A heat dissipation device for dissipating heat from an electronic component (12) mounted on a printed circuit board (10) includes a retention module (30) resting on the printed circuit board, a heat sink (20) disposed on the retention module for contacting the electronic component, a clip (40) for securing the heat sink to the retention module, and a back plate unit mounted below the printed circuit board for engaging with the retention module and supporting the electronic component. The back plate unit includes a back plate (50), a gasket (62) engaging with the back plate, and a bracket (64) being sandwiched between the gasket and the back plate. The gasket has an annular top face contacting the printed circuit board, and a plurality of blocks (6202) contacting the back plate, whereby the gasket can provide a sufficient and uniform support to the electronic component.