability can be obtained. In particular, the effect of suppressing sintering is significantly enhanced. It should be noted here that the above effect can be obtained only when the heat treatment is performed in an inert atmosphere.

At the present time, details of the structure of the noble metal powder after firing in an inert atmosphere according to the present invention cannot be confirmed even with a high-magnification electron microscope, and it is unknown.
However, it is estimated that it is as follows. The organic acid metal salt-coated noble metal powder is considered to have been coated with the metal particles precipitated by removing the organic substance by heat treatment, and it is presumed that the above-mentioned coated particles are extremely fine as compared with the case of heat treatment in air. To be done.

The inert atmosphere means a rare gas such as Ne or Ar or an inert gas such as N ₂ or in vacuum (for example, 1
0 ^-3 to 10 ^-1 Torr) in the atmosphere,
The heat treatment is preferably performed in the range of 350 to 700 ° C. Especially for Ag, Au and Pd, 350-500 ° C
It is preferable to carry out in the range of.

If the temperature is 350 ° C. or lower, the effect of the heat treatment is not sufficiently exhibited, the dispersibility at the time of forming a paste remains, and the effect of suppressing the sintering becomes poor. Further, at 700 ° C. or higher, necking of particles of the noble metal powder progresses, which is not suitable for forming a paste.

The heat treatment time is appropriately adjusted according to the heat treatment temperature, but is preferably about 1 to 5 hours. As a schedule, the temperature is raised at 20 to 30 ° C./minute, the top temperature is kept for 15 to 60 minutes, and then the temperature is lowered at 3 to 30 ° C./minute.

Similar to the conventional method for producing a conductor paste, the conductor paste of the present invention can be obtained by dispersing the noble metal powder for high temperature firing of the present invention in an organic vehicle. Unlike the conventional one, this conductor paste is excellent in that it does not cause defects such as foaming, peeling from the ceramic substrate, shrinkage, and evaporation of the electrodes.

The noble metal powder which can be burned at a high temperature and is incorporated in the paste may be in a usual amount, preferably 30 to 95% by weight, more preferably 35 to 85% by weight, particularly preferably 45 to It is 85% by weight. If the amount is less than 30% by weight, the amount of the precious metal powder is too small, resulting in poor conductivity. On the contrary, if the amount exceeds 95% by weight, the fluidity of the paste is lost and the printability and coatability deteriorate.

The organic vehicle may be selected from those usually used in conductor pastes. Examples of the binder include ethyl cellulose, the solvent is terpineol, and B.I. C. A. , B. C. Etc. Also,
Known additives such as glass frit can be further added to the conductor paste of the present invention.

[0043]

EXAMPLES The present invention will be further described below with reference to examples. However, the present invention is not limited to the following examples. In the following examples, "%" means "% by weight" unless otherwise specified.

Example 1 The naphthenic acid salt of each metal shown in Table 1 placed in a suitable container was dissolved in a suitable organic solvent (one in which the compound does not cause hydrolysis, etc.), and a predetermined amount of noble metal was added. Add powder and stir well to uniformly disperse,
The organic solvent was evaporated to dryness. The coating amount was 1.0% by weight in terms of oxide with respect to the noble metal powder.

Then, the noble metal powder coated with a metal organic acid salt is placed in a predetermined ceramic container, placed in an electric furnace capable of atmosphere replacement, and heat-treated at a temperature shown in Table 1 in an inert atmosphere replaced with Ar atmosphere, A noble metal powder for high temperature firing was obtained.

Next, a paste material was prepared from these powders according to the composition shown in Table 2 and kneaded using a three-roll mill to form a paste.

This conductor paste was screen-printed on a ceramic substrate such as alumina or zirconia or a green sheet to prepare electrodes and circuits, and structural defects such as foaming, peeling and evaporation were examined.

[0048]

[Table 1]

[0049]

[Table 2]

The results are shown in Table 1 above. The paste using the noble metal powder for high temperature firing of the present invention did not cause defects such as foaming, peeling and evaporation even at high temperature firing.

Example 2 Next, the same experiment as in Example 1 was conducted except that the coating amount was variously changed as shown in Table 3.
The occurrence rate of structural defects such as pores and peeling in the prepared electrodes or circuits was examined. The results are shown in Table 3.

[0052]

[Table 3]

If it is less than 0.01%, the amount of coating on the noble metal powder is small, and the effect of suppressing oversintering is not exhibited. On the other hand, if it exceeds 5%, the effect of suppressing the firing shrinkage property of the paste is too large, and it does not match the shrinkage ratio of the ceramic member. It is understood that the more preferable coating amount is 0.1% or more and 5% or less, and particularly preferably 1% or more and 5% or less.

Example 3 The state of the obtained powder was examined by changing the temperature range of the heat treatment after coating the noble metal powder with aluminum naphthenate as shown in Table 4. The heat treatment schedule was as follows:
It was kept in the top temperature range shown for 30 minutes. The results are as shown in Table 4.

[0055]

[Table 4]

When the noble metal powder is made of Ag, Au, Pd or their alloys, the heat treatment is preferably carried out within the range of 350 to 500 ° C., and in the case of Pt, it is 70.
It was good even up to 0 ° C.

Example 4 With respect to silver and platinum, noble metal powders compatible with high temperature firing were produced using aluminum naphthenate, and a conductor paste was prepared according to the composition of Example 1 (Table 2). These conductor pastes were fired, and changes in expansion and contraction at each temperature were examined using TMA as an index. Furthermore, the surface state of the paste thin film at each firing temperature was observed. When the conductor paste is baked, the silver paste is 9
The temperature was 50 ° C., and the platinum paste was 1500 ° C.

