A method for producing a heat exchanger module with at least two fluid circuits each comprising channels, comprising the following steps: a/ producing at least two separate groups of metal tubes (2; 2A, 2B), each tube being of elongated shape and having at least two straight ends, one thereof (20; 20A, 20B) being open and the other (21, 3; 21A, 3A-21B, 3B) being blind; b/ aligning each of the two groups with side-by-side positioning of the tubes in at least one row (2.1, 2.2, 2.3,...2i-l, 2i) per group; c/ alternate stacking with top-to-toe positioning of the row(s) of one group and the row(s) of the other group so as to have the rows on top of one another and the blind ends of the tubes of one group arranged on the same lateral side of the stack as the open ends of the tubes of the other group; d/ offsetting, in a direction at right angles to the stacking direction, of the row(s) of one group relative to the row(s) of the other group, so as to create gaps on each lateral side of the stack, between the blind ends of the tubes of one group and the open ends of the tubes of the other group; e/ encapsulating the stack by positioning respectively one metal casing on the longitudinal sides of the stack of tubes and metal strips (5; 5A, 5B) at the end of the offset blind ends of the tubes in each gap created; f/ welding on the periphery of the casing, each strip and each open end of the tube so as to seal the inside of the encapsulated stack whilst leaving free the open ends of the tubes; i/ applying a hot isostatic pressing cycle at high pressure to the degassed stack, allowing the pressurizing gas to penetrate into all of the tubes via their open ends (20; 20A, 20B) so as to obtain welding by diffusion between the constituent parts of the encapsulated stack, the tubes of each group welded by diffusion forming the channels of a fluid circuit of the module; l/ transverse boring of the tubes, in the plane of each row and in the vicinity of the lateral sides of the stack, the orifices (22, 410) of each group of tubes, produced by boring, opening out onto one longitudinal side of the stack through the casing, forming a column, the two columns of orifices (22, 410) each being arranged in the vicinity of one lateral side of the stack and opposing one another. a/ producing at least two separate groups of metal tubes (2; 2A, 2B), each tube being of elongated shape and having at least two straight ends, one thereof (20; 20A, 20B) being open and the other (21, 3; 21A, 3A-21B, 3B) being blind; b/ aligning each of the two groups with side-by-side positioning of the tubes in at least one row (2.1, 2.2, 2.3,...2i-l, 2i) per group; c/ alternate stacking with top-to-toe positioning of the row(s) of one group and the row(s) of the other group so as to have the rows on top of one another and the blind ends of the tubes of one group arranged on the same lateral side of the stack as the open ends of the tubes of the other group; d/ offsetting, in a direction at right angles to the stacking direction, of the row(s) of one group relative to the row(s) of the other group, so as to create gaps on each lateral side of the stack, between the blind ends of the tubes of one group and the open ends of the tubes of the other group; e/ encapsulating the stack by positioning respectively one metal casing on the longitudinal sides of the stack of tubes and metal strips (5; 5A, 5B) at the end of the offset blind ends of the tubes in each gap created; f/ welding on the periphery of the casing, each strip and each open end of the tube so as to seal the inside of the encapsulated stack whilst leaving free the open ends of the tubes; i/ applying a hot isostatic pressing cycle at high pressure to the degassed stack, allowing the pressurizing gas to penetrate into all of the tubes via their open ends (20; 20A, 20B) so as to obtain welding by diffusion between the constituent parts of the encapsulated stack, the tubes of each group welded by diffusion forming the channels of a fluid circuit of the module; l/ transverse boring of the tubes, in the plane of each row and in the vicinity of the lateral sides of the stack, the orifices (22, 410) of each group of tubes, produced by boring, opening out onto one longitudinal side of the stack through the casing, forming a column, the two columns of orifices (22, 410) each being arranged in the vicinity of one lateral side of the stack and opposing one another.