JPH11307705A - Heat sink for forced air cooling and its cooling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat dissipation of a pin fin type heat sink by increasing the heat transfer rate at the center of the heat sink. SOLUTION: In regard to one row in the flow direction of cooling wind, the draft resistance becomes low at the upper part of a long pin 11a close to the center of a board where the total heat dissipating area of the pins reduces but the temperature is highest, and as the flow velocity of cooling wind that blows over a heating part 13 increases, the heat transfer rate of the heating part 13 is improved. At the same time, as a cool wind whose temperature is not yet increased is made easier to be applied on the long pin 11a, heat dissipation of the heating part 13 is improved. The length of a short pin 11b is preferably 1/2 of that of the long pin 11a or shorter so as to sufficiently supply the cooling wind to the vicinity of the heating part 13. Therefore, by using this heat sink, heat transfer at the center of the heat sink can be improved, and elements that generate heat such as LSI element can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pin-fin type heat sink for forced air cooling which is mounted on a heating element such as an LSI or a power transistor to cool and radiate heat.

[0002]

2. Description of the Related Art In recent electronic devices, LSIs and the like are often used, and the amount of heat generated increases with the speeding up.
Since the surface area of the element is reduced by miniaturization and high-density mounting, heat dissipation and cooling are problems. That is, in an LSI or the like, the Si chip that forms the inside of the LSI generates a large amount of heat.
This is the point where I operates normally and at high speed. LS
In order to dissipate heat of an element such as I, a heat sink having a large heat dissipation area is usually mounted on the element.

FIG. 1 is a schematic diagram showing a state in which a heat sink 22 is mounted on a pin grid array type LSI package 21. The Si chip 23 is joined to the lower surface of the ceramic heat transfer substrate 24, and has a frame-shaped ceramic container 25, a frame-shaped ceramic multilayer wiring board 2.
6 and a hermetic space 27 composed of a metal lid 27
a. Most of the heat generated in the Si chip 23 is transmitted from the heat transfer substrate 24 to the pins 11 through the substrate 12 of the heat sink 22 and is radiated into the air.

In general, in cooling a heat generating element using a heat sink, heat transfer from the heat sink to the air determines the total amount of heat radiation. Therefore, to improve the heat sink performance, the heat transfer coefficient from the heat transfer surface to the air must be reduced. Improvement is paramount. In order to improve the heat transfer coefficient, it is effective to break or thin the temperature boundary layer formed near the heat transfer surface,
Usually, it is effective to forcibly cool the heat sink from a direction parallel to the substrate surface.

FIG. 2 is a perspective view showing the appearance of a pin fin type heat sink. A heat sink 22 of the type shown in FIG.
It has a structure in which a plurality of pins 11 stand at a constant pitch on the substrate 12, and has a leading edge effect of the pins (an effect that maximizes heat transfer at a portion where the cooling air collides) and an unsteady flow of the flow passing through the pins. Due to the effect of turbulence, the temperature boundary layer on the pin surface can always be kept thin, and it is widely used as a heat sink exhibiting excellent cooling performance.

When the substrate 12 of the pin fin type heat sink is viewed locally, the heat radiation performance, that is, the distribution of the heat transfer coefficient is not constant. That is, the heat transfer coefficient tends to be the highest on the windward side where the cooling air is directly applied, and tends to be lower at the center. This is because the ventilation resistance at the center of the heat sink is high,
This is because the speed of the cooling air passing through the heat sink is significantly reduced, and the temperature of the air passing through the heat sink is increased, and the temperature difference between the pin and the air is reduced. Such local nonuniformity of the heat transfer coefficient becomes greater as the space around the pin around which the air bypasses is provided.

[0007] The local variation of the heat transfer coefficient is not so problematic when the heat-generating portion is present almost uniformly over the entire heat sink substrate, and the average heat dissipation performance of the entire heat sink is important. A problem arises when there is a bias.

