Structure and method for sealing cavity of micro-electro-mechanical device

A cavity package (100) for micrometer-scale MEMS devices surrounding the cavity (210) with the MEMS device (220) with a rim (232) of solder-wettable metal, and then covering the cavity with a roof (240) of solder spanning from rim to rim. A solder body, placed over the cavity to rest on the rim, is reflowed; the surface tension of the liquid solder is reduced by the interfacial tension of the rim metal so that the liquid solder spreads over the rim surface and thereby stretches the liquid ball to a plate-like roof over the cavity. After solidifying the solder, the solder-to-metal seal renders the cavity package hermetic.