Lead-Free Solder Alloy

Abstract

A lead-free solder alloy capable of forming solder joints in which electromigration and an increase in resistance during electric conduction at a high current density are suppressed has an alloy composition consisting essentially of 1.0-13.0 mass % of In, 0.1-4.0 mass % of Ag, 0.3-1.0 mass % of Cu, a remainder of Sn. The solder alloy has excellent tensile properties even at a high temperature exceeding 100° C. and can be used not only for CPUs but also for power semiconductors.

1 . A lead-free solder alloy having an alloy composition consisting essentially of, in mass percent, In: 1.0-2.0%, Ag: 0.1-0.3%, Cu: 0.3-1.0%, and a remainder of Sn. 
     
     
         2 . A lead-free solder alloy as set forth in  claim 1  wherein the Cu is 0.5-1.0%, in mass percent. 
     
     
         3 . A lead-free solder alloy as set forth in  claim 1  wherein the Cu is 0.5-0.7%, in mass percent. 
     
     
         4 . A lead-free solder alloy as set forth in  claim 1  wherein the Cu is 0.3-0.5%, in mass percent. 
     
     
         5 . A solder joint made from a lead-free solder alloy as set forth in  claim 1 . 
     
     
         6 . A solder joint as set forth in  claim 5 , wherein when the lead-free solder alloy is used as solder joint under an energizing condition at a current density of 0.12 mA/μm2 in air at 165 degrees C., the percent increase in a resistance value of the solder joint from a resistance value before the energization to a resistance value when 2500 hours have elapsed after the start of the energization is not more than 30% and a difference between the percent increase in a resistance value and a percent increase in a resistance value when 500 hours have elapsed from the start of the energization is not more than 5%. 
     
     
         7 . A method for suppressing electromigration of a solder joint during electrical conduction comprising forming a solder joint using a lead-free solder alloy as set forth in  claim 1 . 
     
     
         8 . A solder joint made from a lead-free solder alloy as set forth in  claim 1 , wherein the solder joint is included in power conversion equipment for solar power generation. 
     
     
         9 . A solder joint made from a lead-free solder alloy as set forth in  claim 1 , wherein the solder joint is included in a high-current inverter. 
     
     
         10 . A solder joint made from a lead-free solder alloy as set forth in  claim 1 , wherein the solder joint is included in a power semiconductor on a motor control inverter for an electric vehicle or plug-in hybrid vehicle. 
     
     
         11 . A solder joint made from a lead-free solder alloy as set forth in  claim 1 , wherein the solder joint is included in a CPU, in which the current density per terminal is around 104-105 A/cm2. 
     
     
         12 . A solder joint made from a lead-free solder alloy as set forth in  claim 1 ,
 wherein a current density of 0.12 mA/μm2 passes through the solder joint.