2. Description of the Related Art Heat sinks are widely used devices that dissipate, or in some case, absorb, heat from objects that need to remain cool, such as machinery or computer equipment. One type of heat sink comprises a block of heat conductive material, or evaporative plate, with a tunnel or bore machined through it. A heat dissipating pipe is inserted through this tunnel in order to absorb and dissipate the heat conducted to it through the heat conducting material of the surrounding heat plate. The heat plate is attached to the object that requires cooling, such as, for example, a wall of a computer cabinet or the mounting of an IC in a laptop computer.

An example of this type of heat sink is shown in FIG. 1, where tunnel 101 is bored through heat plate 110, and heat dissipating pipe 105 is held inside tunnel 101. To achieve the greatest efficiency with this type of heat sink, there needs to be a maximum coupling area between the heat pipe surface and the inner walls or surface area of the tunnel. For most heat sinks of this type, an

adhesive material (shown at 103 in FIG. 1) is used to couple the heat pipe to the inner surface walls of the tunnel.

When assembling the heat sink, this adhesive material 103 is inserted first in order to cover the walls of the tunnel. However, when the heat pipe 105 is inserted afterwards, it displaces some of the adhesive material 103 and results in a less than desirable coupling region. Several solutions to this problem have been proposed in the art.

One solution, which is shown in the perspective and cross-sectional views of FIGS. 2A and 2B, respectively, is a heat sink where an open channel 201, as opposed to a closed tunnel 101, is formed in heat plate 210 with channel 201 having a diameter substantially equal to the diameter of the pipe 205.

This results in a"half-open"design. During assembly, an adhesive 203 can be applied directly to channel 201 and pipe 205 can then be positioned in the channel 201 without displacing the adhesive 203. A drawback to this approach is that a significant amount of pipe surface area 208 is not in contact with the heat plate, thus resulting in a less than optimal heat transfer.

Another solution proposed in U. S. Patent 5,826,645 to Meyer, IV et al. is shown in the perspective

and cross-sectional views of FIGS. 3A and 3B, respectively. In that disclosure, the heat pipe 305 is held in place by two extension tabs 320 and 321. When heat plate 310 is first made, extension tabs 320 and 321 are vertical to the surface of the heat sink, as shown in FIG. 3B. Then extension tabs 320 and 321 are bent down to contact and hold in place heat pipe 305, as shown in FIG. 3A. Filler material 326, which may be a heat conductive adhesive, solder paste or lubricant, fills up the region between heat pipe 305 and extension tabs 320 and 321. There are several problems with this solution.

First, extra manufacturing and assembling steps are required to create and bend the extension tabs. Second, the edges of the extension tabs are pressed against the side of the heat pipe, and might rupture the sides of the heat pipe. Third, the large volume of filler material placed on both sides of the heat pipe is inefficient and wasteful.

Therefore, there is a need for a heat sink assembly which can effectively hold the heat pipe in place, while providing for an efficient transfer of heat between the conductive material and the heat pipe.

SUMMARY OF THE INVENTION One object of the present invention is to provide a heat sink assembly that can effectively hold the heat pipe in place while providing for an efficient

transfer of heat between the conductive material and the heat pipe.

Another object of the present invention is to provide a heat sink assembly in which the bonding material economically and efficiently connects the heat pipe with the inner surface of the heat plate.

Yet another object of the present invention is to provide a heat sink assembly in which the bonding material is easily applied and spread (wicking) between the heat pipe with the inner surface of the heat plate.

These and other objects are achieved by the present invention which is directed to a heat sink assembly having a heat block constraining a heat pipe within an elliptical or circular channel having a transverse slot which opens onto the surface of the heat block, thereby allowing for easier and more efficient application of bonding material and more efficient heat transfer.

The present invention is also directed to a method for forming a heat transfer assembly by forming in a channel in a heat plate, forming a slot in the surface of the heat plate along the length of the channel, inserting a heat pipe into the channel, and disposing heat conductive adhesive material in the gap between the channel and the heat pipe through the slot.

Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a perspective view of a drilled through heat sink according to the prior art ; FIGS. 2A and 2B are the perspective and cross- sectional views, respectively, of a half open heat sink according to the prior art;

FIGS. 3A and 3B are the perspective and cross- sectional views, respectively, of a tabbed heat sink according to the prior art; and FIGS. 4A and 4B are the perspective and cross- sectional views, respectively, of a preferred embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS The presently preferred embodiment of the present invention consists of a heat conductive material block (or heat plate) 410 having a drilled or milled tunnel or channel 401 that has a transverse slot 450 formed in the surface of the heat plate above the channel 401. The channel 401 and/or slot 450 can be formed via a molding process, via drilling techniques, or other machinery techniques as are well-known in the art. The diameter of the channel is larger than the width of the transverse slot 450 and is sized to accept a heat pipe 405 while providing additional space for allowing application of a thermally conductive adhesive material 403 to the channel walls to bond the heat pipe 405 to the channel walls of the heat plate 410, as discussed more fully below.

