NOVELTY - Etched interconnect has a single conductive base sheet (12) with two faces on its opposite sides, anode gas flow passages (16) disposed on the first face (14) of the base sheet, and cathode gas flow passages disposed on the second face of the base sheet. The anode and cathode gas flow passages have a geometry selected to optimize fuel and oxidant gas flow according to system requirements.    USE - The etched interconnect is used for fuel cell elements which are combined into groups to form a fuel cell stack assembly. It is particularly used for planar solid oxide fuel cells for use in a vehicle. It can also be used in co-generation of heat and electric power; distributed electric power generation e.g., small scale power plants for commercial/industrial/marine applications; and portable power generation e.g., military/construction/recreational applications.    ADVANTAGE - The inventive etched interconnect exhibits ease of manufacture and lower fabrication cost with a minimum number of parts, robust component parts enhancing ease of assembly, large heat transfer surface area, low pressure drops in the fuel and oxidant gas streams, shaped flow passages for generating swirl without excessive turbulence, integral manifolding, good electrical contact, thinner interconnects providing a more compact stack assembly, reduced overall mass and volume of the fuel cell assembly, robust structure as assembled, and enhanced fuel utilization resulting in higher power density.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (a) a method for preparing an interconnect, comprising preparing anode and cathode gas flow passages on respective first and second faces of the conductive base sheet, and selecting anode gas flow passage geometry and cathode gas flow passage geometry to optimize fuel and oxidant gas flow according to system; and    (b) a fuel cell stack assembly comprising several fuel cell elements comprising solid oxide electrolyte, an anode, and a cathode.    The fuel cells are stacked anode to cathode and interleaved with etched interconnects.    DESCRIPTION OF DRAWING(S) - The drawing is a view showing details of a portion of the etched interconnect.    base metal sheet (12)    first face (14)    anode gas flow passages (16)