KR19980075602A - How to design the heatsink - Google Patents

Abstract

A heat sink designing method is disclosed in which a heat sink including a base to which components are joined and at least one radiating fin coupled to the base is designed to fit the component.

The heat sink designing method is characterized by including an initial design parameter of the heat sink including an initial objective function, a depth of the heat sink, an interval between the heat dissipation fin and the heat dissipation fin, a thickness of the base, A maximum permissible height of the heat sink, a maximum permissible length of the radiating fin, and a lower limit value of the initial design parameter; A heat transfer analysis step of analyzing the heat transfer from the input data to the junction where the part and the heat sink are bonded, inside the heat sink, and the heat sink to the surrounding fluid; A junction temperature judgment step of comparing and judging the actual junction temperature and the junction temperature detected by the heat transfer analysis step; An objective function and a design parameter changing step of changing an initial objective function and an initial design variable when the design junction temperature is determined to be higher than the actual junction temperature in the step of determining the junction temperature and feeding back the changed value to the heat transfer analysis step; And a design parameter output step of outputting a design parameter when the design junction temperature is determined to be equal to or lower than the actual junction temperature in the step of determining the junction temperature.

Description

How to design the heatsink

The present invention relates to a heat sink design method capable of designing a heat sink that matches the thermal characteristics of a component so as to reduce the heat load of the component.

In general, electronic products tend to minimize the air vents of the cabinet to close to the enclosure in view of noise and electromagnetic problems. In this way, there is a disadvantage that the heat load inside the product increases when the ventilation hole of the cabinet is reduced. In order to solve this problem of increase in heat load, there is a method of adopting a heat sink in a part.

This heat sink is the most widely used heat sink to increase the thermal reliability of parts. 1, the heat sink 10 includes a base 11 on which the component 30 is mounted and a plurality of heat radiating fins 13 coupled to the base 11, The width of the base 11, the number of the radiating fins 13, the distance between the radiating fins 13, the size of the radiating fin 13, and the like are selected differently depending on the use. 2, in order to increase the efficiency of the heat sink 10 configured as described above, a blowing fan 21 and a duct 23 in which the blowing fan 21 is installed are further provided can do.

Conventionally, it is difficult for a designer to use a complex thermodynamic concept when designing a heat sink 10 suitable for a component, and it is difficult to obtain a precise heat sink required for a component.

As a result, designers tend to design the heat sink sensibly. Therefore, there is a fear that the heat sink is designed to be larger or smaller than the heat generation degree of the component.

Here, when the heat sink is designed to be small, it may exceed the safe operating temperature at the time of operation of the component, and there is a possibility that the component malfunctions or the function thereof is lost. If the heat sink is designed to be large, there is no problem in the component itself, but the cost is increased and the weight is increased, so that the risk of breakage upon drop impact is higher.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat sink design method capable of designing an optimized heat sink within a specification range of a component and a constraint condition of the heat sink.

1 is a schematic perspective view showing a general heat sink;

2 is a schematic cross-sectional view showing a conventional heat sink, a ventilation fan having a blowing fan and a duct.

3 is a schematic perspective view showing a first type of heat sink;

4 is a schematic perspective view showing the second type of heat sink;

5 is a schematic perspective view showing a third type of heat sink;

6 is a schematic perspective view showing a fourth type of heat sink;

7 is a schematic perspective view showing a fifth type of heat sink;

8 is a schematic perspective view showing the sixth type of heat sink.

9 is a schematic perspective view showing a seventh type of heat sink;

10 is a flowchart illustrating a method of designing a heat sink according to an embodiment of the present invention.

11 is a schematic perspective view showing the U-channel structure of the heat sink.

