JP2011026697A - Method for producing metallic microsphere - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing metallic microspheres reduced in depressions caused on the surfaces of metallic microspheres and with the characteristics of surface smoothness in order to improve an electrical connection reliability, in the achievement of multilayering a wiring board, micronizing a connection terminal part, or the like by using the metallic microspheres. <P>SOLUTION: In the method for producing metallic microspheres, Cu droplets are subjected to spherical solidification in an atmosphere comprising 10 to 800 vol.ppm oxygen, and the balance inert gas. Further, preferably, the Cu droplets are formed by dropping Cu molten metal to which pressure and vibration are applied from an orifice. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing Cu microspheres used for connection terminal portions of electronic components.

  In recent years, in order to meet the demand for higher mounting density of electronic components, studies on three-dimensional high-density mounting such as package-on-package (POP) and multichip module (MCM) have been advanced. In order to solve this problem, mounting using a composite microball in which a core ball made of, for example, Cu having a melting point higher than that of solder is coated with solder has been proposed. (Patent Document 1)

On the other hand, in the manufacture of Cu microspheres as the core ball of the above-described composite microball, for example, as proposed by the present applicant in Patent Document 2, Cu metal powder is put into thermal plasma and melted, and spherical solidification is performed. A so-called thermal plasma method has been proposed.
In Patent Document 2, a metal microsphere having excellent electrical conductivity and low deformation resistance is manufactured by setting the oxygen content including the surface oxide layer of the metal microsphere to 50 ppm or less using a thermal plasma method. Proposals have been made to improve general connection reliability. This proposal is excellent in that it produces a large amount of metal microspheres in a short time.

  Patent Document 3 proposes a so-called uniform droplet spraying method in which a Cu microsphere is formed by ejecting a Cu melt from an orifice and dispersing it as a method for producing a Cu microsphere used for a core ball. .

JP-A-11-317416 JP 2005-2428 A JP 2004-137530 A

Although the manufacturing method disclosed in Patent Document 2 or Patent Document 3 described above is advantageous in reducing the deformation resistance of the metal microspheres, the surface smoothness of the metal microspheres is caused by solidification shrinkage of Cu. There was a problem that a dent occurred due to the formation of shrinkage nests. The dent appearing on the surface of the metal microsphere is highly likely to cause problems such as voids and poor plating adhesion when solder plating is applied to the surface. In putting parts into practical use, this is a major problem that impairs electrical connection reliability.
An object of the present invention is to provide a method for producing metal microspheres having reduced surface dents on the surface of the metal microspheres and having surface smoothness characteristics.

  The present inventor examines the problem of the surface dent of the metal microsphere, and adopts a configuration that adjusts the oxygen concentration in the atmosphere in which the Cu droplet is solidified into a predetermined range at the time of manufacturing the metal microsphere, The inventors have found that the surface dents of metal microspheres can be reduced and the surface smoothness can be greatly improved, and the present invention has been achieved.

That is, the present invention is a method for producing metal microspheres in which Cu droplets are spherically solidified in an atmosphere of oxygen: 10 to 800 ppm by volume and the remaining inert gas.
Moreover, it is preferable that the said oxygen is 120-800 volume ppm.
Moreover, it is preferable that the said oxygen is 200-760 volume ppm.
The inert gas is preferably argon.
The inert gas is preferably nitrogen.
The Cu droplet is preferably formed by dropping a molten Cu imparted with pressure and vibration from an orifice.

  According to the present invention, the surface dent of the metal microsphere can be reduced, the surface smoothness can be remarkably improved, and the technology indispensable for the practical use of the electronic component using the metal microsphere as the connection terminal. Become.

It is a schematic diagram which shows an example of the manufacturing apparatus applied to the manufacturing method of the metal microsphere of this invention. It is a scanning electron micrograph which shows an example of the external appearance of the metal microsphere manufactured using this invention. It is a scanning electron micrograph which shows another example of the external appearance of the metal microsphere manufactured using this invention. It is a scanning electron micrograph which shows another example of the external appearance of the metal microsphere manufactured using this invention. It is a scanning electron micrograph which shows another example of the external appearance of the metal microsphere manufactured using this invention. It is a scanning electron micrograph which shows the external appearance of the metal microsphere produced as a comparative example.

