JP2010037653A - Copper powder for conductive paste, and conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide copper powder which does not impair both of oxidation resistance and electric conductivity in spite of fineness in grain size, and further, copper powder for conductive paste which has less variation in shape and grain size and low concentration of contained oxygen. <P>SOLUTION: The copper powder for conductive paste comprises 0.1 to 10 atm% In inside the particles. Preferably, the copper powder comprises 0.01 to 0.3 atm% P (phosphorous) inside the particles. Preferably, the copper powder comprises 0.1 to 10 atm% Ag (silver) inside the particles. It is also preferable that the copper powder is produced by an atomizing process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

    The present invention relates to copper powder for conductive paste and conductive paste using the same, and in particular, conductivity for various electrical contact members such as a conductor circuit formation by a screen printing additive method and an external electrode of a multilayer ceramic capacitor. The present invention relates to a copper powder suitable for a conductive material of a paste and a conductive paste using the copper powder.

    Copper powder has been widely used as a conductive material for conductive pastes for various electrical contact members such as conductor circuit formation by screen printing additive method and external electrodes of multilayer ceramic capacitors because of its ease of handling. Has been.

    The said electrically conductive paste can be obtained by mix | blending and knead | mixing various additives, such as resin, such as an epoxy resin, and its hardening | curing agent, for example with copper powder. The copper powder used at this time is a wet reduction method in which a copper salt-containing solution or the like is precipitated by a reducing agent, a vapor phase reduction method in which the copper salt is heated and vaporized and reduced in the gas phase, or a molten copper base. It can be manufactured by an atomizing method or the like in which gold is rapidly cooled with a refrigerant such as an inert gas or water to be powdered.

Among the methods for producing copper powder as described above, the atomizing method can reduce the residual concentration of impurities in the obtained copper powder as compared with a wet reduction method that is generally widely used. There is an advantage that pores extending from the surface to the inside of the copper powder particles can be reduced.
For this reason, when the copper powder manufactured by the atomizing method is used for the conductive material of the conductive paste, the amount of gas generated during paste curing can be reduced and the progress of oxidation can be significantly suppressed.

    However, copper powder is suitable for the conductive material of the conductive paste because of its high conductivity, but as the particle size becomes finer, it becomes inferior in oxidation resistance, and in order to improve it, copper particles A metal powder having a surface coated with indium (Patent Document 1) has been proposed.

Japanese Patent Laid-Open No. 2003-321701

    In recent years, when forming a circuit using a conductive paste or the like, further miniaturization is required, and inevitably, the particle size of the conductive powder used for the conductive paste is also required to be miniaturized. At the same time, in order to ensure the stability and reliability of the paste characteristics, the shape and particle size must be small and the conductivity should not be impaired. And if only oxidation resistance is grasped | ascertained, according to a technique like patent document 1, for example, a corresponding improvement is possible.

However, since the technique of Patent Document 1 depends on the coating technique, the presence and exposure of indium that impairs the conductivity other than copper naturally inevitably sacrifices the conductivity, and the particle surface is reliably coated. This requires a large amount of expensive indium and is not economical. Also, if the particle surface is not coated with a sufficient amount of indium, but rather only present at the adhesion level, the oxidation resistance does not improve.
Therefore, the present invention provides a copper powder for conductive paste that has a fine particle size but does not impair the balance between oxidation resistance and conductivity, and further has a small variation in shape and particle size and a low oxygen concentration. The purpose is to provide.

    As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved when a specific amount of indium is contained inside the copper powder particles, and the present invention has been completed.

That is, the copper powder for conductive paste of the present invention is characterized by containing 0.1 atm% to 10 atm% indium inside the particles.
Further, phosphorus (P) may be contained in the particles in an amount of 0.01 atm% to 0.3 atm%, and the In / P (atm ratio) is preferably 4 to 200.
Moreover, you may contain 0.1atm% -10atm% of Ag inside particle | grains.
And it is preferable that it was manufactured by the atomizing method.
Further, it is preferable that the difference in weight change rate at 250 ° C. and 600 ℃ (Tg (%)) / specific surface area (SSA) is ^{1% / m 2 / cm 3} ~30% / m 2 / cm 3.
Another aspect of the present invention resides in a conductive paste containing the copper powder for conductive paste.

