WO2005006435A1

WO2005006435A1 - Heat sink

Info

Publication number: WO2005006435A1
Application number: PCT/SG2004/000193
Authority: WO
Inventors: Cheong Kong Chang
Original assignee: C C K Innovations Sdn Bhd; Loh, Ean Leng
Priority date: 2003-07-09
Filing date: 2004-07-02
Publication date: 2005-01-20

Abstract

The invention is an improved heat sink, which is mounted onto a CPU processor, comprising a base plate (20) in contact with the processor (5), a conducting column (10) located above the processor (5) on the surface of the said base plate (20) facing away the said processor (5), and a plurality of dividing walls (40) extending from the said conducting column (10), wherein the dividing walls (40) have fins (30) to help in the dissipation of heat.

Description

Description Title of Invention: Heat Sink

Field of invention

The invention relates to a heat sink for an integrated circuit chip, particularly for a microprocessor of a computer.

Background

In this electronic age, many of the electrical appliances now employ integrated circuits (lCs) chips or even microprocessors, that are mounted on printed circuit boards. This is best exemplified in a personal computer. Owing to electrical resistance, circuit components like transistors and capacitors inside an integrated^' circuits chip will generate heat during operation. Normally, these electronic packages can cope with the heat load and can dissipate the heat through exposed die surface without over-heating. However, as we require more efficient integrated circuits, more circuit components are packed into a single electronic package.' As a consequence, this tremendously increases the amount of heat generated within the same volume and an external device such as a heat sink is needed to cope with the extra heat load.

A heat sink, by definition, is a device which receives heat from a heat source. Inevitably, the temperature of any heat sink needs to be colder than the heat source at any time for it to function, and hence itself needs to reject heat to colder sources such as the environment. The rate of heat transfer Q is generally represented by the formula:

Q = hS T

Where h is the heat transfer coefficient, S is the heat transfer area and T is the temperature difference. Most of the heat sinks for-microprocessor are typically metal- plates made of conductive material, for example aluminum and copper. They have plurality of fins to increase the heat transfer area and dissipate heat into the air by convection. An active fan can be designed to mount on top of the heat sink to promote air convection efficiency. A retention mechanism such as a clip is required to secure the heat sink onto microprocessor, or any other electronic packages, across heat dissipation path.

However, the fins of the heat sinks are typically rectangular metal sheets that are arranged parallel to each other as seen in figure 1. A column of moving air, on the other hand, on meeting an obstruction such as a flat surface, will naturally spread out in all direction along the surface. This is best visualised when a stream of water from a faucet continuously falls onto the surface of a sink, creating a puddle of water which spreads in all direction. Therefore, such arrangement will not facilitate the air flow out of the heat sink as its natural path collides with the fins. Moreover, the volume underneath the fan hub often represents a column of stagnant air. Within this column, air either circulates from the bottom to the top and down to the bottom again without leaving the column, or remains still and immobile.

Unfortunately, the central area of the heat sink is the hottest and hence in need of conducting heat away to be dissipated most urgently.

As such there is an area of improvement to the current heat sinks to enhance heat transfer from the chip, in particular heat transfer concerning the core area.

Summary of the invention

The invention is an improved heat sink, which is mounted onto a micro-processor or any other suitable electronic packages, comprising a base plate having a first and a second surface. The first surface is intended to be placed in thermal contact with the micro-processor while a column made of heat conducting material is disposed on the second surface of the said base plate and in thermal contact with the base plate, preferably above the micro-processor. There are walls extending from the said conducting column, and these walls have fins that extend from the base plate to conduct heat away from both the base plate and the conducting column. The base plate, together with the conducting column and the attached fins, provide a large surface area in a compact structure allowing heat to be convected away by air current.

In one embodiment, the fins located in the space between two adjacent wall members are aligned parallel to each other along the radial direction of the heat conducting column, so as to reduce obstruction to the natural path of air flow. The fins may even be curved sideward.

In another embodiment, the heat conducting column has a hyperbolic vertical cross section to cater for the exceptionally high heat flux within area above the micro-processor by helping to conduct heat away from the area.

Whenever needed, the conducting column may also have additional fins to improve the rate of heat dissipation.

Supporting columns are present near the periphery of the heat sink for mounting a fan on its top and attaching the heat sink to the micro-processor below.

It is preferable that the entire structure of the heat sink forms an integral body made of the same heat-conducting material. The conducting material can be copper, aluminium, iron and other heat-conducting alloys.

Preferably, the structure of the heat sink takes on a cuboid. However, a cylindrical heat sink is also feasible for the invention.

