Abstract: A heat exchanger having a plurality of elongated, generally flat tubes is disclosed, each tube including a planar base, a top, and pair of arcuate opposed side portions interposed between the base and the top is disclosed. A partition extends from the top to the base to define a pair of fluid passageways, the partition including a pair of opposing, contacting shoulder portions and a leg portion depending from each of the shoulder portions which contact the base. A first braze receiving of predetermined size is defined between the shoulder portions and the manifold of the heat exchanger. The size of the braze receiving area is controlled by minimizing the curvature of the shoulder portions.