Patent Publication Number: US-2011064604-A1

Title: Particulate tin power and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2009-0085899 filed with the Korea Intellectual Property Office on Sep. 11, 2009, the disclosure of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to particulate tin powder and a manufacturing method thereof. More particularly, the present invention relates to a method of manufacturing particulate tin powder that extracts the particulate tin powder by adding reductant to tin-salt adding complexing agents and particulate in powder manufactured thereby. 
     2. Description of the Related Art 
     World countries are commonly recognize the seriousness which wastes of electronic products that rapidly increase with development of an electronics industry give to an environment and legal regulation for toxic elements is in progress. It is not too much to say that securing a clean technology in a mounting technology part based on a semiconductor and the electronics industry is connected directly with survival of our industries, in a series of international regulation movements. 
     In particular, solder powder is widely used as configuration powder of a conductive adhesive used for via-hole charging on a multilayer printed wiring board or at the time of mounting IC components, etc. on a printed wiring board. As known soldering, eutectic soldering of tin of 63 w % and plumbum of 37 w % has been primarily used. 
     However, plumber which is contained in components of home appliances represented as a Braun tube of a television and other electronic apparatuses is a cause of environmental pollution including causing water pollution, etc., such that a so-called lead-free soldering material is generally used in mounting in order to reduce the total amount of plumber contained in the home appliance. 
     That is, although a Sn—Pb soldering component has been primarily used in the related art, a usage cost or a waste cost of a solder containing plumbum is increased day by day due to groundwater contamination generated by eluting plumbum components when the plumbum components are wasted and buried, restriction or prevention in using plumbum in a developed country, plumbum using company&#39;s economical sanction or tax imposing as an environmental concern is increased worldwide as described above, such as at the present, the lead-free soldering material is primarily used. 
     Soldering powder, etc. is configured by metallic particulate powder and a method for preparing the metallic particulate powder includes a mechanical grinding method, an atomization process, a gas phase reduction method, a gas evaporation method, etc., but the atomization process is generally used to prepare the soldering powder or tin powder configuring the soldering powder. 
     The atomization process prepares the tin powder by atomizing solution containing metal such as tin, etc., using the atomization solution as individual droplets, and cooling the droplet, a solder powder forming device ( FIG. 1 ) using the atomization process includes a metal melting unit  10  melting tin (Sn) metal having a lump form, a powder forming unit  20  forming soldering melting metal (hereinafter, referred to as “molten metal”) discharged from the metal melting unit  10  as solder paste powder (hereinafter, referred to as “powder”), and a collection tank  30  collecting solder paste powder, a switch  40  which is a ball valve or a throttle valve for maintaining airtightness by blocking air in the powder forming unit  20  at the time of exchanging the collection tank  30 . The powder forming unit  20  includes an atomizer  23  a high-speed motor  23   b  that rotates at high speed is fixed to a lower center of a chamber  21  by a support  23   c  and a rotation disk  23   a  crushing and forming the melting metal dropped while being installed on a rotation shaft of the high-speed motor  23   b  by using centrifugal force as powder. 
     An operation process will be described in brief by a spraying device having the above-mentioned configuration. First, when the soldering metal having the lump form is inputted into the chamber  21  under a vacuum state and melted, such that the melting metal is formed, the formed melting metal is discharged in a certain amount through a nozzle by using a tundish  22 . The discharged melting metal is dropped to the rotation disk  23   a  that rotates at high speed of approximately 20,000 to 35,000 rpm by the high-speed motor  23   b  of the atomizer  23  and crushed into small particles by the centrifugal force to be formed as powder. The powder is cooled by a cooler  24  installed on the outer periphery of the chamber  21  and thereafter, is collected in the collection tank  30  through the switch  40 . 
     The soldering powder or tin powder acquired in the preparation method has an advantage in that dispersibility of separation is excellent by comparing the soldering powder or tin powder with powder acquired in other preparation methods such as a wet method, but has a disadvantage in that particle size distribution is extremely wide, a limit of the particle size distribution is generally in the range of 1 um to 10 um, and particulate powder having 5 um or less is difficult to acquire. 
     Since via-hole leveling of a multilayer print wiring board is deteriorated and a particle diameter is large at the time of using large-sized powder prepared by the above-mentioned atomization method, sinterbility is deteriorated at low temperature, thereby degrading reliability. Further, in recent years, as a pitch size of the multilayer print wiring board is also decreased to 50 um or less due to a decrease in weight and size of electronic apparatuses, problems caused at the time of using the large-sized powder will rise more severely. 
