JPH0949007A - Metal powder and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and easily produce nearly spherical fine metal powder almost free from oxidized films on the surfaces of the particles and uniform in particle diameter by dispersing a metal melted in a hot dispersive medium while applying ultrasonic waves and then carrying out solidification. SOLUTION: A low m.p. metal such as Ga or In or a low m.p. alloy such as 67Ag-33Te or 97.2Ag-2.8Ti is melted by putting in a heating medium such as silicone oil or engine oil kept at a high temp. above the m.p. of the metal or alloy. The resultant melt is converted into fine particle-shaped mist by applying ultrasonic vibration and this mist is solidified by cooling and recovered as fine powder. The frequency and energy of applied ultrasonic waves, application time, the m.p. of the metal and the temp. of the melt at the time of production are properly selected. The objective extremely fine, nearly spherical and uniform metal powder is easily obtd.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a low melting point metal or low melting point alloy powder and a method for producing the same, and more particularly to a solder powder and a method for producing the same. The metal powder of the invention is particularly suitable for use in the electronics industry.

[0002]

2. Description of the Related Art Atomizing method, centrifugal atomizing method (rotating disk method) and rotating water atomizing method have been known as conventional methods for producing fine powders of low melting point metals, low melting point alloys, solders and the like.

In the atomizing method, a solder composition prepared to have a desired composition is heated and melted, and the melt is jetted from a thin nozzle by using a high pressure gas to scatter into particles, and solidified to be recovered as fine powder. Is the way. The high-pressure gas used here is air, hydrogen gas, inert gas (N ₂ , C
O ₂ , rare gas, etc.). However, when air is used, an oxide film is likely to be formed on the particle surface, and it is difficult to obtain a fine metal powder having a uniform shape. When an inert gas is used, surface oxidation is suppressed and the shape of the fine metal powder is improved. However, in the atomizing method,
In any case, the characteristics of the solder particles, such as the shape of the fine metal powder and the presence of an oxide film on the particle surface, determine the type and pressure of the spray gas,
It varies significantly depending on the temperature of the melt and the cooling temperature conditions.
Further, if the oxygen concentration in the high-pressure gas or the gas remaining in the recovery container is 8% or more, or the water concentration is 30% RH or more, it is difficult to obtain a fine metal powder having a certain shape. It is considered that this is because the surface of the particles is oxidized before the finely divided metal melt solidifies. For this reason, recently, the oxygen partial pressure and the moisture content of the atmosphere in which the ejected metal particles are collected are strictly controlled to be low.

Next, in the centrifugal atomization method, the melt formed widely and thinly on the surface of the rotor is divided into a large number of strings by the centrifugal force of the rotor, and the distal end of the rotor is sequentially spun off as droplets by the centrifugal force. This is a method of forming fine particles of a melt by utilizing a so-called breaking phenomenon, and cooling and solidifying to obtain fine powder. Therefore, in this method, the size at which the melt is torn is different depending on the balance between the surface tension of the melt and the centrifugal force of the rotating body. Therefore, in order to produce a fine metal powder having a uniform shape and size, strict control and control of the temperature of the melt, the rotation speed of the rotor, and the ambient temperature are necessary, and it is difficult to produce a uniform fine powder. Very difficult. Further, in such a method, since the droplets of the melt are solidified after flying over a relatively long distance, the surface of the particles is easily oxidized, and therefore the shapes and sizes of the metal fine particles become more uneven.

