Refinement of the Microstructure of Sn-Ag-Bi-In Solder, by Addition of SiC Nanoparticles, to Reduce Electromigration Damage Under High Electric Current

The trends of miniaturization, multi-functionality, and high performance in advanced electronic devices require higher densities of I/O gates and reduced area of soldering of interconnections. This increases the electric current density flowing through the interconnections, increasing the risk of interconnection failure caused by electromigration (EM). Accelerated directional atomic diffusion in solder materials under high current induces substantial growth of intermetallic compounds (IMCs) at the anode, and also void and crack formation at the cathode. In the work discussed in this paper, addition of SiC nanoparticles to Sn-Ag-Bi-In (SABI) lead-free solder refined its microstructure and improved its EM reliability under high current stress. Electron back-scattering diffraction analysis revealed that the added SiC nanoparticles refined solder grain size after typical reflow. Under current stress, SABI joints with added nano-SiC had lifetimes almost twice as long as those without. Comparison of results from high-temperature aging revealed direct current affected evolution of the microstructure. Observations of IMC growth indicated that diffusion of Cu in the SiC composite solder may not have been reduced. During current flow, however, only narrow voids were formed in solder containing SiC, thus preventing the current crowding caused by bulky voids in the solder without SiC.