  As described above, an important feature of the present invention is that a configuration in which the oxygen concentration in the atmosphere in which the Cu droplets are spherically solidified is adjusted to a predetermined range when the metal microspheres are manufactured.

In the present invention, the oxygen concentration in the atmosphere in which the Cu droplet is solidified spherically is 10 to 800 ppm by volume. When the oxygen concentration is lower than 10 ppm by volume, a remarkable dent appears on the surface of the metal microsphere due to shrinkage cavities during solidification shrinkage of the Cu droplet. The dents appearing on the surface cause problems such as generation of voids and poor plating adhesion when solder plating is performed on the surface of the metal microspheres.
Moreover, when the crystal grain size varies for each metal microsphere, there is a concern about variations in mechanical properties (strength, hardness, toughness, etc.) for each metal microsphere. When the oxygen concentration is lower than 120 ppm by volume, the crystal size of each metal microsphere may vary, and metal microspheres composed of large crystal grains and metal microspheres composed of small crystal grains are mixed. There is a case. For this reason, the oxygen concentration is preferably 120 ppm by volume or more in order to reduce the variation in crystal grain size for each metal microsphere and make the crystal grain size uniform. More preferably, it is 200 ppm by volume or more.

  On the other hand, when the oxygen concentration exceeds 800 ppm by volume, when the Cu droplet is solidified spherically, the entire surface of the droplet is thickly covered with an oxide film and is not a free surface. Thus, metal microspheres having good sphericity cannot be obtained. Therefore, in the present invention, by adjusting the oxygen concentration in the atmosphere in which the Cu droplets are spherically solidified to 10 to 800 ppm by volume, dents on the surface of the metal microspheres are suppressed, and metal microspheres having good sphericity are obtained. can get. Moreover, preferable oxygen concentration is 120-800 volume ppm, More preferably, it is 200-760 volume ppm.

  In the present invention, the remaining gas other than oxygen in the atmosphere in which Cu droplets are spherically solidified is an inert gas. The kind of the inert gas referred to in the present invention is a rare gas such as argon or nitrogen, and these are preferably used alone or in combination. Thereby, surface oxidation of Cu droplets can be suppressed, and metal microspheres having good sphericity can be obtained. Gases other than the inert gas referred to in the present invention are not preferable because they may react with contamination in the atmosphere and oxygen.

  In the present invention, it is preferable to solidify Cu droplets formed by applying pressure and vibration to the molten Cu and dropping from the orifice. By placing an orifice on the bottom of the crucible where the molten Cu is stored and applying pressure and vibration to the molten Cu inside the crucible, the molten Cu is stabilized in a gas atmosphere containing an appropriate amount of oxygen located at the bottom of the crucible through the hole in the orifice. Thus, Cu droplets having a desired volume can be formed.

  Moreover, when giving a vibration to Cu molten metal by this invention, the longitudinal vibration to the orifice passage direction of Cu molten metal is preferable. By applying longitudinal vibration to the molten Cu, it is possible to continuously drop a certain volume of Cu droplets. In addition, according to the present invention, metal microspheres having a more uniform diameter can be mass-produced by appropriately selecting the orifice hole diameter, the gas pressure for dropping the Cu molten metal, and the frequency of the longitudinal vibration applied to the Cu molten metal. Is possible.

  An example of the manufacturing method of the metal microsphere of this invention is demonstrated based on FIG. In FIG. 1, the molten Cu 6 melted in the crucible 1 using the heating unit 5 passes through the orifice 9 due to the differential pressure between the pressure in the crucible 1 generated by the crucible gas 7 and the pressure in the solidified atmosphere 8. Jets into the solidification chamber 3 to form a jet made of molten Cu. Before the molten Cu passes through the orifice 9, the vibrating member 10 is used to impart longitudinal vibration to the molten Cu in the direction of passing the orifice, whereby the jet made of the molten Cu changes from laminar flow to pulsating flow. The constriction produced as a pulsating flow develops due to the action of the surface tension of the molten Cu, and finally is divided into a single Cu droplet 11 at a period corresponding to the frequency of the longitudinal vibration applied to the molten Cu. The divided Cu droplet 11 falls into the solidification chamber 3 while being spheroidized by the action of its own surface tension and then solidified, and is collected in the collection can 13 as metal microspheres 4.

