Silver compound-coated silver powder and production method therefor

The present invention relates to a silver powder (referred to as "silver compound-coated silver powder" in the present application) in which a silver compound such as silver oxide, silver carbonate, or silver hexanoate is coated on the surface of silver particles, and the production method thereof. More specifically, the present invention relates to a silver compound-coated silver powder suitable as a material for a conductive paste for wiring a substrate for an electronic circuit or for wiring a via hole in a multilayer electronic substrate, and a method for producing the same.

In recent years, with the miniaturization and integration of electronic devices, for example, multilayer electronic boards have become widespread as boards for electronic circuits, and conductive pastes are generally used to form wiring for electronic circuits on these boards. ing.

Then, silver powder having high conductivity suitable as a conductive metal is often mixed and used in such a conductive paste. However, although the melting point of silver is 961.93 ° C, it is mixed into the conductive paste at a sintering temperature considerably lower than the above melting point in order to easily form wiring for electronic circuits, especially wiring for resin multilayer substrates. It is desirable to sinter the silver powder particles together.

By the way, in general, there is a method of atomizing the metal particles constituting the metal powder in order to lower the sintering temperature for sintering the metal powder particles. However, if the metal powder is excessively pulverized, the metal particles aggregate with each other and the dispersibility of the metal powder deteriorates. As a result, cavities are generated in the wiring portion after firing, and the conductivity differs depending on the wiring location. Is easy to come out. Therefore, it is not sufficient to atomize the metal powder (silver powder in the present invention) simply to lower the sintering temperature.

On the other hand, for a conductive paste mixed with silver powder, the fact that silver particles are sintered at a low temperature and that the silver powder has excellent dispersibility are excellent for electrical circuit wiring and on an electronic circuit board. It is an indispensable requirement to realize excellent printability. Therefore, the problem related to the atomization is a problem in the production of the conductive paste.

Therefore, in order to solve the above-mentioned problems, a conductive silver paste is prepared by mixing fine-grained silver powder with coarse-grained silver powder at a constant ratio by utilizing the fact that fine-grained particles have a lower sintering temperature than coarse-grained particles. However, a technique for lowering the overall sintering temperature has been presented, but in this case, the dispersibility of the mixed fine silver powder tends to be insufficient, and the above-mentioned requirements for printability are not sufficiently satisfied.

Further, in the market for resin multilayer substrates for electronic circuits, there is a demand for a conductive paste having a via connection having good conductivity between a copper foil and a conductive silver paste in a via hole of the resin multilayer substrate.

For example, FIG. 10 shows a prior art of the via hole conductive connection portion (part) (see Patent Document 3). The contents will be briefly described below.

FIG. 10 is formed of an insulating substrate 3, a via hole 5, a metal foil (copper foil) 6, metal particles (silver powder particles) 7, low melting point metal (Sn, In, etc.) 8, and this low melting point metal 8. It is a via hole conductive connection portion before firing, which is composed of the low melting point metal layer 9 formed. Although omitted in FIG. 10, the via hole 5 is a through hole formed in the thickness direction of the insulating substrate 3 and having a predetermined depth corresponding to the thickness of the insulating substrate 3, and is a via hole conductive connection in FIG. It is assumed that the lower part of the portion (although not shown) has a structure similar to that of the conceptual diagram of FIG. 10 substantially line-symmetrically with the conceptual diagram of FIG.

In the case of this conventional technique, the intervention of a low melting point metal 8 such as Sn or In is required to improve the reliability of the conductive connection between the copper of the copper foil 6 and the silver powder particles 7 in the conductive paste mixed with silver. To do. This means that the setting of the amount of Sn and In added is complicated, and an additive for suppressing the oxidation of these additives such as Sn and In is further required. In addition to narrowing the degree of freedom in prescribing when mixing the materials, it was also a factor in increasing the cost of materials. Furthermore, since various metals 8 having different ionization tendencies from silver 7 are contained in the wiring portion made of silver, it is possible that a local battery is formed.

