Electromigration in Microscale Interconnects with a Coexisting Liquid-Solid Solder Matrix

  Prof. Wu YUE

  Professor and Dean of the School of Materials Engineering, Lanzhou Institute of Technology, China  

Abstract:

Electromigration (EM) is one of the key factors impairing the reliability of Sn-based interconnects and electronics. Up to now, the major studies on EM are presently focused on the optimizing the composition of the solder alloy, the microstructures and the crystallographic properties of the base metal, and the geometrical configuration, etc., which are based on a premise that the solder matrix is entirely liquid or solid. Nevertheless, due to the packaging structure and the heating dissipation, the temperatures vary significantly across different solder interconnects or across different microregions of the same solder interconnect in electronics, and easily leads to a semi-solid state or a coexistence of liquid and solid states. Correspondingly, it is necessary to study EM at the state coexisted with liquid and solid solder from the real engineering perspective.

In this study, the linear Cu/Sn58Bi/Cu solder interconnects were used, and a coexistence state of liquid and solid solder is obtained in a interconnect by regulating the Joule heating effect and the different heat dissipation conditions at the different microrgions. Then, through observing the phase segregation, the cavity formation and the intermetallic compounds (IMCs) growth, the EM mechanism coexisting the liquid and solid solder is discussed and analyzed. The result reveals that under the higher density current, Sn atoms in the liquid solder layer are prone to metallurgical reactions with the base metals at both interfaces to form a large amount of IMCs, and there are plenty of cavities under the influence of gravity. At the same time, owing to the influence of temperature, there is a solder atom transforming and migration between the liquid and solid solder.

Speaker's Biography: 

Wu Yue, Ph.D in Engineering, is a Professor and Dean of the School of Materials Engineering, Lanzhou Institute of Technology. He is an academic leader of the provincial key discipline “Materials Science and Engineering”, and the lead of the electronic packaging materials and engineering group, and the bearing materials and heat treatment one. His current research focuses on the reliability evaluation and the failure analysis of Sn-based interconnects, the development of the new Cu foil of the lead frames, the analysis of the deformation mechanism of the bearing rings during heat treatment, and the preparation of high wear resistance coatings. Since 2006, he has been occupied in the optimization and design of the electronic packaging processes. After 2010, he has mainly been dedicated on the EM behavior of Sn-based interconnects. Over the past teens years, he has systematically studied the influence of the shape of solder interconnect and the crystallographic characteristics of the base metal on EM behavior. Presently, he is studying EM of microscale interconnection with a coexisting liquid-solid solder matrix. He is the principle investigator (PI) of a National Natural Science Foundation of China (NSFC) project and near 10 provincial projects, including the provincial key talent projects, the provincial key research and development projects, and the provincial basic research key projects, etc. He has published over 30 SCI/EI-indexed papers and obtained 4 invention patents and 5 utility model patents.