Device and method for producing metal particles

Abstract

To provide a device for producing metal particles, which can provide meal particles having small particle sizes such as 10 μm or less, with high production efficiency.SOLUTION: This device for producing metal particles comprises: a first tank for storing a first liquid medium and a metal material; a dissolved gas concentration controller that controls a dissolved gas concentration in the first liquid medium; a second tank for storing a second liquid medium around the first tank; an ultrasonic vibrator disposed in the second liquid medium to generate an ultrasonic wave in the second liquid medium outside the first tank and inside the second tank; and a cavitation measurement instrument that measures cavitation generated in the first liquid medium in the first tank from the ultrasonic wave generated from the ultrasonic vibrator and propagated through the second liquid medium in the second tank and a wall of the first tank to the first liquid medium in the first tank. A shock wave generated due to the cavitation generated from the ultrasonic wave in the first liquid medium in the first tank is applied to the metal material, and metal particles are generated from the metal material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method and apparatus for producing metal particles, for example metal particles made of a metallic material such as a solder alloy. [Background technology]

[0002] There is a demand for smaller particle sizes of alloy metal particles (solder particles). For example, the electrode size of a typical 0.5 mm pitch BGA is 0.25 mm in diameter, and the solder paste used to solder this BGA uses solder particles with a particle size distribution of 20 to 38 μm.

[0003] In contrast, the electrode size of a 0.2 mm pitch BGA is 0.1 mm in diameter, and the conventional solder particles with a particle size distribution of 20 to 38 μm cause clogging in the openings of the metal mask, making stable soldering impossible. For this reason, there is a demand for the use of finer solder particles with a particle size distribution of 10 to 25 μm.

[0004] In addition, the electrode size of a 1608 size chip component is 0.8 mm x 0.8 mm, and solder paste for soldering this chip component uses solder particles with a particle size distribution of 20 to 38 μm. In contrast, the electrode size of a 0201 size chip component is 0.1 mm x 0.1 mm, and the conventional solder particles with a particle size distribution of 20 to 38 μm cause clogging in the openings of the metal mask, making stable soldering impossible, so there is a demand for the use of solder particles with a finer particle size distribution of 10 to 25 μm. Furthermore, since the electrode width of a FOG with a terminal pitch of 0.1 mm is narrow at 0.05 mm, solder particles with a fine particle size distribution of 2 to 12 μm are required, and since the electrode width of a COG with a terminal pitch of 0.03 mm is even narrower at 0.015 mm, solder particles with an even finer particle size distribution of 1 to 6 μm are required. Furthermore, due to the demand for high performance devices, there is an increasing demand for finer joints. For this reason, the methods of supplying solder material to electrodes have also evolved, and screen printing methods using metal masks, gravure offset methods using material transfer technology, dispensing methods that supply solder material without contact, inkjet methods, etc. Solder pastes and solder inks for solder materials suited to each supply method are required, but to prevent clogging during supply, it is preferable for the solder particles to be spherical.

[0005] Under these circumstances, the method of Patent Document 1, which was invented recently, is a method of producing spherical metal particles having a small particle size, for example, a particle size of 10 μm or less, by irradiating a metal with ultrasonic waves. This method can be produced with excellent production efficiency.

[0006] Furthermore, in the method of Patent Document 2, even smaller metal microparticles can be produced by using ultrasonic cavitation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-150005 A [Patent Document 2] JP 2011-089156 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, this method has a problem in that when the continuous ultrasonic irradiation time reaches a certain length, the production efficiency of metal particles drops significantly.

[0009] The present disclosure has been made in consideration of such conventional problems, and aims to provide a metal particle manufacturing apparatus capable of producing metal particles having a small particle size, for example, a particle size of 10 μm or less, with excellent production efficiency. [Means for solving the problem]

[0010] The metal particle manufacturing apparatus of the present disclosure comprises a first tank for containing a first liquid medium and a metal material, a dissolved gas concentration control device for controlling the dissolved gas concentration in the first liquid medium, a second tank for containing a second liquid medium around the first tank, an ultrasonic transducer disposed in the second liquid medium outside the first tank and inside the second tank and generating ultrasonic waves in the second liquid medium, and a cavitation measuring device for measuring cavitation generated in the first liquid medium from ultrasonic waves generated from the ultrasonic transducer and propagated through the second liquid medium of the second tank and the wall of the first tank to the first liquid medium of the first tank, and shock waves due to cavitation generated from the ultrasonic waves in the first liquid medium in the first tank are irradiated to the metal material, producing metal particles from the metal material.

