Wafer-level hermetic MEMS packaging by anodic bonding and its reliability issues

•Wafer-level hermetic MEMS packaging technology by anodic bonding is reviewed.•The review covers from the early works to the latest ones.•Key points for practical implementation are highlighted.•A new MEMS packaging material, anodically-bondable LTCC wafer, is introduced. This paper reviews wafer-level hermetic packaging technology using anodic bonding from several reliability points of view. First, reliability risk factors of high temperature, high voltage and electrochemical O2 generation during anodic bonding are discussed. Next, electrical interconnections through a hermetic package, i.e. electrical feedthrough, is discussed. The reliability of both hermetic sealing and electrical feedthrough must be simultaneously satisfied. In the last part of this paper, a new wafer-level MEMS packaging material, anodically-bondable low temperature cofired ceramic (LTCC) wafer, is introduced, and its reliability data on hermetic sealing, electrical interconnection and flip-chip mounting on a printed circuit board (PCB) are described.