That is, in a general LSI package or the like, the Si chip as a heating element is often located at the center of the substrate, while the local heat transfer coefficient is low at the center of the heat sink. That is, the calorific value is the largest in the portion where the heat transfer coefficient is low. For this reason, even though the average heat dissipation performance of the heat sink is good, it may be difficult to secure the required performance when actually used. For example, in the case of a square heat sink of 60 mm × 60 mm, the heat generating portion is about １ ／ of the center, that is, 30 mm × 30 mm
When the heat is concentrated, the overall heat radiation performance may be reduced to about 50% as compared with the case of the uniform heat generating portion.

As a technique for solving this problem, for example, Japanese Patent Application Laid-Open No. 2-291154 discloses a pin fin type heat sink in which the pin diameter of the heat sink is sequentially changed from the center to the periphery so that the center is thickest and the periphery is thinnest. Has been proposed. The technology disclosed in the publication is to increase the pin heat dissipation area near the center of the package, thereby increasing the heat radiation area of the pins, reducing the distance between the pins, increasing the air flow rate between the pins, and The aim is to increase the heat transfer coefficient of the surroundings to improve the heat dissipation efficiency.

[0010]

However, the above-mentioned Japanese Patent Application Laid-Open
The technique disclosed in Japanese Patent Application Laid-Open No. 291154 has the following problems.

Generally, the flow of air has a property of passing through a place having a small resistance. If the pin diameter is increased, the pin spacing becomes smaller, the cross-sectional area of the flow path decreases, and the resistance of the flow path increases, so that air mainly passes through other spaces,
The increase of the flow velocity in the central part cannot be expected very much. That is,
Improvement of the heat transfer coefficient at the center of the heat sink could not be expected much.

As described above, in the conventional pin fin type heat sink, since the heat transfer coefficient is locally biased (the heat transfer coefficient tends to be small near the center), the heat generating portions are concentrated in a narrow area in the center. In such a case, there is a problem that the cooling effect is reduced.

An object of the present invention is to provide a pin fin type heat sink having excellent heat radiation performance by increasing the heat transfer coefficient at the central portion of the heat sink when the heat generating portion is concentrated at the central portion of the element. To provide.

[0014]

Means for Solving the Problems In the pin fin type heat sink, the inventors have found the following problem that the heat transfer coefficient becomes small at the center of the heat sink corresponding to the heat generating portion of the element.
(a) and (b).

(A) The reason why the heat transfer coefficient at the center of the heat sink decreases is that the flow velocity decreases due to the ventilation resistance inside the pin group.

(B) Further, the temperature of the air flowing between the pins rises along the flow path, and the temperature difference between the air and the pins becomes small at the central portion of the heat sink, so that the heat radiation decreases.

As measures against this, two points can be considered: (A) increasing the flow velocity of the air passing through the central portion, and (B) supplying air whose temperature has not risen to the central portion.

Based on the above findings, the gist of the present invention is as follows (1) to (3). (1) A pin fin type forced air cooling heat sink having a substrate and a plurality of pins arranged at a constant pitch on the substrate, wherein a substrate portion corresponding to a heat generating portion of the element to be cooled is parallel to the substrate surface. A state in which pins in a specific direction and / or an anti-specific direction are shorter than pins in a portion corresponding to the heat generating portion, and a state in which the pins in the specific direction and / or an anti-specific direction are thinned out Wherein the pins are arranged in at least one of the states.

(2) The heat sink for forced air cooling as described in the above item (1) or (2), wherein the area of the substrate portion having short or no pins is 20% or less of the area of the entire substrate.

(3) A method for cooling a heat sink according to the above (1) or (2), wherein cooling air for forced air cooling is sent from a side in a specific direction of the heat sink.

Here, "the state where the pins are standing" means that a large number of pins are arranged substantially upright on the plane of the substrate, and "constant pitch" means that the pins are located at least in the specific direction. It means that the mutual interval is regularly arranged.

"The side in a specific direction parallel to the substrate surface with respect to the substrate portion corresponding to the heat generating portion of the element to be cooled" means, for example,
Assuming an air flow parallel to the specific direction, it means the windward side of the substrate portion and both side portions of the air flow path on the windward side, and the “anti-specific direction side” is directly downwind of the substrate portion. Side and both sides of the air flow path immediately downstream of it.