[0011] The method for producing metal particles according to the present disclosure includes the steps of immersing a metal material in a first liquid medium, irradiating the metal material in the first liquid medium with ultrasonic cavitation shock waves to obtain metal particles from the metal material in the first liquid medium, measuring the cavitation impact pressure generated in the first liquid medium, and controlling the dissolved gas concentration in the first liquid medium, and controlling the dissolved gas concentration in the first liquid medium in accordance with the measured cavitation impact pressure in the first liquid medium. Effect of the Invention

[0012] According to the metal particle manufacturing apparatus and manufacturing method of the present disclosure, it is possible to obtain metal particles having a small particle size, for example, a particle size of 10 μm or less, with excellent production efficiency. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view showing a cross-sectional configuration of a metal particle manufacturing apparatus according to a first embodiment. [Diagram 2] 3 is a flowchart showing the steps of a method for producing metal particles according to the first embodiment. [Diagram 3] FIG. 11 is a schematic diagram showing a cross-sectional configuration of a manufacturing apparatus for metal particles according to a third embodiment. [Figure 4] 5 is a graph showing an example of the relationship between the dissolved gas concentration in a first liquid medium and the amount of metal particles produced. FIG. [Diagram 5] 5A to 5C are diagrams showing an example of a cavitation measurement result in the metal particle manufacturing method according to the first embodiment. [Figure 6] 1 is a schematic diagram showing the configuration of a cavitation measurement device in a metal particle manufacturing apparatus according to a first embodiment. [Figure 7] FIG. 11 is a schematic diagram showing the configuration of a cavitation measurement device in a metal particle manufacturing apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The metal particle manufacturing apparatus of the first embodiment comprises a first tank for containing a first liquid medium and a metal material, a dissolved gas concentration control device for controlling the dissolved gas concentration in the first liquid medium, a second tank for containing a second liquid medium around the first tank, an ultrasonic transducer arranged in the second liquid medium outside the first tank and inside the second tank and generating ultrasonic waves in the second liquid medium, and a cavitation measuring device for measuring cavitation generated in the first liquid medium from ultrasonic waves generated from the ultrasonic transducer and propagated through the second liquid medium of the second tank and the wall of the first tank to the first liquid medium of the first tank, and shock waves due to cavitation generated from the ultrasonic waves in the first liquid medium in the first tank are irradiated to the metal material, producing metal particles from the metal material.

[0015] A second aspect of the metal particle manufacturing apparatus is the above-mentioned first aspect, wherein the first tank has an inlet and an outlet for the first liquid medium, and further has a metal particle recovery section connected to the inlet and outlet of the first tank via a pipe, and the first liquid medium is extracted from the outlet of the first tank together with the metal particles, passes through the metal particle recovery section to separate the metal particles, and then the remaining first liquid medium is returned to the inlet of the first tank.

[0016] A third aspect of the metal particle manufacturing apparatus is the above-mentioned first aspect, wherein the cavitation measurement device uses a reflective optical probe hydrophone as the sole probe.

[0017] A fourth aspect of the present invention relates to an apparatus for producing metal particles according to the first aspect, wherein the cavitation measurement device uses a reflective optical probe hydrophone as a differential action probe.

[0018] The metal particle manufacturing apparatus according to a fifth aspect may be the above-mentioned first aspect, further comprising a temperature control device that controls the temperature of the first liquid medium to be higher than the melting point of the metal material.

[0019] A sixth aspect of the method for producing metal particles includes the steps of immersing a metal material in a first liquid medium, irradiating the metal material in the first liquid medium with ultrasonic cavitation shock waves to obtain metal particles from the metal material in the first liquid medium, measuring the cavitation impact pressure generated in the first liquid medium, and controlling the dissolved gas concentration in the first liquid medium, and controls the dissolved gas concentration in the first liquid medium in accordance with the measured cavitation impact pressure in the first liquid medium.

[0020] A seventh aspect of the method for producing metal particles is the same as the sixth aspect, and in the step of obtaining metal particles, ultrasonic waves generated by operating an ultrasonic transducer in a second liquid medium arranged through a wall of a first tank containing the first liquid medium may be propagated to the first liquid medium through the second liquid medium and the partition wall of the first tank.

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a manufacturing apparatus and a manufacturing method for metal particles according to embodiments will be described in detail with reference to the accompanying drawings, but the present disclosure is not limited to these embodiments.

