JP2008101276A - Copper powder for electrically conductive paste for external electrode having excellent oxidation resistance and sinterability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the oxidation of copper powder in a debindering stage till the sintering of electrically conductive paste using the copper powder as an electrically conductive filler, and simultaneously, to improve the quality of the resultant sintered compact. <P>SOLUTION: Regarding the copper powder used for an electrically conductive filler in electrically conductive paste having excellent oxidation resistance and sinterability, Si is comprised by ≤5 wt.%, substantially all the Si is deposited on the surfaces of copper particles as an SiO<SB>2</SB>-based gel coating film, and at least one of glass formable component is comprised in the SiO<SB>2</SB>-based gel coating film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a copper powder excellent in oxidation resistance and sinterability used for a conductive filler of a conductive paste for external electrodes.

  A conductive paste is often used as a means for forming electric circuits and electrodes on the surface, inside or outside of various substrates. The conductive paste is a fluid fluid in which a conductive filler is dispersed in a vehicle composed of a resin binder and a solvent, and copper powder and silver powder are generally used as the conductive filler. When such conductive paste is applied as an electrode for various circuit boards and electronic components and heated to an appropriate temperature, the vehicle evaporates and decomposes, and the metal powder as the conductive filler sinters together to produce a good electrical conductor. It is formed. Recently, conductive paste using copper powder as a conductive filler (copper-based paste) is less likely to cause migration, has better solder resistance, and is less expensive than conductive paste using silver powder as a conductive filler (silver-based paste). However, it is becoming more and more versatile because it is possible.

  Even if the same copper paste is used for the external electrode of the multilayer ceramic capacitor or for forming various circuits on the substrate, it is required for the conductive paste depending on the form of the electrode and circuit, the formation method, and the substrate material. Different physical and chemical properties.

  For example, when a copper paste is applied to a chip component such as a multilayer ceramic capacitor and the copper powder in the paste is sintered by heating to form a conductor such as an electrode, the copper powder is particularly resistant to oxidation. And good sinterability is required. That is, in the above heat treatment, an inert gas (generally nitrogen gas) atmosphere is employed to prevent the copper powder from being oxidized, but in reality, it is a decomposition product of the resin and solvent in the paste. If the carbonaceous component remains, the sinterability may be adversely affected, so that some oxygen is mixed into the nitrogen gas to promote the vaporization of the resin and solvent in the paste (called debinding). In this case, the copper powder surface may be oxidized.

If the surface of the copper powder is oxidized, the particle surface is covered with copper oxide, so that the sinterability is deteriorated and the conductivity of the formed conductor is also adversely affected. On the other hand, if a means for imparting oxidation resistance to copper powder is adopted, for example, if an oxidation resistant coating is applied to the surface of the copper particles, oxidation during the heating can be prevented, but in general, the sinterability is deteriorated and sintering is performed. The temperature must also be increased. Therefore, there is a need for a copper powder for conductive paste that is prevented from oxidation during heating and at the same time has good sinterability.
JP 2001-307944 A Japanese Patent Laid-Open No. 10-330802 JP 2002-280248 A JP-A-3-54126

  An object of the present invention is to satisfy such a demand, and to obtain a copper powder for a conductive paste for external electrodes, which is excellent in oxidation resistance and sinterability at the same time.

According to the present invention, the copper powder used for the conductive filler of the conductive paste contains 5% by weight or less of Si, and substantially all of the Si is deposited on the surface of the copper particles as a SiO ₂ gel coating film. The present invention provides a copper powder for a conductive paste for external electrodes, which is excellent in oxidation resistance and sinterability, characterized in that the SiO ₂ gel coating film contains at least one glass-forming component. This copper powder exhibits excellent oxidation resistance in the SiO ₂ gel coating film. In addition, when this copper powder is mixed with glass frit to form a conductive paste, the glass-forming component in the SiO ₂ gel coating film promotes the fusion with the glass frit during sintering and is good at low sintering temperatures. Can be formed. Here, the glass-forming component is an element that forms an oxo acid by combining with an alkali metal (referred to as M ₁ ), an alkaline earth metal (referred to as M ₂ ), an amphoteric metal (referred to as M ₃ ), or oxygen / hydrogen. ₄ ), and the atomic ratio of M ₁ / Si, the atomic ratio of M ₂ / Si, the atomic ratio of M ₃ / Si, and the atomic ratio of M ₄ / Si are all 0.5 or less. Is good.

