A back plate assembly (100) for a board (200) comprises a back plate (110) abutting against a side of the board and a plurality of posts (120). Each post comprises at least one latching portion (1206) formed thereon. After the latching portions have passed through the back plate and the board, the latching portions are blocked by one of the board and the back plate to secure the back plate to the board. Screws (330) are used to extend through a heat sink (300) to threadedly engage with the posts thereby mounting the heat sink to the board. Thus, the heat sink can have an intimate contact with an electronic component (210) mounted on the board.