[0022] (Embodiment 1) <Metal particle manufacturing equipment> FIG. 1 is a schematic cross-sectional view showing a cross-sectional configuration of a manufacturing apparatus 100 for metal particles according to the first embodiment. The metal particle manufacturing apparatus 100 according to the first embodiment includes a first tank 101 for storing a first liquid medium 102, and a second tank 103 in which the first tank 101 is placed and a second liquid medium 104 is stored around the first tank 101. The metal particle manufacturing apparatus 100 further includes an ultrasonic transducer 105 disposed in the second liquid medium 104 outside the first tank 101 and inside the second tank 103, a dissolved gas concentration control device 106 for controlling the dissolved gas concentration in the first liquid medium 102, and a cavitation measuring device 107 for measuring the impact pressure of cavitation generated in the first liquid medium by ultrasonic waves. The ultrasonic waves generated from the ultrasonic transducer 105 are propagated to the first liquid medium 102 in the first tank 101 through the second liquid medium 104 in the second tank 103 and the wall of the first tank 101. Cavitation occurs due to the ultrasonic waves propagating through the first liquid medium 102, and the resulting shock waves are irradiated onto the metal material, generating metal particles from the metal material.

[0023] According to this metal particle manufacturing apparatus 100, the cavitation impact pressure in the first liquid medium 102 is measured by the cavitation measuring device 107, and the dissolved gas concentration in the first liquid medium 102 is controlled by the dissolved gas concentration control device 106 so that the cavitation impact pressure in the first liquid medium 102 is always maximized. This makes it possible to obtain metal particles with excellent production efficiency.

[0024] 1, the first tank 101 is disposed inside the second tank 103 and immersed in the second liquid medium 104, but this is not limiting, and for example, the first tank 101 and the second tank 103 may be disposed adjacent to each other. Even in this case, it is only necessary that ultrasonic waves generated from the ultrasonic transducer 105 disposed inside the second tank 103 are propagated to the first liquid medium 102 through the second liquid medium 104 and the wall of the first tank 101.

[0025] In FIG. 1, the ultrasonic transducer 105 is disposed at the bottom of the second tank 103, but this is not limited thereto, and the ultrasonic transducer 105 may be disposed, for example, on the side of the second tank 103 or on the bottom surface of the first tank 101.

[0026] The method for producing metal particles according to the first embodiment can be carried out using the apparatus 100 for producing metal particles according to the first embodiment.

[0027] <Metal Particle Manufacturing Method> FIG. 2 is a flowchart showing each step of the method for producing metal particles according to the first embodiment. The method for producing metal particles according to the first embodiment will be described with reference to the flow chart of FIG. The method for producing metal particles according to the first embodiment includes the following steps. (1) The metal material 110 is immersed in the first liquid medium 102. (2) Next, the first tank 101 containing the first liquid medium 102 (and the metal material 110) is immersed in the second liquid medium 104 in which the ultrasonic transducer 105 is immersed. (3) Ultrasonic cavitation is applied to the surface of a metal material 110 to generate metal particles 111. During the above flows (1) and (2), the dissolved gas concentration in the first liquid medium 102 is controlled to always be within a constant concentration range by the dissolved gas concentration control device 106, and further during the above flow (3), the cavitation impact pressure generated by the ultrasonic waves is measured by the cavitation measurement device 107, and based on the result, the amount of dissolved gas is controlled by the dissolved gas concentration control device 106 and the output of the ultrasonic vibrator 105 is controlled so that the cavitation impact pressure has a constant strength, thereby realizing excellent production efficiency. This will be explained in more detail below.

[0028] <Details of the manufacturing method of metal particles> (1) Regarding the step of immersing the metal material in the first liquid medium 1-1) First, a metal material 110 that is to be the raw material of metal particles 111 is prepared. The metal material 110 may be an alloy for solder paste used for soldering electronic circuit boards, and in this embodiment, for example, Bi-45% by mass In. However, the metal material 110 (and thus the metal particles 111) is not limited to Bi-45% by mass In, but may be a Bi-In alloy with a varying mixture ratio of Bi and In. Also, it is not limited to a combination of Bi-In, but may be at least one metal selected from Sn, Ag, Cu, Sb, Bi, and In, or an alloy thereof. Also, it may be a metal oxide obtained from these metals or alloys. Also, in order to efficiently generate the metal particles 111, the metal material 110 is most preferably about 10 to 1000 μm in size. If it is 10 μm or less, it will be repelled by the impact force caused by cavitation, and the generation efficiency of the metal particles 111 will be low. Also, if it is 1000 μm or more, the surface area per volume of the metal material 110 will be small, and the probability of being affected by the impact force will be low, resulting in a low generation efficiency.

[0029] 1-2) Next, the first liquid medium 102 and the second liquid medium 104 are prepared. Each of these liquid media functions as a medium for ultrasonic waves generated from the ultrasonic transducer 105 described later. The first liquid medium 102 can efficiently propagate ultrasonic waves. In this embodiment, for example, isopropyl alcohol is used. However, as the first liquid medium 102, at least one of water, alcohols, aldehydes, amines, monosaccharides, polysaccharides, linear hydrocarbons, fatty acids, and aromatics can be used.