Further, in the rotary water spray method, a cooling medium is put in a drum container and the drum is rotated to form a layer of the cooling medium on the inner wall surface of the rotating drum. This is a method of continuously injecting into the cooling medium layer to solidify and obtain a metal powder. In this method, pulverization is promoted by using the shearing force based on the difference between the moving speed of the cooling medium and the moving speed of the melt, that is, the flow speed difference. In this method, since the melt injection nozzle can be installed in the immediate vicinity of the cooling medium layer, the liquid droplet can be rapidly cooled. Therefore, the contact time between the droplets and the high temperature atmosphere can be extremely shortened, the surface oxidation of the fine powder can be suppressed as much as possible, and the fine powder having a uniform particle size and being relatively close to a true sphere can be manufactured. However, even when this method is used, the type of high-pressure gas used, the gas pressure, the temperature of the melt, the time until it rushes into the cooling medium, that is, the flight distance and the ambient temperature, the rushed droplets and the flow of the cooling medium. The shape and size of the liquid droplet are remarkably different due to the difference in the magnitude of the shearing force caused by the speed difference. Therefore, even if the rotary water spraying method is used, the drawbacks of the atomizing method, such as unevenness in particle diameter and particle shape, cannot be completely eliminated. In addition, these atomizing method, centrifugal spraying method,
All of the rotary water atomization methods have a large apparatus, and the fine powders produced by these methods are generally expensive. On the other hand, a low melting point metal or a low melting point alloy is charged into a liquid dispersion medium heated to a temperature equal to or higher than the melting point, and the dispersion medium-metal melt system is mechanically stirred by a stirrer or the like to remove the metal. There is also known a method of producing a spherical metal powder in which fine particles are dispersed and then the whole system is cooled to solidify the fine particles. In this method, a melt of a low melting point metal or a low melting point alloy is dispersed in the form of fine particles by utilizing the aggregating action of substances at the liquid-liquid interface, and the melt fine particles are solidified. Is obtained.

However, even with this method, it is very difficult to control the fine metal particles to a predetermined size. That is, in order to atomize the metal melt in the heated liquid medium, a moving speed difference between the liquid medium and the metal melt due to an external force such as mechanical stirring is formed, or between the metal melt and the stirrer. The shear force generated by forming the moving speed difference is used. Therefore, in order to produce a fine metal powder of uniform shape and size, the moving speed difference between the metal melt and the liquid medium, or the moving speed difference between the metal melt and the stirrer is strictly controlled and managed. There is a need to. Further, in order to maintain the shearing force above a certain value, the speed difference must be controlled to above a certain value, and there is a limit to the production of fine powders of uniform shape and size. That is, in order to strictly control the speed difference, the stirring direction is limited in stirring by a rotating propeller, stirring by suction and discharge of liquid, etc., so that movement in the system is likely to be a laminar flow. For this reason, there is an upper limit to the magnitude of the shearing force, and the magnitude tends to vary depending on the position in the system. Therefore, it is extremely difficult to produce fine particles having a narrow particle size distribution and a desired size.
It is considered that this is because there is a limit in obtaining the moving speed of the substance in the liquid medium by mechanical stirring. In order to solve such a drawback, a method of controlling the magnitude of the shearing force by installing an obstacle in the stirring direction or reversing the stirring direction in time series has been considered. However, even with such a method, the movement speed of the substance cannot be increased, a large shearing force that is usually considered necessary cannot be obtained, and further, strict control and management of manufacturing conditions is practically difficult. Therefore, it is extremely difficult to produce a fine metal powder having an arbitrary size.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and surprisingly, by melting and dispersing molten metal in a dispersion medium at high temperature while applying ultrasonic vibration to the surface of the particle, It was found that an almost spherical metal fine powder with a small oxide film and a uniform particle size can be manufactured inexpensively and easily.

The present invention provides a metal powder obtained by cooling a low melting point metal or a low melting point alloy melt-dispersed in a dispersion medium while applying ultrasonic energy. The present invention also provides a method for producing such a metal powder.

As described above, according to the present invention, the metal composition is charged into a high-temperature heating medium maintained at a temperature higher than the melting point of the desired metal composition, and the metal composition is made into a melt in the heating medium. Ultrasonic vibration is applied to the melt to form fine droplets of the melt, and then the droplets are cooled and solidified and recovered as fine powder to produce fine metal powder.

