JP2007314852A - Silver powder and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silver powder which is used for a through-hole paste, for a baking paste and as a filler for radiating heat, and can be filled in a high concentration without degrading printing characteristics. <P>SOLUTION: The silver powder is uniformly coated with a fatty acid of 0.01 to 0.3 wt.%, contains both of spherical and discal particles with an average particle size of 3 to 10 μm, and has a tap density of 6.0 g/cm<SP>3</SP>or more. The preferred production method comprises the steps of: adding the fatty acid of 0.01 to 0.3 wt.% to spherical silver powders with an average particle size of 2.5 to 8 μm; and physically forming the silver powders into a discal shape by using a mill and a spherical medium with a size of 1/16 to 1/4 inch, while coating the silver powders with the fatty acid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a silver powder for conductive paste and a silver powder for heat dissipation in the field of mounting electronic components. Specifically, the present invention provides a silver powder having a large tap density value and a method for producing the same, which shows optimum performance as a through hole, a fired paste, and a high heat dissipation filler filled with silver powder at a higher level.

  Conventional silver powders are spherical, dendritic and granular silver powders obtained by methods such as atomization, electrolysis and wet reduction. For paints or pastes, flaky silver powder obtained by mechanically processing silver powder is used for reasons such as smoothness of the coating film, good printability, and slow sedimentation.

  However, in order to improve more stable conductive performance or solder wettability as an electrode material as silver powder for through-hole paste and fired paste, it is necessary to increase the content of silver powder in the paste component.

  However, with conventional flat silver powder, when the silver powder content in the paste component is increased by a certain amount or more, the fluidity of the paste itself deteriorates, resulting in defects such as inability to print. Spherical silver powder can be highly filled, but has poor printability, cannot be printed, and has a very poor coating appearance. Furthermore, there is a demand for highly filled silver powder in the development of a high heat dissipation material that releases heat generated from electronic components in recent years.

The spherical silver powder by the atomization method is suitable for producing a powder having a large tap density value. Average tap density value in particle size 2.5μm spherical silver powder 4.8 g / cm ^3, with a tap density value 5.3 g / cm ³ with an average particle size of 5 [mu] m, a tap density value 5.5 g / cm ³ more silver powder There is no.

Silver powder of the electrolytic method or wet reduction method has a small tap density value of about 2 g / cm ³ . The flake silver powder has a tap density value of about 4 g / cm ³ , but the tap density value of 5.6 g / cm ³ is the highest even in the high filling type. A silver powder having a tap density value of 6.0 g / cm ³ or more is required in order not to deteriorate the printing characteristics even if the polymer is highly filled with silver powder, but it has not been obtained yet.

  However, a method for producing a silver powder having an apparent density of 0.01 to 0.5 g / cm 3 and a very bulky conductive material for a conductive paste or the like has been proposed (for example, see Patent Document 1). Silver powder is difficult to use as a through hole, a fired paste, and a heat dissipation that require high filling.

Japanese Patent No. 3168023

  As a result of examining the surface treatment, particle size, and particle shape of silver powder, the present invention solves the problem of printability by providing silver powder with a large tap density value, and achieves high filling. It is an object to provide a paste.

The present invention was made for the purpose of solving such conventional problems, and a spherical powder having an average particle diameter of 3 to 10 μm, in which 0.01 to 0.3% by weight of a fatty acid is uniformly coated on silver powder. a disk-shaped particles are mixed, the tap density value as characterized in that 6.0 g / cm ³ or more, to achieve a silver powder be highly filled in the polymer does not deteriorate the printing characteristics.

As a result of research on silver powder that does not deteriorate printability even when high-filled silver powder is filled into the polymer as a through-hole paste, fired paste, and heat dissipation filler, there is a correlation with the tap density value of the silver powder. It has been found that the density value should be 6.0 g / cm ³ or more.

  The silver powder of the present invention needs to coat all spherical and discotic silver powder particles with a fatty acid. If it is uncoated silver powder, the packing density cannot be increased. The amount of oil or fat to be coated needs to be changed depending on the particle diameter, but is preferably 0.01 to 0.3% by weight based on the silver powder. If the amount is too small, the density will not increase. If the amount is too large, the fluidity is poor and the packing density does not increase.

The average particle size of the silver powder is 3 to 10 μm, which is the optimum particle size that can be highly filled by the method of the present invention as a through-hole paste, a fired paste, and a heat dissipation filler. Even finer or larger than this, silver powder having a tap density value of 6.0 g / cm ³ or more cannot be produced.