The term "short pins" includes a pin shorter than any pin on the substrate portion corresponding to the heat generating portion and having a height of zero, that is, a state in which there is substantially no pin. "Pinning out pins" refers to removing at least one pin of the substrate portion.

The area on the board is calculated by using a value obtained by dividing the area of the board of the portion arranged at a constant pitch by the number of pins, excluding the portion having no pins.

[0025]

FIG. 3 is a schematic view showing an example of a heat sink according to the present invention. FIG. 3 (a) is a plan view, and FIG. 3 (b) is a vertical sectional view of one row of pins AA. FIG. Code 11
Is a pin, 111a is a long pin (shown by a circle in FIG. 1A), 11b is a short pin (shown by a circle in FIG. 1A), 1
Reference numeral 2 denotes a substrate, and 13 denotes a heating unit. Normally, an LSI package has an element chip arranged in the center, and unless otherwise specified in this description, the central part of the heat sink corresponding to the heat generating part of the LSI is also called the heat generating part of the heat sink.

In FIG. 2, when viewed in the flow direction of the cooling air, one row of pins passing through the heat generating portion 13 is short in the peripheral portion other than the heat generating portion 13, that is, in the figure, the pin is short on the windward side of the heat generating portion 13. There are parts.

When viewed in one row in the flow direction of the cooling air, the total heat radiation area of the pins is reduced, but the ventilation resistance at the top of the long pin 11a near the center of the substrate where the temperature is the highest becomes low, and the heat is generated. Since the flow velocity of the cooling air flowing through the part 13 increases,
The heat transfer coefficient of the heat generating portion 13 is improved. At the same time, the cold air whose temperature has not yet risen is
The heat radiation performance of the heat generating portion 13 is improved because the heat radiation portion 13 is easily hit. The length of the short pin 11b is desirably not more than の of the length of the long pin 11a so that the cooling air is sufficiently supplied to the vicinity of the heat generating portion 13.

However, if the area of the short pins 11b exceeds 20% of the entire substrate area, the amount of heat radiation is significantly reduced due to the reduction of the heat radiation area, thereby offsetting the partial improvement of the heat transfer coefficient. This is not preferred.

As for the arrangement of the pins of the heat sink according to the present invention, there are various modes other than the type in which the pin on the windward side of the heat generating portion is shortened as shown in FIG.

FIG. 4 is a schematic view showing another example of the heat sink of the present invention. FIG. 4A is a plan view, and FIG.
It is a longitudinal cross-sectional view of the pin of one row of a cross section. In this figure and the following figures, the same parts as those in FIG. 3 are denoted by the same reference numerals. In FIG. 4, the pin 11 on the windward side of the heat generating unit 13 is thinned out. Also in FIG.
Since the number of 1s is small, there is an effect of increasing the flow velocity of the cooling air in the heat generating portion and an effect of making it easier for the cold air to hit the pins 11 of the heat generating portion 13. In the figure, when the area of the thinned portion exceeds 20% of the entire substrate area, the amount of heat radiation is significantly reduced due to the decrease in the heat radiation area, and the improvement in the partial heat transfer coefficient is offset. Not preferred.

FIGS. 5A and 5B are schematic views showing another example of the heat sink of the present invention. FIG. 5A is a plan view, and FIG.
It is sectional drawing of the pin of one row of a cross section. In the figure, there is a portion on the windward side of the heat generating portion 13 where the pin 11 does not exist. Also in the embodiment shown in the drawing, there is an effect of increasing the flow rate of the cooling air in the heat generating portion and an effect of making it easier for cold air to hit the pins 11 of the heat generating portion 13. If the area of the portion without pins in the figure exceeds 20% of the entire substrate area, the amount of heat dissipation is significantly reduced due to the decrease in the heat dissipation area, and the improvement in the partial heat transfer coefficient is offset, which is preferable. Absent.

