TWI680195B - Method for producing metal particle - Google Patents

Abstract

An object of the present invention is to provide a method for producing Cu particles with high true sphericity by UDS method with high mass productivity.

The present invention is a method for manufacturing spherical metal particles. The method includes: Step a, which comprises Cu and trace elements, the mass ratio of Cu obtained by GDMS analysis exceeds 99.995%, and the trace elements include Si, Al or Ca One or more of the metal materials are melted in the crucible 17 to produce a molten metal material; step b, which applies a pressure of 0.05 MPa to 1.0 MPa in the crucible, and is arranged in the vertical direction and the diameter from the central axis The molten metal material is dripped from the orifice 12a of 5 μm or more and 1000 μm or less to prepare molten metal droplets 1; and step c, which is to rapidly condense the molten metal droplets in an environment where the oxygen concentration is 1000 ppm or less by volume; The orifice 12a is provided in the orifice plate 12 formed of artificial single crystal diamond.

Description

Manufacturing method of metal particles

The present invention relates to a method for manufacturing metal particles, and more particularly, to a method for manufacturing spherical metal particles.

In recent years, high-density packaging such as ball grid array (BGA) and three-dimensional high-density packaging such as stacked package (POP) and multi-chip module (MCM) have gradually developed. The diameter reduction and true sphericity of the solder-coated Cu balls with Cu balls as the core.

The applicant has developed a Uniform Droplet Spray Process (hereinafter referred to as "UDS method") suitable for producing spherical copper particles suitable for use as the core of solder-coated Cu balls (Patent Documents 1, 2 ). The UDS method applies pressure and vibration to a molten metal material to rapidly condense molten metal droplets that are continuously dropped, and can stably suppress deviations in particle size while producing metal particles with high true sphericity.

Furthermore, the applicant has found that the mass ratio of Cu obtained by Glow Discharge Mass Spectrometry (hereinafter referred to as "GDMS analysis") containing Cu (copper) and trace elements exceeds 99.995%, and P in trace elements Cu particles (copper particles) with a mass ratio of (phosphorus) and S (sulfur) of 3 ppm or more and 30 ppm or less have high sphericity and appropriate Vickers hardness, and can be manufactured by the USD method (Patent Literature 3). The method for producing Cu particles described in Patent Document 3 has the advantage that the annealing process required in the method for producing Cu particles with high true sphericity including trace elements (Pb and Bi) described in Patent Document 4 is not necessary. .

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 4159012

[Patent Document 2] Japanese Patent No. 5905501

[Patent Document 3] Japanese Patent No. 6256616

[Patent Document 4] Japanese Patent No. 5585751

With the UDS method described above, metal particles with higher true sphericity can be manufactured. However, according to the study by the present inventors, in the method for producing metal particles using the UDS method, sufficient mass productivity cannot be obtained.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a method for producing Cu particles having a high true sphericity by a UDS method with high mass productivity.

A method for manufacturing metal particles according to an embodiment of the present invention is a method for manufacturing spherical metal particles, which includes the following steps: Step a, which includes Cu and trace elements, and the mass ratio of Cu obtained by GDMS analysis exceeds 99.995 % And the above-mentioned trace elements contain one or more metal materials of Si, Al, or Ca, and are melted in the crucible to make a molten metal material; step b, which is to apply 0.05 MPa to 1.0 MPa in the crucible Pressure from the central axis in the vertical direction and the diameter is 5 μm or more and 1000 The molten metal material is dripped in a flow hole below μm to produce molten metal droplets; and step c, the molten metal liquid droplet is rapidly condensed and solidified in an environment where the oxygen concentration is 1000 ppm or less by volume; and the flow hole It is set in a orifice plate made of artificial single crystal diamond. The orifice plate may be mounted on the bottom of the crucible as another component, or may be formed integrally with the crucible.

In one embodiment, the above-mentioned trace elements include at least one of Si in an amount of 0.16 ppm or more, Al in an amount of 0.10 ppm or more, and Ca in an amount of 0.04 ppm or more.

In one embodiment, the trace elements further include P and S, and the total mass ratio of P and S is 3 ppm or more and 30 ppm or less. The total mass ratio of P and S may be 10 ppm or more. That is, it is suitable for the manufacturing method of the metal particle described in patent document 3.

In one embodiment, the flow hole has a linear portion with a length Lx and a diameter dx defined by a side wall parallel to the vertical direction, and the linear portion satisfies dx / 2 ≦ Lx ≦ 10dx.

