JPH0465864A - Heat sink - Google Patents

Abstract

PURPOSE:To improve heat dissipation effect even in a narrow space where a blower can not be installed, by a method wherein a piezoelectric fan is constituted by sticking a piezoelectric member on the base part of a substrate, and the tip part of the substrate functions as a blade capable of vibration, which tip part is formed so as to have an area larger than a base part. CONSTITUTION:When an AC voltage is applied across a substrate 24 of a piezoelectric fan 23 and piezoelectric ceramics 25, the piezoelectric ceramics 25 expands and contracts, and the substrate 24 continues bending motion in the axial direction of a heat introducing part 22. As the result of the bending motion of the substrate 24, a blade 26 vibrates. By the vibration of the blade 26, the air flow shown by arrow C is formed in the vicinity of the blade 26 of each piezoelectric fan 23. Thereby very large effect of heat dissipation can be obtained. In particular, the tip part of the substrate 24 being the blade 26 is formed so as to have an area wider and larger than the base part of the substrate 24, so that the vibration area of the heat dissipating part is increased, and the heat dissipating effect can be more improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a heat sink for cooling electronic equipment, semiconductors, and the like.

(Prior Art) As shown in FIG. 7, a heat sink 1 is configured with a heat introduction section 2 and a large number of fins 3, and is installed in the heat introduction section 2 or a heating element 4 such as an electronic device or a semiconductor. . Forced air is sent to the fins 3 from a separate blower (not shown), and the heating element 4 is
radiates heat from the fins 3.

Furthermore, when a blower is not installed, the area of the fins 3 is increased to dissipate heat from the heat generating portion 4 by natural convection.

However, in general, in the case of forced wind, it is about 50W/m.
While there is a heat dissipation effect (heat transfer coefficient) of 'c, in the case of natural convection, the heat dissipation effect is approximately 5 W/m°C. Therefore, if it is not possible to install a separate blower due to the demand for downsizing of electronic devices, or if a blower can be installed, a sufficient flow path cannot be designed, and the cooling air is supplied to the fins 3 of the heat sink 1. If this is not possible, or if a sufficient space for enlarging the fins 3 cannot be secured when no blower is installed, the heat dissipation effect may be insufficient.

Therefore, it has been proposed that a piezoelectric fan or a small air blower is installed on the heat sink 1, and the air generated by the piezoelectric fan or the small air blower is blown to the fins 3. FIG. 8 shows a heat sink 10 on which a piezoelectric fan 6 is installed.

In general, the piezoelectric fan 6 is constructed by having a substrate 8 fixed to a base 7 and piezoelectric ceramics 9 adhered to the base of the substrate 8, as shown in FIG.

An alternating current voltage of 1 is applied between these substrates 8 and piezoelectric ceramics 9.
When 1 is applied, the piezoelectric ceramic 9 expands and contracts, which causes the free end (blade 12) of the substrate 8 to vibrate.
Wind occurs. This air is supplied to the fins 3 shown in FIG. 8 to promote the heat dissipation effect of the heat sink 10. Note that in FIG. 8, the same parts as in FIG. 7 are given the same reference numerals.

(Problem to be Solved by the Invention) By the way, the wind generated by the piezoelectric fan 6 shows a wind speed (V) distribution as shown in FIG. 10, and the air volume (Q) - wind pressure (
H) The characteristics are as shown by the solid line A in FIG. Also,
The air volume (Q) - wind pressure (H) characteristic of a typical electric blower is shown by the dashed line B in FIG. Therefore, when comparing the wind pressures of the air generated by the piezoelectric fan 6 and the blower at the same amount of air, it can be seen that the piezoelectric fan 6 is significantly lower.

Therefore, as shown in FIG. 8, the wind generated by the piezoelectric fan 6 has a high wind speed near the tips of the blades 11 of the heat sink 10, or rapidly decreases in the longitudinal direction of the fins 3. As a result, even if the piezoelectric fan 6 can cool the area locally, it cannot create a -like cooling air in the longitudinal direction (x) of the fins 3, and even in this case, although the heat dissipation effect of the heat sink 10 is sufficient, There is a possibility that there will be no.

