A heat exchanger (100; 200), including channels for circulation of a fluid, which extend lengthwise along a first axis (X-X) between respective opposite ends of the channels and in which the fluid is intended to flow between said ends along the first axis, the heat exchanger comprising a plurality of layers that are flat and superimposed on one another along a second axis (Z-Z) that is both perpendicular to respective planes of the layers and perpendicular to the first axis (X-X), each of the channels being defined jointly by first, second and third layers among the plurality of layers, the second layer (L2.C) associated with each channel being intercalated, along the second axis (Z-Z), directly between the first layer (L1.C) and the third layer (L3.C) that are associated with this channel, such that each channel is delimited by: - a face (F.L1.C) of the first layer associated with this channel, which faces, along the second axis (Z-Z), toward the second and third layers associated with this channel, - a face (F.L3.C) of the third layer associated with this channel, which faces, along the second axis, toward the first and second layers associated with this channel, and - edges (E1.L2.C, E2.L2.C) of the second layer associated with this channel, which are arranged parallel to the first axis (X-X) and transverse to the plane of this second layer, these edges being formed by strips (B1.L2.C, B2.L2.C; B1, B2) of this second layer that are fusion welded to the first and third layers associated with this channel over fusion zones (Z1.C, Z2.C, Z3.C, Z4.C) that extend continuously over the entire length of the channel between its opposite ends and that are located, along a third axis (Y-Y) perpendicular to the first and second axes, on either side of the channel, characterized in that each layer of the plurality of layers is made up of metal strips (B; B1, B2) such that the strips of a same layer all extend lengthwise along a direction perpendicular to the second axis (Z-Z) and are adjacent to one another, without necessarily touching, in the plane of the considered layer, each of the strips of each layer of the plurality of layers occupying the entire thickness, along the second axis (Z-Z), of the corresponding layer. including channels for circulation of a fluid, which extend lengthwise along a first axis (X-X) between respective opposite ends of the channels and in which the fluid is intended to flow between said ends along the first axis, the heat exchanger comprising a plurality of layers that are flat and superimposed on one another along a second axis (Z-Z) that is both perpendicular to respective planes of the layers and perpendicular to the first axis (X-X), each of the channels being defined jointly by first, second and third layers among the plurality of layers, the second layer (L2.C) associated with each channel being intercalated, along the second axis (Z-Z), directly between the first layer (L1.C) and the third layer (L3.C) that are associated with this channel, such that each channel is delimited by: - a face (F.L1.C) of the first layer associated with this channel, which faces, along the second axis (Z-Z), toward the second and third layers associated with this channel, - a face (F.L3.C) of the third layer associated with this channel, which faces, along the second axis, toward the first and second layers associated with this channel, and - edges (E1.L2.C, E2.L2.C) of the second layer associated with this channel, which are arranged parallel to the first axis (X-X) and transverse to the plane of this second layer, these edges being formed by strips (B1.L2.C, B2.L2.C; B1, B2) of this second layer that are fusion welded to the first and third layers associated with this channel over fusion zones (Z1.C, Z2.C, Z3.C, Z4.C) that extend continuously over the entire length of the channel between its opposite ends and that are located, along a third axis (Y-Y) perpendicular to the first and second axes, on either side of the channel, - a face (F.L1.C) of the first layer associated with this channel, which faces, along the second axis (Z-Z), toward the second and third layers associated with this channel, - a face (F.L3.C) of the third layer associated with this channel, which faces, along the second axis, toward the first and second layers associated with this channel, and - edges (E1.L2.C, E2.L2.C) of the second layer associated with this channel, which are arranged parallel to the first axis (X-X) and transverse to the plane of this second layer, these edges being formed by strips (B1.L2.C, B2.L2.C; B1, B2) of this second layer that are fusion welded to the first and third layers associated with this channel over fusion zones (Z1.C, Z2.C, Z3.C, Z4.C) that extend continuously over the entire length of the channel between its opposite ends and that are located, along a third axis (Y-Y) perpendicular to the first and second axes, on either side of the channel, characterized in that each layer of the plurality of layers is made up of metal strips (B; B1, B2) such that the strips of a same layer all extend lengthwise along a direction perpendicular to the second axis (Z-Z) and are adjacent to one another, without necessarily touching, in the plane of the considered layer, each of the strips of each layer of the plurality of layers occupying the entire thickness, along the second axis (Z-Z), of the corresponding layer.