An exemplary electronic device assembly includes a printed circuit board with an electronic component thereon, and a heat dissipation device. The heat dissipation device includes a heat sink mounted on the printed circuit board and a heat pipe pivotably engaged with the heat sink. The heat sink includes a main body defining a transverse channel therethrough and an injection aperture at a top of the main body to communicate the channel and an exterior of the main body. The heat pipe is pivotably engaging in the channel of the main body. A gap is defined between the heat pipe and the heat sink. Heat conductive grease is injected into the channel and filled in the gap between the heat pipe and the heat sink to thermally connect the heat sink with the heat pipe.