Therefore, in the present invention, to explain using FIGS. 1 (a) and 1 (b), silver powder particles 7 are coated with a silver compound 10 such as silver oxide, and at a thermal decomposition temperature lower than the melting point of silver. The silver compound 10 is configured to be thermally decomposed. As a result, as shown in FIG. 1 (b), the molten silver 100 produced by thermal decomposition welds the silver powder particles 7 to each other, and as a result, the molten silver 100 produced by thermal decomposition (hereinafter simply referred to as "molten silver 100"). (Suppose that) serves as a low melting point metal such as Sn, In, etc. of the above-mentioned prior art (here, "welding" in the present application means that silver particles are bonded to each other by molten silver 100. It shall mean that.). In such a case, the molten silver 100 helps the molten silver 100 to bridge the silver powder particles 7 to each other until the conductive wiring part made of silver is completely formed by firing (see the SEM photograph image in FIG. 9), and the dissimilar metal is purposely formulated as in the prior art. And there is no need to mix. Furthermore, basically all conductive wiring portions are silver and do not form a local battery between dissimilar metals.

By further firing after the state shown in FIG. 1 (b), the silver particles start to melt, the cavity 11 is filled with the molten silver, and the conductive wiring portion made of silver is formed in the via hole. ..

It should be noted that FIGS. 1 and 10 are conceptual diagrams for explaining the present invention and the prior art in an easy-to-understand manner, and it is noted here that the size of each member and the particle size is different from the actual size.

<patcit num="1"><text>Japanese Patent Application Laid-Open No. 2002-324966</text></patcit><patcit num="2"><text>JP-A-2002-334618</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 11-214575</text></patcit>

<p> An object of the present invention is to lower the sintering temperature between silver powder particles, to realize an electrical connection with a silver conductive paste that does not require the intervention of low melting point metals such as Sn and In, and to realize an electrical connection between the conductive silver paste and copper. It is to improve the adhesiveness with the foil.</p>

