Patent ID: 7129433

Claim:
A button assembly, comprising: a casing; a cylindrical key top loosely inserted into a hole formed on said casing, wherein the upper surface of the key top is a pressed face; a deformation member disposed below said key top in the pressing direction, wherein said deformation member deforms to produce repulsive force when said key top is pressed down; a conductive member attached on the bottom of said deformation member; switch contacts which come into contact with said conductive member and become conductive by the deformation of said deformation member; and a tilting prevention assembly for controlling the movement of said key top in the pressing direction to prevent tilting of said key top, wherein said tilting prevention assembly comprises: a protrusion extending in the pressing direction from the side wall of said key top with certain length; and guiding member extending from said casing in the pressing direction with certain length to accommodate said protrusion from at least two directions, wherein said protrusion slides over said guiding member when said key top is pressed down, wherein said protrusion and said guiding member are positioned to contact with each other via at least one surface, and said one surface receives moment of said key top due to the separation between a central axis of said key top and a central axis of said conductive member when said key top is pressed down, wherein said protrusion has at least three surfaces extending in the pressing direction, said guiding member comprises a flat plate and an L-shaped plate having an L-shaped cross section opposite to said flat plate, wherein one surface of said flat plate and two surfaces of said L-shaped plate are positioned on said casing to be in front of three surfaces of said protrusion.