FIG. 6 is a plan view showing another example of the heat sink of the present invention. As shown in the figure, the pin arrangement of the heat sink of the present invention is arranged so that the number of pins changes sequentially from the center in the direction crossing the flow. By arranging the pins in this manner, the supply of the cool air to the heat generating unit 13 is further increased as compared with the example of the heat sink in FIG.

FIG. 7 is a plan view showing another example of the heat sink of the present invention. As shown in the figure, portions where no pins are arranged are on both the leeward and leeward sides of the heat generating portion, so that the number of pins in the ventilation direction is reduced. The portion where the pin is not arranged may be limited only to the leeward side.

In the heat sink of the present invention, the pitch of the pins along the flow of the air passing through the heat generating portion is the same as the pitch of the pins in the other portions. FIG. 8 is a plan view of an example of a heat sink not included in the present invention. In the drawing, the pitch in the flow direction of the pins at the center of the heat sink is reduced without decreasing the number of pins along the flow direction of the air, and a space where no pins exist is provided in front of the heat generating portion. In the example shown in the figure, although the cold air easily hits the pins near the heat generating portion, the ventilation resistance also increases, so that an increase in the amount of air flowing through the central portion of the heat sink cannot be expected.

FIG. 9 is a plan view of another example of a heat sink not included in the present invention. In the figure, if the number of pins of the heat-generating portion of the heat sink is reduced and the pin pitch is increased, the position of the pin on the front surface where the heat transfer coefficient is high is separated from the heat-generating portion, and the heat is released from the central portion of the heat sink. No improvement in calorific value.

As described above, according to the present invention, in the pin fin type heat sink for forced air cooling, the pins on the windward and / or leeward side of the heat generating portion which contributes little to heat radiation are shortened, thinned out, or eliminated. Thus, the heat transfer coefficient of the central pin, which contributes to heat dissipation, is increased, and a heat sink having excellent heat dissipation performance is obtained.

In the present invention, the number of pins to be shortened or thinned out is not particularly limited, and it is desirable to determine an optimum pin arrangement each time according to the size of the heat generating portion and the use environment.

In the above description, the heat generating portion is described as being at the center of the heat sink, but in the case of a special element,
The heating part may not always be at the center. In that case,
It is desirable to leave a pin corresponding to the heat generating portion as it is and to provide a pinless portion on the windward and / or leeward side of the heat generating portion.

[0039]

Next, the present invention will be described with reference to examples. (Embodiment 1) FIG. 10 is a schematic view showing a heat sink used in the test of Embodiment 1, wherein FIG. 10A is an example of the present invention, and FIG.
Is a comparative example. In FIG. 9A, the dimensions of the substrate are 100 mm × 100 mm × 4 mm in thickness, the pin dimensions are φ2.0 mm × 29 mm in height, and the pin pitch is 4.0 mm. The number of pins in one row is 22, and as shown in FIG. 2A, 40 × 10 × 4 pins in front of the flow direction of the pin row at the center of the heat sink of the present invention are removed, and The total number is 444. The heat sink of the comparative example shown in FIG. 9B has the same substrate dimensions and pin dimensions as those of the example of the present invention shown in FIG.

A 40 × 40 mm surface-heating type heater was attached to the back side of the substrate (the area surrounded by the wavy line in the drawing) of the heat sinks of the present invention and comparative examples, and the cross section was 180 × 55 mm.
And the cooling air was flowed while changing the temperature in the range of 0.5 to 4.0 m / s while heating the heater, and the heat dissipation performance of the heat sink was measured by measuring the temperature of the heater surface.

FIG. 11 is a graph showing test results. The vertical axis in the figure is the thermal resistance (elevated value of the substrate temperature per unit heat input: ° C / W), and the horizontal axis is the flow velocity (m / s) of the cooling air.
As shown in the figure, when the wind speed was 2 m / s or less, the heat radiation performance of the heat sink of the present invention was found to be excellent by 5 to 10%.

(Example 2) FIG. 12 is a schematic view showing a heat sink used in the test of Example 2, wherein FIG. 12 (a) is an example of the present invention and FIG. 12 (b) is a comparative example.