    The copper powder for conductive paste of the present invention is excellent in oxidation resistance while being fine in particle size, and has a good balance of conductivity. Furthermore, since the variation in shape and particle size is small and the oxygen content is low, the conductive paste is used for conductive circuit formation by screen printing additive method and for various electrical contact members such as external electrodes of multilayer ceramic capacitors. It can be applied very well to materials and the like.

    Although embodiment of the copper powder for electrically conductive paste by this invention is described, this invention is not limited to the following embodiment.

    The copper powder for conductive paste according to the present invention is characterized by containing 0.1 atm% to 10 atm% of indium inside the particles.

    What is important here is not simply containing In but a specific amount inside the particles.

    That is, as in Patent Document 1, a metal powder in which indium is coated on or attached to the surface of copper powder particles is effective in improving oxidation resistance, but without impairing the conductivity required by the present invention. It is not a fine copper powder with excellent oxidation resistance.

    In short, In contained in the copper powder for conductive paste according to the present invention is distributed in the metal phase inside the particles. Particularly preferred is the case where these components are present inside the particle but are not exposed to the particle surface and are concentrated near the particle surface, in addition to improving oxidation resistance and maintaining excellent conductivity. Can do.

    The In content is 0.1 atm% to 10 atm%, preferably 0.5 atm% to 8 atm%, and more preferably 2 atm% to 6 atm%. If this content is less than 0.1 atm%, the effect sought by the present invention cannot be expected. On the other hand, if it exceeds 10 atm%, not only the conductivity is impaired, but also an effect commensurate with the addition cannot be obtained.

    The copper powder for conductive paste according to the present invention preferably contains P (phosphorus) inside the particles in addition to In, preferably 0.01 atm% to 0.3 atm%, more preferably 0.02 atm% to 0.1 atm%. It is good to contain. If In and P coexist in the copper powder and are in such a specific amount range, there is further variation in shape and particle size while having fine particle size, oxidation resistance and not impairing conductivity. Small and low oxygen content features are improved.

    The copper powder for conductive paste according to the present invention preferably has an In / P (atm ratio) of 4 to 200, more preferably 10 to 100. When the ratio of In / P is within such a range, it is easy to balance the characteristics of fine particle size, oxidation resistance, high conductivity, small variation in shape and particle size, and low oxygen content.

    Further, the copper powder for conductive paste according to the present invention preferably contains 0.1 to 10 atm%, more preferably 0.5 to 5 atm%, most preferably 0.5 to 3 atm% of Ag inside the particle. Good. If it is the range of such a specific amount, electroconductivity can be improved more and the cost can also be suppressed, maintaining the oxidation resistance of the copper powder for electrically conductive pastes.

    And in the case of including any of In, Ag, and P, the copper powder for conductive paste having a more excellent conductivity, in addition to having a fine particle size, small variations in shape and particle size, and excellent oxidation resistance. Become.

    Further, the copper powder for conductive paste according to the present invention can be expected to have a certain effect even if it is obtained by a wet reduction method, but the particle shape is uniform and less gas is generated when used as a conductive paste. In view of the advantages such as the above, it is preferable to be manufactured by the atomizing method.

    As the atomization method, there are a gas atomization method and a water atomization method. The gas atomization method may be selected if the particle shape is to be uniformed, and the water atomization method may be selected if the particles are miniaturized. Moreover, it is preferable that it is what was manufactured by the high pressure atomizing method among the atomizing methods. The copper powder obtained by such a high-pressure atomizing method is preferable because the particles are more uniform or finer. Incidentally, the high pressure atomizing method is a method of atomizing with a water pressure of about 50 MPa to 150 MPa in the water atomizing method, and a method of atomizing with a gas pressure of about 1.5 MPa to 3 MPa in the gas atomizing method.

