High capacitance tantalum flakes and methods of producing the same

Abstract

Methods of maximizing a tantalum capacitor's capacitance are disclosed, as well as tantalum flake powder and anodes. A two step milling process can be used to mill tantalum particles into tantalum flake powder having flakes of the desired thickness. This flake powder can then be pressed and sintered thereby forming an anode. Other flake capacitance methods and products are also described.

1 . Tantalum flake powder, wherein the thickness of said flakes is an average flake thickness within ±200% of a primary flake thickness, wherein said primary flake thickness=2.5KoKta/(Dta*Kf)*1/CV, wherein CV=2.5KoKta/(Dta*2Kf)*1Nf and wherein Ko=vacuum permittivity, Kta=dielectric constant, Dta=density of tantalum material, Kf=formation constant (dielectric thickness per volt), CV=μFV/g and Vf=voltage of formation, wherein Vf is from about 6 volts to about 500 volts.  
     
     
         2 . The tantalum flake powder of  claim 1 , wherein said average thickness is within ±50% of said primary flake thickness.  
     
     
         3 . The tantalum flake powder of  claim 1 , wherein said average thickness is within ±10% of said primary flake thickness.  
     
     
         4 . The tantalum flake powder of  claim 1 , wherein said average thickness is within ±100% of said primary flake thickness.  
     
     
         5 . An anode comprising the tantalum flake powder of  claim 1 .  
     
     
         6 . An anode comprising the tantalum flake powder of  claim 2 .  
     
     
         7 . A capacitor comprising the anode of  claim 5 .  
     
     
         8 . A capacitor comprising the anode of  claim 6 .  
     
     
         9 . A tantalum flake powder having a unimodal flake thickness distribution is from 0.02 micron to 4 microns.  
     
     
         10 . The tantalum flake powder of  claim 9 , wherein said tantalum flake powder has a flake thickness distribution, wherein T 50  is from about 0.08 micron to about 1 micron, T 10  is about −100% of T 50 , and T 90  is about ±100% of T 50 .  
     
     
         11 . An anode comprising the tantalum flake powder of  claim 9 .  
     
     
         12 . A capacitor comprising the anode of  claim 11 .  
     
     
         13 . A tantalum flake powder having a flake thickness distribution, wherein T 50  is from about 0.6 micron, T 10  is about −100% of T 50 , and T 90  is about +100% of T 50 .  
     
     
         14 . The tantalum flake powder of  claim 13 , wherein said capacitance is from about 37,000 to about 39,000 CV/g when formed at a formation voltage of 50V, and sintered at a temperature of from about 1300° C. to about 1400° C. for ten minutes and at a formation temperature of 90° C.  
     
     
         15 . The tantalum flake powder of  claim 1 , wherein said tantalum flake powder has a flake thickness distribution which is unimodal.  
     
     
         16 . The tantalum flake powder of  claim 13 , wherein said tantalum flake powder has a flake thickness distribution which is multi-modal.  
     
     
         17 . The tantalum flake powder of  claim 1 , wherein said tantalum flake powder has a flake thickness distribution which is multi-modal.  
     
     
         18 . A method to maximize capacitance capability in tantalum flake powder of  claim 1  for a certain formation voltage, comprising forming said tantalum flakes to an average flake thickness within ±100% of a primary flake thickness, wherein said primary flake thickness=2.5KoKta/(DtaKf)*1/CV, wherein CV=2.5KoKta/(Dta2Kf)*1Vf and wherein Ko=vacuum permittivity, Kta=dielectric constant, Dta=density of tantalum material, Kf=formation constant (dielectric thickness per volt), CV is measured in μFV/g and Vf=formation voltage, wherein Vf is from about 6 volts to about 500 volts.  
     
     
         19 . The method of  claim 18 , wherein said average thickness is from 0.08 to 1 micron.  
     
     
         20 . The method of  claim 18 , wherein said CV range is from 100,000 to 1,500,000 at 6V.  
     
     
         21 . The method of  claim 18 , further comprising forming said tantalum flakes into an anode.  
     
     
         22 . The method of  claim 18 , wherein said forming comprises milling tantalum particles in a multi-staged milling process.  
     
     
         23 . The method of  claim 22 , wherein said multi-staged milling process is a two staged milling process.  
     
     
         24 . The method of  claim 23 , wherein said two staged milling process comprises a first stage milling, wherein said tantalum particles are milled with a 3/16″ media to obtain tantalum flakes; and a second stage milling, wherein said tantalum flakes are further milled with a ⅛″ or 1/16″ media.  
     
     
         25 . The method of  claim 18 , wherein said average thickness is within ±10% of said primary flake thickness.  
     
     
         26 . The method of  claim 18 , wherein said average thickness is within ±50% of said primary flake thickness.  
     
     
         27 . The method of  claim 18 , wherein said average thickness is within ±35% of said primary flake thickness.  
     
     
         28 . The method of  claim 18 , wherein said CV range is from 25,000 to 400,000 at 25V, from 20,000 to 180,000 at 50V, from 9,000 to 90,000 at 100V, from 6,000 to 60,000 at 150V, from 4,000 to 45,000 at 200V, or from 3,000 to 30,000 at 300V.