Keyboard device and key structure thereof

A keyboard device comprising plural key structures, wherein each key structure comprises:

• a membrane circuit board;
• a supporting plate comprising a perforation through the supporting plate;
• a keycap located over the supporting plate, and movable upwardly or downwardly relative to the supporting plate;
• a connecting member connected between the supporting plate and the keycap;
• and a hook element installed on the supporting plate, wherein the connecting member is connected with the supporting plate through the hook element, wherein the hook element comprises a positioning part penetrated through the perforation of the supporting plate;
• and a fixing structure covering a portion of a bottom surface of the supporting plate, wherein a maximum distance between the positioning part and a side surface of the perforation is less than an overlapping width between the fixing structure and the supporting plate, wherein the supporting plate is made of a first material with a first specific gravity, and the hook element is made of a second material with a second specific gravity, wherein the second specific gravity is higher than the first specific gravity;
• wherein each key structure further comprises a backlight module, wherein the backlight module is located under the supporting plate, and the supporting plate is arranged between the membrane circuit board and the backlight module, the backlight module having an opening, wherein the fixing structure is accommodated within the opening of the backlight module.