A thermally conductive adhesive or bonding agent 403 is used to thermally couple the heat pipe 405 with the channel 401. This is accomplished by applying the adhesive or bonding agent 403 through the slot 450

into a gap 407 formed between the heat pipe 405 and the channel 401. For example, if the bonding agent 403 is a thermally conductive adhesive solder paste, it could be applied through slot 450 to the top portion of channel 401. Then, the heat sink assembly would be heated, causing the solder to flow downward along the sides of the pipe 405. An efficient thermal contact results when the solder flows between the sides of heat pipe 405 and all or substantially all of the contact area between the heat pipe 405 and the walls of channel 401, thereby filling the gap 407.

As another example, the thermally conductive adhesive 403 can be in a preform or paste that is applied to the gap 407, either before or after the heat pipe 405 is disposed in the channel 401, or may be disposed by pressure directly into the gap 407 via the slot 450 once the pipe 405 is in place. Like the solder discussed above, the preform or paste will be cured in the gap 407 by heating the heat sink assembly to allow a preform to flow or by applying a paste or preform and then heating the assembly.

As shown in FIGS. 4A and 4B, and as explained below, the transverse slot 450 is made along the length of the channel 401 for providing access thereto. Heat pipe 405 is enclosed by channel 401 to almost its full

circumference thus insuring that heat pipe 405 is properly constrained by and contained within the channel walls. More particularly, the transverse slot 450 has a width « a which is less than a diameter"b"of channel 401. Thus, when heat pipe 405 is placed within the channel 401, the dimension of the transverse slot 450 prevents the pipe 405 from being removed from the channel 401 in a direction perpendicular to the channel length. As stated above, the transverse slot 450 can be formed via a molding process, via drilling techniques, or other machinery techniques as are well-known in the art.

Although heat pipe 405 is preferably substantially circular in cross-section, the channel 401 of the preferred embodiment has a slightly elliptical cross-section, thus insuring that bonding material may be effectively inserted through transverse slot 450 during assembly. In other embodiments, the cross- sections of both. heat pipe 405 and channel 401 may take a variety of closed curvilinear shapes, from circles to ellipses and ovals.

Regardless of which curvilinear shapes are used for the heat pipe and tunnel, preferred embodiments of the present invention maintain the appropriate interface dimension between the heat pipe and the tunnel

walls for maximizing heat transfer. In other words, as much of the surface area of the heat pipe as possible is interfaced with the heat plate via the tunnel walls.

Since the channel encloses the heat pipe to almost the full cross-sectional circumference, there is an increased pipe surface area for bonding between the heat pipe 405 and the plate 410, thus insuring a maximum amount of heat transfer.

The transverse slot 450 allows for easy application of an adhesive 403 along the top and sides of the heat pipe that are exposed in the channel opening. A suitable adhesive may be an epoxy or solder paste, or other material known by those having ordinary skill which possess the appropriate thermally-conductive properties for thermally coupling and binding the pipe 405 to the plate 410. In the presently preferred embodiment, the gap 407 is provided between the outer surface of the heat pipe and the channel walls in which the solder or epoxy is applied in a known manner for providing optimum wicking action therebetween, such as when the assembly is heated to allow the solder to flow.

Thus, there is effective wicking action of the solder or epoxy to cover the full surface of the heat pipe enclosed in the channel gap.

Optimum heat transfer takes place when the

solder or adhesive 403 completely fills the gap 407 in the interface between the heat pipe and the heat plate.

A most efficient thermal coupling results when all air is removed in the gap and replaced with adhesive 403.

With the inventive channel design described with reference to FIGS. 4A and 4B, the solder or adhesive will wick to fill or nearly fill the heat plate-to-heat pipe interface.

Therefore, a heat sink assembly according to the present invention can effectively hold a heat pipe in place, while providing for a more efficient transfer of heat between. the heat plate and the heat pipe.

Furthermore, the bonding material in a heat sink assembly according to the present invention is easily applied through the slot 450 and spread (wicked) between the heat pipe with the inner surface of the channel, thereby providing an economic and more efficient heat transfer connection.

While there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same

function in substantially the same way to achieve the same results are within the scope of the invention.

Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.