Fabrication and Testing of In-Line Structures for Non-Destructive Study of Solder Electromigration: Applications to SnBi Low Temperature Solder

The challenges due to scale and pitch reduction of solder interconnects include voiding of microbumps with intermetallic formation along the sidewall, and Bi segregation in SnBi Low Temperature Solder (LTS) due to electromigration. The conventional method to characterize such mechanisms is to cross-section and polish the sample after testing. After cross-sectioning, the sample cannot be tested further and surface characteristics such as hillock formations may be made obscure by the polishing process itself. In this work, we describe a fabrication procedure to create micro-scale test devices capable of non-destructive thermal aging and electromigration characterization of solder alloys. These devices can be made using any commercially available solder alloy. We demonstrate the capability of the test devices by characterizing the rate of Bi segregation during electromigration of SnBi solder alloy.