CN1988139A - Method and device for forming enchanced thermal interface - Google Patents

Abstract

A method and related apparatus for providing an enhanced thermal interface. This interface is formed by applying a structure or foil embedded in the alloy in solid form between the two surfaces. Once heat is applied from one or both surfaces, the alloy melts, forming the desired interface.

Description

Method and apparatus for forming an enhanced thermal interface

technical field

The present invention relates generally to a method and apparatus for providing an enhanced thermal interface; and more particularly to a method and apparatus for providing an enhanced thermal interface for use in semiconductor packages for computing environments.

Background technique

The development of the semiconductor industry has given rise to an industry trend of increasing the number of electronic components inside electronic devices. Density allows the selective fabrication of smaller and lighter devices that are more attractive to consumers. In addition, compactness also allows many circuits to operate at higher frequencies and higher speeds due to the shorter electrical distances in these devices. Despite the many advantages associated with this industrial goal, providing many of these components in a small footprint poses many challenges to device performance. One such challenge is that the thermal interface must be established without compromising device conductivity and integrity.

In order to provide a good interface, all surfaces involved must be clean, smooth and free of all particles including air gaps or air bubbles that would form during the manufacturing process. Thermal and mechanical forces applied during normal and continuous device operation must also be considered because they can affect the integrity of the interface. In this regard, the interface must be fabricated in such a way that it does not deteriorate easily after continuous use, and special care must be taken that any such deterioration or related problems could potentially cause electrical damage affecting the operation and integrity of the device as a whole. Short circuit or other such similar problems.

One of the more challenging of these interfaces to fabricate and maintain is the thermal interface, as used in computing environments such as those between a microprocessor chip and a heat sink. In this case, the interface bond needs to be able to provide the required heat transfer and dissipation, which are critical to the speed and power capability of the circuit, and needs to meet the requirement of leaving no gaps and other issues discussed.

The prior art uses several approaches to provide an improved thermal interface. One way is to use hot adhesive. Thermal adhesive is used to fill the gap between the backsides of the chip to provide this interface. However, the use of thermal adhesives has a number of problems associated therewith. Individual assembly of devices with thermal adhesive components is difficult because sufficient adhesive must be applied to completely cover the chip. Additionally, thermal adhesives are sticky and difficult to handle. The use of modular components must also be chemically compatible with thermal adhesives to provide good adhesion. Finally, the adhesive-filled chip must be of sufficient thickness to form a reliable structure.

Another attempt to provide a good thermal interface is by applying the alloy directly between the joints. A metal bond is a preferred thermal bond because it has little thermal resistance. Metals such as these exhibit high thermal conductivity. Liquid metals exhibit high thermal conductivity and additionally have the advantage of being able to fill voids in mechanical joints. However, the same features that make these bonds attractive also raise device integrity issues.

Problems are often caused by poor wetting inherent in the low melting temperature alloy interface between the microprocessor chip and the heat sink. Problems arise due to the fact that when the refractory alloy is melted, while pressing it between two surfaces, due to poor wetting between the refractory alloy and the chip and between the refractory alloy and the heat sink The resulting capillary action, the molten alloy is extruded out of the interface. Without the molten alloy bridging the gap, the thermal performance of the cooling assembly is reduced. Molten alloy squeezed out of the interface can also seep and leak into other areas, especially adjacent areas housing electrical components, and can cause system degradation and failure.

Thus, there is a need to devise a method and apparatus that can be used to provide good thermal interfaces while taking advantage of the benefits provided by the use of molten alloys in these interfaces.

Contents of the invention

The disadvantages of the prior art are overcome and additional advantages are provided by methods and related apparatus for providing an enhanced thermal interface. The interface to be formed is preferably between the heat sink and the chip, and the operation of the chip provides the required heat dissipation for the molten alloy. An interface is formed by applying a structure or foil embedded in an alloy in solid form between two surfaces. Once heat is generated, as by normal device operation, the alloy in the foil or structure melts, forming the desired interface. However, the structure and foil prevent the alloy from leaking and seeping into the surrounding area. In alternative embodiments, the structure may have apertures such as a wire mesh to provide a certain amount of rigidity and compressibility.

Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. The invention with advantages and features may be better understood with reference to the description and drawings.