  In the present invention, Cu droplets fall in the gas atmosphere and solidify spherically to obtain metal microspheres. When the Cu droplets collide with each other before being completely solidified, agglomerated spheres having a volume composed of a plurality of droplets and deformed spheres having a series of spherical shapes are generated. To avoid this collision, the Cu droplets may be repelled by being charged and dropped in a dispersed state. Further, the collision of the Cu droplets may be avoided by dispersing the Cu droplets by the wind force generated by the fan or the jet pressure generated by gas injection.

  As for the pressure of the gas atmosphere in which Cu droplets solidify spherically, atmospheric pressure is appropriate, but it is preferable to appropriately adjust in the range of atmospheric pressure plus 0.2 MPa to minus 0.05 MPa. If the pressure of the gas atmosphere exceeds atmospheric pressure plus 0.2 MPa, a coagulation chamber that can withstand such pressure is required, leading to an increase in the weight of the apparatus and an increase in the cost of manufacturing the apparatus. preferable.

  In addition, if the pressure of the gas atmosphere is lower than atmospheric pressure minus 0.05 MPa, the inert gas molecules necessary for cooling and solidifying the Cu droplets are insufficient, and a long solidification chamber is required for solidification. An atmospheric pressure minus 0.05 MPa or more is preferable because it causes an increase in apparatus manufacturing cost.

FIG. 1 is a schematic cross-sectional view showing an example of a manufacturing apparatus applied to the method for manufacturing metal microspheres of the present invention.
Using the manufacturing apparatus of FIG. 1, a Cu piece having a purity of 99.99% by mass or more is charged into the crucible 1, and the molten Cu 6 melted in the crucible 1 using the heating unit 5 is added to the crucible gas 7. The generated pressure in the crucible 1 and the pressure in the coagulation atmosphere 8 were jetted from the orifice 9 into the coagulation chamber 3. At this time, before the Cu melt 6 passed through the orifice 9, the vibration member 10 was used to apply longitudinal vibration in the direction of passage of the orifice 9 to the Cu melt 6 to drop the Cu droplet 11.
And the solidification atmosphere in the solidification chamber 3 was adjusted with the gas displacement apparatus 2, and the metal microsphere 4 with a target diameter of 200 micrometers was produced on the manufacturing conditions shown below. At this time, the Cu droplet 11 formed by dropping from the orifice 9 is dropped in the coagulation chamber 3 while being dispersed by applying wind force from the fan 12, and is spheroidized and solidified by the action of its own surface tension. The microspheres 4 were collected in the collection can 13.

(Production conditions)
Cu metal piece input weight: 400 g
Solidification atmosphere: Argon Oxygen concentration in solidification atmosphere: 239 ppm by volume
Solidification atmosphere pressure: atmospheric pressure plus 0.02 MPa
Pressure in the crucible: atmospheric pressure plus 0.2 MPa
Temperature in crucible: 1300 ° C

  FIG. 2 shows a photograph of the surface state of the metal microspheres obtained under the above-described manufacturing conditions using a scanning electron microscope.

  Using the same production apparatus as in Example 1, metal microspheres having a target diameter of 200 μm were produced under the production conditions shown below.

(Production conditions)
Cu metal piece input weight: 509 g
Solidification atmosphere: Argon Oxygen concentration in solidification atmosphere: 656 volume ppm
Solidification atmosphere pressure: atmospheric pressure plus 0.01 MPa
Pressure in the crucible: atmospheric pressure plus 0.2 MPa
Temperature in crucible: 1330 ° C

  FIG. 3 shows a photograph of the surface state of the metal microspheres obtained under the manufacturing conditions described above, using a scanning electron microscope.

  Using the same production apparatus as in Example 1, metal microspheres having a target diameter of 200 μm were produced under the production conditions shown below.

(Production conditions)
Cu metal piece input weight: 2700 g
Solidification atmosphere: Argon Oxygen concentration in solidification atmosphere: 15, 50, 120, 200, 240, 310 volume ppm
Solidification atmosphere pressure: atmospheric pressure plus 0.01 MPa
Pressure in the crucible: atmospheric pressure plus 0.2 MPa
Temperature in crucible: 1250 ° C

  FIG. 4 shows a photograph of the surface state of the metal microspheres obtained under the manufacturing conditions described above, using a scanning electron microscope.

