A Modified Electromigration Test Structure for Flip Chip Interconnections

Due to decreasing dimensions, electromigration becomes a major concern for flip chip joint reliability. A novel test structure for in-situ monitoring of electromigration in a flip chip connection is proposed. With this structure, small resistance changes at the cathodic and anodic sides can be mounted separately. This allows studying the asymmetric behavior of solder joints under electromigration conditions. The design of the new test structure is described and compared to the traditional measurement method. As a first test case, a Cu-Sn-Cu flip chip joint, stressed with a current of 6000Amp/cm² at 150degC, is studied. First tests clearly indicate diverging resistance values when comparing the cathodic and anodic side of the flip chip bumps. Microstructural analysis shows extensive Cu-migration from cathode to anode