[0010]

DISCLOSURE OF THE INVENTION In the present invention, when a melt of a low melting point metal such as solder or a low melting point alloy is divided into minute droplets in a heated heating medium, a sphere is formed by the physical properties peculiar to the melt. Powder particles that are close to a true sphere are formed. In the present invention,
By appropriately selecting the frequency of ultrasonic waves to be loaded, energy, loading time and melting point of metal, temperature of melt during production, etc., the shearing force applied to the droplets can be controlled so that metal powder having a desired particle size can be obtained. can get.

Further, according to the manufacturing method of the present invention, unlike the atomizing method, the centrifugal atomizing method, the rotary water atomizing method, etc., the temperature of the metal melt and the temperature of the heating medium can be controlled extremely accurately. For this reason, the size and shape of the droplets of the metal melt become completely uniform by making the temperature of the melt, the frequency of the applied ultrasonic waves, the load energy, the load time, etc. constant. For this reason,
Uniform metal powder can be manufactured with good reproducibility and stability. Further, the metal droplets are dispersed in the dispersion medium throughout the particle formation, and the contact between the fine metal powder particles and oxygen can be sufficiently blocked.

The present invention was made by paying attention to the advantage of using the above heating medium. When the production of the low melting point metal powder and the solder powder was attempted, the grain size of the particles was uniform. It was found that the spherical low-melting-point metal powder and solder powder can be easily manufactured.

As the low melting point metal used as the raw material of the metal powder of the present invention, Ga (29.8 ° C.), In (156 ° C.), Li (186 ° C.), Se
(217 ℃), Sn (232 ℃), Bi (271 ℃), Tl (302 ℃), Pb (3
27 ° C.), Zn (419 ° C.), Te (452 ° C.) and the like can be used. As a low melting point alloy, 67 Ag-33 Te (351 ° C), 9
7.2Ag-2.8Tl (291 ℃), 45.6Ag-54.4Zn (258 ℃), 9
5.3Ag-4.7Bi (262 ℃), 52.7Bi-47.3In (110 ℃), 4
7.2In-52.8Sn (117 ℃), 95.3Ag-4.7Pb (304 ℃), 8
6.6Ag-3.4Li (154 ° C), 8.1Bi-91.9Zn (254.5 ° C) and the like can be used. Further, as the solder alloy, any known solder alloy conventionally used in the electronics industry and other applications such as Pb—Sn eutectic solder can be used. As such a solder composition, for example, 100% Sn (232 ° C), Pb-Sn system (37Pb-63Sn (183
℃), 40Pb-60Sn (183 ℃), 50Pb-50Sn (212 ℃), 44
Pb-56Sn (125 ° C), Pb-In system (50Pb-50In (1
98 ° C), Sn-In system (49Sn-51In (120 ° C), 48Sn
-52In (117-120 ℃), 65Sn-35In (162 ℃), Sn
-Bi system (43Sn-57Bi (139 ° C), 42Sn-58Bi (138 ° C), etc.), Sn-Ag system (98Sn-2Ag (221-226 ° C), 96.5Sn-
3.5Ag (221 ℃), 96Sn-4Ag (232 ℃), 95Sn-5Ag (232
Etc.), Sn-Zn system (91Sn-9Zn (199-203 ° C), 30
Sn-70Zn), Sn-Cu system (99.3Sn-0.7Cu (227
℃)), Cd-Zn system (60Cd-30Zn, etc.), Sn-S
b type (95Sn-5Sb (238 ℃) etc.), Ag-In type (3Ag-9
7In (141 ℃) and Au-Sn system (80Au-20Sn (283 ℃)
Etc.), Sn-Cd-Ag system (10Sn-85Cd-5Ag, etc.),
Sn-Ag-In system (95.5Sn-3.5Ag-1In, etc.), Sn
-Zn-In system (86Sn-9Zn-5In (192 ° C), 81Sn-9Z
n-10In (178 ° C, etc.), Sn-Cu-Ag system (95.5Sn-4
Cu-0.5Ag (216 ℃), Sn-Pb-Bi system (16Sn-32)
Pb-52Bi (99.5 ° C), 19Sn-31Pb-50Bi (96 ° C), 34
Sn-20Pb-46Bi (100 ° C), 43Sn-43Pb-14Bi (136
~ 166 ° C), Sn-Pb-Sb system (35Sn-64.5Pb-0.5
Sb, 32Sn-66Pb-2Sb, etc.), Sn-Bi-In system (17S
n-57Bi-26In), Pb-Ag system (97.5Pb-2.5A
g), Sn-Bi-Ag (90.5Sn-7.5Bi-2Ag (207 to 212)
Any solder having a composition such as (° C.) or the like) may be used.