In one embodiment, the length Lx of the linear portion of the flow hole satisfies 2.5 μm ≦ Lx ≦ 5 mm.

In one embodiment, the true sphericity of the metal particles is 0.997 or more.

In one embodiment, the method for producing the metal particles is to continuously produce the metal particles for 1 hour or more. The manufacturing method of the said metal particle may manufacture the said metal particle continuously for 3 hours or more.

In a certain embodiment, when the diameter (particle diameter) in the manufacturing specifications of the above-mentioned metal particles is set to D, and the standard deviation of the diameter (particle diameter) of the metal particles constituting the above-mentioned metal particle group as a whole is set to S Including the above-mentioned continuously produced metal particles The metal particle group satisfies S ≦ 0.0036 × D. In addition, 0.0036 is a parameter called an evaluation coefficient, and the smaller the value, the smaller the variation in the diameter (particle diameter) of the metal particles constituting the metal particle group.

According to an embodiment of the present invention, a method is provided for producing Cu particles with high true sphericity by UDS method with high mass productivity.

1‧‧‧ molten metal droplets

2‧‧‧ Molten Metal Materials

12‧‧‧ orifice plate

12a‧‧‧ orifice

14‧‧‧ Piezoelectric element

15‧‧‧ shot

16‧‧‧Vibration unit

17‧‧‧ Crucible

19‧‧‧ chamber

100‧‧‧ metal ion manufacturing equipment

Lx‧‧‧ length

Dx‧‧‧ diameter

V, G‧‧‧ arrows

FIG. 1 is a schematic diagram showing a configuration example of a metal particle manufacturing apparatus 100 used in a method for manufacturing metal particles according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view near the orifice 12 a of the orifice plate 12 included in the metal particle manufacturing apparatus 100.

FIG. 3 is an observation image (hereinafter referred to as a “SEM image”) obtained by a scanning electron microscope of the flow holes 12 a included in the metal particle manufacturing apparatus 100. (A) indicates a state before use, and (b) indicates a state after use. status.

FIG. 4 is a SEM image of a flow hole of a comparative example. (A) shows a state before use, and (b) shows a state after use.

Hereinafter, a method for producing metal particles according to an embodiment of the present invention will be described with reference to the drawings. Hereinafter, the example of producing Cu particles described in Patent Document 3 will be described, but the method for producing metal particles according to the embodiment of the present invention is not limited to this, and it can also be applied to the use of GDMS including Cu and trace elements. Method for producing spherical metal particles by analyzing a metal material having a mass ratio of Cu exceeding 99.995% and a trace element containing one or more of Si, Al, or Ca metal materials.

GDMS analysis is performed by using a sample as a cathode in an Ar (argon) environment. Glow discharge, a method of sputtering the surface of a sample in a plasma, and measuring the ionized constituent elements by a mass spectrometer. GDMS analysis can target most elements (Li ~ U) with stable isotopes on the periodic law, and measure most of the elements at a ppb level by mass ratio.

GDMS analysis can more accurately determine the chemical components contained in metal materials than ICP-AES analysis. Specifically, the mass ratio of Cu in the metal particles can be measured at a resolution of 0.0001% (1 ppm) or less. However, in the GDMS analysis, the Ar gas is used to analyze the sample by sputtering under a pressure that generates a glow discharge. Therefore, it is subject to residuals such as C (carbon), N (nitrogen), and O (oxygen) in the Ar gas. ) And other atmospheric constituent elements. Therefore, it is difficult to distinguish whether these elements are contained in the sample or caused by the influence of the background. Therefore, it is preferred that the metal particles whose surface is easily oxidized, such as Cu, be subjected to GDMS analysis after the removal of the surface oxide layer of the sample (metal particles) is performed.

As the metal material used in the method for producing metal particles according to the embodiment of the present invention, for example, JIS C1011 (the mass% of Cu is 99.99 or more) may be used, but as a trace element, one of Si, Al, or Ca may be contained. the above. The metal material may further include one or more of P and S. The above-mentioned metal material is an unavoidable impurity (element) in many cases, but may further include, for example, Pb, Bi, Sn, Sb, Zn, As, Ag, Cd, Ni, Au, U, Th, Cr, Se , Co, Mo, and Fe may be one or more, and further, one or more of H, C, N, and O may be contained as a gas component element.