Such a copper powder is obtained by reacting copper powder, an organosilane compound and water in a water-soluble organic solvent to produce a hydrolyzed product of organosilane, and adding a gelling agent to the resulting suspension. In the method of forming a SiO ₂ gel coating film on the surface of the copper powder particles and then collecting the copper particles having the SiO ₂ gel coating film by solid-liquid separation, the hydrolysis product of the organosilane described above Can be advantageously produced by adding an aqueous solution in which a glass-forming component is dissolved to the suspension produced or during or before production.

  According to the present invention, a copper powder capable of improving the sinterability while maintaining the oxidation resistance could be obtained. As a result, when used as a filler for a conductive paste, voids generated during the firing process can be suppressed, and a conductive paste for external electrodes having excellent sinterability can be obtained. In addition, since the number of voids is reduced, it is possible to solve the problem that the plating solution gets into the void and corrodes when plating is performed on the conductive paste after firing.

In order to solve the above-mentioned problems, the present inventors have made various attempts to coat the surface of the copper powder with a metal oxide while paying attention to the sol-gel method. As a result, when an ultrathin layer of a hydrolysis product derived from an organosilane compound is deposited on the surface of copper particles with a siloxane bond and then subjected to a condensation reaction with a catalyst or the like, a uniform ultrathin SiO ₂ layer is formed on the surface of the copper particles. It was found that a gel coating film can be formed by a wet method. And, the copper powder having the SiO ₂ gel coating film thus obtained can have an oxidation start temperature of about 120 to 200 ° C. higher than that of the copper powder without the film, and the sintering start. It was found that the temperature also changed. Further, by incorporating a suitable glass forming ingredients on the SiO ₂ based gel coating, and glass-forming component containing SiO ₂ based gel coating film with a copper powder, dispersing the ones in a vehicle together with glass frit It was found that the sinterability can be significantly improved by making the conductive paste.

First, the application of the sol-gel method will be described. For the copper powder having an average particle size of preferably 10 μm or less, the sol-gel reaction of hydrolysis / condensation of the organosilane compound on the surface of the copper particle is performed in an organic solvent. As the process proceeds, a thin and uniform SiO ₂ gel coating film can be formed. Specifically, in order to hydrolyze the sol, copper powder, an organosilane compound and water are reacted in a water-soluble organic solvent such as isopropyl alcohol.

  As an organic solvent, in order to function as a sol medium which advances hydrolysis, the thing which dissolves water is preferable, for example, the solubility of water at 20 degreeC is 10 weight% or more. As such an organic solvent, methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxolane, dioxane and the like can be used.

Examples of the organosilane include alkoxysilanes represented by the general formula R ¹⁴ _-a Si (OR ² ) _a (R ¹ is a monovalent hydrocarbon group, R ² is a monovalent hydrocarbon having 1 to 4 carbon atoms) The group a is preferably 3-4), and typical examples include tetraethoxysilane and methyltrimethoxysilane.

In order to cause the alkoxysilane hydrolysis reaction to occur on the surface of the copper powder in the organic solvent, the copper powder is first put in an organic solvent, suspended and suspended, and then the alkoxysilane is added thereto, and then the water is added. After the operation sequence of adding water (pure water) to be decomposed (or adding alkoxysilane after adding pure water), an alkaline catalyst that promotes hydrolysis / condensation reaction, such as ammonia water, is added. It is good to add. As a result, first, alkoxysilane adheres to the surface of the copper powder by a siloxane bond, and the alkoxysilane is hydrolyzed on the surface of the copper powder to undergo a condensation reaction (gelation) to form a uniform SiO ₂ -based film with copper particles. Formed on the surface.