As the heating dispersion medium used for dispersing the metal melt into fine droplets, silicone oil, engine oil, industrial lubricating oil (spindle oil, machine oil, cylinder oil, gear oil, etc.), insulation Oil, vegetable oil (coconut oil (215
℃), palm oil, olive oil, sunflower oil, castor oil (22
9 ℃), soybean oil (282 ℃), linseed oil, rapeseed oil (162 ℃), tung oil
(289 ℃), cottonseed oil (252 ℃), whale oil (230 ℃), beef tallow (265 ℃)
℃), natural resins (rosin, copearl, dammar etc.) and liquid paraffin, decane, dodecane, tetradecane, hexadecane, octadecane, higher hydrocarbon compounds such as undecane, oleic acid (255 ° C), palmitic acid (215 ° C),
Lauric acid (176 ° C), myristic acid (196 ° C), stearic acid (291 ° C), higher hydrocarbon carboxylic acid such as dimer acid (280 ° C), glyceric acid (290 ° C), ethylene glycol,
Glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol, and related compounds, trimethyl phosphate, triethyl phosphate, phosphate derivative compounds such as tributyl phosphate, octylphenol, trichlorophenol, phenol derivatives such as nonylphenol, Trichloroaniline or the like, a diphenyl-based or triphenyl-based organic heat medium, phenylimidazole, undecylimidazole, heptadecylimidazole and the like are preferably used. It is more preferable that these are protected from ignition.

These heating media are appropriately selected within the range of 120 to 460 ° C. depending on the melting temperature of the low melting point metal or alloy used. The heating dispersion medium can be used as long as the use temperature is equal to or lower than the decomposition temperature, and can be practically used up to 470 ° C.

An antioxidant may be added to these high temperature heating media to suppress the oxidation of the heating media. Examples of such antioxidants include phenolic antioxidants (2,6-di-t-butyl-9-cresol, butylated hydroxyanisole, 2,6,6) commonly used in fats and oils, rubber and synthetic resins. -Di-t-butyl-4-methylphenol,
2,6-di-t-butyl-4-butylphenol, 3,5
-Di-t-butyl-4-hydroxyphenylpropionate), bisphenol-based antioxidant (2,2'-methylenebis (4-methyl-6-t-butylphenol),
2,2'-methylenebis (4-ethyl-6-t-butylphenol), 4,4'-thiobis (3-methyl-6-t-butylphenol), 4,4'-butyridinebis (3-methyl-6-t) -Butylphenol, etc.), polymer type phenolic antioxidant (1,1,3-tris (2-methyl-4-)
Hydroxy-5-t-butylphenyl) butane, 1,3,
5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, bis (3,3 ′)
-Bis (4'-hydroxy-3-t-butylphenyl) butyric acid) glycol ester, tocopherol, etc.), sulfur-based antioxidants (dilauryl thiopropionate, dimyristyl thiopropionate, distearyl thiodiprote) Pionate etc.), phosphorus-based antioxidants (triphenylphosphite, diphenylisodecylphosphite, phenyldiisodecylphosphite, cyclic neobentane tetraylbis (octadecylphosphite), tris (nonylphenyl) phosphite, tris ( Mono and / or dinonylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, 9,
10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10 (3,5-di-t-butyl-4-hydroxybenzyl) -9,10-dihydro-
9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9,10-dihydro-9
-Oxa-10-phosphaphenanthrene and the like) may be used.

