A plate-fin style heat exchanger comprising: a tube; and a fin collar for achieving improved contact area on the tube, said fin collar comprising: an elongated fin portion for dissipating heat; and a collar leg connected with said fin portion, said collar leg having a height and including: a straight collar contact portion substantially perpendicular to said fin portion, wherein said contact portion has a collar contact height along which said contact portion contacts the tube; a first curved end portion having a first radius and extending from a first end of said contact portion; the heat exchanger being characterised by said collar height being in the range of 0.20 to 2.0 mm (0.008 to 0.080 inches); and by further comprising: a stepped transitional portion connecting said contact portion and said elongated fin portion, said transitional portion having a second curved end portion having a second radius, said second curved end portion extending from said contact portion opposite said first end to an intermediate portion of said transitional portion, said transitional portion including a jog extending between and connecting said intermediate portion and said elongated fin portion so as to displace said fin portion longitudinally away from said collar contact portion; said tube being expanded to provide an interference fit with said collar contact portion. a tube; and a fin collar for achieving improved contact area on the tube, said fin collar comprising: an elongated fin portion for dissipating heat; and a collar leg connected with said fin portion, said collar leg having a height and including: a straight collar contact portion substantially perpendicular to said fin portion, wherein said contact portion has a collar contact height along which said contact portion contacts the tube; a first curved end portion having a first radius and extending from a first end of said contact portion; the heat exchanger being characterised by said collar height being in the range of 0.20 to 2.0 mm (0.008 to 0.080 inches); and by further comprising: a stepped transitional portion connecting said contact portion and said elongated fin portion, said transitional portion having a second curved end portion having a second radius, said second curved end portion extending from said contact portion opposite said first end to an intermediate portion of said transitional portion, said transitional portion including a jog extending between and connecting said intermediate portion and said elongated fin portion so as to displace said fin portion longitudinally away from said collar contact portion; said tube being expanded to provide an interference fit with said collar contact portion. an elongated fin portion for dissipating heat; and a collar leg connected with said fin portion, said collar leg having a height and including: a straight collar contact portion substantially perpendicular to said fin portion, wherein said contact portion has a collar contact height along which said contact portion contacts the tube; a first curved end portion having a first radius and extending from a first end of said contact portion; the heat exchanger being characterised by said collar height being in the range of 0.20 to 2.0 mm (0.008 to 0.080 inches); and by further comprising: a stepped transitional portion connecting said contact portion and said elongated fin portion, said transitional portion having a second curved end portion having a second radius, said second curved end portion extending from said contact portion opposite said first end to an intermediate portion of said transitional portion, said transitional portion including a jog extending between and connecting said intermediate portion and said elongated fin portion so as to displace said fin portion longitudinally away from said collar contact portion; said tube being expanded to provide an interference fit with said collar contact portion. a straight collar contact portion substantially perpendicular to said fin portion, wherein said contact portion has a collar contact height along which said contact portion contacts the tube; a first curved end portion having a first radius and extending from a first end of said contact portion; the heat exchanger being characterised by said collar height being in the range of 0.20 to 2.0 mm (0.008 to 0.080 inches); and by further comprising: a stepped transitional portion connecting said contact portion and said elongated fin portion, said transitional portion having a second curved end portion having a second radius, said second curved end portion extending from said contact portion opposite said first end to an intermediate portion of said transitional portion, said transitional portion including a jog extending between and connecting said intermediate portion and said elongated fin portion so as to displace said fin portion longitudinally away from said collar contact portion; said tube being expanded to provide an interference fit with said collar contact portion. a stepped transitional portion connecting said contact portion and said elongated fin portion, said transitional portion having a second curved end portion having a second radius, said second curved end portion extending from said contact portion opposite said first end to an intermediate portion of said transitional portion, said transitional portion including a jog extending between and connecting said intermediate portion and said elongated fin portion so as to displace said fin portion longitudinally away from said collar contact portion; said tube being expanded to provide an interference fit with said collar contact portion.