In general, acid or alkali is used as a catalyst for the sol-gel reaction, but the present inventors know that ammonia is most suitable as a catalyst when a SiO ₂ gel coating film is formed on the surface of copper powder. It was. A gel coating film having sufficient oxidation resistance cannot be obtained with an acid such as hydrochloric acid, sulfuric acid or phosphoric acid. On the other hand, when ammonia is used, a gel coating film having good oxidation resistance can be obtained, and it is easy to obtain, has a merit that it is easy to remove at a low cost and has no residual impurities.

The condensation reaction is preferably allowed to proceed by adding ammonia water and then aging at a predetermined temperature for a predetermined time. For example, the liquid temperature may be maintained at 20 to 60 ° C. for a predetermined time. The film thickness of the SiO ₂ -based gel coating film generally depends on the amount of alkoxysilane, liquid temperature, holding time, etc. By adjusting these, a thin film of SiO ₂ -based gel coating film with a uniform thickness is formed on the copper particle surface Can be made. At this time, the particle shape of the copper powder hardly affects the film thickness. Even if the copper particles have any shape such as spherical, plate, flake (foil piece), square, etc., the SiO ₂ film has a uniform thickness. It was confirmed that a gel coating film can be formed. In addition, when using an ammonia catalyst, it was found that aggregation of copper powder with a SiO ₂ gel coating film can be prevented by continuously adding it to the reaction system. Even if agglomerated, it can be dispersed satisfactorily by applying ultrasonic waves to the reaction system and at least to the same extent as the raw material copper powder.

In this way, a uniform SiO ₂ -based gel coating film can be formed on the surface of the copper powder, but the amount of this film is not conductive if the amount of SiO ₂ exceeds 10% by weight with respect to copper. The amount of Si is preferably less than that, and the amount of Si is preferably 5% by weight or less. That is, it is preferable that the copper powder contains 5% by weight or less of Si, and substantially all of the Si is deposited on the surface of the copper particles as a SiO ₂ gel coating film. Here, “substantially” all of Si means that a small amount of Si other than SiO ₂ may inevitably remain in the film. For example, a part of Si may be alkoxy for manufacturing reasons. Even if a silane residue inevitably remains in the film or is present in a small amount as a Si oxide other than SiO ₂ , there is no particular adverse effect as long as the amount is small.

In this way, the SiO ₂ gel coating film can be applied to the surface of the copper powder by the sol-gel method, which can improve the oxidation resistance and sintering property of the copper powder. When a suitable glass-forming component is included in the gel coating film during the process of applying the SiO ₂ -based gel coating film, the sinterability can be further improved while maintaining good oxidation resistance. .

In the following, the addition of glass-forming components to the gel coating film will be described. The gist of the addition is to react copper powder, organosilane compound and water in a water-soluble organic solvent as described above. A hydrolyzed product of organosilane is generated, and a gelling agent is added to the resulting suspension to form a SiO ₂ gel coating film on the surface of the copper powder particles. _{In the} method for producing copper powder by collecting copper particles having a ₂ system gel coating film, the glass-forming component was dissolved in the suspension in which the hydrolysis product of the organosilane was produced, or during or before the production. By adding “aqueous solution”, a glass-forming component is contained in the SiO ₂ -based gel coating film to be formed.

That is, it is characterized in that an aqueous solution in which a glass-forming component is dissolved is added to a suspension in which an organosilane hydrolysis product (sol) is formed, or to a solution in the middle of or before the generation of the sol. At that time, when adding to the suspension formed by the sol, an aqueous solution in which the glass-forming component is dissolved may be added before adding the gelling agent. Sexual components may be added. In the case of the latter, it can also add in the state which made the gelatinizer contain the glass-forming component. When a glass-forming component is added in the form of an aqueous solution and gelation proceeds with a gelling agent (ammonia), an oxide of the glass-forming component is incorporated into the resulting gel, and the glass-forming component is uniformly distributed. The contained SiO ₂ gel coating film is formed on the surface of the copper particles.