In addition, in the UDS method, when a metal material which can contain the above-mentioned trace elements in addition to Cu is heated to produce a molten metal material, a refractory (such as a crucible) containing an oxide is used. Therefore, trace elements such as Si, Al, or Ca may be mixed into the molten metal material from a crucible or the like. Thereafter, as explained in the experimental examples, it can be seen that since Si, Al, and Ca in these trace elements are difficult to completely block oxygen in the UDS method, they will be in a molten state. An oxide is formed or mixed in the state of an oxide, and the oxide accumulates around the pores, eventually blocking the pores.

It was found that the accumulation of the oxide around the orifices occurred significantly in the orifice plate made of artificial sapphire, and the orifice plate made of artificial single crystal diamond could be suppressed. It is believed that the reason why the accumulation of the oxide occurs significantly in the orifice plate made of artificial sapphire is the action of oxygen contained in artificial sapphire, which is a kind of steel jade (including alumina crystalline mineral). Furthermore, since diamond is a kind of allotrope of carbon and carbon atoms are arranged in a special cubic lattice, it does not substantially contain oxygen.

The metal particle manufacturing apparatus 100 shown in FIG. 1 includes a crucible 17 having an orifice plate 12 having an orifice 12a at the bottom; a vibration unit 16 including a piezoelectric element 14 and a rod 15; and a chamber 19 which As shown by an arrow G, an inert gas is introduced into the inside. The orifice plate 12 is formed of artificial single crystal diamond, and the central axis of the orifice 12 a is arranged in a vertical direction indicated by an arrow V. If the center axis of the flow hole 12a is arranged to be consistent with the vertical direction, that is, the direction of gravity, the edge of the molten metal material 2 from the exit side of the flow hole 12a can be suppressed from wetting and spreading along the bottom surface (see FIG. 2). As a result, the molten metal droplet 1 formed by the molten metal material 2 dripping from the orifice 12a into the jet of an inert gas stably moves (falls) in the vertical direction shown by the arrow V. The flow of the plurality of molten metal droplets 1 in the jet stream is referred to as a molten metal jet.

FIG. 2 is a schematic cross-sectional view showing the vicinity of the orifice 12 a of the orifice plate 12. The diameter dx of the orifice 12a is 5 μm or more and 1000 μm or less, and is appropriately set according to the diameter (particle diameter) of the metal particles to be produced. The flow hole 12a has a straight portion having a central axis that coincides with the vertical direction and a length Lx defined by a side wall having a circular cross section. It is preferable that the linear portion of the length Lx and the diameter dx of the flow hole 12a satisfy a predetermined relationship, and specifically, it is preferable to satisfy dx / 2 ≦ Lx ≦ 10dx. The diameter of the metal particles is hereinafter referred to as the particle diameter. The diameter of the metal particles set at the time of manufacturing, that is, the particle diameter of the metal particles to be manufactured is referred to as the target particle diameter.

When the relationship between the diameter dx specified by the straight portion of the orifice 12a and the length Lx of the straight portion satisfies Lx <dx / 2, it is difficult for the molten metal droplet 1 dropped from the orifice 12a to stably reach the vertical direction shown by the arrow V. mobile. Therefore, in the above-mentioned jet stream, the molten metal droplet 1 easily loses linearity, and the flow of several molten metal droplets 1, that is, vibration and splitting of the molten metal jet, and it is difficult to form metal particles having a target particle diameter. When Lx> 10dx is satisfied, the surface area of the linear portion of the flow hole 12a in contact with the molten metal material 2 increases, and the frictional resistance of the linear portion of the flow hole 12a with respect to the molten metal material 2 increases. Therefore, the speed of the molten metal droplet 1 dripped from the self-flow hole 12a tends to become unstable, and it is difficult to form metal particles having a target particle diameter.

The exit side (opening toward the bottom surface) of the straight portion of the orifice 12a is formed, for example, so as not to form a chamfer (C in accordance with JIS B0701) or radian (R in accordance with JIS B0701) at the corner (edge) and maintain the diameter dx opens on the bottom surface. The entrance side of the straight portion of the length Lx (the entrance portion of the molten metal material 2) is formed so that the diameter increases from dx upward (in the direction opposite to the arrow V), and the side wall changes from 90 degrees to 0 degrees with respect to the horizontal direction (horizontal Direction). The molten metal material 枓 2 (see FIG. 1) in the crucible 17 is smoothly introduced into the straight portion by the above-mentioned tapered curved surface.