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a heat sink that can exhibit a large heat dissipation effect even in a narrow place where a blower or the like cannot be installed.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a heat introduction part that can be fixed to a heating element, and a fin that is connected to the heat introduction part and dissipates heat from the heating element to the atmosphere. , the fin is composed of a piezoelectric fan, and the piezoelectric fan has a piezoelectric material attached to the base of a substrate, the tip of the substrate functions as a vibrating blade, and the tip has a larger area than the base. It is characterized by the fact that it was formed.

(Function) Therefore, according to the heat sink according to the present invention, the fins are constituted by a piezoelectric fan, and the vibrating blades of this piezoelectric fan serve as a heat dissipation section, so there is no need to install another blower to generate wind. The wind generated by these blades improves the heat dissipation effect.

Moreover, since the blade area is formed to be large, the heat radiation area increases, and the heat radiation effect can be further improved.

Furthermore, since the piezoelectric fan has a large heat dissipation effect, the heat sink can be made smaller in order to exhibit the same heat dissipation effect, and it can be installed even in a narrow space.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a side view showing a first embodiment of a heat sink according to the present invention, and FIG. 2 is a sectional view taken along line nn in FIG. 1.

The heat sink 20 includes a heat introduction part 22 that can be fixed to a heat generating element 21 of an electronic device, and a piezoelectric fan 23 connected to the heat introduction part 22. This piezoelectric fan 2
3 corresponds to a fin of a heat sink, and a blade 26, which will be described later, serves as a heat dissipation section.

The piezoelectric fans 23 are provided, for example, in two stages in the axial direction of the heat introduction section 22. The piezoelectric fans 23 in each stage are arranged to extend radially from, for example, four locations in the circumferential direction of the heat introducing portion 22 .

The piezoelectric fans 23 of adjacent stages are installed at the same position in the circumferential direction of the heat introduction section 22 and overlapped with each other with a predetermined distance apart from each other in the axial direction of the heat introduction section 22 .

Each piezoelectric fan 23 is constructed by pasting a piezoelectric ceramic 25 as a piezoelectric material to the base of a substrate 24, that is, near the heat introduction section 22. This piezoelectric ceramic 25 is
It is attached to the front and back surfaces of the substrate 24 to form a bimorph structure. The tip of the substrate 24 becomes a swingable blade 26. As shown in FIG. 2, this blade 26 extends in the width direction of the substrate 24 and is formed wide.
It is formed to have a larger area than the base of No. 4. Also, this board 2
An AC voltage (not shown) is applied between the piezoelectric ceramics 25 and the piezoelectric ceramics 25 . The frequency of this AC voltage is
It is set to be almost the same as the natural frequency of the 6th part.

Next, the action and effect will be explained.

Heat from the heating element 21 reaches the piezoelectric fan 23 via the heat introduction section 22. Since the piezoelectric ceramic 25 of the piezoelectric fan 23 has extremely low thermal conductivity compared to metal, there is almost no heat radiation from this part, and the heat is radiated from the blades 26.

In this state, when an alternating current voltage is applied between the substrate 24 and the piezoelectric ceramic 25 of the piezoelectric fan 23, the piezoelectric ceramic 25 expands and contracts, and the substrate 24 bends in the axial direction of the heat introduction section 22. This bending movement of the substrate 24 causes the blade 26 to vibrate. The frequency of the blade 26 matches the frequency of the alternating current voltage, and the frequency of this alternating voltage matches the frequency of the blade 26.
Since the natural frequency of the blade 26 is approximately the same as that of the sixth part, the blade 26 resonates and vibrates greatly. This vibration of the blades 26 forms an air flow (wind) shown by arrow C in FIG. 1 near the blades 26 of each piezoelectric fan 23.

