The invention relates to a soldered heat exchanger, especially a capacitor for a motor vehicle ventilation system, comprising a heat exchanger network made of tubes and ribs and at least one collector pipe made of a base (2) and a cover (3) and separating walls (8), whereby the base (2) and the cover (3) have edges (4, 5, 6, 7) which overlap on the longitudinal sides thereof. The base (2) receives the ends of the tubes and the separating walls (8) are fixed in relation to the cover (3) by means of a first and second shoulder (8b, 8c and a lug (8a). According to the invention, groove-shaped recesses (3b, 3c) are arranged in the edges (6, 7) of the cover (3) in the region of the separating walls (8), wherein the shoulders (8b, 8c) of the separating walls (8) engage. A secure positioning of the separating walls in the collector pipe is obtained in addition to a leakage-free soldering of the capacitor.