<p> As a result of diligent studies, the present inventors have solved the problems of the prior art by using silver compound-coated silver powder containing silver compound-coated silver particles in which the surface of silver particles is coated with a silver compound as a material for a conductive paste. It was found that a conductive silver paste could be obtained and the above object could be achieved. &lt;Silver compound-coated silver powder&gt; Hereinafter, the silver compound-coated silver powder according to the present invention will be described. The present invention provides a silver compound-coated silver powder containing silver particles as a core material and silver compound coated on the surface of the silver particles.</p><p> The present invention also provides the silver compound-coated silver powder having the following powder characteristics. a.SSA (m3 / g): 0.1 ~ 5 b.D50 (μm): 0.1 ~ 10 c.Dmax (μm): 0.5 ~ 30 (Here, SSA is the specific surface area by the BET method, and D50 and Dmax are lasers, respectively. 50% volume cumulative particle size and maximum volume cumulative particle size by diffraction / scattering type particle size distribution measurement method. The same shall apply hereinafter.)</p><p> The reasons for the range of powder properties are as follows. a: For SSA (m3 / g), if it is less than 0.1, it will not be sintered at low temperature, and if it is more than 5, the oil absorption will be large at the time of paste preparation and it will be difficult to make a paste.</p><p> b: For D50 (μm), if it is less than 0.1, the amount of oil absorbed during paste preparation is large and it becomes difficult to make a paste, and if it is more than 10, it hinders the finening of the wiring of the electronic circuit that should be formed on the substrate. Get out.</p><p> Regarding c: Dmax (μm), if it is less than 0.5, it is practically difficult to realize it in manufacturing, and if it is more than 30, there is an adverse effect that the coating film of the conductive paste is not smoothed.</p><p> In the present invention, the silver compound is coated on the silver powder at a ratio of 5 wt% to 30 wt% with respect to 100 wt% of the silver compound-coated silver powder. Further, it is more preferable that the silver powder particles are coated with the silver compound at a ratio of 10 wt% to 20 wt% with respect to 100 wt% of the silver compound coated silver powder.</p><p> If the amount of the silver compound is less than 5 wt% with respect to 100 wt% of the silver compound coated silver powder, it is not possible to supply an amount sufficient to weld and bridge the silver particles, while if it is larger than 30 wt%, the silver compound Thermal decomposition is not performed smoothly, and as a result, silver particles are not well sintered, and it becomes difficult to form a conductive wiring portion.</p><p> According to the present invention, silver particles are welded to each other by silver decomposed from the silver compound at a silver compound decomposition temperature lower than the sintering temperature of the silver particles of the silver compound-coated silver powder as described with reference to FIG. The above-mentioned silver compound-coated silver powder characterized by the above can be provided.</p><p> Here, the melting point of silver is 961.93 ° C, but the temperature at which silver powder particles are sintered can be greatly lowered by pulverizing silver. However, as described above, excessive atomization causes problems such as easy aggregation of fine powder.</p><p> Therefore, in the present invention, for example, a silver compound having a decomposition temperature significantly lower than the melting point of silver (961.93 ° C), such as silver oxide (decomposition temperature (160 ° C)), is coated on the surface of silver particles. Let me. As a result, silver produced by thermal decomposition of silver oxide or the like covering the surface of the silver particles is welded to the adjacent silver particles at the time of firing for forming the wiring of the substrate for the electronic circuit.</p><p> As a result, the above-mentioned problem caused by the insufficient dispersibility of the mixed fine-grained silver powder in the prior art (see FIG. 2 of Patent Document 2) is caused by the silver compound coating which serves as a fine-grained silver powder. It will be resolved.</p><p> Further, as a result of the above, the above-mentioned problem of mixing low melting point metals such as Sn and In of the prior art (see FIG. 1 of Patent Document 3) into the conductive paste is solved, and the excellent conductivity of only silver metal is solved. Can be brought.</p><p> Further, as a result of the above, by applying the conductive paste according to the present invention to the via holes of the resin multilayer substrate, excellent conductivity is achieved through silver between the copper wiring portions formed on the vertically overlapping substrates. Can bring sex.</p><p> In the present invention, if the particle size of the silver particles is set so as to suppress the aggregation of the silver powder and to sinter the silver fine particles at a temperature as close as possible to the decomposition temperature of the silver compound, it is almost the same as the decomposition of the silver compound. At the same time, the sintering of silver particles can be started.</p><p> However, it goes without saying that the particle size of the silver particles may be set so that the silver particles are sintered at a temperature higher than the thermal decomposition temperature. That is, even when the particle size of the silver particles is large and the sintering temperature of the silver particles is significantly higher than the decomposition temperature of the silver compound, the silver thermally decomposed from the silver compound is first welded to the adjacent silver particles, and then. , It is considered that the sintering of silver particles is started.</p><p> FIG. 9 is an SEM photographic image of the process in which silver particles are sintered against each other during the firing of the silver oxide-coated silver powder of the present invention. In this way, it is considered that the silver particles are first sintered and formed in a network shape, and finally the black portion in the photograph is also filled with the silver particles to form a conductive wiring portion made of silver. It is considered that the trigger for starting sintering of the silver particles is molten silver that is thermally decomposed from the silver compound (for example, silver oxide) coated on the silver particles.</p><p> Further, the present invention provides the silver compound-coated silver powder, which is characterized in that the silver compound-coated silver powder is wetted with an organic solvent.</p><p> Further, the present invention provides the silver compound-coated silver powder, which is characterized in that the silver compound-coated silver powder is mixed with the conductive paste and becomes a material for the conductive silver paste.</p><p> &lt;Method for Producing Silver Powder Coated with Silver Compound&gt; Further, according to the present invention, Step a: A slurry step of adding silver powder to a silver nitrate aqueous solution, stirring the mixture, and making a slurry so that the silver nitrate aqueous solution and the silver powder are well blended. b: Includes a neutralization step in which the silver compound is coated on the silver powder particles by adding an equivalent amount of a basic solution such as a sodium hydroxide solution or an ammonium hydroxide solution to the slurry and performing a neutralization reaction. Provided is a method for producing a silver compound-coated silver powder containing silver compound-coated silver particles in which the surface of the silver powder particles is coated with the silver compound.</p><p> Further, the surface of the silver particles is coated with the silver compound, further comprising a washing step of washing the silver compound-coated silver powder produced in step b with water and a drying step of drying the silver compound-coated silver powder washed in this washing step. It is also possible to provide the above-mentioned method for producing a silver compound-coated silver powder containing the silver compound-coated silver particles. At this time, it is preferable that the water is pure water.</p><p> Further, in the washing step, the silver compound-coated silver powder is washed with a volatile organic solvent such as methanol, ethanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, isobutanol, isopropanol, hexane, toluene, terpineol, and butyl carbitol acetate. It is also possible to remove the contained water and obtain a dry silver compound-coated silver powder.</p><p> On the other hand, after washing the silver compound-coated silver powder with a volatile solution or drying the silver compound-coated silver powder, the silver compound-coated silver powder is wetted with a solvent similar to the volatile organic solvent listed above, and the silver compound-coated silver powder is coated as an organic solvent-wet product. Silver powder can also be provided.</p><p> The method for producing the silver compound-coated silver powder described above will be described in detail in the section on the best mode for carrying out the invention described later.</p>

