Abstract: The invention relates to a heat exchanger (1), in particular a charge intercooler or coolant cooler for motor vehicles, which comprises a soldered block which is made of pipes (4), ribs and at least one pipe base (2), in addition to at least one plastic box (3) which has a wall (3a) which extends in the cross-section and which is approximately U shaped and a surrounding flange (3b). The box is mechanically connected to the pipe base over flange (3b). According to the disclosure, reinforcing ribs are arranged on the inner side of the plastic box (3) in a transition area between the flange (3b) and the wall (3a).