The results show changes in TMA (thermal expansion and contraction) of silver for high temperature firing and platinum for high temperature firing in FIGS. 1 and 2. FIG. 3 and FIG. 4 are photographs showing the surface condition of the paste prepared by using silver for high temperature firing and platinum for high temperature firing after firing. In both cases, uncoated silver and platinum powders were used as comparative products.

With the conductor paste of the present invention, the temperature at which contraction starts during firing can be significantly delayed,
Suitable for high temperature firing. Further, it can be seen that the case where the conductor paste of the present invention is used is superior to the comparative product in that there is no generation of pores due to contraction and evaporation and a dense electrode film is formed.

[Embodiment 5] Heat treatment of each noble metal powder after coating each noble metal powder with a metal salt of naphthenic acid is performed in air and Ar (inert gas), and structural defects of each noble metal paste due to the difference in atmosphere between the two. Was investigated. The composition of the paste is the same as in Example 1 (Table 2) above. Details of the experimental method and the results are summarized in Table 5.

[0061]

[Table 5]

When the coated noble metal powder is heat-treated in an inert gas, a good product free from structural defects can be obtained. Therefore, even if the noble metal powder was coated with another metal compound by the same method, when the subsequent heat treatment was performed in air, a sufficient oversintering suppression effect was not obtained, and the treatment was performed in an inert gas. Only at this time, an extremely excellent effect of suppressing oversintering is exhibited.

[0063]

EFFECTS OF THE INVENTION The noble metal powder for high temperature firing of the present invention does not easily oxidize even when fired at high temperature, and abnormal grain growth does not easily occur. It also has excellent dispersibility in organic vehicles. Therefore, the conductor paste produced by using the noble metal powder for high temperature firing of the present invention has excellent printability and, at the time of firing, matches the difference in shrinkage ratio with the ceramic substrate, etc. Not give excellent electronic components. Furthermore, it is an excellent one which gives a very dense electrode film, and enables further miniaturization of electronic parts.

Accordingly, the noble metal powder and conductor paste for high temperature firing of the present invention are epoch-making ones capable of solving structural defects which could not be prevented by the prior art.

[Brief description of drawings]

FIG. 1 is a conductor paste obtained by coating silver with aluminum naphthenate, which is an embodiment of the present invention, and heat-treating it in an Ar atmosphere to disperse silver powder compatible with high temperature in an organic vehicle. 6 is a graph showing a TMA (thermal expansion / contraction) curve at each temperature when firing a conductor paste prepared by dispersing ordinary untreated silver powder in an organic vehicle.

FIG. 2 is another embodiment of the present invention, in which platinum is coated with aluminum naphthenate and is heat-treated in an Ar atmosphere, and a high-temperature-compatible platinum powder is dispersed in an organic vehicle. And a conductor paste in which ordinary untreated platinum powder is dispersed in an organic vehicle,
It is a graph showing a TMA (thermal expansion and contraction) curve at each temperature when firing each.

FIG. 3 (a) is a photograph showing the surface of the texture when a conductor paste prepared by dispersing silver powder compatible with high temperature firing in an organic vehicle is fired, and FIG. 3 (b) is an ordinary untreated silver powder. 3 is a photograph showing the surface of the texture when a conductor paste in which is dispersed in an organic vehicle is fired.

FIG. 4 (a) is a photograph showing the surface of the texture when a conductor paste prepared by dispersing platinum powder for high temperature firing in an organic vehicle is fired, and FIG. 4 (b) is an ordinary untreated silver powder. 3 is a photograph showing the surface of the texture when a conductor paste in which is dispersed in an organic vehicle is fired.

[Procedure amendment]

[Submission date] September 22, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

Claims (9)

[Claims] 1. A high temperature obtained by coating the surface of a noble metal powder with a compound of a metal and an organic acid (hereinafter referred to as "organic acid metal salt"), and then heat treating in an inert atmosphere. Precious metal powder for firing. 2. The surface of the noble metal powder is coated with an organic acid metal salt, and then the organic compound portion is removed by heat treatment in an inert atmosphere to deposit ultrafine metal particles on the surface of the noble metal powder. A noble metal powder for high temperature firing characterized by being coated. 3. The noble metal powder for high temperature calcination according to claim 1, wherein the metal constituting the organic acid metal salt is at least one selected from aluminum, calcium, titanium, yttrium and zirconium. 4. The organic compound portion constituting the metal salt of an organic acid is selected from at least one of naphthenic acid, abietic acid, octylic acid, and ethylhexanoic acid. Precious metal powder for high temperature firing described. 5. The high temperature according to claim 1, wherein the coating amount of the organic acid metal salt is 0.01 to 5% by weight in terms of oxide of the metal with respect to the noble metal powder. Precious metal powder for firing. 6. The high temperature calcining-compatible precious metal powder according to claim 1, wherein the heat treatment is performed within a range of 350 ° C. to 700 ° C. 7. When the noble metal powder is selected from Ag, Au, Pd or alloys thereof, the heat treatment is 350-50.
The precious metal powder for high temperature calcination according to claim 6, which is performed within a range of 0 ° C. 8. A conductor paste comprising the noble metal powder for high temperature firing according to claim 1 dispersed in an organic vehicle. 9. The conductor paste according to claim 8, wherein the noble metal powder for high temperature firing is blended in an amount of 35 to 85% by weight based on the total weight of the paste.