The glass-forming component is preferably added using a solution in which the component hydroxide, oxide, inorganic acid salt, oxo acid or oxo acid salt is dissolved. Glass-forming components for use in the present invention are alkali metal (M _1), alkaline earth metal (M _2), amphoteric metal element (M ₃₎ or bonded to the oxygen-hydrogen to an element forming the oxo acid (M ₄ ). Such a glass-forming component is a component that is easily vitrified when a conductive paste containing copper powder as a filler is fired. Actually, when a glass frit coexists in the conductive paste, It is familiar and therefore means a component having the property of improving the wettability of the SiO ₂ gel coating film to glass frit.

Examples of the alkali metal element (M ₁ ) include Na or K. Alkaline earth metal (M ₂ ) includes Ca, Sr or Ba. However, since the vitrification range of SiO ₂ and BaO is wider than the vitrification range of SiO ₂ and CaO or SrO, Ba is fired. Of these, it is preferable to use Ba because crystallization of the glass hardly occurs. The atomic ratio of M ₂ / Si The addition amount of M ₂ (molar ratio), 0.1 or more, preferably 0.5 or less. If M ₂ / Si is less than 0.1, the wettability with glass is insufficient, and if it exceeds 0.7, crystallization of the glass tends to occur. Therefore, it is preferably 0.5 or less.

Examples of the amphoteric metal element (M ₃ ) include Al, Zn, Sn, Bi, Pb, As, and Sb. Al, Zn, or Sn, which has low toxicity and low environmental load, is more preferable. Examples of the element capable of forming oxo acid (M ₄ ) include P 1, B 2, Al, S, or Cl, and in particular, P and B are easily mixed with SiO ₂ to form a glass. Since the wettability of a metal can be improved, it is more preferable.

In this way, by adding an appropriate amount of M ₁ M ₂ M ₃ or M ₄ to the SiO ₂ -based gel coating film, as shown in the examples described later, the SiO ₂ -based gel coating film not containing these elements is used. Compared with pastes, conductive pastes with fillers should have high-quality conductors because the number of voids is reduced and the sinterability is improved due to improved wettability to glass and lower softening point. Can do.

Specifically, at the time of baking of the suitable amount is to the conductive paste M ₁ or M ₂ in SiO ₂ based gel coating, the viscosity at the time of SiO ₂ based gel coating film dissolved in the glass phase varies, lower temperatures With this, sintering can be promoted. When an appropriate amount of M ₃ or M ₄ is contained in the SiO ₂ gel coating film, the wettability between the glass phase and the copper powder is improved during sintering, and a denser sintered body can be obtained. Furthermore, by including M ₁ M ₂ M ₃ or M ₄ in combination, the sinterability can be further improved.

The glass frit to be coexisted with the conductive filler is not particularly limited, but a glass frit containing a metal oxide component such as SiO ₂ , Na ₂ O _, B ₂ O ₃ , or PbO is preferably used. If the blending amount of the glass frit is too large, the conductive properties as a conductor will be affected. Therefore, the glass frit is 10 parts by weight or less, preferably 7 parts by weight with respect to 100 parts by weight of the copper powder according to the present invention. It should be a range.

As the copper powder (copper powder to be treated) for forming the SiO ₂ gel coating film on the surface according to the present invention, the copper powder manufactured by the wet reduction method or the atomized method may be used. In other words, it is not limited to the copper powder production method, and copper powder obtained by any production method can be applied. However, the copper powder produced by the wet reduction method in which copper hydroxide → copper oxide → metal copper is changed. In some cases, various particle size distributions can be obtained relatively easily, and spherical powders or plate-like powders can be obtained relatively easily.

Note that the SiO ₂ gel coating film on the surface of the copper powder does not require a treatment for vitrification. The SiO ₂ -based gel coating film can be vitrified by heating it to a certain temperature exceeding 200 ° C., but without conducting the heat treatment for vitrification, the gel coating remains as a conductive paste. It has sufficient oxidation resistance as required. When heat treatment for vitrification is performed, cracks occur in the coating film or the gel coating shrinks and the surface of the copper particles is exposed, which adversely affects the oxidation resistance and adversely affects the sintering characteristics. Therefore, it is not preferable for the present invention.