Description of drawings

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a cross-sectional view of an enhanced thermal bond;

Figure 2 is a cross-sectional view of one embodiment of the invention using a wire mesh structure in forming the thermal interface of the embodiment of Figure 1; and

3 is a cross-sectional view of an alternative embodiment of the invention using an alloy embedded foil in forming the thermal interface of the embodiment of FIG. 1 .

Detailed ways

Figure 1 provides a cross-sectional illustration of the enhanced thermal interface. As shown in Figure 1, first and second surfaces, respectively designated 110 and 120, are provided between which a thermal interface is to be formed. In a preferred embodiment of the invention, surfaces 110 and 120 are chip and heat sink components of a computing environment, but this is not required.

Thereafter, a thermal interface is formed between surfaces 110 and 120 as shown at 130 . Thermal interface 130 preferably includes a metal alloy. As shown, no air gaps or other surface irregularities occur, and the thermal interface 130 is confined to the area bounded by the first and second surfaces 110 and 120 without any part of the interface 130 leaking from either side thereof. out or leak into its surroundings and/or adjacent areas.

As described below, interface 130 may first be formed by applying the alloy in solid form. When an appropriate material is chosen for the interface alloy, the heat dissipated from the computing environment (or alternatively, the first and second components 110 and 120) will be able to melt the alloy, resulting in the The smooth thermal interface 130 of .

Heat dissipation is an important challenge for designers of computing environments, especially those involving large and complex environments. However, an environment of any size, if not addressed, can introduce electrical and mechanical failures that will affect overall system performance. It is easy to understand that heat dissipation increases as packaging density increases. Not only are there more heat-generating electronic components in larger computing system environments than in smaller environments, but because heat dissipation can cause a variety of other seemingly unrelated problems, thermal management solutions must be provided, To consider other requirements of the system environment. Specifically, this is why the thermal interface is the focus in these environments.

In fact, efficiently extracting heat from integrated circuit packages used in any computing environment presents a very significant limitation on the design capabilities of these circuits. Whenever heat needs to be transferred or dissipated from one object to another by conduction, a critical factor is the maintenance of the bond between surfaces.

Effective removal of heat from a heat generating device, such as a microprocessor silicon chip, requires that the heat generating device be in intimate contact with a heat dissipating device, such as a heat sink. However, in such interfaces, the smoothness of the surfaces and even sometimes some measure of the pressure applied continuously to the joint can be key to maintaining a good joint.

In this regard, the mating surfaces can be maintained flat and pressure applied to hold them together. Unfortunately, however, microscopic surface irregularities are always present, and this irregularity combined with manufacturing process steps creates air gaps between the chip and the heat sink, which seriously deteriorates the heat transfer performance. Known materials that can enhance this bond are adhesives and greases, which are either difficult to apply or reduce the thermal resistance of the contact surfaces in question.

Another known solution for creating smooth joint surfaces free of air gaps and other irregularities is to fill such gaps with low melting point alloys that may be liquid or even solid at normal operating temperatures. The problem is that when the refractory alloy melts to fit the gap, if there is poor wetting between the refractory alloy and the surface of the gap, the surface tension will force the liquid alloy out of the gap.

It is not easy to make the interfacial surface very clean and easily wetted by low-melting point alloys. Likewise, foils of low melting point alloys that may be placed at the interface have surface oxides formed thereon during storage. Incompletely clean interface surfaces and oxides on the eutectic alloy foil cause poor wetting of the eutectic alloy. Therefore, there is a need for a means for holding the eutectic alloy in its intended position, filling the interfacial gap and providing a thermal bridge between the chip and the heat sink as previously described.

The present invention provides a device for bridging the gap between the chip and the heat sink by the low melting alloy even when the low melting alloy does not wet the chip and the heat sink. Without good wetting, capillary action will force the molten alloy out of the gap. The present invention provides a means by which the eutectic alloy can be kept in the gap even when wetting is poor. The precise structure of alloy 130 can be further investigated with the aid of the examples provided below in conjunction with FIGS. 2 and 3 .

It should be noted that while various different embodiments may be implemented as those skilled in the art will recognize, a pair of such embodiments are provided below in FIGS. 2 and 3 with the understanding that they are provided for discussion only purpose and therefore do not limit the subject matter of the invention. Two such devices will now be studied in more detail.

