JP6380220B2 - Copper powder for paste - Google Patents

Description

  The present invention relates to a copper powder for paste, and more particularly to a copper powder for forming a conductive copper paste used for a fired electrode used for, for example, an internal electrode or an external electrode of a chip-type electronic component.

  In general, when forming an electrode such as an internal electrode or an external electrode of an electronic component, there is a demand for forming it at low cost by using a copper paste instead of a silver paste or a nickel paste. The specific resistance of nickel is higher than that of silver and copper, and the price of silver is higher than that of nickel and copper. Therefore, it is desirable to use copper which has good electrical characteristics and is inexpensive.

  A technique for forming an internal electrode and an external electrode using copper as an electrode has existed for a long time as described in, for example, Patent Document 1 and Patent Document 2, but since copper is easily oxidized, silver using silver powder is used. Nickel pastes using pastes or nickel powders have been generally used.

  Therefore, in order to satisfy the above-mentioned requirements, when using oxidizable copper powder, an organic substance such as an antioxidant or a reducing agent must be added, and the oxidation of the copper particle surface is likely to proceed. It is necessary to suppress copper oxidation by increasing the amount of the organic substance added or by lowering the firing temperature.

  However, when an organic substance is added, a residue of the organic substance remains as carbon between the particles, and sintering does not proceed efficiently, resulting in a new problem that the specific resistance increases. For this reason, it is conceivable to reduce the addition amount by using an organic substance having a high antioxidant or reducing effect. However, it is difficult to develop an organic substance with a small environmental load at present, and there is no effective solution.

JP 59-184511 A JP 61-2425 A

Toyota Central R & D Review, p. 63, Vol. 31 No. 4 (1996.12)

  This invention is made | formed in view of the above situations, and it aims at providing the copper powder for pastes for a firing electrode which suppresses oxidation of copper and is easy to be reduced and can be fired even at a low temperature. .

  The inventors of the present invention have made extensive studies in order to solve the above-described problems. As a result, it was found that the copper powder containing copper as a main component contains nickel at a predetermined ratio, so that oxidation can be suppressed and excellent reduction characteristics are exhibited, and the present invention has been completed. It was. That is, the present invention provides the following.

  (1) 1st invention of this invention has copper as a main component, nickel is contained 0.01 mass% or more and 0.8 mass% or less, and content of other impurity elements is less than 0.01 mass%. It is a copper powder for paste characterized by being.

  (2) According to a second aspect of the present invention, in the first aspect, three electrodes of a copper alloy comprising Pt as a counter electrode in electrochemical measurement, silver / silver chloride as a reference electrode, and the copper powder as a working electrode are provided. In the potential change curve by chronopotentiometry when each electrode is immersed in a sodium borate buffer solution that is an electrolytic solution and a voltage is applied, the reduction time of the oxide film in the copper alloy is not long. The copper powder for paste is characterized by being shorter than the reduction time of the oxide film when oxygen copper is used as the working electrode.

  The copper powder for paste according to the present invention contains nickel in a proportion of 0.01% by mass or more and 0.8% by mass or less, and the content of other impurity elements is less than 0.01% by mass. It has a superior feature that it is cheaper, has a thinner oxide film thickness than oxygen-free copper, is less likely to be oxidized, and is easier to reduce. In addition, since it is easily reduced, oxygen is easily released, and the organic matter in the paste is easily decomposed and removed.

It is a figure which shows the electric potential change curve of the oxide film of a copper alloy by chronopotentiometry. It is a figure which shows an example which calculated | required the reduction | restoration time of the oxide film from the electric potential change curve in chronopotentiometry.

  Hereinafter, a specific embodiment of the copper powder for paste according to the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, A various change is possible in the range which does not change the summary of this invention.

<< 1. Copper powder for paste >>
The copper powder for paste according to the present embodiment is a copper alloy composed mainly of copper and contains nickel as an additive component at a predetermined ratio. Specifically, the copper powder for copper paste contains copper as a main component, nickel is contained in a proportion of 0.01% by mass or more and 0.8% by mass or less, and the content of other impurity elements is 0.1% by mass. It is characterized by being less than%. In addition, a main component means that the content rate is 51 mass% or more.

In general, copper is oxidized in the air to form a Cu ₂ O or CuO copper oxide layer (hereinafter also referred to as “oxide film”) on the surface. If the CuO layer is not formed and the thickness of the Cu ₂ O layer is large, the reduction is difficult. On the other hand, if the thickness is thin, the reduction is easy.

