Packaging-compatible wafer level capping of MEMS devices

A cost-effective, wafer-level package process for microelectromechanical devices (MEMS) is presented. The movable part of MEMS device is encapsulated and protected while in wafer form so that commodity, lead-frame packaging can be used. A polymer epoxycyclohexyl polyhedral oligomericsilsesquioxanes has been used as a mask material to pattern the sacrificial polymer as well as overcoat the air-cavity. The resulting air-cavities are clean, debris-free, and robust. The cavities have substantial strength to withstand molding pressures during lead-frame packaging of the MEMS devices. A wide range of cavities from 20 μm × 400 μm to 300 μm × 400 μm have been fabricated and shown to be mechanically stable. These could potentially house MEMS devices over a wide range of sizes. The strength of the cavities has been investigated using nano-indentation and modeled using analytical and finite element techniques. Capacitive resonators packaged using this protocol have shown clean sensing electrodes and good functionality.

Process sequence for new in-situ packaging approach.Figure optionsDownload as PowerPoint slideHighlights
► A low-cost, high-volume, lead frame based packaging approach form MEMS devices is described.
► MEMS device is protected with sacrificial material during lead frame packaging and released in the final step.
► MEMS device is released after epoxy encapsulation structure is complete.
► Release after full encapsulation allows nearly any size MEMS device to be packaged.