<p> According to the silver compound-coated silver powder of the present invention, the sintering temperature of silver particles can be lowered by coating the surface of the silver particles with the silver compound, and the intervention of low melting point metals such as Sn and In is required. It is possible to achieve sintering that realizes electrical connection (wiring) with highly conductive silver, and further improve the adhesiveness between the conductive paste mixed with the silver powder and the copper foil.</p>

Hereinafter, the best mode for carrying out the present invention will be described.

FIG. 2 is a flow chart for explaining a manufacturing process for producing the silver compound-coated silver powder of the present invention. In the following description, the numerical values of each reagent, each solution, etc. are shown, but the numerical values are not limited to the following values in carrying out the present invention. Needless to say, the amount of each reagent, each solution, and other conditions can be appropriately changed by a person skilled in the art.

As shown in FIG. 2, the production step for producing the silver compound-coated silver powder of the present invention includes a slurrying step 10 and a neutralization step 20.

In the slurrying step 10, 10 g to 300 g of silver powder (average particle size 0.2 μm to 10 μm) is added to the silver nitrate aqueous solution prepared by dissolving 4 g to 250 g of silver nitrate in about 1000 cc of water (preferably pure water). Add, stir, slurry, and mix well with silver nitrate aqueous solution and silver powder.

In the neutralization step 20, at least the nitrate ion (NO) contained in the system is contained in the slurry in the slurrying step 10.₃By adding a basic solution such as sodium hydroxide solution or ammonium hydroxide solution in the equivalent amount required to neutralize-) and performing a neutralization reaction, silver oxide (silver oxide (-) is applied to the surface of the silver powder particles of the core material. Ag₂Considering O) as a typical example of a silver compound, silver oxide coats the surface of silver powder particles (see the following formula: when the above basic solution is sodium hydroxide). 2AgNO₃+ 2 NaOH Ag₂O + 2NaNO₃+ H₂O

The coating form may be such that the silver compound covers the entire surface of the silver powder particles or a part thereof. It is desirable to cover the whole.

FIG. 8 (a) shows the silver powder particles before the silver compound is coated, and FIG. 8 (b) is an SEM photographic image showing the silver powder particles after the silver compound is coated. As can be seen from FIG. 8 (b), not only those in which the silver compound is coated on the silver powder particles but also those in which the silver compound is fixed or adhered in the form of dots or islands are present. Therefore, the term "coating" as used in the present application includes the meaning of sticking or sticking.

Using a thermogravimetric / differential thermal analyzer (TG-DTA device (TG / DTA6300 manufactured by Seiko Instruments), the amount of silver compound covered by the silver compound coated silver powder of the present invention is 150 ml / min, and the temperature rise is 2 °. Under the condition of C / min, the measurement was carried out with a sample amount of 15 mg of silver compound-coated silver powder.

Here, an example of a method for measuring the amount of silver oxide is shown as a typical example of a silver compound using a TG-DTA apparatus. The amount of silver nitrate charged was set so that silver oxide was 10 wt%. In this device, if the weight loss up to 200 ° C is 0.8 wt%, O (oxygen) / Ag₂From O (silver oxide) = 6.89%, the coating amount of silver oxide can be determined to be 0.8 / 6.89 × 100 = 11.6 wt%. In this way, the amount of silver oxide coated on the silver particles (wt%) was determined. By the way, in order to confirm the reproducibility here, when the coating amount (wt%) was calculated under the same conditions with n = 10, it was within the range of 9.8% to 12.9%, and the silver oxide was 10 wt% almost as intended. It became the coating amount.

Further, in the silver oxide-coated silver powder of the present invention, in order to have a weight ratio of silver oxide of 5 wt% to 30 wt% with respect to 100 wt% of silver oxide-coated silver powder, the ratio of silver nitrate is 7.25 wt% to 43.8 wt%. It may be added as appropriate.

