A plate fin heat exchanger includes a plate fin core having a plurality of plates defining a set of hot air passages extending from a hot air inlet region of the plate fin core to a hot air outlet region of the plate fin core and a set of cool air passages extending from a cool air inlet region of the plate fin core to a cool air outlet region of the plate fin core. The plate fin heat exchanger further includes a mounting flange circumscribing the cool air outlet region. At least a portion of the mounting flange has a plurality of heat transfer structures that extend into a flow path of cooling air exiting the cool air outlet region of the plate fin core.