A heat dissipation device assembly includes a heat dissipation device mounted on a printed circuit board and a retainer device mounted below the printed circuit board. The retainer device includes a back plate and a crank pivotably mounted to the back plate. The crank includes a pressing portion and a handle for receiving a rotation force. Posts are extended from the heat dissipation device through the printed circuit board to engage with the back plate, thereby to pre-assemble the heat dissipation device on the printed circuit board. The handle is pushed to rotate between a released position and a locked position. In the locked position, the pressing portion extends through the back plate to push the printed circuit board toward the heat dissipation device, whereby an electronic component on the printed circuit board has an intimate contact with the heat dissipation device.