TWI521142B - Miniature fan - Google Patents

Description

Micro cooling fan

The present invention relates to a heat dissipating fan, and more particularly to a micro cooling fan suitable for use in small electronic products.

In general, since electronic components in electronic products generate heat during operation, many electronic products have been equipped with a cooling fan for a long time, and the airflow is forced by the driving effect of the cooling fan to discharge the electronic products. The internal high-temperature gas discharge increases the heat dissipation efficiency of the electronic product during operation, so that the electronic product can maintain stable operation; among them, the common cooling fan can be roughly divided into radial gas according to the air gap type between the magnetic element and the stator. The gap motor fan 8 (shown in Figure 1) and the axial air gap motor fan 9 (shown in Figure 2) are two types.

Referring to FIG. 1 , a conventional radial air gap motor fan 8 generally includes a housing 81 , an impeller 82 , a circuit board 83 , and a stator 84 . The housing 81 has a bottom plate 811 . And a shaft tube 812, the shaft tube 812 is disposed on the bottom plate 811; the impeller 82 is connected to a hub 822 by a rotating shaft 821 and rotatably disposed on the shaft tube 812, and a plurality of blades 823 are disposed on the outer edge of the hub 822. A magnetic component 824 is disposed on the inner annular surface of the hub 822. The circuit board 83 and the stator 84 are respectively sleeved on the outer circumferential surface of the shaft tube 812 and electrically connected to each other. The stator 84 is opposite to the magnetic component 824. There is a radial air gap G1 between the stator 84 and the magnetic element 824. According to this configuration, the conventional radial air gap motor fan 8 can be magnetically acted upon by the excited stator 84 and the magnetic member 824, causing the impeller 82 to rotate relative to the housing 81. An embodiment of the conventional radial air gap motor fan 8 has been disclosed in the Republic of China Announcement No. M443376 "Ma" And the fan" patent case.

Referring to FIG. 2, a conventional axial air gap motor fan 9 generally includes a housing 91, an impeller 92, a circuit board 93 and a stator 94 having a bottom plate 911. And a shaft tube 912, the shaft tube 912 is disposed on the bottom plate 911; the impeller 92 is connected to a hub 922 by a rotating shaft 921 and rotatably disposed on the shaft tube 912, and a plurality of blades 923 are disposed on the outer edge of the hub 922. a magnetic element 924 is disposed on a surface of the hub 922 facing the bottom plate 911; the circuit board 93 is sleeved on the outer circumferential surface of the shaft tube 912; and the stator 94 is an array coil wound by winding. The stator 94 is disposed on the circuit board 93 and electrically connected to the circuit board 93. The stator 94 is opposite to the magnetic element 924. The stator 94 and the magnetic element 924 have an axial air gap G2. According to this configuration, the conventional axial air gap motor fan 9 can be magnetically acted upon by the excited stator 94 and the magnetic member 924, causing the impeller 92 to rotate relative to the housing 91. An embodiment of a motor similar to the conventional axial air gap motor fan 9 has been disclosed in the "Motor" patent case of the Republic of China Announcement No. I342098.

However, although the above-described conventional radial air gap motor fan 8 and axial air gap motor fan 9 are both sufficient to provide good heat dissipation for early electronic products, the conventional radial air gap motor fan 8 and the axial direction are known. The air gap motor fan 9 is a cooling fan of a general size, and the total height of the motor in the axial direction (i.e., the maximum axial height between the bottom plates 811, 911 of the housings 81, 91 and the hubs 822, 922) is about It is 30mm or more, and it is not suitable for small electronic products that are currently in line with the trend of thin and light. Moreover, when it is desired to manufacture a micro fan that can be incorporated into a small electronic product (the total height of the motor in the axial direction is about 7 mm or less), it is not a conventional radial air gap motor fan 8 or an axial air gap motor. The fan 9 can be scaled down; it is necessary to consider whether the miniaturization of each component is limited in the process technology, and whether the obtained component can still achieve the desired fan performance after assembly (for example, between the stator and the magnetic component) Whether the magnetic action can generate enough rotational torque to drive the fan wheel to rotate relative to the housing and generate the expected air volume, etc., the development of the micro fan is facing great difficulties and challenges.

