Microstructural Characterization and Mechanical Performance of Wafer-Level SLID Bonded Au-Sn and Cu-Sn Seal Rings for MEMS Encapsulation

Antti Rautiainen, Hongbo Xu, Elmeri Österlund, Jue Li, Vesa Vuorinen, Mervi Paulasto-Kröckel

Research output: Contribution to journalArticleScientificpeer-review

25 Citations (Scopus)

Abstract

Special applications, such as microelectromechanical systems (MEMS), often require hermetic sealing in order to achieve a desired operation. Solid–liquid interdiffusion (SLID) bonding is an attractive method for encapsulating MEMS devices at the wafer-level, providing, e.g., high re-melt temperatures and tolerance for topographical variations. Several different SLID bond solutions have been investigated; however, there are only a limited number of published reliability studies available. In this paper, wafer-level Au-Sn and Cu-Sn SLID seal rings were mechanically characterized with shear and tensile tests. The evolution of bond microstructures and consequent effects on mechanical reliability were evaluated with a mixed flow gas test, a high temperature storage test and a thermal shock (TS) test. Virgin samples showed high mechanical strength. The Au-Sn system, with a thin Ni layer between the TiW adhesion layer and the bond, demonstrated a shear strength of 170 MPa. Cu-Sn, with a Cu-Cu3Sn-Cu structure, exhibited a shear strength of 275 MPa. Statistically significant decreases in strength were identified after reliability tests. The shear strength of the Au-Sn bond with an (AuSn + Au5Sn)eut structure decreased 40% in a corrosive environment. After 3000 TS cycles, the tensile strength of the Cu-Sn bond reduced by 45%. Fracture surface analysis revealed through-bond failures that were not observed previously. In cross-sectional analysis, vertical cracks were observed, which may contribute to the decrease in tensile strength.
Original languageEnglish
Pages (from-to)4533-4548
JournalJournal of Electronic Materials
Volume44
Issue number11
DOIs
Publication statusPublished - 2015
MoE publication typeA1 Journal article-refereed

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