Kinetics of Intermetallic Compounds Growth Induced by Electromigration of Sn-0.7Cu Solder

摘要

The reliability of printed circuit boards (PCB) has emerged as a critical concern as the size of solder bump decreases and current density to solder bump increases by fine pitch formation. The main failure mode of solder bumps is open-circuits due to void formation as intermetallic compounds (IMC) grow, mainly due to electromigration. This study modeled IMC growth by electromigration in Sn-0.7Cu solder bumps. The IMC produced in the reflow process grew again significantly due to electromigration upon application of electric current. The thickness of the IMC under electromigration increased as the current increased from 1 A (current density: 1.3 x 10(4) A/cm(2)) to 1.5 A (current density: 1.9 x 10(4) A/cm(2)). For the current density applied in the study, IMC growth of Cu6Sn5 was faster than that of Cu3Sn. The Nernst-Einstein relation was used to model the IMC growth induced by electromigration. The modeling results of Cu3Sn and Cu6Sn5 thickness showed good agreement with the experimental observations of IMC growth under electromigration. Specifically, a good prediction for Cu3Sn growth was derived for the current density of 1.3 x 10(4) A/cm(2). However, the modeling values of 1.9 x 10(4) A/cm(2) and Cu6Sn5 thickness showed a minor difference as compared with the experimental IMC thickness results. As the current density increased from 1.3 x 10(4) A/cm(2) to 1.9 x 10(4) A/cm(2), the solder bump probably evolved under heat generation, and the further effects of aging and thermomigration should be incorporated in the IMC growth.