Since silver nitrate is indispensable for producing a silver compound, the other two types, that is, the coating amount of the silver compound of silver carbonate or silver hexanate on the silver particles of other silver carbonate or silver hexanate is also oxidized. The production conditions can be obtained in the same manner as the silver coating amount.

Now, let's return to Fig. 2 and resume the explanation. After the neutralization step 20, the cleaning step of cleaning the silver compound-coated silver powder of the present invention and the dehydration to obtain the silver compound-coated silver powder from which the water contained in the silver compound-coated silver powder is removed in the neutralization step 20 by volatilizing the volatile solvent. Further steps can be included.

That is, in the washing step, the silver compound-coated silver powder obtained in the neutralization step 20 of FIG. 1 is washed with 100 cc to 10000 cc of water (preferably pure water), and then in the drying step, 10 cc to 10000 cc of methanol and ethanol are washed. , Acetone, methyl ethyl ketone, methyl isobutyl ketone, isobutanol, isopropanol, hexane, toluene, terpineol, and butyl carbitol acetate are added to remove the water contained in the silver compound-coated silver powder together with the volatile solvent. The silver compound-coated silver powder is dried.

Hereinafter, the present invention will be specifically described based on examples.

&lt;Production process of silver oxide-coated silver powder including neutralization step with sodium hydroxide NaOH (1)&gt; FIG. 3 shows a flow chart of a production process of silver oxide-coated silver powder according to Example 1 of the present invention. In particular, Example 1 is a manufacturing process in which sodium hydroxide is used in the neutralization process.

Hereinafter, the first embodiment will be described with reference to FIG. (1) Add 285 g of silver powder to the silver nitrate aqueous solution obtained by adding 21.6 g of silver nitrate to 1000 cc of pure water, and stir to form a slurry. Let stand for 5 minutes so that the silver nitrate aqueous solution becomes familiar with the whole silver powder. (2) Next, an aqueous solution prepared by dissolving 9.6 g of sodium hydroxide in 29 cc of pure water is added to the above slurry to carry out a neutralization reaction treatment. As a result, the surface of the silver powder particles can be coated with silver oxide. (3) After that, when the silver oxide-coated silver powder is dried, 100 cc of pure water and 50 cc of methanol are added, and the mixture is washed and dehydrated with stirring to obtain a dried silver oxide-coated silver powder.

&lt;Ammonia hydroxide NH₄Production process of silver oxide-coated silver powder including neutralization step with OH&gt; FIG. 4 shows a flow chart of the production process of silver oxide-coated silver powder according to Example 2 of the present invention. In particular, Example 2 is a manufacturing process in which ammonium hydroxide is used in the neutralization process.

Hereinafter, the second embodiment will be described with reference to FIG. (1) Add 21.6 g of silver nitrate to 1000 cc of water (preferably pure water), add 285 g of silver powder to the obtained silver nitrate aqueous solution, and stir to form a slurry. Let stand for 5 minutes so that the silver nitrate aqueous solution becomes familiar with the whole silver powder. (2) Next, 18.1 ml of 25% NH was added to the above slurry.₃Add (wt%) ammonium hydroxide and let it undergo a neutralization reaction treatment. As a result, the surface of the silver powder particles can be coated with silver oxide. (3) After that, when drying the silver oxide-coated silver powder, 100 cc of pure water (preferably pure water) and 50 cc of methanol are added, and the mixture is washed and dehydrated with stirring to obtain a dried silver oxide-coated silver powder. ..

&lt;Production process of silver oxide-coated silver powder including neutralization step with sodium hydroxide NaOH (2)&gt; FIG. 5 shows a flow chart of the production process of silver oxide-coated silver powder according to Example 3 of the present invention. In particular, Example 3 is a modification of Example 1, wherein silver powder is put into ethylene glycol (1000 cc of pure water in Example 1) before the slurrying step to prepare an ethylene glycol solution of silver powder. Is different from Example 1. By doing so, the silver powder tends to be more easily dispersed in the ethylene glycol solution than in water (pure water).

Hereinafter, the third embodiment will be described with reference to FIG. (1) To the ethylene glycol solution of the silver powder obtained by adding 50 g of silver nitrate to 1500 g of ethylene glycol solution, add 16.67 g of silver powder together with 500 cc of water (preferably pure water), stir, and slurry. Make the silver nitrate aqueous solution compatible with the entire silver powder. (2) Next, an aqueous solution prepared by dissolving 3.92 g of sodium hydroxide in 500 cc of water (preferably pure water) is added to the above slurry to carry out a neutralization reaction treatment. As a result, the surface of the silver powder particles can be coated with silver oxide. (3) After that, when the silver oxide-coated silver powder is dried, 500 cc of pure water and 50 cc of methanol are added, and the mixture is washed and dehydrated with stirring to obtain a dried silver oxide-coated silver powder.