DESCRIPTION OF THE REFERENCE NUMERALS

10 ... Heatsink 11 ... Base

13 ... radiating fin 21 ... blowing fan

23 ... duct 30 ... parts

According to an aspect of the present invention, there is provided a heat sink designing method for designing a heat sink including a base to which components are bonded and at least one radiating fin coupled to the base, An initial design parameter of the heat sink including at least one of a width of the heat sink, an interval between the heat dissipation fin and the heat dissipation fin, a thickness of the base, and a number of the heat dissipation fins, an initial design parameter of the heat sink, a maximum allowable width of the heat sink, A maximum permissible length of the radiating fin, and a lower limit of the initial design parameter; A heat transfer analysis step of analyzing the heat transfer from the input data to the junction where the part and the heat sink are joined, inside the heat sink, and from the heat sink to the surrounding fluid; A joint temperature determination step of comparing and comparing the actual temperature of the joint and the design junction temperature detected by the heat transfer analysis step; An objective function and a design parameter changing step of changing an initial objective function and an initial design variable when the design junction temperature is determined to be higher than the actual junction temperature in the step of determining the junction temperature and feeding back the changed value to the heat transfer analysis step; And a design parameter output step of outputting a design parameter when the design junction temperature is determined to be equal to or lower than the actual junction temperature in the determination of the junction temperature.

Hereinafter, a method of designing a heat sink according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The heat sink shown in FIG. 1 can be divided into seven types as shown in FIG. 3 to FIG. 9 according to the arrangement relationship of the base and the radiating fin.

3 is a perspective view showing the first type of heat sink. As shown in the drawing, the surface to which the base 11 and the part 30 of the base 11 are joined is formed in a planar shape and includes a plurality of radiating fins 13 arranged on the back surface of the base 11 at regular intervals. This first type is mainly used when the circuit board is adjacent to the surface to which the component 30 is bonded or when the space is narrow. In the figure, W is the width of the heat sink, H is the height of the heat sink, L is the length of the radiating fin, Is the base thickness, P is the pitch of the heat sink, D is the depth of the heat sink, and N is the number of heat dissipation fins. And, Direction start point of the component joint, Is the x-direction end point of the component joint, Direction starting point of the component joint, Is the y-direction end point of the component joint.

4 is a perspective view showing the second type of heat sink. As shown in the drawing, the base 11 and the base 30 are relatively small in size to facilitate the installation of the components, and the heat radiating fins 13 are formed on the back surface of the base 11 at regular intervals . This type 2 is mainly used when there are no obstacles on the surface where the parts are bonded or when there is space. Here, St is the width between the heat dissipating fins of the component connecting portion of the heat sink, and the reference numerals not described are as described with reference to Fig.

5 is a perspective view showing the third type of heat sink. And a plurality of radiating fins 13 formed around the base 11 and a part of the base 11 where the base 11 is joined and the back surface of the base 11 so as to provide a clearance space therebetween . This type 3 is suitable when there is an obstacle in the base of the back surface to which the parts are bonded and there is no spatial margin. Here, the reference numerals not described are as described with reference to Figs. 3 and 4.

Fig. 6 is a perspective view showing the fourth type of the heat sink, and Fig. 7 is a perspective view showing the fifth type of the heat sink. The fourth and fifth molds are used when the heat capacity of the component 30 is not so large. Here, the reference numerals not described are as described with reference to Figs. 3 and 4.

Fig. 8 is a perspective view showing the sixth type of heat sink, which is substantially the same as the second type shown in Fig. 4, in which the heat radiating fins 13 formed on the back surface of the part 30 are arranged at a non- There is a difference. This sixth type is mainly used when there is no room in the central portion of the back surface to which the component 30 is bonded. here, Is the distance between the radiating fins at the boiling interval of the back surface to which the parts are bonded, and the reference numerals not described are as described with reference to Figs. 3 and 4.

Fig. 9 is a perspective view showing a seventh type of heat sink, which comprises a base 11 and a plurality of heat-radiating fins 13 arranged at equal intervals on both sides of the base 11. Fig. This type 7 is mainly used in cases where the pitch of the radiating fins and the length of the radiating fins are different from each other in the second type. Here, L1 is the length of the radiating fin of the base back surface where the components are not bonded, and L2 is the radiating fin length of the base surface to which the components are bonded. The reference numerals not described are as described with reference to Figs. 3 and 4.

10 is a flowchart illustrating a method of designing a heat sink according to an embodiment of the present invention.