Besides, imidazoles (imidazole, 2-methylimidazole,
2-Ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-benzyl-2-methylimidazole, 2-phenyl-4-methylimidazole, 1-
Cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-
2-ethyl-4-methylimidazole, 1-aminoethyl-2-methylimidazole, 1- (cyanoethylaminoethyl) -2-methylimidazole, N- (2-methylimiazolyl-1-ethyl) urea, 1- Cyanoethyl-
2-undecylimidazole, 1-cyanoethyl-2-
Methylimidazole trimellitate, 1-cyanoethyl-2-phenylimidazole trimellitate, 1-cyanoethyl-2-ethyl-4-methylimidazole trimellitate, 1-cyanoethyl-2-undecylimidazole trimellitate, 2,4 -Diamino-6- (2-methylimidazole (1 ') ethyl-S-triazine, 2,4
Diamino-6- (2'-undecylimidazolyl (1 ') ethyl-S-triazine, 2,4-diamino-6- (2'-
Ethyl-4′-methylimidazolyl (1 ′) ethyl S-triazine, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, N, N′-bis (2-methylimidazolyl-1-ethyl) urea, N, N- (2 methylimidazole (1) ethyl-9-adipoyldiamide, 2,4-dialkylimidazole-5-dithiocarboxylic acid, 1,3-dibenzyl-2-methylimidazolium chloride, 2-
Phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1, -sianoethyl-2-phenyl-4,
5-di (cyanoethoxymethyl) imidazole, 2-methylimidazole isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2,4-diamino-
6- (2'-methylimidazole (1 ') ethyl-S-triazine isocyanurate acid adduct, 2-alkyl-4-
Formyl imidazole, dialkyl-5-formyl imidazole, etc.) may be used.

In the production of the metal powder of the present invention, the low melting point metal, the low melting point alloy and the solder alloy described above are put into these appropriate heating media and dispersed by heating. When dispersing the low melting point metal, the low melting point alloy, and the solder alloy in the medium, it is preferable to apply ultrasonic energy while mechanically stirring to uniformly and efficiently divide and disperse the fine droplets of the molten metal. . Mechanical stirring can be performed by a homogenizer or a conventionally known stirrer. In order to generate ultrasonic vibration, any conventionally known device such as a separate type in which an oscillator and a vibrator are separated, an integrated type or a throwing type, or a flat type may be used. A combined type using ultrasonic vibrations of different frequencies may also be used.

The melting and dispersing conditions of the low melting point metal, the low melting point alloy, and the solder alloy vary greatly depending on the kind and composition of the metal. For example, in the case of Pb-Sn eutectic solder, the solder melt 1
A uniform solder powder can be manufactured at 83 to 280 ° C., ultrasonic frequency of 10 to 48 KHz, and ultrasonic irradiation time of 1 to 5 minutes.

Low melting point metal, low melting point alloy, solder alloy
Once dispersed in the heating medium into sufficiently uniform fine droplets, low temperature
A liquid medium (below the solidification temperature of the metal melt) is charged and rapidly cooled, or it is continuously charged into a low temperature liquid medium to cool and solidify the metal droplets. The cooling medium used here may be the same as or different from the above heating medium. The metal solidified body produced by cooling and solidification is a fine metal powder determined by the droplet diameter in the heating medium, and the particle shape of the metal powder has a substantially true sphere formed by the physical action of the liquid. The size of the metal particles is determined by the frequency of the added ultrasonic waves, energy, load time and temperature of the heating medium, the type of metal composition, the composition ratio, etc., and if desired, the size of the commonly used metal powder (10 to 10). 15μ
m) can be controlled and manufactured uniformly.

In FIGS. 1 to 3, 40Pb-60Sn (mp183 ° C.)
The relationship between the temperature of the heating medium, the frequency of the ultrasonic wave and the ultrasonic loading time, and the average particle size of the obtained solder powder in the heating medium (soybean oil) at 3 to 280 ° C. The results of examination are shown below.

