Lead-free and antimony-free tin solder reliable at high temperatures

Abstract

A lead-free, antimony-free tin solder which is reliable at high temperatures and comprises from 3.5 to 4.5 wt. % of silver, 2.5 to 4 wt. % of bismuth, 0.3 to 0.8 wt. % of copper, 0.03 to 1 wt. % nickel, 0.005 to 1 wt. % germanium, and a balance of tin, together with any unavoidable impurities.

1 . A lead-free, antimony-free solder alloy comprising:
 (a) 3 to 5 wt % of silver   (b) 2.5 to 5 wt % of bismuth   (c) 0.3 to 2 wt % of copper   (d) at least one of the following elements
 up to 1 wt. % of nickel 
 up to 1 wt. % of titanium 
 up to 1 wt. % of cobalt 
 up to 3.5 wt. % of indium 
 up to 1 wt. % of zinc 
 up to 1 wt. % of arsenic 
   (e) optionally one or more of the following elements   0 to 1 wt. % of manganese   0 to 1 wt. % of chromium   0 to 1 wt. % of germanium   0 to 1 wt. % of iron   0 to 1 wt. % of aluminum   0 to 1 wt. % of phosphorus   0 to 1 wt. % of gold   0 to 1 wt. % of gallium   0 to 1 wt. % of tellurium   0 to 1 wt. % of selenium   0 to 1 wt. % of calcium   0 to 1 wt. % of vanadium   0 to 1 wt. % of molybdenum   0 to 1 wt. % of platinum   0 to 1 wt. % of magnesium   0 to 1 wt. % of rare earths   (f) the balance tin, together with any unavoidable impurities;   wherein the alloy affirmatively contains said Ni in a concentration of 0.01 to 1 wt %; and   wherein the alloy affirmatively contains said Ge in a concentration of 0.005 to 1.   
     
     
         2 . The solder alloy according to  claim 1 , wherein the alloy comprises:
 from 3.5 to 4.5 wt. % of silver;   from 2.5 to 4 wt. % of bismuth;   from 0.3 to 0.8 wt. % of copper;   from 0.03 to 1 wt. % nickel;   from 0.005 to 1 wt. % germanium,   the balance tin, together with any unavoidable impurities.   
     
     
         3 . The solder alloy according to  claim 2 , wherein the alloy comprises from 2.8 to 4 wt % bismuth. 
     
     
         4 . The solder alloy according to  claim 2 , wherein the alloy comprises from 0.6 to 0.8 wt % copper. 
     
     
         5 . The solder alloy according to  claim 2 , wherein the alloy comprises from 0.03 to 0.6 wt. % nickel. 
     
     
         6 . The solder alloy according to  claim 2 , wherein the alloy comprises:
 from 2.8 to 4 wt. % bismuth;   and from 0.1 to 0.3 wt. % nickel.   
     
     
         7 . The solder alloy as claimed in  claim 2 , wherein the alloy has melting point of from 195 to 222° C. 
     
     
         8 . The solder alloy as claimed in  claim 2  in the form of a bar, a stick, a solid or flux cored wire, a foil or strip, or a powder or paste (powder plus flux blend), or solder spheres for use in ball grid array joints or chip scale packages, or other pre-formed solder pieces, with or without a flux core or a flux coating. 
     
     
         9 . A soldered joint comprising an alloy as defined in  claim 2 . 
     
     
         10 . A method of forming a solder joint comprising:
 (i) providing two or more work pieces to be joined;   (ii) providing a solder alloy as defined in  claim 2 ; and   (iii) heating the solder alloy in the vicinity of the work pieces to be joined.