Furthermore, the shape of the corner (edge) on the exit side of the straight portion is not limited to this, and a chamfer or radian may be formed. The angle (edge) of the exit side of the flow hole 12a illustrated in FIG. 2 is a cross-sectional shape without a chamfer or an arc before use, and will be gradually reduced due to the passage of the molten metal material 2 during use, and gradually Although it has a chamfered or radian shape, the molten metal droplet 1 can be formed stably. If the length Lx of the straight portion is, for example, less than 2.5 um, as described above, it is difficult to form the molten metal droplet 1 stably, or the molten metal formed is molten. The volume of the metal droplet 1 becomes smaller, and the variation in the volume of the molten metal droplet 1 becomes larger. Therefore, the length Lx of the straight portion can satisfy 2.5 μm ≦ Lx ≦ 10 mm, preferably 2.5 μm ≦ Lx ≦ 5 mm, and more preferably 2.5 μm ≦ Lx ≦ 1 mm. The upper limit of the length Lx of the straight portion is not particularly limited as long as the molten metal is sprayed stably, but if the artificial single crystal diamond exceeds 10 mm, it is difficult to process and / or the material cost is high. Therefore, the length Lx of the straight portion is preferably 10 mm or less, and it is preferable that the artificial single crystal diamond can be easily processed by reducing the length as much as possible to 5 mm or less, 3 mm or less, and further 1 mm or less.

The shape (cross-sectional shape perpendicular to the central axis direction) when the straight portion of the flow hole 12a is viewed from the central axis direction is preferably a roundness of 0.9 or more, and more preferably 0.99 or more. If the shape of the straight portion of the flow hole 12a, especially the shape of the exit side, is less than 0.9, the direction of action of the pressure (spray pressure) on the flow of the molten metal material 2 changes, and several molten metal The flow of the droplet 1 (jet of molten metal) is prone to split, and the deviation of the volume of the molten metal droplet 1 is liable to become large.

Referring to FIG. 1 again, a method for manufacturing metal particles (metal particle group) using the metal particle manufacturing apparatus 100 will be described. The orifice plate 12 may be the same as the manufacturing method described in Patent Document 3, except that the orifice plate 12 is formed of artificial single crystal diamond.

(Production steps of molten metal materials)

First, a metal material serving as a raw material of metal particles is put into the crucible 17 and heated to produce a molten metal material 2. The metal material used as the raw material contains Cu and trace elements. The mass ratio of Cu obtained by GDMS analysis exceeds 99.995%. The trace element contains one or more of Si, Al, or Ca. A molten metal material produced by using the metal material 2 It also contains substantially the same components. Therefore, the metal particles produced in the subsequent steps also contain substantially the same components. Moreover, the mass of trace elements contained in metal materials The ratio is adjusted by, for example, the following method. The composition of pure copper (pure Cu) as the master alloy ingot of Cu in the metal material was obtained by GDMS analysis. The missing trace element itself in the master alloy ingot, or a copper alloy (Cu alloy) containing the lacking element, is added to the master alloy ingot and dissolved to obtain a target composition. Furthermore, the composition of the copper alloy added to make up for the lack of elements was also determined in advance by GDMS analysis.

Table 1 shows an example of the composition of a copper raw material (metal material) containing Cu and trace elements. Here, C1011 (mass% of Cu is 99.99 or more) of JIS standard was used.

As shown in Table 1, as a trace element, one of Si, Al, or Ca is included. More than one, and in addition to P and S, for example, Pb, Bi, Sn, Sb, Zn, As, Ag, Cd, Ni, Au, U, Th, Cr, Se, Co, Mo, and Fe are included. The trace elements Si, Al and Ca exist as oxides in the molten metal material 2 maintained at a predetermined temperature range. When the orifice plate 12 is made of artificial sapphire, the oxides are accumulated in the orifice 12a. In the periphery, the flow hole 12a is finally blocked. The minimum content of Si contained in the five copper raw materials (metal materials) exemplified here is 0.16 ppm, the minimum content of Al is 0.10 ppm, and the minimum content of Ca is 0.04 ppm.

