Centrifugal fan

A centrifugal fan comprising:

• a motor that has a stator and a rotor rotatable with respect to the stator;
• a circuit board electrically connected to the motor;
• an impeller fixed to the rotor, wherein the impeller is configured to rotate together with the rotor, wherein the impeller includes:
• a boss portion fixed to the rotor,
• a plurality of blade portions arranged at intervals in a circumferential direction on an outer peripheral surface of the boss portion, wherein each of the plurality of blade portions extends outward in a radial direction,
• an upper shroud connected to at least a first portion of each of the plurality of blade portions, and
• a lower shroud connected to at least a second portion of each of the plurality of blade portions, wherein the second portion is closer to the circuit board than the first portion, and a lower surface of the second portion of each of the plurality of blade portions is opposed to an upper surface of the circuit board in the axial direction;
• a gap for conducting airflow across the circuit board, wherein the gap is defined between a surface of the second portion of each of the plurality of blade portions and a surface of the circuit board;
• and
• a casing that accommodates the motor, the impeller, and the circuit board, wherein the casing includes:
• a lower casing recessed outward from the impeller in an axial direction, wherein the lower casing comprises a board housing portion that accommodates the circuit board.