     Further, although a method for preparing the soldering metal powder such as tin, etc. using the existing wet method includes a method using a substitution wet method or a method for preparing colloidal solution containing tin power by reducing tin components from organic solvent, these methods have a disadvantage in that an additional separation process is required, such that a process is complicated and a manufacturing cost is high to acquire a large amount of tin powder and another advantage in that it is difficult to acquire tin powder particulates having high purity while having a means particle size of 1 μm or less and narrow particle distribution. 
     As a result, the inventor has invented particulate tin power having narrow particle size distribution and high purity, which is a particulate having reliability enough to for a minute circuit or charge a via-hole having a minute diameter as well as the process is simple and economical without requiring an additional separation process or substitution process and a manufacturing method thereof. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide particulate tin powder which has a simple manufacturing process and is economical, and a manufacturing method thereof without requiring an additional separation process or substitution process. 
     It is, therefore, another object of the present invention to provide particulate tin powder having narrow particle size distribution and high purity, which is a particulate having reliability enough to form a minute circuit and fill a via-hole having a minute diameter, and a manufacturing method thereof. 
     In order to achieve the above-mentioned object, in accordance with one aspect of the present invention, there is a method of manufacturing particulate tin powder including i) preparing tin salt solution, ii) adding chelating agents to the tin salt solution, iii) adjusting pH of the tin salt solution to which the chelating agents are added, and iv) reductively depositing tin powder by adding reductant to the tin salt solution. 
     Further, the present invention provides the method of manufacturing particulate tin powder wherein the concentration of the tin salt solution is 0.01 to 5 mol/L and the tin salt solution is composed of SnCl 2 , SnSO 4 , SnI 2 , SnF 2  SnBr 2 , Na 2 SnO 3 , or SnCH 3 SO 3  solution. 
     Further, the present invention provides the method of manufacturing particulate tin powder wherein the concentration of the chelating agents is 0.05 to 15 mol/L and the chelating agents are composed of nitrogen (N) or oxygen (O) containing compound or the chelating agents are composed of thiourea or thiourea derivatives. 
     In addition, the present invention provides the method of manufacturing particulate tin powder wherein the reductant is composed of boron (B), phosphorus (P), or nitrogen (N) containing compound or the reductant is composed of sulfide, disulfide, or thiol. 
     In order to achieve the above-mentioned object, in accordance with another aspect of the present invention, there is particulate tin powder manufactured by a manufacturing method including i) preparing tin salt solution, ii) adding chelating agents to the tin salt solution, iii) adjusting pH of the tin salt solution to which the chelating agents are added, and iv) reductively depositing tin powder by adding reductant to the tin salt solution. 
     Further, the present invention provides the particulate tin powder wherein the purity of the tin powder is equal to or larger than 95%, a mean particle size (Dv50) of the tin powder is equal to or smaller than 1 μm, and the particle size distribution of the tin powder is 0.1 to 5 μm. 
     In accordance with an embodiment of the present invention, through a method of manufacturing particulate tin powder can be acquired particulate tin powder having narrow particle size distribution and high purity, which is a particulate having reliability enough to form a minute circuit and fill a via-hole having a minute diameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a partial cut perspective view of an apparatus for preparing solder paste powder by a centrifugal atomization process; 
         FIG. 2  is an SEM photograph of particulate tin powder in accordance with a manufacturing method of the present invention; 
         FIG. 3  is a graph showing an EPMA qualitative analysis result of particulate tin powder in accordance with a manufacturing method of the present invention; and 
         FIG. 4  is a graph showing a thermal analysis (DSC) melting point analysis result of particulate tin powder in accordance with a manufacturing method of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERABLE EMBODIMENTS 
     Particulate tin powder and a manufacturing method thereof in accordance with the present invention will be now described in detail with reference to the accompanying drawings. 
       FIG. 1  is a partial cut perspective view of an apparatus for preparing solder paste powder by a centrifugal atomization process,  FIG. 2  is an SEM photograph of particulate tin powder in accordance with a manufacturing method of the present invention,  FIG. 3  is a graph showing an EPMA qualitative analysis result of particulate tin powder in accordance with a manufacturing method of the present invention, and  FIG. 4  is a graph showing a thermal analysis (DSC) melting point analysis result of particulate tin powder in accordance with a manufacturing method of the present invention. 
     A method of manufacturing particulate tin powder in accordance with the present invention includes i) preparing tin salt solution, ii) adding chelating agents to the tin salt solution, iii) adjusting pH of the tin salt solution to which the chelating agents are added, and iv) reductively depositing tin powder by adding reductant to the tin salt solution. 