(Production steps of molten metal droplets)

In the crucible 17, the molten metal material 2 is controlled to a predetermined temperature range, and a pressure of 0.05 MPa or more and 1.0 MPa or less is applied in the crucible 17, and the molten metal material 2 is passed from the orifice 12a having a diameter of 5 μm to 1,000 μm As shown by an arrow V, a spherical molten metal droplet 1 is produced. In addition, in FIG. 1, for the sake of simplicity, the flow of a plurality of molten metal droplets 1 (molten metal spray) continuously dropped in a jet of an inert gas is indicated by an arrow V. At this time, the vibration unit 6 is used to apply a predetermined periodic vibration to the molten metal material 2 in the crucible 17, whereby the molten metal droplets 1 which become metal particles after solidification can be controlled to a size corresponding to the vibration period. The manufacturing method of such metal particles belongs to the UDS method.

The orifice 12a for dripping the molten metal droplet 1 is arrange | positioned so that the center axis may correspond to a vertical direction, that is, a gravity direction. With this configuration, it is possible to suppress the wetting and diffusion of the edge of the molten metal material 2 from the exit side of the self-flow hole 12a along the bottom surface (see FIG. 2). As a result, the molten metal droplet 1 is stably dropped in the vertical direction indicated by the arrow V. The reason why the molten metal material 2 is difficult to wet and diffuse along the bottom surface is considered to be because the static contact angle of the side wall including the flow hole 12a with respect to the molten metal material 2 including the copper raw material shown in Table 1 is large (about 160 °) artificial single crystal diamond, which helps to reduce the wettability of the molten metal material 2 with respect to the side wall of the flow hole 12.

The pressure (additional pressure) applied in the crucible 17 is preferably controlled in a range of not less than 0.05 MPa and not more than 1.0 MPa, whereby a spherical molten metal droplet 1 having a high true sphericity can be formed. This additional pressure can be obtained by means of introducing a controlled amount of inert gas into the crucible 17 or the like. If the additional pressure is less than 0.05 MPa, the influence of friction when the molten metal material 2 passes through the orifice 12a becomes larger, and the molten metal material 2 dropped from the orifice 12a tends to become unstable. Therefore, by the molten metal droplet 1 The variation in the particle diameter of the metal particles produced by solidification is likely to increase. In addition, if the additional pressure exceeds 1.0 MPa, the molten metal droplet 1 dropped from the orifice 12a tends to form a spherical shape like an ellipsoid. Therefore, the true sphericity of metal particles produced by the solidification of the molten metal droplet 1 is liable to decrease. .

The diameter dx of the flow hole 12a is preferably set to an appropriate value in consideration of the particle diameter and true sphericity of the metal particles to be produced, and the adjustable range of the above-mentioned additional pressure and vibration period. For example, when the diameter dx of the orifice 12a is small, adjustments such as increasing the additional pressure and extending the vibration period are performed. When the diameter dx of the orifice 12a is large, only the opposite adjustment to the smaller case is required. Just fine. Moreover, if the setting of the magnitude of the applied pressure and the vibration period is too biased, the deviation of the particle size and true sphericity of the metal particles will increase. In order to suppress this deviation, it is preferable to set the diameter dx of the orifice 12a to a range of 5 μm or more and 1000 μm or less. If a flow hole 12a having a diameter dx of 5 μm or more and 1000 μm or less is used, metal particles having a particle size of 10 μm or more and 1000 μm or less can be produced corresponding to the diameter dx of the flow hole 12a.

The orifice plate 12 can be replaced for each manufacturing step of the metal particles, but it is difficult to replace the orifice plate 12 in one manufacturing step. Therefore, it is preferable to adjust the additional pressure and vibration after setting the diameter dx of the flow hole 12a corresponding to the target diameter of the metal particles to be produced. And other conditions.

(Production steps of metal particles)

At the same time, the above-mentioned manufacturing step of the molten metal droplet 1 is performed, and simultaneously, the molten metal droplet 1 is dropped from the orifice 12a into a jet of an inert gas having an oxygen concentration of 1000 ppm or less in volume ratio. The molten metal droplets 1 are rapidly condensed in this jet. Thereby, the molten metal droplet 1 dripped from the flow hole 12a can be rapidly condensed and solidified in the environment where the oxygen concentration is 1000 ppm or less by volume ratio. Through the above steps, it is possible to produce a particle size of 10 μm or more and 1000 μm or less, containing Cu and trace elements, containing Cu in a mass ratio exceeding 99.995% by GDMS analysis, and containing one of Si, Al, or Ca as a trace element. Several of the above metal particles. By continuously condensing a large number of molten metal droplets 1 continuously dripped from the self-flow hole 12a, a metal particle group including a large number of the above-mentioned metal particles can be produced.

