Method of manufacturing sealed functional elements for enabling a process-safe and economical manufacture of surface acoustic wave functional elements and sensors, as well as an efficient protection of the surface of the surface acoustic wave functional elements against contamination

A method for manufacturing a plurality of, in particular hermetically, sealed functional elements, includes the following steps: providing a first wafer having a plurality of functional elements; providing a second wafer; applying a sealing material in the form of a plurality of frame structures on a first surface of the second wafer; placing the second wafer on the first wafer or placing the first wafer on the second wafer; and joining the first wafer with the second wafer. Moreover, some of the sealed functional elements are surface acoustic wave functional elements, and at least one frame structure surrounds at least one functional element of the plurality of sealed functional elements after the placing. The method further includes: performing a heat treatment in the form of the plurality of frame structures on the second wafer on which the sealing material is applied, wherein the heat treatment includes: heating the second wafer during a first period to a first temperature, the first period being between