The metal powder such as the solder powder thus produced is washed with a suitable solvent to remove the heating medium and dried. Since the obtained dry powder is easily oxidized, it is advisable to add an antioxidant to the heating medium in advance in the process of pulverization, but the powder may be treated with an antioxidant again during dry collection. In the case of solder powder, it is more preferable to perform flux treatment at this time.

When the obtained powder is a solder powder, it can be applied to a solder paste or a solder cream by a conventionally known method. For the flux treatment of the solder powder, imidazole treatment or organic acid treatment can be used, but conventionally known active rosin, metal chlorides such as zinc chloride, inorganic halides or inorganic acids are preferably used alone or as a mixture.

[0024]

EXAMPLES Next, the present invention will be described more specifically based on examples.

Five kinds of solder alloys; 40Pb-60Sn (mp183
℃), 49Sn-51In (mp120 ℃), 43Sn-57Bi (mp139)
C), 96.5Sn-3.5Ag (mp221C) and 91Sn-9Zn (mp199)
Each was cut into chips with a size of approximately 3-5 mm. 50 g of each solder chip was weighed and placed in a tall beaker (600 cc) separately. Then, 300 cc of cottonseed oil at 230 ° C. was poured into this tall beaker as a high-temperature heating medium to make an alloy melt. Then, the melt and the heating medium were maintained at 300 ° C., while a three-one motor was used to stir the propeller, ultrasonic waves of 28 KHz were applied for 5 minutes using a throw-in type vibrator. In this way, the melted alloy was divided into sufficiently fine droplets and dispersed in cottonseed oil at 300 ° C. Then, heating was stopped and 200 cc of cottonseed oil at room temperature (23 ° C.) prepared separately was charged into the tall beaker all at once while applying ultrasonic waves, and the dispersion system was rapidly cooled to produce fine alloy powder. The obtained alloy powder was separated and recovered from the cottonseed oil by decantation and washed with toluene to obtain spherical alloy powder.

Next, using soybean oil as a heating medium, 260
Alloy powder was obtained under the same conditions as above at 280 ° C. and 280 ° C.

Further, under the same conditions as above, only the frequency of ultrasonic waves was changed to 10 KHz, 20 KHz and 47 KHz, and spherical alloy powder was manufactured in the same manner.

Table 1 shows the average particle size of the obtained alloy powder. The shape of each alloy powder is almost spherical,
The particle size was also almost uniform.

[0029]

[Table 1]

[0030]

EFFECTS OF THE INVENTION The low melting point metal and low melting point alloy powder of the present invention have very fine particles and are almost spherical and uniform.
For this reason, it is preferable for applications that require particularly high precision, such as for the electronic industry. Further, when used as a paste, cream or paint for screen printing, dip coating, and other general coating machines, it is easy to form a fine pattern, and a smooth and dense coating film can be formed extremely accurately. It is useful.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the temperature of a high-temperature dispersion medium and the average particle size of generated solder powder, using the frequency of ultrasonic waves (loading time is 5 minutes) as a parameter.

FIG. 2 is a graph in which the relationship between the frequency of ultrasonic waves applied and the average particle diameter of the generated solder powder is set with the temperature of the high temperature dispersion medium as a parameter, and the ultrasonic wave loading time is fixed at 5 minutes.

FIG. 3 is a graph showing the relationship between the ultrasonic loading time and the average particle size of the generated solder powder with the heating medium temperature as a parameter, with the ultrasonic frequency fixed at 47 KHz.

Claims (2)

[Claims] 1. A low melting point metal or low melting point alloy is melt-dispersed in a heating dispersion medium while applying ultrasonic energy,
Then, after cooling to solidify the fine particles, a method for producing a metal powder is carried out. 2. A metal powder obtained by cooling a low melting point metal, a low melting point alloy or a solder alloy melted and dispersed in a dispersion medium while applying ultrasonic energy.