  As a method for producing the silver powder of the present invention, 0.01 to 0.3% by weight of a fatty acid is added to a spherical silver powder having an average particle size of 2.5 to 8 μm, and a 1/16 to 1/4 inch spherical medium is formed. It can be manufactured by using a pulverizer to form a disk while physically coating the fatty acid on the silver powder.

  When spherical silver powder is processed with a ball mill or agitator arm pulverizer using spherical steel balls of 1/16 to 1/4 inch and ceramic balls as pulverizing media, the fine particles of spherical silver powder remain spherical without being subjected to the stress of the pulverizing media Large particles are processed into a disk shape.

As a result, the obtained silver powder is filled between disk-shaped silver powders having large spherical particles, and a silver powder having a tap density value of 6.0 g / cm ³ or more is obtained.

  The fatty acid is preferably a higher fatty acid such as myristic acid, palmitic acid or stearic acid. The amount of fatty acid, the size of the grinding medium, the number of rotations and the time for grinding force can be changed within the scope of the present invention depending on the particle diameter of the silver powder to be ground and the target tap density value.

As a method of obtaining the silver powder of the present invention other than the method of the present invention, a spherical silver powder coated with a fatty acid and a disc-shaped silver powder coated with a fatty acid are blended separately, and the tap density value is 6.0 g / cm ³ or more. It is possible to do this, but it is not industrial.

  By obtaining a silver powder having a large tap density value, the silver powder of the present invention can be printed without deteriorating the printing characteristics even when the content of the silver powder in the paste component is increased. This makes it possible to use as a filler for through-hole paste, fired paste, or high heat dissipation, which has been difficult to use until now. In addition, since the spherical and discoidal particles are mixed, the printing characteristics are dramatically improved, and the dispersibility is improved because the fatty acid is uniformly coated on the silver powder.

  In the silver powder and the production method of the present invention, 0.01 to 0.3% by weight of a fatty acid is added to a spherical silver powder having an average particle diameter of 2.5 to 8 μm, and a spherical medium of 1/16 to 1/4 inch is used. Then, a high-filled silver powder having a large tap density value can be obtained by performing disk-like processing while physically coating the silver powder with fatty acid using a pulverizer. The configuration of the present invention will be described in detail as follows.

Example 1.

2 g of stearic acid was added to 1 kg of spherical silver powder having an average particle diameter of 2.5 μm and a tap density value of 4.8 g / cm ³ , and charged into a medium stirring mill. Disc processing was performed for 10 hours at a mill rotation speed of 40 rpm with 10 kg of spherical steel balls having a diameter of 1/16 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 3 μm and a tap density value of 6.2 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Example 2

1 g of stearic acid was added to 1 kg of spherical silver powder having an average particle diameter of 5.0 μm and a tap density value of 5.3 g / cm ³ , and charged into a medium stirring mill. Disc processing was performed for 5 hours at a mill rotation speed of 40 rpm with 10 kg of spherical steel balls having a diameter of 1/8 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 6.5 μm and a tap density value of 6.5 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Example 3

To 1 kg of spherical silver powder having an average particle size of 8.0 μm and a tap density value of 5.4 g / cm ³ , 0.2 g of stearic acid was added and put into a medium stirring mill. Disc processing was performed for 5 hours at a mill rotational speed of 40 rpm with a spherical steel ball having a diameter of 1/4 inch as a grinding medium. As a result, a disc-shaped silver powder coated with a fatty acid having an average particle size of 10.0 μm in which spherical and disc-shaped particles are mixed and a tap density value of 6.2 g / cm ³ was obtained.

Example 4

0.1 g of stearic acid was added to 1 kg of spherical silver powder having an average particle size of 8.0 μm and a tap density value of 5.4 g / cm ³ , and charged into a medium stirring mill. Disc processing was performed for 10 hours at a mill rotational speed of 40 rpm with 10 kg of spherical steel balls having a diameter of 1/8 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 9.5 μm and a tap density value of 6.5 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Example 5 FIG.

