Flux for soldering and circuit board

Abstract

A flux contains resin having film forming ability, activator, solvent, and at least one complex selected from silver complex and copper complex. The flux is used when soldering is performed onto a circuit having electroless nickel plating or further having gold plating on the electroless nickel plating. Allowing a barrier layer of silver or copper to deposit on the surfaces of lands suppresses the diffusion of nickel into the melted solder alloy during soldering, and also prevents phosphorous concentration. This improves the bonding strength of soldering and suppresses the reduction deposition of silver and/or copper to portions other than circuit patterns.

1 . A flux containing resin having film forming ability, activator, solvent, and at least one complex selected from silver complex and copper complex, said flux being used when soldering is performed onto a circuit having electroless nickel plating or further having gold plating on said electroless nickel plating.  
   
   
       2 . The flux according to  claim 1  wherein said complex does not substantially cause substitution deposition of at least one selected from silver and copper on a circuit pattern at temperatures of less than 150° C., and causes substitution deposition at temperatures of not less than 150° C.  
   
   
       3 . The flux according to  claim 2  wherein said complex does not substantially cause deposition of at least one selected from silver and copper at portions other than a circuit pattern at temperatures of not more than 280° C.  
   
   
       4 . The flux according to  claim 1  wherein said complex is a complex of silver ion and/or copper ion and phosphine, nitrogenated heterocyclic compound, or a compound having thiol, thioether or disulfide bond.  
   
   
       5 . The flux according to  claim 4 , wherein said phosphine is aryl phosphine or alkyl phosphine represented by the following general formula 1.  
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2  and R 3  each represents a substituted or non-substituted aryl group, or a substituted or non-substituted chain or cyclic alkyl group having 1 to 8 carbon atoms; hydrogen of the aryl group may be substituted with an alkyl having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a hydroxyl group, an amino group or a halogen atom at any position; hydrogen of the alkyl group may be substituted with an alkoxy group having 1 to 8 carbon atoms, an aryl group, a hydroxyl group, an amino group or a halogen at any position; and R 1 , R 2  and R 3  may be the same or different.  
   
   
       6 . The flux according to  claim 5 , wherein said aryl phosphine or the alkyl phosphines are triphenyl phosphine, tri(p-tolyl)phosphine, tri(p-methoxyphenyl)phosphine, trioctyl phosphine and tris(3-hydroxypropyl)phosphine.  
   
   
       7 . The flux according to  claim 4 , wherein said nitrogenated heterocyclic compounds is at least one selected from five-ring compound, six-ring compound and derivatives thereof.  
   
   
       8 . The flux according to  claim 4 , wherein said complex contain organic sulfonic acid ion, organic carboxylic acid ion, halogen ion, nitric acid ion or sulfuric acid ion as counter anion.  
   
   
       9 . The flux according to  claim 8 , wherein said organic sulfonic acid is at least one selected from organic sulfonic acids represented by the following general formulas 2, 3 and 4.  
       (X 1 ) n —R 4 —SO 3 H   general formula 2:  
     wherein R 4  represents an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms or an alkynyl group having 2 to 18 carbon atoms, X 1  represents a hydrogen, a hydroxyl group, an alkyl group having 1 to 8 carbon atoms or an alkoxy group, an aryl group, an aralkyl group, a carboxyl group or a sulfo group, n represents an integer of 0 to 3, and X 1  may be bonded at any position of R 4 .  
       (X 2 ) n —R 5 —(SO 3 H) m    general formula 3:  
     wherein R 5  represents an alkyl group having 1 to 18 carbon atoms or an alkylene group having 1 to 3 carbon atoms, and when an alkylene group, a hydroxyl group may be bonded at any position of the alkylene group; X 2  represents chlorine and/or fluorine; n represents an integer of not less than 1 and not more than the number of hydrogen capable of bonding with R 5 ; and m represents an integer of I to 3. X 2  may be bonded with R 5  at any position.  
     
       
         
         
             
             
         
       
     
     wherein X 3  represents a hydroxyl group, an alkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an aryl group, an aralkyl group, an aldehyde group, a carboxyl group, a nitro group, a mercapto group, a sulfo group or an amino group, or two adjacent X 3 (s) may form a ring to form a naphthalene ring with a benzene ring, and n represents an integer of 0 to 3.  
   
   
       10 . The flux according to  claim 8 , wherein said organic carboxylic acid ion is at least one selected from formic acid, acetic acid, oxalic acid, lactic acid, trichloroacetic acid, trifluoroacetic acid and perfluoropropionic acid.  
   
   
       11 . A circuit board comprising: 
 lands having on their surfaces electroless nickel plating or further having gold plating on said electroless nickel plating; and    a barrier layer formed on the surfaces of said lands, said barrier layer being composed of a metallic layer of at least one selected from silver and copper that are substituted by nickel in said electroless nickel plating and deposited, and    said metallic layer being formed by printing or applying a flux for soldering according to  claim 1  onto the surface of said circuit board, followed by heating.    
   
   
       12 . A circuit board comprising: 
 lands having on their surfaces electroless nickel plating or further having gold plating on said electroless nickel plating; and    a barrier layer formed on the surfaces of said lands,    said barrier layer being composed of a metallic layer of at least one selected from silver and copper that are substituted by nickel in said electroless nickel plating and deposited, and    said metallic layer being formed by heating involved when a flux for soldering according to  claim 1  is printed or applied onto the surface of a circuit board, and then solder balls placed on said lands are allowed to reflow so as to connect said solder balls to said lands.    
   
   
       13 . A soldering method comprising the steps of: 
 printing or applying a flux for soldering according to  claim 1  onto a substrate having copper lands which have on their surfaces electroless nickel plating or further have gold plating on said electroless nickel plating, and heating to form a barrier layer of at least one selected from silver and copper on the surfaces of said lands; and    placing solder balls on said lands with said barrier layer formed on their surfaces, and heating to have said solder balls reflow so as to connect said solder balls to said lands.    
   
   
       14 . A soldering method comprising the steps of: 
 printing or applying a flux for soldering according to  claim 1  onto a substrate having copper lands which have on their surfaces electroless nickel plating or further have gold plating on said electroless nickel plating; and    placing solder balls on said lands, and heating to have said solder balls reflow so as to form on the surfaces of said lands a barrier layer of at least one selected from silver and copper, and connect said solder balls via said barrier layer to said lands.    
   
   
       15 . The soldering method according to  claim 13  or  14 , wherein said solder balls are lead-free.  
   
   
       16 . A soldering method including: 
 printing paste, which a mixture of a flux for soldering according to  claim 1  and solder powder, on a substrate having lands that have on their surfaces electroless nickel plating or further have gold plating on said electroless nickel plating, and then heating to have said paste reflow so as to form solder alloy on said lands.    
   
   
       17 . A soldering method according to  claim 13 ,  14 , wherein the reflow temperature of solder balls is 150° C. to 280° C.  
   
   
       18 . A soldering method according to  claim 15 , wherein the reflow temperature of solder balls is 150° C. to 280° C.