Method of manufacturing fine metal particles, substance containing fine metal particles, and paste solder composition

Abstract

There is provided an in-oil atomization method wherein a solder is fused and dispersed in a heated particle dispersion medium, the method being featured in that even if the quantity of the particle dispersion medium to be employed is relatively small, fine solder particles can be effectively obtained. Namely, this invention provides a method of manufacturing fine particles, wherein solder is fused in the heated particle dispersion medium to obtain a molten solder, which is then dispersed by means of an agitator to obtain molten solder particles which are subsequently cooled and solidify, the method being characterized in that the above dispersing step is performed in the presence of a particle coalescence-preventing agent. This invention also provides a fine metal particles-containing substance and a paste solder composition.

What is claimed is:  
     
         1 . A method of manufacturing fine metal particles, which comprises the steps of: 
 dispersing molten metal particles in a dispersion medium by way of a process wherein a low melting point metal containing at least 10% by mass of tin and selected from metals excluding alkali metals is mixed with the dispersion medium to obtain a mixture which is subsequently heated to melt the low melting point metal, and a dispersing energy is applied to the dispersion medium to disperse the low melting point metal in the dispersion medium to obtain a molten metal particle-dispersed substance; and    forming solid particles having an average particle diameter of 15 μm or less by cooling the molten metal particle-dispersed substance to thereby solidify the molten metal particles;    wherein said step of dispersing molten metal particles in a dispersion medium and said step of forming solid particles are preceded by a step of mixing the dispersion medium with a particle coalescence-preventing agent which is capable of adsorbing onto and/or reacting with at least the molten metal particles and also capable of preventing the generation of coalescence at least among the molten metal particles, said particle coalescence-preventing agent being selected from the group consisting of rosin and/or derivatives thereof, tin salts of rosin and/or derivatives thereof, fatty acids, tin salts of fatty acids, organic acids and tin salts of organic acids.    
     
     
         2 . The method of manufacturing fine metal particles according to  claim 1 , wherein said particle coalescence-preventing agent is rosin and/or a derivative thereof.  
     
     
         3 . The method of manufacturing fine metal particles according to  claim 1 , wherein said particle coalescence-preventing agent is rosin soap.  
     
     
         4 . The method of manufacturing fine metal particles according to  claim 1 , wherein said particle coalescence-preventing agent is a tin salt of an organic acid having a carboxyl group.  
     
     
         5 . The method of manufacturing fine metal particles according to any one of  claims 1  to  4 , which further comprises a step of removing the solidified metal particles obtained in said step of forming solid particles from said dispersion medium, thereby leaving a residual liquid, which is then recycled as a particle dispersion medium.  
     
     
         6 . The method of manufacturing fine metal particles according to any one of  claims 1  to  4 , wherein the low melting point metal is employed at a ratio of 0.1-100 g per 100 g of the dispersion medium, and the particle coalescence-preventing agent is employed at a ratio of 0.01-100 g per 100 g of the dispersion medium.  
     
     
         7 . The method of manufacturing fine metal particles according to any one of  claims 1  to  4 , wherein the application of said dispersing energy to the dispersion medium is performed by making use of a high-speed agitator comprising a cup-shaped stator having slits in the sidewall thereof, and a rotator mounted inside the stator and having a rotary vane, wherein a fluid material is permitted to be introduced through said slits into said stator, in which the fluid material is subjected to a high shearing force through an interaction between said stator and said rotator by actuating said rotator to rotate at a high speed relative to said stator, the fluid material being subsequently discharged from the stator.  
     
     
         8 . The method of manufacturing fine metal particles according to  claim 7 , wherein the number of revolutions of the high-speed agitator is at least 5000 per minute, and the temperature of said heating is at least 10° C. higher than the melting point of the low melting point metal.  
     
     
         9 . The method of manufacturing fine metal particles according to any one of  claims 1  to  4 , wherein the low melting point metal is employed at a ratio of 0.1-100 g per 100 g of the dispersion medium, the particle coalescence-preventing agent is employed at a ratio of 0.01-10 g per 100 g of the dispersion medium, and the application of said dispersing energy to the dispersion medium is performed by making use of a high-speed agitator comprising a cup-shaped stator having slits in the sidewall thereof, and a rotator mounted inside the stator and having a rotary vane, wherein a fluid material is permitted to be introduced through said slits into said stator, in which the fluid material is subjected to a high shearing force through an interaction between said stator and said rotator by actuating said rotator to rotate at a high speed relative to said stator, the fluid material being subsequently discharged from the stator.  
     
     
         10 . The method of manufacturing fine metal particles according to any one of  claims 1  to  4 , wherein the low melting point metal is employed at a ratio of 0.1-100 g per 100 g of the dispersion medium, the particle coalescence-preventing agent is employed at a ratio of 0.01-10 g per 100 g of the dispersion medium, and the application of said dispersing energy to the dispersion medium is performed by making use of a high-speed agitator comprising a cup-shaped stator having slits in the sidewall thereof, and a rotator mounted inside the stator and having a rotary vane, wherein a fluid material is permitted to be introduced through said slits into said stator, in which the fluid material is subjected to a high shearing force through an interaction between said stator and said rotator by actuating said rotator to rotate at a high speed relative to said stator, the fluid material being subsequently discharged from the stator, and the number of revolution of the high-speed agitator is at least 5000 per minute, and the temperature of said heating is at least 10° C. higher than the melting point of the low melting point metal.