STUDIES ON SOLDER ELECTOMIGRATION IN LEAD-FREE FLIP CHIP JOINT SYSTEM
Authors: Kimihiro Yamanaka, Takafumi Ooyoshi, Takayuki Nejime, and Yutaka Tsukada Company: KYOCERA SLC Technologies Corporation and i-PACKS Date Published: 2/12/2009
Pan Pacific Symposium
Abstract: Electromigration phenomena in Sn-3Ag-0.5Cu and In solders in flip chip joint systems were investigated. An electromigration lifetime increased with an underfill, and significant solder joint deformation toward the cathode occurred without an underfill. An underfill stress was newly introduced as an additional factor to a conventional back stress in order to explain the above phenomena. It was an internal stress induced by the existence of the underfill, and was relieved by the solder deformation. Thus, a greater Young’s modulus of the underfill created a greater underfill stress resulting in a longer electromigration lifetime. However, the underfill became not effective on the electromigration lifetime at a high current density. In addition, a unique method employing a resistance change in the junction line between the two solder joints was introduced to determine the solder joint temperature. The method successfully demonstrated its capability of measuring the temperature increase due to electromigration void growth.
Key words: electromigration, Cu, Sn-Ag-Cu, In, Flip chip