A cassette for use in cassette-type heat exchanger has an inlet and an outlet, and include an upper plate and a lower plate. The upper and lower plates are sealed together around an edge area of the cassette, thereby forming a flow path within the cassette between the inlet and outlet. The plates are formed with a stamped pattern that increases the surface area of the plates as compared to a flat plate surface. The pattern includes a series of weld points whereby the upper and lower plate are welded or bonded together at a point location.