Abstract: A unitary plate type heat exchanger structure in which stacked core sheets, tube sheets, continuous frame members, nose pieces and corrugated fin material are joined together as by brazing to form a one-piece construction with integrated flow passages for at least one of the fluids. The parts combine with one another in a manner facilitating assembly and obviating separate attachment of a manifold means. Interior parts, including nose pieces, frame members and tube sheets are structured inherently to provide flow passages for a confined fluid. In the brazing process the parts are interconnected in a manner to resist deformation and separation of formed joints, and, means are installed to obviate the effects of high internal pressure, particularly at confined fluid inlet and outlet locations.