In the copper powder for paste according to the present embodiment, as described above, nickel is contained at a predetermined ratio in copper as a main component, and the alloy contains almost no content of other impurity elements. As the oxide layer, Cu ₂ O is mainly used, and the thickness thereof is reduced, so that it can be easily reduced.

  Specifically, in the copper powder for paste, as described above, the surface oxidation of the copper powder itself is suppressed by containing nickel in a proportion in the range of 0.01% by mass to 0.8% by mass. Therefore, the amount of the antioxidant and the reducing agent to be added to the paste can be reduced, and sintering can proceed without lowering the firing temperature, so that a good copper powder paste is obtained.

  Regarding the nickel content, if the nickel content in the copper powder for paste is less than 0.01% by mass, the oxide film becomes thick and the copper powder is difficult to reduce. In addition, the oxide film thickness is comparable to oxygen-free copper, and the amount of antioxidant and reducing agent in the paste cannot be effectively reduced, and it is difficult to reduce, so that sintering does not proceed easily.

  On the other hand, even if the nickel content exceeds 0.8% by mass, the oxide film thickness becomes thick and the copper powder is difficult to reduce, and the electrical resistivity increases as an alloy. In addition, the oxide film thickness is equal to or higher than that of oxygen-free copper, and the amount of antioxidant and reducing agent in the paste cannot be effectively reduced. Since the electrical specific resistance of the alloy itself also increases, it becomes a high resistance electrode film.

  Moreover, the copper powder for paste which concerns on this Embodiment has content of impurity elements other than nickel less than 0.01 mass%. Thus, when the content of the impurity element is less than 0.01% by mass, the surface oxidation due to the addition of the predetermined amount of nickel described above can effectively exert a suppressing action, and the sintering proceeds. It becomes easy and becomes a good copper powder paste.

  Here, FIG. 1 shows an example of a potential change curve by chronopotentiometry capable of estimating the ease of reduction of the oxide formed on the surface and the thickness of the oxide layer. This method is an application of the electrochemical reduction potential measurement described in Non-Patent Document 1. Specifically, as an accelerated oxidation test, a 99.99% pure copper plate was heated in the atmosphere at 150 ° C. for 30 minutes, and a boric acid-sodium borate buffer solution (pH 9.3) was used as an electrolytic solution. Is a result of chronopotentiometry in which a change with time in potential between a copper plate and a reference electrode (silver / silver chloride electrode) when a constant current of 50 μA is applied in the reduction direction is measured.

  As shown in FIG. 1, a plateau region having a potential of −0.7 V is observed when a constant current is applied in the reduction direction. This plateau region indicates the time required for the oxide that can be reduced to be present on the sample surface and reduced.

  The time during which the oxide film is reduced can be obtained from the intersection of the slope at which the potential decreases through the plateau region and the slope at which the potential is constant after the reduction is completed. FIG. 2 shows an example in which chronopotentiometry of oxygen-free copper is measured to determine the time during which the oxide film is reduced. The time corresponding to the intersection P in FIG. 2 is the time during which the oxide film is reduced. Thus, by preparing alloy samples in which various elements are added to copper having a purity of 99.99% and comparing the reduction time of the oxide film by chronopotentiometry, the thickness of the oxide layer and the reduction easily It is possible to infer.

  The example shown in FIG. 1 is oxygen-free copper (Cu), a copper alloy containing nickel at a ratio of 0.11% by mass (Cu-0.11Ni), and a copper alloy containing nickel at a ratio of 0.46% by mass. It is a measurement result of the chronopotentiometry of three samples of (Cu-0.11Ni). As shown in the results of FIG. 1, the main component copper contains nickel in a proportion of 0.01% by mass or more and 0.8% by mass or less, so that the reduction time of the oxide film by chronopotentiometry is long. It can be seen that is shorter than oxygen-free copper and becomes an oxide film that is easier to reduce than an oxide film generated by oxygen-free copper.

  Thus, in the copper powder for paste according to the present embodiment, since the surface oxidation of the copper powder itself is suppressed, the amount of antioxidant and reducing agent to be added to the paste can be reduced, and Since it is easy to be reduced without lowering the firing temperature, sintering is likely to proceed, and a good copper powder paste can be obtained from which a low resistance electrode can be obtained.

≪2. Manufacturing method of copper powder for paste >>
It does not specifically limit as a manufacturing method of the copper powder for pastes concerning this Embodiment, It can manufacture by a well-known method.

  Specifically, for example, after a copper alloy having a predetermined composition as described above is melted in a vacuum or an inert atmosphere, the molten metal is poured into a non-oxidizing atmosphere from a small-diameter nozzle, and the molten metal stream is flowed at high speed. It can be produced by a gas atomization method in which it is pulverized and solidified.