The above-mentioned jet formed by the inert gas becomes an ambient gas when the molten metal droplet 1 is rapidly condensed and solidified. As the inert gas used as the ambient gas, for example, non-oxidizing argon or nitrogen can be used. That is, when it is convenient to use any gas as an ambient gas, it is also set to an environment where the oxygen concentration is 1000 ppm or less by volume ratio. Furthermore, an inert gas equivalent to the inert gas used as the ambient gas can be used as the inert gas introduced into the crucible 17 and the inert gas introduced into the chamber 19.

In the example shown in FIG. 1, the oxygen concentration in the chamber 19 is set to 1000 ppm or less (for example, about 300 ppm) by volume ratio. If the oxygen concentration in the ambient gas is increased, copper oxide will be generated during the solidification of the molten metal droplet 1, which will become a fine nucleation core, refine the solidified structure, and form a surface oxide layer on the metal particles, which will increase its thickness Increasing tendency. If a thicker surface oxide layer is formed on the metal particles, the removal process requires more time, and the particle size and true sphericity of the metal particles may be caused by the removal process. Risk of defects. In addition, for example, when a nickel plating layer (Ni layer) serving as a barrier layer with respect to a solder layer is formed on the surface of metal particles having a surface oxide layer, there are areas where poor adhesion of the Ni layer occurs and areas where there is no Ni layer are mixed. Surface morphology (plating spots). If such a defect exists, the Ni layer cannot function as a barrier layer that prevents the solder layer from contacting the metal particles. When the solder layer becomes molten solder, it is formed from Cu contained in the metal particles and Sn (tin) contained in the solder. The possibility of CuSn alloy layer increases. Therefore, in the embodiment of the present invention, in order to suppress the formation of the surface oxide layer of copper oxide on the metal particles containing Cu, it is set to an environment where the oxygen concentration is 1000 ppm or less by volume ratio.

Hereinafter, experimental examples (inventive examples, comparative examples) will be described, and a method for producing metal particles (metal particle groups) according to an embodiment of the present invention will be described in more detail.

The metal particles (group of metal particles) serving as an example of the present invention are manufactured using a metal particle manufacturing apparatus 100 having an orifice plate 12 made of artificial single crystal diamond. The metal particles (group of metal particles) as a comparative example are manufactured in the metal particle manufacturing apparatus 100 using an orifice plate made of artificial sapphire instead of the orifice plate 12 made of artificial single crystal diamond.

(Example of the invention)

Target particle diameter of the metal particles: Refer to Table 2 for the production specifications D of Cu particle diameters.

Orifice diameter dx: 90μm

Angle (edge) of exit side of orifice: 90 degrees (shape without chamfer or radian)

Length of straight part Lx: 0.06mm

True roundness of circular cross section of orifice: 0.999

In the example of the present invention, metal particles (metal particle groups) were continuously produced for about 4 hours. The mass of the molten metal material sprayed from the orifice is about 3.6 kg. In Figure 3, SEM image of a flow hole made of artificial single crystal diamond of the present invention. Fig. 3 (a) shows the state before use, and Fig. 3 (b) shows the state after use (after about 4 hours).

In the example of the present invention, after 4 hours from the start of dripping of the molten metal material 2, no vertical vibration (fluctuation of the flow rate in the direction of gravity) of the flow (molten metal jet) of the dripping molten metal droplets 1 was found. Vibration (variation of flow velocity in the horizontal direction) and other particularly noticeable changes in the state. In the example of the present invention, no attachment was found at the corner (edge) on the exit side of the straight portion of the orifice and its periphery (the bottom surface of the orifice plate), but the corner (edge) of the wall surface of the orifice was slightly lost. The variation in the particle diameter of the metal particles (metal particle group) obtained by the manufacturing method of the example of the present invention is small, and the production yield of the metal particles (metal particle group) is about 90%. Thereafter, the same flow orifice plate can be used to repeat the manufacturing step of dropping metal particles (metal particle groups) of the molten metal material 2 of the same quality as described above, which is performed about 10 times. As a result, it is possible to use the orifice plate made of artificial single crystal diamond for about 40 hours while continuously manufacturing the metal particles (metal particle group).