&lt;Sodium bicarbonate LVDS₃Manufacturing process of silver carbonate-coated silver powder including neutralization process by

Hereinafter, Example 6 will be described with reference to FIG. (1) Add 100 g of silver powder to the silver nitrate aqueous solution obtained by adding 17 g of silver nitrate to 1000 cc of pure water, and stir to form a slurry. Let stand for 5 minutes so that the silver nitrate aqueous solution becomes familiar with the whole silver powder. (2) Next, an aqueous solution prepared by dissolving 12 g of sodium hydrogen carbonate in 100 cc of pure water is added to the above slurry to carry out a neutralization reaction treatment. As a result, the surface of the silver powder particles can be coated with silver carbonate. (3) After that, when the silver carbonate-coated silver powder is dried, 100 cc of pure water and 50 cc of methanol are added, and the mixture is washed and dehydrated with stirring to obtain a dried silver carbonate-coated silver powder.

&lt;Sodium Hexate CH₃(CH₂)₄Production Step of Silver Caproate Coated Silver Powder Including Neutralization Step with COONa&gt; Hereinafter, Example 5 will be described with reference to FIG. 7.

(1) Add 100 g of silver powder to the silver nitrate aqueous solution obtained by adding 6 g of silver nitrate to 100 cc of pure water, and stir to form a slurry. Let stand for 5 minutes so that the silver nitrate aqueous solution becomes familiar with the whole silver powder. (2) Next, an aqueous solution prepared by dissolving 6 g of sodium hexanoate in 100 cc of pure water is added to the above slurry to carry out a neutralization reaction treatment. As a result, the surface of the silver powder particles can be coated with silver hexanoate. (3) After that, when drying the silver caproate-coated silver powder, 100 cc of pure water and 50 cc of methanol are added, and the mixture is washed and dehydrated with stirring to obtain a dried silver caproate-coated silver powder.

&lt;Evaluation of Examples 1 to 5 (silver compound-coated silver powder) and Comparative Examples 1 and 2&gt; Table 1 summarizes the evaluation results of Examples 1 to 5 and Comparative Examples 1 and 2. It is a thing.

Substantial evaluation items are the specific resistance (μΩ · m) and the adhesiveness to the copper foil corresponding to the treatment temperature × the treatment time of the conductive paste mixed with each silver compound-coated silver powder. In order to make these evaluations accurate and fair for each Example and Comparative Example, each measurement and evaluation was performed so that the SSA, D50, Dmax, and crystallite diameter were constant in each Example and each Comparative Example. It was. The "crystallite diameter" was measured by the WILSON method (crystallite diameter measurement method by X-ray diffraction) using a RINT2000 X-ray diffractometer manufactured by Rigaku Denki Co., Ltd.

&lt;Production of Conductive Paste&gt; The conductive paste of the present invention was prepared by kneading each substance at a composition ratio of 85 wt% of silver compound-coated silver powder, 0.75 wt% of ethyl cellulose, and 14.25 wt% of turbineol.

&lt;Measurement of Specific Resistance&gt; The specific resistance when the silver compound-coated silver powder of the present invention is used as a paste is 150 ° C. by routing a 1 mm wide circuit on a ceramic substrate using a conductive paste prepared with the above composition. It was measured using a circuit obtained by sintering at a temperature of ~ 180 ° C.

&lt;Measurement of Adhesion with Copper Foil&gt; A conductive paste similar to the above was prepared, and a copper foil with a size of 5 cm × 2 cm and a thickness of about 30 μm (the copper foil here is the conductive paste according to the present invention). The above conductive paste was applied to almost the entire surface of the copper foil using a coating machine (Yoshimitsu Seiki Model YOA) so that the coating thickness was 500 μm. did. Then, another copper foil of the same size as above was laminated on the coating film obtained by this coating. Further, these two copper foils sandwiched with the conductive paste were further sandwiched between two ceramic substrates having a size of 10 cm × 3 cm and a thickness of about 500 μm. Then, use a simple crimping / holding means such as a double clip for office work (here, the double clip type BCS-30 (silver) manufactured by ITOCHU Corporation is used) to pinch it from above the ceramic substrate, and the whole. Was crimped, sandwiched and fixed, and the whole was heated in a constant temperature bath under the condition of 150 ° C × 1 hour.