That is to say, with the trend of thinner and lighter and higher performance of small electronic products, when the small electronic products are operated, the heating temperature of the electronic components will be improved, and the heat dissipation space is limited, etc., so that the heat dissipation of the electronic components is further improved. It is not easy, so it is easy to produce unstable performance, affect the reliability of small electronic products, and cause functional characteristics to decline, unable to play or even crash; therefore, even when making miniature fans, it can overcome the limitations of process technology, according to the knowledge The radial air gap motor fan 8 or the axial air gap motor fan 9 is scaled down to produce a micro fan, but after the micro fan is assembled into a small electronic product, the amount of air generated by the micro fan may not be able to operate. Meet the cooling needs of small electronic products.

In addition, in view of the structure of the conventional radial air gap motor fan 8 and the axial air gap motor fan 9, the circuit board 83 of the conventional radial air gap motor fan 8 is fitted to the outer ring of the shaft tube 812. The circumferential surface is such that a space is left between the bottom of the circuit board 83 and the bottom plate 811, so that the axial height of the conventional radial air gap motor fan 8 is difficult to reduce; similarly, the axial air gap motor fan The stator 94 of 9 is obtained by winding a coil, and the coil must be wound with a sufficient number of turns to provide an appropriate excitation effect. Therefore, the stator 94 must have a certain axial thickness, which also becomes the conventional axis. The reason why the overall axial height of the air gap motor fan 9 is difficult to reduce.

Therefore, the structure types of the conventional radial air gap motor fan 8 and the axial air gap motor fan 9 and the proportional relationship between the components are not suitable as reference standards for the micro fan, so that the micro fan is in the development process. In the process, the structural design of the components must be carried out by the designer's experience or through trial and error, and the fan performance test is repeated until the fan performance meets the specifications, and the development time and labor are increased. .

The object of the present invention is to provide a micro-cooling fan whose fan member size conforms to a preferred ratio, so that the total axial height of the motor of the micro-cooling fan can be maintained below 7 mm, and the micro-cooling fan can ensure proper operation when operating. Air volume and wind pressure for installation in small electronic products, with good fan performance to meet the cooling needs of small electronic products.

Another object of the present invention is to provide a micro-cooling fan which can be used as a design reference standard for a micro-fan with a total axial height of 7 mm or less. As long as the proportional relationship between the components in the micro-fan is in accordance with a preferred ratio, Ensuring that the micro fan has good fan performance helps reduce the development time and labor of the design micro fan.

In order to achieve the foregoing objectives, the technical content of the present invention includes: a micro-cooling fan comprising: a frame having a bottom plate and a shaft joint, the shaft joint being disposed on the bottom plate; and a fan wheel being rotated by a shaft Connecting a hub and rotatably disposed at a shaft portion of the fan frame, a plurality of blade rings are disposed on an outer edge of the hub, a magnetic component is disposed on an inner surface of the hub; and a circuit board is disposed on the shaft An outer periphery of the portion is attached to the bottom plate; and a stator electrically connected to the circuit board and opposite to the magnetic component, the stator and the magnetic component having a magnetic air gap; wherein, in the micro cooling fan In the axial direction, a bottom wall of the fan frame and a hub of the fan wheel have a first maximum axial height (A), and the bottom plate and the circuit board have a second maximum axial height (B), the first a maximum axial height is less than or equal to 7 mm, and a ratio (B/A) of the second maximum axial height to the first maximum axial height is 0.05-0.45; wherein the bottom plate has an opposite outer surface and a An inner surface, the shaft portion protrudes from an inner surface of the bottom plate; the hub a radial extension, the hub being coupled to the rotating shaft by the radial extension, the radially extending portion having an opposite outer surface and an inner surface, the inner surface of the radially extending portion facing an inner surface of the bottom plate, a magnetic element is disposed on an inner surface of the radially extending portion; the circuit board has an opposite first surface and a second surface, the circuit board is attached to the inner surface of the bottom plate by the first surface; the stator has a a wiring layer, the wiring layer is disposed on the second surface of the circuit board, the stator is opposite to the magnetic component by the wiring layer, the magnetic interference air gap is located between the wiring layer and the magnetic component, and the wiring layer and the wiring layer The magnetic element is axially spaced apart; in the axial direction of the micro cooling fan, the first maximum axial height (A) is a maximum axial height of an outer surface of the bottom plate to an outer surface of the radially extending portion of the hub, the first The maximum axial height (B) is the maximum axial height of the outer surface of the bottom plate to the second surface of the circuit board.

Among them, the ratio is preferably from 0.15 to 0.30.