As shown in the figure, the data input step 110, the heat transfer analysis step 120, the junction temperature determination step 130, the objective function and design parameter change step 140, and the design parameter output step 150 .

The data input step 110 is a step of inputting an initial objective function, an initial design parameter of the heat sink, and a constraint condition. Here, the initial objective function is the weight of an acceptable heat sink inside the product. This objective function is changed so as to be minimized within the range in which the other conditions are satisfied in the objective function and design parameter change step 140. [ The initial design parameter includes at least one of a depth D of the heat sink, a gap S between the heat radiating fin and the heat radiating fin, a thickness tb of the base, a number of radiating fins N, and a height H of the heat sink . In the case of inputting all of the initial design variables, it corresponds to an evaluation method for evaluating whether a set value is correct. These values are determined through a junction temperature determination step 130 and an objective function and a design parameter change step 140 Lt; / RTI > The constraint condition includes an allowable range of the sizes of the heat sink, the fan, and the duct in the product, a condition suitable for installation of the component, and a difficulty in manufacturing the heat sink. That is, the constraint condition includes at least one of a maximum allowable width of the heat sink, a maximum allowable height of the heat sink, a maximum permissible length of the heat dissipation fin, and a lower limit value of the initial design variable.

The heat transfer analysis step 120 analyzes the heat transfer at the junction where the component and the heat sink are joined from the input data. The heat transfer analysis step 120 includes a heat transfer analysis step by conduction in the junction, a heat sink inside, a heat transfer analysis step by natural convection from the heat sink to ambient fluid and forced convection, And a heat transfer analysis step.

The analysis of heat transfer by conduction uses the phenomenon that energy flows from a high temperature to a low temperature through a contact part when there is a temperature difference between the part and the base, and this phenomenon is referred to as conduction heat transfer. The heat transfer per unit area is proportional to the temperature gradient in the direction perpendicular to the area. That is, the heat transfer amount per unit area is expressed by Equation (1).

[Equation 1]

here, Is a thermal conductivity coefficient, Is an area, Is the temperature gradient. And - denotes the transmission direction of the column. Silicone grease or rubber is adhered to the base so that the component is in close contact with the base to improve the thermal conductivity at the contact portion.

The heat transfer analysis by natural convection can be roughly divided into two stages. That is, when the heat sink is designed to include a base and a plurality of heat dissipating fins attached to the base, the heat transfer is analyzed by the heat transfer coefficient h satisfying Equation (2) The heat transfer is analyzed by the heat transfer coefficient h satisfying the expression (3). Here, Equations (2) and (3) are as follows.

&Quot; (2) "

&Quot; (3) "

here, &Quot; (4) " (5) as a characteristic length, Satisfies the expression (6).

&Quot; (4) "

&Quot; (5) "

here, ego, ; A gap between the heat radiation fin and the heat radiation fin of the heat sink, ; The height of the radiating fin, to be.

&Quot; (6) "

to be.

remind Is expressed by Equation (7) below, which is a Rayleigh channel.

&Quot; (7) "

here, Is the gravitational acceleration, ; Thermal expansion coefficient, ; The surface temperature of the base of the heat sink, ; The fluid temperature around the heat sink, ; The viscosity of the fluid, ; Prandtl number, H; Height of the heat sink.

Also, Is expressed by the following equation (8).

&Quot; (8) "

The analysis of the heat transfer by the forced convection of the heat sink can be divided into the following two cases in the case where the heat sink includes the heat radiation fan and the duct where the heat radiation fan is installed. That is, when the heat sink includes a base and a plurality of heat dissipating fins attached to the base, and a duct enclosing the heat sink and a heat dissipating fan installed in the duct, the following expression (9) is satisfied Heat transfer coefficient And the heat sink includes only the base to which the components are joined and is designed to include a duct surrounding the heat sink and a heat dissipation fan installed in the duct, the heat transfer coefficient satisfying the following expression (10) To analyze the heat transfer.

&Quot; (9) "

&Quot; (10) "

here, Is the Reynolds number based on the speed between the radiating fins, and satisfies the following equation (11).