[Example 1]
200 g of copper powder having an average particle size of 3 μm was added to 500 g of isopropyl alcohol to obtain a slurry having a slurry concentration of 28.6% by weight, and stirring was performed in a nitrogen atmosphere to confirm that the oxygen concentration became zero. Thereafter, the temperature was raised to 40 ° C., and 6.3 g of tetraethoxysilane was added and aged for 5 minutes. Subsequently, 72.6 g of an aqueous barium solution in which Ba (OH) ₂ was dissolved in pure water so that the Ba concentration was 3.0% was added all at once, and the mixture was aged again for 5 minutes. Finally, NH ₃ (20.73%) 69.5 g of ammonia water is continuously added, and then aged for 60 minutes. After completion of the reaction, it is suction filtered in air and dried at 120 ° C. for 11 hours in a nitrogen atmosphere.

  The obtained powder was chemically analyzed, and the oxidation start temperature and sintering start temperature were measured. The results are shown in Table 1 and FIG. In Table 1 and FIG. 1, for comparison, the same measurement was performed on the powder obtained by repeating Example 1 except that no barium aqueous solution was added, and these were shown as [Comparative Example 1]. .

  The oxidation start temperature was measured with a differential thermal analyzer (TG) in air. The oxidation start temperature is defined as “temperature at which the weight of the sample copper powder increases by 0.5% from the initial value in the differential thermal analyzer”. The sintering start temperature was measured as follows. That is, copper powder and an organic vehicle are mixed and formed into a cylindrical shape. This molded body was loaded in a heating furnace in a vertical direction and with a load applied in the axial direction, and the temperature rising rate was 10 ° C./min in a nitrogen atmosphere, and the measurement range was continuously elevated from room temperature to 1000 ° C. As it warms, the height change (shrinkage / expansion change) of the compact is automatically recorded. The temperature at which the height change (shrinkage) of the compact starts and the shrinkage rate reaches 0.5% is defined as “sintering start temperature”.

As can be seen from the results in Table 1 and FIG. 1, the copper powder of Example 1 has a Si content of 0.42 wt%, a Ba content of 0.71 wt%, and an atomic ratio of Ba / Si = 0.35. A BaO-containing SiO ₂ -based gel coating film is formed, and its oxidation start temperature is 308 ° C., which is preferably 300 ° C. or more, which is preferable for oxidation resistance. In addition, although the sintering start temperature is slightly higher than that of the SiO ₂ gel coating film not containing Ba in Comparative Example 1, as shown in FIG. It is considered that the shrinkage rate is larger and the sinterability of the conductive paste is improved in this respect.

  Actually, when the conductive paste was prepared using the copper powder of Example 1 and the copper powder of Comparative Example 1 and the sinterability was evaluated, the following results were obtained. The sinterability test is as follows.

[Sinterability test] After mixing 4.2 g of test copper powder, 0.2720 g of diluent, 0.8180 g of vehicle and 0.1600 g of glass frit, this mixture was kneaded with three rolls to prepare a conductive paste. To do. The obtained conductive paste is applied as an external electrode of a multilayer ceramic capacitor and baked in a nitrogen atmosphere at 830 ° C. for 30 minutes. The surface after firing is observed with an electron microscope (FE-SEM), and the number of voids is counted. As shown in Fig. 2, the number of voids is fixed so that the upper right corner of the measurement range (80 µm in length and 100 µm in width) is at a position 60 µm wide and 40 µm long from the corner of the formed external electrode. Then, the number of voids having a diameter of 6 μm or more and the number of voids having a diameter of 12 μm or more existing in this measurement range are counted (the number of voids on the frame in FIG. 2 is also counted).

[Results of Sinterability Test] The results of the firing test of the conductive paste using the powders of Example 1 and Comparative Example 1 are as follows.
Number of voids of 6 μm or more Copper powder of Comparative Example 1 having a number of voids of 12 μm or more 25 8
Copper powder of Example 1 17 2

That is, the copper powder of this example containing Ba in the SiO ₂ gel coating film has a smaller number of large voids than that of Comparative Example 1 not containing Ba, and a good fired product was obtained.

