A backlight module is configured to illuminate at least one key cap. The backlight module includes a light emitting unit, a light guide plate and a lighting board. The light guide plate has a light guide plate hole for accommodating the light emitting unit. The lighting board has at least one pair of pads connected to the light emitting unit respectively. The lighting board includes a first reflective layer surrounding the light emitting unit and at least partially covering the at least one pair of pads. Each of the at least one pair of pads has a plurality of branches and at least one hollow area. The at least one hollow area overlaps with at least one part of the light emitting unit. At least one lighting area is located between the at least one pair of pads.