(Comparative example)

Target particle size of metal particles: Refer to Table 2 for manufacturing specifications D of Cu particle diameters

Orifice diameter dx: 90μm

Angle (edge) of exit side of orifice: 90 degrees (shape without chamfer or radian)

Length of straight part Lx: 0.25mm

True roundness of circular cross section of orifice: 0.999

In the comparative example, there was no particular problem immediately after the dripping of the molten metal material 2 was started. However, after 10 minutes have elapsed since the molten metal material 2 started to drip, a longitudinal vibration and a lateral vibration of the flow (molten metal jet) of several molten metal droplets 1 that have dropped are generated. As a result, the particle size of the produced metal particles starts to decrease.

FIG. 4 shows an SEM image of a flow hole made of artificial sapphire used in a comparative example. Fig. 4 (a) shows the state before use, and Fig. 4 (b) shows the state after use (after about 10 minutes). Observe the SEM image shown in Figure 4 (b) of the orifice from the upward direction (opposite to the direction of gravity), the corner (edge) at the exit side of the straight portion of the orifice and its periphery (the bottom surface of the orifice plate) Found attachments. As a result of SEM-EDX analysis, it was found that the adherend included oxides of Si, Al, and Ca. The production yield of the metal particles (metal particle group) obtained by the production method of the comparative example was about 30%.

From the results of the above examples of the present invention and comparative examples, it can be seen that by using an orifice plate made of artificial single crystal diamond, it is possible to suppress the accumulation of oxides of Si, Al, and Ca on the corner (edge) of the exit side of the orifice and its periphery. (The bottom surface of the orifice plate). That is, when spherical metal particles (metal particle groups) are produced using a metal material containing Cu and trace elements, a mass ratio of Cu obtained by GDMS analysis exceeding 99.995%, and a trace element containing one or more of Si, Al, or Ca , Through the use of artificial single crystal diamond orifice plate, can improve mass productivity.

Table 2 shows the evaluation results of the variation in the particle diameter of the metal particles constituting the metal particle group and the true sphericity. The manufacturing results of metal particles (metal particle groups) having different manufacturing specifications D (target particle diameter D) are shown in Table 2 in the same manner as the examples of the present invention and the comparative examples described above.

The particle diameter and true sphericity of the metal particles shown in Table 2 are values based on the circle-equivalent diameter obtained from the image data of the metal particles. Specifically, first, the metal particles placed on a flat plate are irradiated with parallel light, a telecentric lens is used to form an image on a charge coupled device (CCD), and the area of the metal particles is obtained based on the obtained image data. Then, a circle equivalent diameter is obtained from the area of the metal particles, and a length ratio obtained by dividing the circle equivalent diameter by the maximum projection length obtained from the image data is obtained. In the present invention, the circular equivalent diameter is taken as the particle diameter of the metal particles, and the length ratio is taken as the true sphericity of the metal particles. The true sphericity of the metal particles shown in Table 2 is an average value obtained by arithmetically averaging the true sphericity of 500 metal particles.

As shown in Table 2, when the particle diameter (target particle diameter) in the manufacturing specifications of metal particles is set to D, and the standard deviation of the particle size of the metal particle group as a whole is set to S, the examples of the present invention include The metal particle group of continuously produced metal particles satisfies S ≦ 0.0036 × D. Here, 0.0036 is a parameter called the evaluation coefficient A. The smaller the value, the smaller the variation in the diameter of the metal particle group. The particle diameter of the metal particle group refers to the particle diameter of several metal particles extracted from the metal particle group. In addition, the number of pieces of data of the particle diameter of the metal particle group as a whole is the same as the number (number of samples) of metal particles extracted from the metal particle group.

When the above-mentioned standard deviation S is obtained and the metal particle group is evaluated to be within the scope of the present invention, from the viewpoint of the reliability of the population and the standard deviation S, it is expected that the number of particles j of the particle size of the metal particle group as a whole (sampling number) The number j) is based on JIS-Z9015 (normative test standard II, standard test). Specifically, the number of metal particles (sampling number j) extracted from the metal particle group is set to 125 or more (j ≧ 125), preferably 1250 or more, and more preferably 2000 or more. Here, the number of samples j in the examples and comparative examples is set to "500".