[Example 2]
Example 1 was repeated except that an aqueous solution of NaOH was added instead of the aqueous solution of Ba (OH) ₂ to obtain a copper powder having an Na ₂ O-containing SiO ₂ gel coating film. The obtained copper powder was chemically analyzed and the oxidation start temperature and the sintering start temperature were measured in the same manner as in Example 1. The results are shown in Table 2 and FIG.

As can be seen from these results, the copper powder with Na ₂ O-containing SiO ₂ gel coating film of this example has an oxidation start temperature of 267 ° C., which is slightly inferior to that of Comparative Example 1 with SiO ₂ alone. The oxidation start temperature of the copper powder without the SiO ₂ gel coating film is about 180 ° C., which is about 80 ° C. higher than this. The copper powder of this example has a sintering start temperature of 550 ° C., which is 80 ° C. lower than that of Comparative Example 1. In particular, FIG. 3 shows that the shrinkage rate is higher than that of Comparative Example 1 up to around 830 ° C., which is the firing temperature of the paste.

Next, the sinterability evaluation of the conductive paste using the obtained copper powder was carried out in the same manner as in Example 1, but the sample powder had the following composition. That is, instead of 4.2 g of the copper powder used in Example 1, 66% of the copper powder of Example 2 was mixed with 33% of copper powder obtained by applying a SiO ₂ gel coating film to flake copper powder. The sinterability test described in Example 1 was performed except that 4.2 g of powder was used. Also in the comparative example, 4.2 g of mixed copper powder obtained by mixing 33% of the copper powder obtained by applying the SiO ₂ gel coating film to the flake copper powder to 66% of the copper powder of the comparative example 1 was used. The described sinterability test was performed.

All the fired electrodes were observed with an electron microscope (FE-SEM), and the number of voids was counted in the same manner as in Example 1. The results are shown below. The copper powder of this example with a SiO ₂ -based gel coating film to which Na was added had the same number of large voids and good sinterability as that to which Ba was added. It has become. In particular, it can be seen that the number of voids of 12 μm or more is reduced to 1/6 compared with those not containing Na.
Number of voids of 6 μm or more Copper powder of comparative example of number of voids of 12 μm or more 15 6
Copper powder of this example 8 1

Example 3
200 g of copper powder having an average particle size of 2.5 μm was added to 500 g of isopropyl alcohol to make a slurry having a slurry concentration of 28.6%, and stirring was performed in a nitrogen atmosphere, and it was confirmed that the oxygen concentration became zero. Next, after raising the temperature to 40 ° C., 7.8 g of tetraethoxysilane was added and aged for 5 minutes. Thereafter, an aqueous boric acid solution obtained by dissolving 1.7 g of H ₃ BO ₃ in 61.9 g of pure water which had been evacuated was added all at once and aged again for 5 minutes. Finally, NH ₃ (19.87%) 72.5 g of ammonia water was continuously added, followed by aging for 60 minutes. After completion of the reaction, the mixture was suction filtered in air and dried at 120 ° C. for 11 hours in a nitrogen atmosphere.

  The obtained copper powder was chemically analyzed and the oxidation start temperature and the sintering start temperature were measured in the same manner as in Example 1. The results are shown in Table 3 and FIG. For comparison, the copper powder obtained by repeating Example 3 was shown in Tables 3 and 4 as “Comparative Example 3” except that the boric acid aqueous solution was not added.

As can be seen from these results, the copper powder with the B ₂ O ₃ -containing SiO ₂ gel coating film of this example has a high oxidation start temperature of 400 ° C., which is higher than that of Comparative Example 3 using SiO ₂ alone. In addition, the sintering start temperature is 613 ° C., and as shown in FIG. 4, it is considered that the shrinkage rate is higher than that of Comparative Example 3 and the sinterability is good.