[0030] It is known that the crushing effect of metal lumps by ultrasonic cavitation varies depending on the physical and chemical properties of the solvent. For example, in a solvent with a high boiling point or viscosity, the number (or frequency) of cavitation occurrences itself decreases, but the individual energy increases, so the crushing effect of cavitation is rather high. In addition, the temperature and pressure at the time of cavitation collapse also change depending on the type of solvent and the type of gas dissolved in the solvent. In addition, some solvents may react with the metal particles generated by crushing the metal lumps, causing metal corrosion and forming metal complexes. For this reason, it is necessary to appropriately select a solvent that can increase the crushing effect of metal lumps by ultrasonic cavitation and promote the generation efficiency of fine metal particles, and that does not cause metal corrosion of the generated metal particles or the formation of metal complexes. To meet such conditions, it is effective to combine multiple types of solvents, add a reducing agent or dispersing agent, or improve the thermal conductivity and chemical reduction ability of the working atmosphere by replacing it with an atmospheric gas.

[0031] A temperature control device (not shown) may be further provided to control the temperature of the first liquid medium 102 to a temperature equal to or higher than the melting point of the metal material 110. This allows the metal material 110 to be in a molten state in the first liquid medium 102.

[0032] In the first embodiment, the second liquid medium 104 is, for example, water. However, the second liquid medium 102 may be at least one of water, alcohols, aldehydes, amines, monosaccharides, polysaccharides, linear hydrocarbons, fatty acids, and aromatics.

[0033] The first liquid medium 102 and the second liquid medium 104 are placed in a first tank 101 and a second tank 103, respectively. In the second tank 103, an ultrasonic transducer 105 is installed in the second liquid medium 104, and in the case of a throw-in type ultrasonic transducer 105, the entirety of the transducer 105 may be immersed in the second liquid medium 104. The thickness and material of the first tank 101 may be selected so that ultrasonic waves generated from the ultrasonic transducer 105 can be efficiently propagated from the second liquid medium 104 to the first liquid medium 102. The thickness of the first tank 101 may be, for example, 1.0 mm or less, typically 0.3 mm or more and 0.5 mm or less. The material of the first tank 101 may be, for example, metals such as SUS and Ti, or inorganic substances such as glass and ceramics. The second tank 103 is not particularly limited and may be made of any appropriate thickness and material. The ultrasonic transducer 105 generally refers to a component that receives high-frequency power from an ultrasonic oscillator, vibrates, and generates ultrasonic waves by such vibration. In the present invention, any ultrasonic transducer 105 can be used as long as it can generate ultrasonic waves of an appropriate frequency in the second liquid medium 104, and commercially available ultrasonic transducers 105 that may include a throw-in type, a flange type, etc. may be used. As shown in FIG. 2, the second liquid medium 104 may be subjected to a degassing process in order to suppress the occurrence of cavitation in the second liquid medium.

[0034] (2) A step of immersing a first tank containing a first liquid medium into a second liquid medium in which an ultrasonic transducer is immersed. The first tank 101 containing the first liquid medium 102 (and the metal material 110) is immersed in the second liquid medium 104 in the second tank 103 in which the ultrasonic transducer 105 is immersed as described above. Thereafter, a dissolved gas concentration measuring unit and a dissolved gas degassing / introducing unit connected to the dissolved gas concentration control device 106 are installed so as to be immersed in the first liquid medium 102 in the first tank 101. Furthermore, a measuring unit of the cavitation measuring device 107 is installed so as to be immersed in the first liquid medium 102 in the first tank 101. After the installation of the dissolved gas concentration control device 106, the dissolved gas concentration control device 106 is used on the first liquid medium 102 at any timing to control the dissolved gas concentration in the first liquid medium to a concentration range in which the intensity of the ultrasonic shock wave is maximized.

[0035] (3) The process of applying ultrasonic cavitation to the surface of a metal material to generate metal particles Then, in a state in which the second liquid medium 104 is adjacent to the first liquid medium 102 via the partition wall of the first tank 101, the ultrasonic transducer 105 is operated in the second liquid medium 104. As a result, ultrasonic waves generated by the vibration of the ultrasonic transducer 105 are transmitted to the first liquid medium 102 through the second liquid medium 104 and the partition wall of the first tank 101 (and possibly the molten metal material 110), and ultrasonic cavitation occurs in the first liquid medium 102. Shock waves generated by such ultrasonic cavitation act on the surface of the metal material 110, generating metal particles 110 from the metal material 110.

