JP5405814B2 - Copper powder for conductive paste and conductive paste - Google Patents

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, the copper powder produced by the atomization method has the advantage that, when used as a conductive material of a conductive paste, the amount of gas generated during paste curing can be reduced and the progress of oxidation can be greatly suppressed. Yes.

  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. Measures such as coating with silver having oxidation resistance (Patent Document 1) and coating with inorganic oxide (Patent Document 2) have been taken.

Japanese Patent Laid-Open No. 10-152630 JP 2005-129424 A

  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. If only the oxidation resistance improvement is grasped, it is possible to cope with the techniques of Patent Documents 1 and 2.

  However, in the techniques of Patent Documents 1 and 2 and the like, depending on the coating technique, not only a component that impairs the conductivity other than copper is required, but also a problem of peeling from the copper powder particles as the core material. Occurs. Also, in reducing the variation in shape and particle size, it is desired that the constituent particles are uniformly homogeneous and have a low oxygen concentration. However, what is still satisfactory for such copper powder is Not found.

  The present invention provides a copper powder that does not impair the balance between oxidation resistance and conductivity while being fine in particle size, and further has a small variation in shape and particle size and a low oxygen concentration, and a copper powder for conductive paste and a conductive paste. For the purpose.

  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 by containing a specific amount of Si inside the copper powder particles, thereby completing the present invention.

That is, the copper powder for conductive paste of the present invention has Cu (copper), Si (silicon) in the range of 0.1 atm% to 10 atm% , and P (phosphorus) in the range of 0.01 atm% to 0.3 atm%. And Si / P (atm ratio) is 4 to 200, and the oxygen concentration is 30 ppm to 2500 ppm .

  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 240 ° 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 in that Si is contained in the particles in an amount of 0.1 atm% to 10 atm%.

  What is important here is not to simply contain Si but to contain a specific amount inside the particles.

In other words, copper powder in which various compounds such as SiO ₂ , represented by the above-mentioned patent document, which are widely disclosed in the prior art, are coated on or attached to the surface of the copper powder particles as the core material is effective in improving oxidation resistance. However, it is impossible to obtain a copper powder which is fine in particle size and which does not impair the balance of conductivity in addition to oxidation resistance, as required by the present application.

  In addition, it is preferable that the Si component contained in the copper powder for conductive paste according to the present invention is uniformly distributed in the metal phase inside the particle, and is assumed to exist inside the particle as an alloy component. Is done.

  Further, the Si content is 0.1 atm% to 10 atm%, preferably 0.5 atm% to 5 atm%, and more preferably 0.5 atm% to 3 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.

  In addition to Si, the copper powder for conductive paste according to the present invention preferably contains P (phosphorus) inside the particles, preferably 0.01 atm% to 0.3 atm%, more preferably 0.02 atm% to 0.1 atm%. It is good to contain. If Si 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.

  Moreover, as for the copper powder for electrically conductive pastes which concerns on this invention, Si / P (atm ratio) becomes like this. Preferably it is 4-200, More preferably, it is 10-100. When the ratio of P / Si is within such a range, it is easy to balance the characteristics of fine particle size, oxidation resistance, high conductivity, small variations in shape and particle size, and low oxygen content.

  Moreover, the copper powder for conductive paste according to the present invention preferably has an Ag content of 0.1 atm% to 10 atm%, more preferably 0.3 atm% to 5 atm%, and most preferably 0.5 atm% to 3 atm%. It is good to contain. If it is the range of such a specific amount, while maintaining the oxidation resistance of the copper powder for electrically conductive paste, electroconductivity can be improved more and cost can also be suppressed.

  And when Si, Ag, and P are included, the copper powder for conductive paste is more excellent in conductivity, in addition to being excellent in oxidation resistance in addition to small variation in shape and particle size despite being fine in particle size. It becomes.

  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.

Further, the copper powder for conductive paste according to the present invention has a difference in weight change rate (Tg (%)) / specific surface area (SSA) at 240 ° C. and 600 ° C. (hereinafter referred to as ΔSA) by a thermogravimetric / differential thermal analyzer. (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 240 ° 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, Ti, Fe, Co, Cr, Mg, Mn, Mo, W, Ta, In, 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.

  Moreover, 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.

The conductive paste of copper powder according to the present invention, for example, can be measured by a laser diffraction scattering particle size distribution measuring apparatus or the like, variation coefficient determined from the volume cumulative particle diameter D ₅₀ and the standard deviation SD (SD / D ₅₀ ) of 0.2 to 0.6 is very preferable because 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. .

  In addition, 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 to 0.5 μm to 50 μm. .

  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 Si component to molten copper in the form of a mother alloy or a compound and then pulverizing it by a predetermined atomizing 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 Si added to the molten copper or copper alloy captures oxygen in the produced copper powder particles and suppresses the oxidation to such an extent that the conductivity is not impaired.