In fact, when the obtained powder and the powder of Comparative Example 3 were subjected to the same sinterability test as in Example 1, the following results were obtained, and the sinterability was increased until the number of large voids became zero. Improved.
Number of voids of 6 μm or more Copper powder of Comparative Example 3 having a number of voids of 12 μm or more 9 4
Copper powder of Example 3 50

Example 4
After adding 200 g of copper powder with an average particle size of 3.0 μm to 500 g of isopropyl alcohol and 70.6 g of pure water, stirring in a nitrogen atmosphere and confirming that the oxygen concentration becomes zero, the temperature was raised to 40 ° C. Then, 5.85 g of tetraethoxysilane was added and aged for 5 minutes. Thereafter, 63.8 g of a solution of 2 g of zinc oxide dissolved in 191.4 g of NH ₃ (22.58%) aqueous ammonia was continuously added and aged for 60 minutes. After completion of the reaction, the mixture was suction filtered in air and dried at 120 ° C. for 11 hours in a nitrogen atmosphere.

The obtained copper powder with ZnO-containing SiO ₂ -based gel coating film was subjected to the same sinterability test as in Example 1. The results are shown below in comparison with Comparative Example 1 described above. The copper powder with SiO ₂ gel coating film to which amphoteric metal Zn was added was also added with Ba, Na, B, etc. of the previous example. Similarly, it can be seen that the number of large voids is reduced and the sinterability is improved.
Number of voids of 6 μm or more Copper powder of Comparative Example 1 having a number of voids of 12 μm or more 25 8
Copper powder of Example 4 18 3

Example 5
In the same manner as in Example 1, copper powder with BaO-containing SiO ₂ -based gel coating film having a Ba 2 / Si atomic ratio (molar ratio) of about 0.4, 0.6, and 0.8 was prepared. Table 4 shows the chemical analysis values and the measurement results of the oxidation start temperature of the obtained copper powders (Examples 5-1, 5-2, and 5-3). As can be seen from the results of Table 4, the oxidation start temperature is higher than that of Comparative Example 1 (oxidation start temperature 319 ° C.) in which Ba is not added due to the addition of Ba, and the oxidation resistance is improved.

  Furthermore, each obtained copper powder was used for the sinterability test similar to Example 1. FIG. The results are shown below in comparison with those of Comparative Example 1 described above. The numerical value in parentheses indicates how much the number of voids has decreased with respect to that in Comparative Example 1 in%. This is called the improvement rate.

Number of voids of 6 μm or more Copper powder of Comparative Example 1 having a number of voids of 12 μm or more 25 8
Copper powder of Example 5-1 7 (72%) 3 (63%)
Copper powder of Example 5-2 14 (44%) 6 (25%)
Copper powder of Example 5-3 3 (88%) 0 (100%)

  Among these, the improvement rate of the void is high for the copper powder of Example 5-3 having the largest Ba / Si molar ratio. However, if the Ba / Si molar ratio is too high, Ba may be crystallized in the sintered body. Therefore, even if the Ba / Si molar ratio is 0.5 or less, a good void improvement rate can be obtained. For example, the molar ratio of Ba / Si is preferably 0.5 or less.

Example 6
A copper powder with a B ₂ O ₃ -containing SiO ₂ -based gel coating film having an atomic ratio (molar ratio) of B / Si of about 0.4, 0.5, and 0.8 was prepared in the same manner as in Example 3. . Table 5 shows the chemical analysis of the obtained copper powders (Examples 6-1, 6-2, and 6-3) and the measurement results of the oxidation start temperature. As can be seen from the results in Table 5, the oxidation start temperature is higher by the addition of B than that of Comparative Example 3 (oxidation start temperature 326 ° C.) in which B is not added, and the oxidation resistance is improved. In particular, when the molar ratio of B / Si is 0.4 and 0.5, the oxidation start temperature reaches 400 ° C. or more, and the effect of improving oxidation resistance is great.

  Furthermore, each obtained copper powder was used for the sinterability test similar to Example 1. FIG. The results are shown below in comparison with those of Comparative Example 1 (original powder particle size 3 μm) and Comparative Example 3 (original powder particle size 2.5 μm). The numerical value in parentheses represents the improvement rate of the number of voids for the comparative example having the same particle size of the base powder. That is, the improvement rates of Examples 6-1 and 6-2 are relative to Comparative Example 3, and the improvement rate of Example 6-3 is relative to Comparative Example 1. From these results, it can be seen that the effect of reducing the number of voids appears sufficiently even when the molar ratio of B / Si is 0.5 or less.