This air flow (wind) is transmitted through the blades 26 of each piezoelectric fan 23.
The wind speed is approximately 2 to 3 m/sec.

Therefore, an air flow is formed on the front and back surfaces of the blades 26 as a heat radiating part of the heat sink 20, and this air flow has a wind speed of about 2 to 3 m/sec. Compared to a structure in which the fins 3 do not vibrate, an extremely large heat dissipation effect can be exhibited. Furthermore, compared to the heat sink 10 in which negative wind speeds are not generated around the fins 3, a greater heat dissipation effect can be achieved.

In particular, the tip of the substrate 24, which is the blade 26,
Since it is formed to be wider and have a larger area than the base, the area of the vibrating heat dissipating portion becomes larger, and the heat dissipation effect can be further improved.

4 Here, the heat transfer equivalent circuit in the above example is expressed as the third
As shown in the figure.

The thermal resistance R, (°C/W) between the blade 26 and the atmosphere is:
When the heat transfer coefficient is α (W/rri0C) and the surface area of the blade 26 is A (ttf), R'=aA. Since the heat transfer coefficient α is a function of the wind speed V flowing near the blade 26, the thermal resistance R1 (°C W/) is
As shown in FIG. 4, the wind speed V flowing near the blade 26
, and decreases rapidly as the wind speed V increases.

That is, when V = Om/sec, R1 = 3°C/W. When V = 2 m/sec, R1 = 0.5°C/W. Moreover, since the surface area of the blade 26 is larger than the area of the base of the substrate 24, the thermal resistance R1 becomes significantly smaller than the above value.

The thermal resistance R2 between the heat introduction part 22 and the blade 26 is defined by the thermal conductivity between them being λ (W/m'C) and the conduction length being j! (m), and if the conduction cross section is B (rJi), then R2'' is obtained. Since the substrate 24 is made of metal, the thermal conductivity λ is large, and therefore the thermal resistance R2 is extremely small compared to the thermal resistance R1. In addition, the thermal resistance R3 between the heating element 21 and the heat introduction part 22 is experimentally determined to be approximately 0.5 to 1 ('C/W
).

Therefore, if the total thermal resistance is Rt (℃/W), then Rt=R, 10R,, 10R3, and if the amount of heat generated by the heating element 21 is q (W),
The temperature rise θ ('C) of the heating element 21 is θ=Rtφq. Here, since the thermal resistance Rt is the largest among the thermal resistances Rt, when comparing the conventional heat sink 1 and the heat sink 20 of this embodiment as Rt'-R, the fin 3
In the case of heat sink 1 with no wind, R,1==H3
°C/W, and in the case of the heat sink 20 of this embodiment, R1 = 0.5 °C/W. As a result, the heat sink 20 can exhibit a heat dissipation effect approximately 5 to 6 times greater than that of the conventional heat sink 1.

Further, according to the above embodiment, since the heat dissipation effect is large as described above, the area of the heat dissipation surface (blade 26) of the heat sink 20 can be reduced in order to exhibit the same heat dissipation effect. For example, since the heat sink 20 has a heat dissipation effect about 5 to 6 times that of the conventional heat sink 1, the area of the blade 26 can be reduced to about 115 to 1/6. As a result, the heat sink 20 can be made smaller and can be installed even in narrow spaces where a blower or the like cannot be installed. Since the heat sink 20 can be miniaturized in this way, the power consumption of the heat sink 20 can be reduced to about 1710 watts of power compared to a blower, and the electronic equipment to which the heat sink 20 is attached can also be miniaturized.

Furthermore, when the conventional heat sink 1 is to function using natural convection, it is necessary to set the fins 3 so that the extending direction thereof is vertical. In contrast, in the heat sink 20 of this embodiment, the piezoelectric fan 23 is connected to the blade 26.
Since the heat sink 20 generates various winds, there is no need to consider the installation direction of the heat sink 20, and the heat sink 20 can be attached to the heat generating element 21 from any direction.