[0036] During ultrasonic irradiation, the cavitation impact pressure generated in the first liquid medium 102 is measured by a cavitation measuring device 107, and the change in the dissolved gas concentration in the first liquid medium 102 is constantly monitored by a dissolved gas concentration control device 106. By controlling the dissolved gas concentration in the first liquid medium 102 as needed within the concentration range in which the intensity of the ultrasonic shock wave is maximized, a constant and excellent production efficiency of metal particles can be achieved.

[0037] In the present disclosure, the cavitation effect of ultrasonic waves is utilized, instead of the turbulent state caused by ultrasonic agitation, which has been widely known in the past. In the present embodiment 1, the second liquid medium 104 and the first liquid medium 102 are isolated from each other via a partition wall in the first tank 101, and no agitation force is applied to the first liquid medium 102 by an external force (e.g., an agitating blade or a stirring bar) (that is, in the present embodiment 1, the first liquid medium 102 is an apparently stationary system), so that the first liquid medium 102 does not enter a turbulent state, and the cavitation effect caused by ultrasonic waves is predominant. However, when the metal material 110 settles in the first liquid medium 102, agitation force may be applied by an agitating blade or a stirring bar to promote the propagation of ultrasonic waves.

[0038] The longitudinal waves (ultrasonic waves) generated by the vibration of the ultrasonic transducer 105 propagate through the interior of each of the above-mentioned liquid media, and alternately generate sparse and dense portions within the first liquid medium 102 in a short period of time. The pressure drops in the sparse portions, and when the pressure becomes lower than the saturated water vapor pressure, a large number of minute air bubbles on the order of microns are generated in the liquid of the first liquid medium 102. The pressure increases in the dense portions, and the surrounding liquid gathers toward the center of the air bubbles, and at the moment the air bubbles disappear, a strong shock pressure of several thousand atmospheres is generated. This generation and disappearance of the air bubbles is cavitation, and the shock waves caused by the cavitation, more specifically, the shock pressure at the moment the air bubbles disappear, act on the surface of the metal material 110, generating countless fine metal particles 111. The frequency of the ultrasonic vibrator 105 operated in the second liquid medium 104 can be appropriately selected, for example, from 0.5 kHz to 2000 kHz, preferably from 20 kHz to 100 kHz. The frequency of the ultrasonic vibrator can be selected within this range based on the particle size and production efficiency that are specifically desired according to individual circumstances.

[0039] The impact force of cavitation is proportional to the production amount of metal particles, that is, the higher the intensity of the impact force of cavitation, the greater the production amount of metal particles. Meanwhile, the relationship between the dissolved gas concentration in the first liquid medium 102 and the production amount of metal particles is as shown in FIG. 4. It can be seen from FIG. 4 that the production amount of metal particles does not increase in proportion to the dissolved gas concentration even if the dissolved gas concentration increases. As shown in FIG. 4, when the dissolved gas concentration is low, the production amount of metal particles increases as the dissolved gas concentration increases, but when the dissolved gas concentration exceeds about 2 mg / L, the production amount of metal particles gradually decreases. For this reason, in the first embodiment, a preferable production amount of metal particles can be obtained when the dissolved gas concentration is about 1.5 mg / L or more and 5 mg / L or less. Usually, the dissolved gas concentration in the first liquid medium 102 is 5 mg / L or more before ultrasonic irradiation. In this case, the transmission of ultrasonic waves is hindered by a large number of large bubbles present in the liquid solvent, and the intensity of the shock waves is reduced, resulting in a decrease in production efficiency. Therefore, it is necessary to reduce the dissolved gas concentration by the degassing function of the dissolved gas degassing unit of the dissolved gas concentration control device 106. In addition, ultrasonic irradiation also has the effect of reducing the dissolved gas concentration in the first liquid medium 102. If the dissolved gas concentration in the first liquid medium 102 becomes approximately 1.5 mg / L or less, the amount of dissolved gas contributing to the generation of cavitation is too small, resulting in a decrease in the production amount of metal particles. Therefore, the dissolved gas concentration in the first liquid medium 102 is constantly monitored by the sensing function of the dissolved gas concentration control device 106, and when the dissolved gas concentration becomes about 1.5 mg / L or less during ultrasonic irradiation, it is necessary to increase the dissolved gas concentration in the first liquid medium 102 by the gas dissolving function in the dissolved gas introduction part of the dissolved gas concentration control device 106. As described above, by controlling the dissolved gas concentration in the first liquid solvent by the dissolved gas concentration control device 106, it is possible to always form metal particles with high efficiency. However, the dissolved gas concentration range that maximizes the intensity of the ultrasonic shock wave may differ depending on the type of liquid solvent. In other words, the relationship between the dissolved gas concentration in the first liquid medium 102 in FIG. 4 and the production amount of metal particles is limited to a specific case. FIG. 4 shows that when the dissolved gas concentration is about 1.5 mg / L or more and 5 mg / L or less, the intensity of the cavitation impact pressure is considered to be high, and in that case, the production amount of metal particles is high. For this reason, it is important to directly measure the cavitation impact pressure and obtain a corresponding relationship with the range of dissolved gas concentration when the cavitation impact pressure is high.