Wherein, the circuit board is tightly fitted to the shaft joint portion, and the first surface of the circuit board is directly attached to the inner surface of the bottom plate of the fan frame. Alternatively, the circuit board is tightly fitted to the shaft portion, and the first surface of the circuit board is provided with an insulating sheet, and the circuit board is indirectly attached to the inner surface of the bottom plate of the fan frame by the insulating sheet.

The loose fit ring of the circuit board is sleeved on the shaft joint, and the first surface of the circuit board is directly adhered to the inner surface of the bottom plate of the fan frame. Alternatively, the circuit board loosely fits around the shaft portion, and the first surface of the circuit board is provided with an insulating sheet, and the circuit board is indirectly adhered to the inner surface of the bottom plate of the fan frame by the insulating sheet.

Accordingly, the micro-cooling fan of the present invention has a fan member size conforming to a preferred ratio, so that the total axial height of the motor of the micro-cooling fan can be maintained below 7 mm, and the appropriate air volume can be generated when the micro-cooling fan operates. With wind pressure for installation in small electronic products, and with good fan performance to meet the cooling needs of small electronic products. In addition, the micro-cooling fan of the present invention can also be used as a design reference standard for a micro-fan with a total axial height of the motor of 7 mm or less. As long as the ratio between the components in the micro-fan is matched to a preferred ratio, the micro-fan can be ensured. Good fan performance helps reduce the development time and labor of designing miniature fans.

〔this invention〕

1‧‧‧Fan frame

11‧‧‧floor

11a‧‧‧Outer surface

11b‧‧‧ inner surface

12‧‧‧ Side wall

13‧‧‧ Cover

14‧‧‧Axis joint

2‧‧‧fan wheel

21‧‧‧ shaft

22‧‧·wheels

22a‧‧‧ Inner torus

221‧‧‧ Radial extension

221a‧‧‧Outer surface

221b‧‧‧ inner surface

222‧‧‧ axial extension

23‧‧‧ fan leaves

24‧‧‧Magnetic components

3‧‧‧Circuit board

3a‧‧‧ first surface

3b‧‧‧ second surface

4‧‧‧ Stator

41‧‧‧Magnetic pole set

42‧‧‧Insulation kit

43‧‧‧ coil group

5‧‧‧fan wheel

51‧‧‧ shaft

52‧‧·wheels

521‧‧‧ Radial extension

521a‧‧‧ outer surface

521b‧‧‧ inner surface

53‧‧‧ fan leaves

54‧‧‧Magnetic components

6‧‧‧ Stator

61‧‧‧ wiring layer

S‧‧‧室

G‧‧‧Magnetic air gap

A, A’‧‧‧ first maximum axial height

B, B’‧‧‧ second maximum axial height

[Use]

8‧‧‧ Radial air gap motor fan

81‧‧‧Shell

811‧‧‧floor

812‧‧‧ shaft tube

82‧‧‧ Impeller

821‧‧‧ shaft

822‧‧ wheels

823‧‧‧ fan leaves

824‧‧‧Magnetic components

83‧‧‧ boards

84‧‧‧ Stator

9‧‧‧Axial air gap motor fan

91‧‧‧Shell

911‧‧‧floor

912‧‧‧ shaft tube

92‧‧‧ Impeller

921‧‧‧ shaft

922‧‧·wheels

923‧‧‧ fan leaves

924‧‧‧Magnetic components

93‧‧‧Circuit board

94‧‧‧ Stator

G1‧‧‧radial air gap

G2‧‧‧ axial air gap

Figure 1: Schematic diagram of a side cross-sectional view of a conventional radial air gap motor fan.

Figure 2: Schematic diagram of a side cross-sectional view of a conventional axial air gap motor fan.

Fig. 3 is a side sectional view showing the first embodiment of the present invention.

Fig. 4 is a partial enlarged view of Fig. 3.

Fig. 5 is a side sectional structural view showing a second embodiment of the present invention.

Fig. 6 is a partial enlarged view of Fig. 5.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

Referring to FIG. 3, which is a first embodiment of the micro-cooling fan of the present invention, the micro-heating fan generally comprises a frame 1, a fan wheel 2, a circuit board 3 and a stator 4, and the fan wheel 2 The circuit board 3 and the stator 4 are all disposed in the fan frame 1. The stator 4 is electrically connected to the circuit board 3 to drive the fan wheel 2 to rotate and generate airflow. The micro cooling fan may be an axial fan or a drum. In the form of a wind fan or the like, the present invention is described below as an example of an air blower fan, but is not limited thereto.