The total number of the above data is j, as long as the measurement includes the number of (125 or more) metal particles extracted from the metal particle group manufactured by the manufacturing step with the same target particle size. The j pieces of data obtained by the particle size may be sufficient, and they may not be samples from metal particles (metal particle groups) of the same manufacturing batch. For example, one batch of metal particle groups resulting in manufacturing specification D (target particle size D) is produced by removing non-spherical metal particles (double spheres) that combine two or more metal particles to obtain spherical particles (single spheres). Swarm of metal particles. Thereafter, the particle diameters of several (125 or more) metal particles extracted from the metal particle group were measured to obtain j particle diameter data (measured particle diameter dj). The j particle size data (measured particle size dj) obtained in this way can be used as the metal particle group manufactured by the manufacturing specification D (for example, in the case of j = 1 to 500, 500 particles satisfying j ≧ 125 are included) Metal particle group).

A×D(評價係數A=0.0036)進行評價。其結果，於作為評價對象之金屬粒子群(取樣500個)滿足S≦A×D之情形時，可將成為經過該取樣之母體之金屬粒子群(製造成目標粒徑D者)全部視作良品之金屬粒子。 Then, the average particle diameter Dm can be obtained from the measured particle diameter dj (j = 1 to 500) of j (j = 500) metal particles that become the total metal particle group, and the standard deviation S = √ [{( d1-Dm) ² + (d2-Dm) ² + ... (dj-Dm) ² } / j], depending on whether S is satisfied

A × D (evaluation coefficient A = 0.0036) was evaluated. As a result, when the group of metal particles to be evaluated (500 samples are sampled) satisfies S ≦ A × D, all the metal particle groups (those manufactured to the target particle diameter D) that become the sampled body can be considered Good metal particles.

The upper limit of the evaluation coefficient A is 0.0036. As the evaluation coefficient A decreases from 0.0036 to 0.0035, 0.0030, and 0.0025, the variation in the particle size of the metal particle group becomes smaller. In the particle size distribution curve (graph) of the metal particle group, the peak of the mountain-shaped curve becomes It is steep and the width at the lower end of the mountain-shaped curve becomes narrower.

(Industrial availability)

According to the embodiment of the present invention, it is suitable for producing metal particles (metal particle groups) suitable for use as a core of a solder-coated Cu ball, for example.

Claims (8)

A method for manufacturing metal particles, which is a method for manufacturing spherical metal particles, including: step a, containing Cu and trace elements, the mass ratio of Cu obtained by GDMS analysis exceeds 99.995%, and the above-mentioned trace elements contain Si, One or more metal materials of Al or Ca are melted in a crucible to produce a molten metal material; step b, a pressure of 0.05 MPa or more and 1.0 MPa or less is applied to the crucible, and the central axis is arranged in a vertical direction and The molten metal material is dripped through a flow hole having a diameter of 5 μm or more and 1000 μm or less to prepare molten metal droplets; and step c, the molten metal droplets are rapidly condensed and solidified in an environment where the oxygen concentration is 1000 ppm or less by volume; and The orifice is provided in an orifice plate made of artificial single crystal diamond. The method for producing metal particles according to claim 1, wherein the trace element contains at least one of Si in an amount of 0.16 ppm or more, Al in an amount of 0.10 ppm or more, and Ca in an amount of 0.04 ppm or more. The method for producing metal particles according to claim 2, wherein the trace elements further include P and S, and the total mass ratio of the P to the S is 3 ppm or more and 30 ppm or less. The method for manufacturing metal particles according to any one of claims 1 to 3, wherein the flow hole has a linear portion of length Lx and diameter dx defined by a side wall parallel to the vertical direction, and the linear portion satisfies dx / 2 ≦ Lx ≦ 10dx. The method for manufacturing metal particles according to claim 4, wherein the length Lx of the linear portion of the flow hole satisfies 2.5 μm ≦ Lx ≦ 5 mm. The method for manufacturing metal particles according to any one of claims 1 to 3, wherein the true sphericity of the metal particles is 0.997 or more. The method for producing metal particles according to any one of claims 1 to 3, wherein the above-mentioned metal particles are continuously produced for at least one hour. For example, the method for manufacturing metal particles according to claim 7, wherein the diameter of the above-mentioned metal particle manufacturing specification is set to D, and the diameter of the metal particles constituting the above-mentioned metal particle group is taken as the standard deviation obtained as a whole. The metal particle group including the above-mentioned metal particles continuously manufactured satisfies S ≦ 0.0036 × D.