Brief description of the drawing Figure 1 is the prior art which is a heat sink with parallel plate fins

Figure 1 a shows the flow of air on a flat plate when air is blown from a fan.

Figure 1b shows the flow of air around the body of the invented heat sink along a vertical cross section when the air is blown from a fan which is mounted on top.

Figure 2 shows the perspective view of the preferred embodiment of the invention

Figure 2a shows the top view of the preferred embodiment of invention

Figure 2b shows a vertical cross section similar to figure 1b of the preferred embodiment

Figure 2c shows a side view of the preferred embodiment

Figure 3, 4a, 4b and 4c show the plan view of each of the different embodiments of the invention.

Detail description

In the present invention, the heat sink consists of a base plate (20) which is placed adjacent to and in thermal contact with the surface of an electronic package (5), particularly an IC chip or a microprocessor. In this context, when two objects are described to be in thermal contact (with each other), it means that positional arrangement between the two objects facilitates heat conduction. Therefore, the heat sink and the chip (5) can be either in direct physical contact, or be separated by a layer of material, provided heat conduction is not hindered. A column (10) of conductive material is disposed in line with the chip on the other surface of the said plate away from the chip. This column (10) is in thermal contact with the chip so that heat can be conducted away from the central part of the base plate (20) along this column (10) without causing overheating to the chip. It is usually located at the center of the base plate (20) where the chip (5) normally lies.

Furthermore, the presence of the heat conducting column (10) will also reduce, if not completely eliminate, the volume of air re-circulation underneath the fan hub; no air will be trapped and heated up. At the same time, the heat conducting column (10) can also reject heat to the air current as the stream of air nearest to the fan hub flows along the surface of the column (10) before reaching the base plate (20). This, inadvertently, also increases the heat transfer area for air convection at the central region as compared to flat surface.

In one embodiment, the heat conducting column (10) and the base plate (20) form an integral body of the heat sink having a hyperbolic cross section of which column width progressively becomes shorter as one moves away from the base plate to measure it. This shape is designed to match the heat flux profile, which has the same shape as the temperature profile, of a flat plate. This shape also has an advantage of maximising contact time of the air with the heat sink given the same volume of conductive material without disrupting the smooth flow of air.

To enhance conduction and dissipation of heat at the central area, walls (40) extending from the heat conducting column (10) are constructed on the surface of the base plate (20). These walls (40) divide the structure of the heat sink into multiple sections. There will be fins (30) branching out along these walls (40), and these fins (30) will be disposed on the base plate (20) so that they are in thermal contact. Preferably, the fins are perpendicular to the base plate (20). Additional fins may be attached directly to the heat conducting column (10).

It is obvious to a person skilled in the art that adding fins to the heat sink will enable heat from the conducting column (10), as well as the base plate (20), to spread out over an even greater area (by conduction) to be convected away by the air current than the base plate (20) and central column (10) alone can have. In addition, since the base plate (20) is in contact with the fins, heat from the chip (5) will experience less thermal resistance when being conducted towards the fins from where most heat will be rejected to the air current. Furthermore, the presence of walls (40) to hold the fins (30) will avoid over-packing all the fins around the central column (10). This is because fins that are spaced closely to each other tend to retard air flow between the fins due to significant drag exerted by the wall. This in turn will have adverse effect on the rate of heat convection.

It should be noted at this point that the base plate (20), the heat conducting column (10), the walls (40) and the fins (30) are thermally integrated, meaning that heat that is absorbed from chip (5) can be conducted to every part of the sink, namely the base plate (20), the heat conducting column (10), the walls (40) and the fins (30). Heat absorbed from the chip (5) is first spread out along the base plate (20), and the same base plate is sometimes referred to as heat-spreader base because of this function. Subsequently, heat may be conducted towards the base of the column (10) and the walls (40), as well as the base portion of a few fins (30), particularly for those fins which are located near the chip (5). However, as the heat conducting column (10) becomes hotter, heat from the column will also be conducted to walls (40) and spread towards the fins (30) which branch from the walls (40). Therefore, the heat sink is able to provide multiple pathways for heat conduction from the base plate towards the fins, which are: 1 ) from the base plate directly to the fins, 2) from the base plate, to the walls and then to the fins, and 3) from the base plate, to the central column, the walls and finally to the fins.

