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

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.