  EXAMPLES Hereinafter, although the Example of this invention is shown with a comparative example and this invention is demonstrated further in detail, this invention is not limited to a following example at all.

<< Examples and Comparative Examples >>
<Manufacture of copper alloy>
In Examples and Comparative Examples, a copper alloy molten metal was prepared so as to have a component composition as shown in Table 1 below, and a copper alloy sample was manufactured. In addition, as shown in Table 1, each element contains various elements as predetermined components.

  Specifically, using an arc melting furnace manufactured by Nisshin Giken Co., Ltd., the inside of the chamber was evacuated to 0.005 Pa or less, then argon gas was introduced to 40000 Pa, and the component composition shown in Table 1 below was set. The molten copper alloy was poured into a copper hearth mold to produce a button-shaped ingot having a diameter of about 30 mm and a thickness of about 6 mm. In order to uniformly disperse the additive elements, a total of five melt castings were performed by reversing the sample after melting and casting to obtain an ingot. And the produced ingot was cut out in the strip shape of width 5mm, thickness 0.3mm, and length 15mm, and it was set as the copper alloy board sample, and used for evaluation shown below.

<Evaluation (redox evaluation) and evaluation results>
Evaluation of the oxide film in the sample was performed by chronopotentiometry using a sodium borate solution as a buffer solution. In the measurement, a 5 mm × 5 mm surface of the sample was exposed and immersed in a buffer solution. Further, constant current application and measurement of potential change with time were performed using a potentiogalvanostat Versstat 3 manufactured by Princeton Applied Research.

  Further, in order to accelerate the oxidation of the sample, an oxidation treatment was performed in the atmosphere at 150 ° C. for 30 minutes. The case where the reduction time was shorter than the oxygen-free copper comparative sample was evaluated as “good”, and the case where the reduction time was equal to or longer than the oxygen-free copper comparative sample was evaluated as “bad”.

  Table 1 below shows the evaluation results. In addition, as above-mentioned in Table 1, the component composition of the copper alloy in Examples 1-5 and Comparative Examples 1-14 is also shown collectively. Metal prices are 700 yen / kg for copper, 65 yen / g for silver, 1750 yen / kg for nickel, 3,000 yen / g for palladium, 200 yen / kg for aluminum, and 2,300 yen / kg for tin. The alloy price per 1 kg calculated by rounding up to 1 yen unit was calculated with zinc as 250 yen / kg and magnesium as 300 yen / kg.

  As shown in the results of Table 1, for the copper alloys produced in Examples 1, 2, 3, 4, and 5, the reduction time of the oxide film is shorter than the reduction time of the oxygen-free copper oxide film. The evaluation result showed good. That is, it showed the property that it was difficult to oxidize and was easy to reduce. The alloy price was 708 yen / kg or less.

  On the other hand, in the comparative example, the reduction time of the oxide film having the alloy composition of comparative examples 2 to 14 is longer than that of the reference comparative example 1 (oxygen-free copper) and is shown to be less likely to be reduced than oxygen-free copper. It was.

  The copper powder for copper paste according to the present embodiment contains copper as a main component and contains nickel in an amount of 0.01% by mass to 0.8% by mass. According to such a copper powder, an oxide film generated under the same conditions is reduced more easily than an oxygen-free copper oxide film, so that the amount of addition of an antioxidant and a reducing agent is effective when it is made into a paste. Can be reduced. Therefore, residual carbon between the fired copper particles can be reduced, and an oxide film on the surface of the copper powder is easily removed, so that the sinterability is improved and an electrode having a low electrical resistance after firing can be formed.

  Moreover, since it is easy to reduce | restore at the time of baking, the organic substance in a paste is easy to decompose and remove, and the organic substance residue between copper particles can be reduced. In addition, the metal price is cheaper than silver and nickel, and the utility value in the electronic component industry is extremely large.

Claims (2)

Copper as a main component, nickel is contained 0.8 wt% or less than 0.01 wt%, pastes total copper content and nickel content, characterized in Rukoto a 99.99 wt% greater than the alloy Copper powder.   Three electrodes of Pt as the counter electrode in electrochemical measurement, silver / silver chloride as the reference electrode, and a copper alloy composed of the copper powder as the working electrode are immersed in a sodium borate buffer solution that is an electrolyte. In the potential change curve by chronopotentiometry when a voltage is applied, the reduction time of the oxide film in the copper alloy is shorter than the reduction time of the oxide film when oxygen-free copper is used as the working electrode. The copper powder for paste according to claim 1, wherein:

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