A retention module (10) for securing a heat sink (20) to a printed circuit board (30) includes a pair of carriage arms (12) separated by a space and a connecting wall (14) interconnecting opposite rear free ends of the carriage arms. Each of the carriage arms integrally forms a lock catch (122) thereon to clasp the heat sink. A pair of opposite positioning ears (15) extend upwardly from corners where the carriage arms are connected with the connecting wall. The retention module and the heat sink are preassembled together via the lock catches clasping the heat sink before the retention module is mounted on the printed circuit board.