Lead-free solder alloy and preparation thereof

Abstract

The invention relates to a lead-free solder alloy including 1 to 15 percent by weight of Bi, 0.01 to 2 percent by weight of Sb, 0.001 to 2 percent by weight of Co, and the balance percent of Sn, so as to make the individual amounts of Bi, Sb, Co and Sn summing up to 100 % by weight, in which Sb is substantially present as a solid solution with Bi. The alloy is prepared by solidifying a melt obtained by melting Bi together with Sb to give a mother alloy of Bi and Sb, i.e. the solid solution of Bi and Sb, and then solidifying a melt obtained by melting the mother alloy of Bi and Sb together with Sn and Co. The lead-free solder alloy according to the present invention has high tensile strength and low melting temperature. Furthermore, the alloy displays improved performance in practical characteristics such as wettability, thermal shock resistance, and is inexpensive.

1 . A lead-free solder alloy comprising: 
 1 to 15 percent by weight of Bi;    0.01 to 2 percent by weight of Sb;    0.001 to 2 percent by weight of Co; and    the balance percent by weight of Sn, so as to make the individual amounts of Bi, Sb, Co and Sn summing up to 100% by weight, Sb being substantially present as a solid solution with Bi.    
   
   
       2 . The lead-fee solder alloy as limed in  claim 1 , wherein 10 to 15 percent by weight of Bi, 0.1 to 2 percent by weight of Sb, and 0.01 to 0.05 percent by weight of Co are included.  
   
   
       3 . A process of preparing a lead-free solder alloy a claimed as  claim 1 , comprising: 
 solidifying a melt obtained by melting Bi together with Sb to give a mother alloy of Bi and Sb; and    solidifying a melt obtained by melting the mother alloy of Bi and Sb together with Sn and Co.    
   
   
       4 . A process of preparing a lead-free solder alloy as claimed in  claim 2 , comprising: 
 solidifying a melt obtained by melting Bi together with Sb to give a mother alloy of Bi and Sb; and    solidifying a melt obtained by melting the mother alloy of Bi and Sb together with Sn and Co.    
   
   
       5 . A process of preparing a lead-free solder alloy as claimed in  claim 1 , comprising: 
 solidifying a melt obtained by melting Bi together with Sb to give a mother alloy of Bi and Sb;    solidifying a melt obtained by melting Sn together with Co to give a mother alloy of Sn and Co; and    solidifying a melt obtained by melting Sn together with the mother alloy of Bi and Sb and the mother alloy of Sn and Co.    
   
   
       6 . A process of preparing a lead-free solder alloy as claimed in  claim 2 , comprising: 
 solidifying a melt obtained by melting Bi together with Sb to give a mother alloy of Bi and Sb;    solidifying a melt obtained by melting Sn together with Co to give a mother alloy of Sn and Co; and    solidifying a melt obtained by melting Sn together with the mother alloy of Bi and Sb and the mother alloy of Sn and Co.