An improved electric device and manufacturing method for the same are described. The device is for example an IC chip (28) with associated leads (37) encapsulated within a moulded plastic package (41). In advance of the moulding process, the IC chip and its associated lead structure is kept in a high vacuum condition and coated with silicon nitride or other electrically insulating material in order to protect the IC chip from moisture invasions through cracks (33, 33', 33") or gaps in the encapsulation. The coating of the silicon nitride is advantageously carried out after cleaning of the surface of the IC chip and its associated structures by plasma CVD.