In the preferred embodiment, fins (30) that are located within the same section between two adjacent dividing walls (40) may be aligned parallel to each other so that the adjacent fins are equidistantly separated from each other. They are best aligned to meet the periphery of the base plate (20) (or the tangent of the periphery if the periphery is curved) that are enclosed within the two adjacent dividing walls (40) at an oblique angle. This is to reduce the obstruction to the natural path of air flow, ensuring the heated air leave at all sides of the heat sink structure. The fins (30) are not limited to flat plates; they may even be curved sidewards, as shown in figure 4a. At the end of the dividing walls (40), additional supporting column (50) may be erected for mounting the fan on the top of the heat sink and attaching the heat sink on top of the IC chip (5).

It is best that the free (unbound) edges of the fins (30) are aligned either along a flat plane or a curvature. In particular, the top edges of the fins (i.e the free edges which are furthest away from the base plate) are level with the top ends of both the conducting column (10) and supporting columns (50), as opposed to the bottom ends which are integral with the base plate (20). All the top edges and the top of columns (10,50) lie on a planar surface which is parallel to the base plate (20) and this makes mounting a fan onto the heat sink convenient. Moreover, in the preferred embodiment (as shown in figure 2 and 2a), the free ends of the fins (i.e the free edges which are furthest away from the central column of the heat sink) are aligned to four planar surfaces that are perpendicular with base plate (20). Therefore, the whole heat sink will have a cuboidal shape. The same heat sink may contain more than four dividing walls as shown in figure 4b and 4c.

The invention, however, does not have to take on cuboidal shape. It can also be cylindrical in shape with the free ends of the fins aligned to the curved surface of a cylinder, as exemplified in figure 3.

It is preferable that the entire structure of the heat sink, meaning the base plate (20), the conducting column (10), the walls (40), the fins (30) and the supporting columns (50), forms an integral body made up of a single heat conducting material, though there is no restriction in which the different components of structure cannot be made from different material. The heat sink can be made of copper, aluminium, iron and good heat-conducting alloy. Operation of heat sink

During operation of the chip, the heat sink draws heat from the die surface of the chip (5) to the base plate (20) and subsequently spreads the heat to the conducting column (10), the dividing walls (40) and the fins (30), as described earlier.

The fan blows air from the top of the heat sink towards the base plate (20) and the air current continuously extracts heat from every part of the heat sink which it comes into contact with. The fins first partition the flow of air into the space in between the fins (30). The path of flow will generally follow a hyperbolic curve, as the air current flows from the fan to the base plate (20). In a once-through fashion, the air will then leave from all sides of the heat sink. The path and direction of the air flow is as shown in figure 1b.

While the invention has been described with reference to various illustrative embodiments, the description should not be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those people skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments, the principle of which is as defined by the following claims.

Reference list

5 Chip/micro-processor

10 heat conducting column

20 base plate

30 fins

40 wall member

50 supporting column

Claims

Claims :

1. A heat sink for an electronic package (5), comprising: i) a thermally conductive base plate (20) having a first and a second surface wherein the first surface is to be brought into thermal contact with the electronic package (5); ii) at least one conducting column (10) disposed on the second surface of the said plate (20) and in thermal contact with base plate (20) to conduct the heat away from the region of the base plate (20) where the electronic package (5) resides; iii) a plurality of walls (40) extending from the said conducting column (10) and dividing the structure of the heat sink into sections, wherein each section has a plurality of fins (30) extending from the walls (40) towards the periphery of the base plate (20) and perpendicularly from the base plate (20).

2. A heat sink according to claim 1 wherein the fins (30) and the dividing walls (40) are curved and parallel.

3. A heat sink according to claim 1 wherein the fins and the dividing walls are straight, and the fins are parallel, meeting the periphery of the base plate (20), or the tangent of the periphery if the periphery is curved, that are enclosed within two adjacent walls (40) at an oblique angle.

4. A heat sink according to claim 1 , 2 or 3 wherein the heat conducting column(s) (10) has a hyperbolic vertical cross section, the column diameter of which progressively decreases as it gets further away from the base plate.

5. A heat sink according to any one of the preceding claims wherein additional fins extend from the conducting column(s) (10).

6. A heat sink according to one any of the preceding claims wherein there are supporting columns (50) near the periphery of the heat sink for mounting a fan on its top and attaching the heat sink to the electronic package (5) below.

7. A heat sink according to any one of the preceding claims wherein the heat sink has a cuboidal shape.

8. A heat sink according to any one of the preceding claims except claim 6 wherein the heat sink has a cylindrical shape.

9. A heat sink according to any one of the preceding claims wherein the base plate (20), the conducting column (10), the dividing walls (40) and the fins (30) form an integral structure made up of a single conducting material.

10. A heat dissipating apparatus for an electronic package comprising a heat sink as claimed in any of the preceding claims and a fan mounted on top of the said heat sink to blow air towards the base plate (20) of the heat sink.