Reliability Verification of Hermetic Package With Nanoliter Cavity for RF-Micro Device

With the advance of high-performance and small-size microelectromechanical systems (MEMS) devices, wafer-level packaging has gained increased attention over the past few years. Most MEMS packages must protect the often-fragile mechanical structures against the environment and provide the interface for the interaction with the next level in the packaging hierarchy. It is obvious that stable performance and high reliability are essential requirements of a packaged device. In this paper, a novel hermetic package, called the WL-¿P, recently developed for radio-frequency (RF)-filter and RF-duplexer, will be reviewed in terms of its construction, fabrication process, and electrical/mechanical performance. The package consists of a device wafer for a MEMS device and a cap wafer that has a micromachined cavity and through-wafer vias for electrical connections. The cap and device wafers are bonded to each other through a closed square loop of gold/tin eutectic solder at the peripheral edge. The via-in-cavity structure is designed in the cap substrate, with vertical via holes fabricated and fully electroplated with copper. The detailed design and fabrication technology of this new type of hermetically sealed package are presented with process flow. The performance evaluation and reliability results of a hermetic package will also be presented. The developed wafer-level hermetic package technology is able to fulfill today's requirements for hermetic and cost-effective packaging of high-speed RF-MEMS applications.