&Quot; (11) "

Is a velocity distribution representing the fluid velocity in the duct relative to the fluid inflow velocity into the duct, ; It is the average velocity of the fluid passing through the radiating fin region. And, Is expressed by Equation (12) as the Reynolds number based on the velocity between the duct and the heat sink.

&Quot; (12) "

here, Is the average velocity of the fluid passing between the duct and the heat sink.

The heat transfer analysis step by radiation is performed by using a heat transfer coefficient < RTI ID = 0.0 > And a gray body exchange factor F relating to the heat transfer between the heat sink pin and the pin and the heat transfer from the fin to the surrounding fluid satisfying Equation (14) below. FIG. 11 is a view showing a U-channel structure of a heat sink shown for explaining the gray body heat exchange rate F. FIG. In the drawings, reference numerals 1, 3 and 4 denote the surfaces of the heat sink, and reference numerals 2, 5 and 6 denote the air on the corresponding surfaces, respectively.

&Quot; (13) "

here, Is a Stefan-Boltzmann constant, Is the surface temperature (占 폚) It is the atmospheric temperature (℃).

&Quot; (14) "

Is expressed by the following equation (15).

&Quot; (15) "

In Equation (15) , , , And Each can be expressed by the following equation (20) in the equation (16).

&Quot; (16) "

here, Represents the radiation absorption rate, Is the surface area of the heat sink surface (3).

&Quot; (17) "

here, Is the surface area of the heat sink surface (1).

&Quot; (18) "

here, The pin In the pin .

&Quot; (19) "

&Quot; (20) "

The design temperature can be determined through the heat transfer analysis step analyzed through Equations (1) to (20) as described above.

The joint temperature determination step 130 compares the actual temperature of the joint, which is known through the data book of the part, with the temperature of the design joint detected by the heat transfer analysis step. If the design junction temperature is determined to be higher than the actual junction temperature through the step, the objective function and the design parameter change step 140 are performed. Otherwise, the design parameter output step 150 is performed.

The objective function and design variable changing step 140 changes the initial objective function and the initial design variable and feeds the changed value to the heat transfer analysis step 120. [

Here, the initial design parameter changing step 140 minimizes the objective function, that is, the weight of the heat sink, while maintaining the same temperature rise for a given heat load, and satisfies the constraint described later.

As described above, the design parameters of the heat sink are such that the distance S between the radiating fins and the radiating fins, the radiating fin thickness tf, the base thickness tb, the heatsink depth D, the heatsink height H, N, and are defined differently depending on the type of the heat sink as shown in FIGS. The thickness tf of the radiating fin is within 1.0 mm although the radiating fin efficiency is 98% or more. That is, since it is a value within the compressible dimension, there is no need to change it. Therefore, five design variables other than the heat radiation fin thickness (tf) are set as shown in Equation (21).

&Quot; (21) "

X (1) = heat sink depth (D)

X (2) = distance between the radiating fin and the radiating fin (S)

X (3) = height of radiating fin (H)

X (4) = base thickness (tb)

X (5) = number of radiating fins (N)

The objective function is set as shown in Equation (22).

&Quot; (22) "

Objective function: F (x) = Heatsink weight

The constraint is a condition for setting the range of change of the design parameters referred to in Equation (21), where the heat sink surface temperature is the target design temperature (< RTI ID = 0.0 > ) And the maximum allowable outline dimensions of the heat sink are determined by the designer and can be divided into dimensional constraints within the range or dimensional constraints of the interconnected dimensions by geometric shape .

The above temperature and dimensional constraint conditions are shown in the following Equation (23).

&Quot; (23) "

here, Is the maximum allowable heat sink width, Is the maximum allowable heat sink fin length, Is the maximum allowable heat sink height, Each design variable Lt; / RTI > Is a constraint condition in which the length of the heat sink radiating fin to the radiating fin gap does not exceed 5. This constraint is a condition for preventing the molding of the mold and the deformation of the heat sink at an above-mentioned value during extrusion molding.

Among the above constraint conditions Is a constraint condition for the first and fourth types of heat sinks shown in Figs. 3 and 6, and a slight modification is required for the other types. A description of the constraints on the other type The detailed description thereof will be omitted.