  Furthermore, when the P component is added in addition to the Si 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 Si 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 including an Ag component in addition to the Si 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 yield of additive components other than copper may be low in the water atomization method as compared to the gas atomization method, the amount of Si in the case of Si is 1 to 10 times the amount of the net amount in the target copper powder, In the case of P, 1 to 100 times the amount, and in the case of Ag, 1 to 10 times the amount needs to be added.

  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 is 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 components such as inductors and resistors, single plate capacitor electrodes, tantalum capacitor electrodes, resin multilayer substrates, ceramic (LTCC) multilayer substrates, flexible Printed circuit boards (FPC), antenna switch modules, modules such as PA modules and high-frequency active filters, PDP front and back plates, electromagnetic shielding films for PDP color filters, crystalline solar cell surface electrodes and rear lead electrodes, conductive adhesives 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 further described in detail based on the following examples and comparative examples.
Example 1
After filling the gas atomizing device (manufactured by Nisshin Giken Co., Ltd., NEVA-GP2 type) with nitrogen gas, the raw material is heated and melted in a carbon crucible in the melting chamber to obtain a molten material (electric copper 1.77 g of metallic silicon (NIKSIL manufactured by Nippon Metal Chemical Co., Ltd.) 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 silicon 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)
Except having changed metal silicon addition amount as shown in Table 1, operation similar to Example 1 was performed and copper powder was obtained.

(Examples 5 to 11)
In addition to metal silicon, a copper-phosphorus mother alloy (phosphorus grade 15 mass%) was added as shown in Table 1, and the same operation as in Example 1 was performed to obtain copper powder.

(Examples 12 and 13)
Except for adding metallic silver as shown in Table 1 in addition to metallic silicon and copper-phosphorus mother alloy, the same operation as in Example 1 was performed to obtain copper powder.

(Comparative Examples 1-4)
A copper powder was obtained in the same manner as in Example 1 except that the addition amount of metal silicon and / or copper-phosphorus mother 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 to 4 and FIGS.

(1) Content of silicon 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 3.

(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 240 ° 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 was calculated arithmetically from both numerical values. TG / SSA of Examples 1 to 13 and Comparative Examples 1 to 4 corresponding to the temperature are shown in FIGS. Moreover, the result of dividing TG / SSA of Examples 1 to 13 and Comparative Examples 2 to 4 by TG / SSA of pure copper powder of Comparative Example 1 (described as [Tg (%) / SSA] _Cu in the figure) is shown in FIG. 4 and FIG.

(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 cumulative volume particle diameter _{D 50} and the standard deviation value SD as well as coefficient of variation (SD _{/ D 50),} respectively.

(6) Powder resistance Samples of 15 g were put into a cylindrical container and a measurement sample compression-molded at a press pressure of 40 × 10 ⁶ Pa (408 kgf / cm ² ) was formed. Loresta AP and Loresta PD-41 type (both Mitsubishi Chemical) (Made by Co., Ltd.).

  As shown in FIGS. 1 to 6, the copper powders of the examples are superior in oxidation resistance as compared with comparative examples not containing silicon or containing silicon and phosphorus, particularly in the temperature range of 240 to 600 ° C. I found out.

  In addition, as shown in Table 3, 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 remarkably superior to the copper powder of the comparative example. .

  In addition, as shown in Table 4, it was confirmed that the copper powder of the example did not change much in volume resistivity as compared with the copper powder of the comparative example and had good conductivity. It was.

It is a figure which shows the result of TG / SSA of the copper powder of an Example and a comparative example. It is a figure which shows the result of TG / SSA of the copper powder of an Example and a comparative example. It is a figure which shows the result of TG / SSA on the basis of the pure copper powder of the copper powder of an Example and a comparative example. It is a figure which shows the result of TG / SSA on the basis of the pure copper powder of the copper powder of an Example and a comparative example. It is a figure which shows the result of TG / SSA of the copper powder of an Example. It is a figure which shows the result of TG / SSA on the basis of the pure copper powder of the copper powder of an Example.

Claims (5)

The particles consist of Cu (copper), Si (silicon) 0.1 atm% to 10 atm% , P (phosphorus) 0.01 atm% to 0.3 atm%, unavoidable impurities, Si / P (atm Ratio) is 4 to 200, and the oxygen concentration is 30 ppm to 2500 ppm . Copper powder for conductive paste according to claim 1, characterized in that it contains 0.1atm% ~10atm% of Ag within the grains. The copper powder for conductive paste according to claim 1 or 2 , wherein the copper powder is produced by an atomizing method. The difference in weight change rate (Tg (%)) / specific surface area (SSA) at 240 ° C. and 600 ° C. is 1% / m ² / cm ³ to 30% / m ² / cm ^3. Item 4. The copper powder for conductive paste according to any one of Items 1 to 3 . A conductive paste comprising the copper powder for conductive paste according to any one of claims 1 to 4 .

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