3 g of stearic acid was added to 1 kg of spherical silver powder having an average particle diameter of 2.5 μm and a tap density value of 4.8 g / cm ³ , and charged into a medium stirring mill. Disc processing was performed for 5 hours at a mill rotation speed of 40 rpm with 10 kg of spherical steel balls having a diameter of 1/8 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 3.5 μm and a tap density value of 6.0 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Example 6

1 g of spherical silver powder having an average particle diameter of 5.0 μm and a tap density value of 5.3 g / cm ³ was added to 1 kg of palmitic acid, and the mixture was put into a medium stirring mill. Disc processing was performed for 5 hours at a mill rotation speed of 40 rpm with 10 kg of spherical steel balls having a diameter of 1/8 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 6.6 μm and a tap density value of 6.4 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Example 7

1 g of myristic acid was added to 1 kg of spherical silver powder having an average particle size of 5.0 μm and a tap density value of 5.3 g / cm ³ , and charged into a medium stirring mill. Disc processing was performed for 5 hours at a mill rotation speed of 40 rpm with 10 kg of spherical steel balls having a diameter of 1/8 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 6.5 μm and a tap density value of 6.6 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Example 8 FIG.

0.5 g of stearic acid was added to 1 kg of spherical silver powder having an average particle diameter of 5.0 μm and a tap density value of 5.3 g / cm ³ , and charged into a medium stirring mill. Disc processing was performed for 5 hours at a mill rotation speed of 40 rpm with 10 kg of spherical steel balls having a diameter of 1/8 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 6.2 μm and a tap density value of 6.8 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Example 9

0.5 g of stearic acid was added to 1 kg of spherical silver powder having an average particle diameter of 5.0 μm and a tap density value of 5.3 g / cm ³ , and charged into a medium stirring mill. Disc processing was performed at a mill rotational speed of 40 rpm for 5 hours at 10 kg of spherical ceramic balls having a diameter of 1/8 inch as a grinding medium. As a result, a disc-like silver powder coated with a fatty acid having an average particle size of 6.1 μm and a tap density value of 6.3 g / cm ³ in which spherical and disc-like particles are mixed was obtained.

Comparative Example 1

90% by weight of spherical silver powder having an average particle diameter of 5.0 μm and a tap density value of 5.4 g / cm ³ and 10% by weight of high-density flaky silver powder having a tap density value of 5.6 g / cm ³ were put into a mixer and mixed. . As a result, a silver powder having a tap density value of 5.5 g / cm ³ was obtained, and a silver powder having a tap density value of 6.0 g / cm ³ or more was not obtained.

Comparative Example 2

50% by weight of spherical silver powder having an average particle size of 5.0 μm and a tap density value of 5.4 g / cm ³ and 50% by weight of high-density flaky silver powder having a tap density value of 5.6 g / cm ³ were put into a mixer and mixed. . As a result, although spherical and flake shaped particles were mixed, the tap density value was 5.6 g / cm ³ silver powder, and no silver powder having a tap density value of 6.0 g / cm ³ or more was obtained.

Comparative Example 3

90% by weight of spherical silver powder having an average particle diameter of 5.0 μm and a tap density value of 5.4 g / cm ³ and 10% by weight of high-density flaky silver powder having a tap density value of 5.6 g / cm ³ were put into a mixer and mixed. . As a result, although spherical and piece-like particles were mixed, the tap density value was a silver powder having a tap density value of 5.8 g / cm ^{3, and} a silver powder having a tap density value of 6.0 g / cm ³ or more was not obtained.

  By obtaining a silver powder having a large tap density value, the silver powder of the present invention can be printed without deteriorating the printing characteristics even when the content of the silver powder in the paste component is increased. This makes it possible to use as a filler for through-hole paste, fired paste, or high heat dissipation, which has been difficult to use until now. In addition, since the spherical and discoidal particles are mixed, the printing characteristics are dramatically improved, and the dispersibility is improved because the fatty acid is uniformly coated on the silver powder.

  Therefore, it can be said that the industrial applicability of the present invention is very high.

Claims (3)

A silver powder having a tap density value of 6.0 g / cm ³ or more, in which spherical and disk-shaped particles having an average particle diameter of 3 to 10 μm uniformly coated with a fatty acid are mixed.   2. The silver powder according to claim 1, wherein 0.01 to 0.3% by weight of fatty acid is uniformly coated on the spherical and discotic silver powder with respect to the silver powder. 3. In producing the silver powder according to claim 1 or 2, 0.01 to 0.3% by weight of a fatty acid is added to a spherical silver powder having an average particle size of 2.5 to 8 μm, and a spherical shape of 1/16 to 1/4 inch is added. A method for producing a silver powder, characterized in that a medium is used to physically coat a fatty acid with a pulverizer and perform a disk-like process.