Low-temperature hermetic thermo-compression bonding using electroplated copper sealing frame planarized by fly-cutting for wafer-level MEMS packaging

• Published in: Sensors and actuators. A. Physical. 2018-08, Vol.279, p.671-679
• Main Authors: Al Farisi, Muhammad Salman, Hirano, Hideki, Tanaka, Shuji
• Format: Article
• Language: English
• Subjects: Bonding strength; Copper; Cu–Cu thermo-compression bonding; Diamond machining; Electric contacts; Electronic packaging; Flying cutting; Hermetic sealing; Heterogeneous integration; Low temperature; Mechanical systems; Microelectromechanical systems; Pressure measurement; Reliability; Sealing; Shear strength; Silicon wafers; Single-point diamond fly-cutting; Wafer-level hermetic packaging
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2018.06.021

•Cu–Cu thermo-compression bonding was demonstrated at a temperature as low as 250 °C. At such a low bonding temperature, a sealed cavity pressure lower than 100 Pa was obtained.•The leak rate into the packages was less than 1.67 × 10−15 Pa m3s−1, which was estimated by sealed cavity pressure measurements over 7 months.•An average shear strength of 207 MPa and 119 MPa was achieved using 50 μm and 30 μm wide sealing frame, respectively.•The low-temperature bonding mechanism relies on the formation of the fine grains at the electroplated Cu surface after fly-cutting. Hermetic packaging plays an important role for optimizing the functionality and reliability of a wide variety of micro-electro-mechanical systems (MEMS). In this paper, we propose a low-temperature wafer-level hermetic packaging method based on the thermo-compression bonding process using an electroplated Cu sealing frame planarized by a single-point diamond mechanical fly-cutting. This technology has an inherent possibility of hermetic sealing and electrical contact as well as a capability of integration of micro-structured wafers. Hermetic sealing can be realized with the sealing frame as narrow as 30 μm at a temperature as low as 250 °C. At such a low bonding temperature, a less amount of gases is desorbed, resulting in a sealed cavity pressure lower than 100 Pa. The leak rate into the packages is estimated by a long-term sealed cavity pressure measurement for 7 months to be less than 1.67 × 10−15 Pa m3 s−1. In addition, the bonding shear strength is also evaluated to be higher than 100 MPa.