  Using the same production apparatus as in Example 1, metal microspheres having a target diameter of 200 μm were produced under the production conditions shown below.

(Production conditions)
Cu metal piece input weight: 2000 g
Solidification atmosphere: Nitrogen Oxygen concentration in solidification atmosphere: 16, 51 volume ppm
Solidification atmosphere pressure: atmospheric pressure plus 0.02 MPa
Pressure in the crucible: atmospheric pressure plus 0.1 MPa
Temperature in crucible: 1250 ° C

  FIG. 5 shows a photograph of the surface state of the metal microspheres obtained under the manufacturing conditions described above, using a scanning electron microscope.

Comparative example

  As a comparative example, using the same production apparatus as in Example 1, metal microspheres having a target diameter of 200 μm were produced under the production conditions shown below, with the oxygen concentration in the solidification atmosphere set lower than the range of the present invention.

(Production conditions)
Cu metal piece input weight: 482 g
Solidification atmosphere: Argon Oxygen concentration in solidification atmosphere: 7 ppm by volume
Solidification atmosphere pressure: atmospheric pressure plus 0.01 MPa
Pressure in the crucible: atmospheric pressure plus 0.2 MPa
Temperature in crucible: 1330 ° C

  FIG. 6 shows a photograph of the surface state of the metal microspheres obtained under the manufacturing conditions described above, using a scanning electron microscope.

As shown in FIGS. 2 to 5, in the metal microsphere to which the present invention is applied, the dent appearing on the surface of the metal microsphere is significantly reduced as compared with FIG. 6 which is a comparative example. Therefore, by applying the method for producing metal microspheres of the present invention, it is possible to reduce the dents generated on the surface of the metal microspheres and to produce metal microspheres having surface smoothness characteristics.
Sample numbers 4 to 6 in FIG. 4 are metal microspheres manufactured in a solidified atmosphere with an oxygen concentration of 200 ppm by volume or more. Compared with sample numbers 1 to 3, the crystal grain size for each metal microsphere is shown in FIG. It was confirmed that the variation in the thickness was reduced, the crystal grain size was uniformly refined, and the surface morphology was more favorable.
Thus, metal microspheres with surface smoothness characteristics can reduce the possibility of causing problems such as voids and poor plating adhesion when solder plating is performed on the surface. The electrical connection reliability can be greatly improved when the electronic component used as the connection terminal portion is put into practical use.

By adopting a configuration in which the oxygen concentration in the atmosphere in which the Cu droplets are spherically solidified is adjusted to a predetermined range, the method for producing the metal microspheres of the present invention, in which the surface smoothness is greatly improved, Metal microspheres suitable for use in electrical wiring, and it is possible to improve the electrical connection reliability and the dimensional accuracy in the multilayered wiring board when the wiring board is multi-layered and the connection terminal part is miniaturized. Become.
In addition, in the method for producing a metal sphere in which metal droplets are spherically solidified in a gas atmosphere, the method can be applied to the production of metal spheres other than Cu having excellent surface smoothness by adjusting the oxygen concentration in the atmosphere to be spherically solidified. .

  1. Crucible, 2. 2. gas displacement device; Coagulation chamber; 4. 4. metal microspheres; 5. heating unit; 6. Cu melt, Gas for crucible, 8. 8. solidification atmosphere; Orifice, 10. 10. vibration member; Cu droplet, 12. Fan, 13. Collection can

Claims (6)

  A method for producing metal microspheres, characterized in that Cu droplets are spherically solidified in an atmosphere of oxygen: 10 to 800 ppm by volume and the remaining inert gas.   The said oxygen is 120-800 volume ppm, The manufacturing method of the metal microsphere of Claim 1 characterized by the above-mentioned.   The said oxygen is 200-760 volume ppm, The manufacturing method of the metal microsphere of Claim 1 characterized by the above-mentioned.   The method for producing metal microspheres according to claim 1, wherein the inert gas is argon.   The method for producing metal microspheres according to claim 1, wherein the inert gas is nitrogen.   The method for producing metal microspheres according to any one of claims 1 to 5, wherein the Cu droplet is formed by dropping a molten Cu to which pressure and vibration are applied from an orifice.