Wafer-level hermetic vacuum packaging by bonding with a copper–tin thin film sealing ring. (15th February 2018)

• Record Type: Journal Article
• Authors: Akashi, Teruhisa; Funabashi, Hirofumi; Takagi, Hideki; Omura, Yoshiteru; Hata, Yoshiyuki
• Is Part Of: Journal of micromechanics and microengineering. Volume 28:Number 4(2018:Apr.)
• Publication Date: 2018-02-15
• Subjects: wafer-level packaging -- hermetic vacuum packaging -- copper–tin -- residual gas analyzer -- leak rate -- long-term hermeticity; Microelectromechanical systems -- Periodicals; Micromechanics -- Periodicals; 621.38105
• DOI: 10.1088/1361-6439/aaab35
• Languages: English
• ISSNs: 0960-1317

Abstract

Abstract: A wafer-level hermetic vacuum packaging technology intended for use with MEMS devices was developed based on a copper–tin (CuSn) thin film sealing ring. To allow hermetic packaging, the shear strength of the CuSn thin film bond was improved by optimizing the pretreatment conditions. As a result, an average shear strength of 72.3 MPa was obtained and a cavity that had been hermetically sealed using wafer-level packaging (WLP) maintained its vacuum for 1.84 years. The total pressures in the cavities and the partial pressures of residual gases were directly determined with an ultra-low outgassing residual gas analyzer (RGA) system. Hermeticity was evaluated based on helium leak rates, which were calculated from helium pressures determined with the RGA system. The resulting data showed that a vacuum cavity following 1.84 years storage had a total pressure of 83.1 Pa, contained argon as the main residual gas and exhibited a helium leak rate as low as 1.67 × 10 −17 Pa · m 3 s −1, corresponding to an air leak rate of 6.19 × 10 −18 Pa · m 3 s −1 . The RGA data demonstrate that WLP using a CuSn thin film sealing ring permits ultra-high hermeticity in conjunction with long-term vacuum packaging that is applicable to MEMS devices.