In addition, the copper powder for conductive paste according to the present invention has a difference in weight change rate (Tg (%)) / specific surface area (SSA) at 250 ° C. and 600 ° C. by a thermogravimetric / differential thermal analyzer (hereinafter referred to as ΔS). (Referred to as (TG / SSA)) is preferably 1% / m ² / cm ³ to 30% / m ² / cm ³ , more preferably 1% / m ² / cm ^{3 to} 25% / m ² / cm ³ Preferably there is.

    According to this characteristic value Δ (TG / SSA), the oxidation resistance of the copper powder can be observed. The temperature range of 250 ° C. to 600 ° C. is a heating temperature range when using a main conductive paste, such as a conductive paste for firing an external electrode of a ceramic capacitor, and has oxidation resistance in this region. Very important. When Δ (TG / SSA) is in the above preferred range, the oxidation resistance is sufficiently exhibited, and it is suitable for ensuring high conductivity.

    In addition, the copper powder for conductive paste according to the present invention further includes Ni, Al, Si, Ti, Fe, Co, Cr, Mg, Mn, Mo, W, Ta, Zr, Nb, B, Ge, Sn, Zn By adding at least one elemental component of Bi, etc., it is possible to improve various properties required for the conductive paste, such as lowering the melting point and improving the sinterability. . The amount of these elements added to copper is appropriately set based on the conductive characteristics and other various characteristics depending on the type of element to be added, but is usually about 0.001% by mass to 2% by mass.

    The copper powder for conductive paste according to the present invention preferably has a granular shape, and more preferably has a spherical shape. Here, granular means a shape in which the aspect ratio (value obtained by dividing the average major axis by the average minor axis) is about 1 to 1.25, and the aspect ratio is about 1 to 1.1. Is called spherical. A state where the shapes are not aligned is called an indefinite shape. Such a granular copper powder is very preferable because it causes less mutual entanglement and improves dispersibility in the paste when used as a conductive material for a conductive paste.

Further, the copper powder for conductive paste according to the present invention can be measured by, for example, a laser diffraction scattering type particle size distribution measuring device or the like, and a coefficient of variation (SD) obtained from a volume converted 50% cumulative diameter D ₅₀ and a standard deviation value SD. / D ₅₀ ) is 0.2 to 0.6, there is little variation in the particle size distribution, and the dispersibility of the conductive paste in the paste when used as a conductive material can be improved. Is preferable.

    Moreover, the copper powder for conductive paste according to the present invention is suitable for a conductive material of a fine conductive paste for forming a conductive circuit by setting the number average particle size of primary particles to 0.5 μm to 50 μm. It will be a thing.

    Moreover, the copper powder for electrically conductive pastes which concerns on this invention can ensure electrical conductivity reliably by making content oxygen concentration into 30 ppm-2500 ppm, and will become a suitable thing for the electrically conductive material of an electrically conductive paste, etc. .

    Next, the preferable specific manufacturing method of the copper powder for electrically conductive paste which concerns on this invention is demonstrated.

    The copper powder for conductive paste of the present invention can be produced by adding a predetermined amount of In component in the form of a mother alloy or a compound to molten copper and then pulverizing it by a predetermined atomization method.

    According to the said manufacturing method, the copper powder which does not impair both oxidation resistance and electroconductivity balance with fine particle size, and also the copper powder which is small in the variation of a shape and a particle size and is a low content oxygen concentration can be manufactured.

    The reason for this is not clear, but it is presumed that In added to molten copper or copper alloy captures oxygen in the produced copper powder particles and suppresses oxidation to the extent that conductivity is not impaired.

    Furthermore, when the P component is added in addition to the In component, the surface tension of the molten metal during atomization can be reduced, and it is presumed that the particle shape can be leveled and the deoxygenation in the molten metal can be effectively performed. As with the In component, the P component may be added in a predetermined amount in the form of a mother alloy or a compound to the molten copper.