It is preferable to extract the new design parameters by applying the Gradient Projection Method (GPM) developed by Rosen in 1961 to the above temperature and dimensional constraint conditions.

The variable output step 150 is performed when the determination condition is satisfied in the junction temperature determination step 130, and outputs an objective function and a design variable corrected for the initial objective function and the design variable. Here, the output uses a monitor, a printer, a plotter, or the like.

As described above, the specifications of the heat sink designed through the heat sink designing method according to the embodiment of the present invention will be described with reference to Tables 1 to 3.

Table 1 shows the design values of the initial heat sink to verify the heat transfer characteristics by natural convection.

[Table 1]

Width (W) 60mm Part (transistor) type TO-220 Height (H) 60mm Junction temperature 150 ℃ Width (D) 12mm Ambient air temperature 25 ℃ Height of radiating fin (H) 9mm Total power loss 7W Heat sink fin thickness ( ) 1.2 mm Collector power dissipation 30W Emissivity 0 Insulation type Silicone grease material Aluminum (A-3003) Component joint location x-axis: 25 - 35mm axis: 15 - 22mm

The model was created by varying the number of pins from 2 to 20. The results of numerical analysis for each of these models were compared with those of the method according to the present invention, Respectively.

[Table 2]

Number of pins to be compared Surface temperature (℃) Calculation time (seconds) FLOTHERM Invention of the present invention FLOTHERM Invention of the present invention 2 109.445 108.694 5400 2 4 99.867 98.075 5600 2 6 92.652 91.484 5800 2 8 87.801 87.014 6000 2 10 84.845 84.767 6200 2 12 85.494 85.337 6400 2 14 87.691 89.488 6600 2 16 90.725 97.888 6800 2 18 93.598 109.999 7000 2 20 96.413 123.438 7200 2

Here, FLOTHERM is a numerical analysis program of FLOMETICS. As a result of the analysis by the two methods, it can be seen that the analysis results are almost identical when the number of pins is 14, when the surface temperature is compared with respect to each number of pins. On the other hand, when the number of pins is 16 or more, that is, when the distance between the pins is 2.7 mm or less, the analysis error with respect to the surface temperature increases. However, since there is no machining in the area of 3.0 mm or less between the radiating fins when the radiating fin is actually processed, there is no great problem.

The calculation time of FLOTHERM takes about 5400 to 7200 seconds as the number of radiating fins is added and the finite volume of the analysis area increases. On the other hand, since the calculation time of the present invention takes about 2 seconds regardless of the number of the radiating fins, the analysis time can be drastically reduced.

Using the initial design parameters in Table 1, the target design temperature in a model with 12 radiating fins is 100.862 ° C. The design variables that minimize the weight of the heat sink while satisfying the target design temperature are shown in Table 3.

[Table 3]

Number of algorithm iterations 81 Width of heat sink (W) 30.109 mm Height of heat sink (H) 30.000mm Heatsink depth (D) 34.044 mm Height of component side (L1) 31.044 mm Height of component side radiating fin (L2) 0.000mm Base Thickness ( ) 3.000mm Heat sink fin thickness ( ) 1.200mm Radiating fin pitch (P) 9.636 mm The x-axis starting point of the part ( ) 10.05 mm The x-axis end point of the part ( ) 20.05 mm The y-axis starting point of the part ( ) 15.00 mm The y-axis end point of the part ( ) 22.00 mm Number of radiating fins 4

As described above, the method of designing the heat sink according to the embodiment of the present invention configured as described above enables the heat sink to be designed in a short time in accordance with the thermal characteristics of the component so as to reduce the thermal load of the component. In addition, when the design method of the heat sink is applied to a computer program, the designer inputs desired design initial design variables so that the design junction temperature is less than the actual junction temperature while minimizing the objective function, that is, the weight of the heat sink. Can be obtained.