Number of voids of 6 μm or more Copper powder of Comparative Example 1 having a number of voids of 12 μm or more 25 8
Copper powder of Comparative Example 3 9 4
Copper powder of Example 6-1 5 (44%) 0 (100%)
Copper powder of Example 6-2 6 (33%) 0 (100%)
Copper powder of Example 6-3 20 (20%) 6 (25%)

Example 7
BaO-containing copper powder with SiO ₂ -based gel coating film having a Ba / Si molar ratio of 0.35 produced according to Example 1 and B ₂ O ₃ having a B / Si molar ratio of 0.499 produced according to Example 3 The copper powder with SiO ₂ gel coating film was mixed at a weight ratio of 1: 3, and the mixed powder was subjected to the same sinterability test as in Example 1. The results are shown below in comparison with those of Comparative Example 1. Both the number of voids of 6 μm or more and the number of voids of 12 μm or more are reduced compared to those of Comparative Example 1, and when used as a mixed powder, It can be seen that the sinterability is further improved.

Number of voids of 6 μm or more Copper powder of Comparative Example 1 having a number of voids of 12 μm or more 25 8
Mixed powder of Example 7 7 3

Figure sintering initiation temperature (● mark), shown in comparison with that of the SiO ₂ based gel coating film with copper powder not containing BaO (○ mark) of BaO-containing SiO ₂ based gel coating film with copper powder according to the present invention It is. The conductive paste using the BaO-containing SiO ₂ -based gel coating film-coated copper powder as a conductive filler according to the present invention is subjected to a sintering treatment, and the surface state of the obtained sintered body is changed to a copper-containing SiO ₂ gel coating film that does not contain BaO. It is the electron micrograph shown by contrasting with that of powder | flour (what was described as the comparative example 1 in the figure). The sintering start temperature (■ mark) of the Na ₂ O-containing copper powder with SiO ₂ gel coating film according to the present invention (■ mark) is compared with that of the copper powder with SiO ₂ gel coating film not containing Na ₂ O (□ mark). FIG. The sintering start temperature of the copper powder with SiO ₂ -based gel coating film containing B ₂ O ₃ according to the present invention (marked with ●) is the same as that of the copper powder with SiO ₂ -based gel coating film not containing B ₂ O ₃ (marked with ○). It is the figure shown by contrast.

Claims (8)

The copper powder used for the conductive filler of the conductive paste contains 5% by weight or less of Si, and substantially all of the Si is deposited on the copper particle surface as a SiO ₂ gel coating film. This SiO ₂ gel A copper powder for an external electrode conductive paste excellent in oxidation resistance and sinterability, wherein the coating film contains at least one glass-forming component. Glass forming ingredients, alkali metal (referred to M ₁₎ or external electrode conductive paste of copper powder according to claim 1 is an alkaline earth metal (referred to M _2). Glass forming ingredients, the external electrode conductive paste of copper powder according to claim 1 which is an amphoteric metal element (referred to M _3). Glass forming ingredients, the external electrode conductive paste of copper powder according to claim 1 combined with oxygen-hydrogen is an element that forms an oxo acid (referred to M _4). 5. The atomic ratio of M ₁ / Si, the atomic ratio of M ₂ / Si, the atomic ratio of M ₃ / Si, and the atomic ratio of M ₄ / Si are all 0.5 or less. Copper powder for conductive paste for external electrodes. The copper powder according to claim ₂ containing M ₂ as a glass-forming component and the copper powder according to claim 4 containing M ₄ as a glass-forming component in a required ratio. Copper powder for conductive paste for electrodes.   The filler for electrically conductive paste for external electrodes which mix | blends glass frit with the ratio of 10 weight part or less with respect to 100 weight part of copper powder of Claim 1.   A conductive paste for external electrodes, wherein the copper powder and glass frit according to claim 1 are dispersed in a vehicle comprising a resin binder and a solvent.