A multiple bank, flattened tube heat exchanger comprising: a first tube bank including at least a first flattened heat exchange tube segment and a second flattened heat exchange tube segment extending longitudinally and arrayed in spaced parallel relationship between a first manifold and a second manifold; a second tube bank including at least a first flattened heat exchange tube segment and a second flattened heat exchange tube segment extending longitudinally and arrayed in spaced parallel relationship between a first manifold and a second manifold, the second tube bank disposed in spaced relationship at a spacing gap behind the first tube bank; a longitudinally extending folded fin disposed between said first and second heat exchange tube segments of the first tube bank and between said first and second heat exchange tube segments of the second tube bank and spanning said spacing gap, said folded fin having a plurality of spaced fin faces extending between said first and second heat exchange tube segments of the first tube bank and between said first and second heat exchange tube segments of the second tube bank and a plurality of fin caps interconnecting the fin faces and abutting said first and second heat exchange tube segments of the first tube bank and said first and second heat exchange tube segments of the second tube bank; and a plurality of fin notches protruding outwardly from said folded fin into said spacing gap, each fin notch protruding outwardly from a respective one of said plurality of fin caps into said spacing gap; characterized in that each fin notch has a height in the range from at least a half of the thickness of said heat transfer tube segments up to the thickness of the heat transfer tube segments. a first tube bank including at least a first flattened heat exchange tube segment and a second flattened heat exchange tube segment extending longitudinally and arrayed in spaced parallel relationship between a first manifold and a second manifold; a second tube bank including at least a first flattened heat exchange tube segment and a second flattened heat exchange tube segment extending longitudinally and arrayed in spaced parallel relationship between a first manifold and a second manifold, the second tube bank disposed in spaced relationship at a spacing gap behind the first tube bank; a longitudinally extending folded fin disposed between said first and second heat exchange tube segments of the first tube bank and between said first and second heat exchange tube segments of the second tube bank and spanning said spacing gap, said folded fin having a plurality of spaced fin faces extending between said first and second heat exchange tube segments of the first tube bank and between said first and second heat exchange tube segments of the second tube bank and a plurality of fin caps interconnecting the fin faces and abutting said first and second heat exchange tube segments of the first tube bank and said first and second heat exchange tube segments of the second tube bank; and a plurality of fin notches protruding outwardly from said folded fin into said spacing gap, each fin notch protruding outwardly from a respective one of said plurality of fin caps into said spacing gap; characterized in that each fin notch has a height in the range from at least a half of the thickness of said heat transfer tube segments up to the thickness of the heat transfer tube segments.