Effects of W contents on the solid-state interfacial reactions of Sn/Co-W.

Co-based alloys have received extensive attention as barrier layers of Sn/Cu joints in the microelectronic packaging. However, little attention has been paid to the combine effect of alloy content and grain size on the diffusion barrier performance. In this work, the 150 °C solid-state interfacial reactions of Sn/Co and Sn/Co-W with different W contents were investigated. Besides crystalline Co-Sn intermetallic compounds (IMCs), amorphous Co0.36Sn0.64 and amorphous Co-W-Sn IMCs formed at Sn/Co and Sn/Co-W interfaces, respectively. The IMCs growth kinetics of Sn/Co interface was reaction-controlled. Meanwhile, that of Sn/Co-W interface was diffusion-controlled, due to the diffusion barrier of the amorphous Co-W-Sn. The decreased grain size of Co-10 at%W made larger contribution to the Co diffusion; thus, the IMCs growth rate of Sn/Co-10 at%W was faster than Sn/Co-5 at%W interface. While those of Sn/Co-15 at%W and Sn/Co-20 at%W interfaces dramatically slowed down, due to the increased pinning effect of W atoms and amorphous structure of Co-W. This research can contribute to providing insights into the reliability of electronic packaging. [ABSTRACT FROM AUTHOR]