The fan frame 1 is a hollow frame structure capable of introducing and extracting airflow. In the embodiment shown in FIG. 3, the frame 1 may include a bottom plate 11, a side wall 12 and a cover plate 13, the bottom plate 11 has an opposite outer surface 11a and an inner surface 11b. The side wall 12 is disposed on the inner surface 11b of the bottom plate 11. The cover plate 13 is connected to the side wall 12 and opposite to the inner surface 11b of the bottom plate 11 to A chamber S is formed between the bottom plate 11, the side wall 12 and the cover plate 13 for receiving the remaining members of the micro cooling fan. The fan frame 1 further includes a shaft portion 14 disposed on the bottom plate 11 and protruding from the inner surface 11b of the bottom plate 11. The shaft portion 14 can be integrally connected with the bottom plate 11, or It is detachably coupled to the bottom plate 11.

The fan wheel 2 is disposed in the chamber S of the fan frame 1 and is connected to a hub 22 by a rotating shaft 21 and rotatably disposed on the shaft connecting portion 14 of the fan frame 1. A plurality of blades 23 are disposed on the hub. At the outer edge of 22, a magnetic element 24 is provided on the inner surface of the hub 22. In this embodiment, the hub 22 has a radial extension portion 221 and an axial extension portion 222. The rotation shaft 21 is connected to the radial extension portion 221 by one end, and the rotation shaft 21 is preferably connected to the radial extension portion. a central position of the 221; the radially extending portion 221 has an opposite outer surface 221a and an inner surface 221b, and the inner surface 221b of the radially extending portion 221 faces the inner surface 11b of the bottom plate 11 of the frame 1; The extending portion 222 is coupled to the end edge of the radially extending portion 221 and extends toward the inner surface 11b of the bottom plate 11 The inner extending surface 22a of the hub 22 is formed by the axial extending portion 222 facing the surface of the rotating shaft 21. The other end of the rotating shaft 21 is rotatably disposed on the shaft connecting portion 14 of the fan frame 1; the plurality of blades 23 are annularly disposed on the outer edge of the hub 22, and the plurality of blades 23 are selectable with the hub 22 is integrally formed or removably coupled; the magnetic member 24 is disposed on the inner surface of the hub 22 (in this embodiment, the inner annular surface 22a of the hub 22 is selected).

Referring to FIGS. 3 and 4, the circuit board 3 is disposed on the outer periphery of the shaft portion 14 and attached to the bottom plate 11 of the fan frame 1. In the embodiment, the circuit board 3 has a first one. The surface 3a and the second surface 3b, the circuit board 3 may be tightly fitted to the shaft portion 14 and maintain the first surface 3a of the circuit board 3 attached to the inner surface of the bottom plate 11 of the fan frame 1. 11b; Alternatively, the circuit board 3 may be loosely fitted around the shaft portion 14 and passed through the first surface 3a of the circuit board 3 through a glue such as a backing glue or a glue, or may be adhered and fixed by hot melt. The inner surface 11b of the bottom plate 11 of the fan frame 1. When the bottom plate 11 of the fan frame 1 is made of an insulating material, the circuit board 3 can be directly attached to the inner surface 11b of the bottom plate 11 of the fan frame 1 by the first surface 3a; when the bottom plate 11 of the fan frame 1 is In the non-insulating material, the first surface 3a of the circuit board 3 may be provided with an insulating sheet (not shown), and the circuit board 3 is indirectly attached to the inner surface 11b of the bottom plate 11 of the fan frame 1 by the insulating sheet. .

The stator 4 may include a pole piece set 41, an insulating sleeve set 42 and a coil set 43; the pole piece set 41 has at least one pole piece, the pole piece is made of a magnetically permeable material, and the pole piece may be For example, in the embodiment, the number of pole pieces of the pole piece group 41 may be several, and each pole piece is arranged in an axial direction, and the insulating sleeve set 42 is disposed on two axes of the pole piece group 41. To the end, the coil assembly 43 is wound around a predetermined portion of the insulating sleeve 42 and electrically connected to the circuit board 3; further, the combined coil set 41 and the insulating sleeve set 42 are wound by the coil assembly 43 and are selectable. The outer peripheral wall of the shaft portion 14 of the fan frame 1 is sleeved so that the pole piece group 41 faces the magnetic element 24 of the fan wheel 2, and maintains a magnetic air gap G therebetween, and the magnetic pole The set 41 is radially spaced from the magnetic element 24 to be excited by the pole piece set 41 Magnetic interaction with the magnetic element 24 causes the fan wheel 2 to rotate relative to the frame 1.

