Heat exchanger with a finned flat tubes block and method of assembling

The heat exchanger with a rib (3)-flat tube (2)-block comprises a series of flat tubes, between which are ribs, the ends of the flat tubes issuing into opposing collection or changeover casings. The ends of the flat tubes are so formed that a wide side of a tube is connectable with the wide side of an adjacent tube. The wide sides thus close the collection or changeover casings at least partially. The ends of the flat tubes with their narrow sides are in contact with connecting edges of the collection or changeover casings, to which they are joined by soldering. The ends are so formed that the wide sides of adjacent flat tube ends are connectable at their insides (10) or so that the connection between the outside of the wide side of a flat tube end and the inside of the wide side of the adjacent flat tube end can be effected.