[0040] <Cavitation measurement device> The cavitation measurement device 107 uses a reflective optical probe hydrophone (FOPH) to measure the change in refractive index caused by the density change due to the sound pressure of the solvent in the reaction vessel as the change in the intensity of the reflected light. This makes it possible to measure the impact pressure caused by the collapse of cavitation bubbles in addition to the irradiated sound pressure. Figure 5 shows the results of FFT conversion of the measurement data when the ultrasonic transducer 105 generates ultrasonic waves at a driving frequency of 35 kHz and an output of 600 W using the cavitation measurement device 107. 6 is a diagram showing the configuration of a cavitation measurement device 107 in the manufacturing apparatus for metal particles according to the first embodiment. The cavitation measurement device 107 is a device using a FOPH as a single probe, and the light output from an ASE light source 301 is incident on an optical fiber 303 immersed in a liquid medium 102 through a circulator 302. The intensity of the reflected light at the tip of the optical fiber 303 is determined by a refractive index change caused by a density change in the liquid medium 101 due to a sound pressure change caused by an ultrasonic wave. The intensity of the reflected light then passes through the optical fiber 303 and is converted into a current value by a photodiode (PD) 304 via a circulator 302, and is converted into a voltage by an I-V converter 305. The waveform amplified by an amplifier circuit 306 is acquired as digital data by an oscilloscope 307 or the like, and observed by a device capable of FFT processing. According to the measurement results shown in Fig. 5, in addition to the main peak and sub-peaks in the range of 20kHz to 200kHz that contribute to the ultrasonic driving frequency, a high frequency peak due to the collapse of bubbles generated by cavitation can be observed in the 2-2.5MHz region, and the impact pressure of cavitation can be measured. The collapse time τ of the bubbles is obtained by the Rayleigh-Presset formula, and when the first liquid medium is water, the collapse time (lifetime) τ of the bubbles is approximately 0.45μs when the size of the bubbles is assumed to be approximately 5μm. In contrast, the reciprocal of 2.5MHz is also 0.4μs, and it can be seen that the frequency and the lifetime of the bubbles are consistent. In the first embodiment, the optical fiber in the detection portion of the FOPH has a core diameter of 6 μm, but this is not limiting, and optical fibers of different sizes may be used as appropriate.

[0041] In this manner, metal particles 111 generated in first liquid medium 102 can be obtained. The metal particles 111 obtained in this way have a small particle size. The particle size of such metal particles is, for example, 10 μm or less, preferably 6 μm or less, typically 0.1 μm or more and 10 μm or less, and more typically 0.1 μm or more and 6 μm or less. Here, the particle size of the metal particles refers to the volume average particle size of the metal particles. The particle size of the metal particles and the volume ratio of metal particles having a particle size in a specific range can be obtained by measuring the particle size distribution of the metal particles with a laser diffraction / scattering type particle size distribution measuring device. In this way, the volume average particle size of the metal particles is obtained. <Effects> In this way, according to the metal particle manufacturing method and manufacturing apparatus of the first embodiment, metal particles having a small particle size, for example a particle size of 10 μm or less, can be obtained with consistently high production efficiency.

[0042] (Embodiment 2) <Cavitation measurement device> The metal particle manufacturing apparatus according to the second embodiment differs from the metal particle manufacturing apparatus according to the first embodiment in that the cavitation measurement device 107a uses another set of FOPHs in the differential motion probe. This allows the measurement of cavitation impact pressure to be achieved with higher resolution. In other respects, the same explanation as in the first embodiment applies unless otherwise specified. 7 is a diagram showing the configuration of a cavitation measurement device 107a in a manufacturing apparatus for metal particles according to the second embodiment. The cavitation measurement device 107a is a device using another pair of FOPHs as a differential operation probe, and can perform differential operation by splitting light output from an ASE light source 301 by an optical coupler 308, one of which is immersed in a first liquid medium 102 on which ultrasonic waves are applied, and the other is immersed in a third liquid medium 202 that is the same as the first liquid medium 102. By performing differential operation, signal noise can be removed, and the impact pressure of cavitation can be measured with higher resolution.