Wherein, in the axial direction of the micro cooling fan, the bottom plate 11 of the fan frame 1 and the hub 22 of the fan wheel 2 have a first maximum axial height A, and the bottom plate 11 and the circuit board 3 have a a second maximum axial height B; in the embodiment as shown in Fig. 3, the first maximum axial height A is the outer surface 11a of the bottom plate 11 to the outer surface 221a of the radially extending portion 221 of the hub 22. The maximum axial height B is the maximum axial height of the outer surface 11a of the bottom plate 11 to the second surface 3b of the circuit board 3. Moreover, the first maximum axial height A is less than or equal to 7 mm, and the ratio of the second maximum axial height B to the first maximum axial height A (B/A) is in accordance with 0.05 to 0.45, preferably 0.15~ 0.30, the micro-cooling fan can generate proper air volume and wind pressure when it operates.

Referring to FIG. 5 , which is a second embodiment of the micro cooling fan of the present invention, the micro cooling fan generally includes a frame 1 , a fan wheel 5 , a circuit board 3 and a stator 6 , wherein the fan frame 1 The circuit board 3 is substantially the same as the first embodiment described above, and thus will not be described again.

The fan wheel 5 is disposed in the chamber S of the fan frame 1. The fan wheel 5 includes a rotating shaft 51, a hub 52, a plurality of blades 53 and a magnetic component 54. The rotating shaft 51 is connected to the hub 52 by one end. And the other end is rotatably disposed on the shaft joint portion 14 of the fan frame 1; the hub 52 has a radial extending portion 521, the rotating shaft 51 is connected to the radial extending portion 521 by one end, and the rotating shaft 51 is preferably connected. At a central position of the radially extending portion 521; the radially extending portion 521 has an opposite outer surface 521a and an inner surface 521b, and the inner surface 521b of the radially extending portion 521 faces the bottom plate 11 of the fan frame 1. The surface of the hub 52 is disposed on the outer edge of the hub 52, and the plurality of blades 53 may be integrally formed or removably coupled to the hub 52; the magnetic component 54 is disposed on the hub The inner surface 521b of the radially extending portion 521 of 52 faces the inner surface 11b of the bottom plate 11.

Referring to FIGS. 5 and 6, the stator 6 has a wiring layer 61 disposed on the second surface 3b of the circuit board 3. The wiring layer 61 can also be printed by coil or electroformed. a process or the like is received in the circuit board 3, and the wiring layer 61 is electrically connected to the circuit board 3, so that the stator 6 forms a micro stator having an extremely small axial height; further, the stator 6 is composed of the wiring layer 61 and the The magnetic member 54 is opposed to each other and maintains a magnetic air gap G therebetween, and the wiring layer 61 is axially spaced from the magnetic member 54 to generate a magnetic effect from the excited wiring layer 61 and the magnetic member 54. The rotation of the fan wheel 5 relative to the frame 1 is caused.

Wherein, in the axial direction of the micro cooling fan, the bottom plate 11 of the fan frame 1 and the hub 52 of the fan wheel 5 have a first maximum axial height A', and the bottom plate 11 and the circuit board 3 have a second maximum axial height B'; in the embodiment as shown in FIG. 5, the first maximum axial height A' is the outer surface 11a of the bottom plate 11 to the radially extending portion 521 of the hub 52 The maximum axial height of the outer surface 521a, which is the maximum axial height of the outer surface 11a of the bottom plate 11 to the second surface 3b of the circuit board 3, but the wiring layer of the stator 6 61 is almost flat on the second surface 3b of the circuit board 3, so the second maximum axial height B' can also be regarded as the maximum axial height between the outer surface 11a of the bottom plate 11 and the wiring layer 61 of the stator 6. . Moreover, the first maximum axial height A' is less than or equal to 7 mm, and the ratio of the second maximum axial height B' to the first maximum axial height A' (B'/A') is 0.05 to 0.45. Preferably, it is 0.15~0.30, so that the micro cooling fan can generate proper air volume and wind pressure when operating.

In summary, the micro-cooling fan of the present invention has a fan member size conforming to a preferred ratio, so that the total axial height of the motor of the micro-cooling fan can be maintained below 7 mm, and the micro-cooling fan can be generated to operate. Appropriate air volume and wind pressure for installation in small electronic products, with good fan performance to meet the cooling needs of small electronic products.