    Moreover, by containing an Ag component in addition to the In component, the conductivity can be further improved while ensuring the oxidation resistance of the copper powder.

    Moreover, in the said manufacturing method, it is preferable to employ | adopt a high pressure atomizing method from the reason demonstrated previously. However, since the content yield of additive components other than copper may be low in the water atomization method as compared with the gas atomization method, the amount in the case of In is 1 to 10 times the net amount in the target copper powder. In the case of P, it is necessary to add 1 to 100 times the amount.

    Moreover, in the said manufacturing method, after atomizing, you may reduce | restore. By this reduction treatment, it is possible to further reduce the oxygen concentration on the surface of the copper powder that is easily oxidized. Here, the reduction treatment is preferably gas reduction from the viewpoint of workability. The reducing gas is not particularly limited, and examples thereof include hydrogen gas, ammonia gas, and butane gas.

    Furthermore, the reduction treatment is preferably performed at a temperature of 150 ° C. to 300 ° C., and more preferably performed at a temperature of 170 ° C. to 210 ° C. This is because if the temperature is less than 150 ° C., the reduction rate becomes slow, and the treatment effect cannot be sufficiently exhibited, and if the temperature exceeds 300 ° C., it causes aggregation and sintering of copper powder. This is because when the temperature is 170 ° C. to 210 ° C., aggregation and sintering of copper powder can be reliably suppressed while efficiently reducing the oxygen concentration.

Moreover, in the said manufacturing method, it is preferable to classify after pulverizing. This classification can be easily carried out by separating coarse powder and fine powder from the obtained copper powder using an appropriate classifier so that the target particle size becomes the center. Here, it is desirable to classify so that the coefficient of variation (SD / D ₅₀ ) described above is 0.2 to 0.6.

    Conductivity containing the copper powder for the conductive paste of the present invention produced by mixing and kneading various additives such as a resin such as an epoxy resin and its curing agent with the copper powder as described above, for example. Since the copper powder is fine in particle size, the paste has a good balance between oxidation resistance and electrical conductivity, has little variation in shape, and has a low oxygen concentration. The present invention can be applied extremely well to conductive materials of conductive pastes for various electrical contact members such as external electrodes of ceramic capacitors.

    In addition, the copper powder for conductive paste of the present invention is used for internal electrodes of multilayer ceramic capacitors, chip parts such as inductors and resistors, single plate capacitor electrodes, tantalum capacitor electrodes, resin multilayer substrates, ceramic (LTCC) multilayer substrates, flexible prints. Substrate (FPC), antenna switch module, module such as PA module and high frequency active filter, PDP front and back plate, electromagnetic shielding film for PDP color filter, crystal type solar cell surface electrode and back extraction electrode, conductive adhesive, It can also be used for EMI shield, RF-ID, membrane switch such as PC keyboard, anisotropic conductive film (ACF / ACP) and the like.

Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples.
Example 1
After filling the chamber and raw material melting chamber of the gas atomizer (Nisshin Giken Co., Ltd., NEVA-GP2 type) with nitrogen gas, the raw material was heated and melted in a carbon crucible in the melting chamber to obtain a molten material (electro-copper) 7.20 g of metal indium was added to the molten metal in which the molten metal was dissolved to obtain 800 g of molten metal, which was sufficiently stirred and mixed. Thereafter, the molten metal was sprayed from a nozzle having a diameter of φ1.5 mm at 1250 ° C. and 3.0 MPa to obtain copper powder containing indium inside the particles. Thereafter, it was sieved with a 53 μm test sieve, and the product under the sieve was made the final copper powder. Table 2 shows the characteristics of the obtained copper powder.
(Examples 2 to 4)
A copper powder was obtained by performing the same operation as in Example 1 except that the amount of metal indium added was changed as shown in Table 1.
(Examples 5 to 10)
In addition to metallic indium, a copper powder was obtained in the same manner as in Example 1 except that a copper-phosphorus mother alloy (phosphorus grade 15% by mass) was also added as shown in Table 1.
(Examples 11 and 12)
In addition to metallic indium and copper-phosphorus mother alloy, copper powder was obtained by performing the same operation as in Example 1 except that electrical silver was added as shown in Table 1.
(Comparative Examples 1-4)
A copper powder was obtained in the same manner as in Example 1 except that the addition amount of metal indium and / or copper-phosphorus alloy was added as shown in Table 1.

