The invention relates to a method for manufacturing a heat exchanger including stacking a set of plates parallel to one another and to a longitudinal direction so as to define a plurality of passages suitable for the flow in the longitudinal direction of a first fluid to be brought into a heat-exchange relationship with at least a second fluid, said plates being delimited by a pair of longitudinal edges extending in the longitudinal direction and a pair of lateral edges extending in a lateral direction perpendicular to the longitudinal direction, and forming at least one of the plates by superposing at least a first flat product and a second flat product on top of one another, having at least one groove that extends parallel to the plates and leads towards the outside of the stack through at least one opening in a lateral or longitudinal edge.