Claims (7)

A heat sink design method for designing a heat sink including a base to which components are joined and at least one radiating fin coupled to the base, The initial design parameters of the heat sink including at least one of the initial objective function, the depth of the heat sink, the distance between the heat dissipation fin and the heat dissipation fin, the thickness of the base, and the number of the heat dissipation fins and the maximum allowable width of the heat sink, A constraining condition including at least one of an allowable height, a maximum permissible length of a radiating fin, and a lower limit of the initial design parameter; A heat transfer analysis step of analyzing the heat transfer from the input data to the junction where the part and the heat sink are bonded, inside the heat sink, and the heat sink to the surrounding fluid; A joint temperature determination step of comparing and comparing the actual temperature of the joint and the design junction temperature detected by the heat transfer analysis step; An objective function and a design parameter changing step of changing an initial objective function and an initial design variable when the design junction temperature is determined to be higher than the actual junction temperature in the step of determining the junction temperature and feeding back the changed value to the heat transfer analysis step; And a design parameter output step of outputting a design parameter when the design junction temperature is determined to be equal to or lower than an actual junction temperature in the determination of the junction temperature. The method of claim 1, wherein the objective function is a weight of the heat sink. 2. The method of claim 1, wherein the heat transfer analysis step comprises the steps of: analyzing the heat transfer by conduction in the junction, heat sink, natural convection from the heat sink to ambient fluid and heat transfer analysis by forced convection; And analyzing the heat transfer by radiation to the fluid. 4. The method of claim 3, wherein the step of analyzing the heat transfer by the natural convection comprises: When the heat sink is designed to include a base and a plurality of radiating fins attached to the base The heat transfer coefficient h satisfying the equation When the heat sink is designed to include only the base to which components are bonded And the heat transfer coefficient h satisfies the following equation: " (1) " here, , , , ; Rayleigh, ; Characteristic length, , , , ; Thermal expansion coefficient, ; A gap between the heat radiating fin and the heat radiating fin of the heat sink, ; Heat sink fin height, ; The surface temperature of the base of the heat sink, ; The fluid temperature around the heat sink, ; Viscosity of fluid, ; Prandtl, H; Height of the heat sink, ; Heat conduction coefficient. The method according to claim 3, wherein the heat transfer analysis step of the heat sink by the forced convection comprises: In the case where the heat sink includes a base and a plurality of heat dissipating fins attached to the base, a duct surrounding the heat sink, and a heat dissipation fan installed in the duct Heat transfer coefficient satisfying The heat transfer is analyzed by the < RTI ID = 0.0 > In the case where the heat sink includes only a base to which components are bonded and includes a duct surrounding the heat sink and a heat radiating fan installed in the duct Heat transfer coefficient satisfying And the heat transfer is analyzed by the heat sink. here, ; The number of Reynolds numbers based on the speed between the radiating fins, ; A velocity distribution representing the velocity of the fluid inside the duct relative to the velocity of the fluid flow into the duct, ; The average velocity of the fluid passing through the radiating fin region, ; The number of Reynolds numbers based on the velocity between the duct and the heat sink, ; It is the average velocity of the fluid passing between the duct and the heat sink. 4. The method of claim 3, wherein the radiative heat transfer analysis step Heat transfer coefficient satisfying And the heat transfer between the heat sink pin and the fin and the heat transfer from the fin to the surrounding fluid And the heat transfer is analyzed by the gray body heat exchange rate F satisfying the following equation. here, ; Stefan-Boltzmann constant ; Surface temperature (캜), ; Air temperature (℃), , ; Radiation absorption rate, , ; The surface area of the heat sink surface, , ; pin In the pin , , to be. 3. The method according to claim 1 or 2, wherein the objective function and the design parameter changing step minimize the objective function and determine a constraint function according to the relation between the constraint condition and the initial design variable ( ) Satisfy the following equation: < EMI ID = 1.0 > Where X (1) is the depth of the heat sink (D), X (2) is the spacing S between the radiating fins and the radiating fins, X (3) (Tb), X (5) = number of radiating fins (N) Is the target design temperature, Is the maximum allowable heat sink width, Is the maximum allowable heat sink height, Is the maximum allowable heat sink fin length, Each design variable Lt; / RTI > Is a constraint condition in which the length of the heat sink radiating fin to the radiating fin gap does not exceed 5.