Copper alloy powder

Abstract

To provide a copper alloy powder that exhibits electrical conductivity comparable to pure copper and enables control of a sintering start temperature.SOLUTION: A copper alloy powder containing at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, the total content of the at least one element being 0.1-2.0 mass%, the balance being Cu and unavoidable impurity elements.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a copper alloy powder and a method for producing the same. [Background technology]

[0002] Conductive paste is prepared by dispersing conductive filler made of metal powder such as copper powder in a resin binder or solvent vehicle, and can form a conductive circuit in the coated area by coating and firing. Therefore, it is used to form conductive circuits on electronic component boards and electrodes on multilayer ceramic capacitors. In recent years, conductive paste has also been attracting attention as a joining material for power semiconductors. This is because conductive paste has superior heat resistance and heat dissipation properties compared to lead solder, the conventional joining material, and can solve the problem of high temperature in power semiconductor devices.

[0003] As mentioned above, conductive pastes have a variety of uses, and the properties required vary depending on the use. One of the properties required is high-temperature sintering ability. For example, when forming the internal electrodes of a multilayer ceramic capacitor, the ceramic and copper powder have different sintering temperatures, which can lead to problems such as peeling and cracking due to mismatched shrinkage timing. To reduce the risk of such defects, it is important to design the copper powder so that its dimensional change balances with the dimensional change due to ceramic shrinkage caused by sintering and thermal expansion, i.e., to raise the sintering start temperature of the copper powder and control the amount of this increase.

[0004] Methods for imparting high-temperature sinterability to copper powder include alloying by adding high-melting-point metal elements and surface treatment, but both approaches result in a decrease in electrical conductivity. Patent documents 1 to 4 listed below also describe approaches for increasing the sintering initiation temperature. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2009 / 051254 publication [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-168321 [Patent Document 3] Japanese Patent Application Publication No. 2017-122252 [Patent Document 4] Patent Publication No. 2021-110034

[0006] Patent Document 1 describes that a high sintering initiation temperature can be achieved by using a Cu-Al-B copper alloy powder produced by water atomization. However, there is a problem that the electrical conductivity decreases due to the solid solution of Al and B.

[0007] Patent Document 2 describes that low electrical resistivity and a high sintering initiation temperature can be achieved by using copper alloy powder containing Ta and W produced by a chemical vapor reaction method. Ta and W are elements that are difficult to dissolve in Cu, so there is almost no loss in electrical conductivity even when they are alloyed. However, Ta and W have melting points exceeding 3000°C, making them difficult to melt, and manufacturing them using the atomization method, which is excellent for mass production, is difficult, resulting in the problem of low mass productivity.

[0008] Patent Document 3 describes that oxidation of copper powder can be suppressed and the sintering initiation temperature can be increased by performing surface treatment by adding an aqueous solution containing one or more elements selected from the group consisting of Y, Zr, and La to a slurry in which copper powder produced by a wet reduction method is dispersed. However, this requires a surface treatment step in a nitrogen atmosphere, making the production process complicated, and since it is a wet process, it generates waste liquid, which poses a problem in terms of disposal costs.

[0009] Patent Document 4 describes that the sintering start temperature can be increased by controlling the physical shape parameters of average particle size, average circularity, and BET specific surface area. However, while Patent Documents 1 to 3 allow the sintering start temperature to be controlled simply by increasing or decreasing the amount of elements added to copper, Patent Document 4 has the problem of requiring precise adjustment of three non-independent shape parameters (average particle size, average circularity, and BET specific surface area) in order to control the sintering start temperature. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, an object of the present invention is to provide a copper alloy powder that has electrical conductivity close to that of pure copper and allows control of the sintering start temperature by a simple and low-cost means such as the addition of elements. [Means for solving the problem]

[0011] The present inventors conducted numerous trials and evaluations to solve the above-mentioned problems, and as a result, they discovered that an element selected from Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium) can be easily produced by an atomization method (because all of these elements have melting points below 2000°C), can impart sintering inhibition due to oxide stability (because all of these oxides have Gibbs energies equal to or less than SiO2), and is not involved in the loss of conductivity due to alloying (because all of these elements are hardly dissolved in Cu). The inventors then discovered that by adding one or more elements selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu to copper so that the total content falls within a predetermined range, mass productivity is high and it is possible to control the sintering start temperature while maintaining electrical conductivity comparable to that of pure copper, thereby solving the above technical problem.

[0012] The present invention, which can solve the above problems, is as follows. [1] A copper alloy powder containing at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, wherein the total content of the at least one element is 0.1 to 2.0 mass%, and the remainder is Cu and unavoidable impurity elements. [2] The copper alloy powder according to [1], having a median diameter D50 measured by a laser diffraction / scattering method of 0.1 μm to 10.0 μm. [3] The copper alloy powder according to [1] or [2], which is an atomized powder. [4] The copper alloy powder according to any one of [1] to [3], which is used as a metal filler for a conductive paste. [5] A conductive paste containing the copper alloy powder according to any one of [1] to [4].