After heating, let it cool naturally, remove the double clip, and pinch the ends of the two overlapping copper foils sandwiched between the two ceramic substrates, one by one, with the fingers and thumbs of the right and left hands. A qualitative evaluation was made as to whether or not the two copper foils were in close contact with each other. If the copper foils are in close contact with each other, the adhesion with the copper foil is evaluated as "good", and if they are not in close contact with each other, the adhesion is evaluated as "poor adhesion" in the predetermined column of Table 1.

Regarding the adhesion, a quantitative test method such as JIS standard was adopted, and the difference between the adhesion of the copper foil according to Examples 1 to 5 and the adhesion of the copper foil according to Comparative Examples 1 and 2 was determined. It is desirable to measure quantitatively, but since the copper foils were not in close contact with each other in Comparative Example 1 and Comparative Example 2, further, in Examples 1 to 5, the qualitative adhesion by the above manual operation was performed. In all the tests, the copper foil itself had enough adhesion to be torn when it was forcibly peeled off. Therefore, it was difficult to make a meaningful quantitative measurement, so the adhesion test of the present application was limited to the above qualitative measurement (see Table 1).

&lt;Evaluation Results of Examples 1 to 5 and Comparative Examples 1 and 2&gt; (1) Evaluation of Specific Resistance Value: As can be seen from Table 1, the silver compound-coated silver powder conductive paste of the present invention was used. As the specific resistance value of the produced wiring portion, a value having no practical problem was obtained for Examples 1 to 5 and Comparative Example 2. However, the resistivity value of Comparative Example 1 could not be measured.

(2) Evaluation of Adhesion between Copper Foil and Silver: As can be seen from Table 1, the silver compound-coated silver powder conductive paste obtained good adhesion to the copper foil at 150 ° C. × 1 hour (Example). 1 to 5). However, the silver compound uncoated silver powder paste has good adhesion to the copper foil under the conditions of 150 ° C × 1 hour and further increased temperature of 180 ° C × 1 hour (Comparative Example 1 and Comparative Example 2). I couldn't get it. From the above, it has been found that the silver compound coated on the surface of the silver powder particles according to the present invention has the effect of lowering the sintering temperature of the silver powder particles and improving the adhesiveness with the copper foil.<tables num="1"><img file="JP2005298933A_D0001.tif" /></tables>

The silver compound-coated silver powder of the present invention and the production method thereof can be applied as a conductive material for a conductive paste of an electronic circuit wiring portion such as a connection portion of a via hole for a multilayer resin substrate.

<figref num="1">It is a conceptual diagram which shows the conductive part of the via hole part by the conductive paste (silver powder) containing silver compound coated silver powder particles of this invention ((a) conceptual diagram in the via hole before firing; (b) in the middle of a firing process. Conceptual diagram in the via hole after the firing temperature reaches a temperature higher than the thermal decomposition temperature of the silver compound and the silver is decomposed).</figref><figref num="2">It is a flow figure for demonstrating the best embodiment which concerns on this invention.</figref><figref num="3">It is a flow figure for demonstrating Example 1 which concerns on this invention.</figref><figref num="4">It is a flow figure for demonstrating Example 2 which concerns on this invention.</figref><figref num="5">It is a flow figure for demonstrating Example 3 which concerns on this invention.</figref><figref num="6">It is a flow chart for demonstrating Example 4 which concerns on this invention.</figref><figref num="7">It is a flow figure for demonstrating Example 5 which concerns on this invention.</figref><figref num="8">(a) An SEM photographic image showing silver powder particles not coated with a silver compound is shown. (b) An SEM photographic image showing silver powder particles coated with a silver compound is shown.</figref><figref num="9">An SEM photographic image showing a state in which the silver powder particles are welded to each other in the process of sintering the silver compound-coated silver powder is shown.</figref><figref num="10">It is a conceptual diagram which shows the conductive part of the via hole part by the mixed powder of the silver powder particle and the low melting point metal of the prior art.</figref>