Glass frit bonding with controlled width and height using a two-step wet silicon etching procedure

Abstract

A simple and versatile two-step silicon wet etching technique for the control of the width and height of the glass frit bonding layer has been developed to improve bonding strength and reliability in wafer-level microelectromechanical systems (MEMS) packaging processes. The height of the glass frit bonding layer is set by the design of a vertical reference wall which regulates the distance between the silicon wafer and the encapsulation capping substrate. On the other hand, the width of the bonding layer is constrained between two micro grooves which are used to accommodate the spillages of extra glass frit during the bonding process. An optimized thermal bonding process, including the formation of glass liquid, removal of gas bubbles under vacuum and the filling of voids under normal atmospheric condition has been developed to suppress the formation of the bubbles/voids. The stencil printing and pre-sintering processes for the glass frit have been characterized before the thermal bonding process under different magnitudes of bonding pressure. The bonding gap thickness is found to be equal to the height of the reference wall of 10 μm in the prototype design. The bubbles/ voids are found to be suppressed effectively and the bonding strength increases from 10.2 to 19.1 MPa as compared with a conventional thermal annealing process in air. Experimentally, prototype samples are measured to have passed the high hermetic sealing leakage tests of 5 × 10 −8 atm cc s −1 .

Metal‐bonding‐based hermetic wafer‐level MEMS packaging technology using in‐plane feedthrough: Hermeticity and high frequency characteristics of thick gold film feedthrough

“…There are techniques to restrict the print area of glass frit by raising the seal ring, or to prevent the molten glass frit from expanding inside a device through providing grooves on the internal side of the seal ring. 18 However, these techniques not only require additional cost, but also make it difficult for feedthrough wiring to traverse the seal ring.…”