[0013] The copper alloy powder of the present invention contains at least one element selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, which are hardly dissolved in Cu, and therefore does not suffer from a decrease in conductivity due to solid solution as indicated by Nordheim's law, and exhibits a conductivity close to that of pure copper (a conductivity of 90% IACS or more, more preferably 95% IACS or more, and particularly preferably 97% IACS or more) despite being an alloy. Furthermore, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu are located below Si, an element that is difficult to sinter, on the Ellingham diagram of oxides, and are therefore elements that are difficult to sinter like Si, and adding trace amounts of these elements can shift the sintering temperature to the higher temperature side (for example, the sintering start temperature can be set to 600°C or higher, more preferably 700°C or higher, and particularly preferably 800°C or higher). The amount of shift can also be changed by adjusting the amount. Furthermore, if the copper alloy powder of the present invention has a median diameter D50 of 0.1 μm to 10.0 μm as measured by a laser diffraction / scattering method, it can be used to form fine conductive circuits and electrodes, and therefore can be suitably used as a conductive filler for conductive pastes. [Effects of the Invention]

[0014] As described above, according to the present invention, it is possible to provide a copper alloy powder suitable for a conductive filler, which has electrical conductivity comparable to that of pure copper despite being an alloy, and the amount of sintering temperature shift to the higher temperature side can be adjusted by adjusting the amount of added elements. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a copper alloy powder containing one or more elements selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, with the balance being Cu and unavoidable impurity elements. In particular, it is preferable that the copper alloy powder contains one or more elements selected from the group consisting of Y, La, and Nd.

[0016] The total content of the above elements is preferably 0.1 to 2.0 mass %, more preferably 0.4 to 2.0 mass %. If the total content of at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu is less than 0.1% by mass, the desired high-temperature sinterability may not be achieved. On the other hand, if the total content exceeds 2.0% by mass, the sintering resistance effect may be too strong, resulting in insufficient sintering.

[0017] Furthermore, the copper alloy powder of the present invention preferably has a median diameter D50 measured by a laser diffraction / scattering method of 0.1 μm to 10.0 μm, more preferably 3 μm to 7 μm, and particularly preferably 4 μm to 6 μm. If the D50 of the copper alloy powder is less than 0.1 μm, the sintering neck will be thin and the electrical resistance will be high. Furthermore, if such fine powder is produced by a manufacturing method such as atomization, the yield will be significantly reduced, which may result in extremely high costs. On the other hand, if the D50 of the copper alloy powder exceeds 10 μm, it becomes difficult to form fine circuits or electrodes, and there is a risk that the powder will not be suitable as a metal filler for conductive pastes.

[0018] The BET specific surface area of ​​the copper alloy powder of the present invention is 0.1 to 0.7 m 2 / g, and 0.15 to 0.5m 2 / g, and more preferably 0.2 to 0.4m 2 / g is particularly preferred.

[0019] In this specification, "unavoidable impurity elements" refers to elements that are not intentionally added but are inevitably mixed in during the manufacturing process of each raw material. The total amount of unavoidable impurity elements is usually 0.4% by mass or less, which is not enough to affect the effects of the present invention. Since the amount of unavoidable impurity elements is preferably small, the total amount is more preferably 0.3% by mass or less, 0.2% by mass or less, or 0.1% by mass or less, and may even be 0% by mass.

[0020] Although the method for producing the copper alloy powder of the present invention is not particularly limited, copper alloy powder produced by atomization is preferred, and copper alloy powder produced by high-pressure water atomization is more preferred, because the copper alloy powder produced by high-pressure water atomization has a finer particle size and therefore has an excellent yield in the particle size range suitable for conductive fillers.

[0021] The powder obtained by the atomization method or the like may be pulverized in a ball mill or the like to deform the particles into flakes. The powder may also be made oxidation-resistant, and may be surface-treated to improve affinity with resins when used as a conductive paste. [Example]

[0022] Examples of the present invention are shown below, but the present invention is not limited to these.

[0023] [Preparation of raw powder] The copper alloy powders of Examples 1 to 7 and Comparative Examples 2 to 7 were produced by melting raw materials, high-purity copper metal (99.99% or higher) and one or more metals selected from the group consisting of Y, La, and Nd, in a melting furnace, and then spraying the molten copper alloy with high-pressure water, followed by rapid cooling and solidification, using a water atomization method. The particle size of the obtained powder was adjusted by air classification. In Comparative Example 1, Y, La, and Nd were not used, and only the high-purity copper ingot was used to prepare powder by the water atomization method. The copper alloy powders of Examples 1 to 7 and Comparative Examples 1 to 7 were obtained by adjusting the atomization conditions and classification conditions to have a median diameter D50 of 4.0 to 6.0 μm and a specific surface area of ​​0.25 to 0.35 m.2 / g.

[0024] [Measurement of added element content] The contents of Y, La, and Nd were measured using an ICP optical emission spectrometer (iCAP7600 manufactured by Thermo Fisher Scientific Co., Ltd.) after dissolving the copper alloy powders of Examples 1 to 7 and Comparative Examples 1 to 7 in acid to form solutions.