    With respect to the copper powder obtained in the examples and comparative examples, various properties were evaluated by the following methods. The results are shown in Tables 2-6.

(1) Total content of indium and phosphorus Samples were dissolved with acid and analyzed by ICP.
(2) Oxygen concentration The oxygen concentration was analyzed by an oxygen / nitrogen analyzer (“EMGA-520 (model number)” manufactured by Horiba, Ltd.). The results are shown in Table 2. In addition, in order to evaluate the oxidation resistance deterioration with time, a sample was heated to 200 ° C. at 10 ° C./min with an Air flow rate of 8 L / min using SK-8000 manufactured by Sanyo Seiko, and then held for 1 hour. The oxygen concentration of was also measured. The results are shown in Table 5.
(3) Δ (TG / SSA)
Tg (%) at 40 ° C. to 600 ° C. Differential thermogravimetric simultaneous measurement apparatus (TG / DTA) (SII, TG / DTA6300 high temperature type) (heating rate: 10 ° C./min, Air flow rate: 200 mL / min ) And the difference in weight change rate at 250 ° C. to 600 ° C. was determined. On the other hand, the specific surface area was obtained from the particle size distribution measured with a particle size measuring device (manufactured by Nikkiso Co., Ltd., Microtrac MT-3000 type) and arithmetically obtained from both numerical values. Table 3 shows TG / SSA of Examples 1 to 11 and Comparative Examples 1 to 4 corresponding to the temperature. Table 4 shows the results of dividing TG / SSA of Examples 1 to 11 and Comparative Examples 2 to 4 by TG / SSA of the pure copper powder of Comparative Example 1 (described as [TG / SSA] _Cu in the table).
(4) Particle shape It observed with the scanning electron microscope.
(5) D ₅₀ , SD, SD / D ₅₀
A sample (0.2 g) is placed in pure water (100 ml) and irradiated with ultrasonic waves (for 3 minutes) to disperse, and then a particle size distribution analyzer ("Microtrack (trade name) FRA (model number) manufactured by Nikkiso Co., Ltd." by) "), it was determined in terms of volume of 50% cumulative diameter _{D 50} and the standard deviation value SD and coefficient of variation (SD _{/ D 50),} respectively.

    As shown in Tables 3 and 4, the copper powders of the examples are superior in oxidation resistance as compared with comparative examples not containing indium or not containing indium and phosphorus, particularly in the temperature range of 250 ° C to 600 ° C. Was found to be excellent.

    In addition, as shown in Table 5, when the copper powder of the example was kept for a long time in an environment that is easily oxidized, the oxidation resistance over time was significantly superior compared to the copper powder of the comparative example. .

Claims (7)

    A copper powder for conductive paste containing 0.1 atm% to 10 atm% of indium inside the particles.     2. The copper powder for conductive paste according to claim 1, wherein P (phosphorus) is contained in the particles in an amount of 0.01 atm% to 0.3 atm%.     In / P (atm ratio) is 4-200, The copper powder for electrically conductive pastes of Claim 2 characterized by the above-mentioned.     The copper powder for conductive paste according to any one of claims 1 to 3, wherein Ag (silver) is contained in the particles in an amount of 0.1 atm% to 10 atm%.     It is manufactured by the atomizing method, The copper powder for electrically conductive pastes in any one of Claims 1-4 characterized by the above-mentioned. The difference in weight change rate (Tg (%)) / specific surface area (SSA) at 250 ° C. and 600 ° C. is 1% / m ² / cm ³ to 30% / m ² / cm ^3. The copper powder for conductive pastes in any one of claim | item 1 -5.     A conductive paste comprising the copper powder for conductive paste according to claim 1.