In FIG. 5A, each dimension of the substrate is 60 mm × 60 mm × 3 mm in thickness, and the pin dimension is φ
1.5 mm x height 20 mm, pin pitch 2.7 mm. The number of pins in one row is 22, and as shown in FIG. 7A, 72 pins 36 × 2 = 72 before and after in the flow direction of the pin row at the center of the heat sink of the present invention are removed. Therefore, the total number of pins is 412. The heat sink of the comparative example shown in FIG. 6B has the same substrate dimensions and pin dimensions as those of the present invention shown in FIG.

A 32 mm × 32 mm surface heating type heater was attached to the back side of the substrate of each of the heat sinks of the present invention and comparative examples (the area surrounded by the wavy line in the figure), and the cross section was 200 mm ×
It was set in a 100 mm duct, the cooling air was flowed while changing the temperature in the range of 0.5 to 4.0 m / s while heating the heater, the temperature of the heater surface was measured, and the heat radiation performance of the heat sink was measured.

FIG. 10 is a graph showing test results of the second embodiment. The vertical and horizontal axes are the same as in FIG. As shown in the figure, when the wind speed is 2 m / s or less, the heat radiation performance of the heat sink of the present invention is superior by 5 to 10%.

[0046]

By using the heat sink of the present invention, the heat transfer at the central portion of the heat sink can be improved, and the heat generating element such as an LSI element can be stabilized.

[Brief description of the drawings]

FIG. 1 shows a pin grid array type LSI package 21.
FIG. 4 is a longitudinal sectional view showing a state where a heat sink 22 is attached to the radiator.

FIG. 2 is a perspective view showing an appearance of a pin fin type heat sink.

FIG. 3 is a schematic view showing an example of a heat sink according to the present invention, wherein FIG. 3 (a) is a plan view and FIG. 3 (b) is a longitudinal sectional view of one row of pins taken along the line AA.

FIG. 4 is a schematic view showing an example of a heat sink according to the present invention. FIG. 4 (a) is a plan view, and FIG. 4 (b) is a longitudinal sectional view of one row of pins taken along the line AA.

FIGS. 5A and 5B are schematic views showing another example of the heat sink of the present invention, wherein FIG. 5A is a plan view and FIG. 5B is a cross-sectional view of one row of pins taken along the line AA.

FIG. 6 is a plan view showing an example of a heat sink according to the present invention.

FIG. 7 is a plan view showing an example of a heat sink of the present invention.

FIG. 8 is a plan view of an example of a heat sink not included in the present invention.

FIG. 9 is a plan view of an example of a heat sink not included in the present invention.

FIG. 10 is a schematic view showing a heat sink used in the test, wherein FIG. 10 (a) is an example of the present invention and FIG. 10 (b) is a comparative example.

FIG. 11 is a graph showing test results.

FIG. 12 is a schematic view showing a heat sink used in the test, wherein FIG. 12 (a) is an example of the present invention and FIG. 12 (b) is a comparative example.

FIG. 13 is a graph showing test results.

[Explanation of symbols]

 11 Pin 11a Long Pin 11b Short Pin 12 Substrate 13 Heating Part 21 LSI Package 22 Heat Sink 23 Si Chip 24 Heat Transfer Board 25 Container 26 Multilayer Wiring Board 27 Lid 27a Airtight Space

Claims (3)

[Claims] 1. A pin fin type forced air cooling heat sink having a substrate and a plurality of pins arranged at a constant pitch on the substrate, wherein a substrate portion corresponding to a heat generating portion of an element to be cooled is disposed on a substrate surface. A state in which pins on the side of the parallel specific direction and / or on the side opposite to the specific direction are shorter than pins on a portion corresponding to the heat generating portion, and the pins on the side of the specific direction and / or on the side opposite to the specific direction are thinned out. Characterized in that the pins are arranged in at least one of the states of the forced air cooling. 2. The heat sink for forced air cooling according to claim 1, wherein the area of the substrate portion having short or no pins is 20% or less of the area of the entire substrate. 3. A method for cooling a heat sink, comprising: sending cooling air for forced air cooling from a side of a specific direction of the heat sink according to claim 1 or 2.