     At the first step, tin salt solution may be all kinds of tin salt solution which is commercially usable such as SnCl 2 , SnSO 4 , SnI 2 , SnF 2  SnBr 2 , Na 2 SnO 3 , or SnCH 3 SO 3  and the concentration of tin salt solution is preferably 0.01 to 5 mol/L in order to reductively deposit particulate tin powder having high purity. 
     Meanwhile, at the second step, chelating agents for forming tin ions in tin salt solution manufactured at the first step and chelates are added. The chelating agents may use all kinds of tin salt solution which is commercially usable such as triethanolamine (TEA), tartrate, cyanide, malonate, citrate, nitrilotriacetate, pyrocatecol, EDTA, etc. Preferably, chelating agents may be used which are composed of nitrogen (N) or oxygen (O) containing compound providing unshared electron pairs or thiourea or thiourea derivative. 
     Further, depending on the kind and density of the used tin salt solution, chelating agents of an appropriate amount may be added and preferably, chelating agents having a density 0.05 to 15 mol/L may be added. 
     At the third step, in order to reductively depositing tin ions forming chelates with the added chelating agents, the tin salt solution should be adjusted with appropriate pH by adding acid or base such as NaOH or HCl so that reductant reacts. 
     At the fourth step, tin powder is finally deposited without an additional separation process by adding the reductant to tin salt solution adjusted with appropriate pH where the reductant can operate. The reductant may adopt all kinds of tin salt solution which can be commercially used such as formaldehyde (HCHO), hypophsphites (H 2 PO 2 ), hytrazine (N 2 H 4 ), dimethylamine borane (DMAB), sodium boron hydride (NaBH 4 ), SPS (bis-3 sulfopropyl disulfide), etc. Preferably, the reductant may be composed of boron (B), phosphorus (P), or nitrogen (N) containing compound or may be composed of sulfide, disulfide, or thiol. 
     At this time, reaction temperature can be adjusted for each reducing agent at room temperature to 80° C. 
     The particulate tin powder finally manufactured by the manufacturing method i) preparing tin salt solution, ii) adding chelating agents to the tin salt solution, iii) adjusting pH of the tin salt solution to which the chelating agents are added, and iv) reductively depositing tin powder by adding reductant to the tin salt solution has high purity of 95% or higher. 
     Further, the reductively deposited tin powder has a spherical particulate shape and narrow particle size distribution and preferably, a particulate shape having a mean particle size (Dv50) of 1 μm or less and narrow particle size distribution of 0.1 to 5 μm. 
     Hereinafter, an embodiment of a method for manufacturing particulate tin powder in accordance with the present invention will be described. 
     Embodiment 
     After tin(II) methane sulfonate solution of 0.35 mol/L is manufactured and agitated, thiourea of 1 mol/L is added and agitated. Tin salt solution to which thiourea is added is adjusted to pH of 1 to 2 by using HCL and thereafter, agitated. Tin is finally reductively deposited by slowly adding NaS2O4 (sodium dithionite) which is disulfide of 0.03 mol/L to tin salt solution of which pH is adjusted. 
     As a result of analyzing particle sizes of particulates of finally deposited particulate tin powder by using the MSS instrument of Malvern Instruments Ltd. as shown in  FIG. 2 , a mean particle size (Dv50) is 0.58 um and particle size distribution is in the range of 0.1 um to 5 um. Further, it is verified that particulate tin powder deposited through SEM is a spherical particulate tin particle. 
     In addition, it is verified that the deposited particulate tin powder is composed of Sn and O through the EPMA analysis result of  FIG. 3  (however, C is an analysis pre-processing coating and carbon tape component) and as a result of thermal analysis (DSC) for verifying pure tin particles (mp. 210° C.) or tin oxide particles (mp. 1080° C.), it is verified that the deposited particulate tin powder is pure tin particles having a melting point of approximately 214° C. 
     By applying the method of manufacturing the particulate tin powder using the reduction wet method in accordance with the present invention, it is possible to manufacture pure particulate tin powder having a mean particle size of approximately 0.5 um which could not be acquired by the known method (atomization method). 
     Accordingly, it is possible to acquire the particulate tin powder having narrow particle size distribution and high purity by improving via-hole leveling of a multilayer print wiring board and improving sinterbility at low temperature by atomizing the particle diameter to solve a problem in that reliability is deteriorated through the method of manufacturing the particulate tin powder. 
     As described above, although the preferable embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that substitutions, modifications and changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.