[0043] (Embodiment 3) <Metal particle manufacturing equipment> 3 is a schematic diagram showing a cross-sectional configuration of a metal particle manufacturing apparatus 900 according to embodiment 3. According to the metal particle manufacturing apparatus according to embodiment 3, metal particles can be manufactured continuously. Note that, with respect to the metal particle manufacturing method and manufacturing apparatus, the same explanations as those of embodiment 1 and embodiment 2 above apply unless otherwise specified.

[0044] The method for producing metal particles according to the third embodiment can be carried out using a manufacturing apparatus 900 for metal particles shown in Fig. 3. The manufacturing apparatus 900 for metal particles according to the third embodiment includes a first tank 902 for accommodating a first liquid medium 901, and a second tank 904 in which the first tank 902 is placed and which accommodates a second liquid medium 903 around the first tank 902. Furthermore, the manufacturing apparatus 900 for metal particles includes an ultrasonic transducer 912 disposed in the second liquid medium 903 outside the first tank 902 and inside the second tank 904. In this embodiment, the ultrasonic waves (longitudinal waves) generated by the ultrasonic transducer 912 are adjusted to reach the first liquid medium 901, and a cavitation measuring device 918 for measuring cavitation caused by ultrasonic waves is installed in the first tank 902.

[0045] Furthermore, in the metal particle manufacturing apparatus 900 of the third embodiment, the first tank 902 has an inlet portion X and an outlet portion Y for the first liquid medium 901. Furthermore, the metal particle recovery section 906 is provided so as to be connected to the inlet portion X and the outlet portion Y of the first tank 902 via pipes such as an inlet side pipe 910 and an outlet side pipe 905 (the pipes from point A to point B are not shown). Thus, the first liquid medium 901 is configured to be circulated by the pump 907 through the dissolved gas concentration control device 917, the first tank 902, and the metal particle recovery section 906. The metal particle recovery unit 906 may be, for example, a liquid cyclone, etc. The pipe is not particularly limited, but may be made of metal or other suitable materials (the same applies below).

[0046] A hopper 908 for introducing metal material may be provided on the circulation path of the first liquid medium 901 before the inlet X of the first tank 902 .

[0047] On the other hand, the second liquid medium 903 in the second tank 904 is configured to be circulated through a circulating cooling device 913 connected to the second tank 904 via a pipe 914, thereby enabling temperature control. The circulating cooling device 913 may be, for example, a chiller.

[0048] <Details of the manufacturing method of metal particles> The method for producing metal particles according to the third embodiment can be carried out as follows. The metal material 916, the first liquid medium 901, and the second liquid medium 903 can be the same as those described above in the first embodiment. The metal material 916 is processed into granules or the like and placed in a hopper 908 in advance. The first liquid medium 901 is circulated by a pump 907 through an inlet pipe 910, a dissolved gas concentration control device 917, a first tank 902, an outlet pipe 905, and a metal particle recovery unit 906. On the other hand, the second liquid medium 903 is circulated through an external circulation cooling device 913 .

[0049] Here, when the ultrasonic transducer 912 is operated in the second liquid medium 903, ultrasonic waves generated by the vibration of the ultrasonic transducer 912 are transmitted to the first liquid medium 901 through the second liquid medium 903 and the partition wall of the first tank 902 (possibly a molten metal material), and ultrasonic cavitation occurs in the first liquid medium 901. Shock waves generated by such ultrasonic cavitation act on the surface of metal material 916 , generating metal particles 915 from metal material 916 .

[0050] In the third embodiment, the second liquid medium 903 and the first liquid medium 901 are isolated from each other via a partition wall in the first tank 902. In other words, no stirring force is applied to the first liquid medium 901 by an external force (e.g., agitation blades or stirrers) (in the third embodiment, the first liquid medium 901 appears to be in a laminar flow). Therefore, it should be noted that the first liquid medium 901 does not enter a turbulent state, and the cavitation effect caused by the ultrasonic waves is predominant.

[0051] Then, the first liquid medium 901 is extracted from the outlet Y of the first tank 902 together with the metal particles 915. More specifically, since these metal particles 915 are suspended in the first liquid medium 901, they are carried along with the flow of the first liquid medium 901 and sent to the metal particle recovery section 906 through the outlet pipe 905.

[0052] The generated metal particles 915 can be separated from the first liquid medium 901 in the metal particle recovery section 906 (for example, by difference in specific gravity in the case of a liquid cyclone) and extracted from point P. On the other hand, the remaining first liquid medium 901 from which the metal particles 915 have been separated is transported through a pipe from point A to point B by a pump 907, and returned to the inlet part X of the first tank 902 through an inlet pipe 910 after the dissolved gas concentration is appropriately adjusted by a dissolved gas concentration control device 917 to a concentration range in which the impact pressure of the ultrasonic cavitation is maximized.

