The present invention relates to a power unit comprising at least one power electronics module, a circuit carrier, which is connected to said power electronics module, and at least one heat sink, which is connected to said power electronics module, in order to dissipate heat. The invention also relates to an associated heat sink and a corresponding assembly method. In order to provide a power unit and an associated assembly method which allows improved dissipation of air heat, as well as adequate electrical insulation of the power modules and simplified implementation, the circuit carrier comprises at least one through hole. At least one contact extension located on the heat sink, which is at least partially received by the through hole. The contact extension of the heat sink is thermally contacted with the power electronics module by means of a heat-conductive material.