US Patent 7903421 Locking device and electronic device using the same

An electronic device comprises a printed circuit board, a heat sink and a plurality of locking devices securing the heat sink to the printed circuit board. Each locking device comprises a shaft, a knob and an elastic member. The shaft has a plurality of outer teeth protruding outwardly from an outer surface of a top end thereof. The outer teeth are arranged along an axial direction of the shaft. The knob has an inner tooth meshing with the outer teeth of the shaft. The elastic member is compressed between a bottom of the knob and the heat sink. A length of the elastic changes when the inner tooth of the knob meshes with different outer teeth along the axial direction of the shaft to adjust a pressure of the locking device on the heat sink.