[0053] Since the metal material spreading at the bottom of the first tank 902 is consumed by releasing metal particles 915, new metal material may be supplied from the hopper 908, for example, at predetermined time intervals. By repeatedly and continuously carrying out the above-mentioned operations, metal particles can be produced continuously.

[0054] The metal particle manufacturing method and manufacturing apparatus of this embodiment 3 can also obtain the same effects as those of embodiment 1, and can always produce spherical metal particles having a small particle size, for example a particle size of 10 μm or less, with a consistent, excellent production efficiency.

[0055] Although the method and apparatus for producing metal particles according to the present disclosure have been described above based on three embodiments, the present disclosure is not limited to these embodiments and various modifications are possible. For example, the method and apparatus for producing metal particles according to the present disclosure can be conveniently carried out and used under normal pressure, but may also be carried out and used under increased or reduced pressure as appropriate. [Industrial Applicability]

[0056] According to the method and apparatus for producing metal particles disclosed herein, metal particles having a small particle size, for example, a particle size of 10 μm or less, can be obtained with excellent production efficiency. Such metal particles can be used as, but are not limited to, solder particles contained in solder paste used for mounting (soldering) electronic components on electronic circuit boards. [Explanation of symbols]

[0057] 100 Metal particle manufacturing equipment 101 First Tank 102 First liquid medium 103 Second Tank 104 Second Liquid Medium 105 Ultrasonic transducer 106 Dissolved gas concentration control device 107 Cavitation Measuring Device 110 Metal materials 111 Metal particles 201 Third Tank 202 Third Liquid Medium 301 ASE light source 302, 302a, 302b Circulator 303, 303a, 303b Photodiode (PD) 304 IV conversion circuit 305 Amplification circuit 306 Oscilloscope 307a, 307b Optical fiber 900 Metal particle manufacturing equipment 901 First liquid medium 902 First tank 903 Second liquid medium 904 Second Tank 905 Outlet pipe 906 Metal particle recovery section 907 Pump 908 Hopper 910 Inlet pipe 912 Ultrasonic transducer 913 Circulating cooling device 914 Pipe 915 Metal particles 916 Metal materials 917 Dissolved gas concentration control device 918 Cavitation Measuring Device

Claims

1. a first vessel for containing a first liquid medium and a metallic material; a dissolved gas concentration control device that controls a dissolved gas concentration in the first liquid medium; a second vessel for containing a second liquid medium around the first vessel; an ultrasonic transducer disposed in the second liquid medium outside the first tank and inside the second tank, the ultrasonic transducer generating ultrasonic waves in the second liquid medium; a cavitation measuring device that measures cavitation generated in the first liquid medium from the ultrasonic waves that are generated from the ultrasonic transducer and propagate through the second liquid medium in the second tank and a wall of the first tank to the first liquid medium in the first tank; Equipped with The shock wave caused by the cavitation generated by the ultrasonic waves in the first liquid medium in the first tank is irradiated to the metal material, thereby generating metal particles from the metal material. Metal particle manufacturing equipment.

2. the first tank has an inlet and an outlet for the first liquid medium, and further has a metal particle recovery unit connected to the inlet and the outlet of the first tank via a pipe; The first liquid medium is extracted from the outlet of the first tank together with the metal particles, and the metal particles are separated from the first liquid medium through the metal particle recovery section, and then the remaining first liquid medium is returned to the inlet of the first tank. The apparatus for producing metal particles according to claim 1 .

3. The cavitation measurement device uses a reflection type optical probe hydrophone as a single probe. The apparatus for producing metal particles according to claim 1 .

4. The cavitation measurement device uses a reflection type optical probe hydrophone as a differential action probe. The apparatus for producing metal particles according to claim 1 .

5. The apparatus for producing metal particles according to claim 1 , further comprising a temperature control device that controls the temperature of the first liquid medium to be higher than the melting point of the metal material.

6. Immersing a metal material in a first liquid medium; a step of irradiating the metallic material in the first liquid medium with shock waves of ultrasonic cavitation to obtain metallic particles from the metallic material in the first liquid medium; Measuring the impact pressure of cavitation occurring in the first liquid medium; controlling a dissolved gas concentration in the first liquid medium; Including, controlling a dissolved gas concentration in the first liquid medium in response to the measured impact pressure of cavitation in the first liquid medium; A method for producing metal particles.

7. 7. The method for producing metal particles according to claim 6, wherein in the step of obtaining the metal particles, ultrasonic waves generated by operating an ultrasonic transducer in a second liquid medium arranged through a wall of a first tank containing the first liquid medium are propagated to the first liquid medium through the second liquid medium and a partition wall of the first tank.

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