Keyboard and backlight module

A backlight module, applied to a keyboard, wherein the keyboard comprises a base plate having a short axis direction and a long axis direction, wherein the base plate comprises at least one long slit disposed on the base plate along the short axis direction, and the backlight module is disposed on a side of the base plate such that a length of the base plate can be adjusted along the long axis direction, the backlight module comprising:

• a shielding sheet comprising an upper surface and a lower surface, the upper surface facing toward the base plate;
• a light guide plate disposed on the lower surface of the shielding sheet;
• and
• a reflecting sheet disposed below the light guide plate and comprising a plurality of first slits, wherein when the length of the base plate is adjusted along the long axis direction, the reflective sheet is adjusted and moved along with the base plate by expansion of the plurality of first slits.