The micro-cooling fan of the invention can be used as a reference standard for designing a micro-fan with a total axial height of the motor of 7 mm or less. As long as the ratio between the components in the micro-fan is matched to the preferred ratio, the micro-fan can be ensured to be good. The fan performance helps reduce the development time and labor of the design micro fan and improve design efficiency.

Although the present invention has been disclosed using the above preferred embodiments, it is not intended to be limiting The present invention is not limited to the spirit and scope of the present invention, and various modifications and changes to the above embodiments are still within the technical scope of the present invention. Therefore, the scope of protection of the present invention is attached. The scope defined in the scope of application for patent application shall prevail.

1‧‧‧Fan frame

11‧‧‧floor

11a‧‧‧Outer surface

11b‧‧‧ inner surface

12‧‧‧ Side wall

13‧‧‧ Cover

14‧‧‧Axis joint

2‧‧‧fan wheel

21‧‧‧ shaft

22‧‧·wheels

22a‧‧‧ Inner torus

221‧‧‧ Radial extension

221a‧‧‧Outer surface

221b‧‧‧ inner surface

222‧‧‧ axial extension

23‧‧‧ fan leaves

24‧‧‧Magnetic components

3‧‧‧Circuit board

3a‧‧‧ first surface

3b‧‧‧ second surface

4‧‧‧ Stator

41‧‧‧Magnetic pole set

42‧‧‧Insulation kit

43‧‧‧ coil group

S‧‧‧室

G‧‧‧Magnetic air gap

A‧‧‧first maximum axial height

B‧‧‧Second maximum axial height

Claims (6)

A micro-cooling fan comprises: a frame having a bottom plate and a shaft joint, wherein the shaft joint is disposed on the bottom plate; a wheel is connected to a hub by a rotating shaft and is rotatably disposed on the shaft of the frame a plurality of blade rings are disposed on an outer edge of the hub, a magnetic component is disposed on an inner surface of the hub; a circuit board is disposed on an outer periphery of the shaft joint and attached to the bottom plate; and a stator Electrically connecting the circuit board and opposite to the magnetic component, the stator and the magnetic component have a magnetic air gap; wherein, in the axial direction of the micro cooling fan, the bottom plate of the fan frame and the hub of the fan wheel Having a first maximum axial height (A), the bottom plate and the circuit board having a second maximum axial height (B), the first maximum axial height being less than or equal to 7 mm, and the second maximum The ratio of the axial height to the first maximum axial height (B/A) is 0.05-0.45; wherein the bottom plate has an opposite outer surface and an inner surface, and the axial joint protrudes from the inner surface of the bottom plate The hub has a radial extension, the hub being connected by the radial extension The radial extension has an outer surface facing the inner surface of the bottom plate, and an inner surface facing the inner surface of the radially extending portion; the circuit board has The first surface and the second surface are opposite to each other, the circuit board is attached to the inner surface of the bottom plate by the first surface; the stator has a wiring layer, and the wiring layer is disposed on the second surface of the circuit board, The stator is opposite to the magnetic element by the wiring layer, the magnetic interference gap is located between the wiring layer and the magnetic element, and the wiring layer is axially spaced from the magnetic element; in the axial direction of the micro cooling fan, the first a maximum axial height (A) is a maximum axial height of an outer surface of the bottom plate to an outer surface of the radially extending portion of the hub, the second maximum axial height (B) being an outer surface of the bottom plate to the The maximum axial height of the second surface of the board. The micro cooling fan according to claim 1, wherein the ratio is 0.15~ 0.30. The micro-cooling fan of claim 1 or 2, wherein the circuit board is tightly fitted to the shaft portion, and the first surface of the circuit board directly abuts the inner surface of the bottom plate of the fan frame. The micro-cooling fan of claim 1 or 2, wherein the circuit board is tightly fitted to the shaft portion, and the first surface of the circuit board is provided with an insulating sheet, and the circuit board is made of the insulating sheet. Indirectly attached to the inner surface of the bottom plate of the fan frame. The micro-cooling fan of claim 1 or 2, wherein the circuit board loosely fits around the shaft portion and directly adheres to the bottom surface of the fan frame with the first surface of the circuit board. surface. The micro-cooling fan of claim 1 or 2, wherein the circuit board loosely fits over the shaft portion, and the first surface of the circuit board is provided with an insulating sheet, and the circuit board is made of the insulating sheet Indirectly adhered to the inner surface of the bottom plate of the frame.