[0025] [Median diameter measurement] For each of the copper alloy powders of Examples 1 to 7 and Comparative Examples 1 to 7, the median diameter D50 was determined using a laser diffraction particle size distribution measuring device (MT3000II, manufactured by Microtrack Bell Corporation).

[0026] [Measurement of specific surface area] For each of the copper alloy powders of Examples 1 to 7 and Comparative Examples 1 to 7, the BET specific surface area was measured using a specific surface area measuring device (Macsorb, a fully automatic specific surface area measuring device manufactured by Mountec Co., Ltd.) according to the BET method.

[0027] [Measurement of sintering start temperature] 1.5 g of each of the copper alloy powders of Examples 1 to 7 and Comparative Examples 1 to 7 was weighed and filled into a 5 mm × 11 mm mold, and the molding density was 5.5 g / cm 3 (±0.03g / cm 3 The thermal shrinkage behavior of this powder compact during heating was measured using a thermomechanical analyzer (Rigaku Corporation, Thermo plus EVOII TMA8310) at a heating rate of 10°C / min from room temperature to 1000°C in an atmosphere of nitrogen gas flowing continuously at 300 ml / min. The thermal shrinkage behavior of the green compact increased linearly in accordance with the thermal expansion coefficient of the copper alloy until the start of sintering, and then the dimensions rapidly contracted once sintering began. Therefore, the temperature at the intersection of the tangents to the TMA curves before and after the start of sintering was defined as the sintering start temperature.

[0028] [conductivity] When measuring the conductivity of an alloy composition, the conductivity of a sintered body is reduced by pores, making it difficult to obtain an accurate conductivity. Therefore, ingots with the alloy compositions shown in Examples 1 to 7 and Comparative Examples 1 to 7 were prepared, and test pieces measuring 30 mm x 5 mm x 1 mm were prepared by wire electric discharge machining. The resistance values ​​of these test pieces were measured using the four-terminal method (electrode distance 20 mm), and the conductivity (specified in JIS H 0500) was calculated from the resistance value and sample dimensions. A resistance meter (RM3545, manufactured by Hioki E.E. Corporation) was used to measure the resistance values.

[0029] [Evaluation method] The present invention exhibits electrical conductivity comparable to that of pure copper, and the sintering start temperature can be controlled to a high level by adjusting the amount of added elements. As a copper alloy powder having the effects of the present invention, any copper alloy powder that satisfies the following evaluation criteria was deemed to be effective. (1) As an evaluation of high-temperature sinterability, the sintering start temperature is 600°C or higher (approximately 100°C higher than that of the pure copper powder of Comparative Example 1). (2) For the evaluation of sinterability, the sintering start temperature must be 1000°C or less (within the TMA measurement temperature range). (3) The conductivity must be 90% IACS or higher.

[0030] The results are shown in Table 1. [Table 1]

[0031] All of the copper alloy powders of Examples 1 to 7 met the evaluation criteria for effectiveness. The powder of Comparative Example 1 is a high-purity copper powder containing no additive elements. The pure copper powder of Comparative Example 1 had a sintering start temperature of less than 600°C and did not satisfy the evaluation criteria for effectiveness. The copper alloy powders of Comparative Examples 2 to 4 each had a content of La, Y, or Nd of less than 0.1 mass %. The copper alloy powders of Comparative Examples 2 to 4 all had a sintering start temperature of less than 600°C and did not satisfy the evaluation criteria for effectiveness. The copper alloy powders of Comparative Examples 5 to 7 each had a La, Y, or Nd content exceeding 2.0 mass%. None of the copper alloy powders of Comparative Examples 5 to 7 showed any dimensional shrinkage within the TMA measurement temperature range, and the sintering start temperature was higher than 1000°C, so they did not satisfy the evaluation criteria for effectiveness. [Industrial Applicability]

[0032] Although the present invention is an alloy, it has electrical conductivity comparable to that of pure copper, and the amount of sintering start temperature shifted to the higher temperature side can be adjusted by adjusting the amount of added elements. Therefore, the copper alloy powder of the present invention is suitable for use as a conductive filler for conductive pastes, and has industrial applicability in various fields, such as forming conductive circuits in electronic component substrates, forming electrodes in multilayer ceramic capacitors, and as bonding materials for power semiconductors.

Claims

1. A copper alloy powder comprising at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, wherein the total content of the at least one element is 0.1 to 2.0 mass%, and the balance is Cu and unavoidable impurity elements.

2. The copper alloy powder according to claim 1, wherein the median diameter D50 measured by a laser diffraction / scattering method is 0.1 μm to 10.0 μm.

3. The copper alloy powder according to claim 1 or 2, which is an atomized powder.

4. The copper alloy powder according to claim 1 or 2, which is used as a metal filler for a conductive paste.

5. A conductive paste comprising the copper alloy powder according to claim 1 or 2.

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