Electromigration Behavior of Cu-Cored Sn-Bi Solder Balls

Sn-Bi base solder alloy with a low melting point has become an attractive material to suppress an assembly temperature.Still, its lower electrical conductivity and electromigration (EM) resistivity are a considerable risk when used as a small BGA joint.This study reports on the functional effect of Cu-cored structure as a remedy to improve the electrical performance of Sn-Bi base lowtemperature solder (LTS).The circuit with Cu-cored LTS joint showed 40% less electrical resistance by its current flow attraction effect of high-conductive Cu-core, and it also succeeded in suppressing conductivity deterioration during long-term EM as long as the joint keeps ideal geometry balances.Cu-cored structure also showed improved reliability under thermal cycle and drop shock.