3 and 4 are a plan view and a side view, respectively, showing a second embodiment of the heat sink according to the present invention.

In this second embodiment, parts similar to those in the first embodiment are designated by the same reference numerals, and a description thereof will be omitted.

The heat sink 30 of the second embodiment differs from the heat sink 20 of the first embodiment in the shape of the substrate 32 that constitutes the piezoelectric fan 31. In other words, the substrate 32 is formed so that its width gradually increases from the side (base) of the heat introduction part 22 toward the tip.

Therefore, also in the case of this second embodiment, the blade 33
The tip of the substrate 32 is formed to have a larger area than the base of the substrate 32, increasing the heat dissipation area and improving the heat dissipation effect.

In both of the above embodiments, two stages of piezoelectric fans 23.31 are arranged in the axial direction of the heat introduction section 22, and each stage is composed of four piezoelectric fans 23.31.
Each stage may be composed of five or more piezoelectric fans 23.31, and the heat introduction section 22 may include three or more piezoelectric fans 23.31.
may be attached.

Furthermore, in both of the above embodiments, each piezoelectric fan 2 in an adjacent stage
3.31 has been described with reference to the parts arranged at the same position in the circumferential direction of the heat introduction part 22; It may be arranged so that it is not present.

Furthermore, according to both of the above embodiments, the piezoelectric fan 23 of each stage
．． 31 boards 24 are separately separated from each other, but one metal plate is shaped like a cross from the front with a wide tip, and each radial piece of this metal plate is connected to each piezoelectric fan 23.31. The substrate 24.32 may also be configured.

〔Effect of the invention〕

As described above, according to the heat sink according to the present invention,
The fin is composed of a piezoelectric fan, and the piezoelectric fan is made of piezoelectric material attached to the base of the board, and the tip of the board functions as a vibrating blade, so the vibrating blade becomes a heat dissipation part. The wind generated by the blades improves the heat dissipation effect, and it can be made smaller so that it can be installed in narrow spaces. The above heat dissipation effect can be achieved within the layer because the tip of the substrate as a blade is formed to have a larger area than the base of the substrate.

[Brief explanation of drawings]

FIG. 1 is a side view showing a first embodiment of a heat sink according to the present invention, FIG. 2 is a sectional view taken along line nn in FIG. 1, and FIG. 3 is an equivalent heat transfer in this first embodiment. A diagram showing the circuit, FIG. 4 is a graph showing the relationship between thermal resistance R1 and wind speed,
FIG. 5 is a plan view of a heat sink showing the second embodiment;
The figure is a cross-sectional view taken along the line VI-VI in Fig. 5, Fig. 7 is a perspective view showing a conventional heat sink, Fig. 8 is a front view showing another conventional heat sink, and Fig. 9 is a piezoelectric FIG. 10 is a side view showing the fan, FIG. 10 is a diagram showing the piezoelectric fan of FIG. 9 and its wind speed distribution, and FIG. 11 is a graph comparing the characteristics of the piezoelectric fan and the blower. 20.30... Heat sink, 21... Heating element, 2
2...Heat introduction part, 23.31...Piezoelectric fan, 24
゜32...Substrate, 25...Piezoelectric ceramics, 26
．． 33...Blade. Patent Applicant: Toshiba Ceramics Co., Ltd. Applicant's Agent Hatano Very popular heating part 13 Figure 4f (m/S) I4 Figure N5 I7 Figure s8 Figure 10wJ Figure 11

Claims (1)

[Claims] The piezoelectric fan has a heat introduction part that can be fixed to a heat generating element, and a fin that is connected to the heat introduction part and dissipates heat from the heat generating element to the atmosphere, and the fin is composed of a piezoelectric fan. A heat sink characterized in that a piezoelectric material is adhered to the base of a substrate, the tip of the substrate functions as a vibrating blade, and the tip has a larger area than the base.