Fig. 2 is a cross-sectional view of a first embodiment of the present invention. In Fig. 2, a first embedded structure 200 is illustrated. The structure preferably comprises metal and is in a porous form such that it maintains a level of structural integrity and rigidity while becoming capable of being embedded in the alloy 210, as will be discussed.

While there is some desired structural rigidity, in some cases the interfaces involved and structure 200 require their structural rigidity to maintain a certain level of flexibility and compressibility. It should be noted in this regard that by increasing or decreasing the level of surface pore size, the level of stiffness (or even compressibility) can be selectively achieved, maintained or increased. In one embodiment of the invention, structure 200 has a mesh structure to provide both rigidity and compressibility. In a preferred embodiment, structure 200 is a wire mesh that can readily contain alloy 210 as shown.

The alloy 210 used is preferably a low melting alloy. Additionally, the materials used for the eutectic alloy and apertured structure 200 must be such that they do not readily react with each other.

The wire mesh (200) is embedded in the eutectic alloy 210 as shown in the preferred embodiment of FIG. 2 where the wire mesh (200) is employed. As previously mentioned, any material that can hold the alloy in molten form and that can be embedded in the alloy can be used as the wire mesh.

In preferred embodiments, the wire mesh or other such material is well cleaned by means known to those skilled in the art prior to embedding it in the alloy. In one embodiment, the screen is cleaned by sputter etching prior to applying the eutectic alloy.

It should be noted that the thickness of the alloy embedded structure (200) depends on how much metal alloy is applied thereto, and can be selectively changed to suit different purposes. Eutectic alloys may also be applied by various methods known to those skilled in the art. For example, the metal alloy may be sputtered onto the screen or other such structure, or alternatively deposited on the screen using chemical or physical vapor deposition techniques. The alloy should be applied to at least two sides 201 and 202 of the structure 200, and when the structure 200 provides such apertures in its design, the alloy should preferably be deposited on all sides of the structure, including between the apertures.

Returning to FIG. 1 , the embedded structure 200 of FIG. 2 is then applied between the two surfaces 110 and 120 , preferably in solid or substantially solid form. As previously mentioned, heat dissipated from the computing environment or from surfaces that are not the computing environment during normal device operation causing heat dissipation in turn causes the alloy to melt and form the gap-free, bubble-free interface 130 of FIG. 1 .

The structural rigidity of structure 200 will hold the molten alloy in place and prevent it from capillary action due to poor wetting as previously discussed. It should be noted at this point that the structural rigidity of structure 200 also provides ease of application. The process of fabricating structure 200 is inexpensive and flexible. This fabrication process can easily be combined with fabrication processes of other semiconductor components to be used in this environment. Therefore, existing manufacturing processes and components may be used in its formation.

Figure 3 provides an alternative embodiment of the present invention. In FIG. 3 , a cross-sectional view of a second embodiment using foil 300 for forming interface 130 of FIG. 1 is provided. The foil 300 is embedded in a low melting alloy 310 as shown. As previously stated, the materials of foil 300 and eutectic alloy 310 must be such that they do not readily react with each other.

In a preferred embodiment, foil 300 is well cleaned prior to its incorporation into alloy 310 by means known to those skilled in the art. To this end, in a preferred embodiment, the foil 300 is cleaned by sputter etching as described above.

The thickness of the alloy embedded structure (300) can be selectively varied. In this case, the thickness may be a combination of the thickness of the foil 300 or the applied alloy 310 . The eutectic alloy may also be applied by various methods known to those skilled in the art, as previously discussed. For example, the metal can be sputtered on the foil, or alternatively deposited on the foil using chemical or physical vapor deposition techniques. Alloy 310 should be applied at least to both sides 310 and 302 of foil 300 that will form the interface, but could also be deposited on all sides of foil 300 as shown.

Returning to FIG. 1 , the embedding structure 300 of FIG. 3 is then applied in solid or substantially solid form between the two surfaces 110 and 120 as before. As discussed above, heat dissipated from the computing environment or surfaces 110 and 120 during normal device operation will melt the alloy and form a gap-free, bubble-free interface as discussed in connection with FIG. 1 .

It should be noted that the structures 200 and foils 300 of Figures 2 and 3 can be readily provided when desired in the size and shape of the chip to be cooled. Once in place between the chip and the heat sink, when the chip is energized, for example, the heated chip alone provides the desired melting of the eutectic alloy and then bridges the gap between the chip and the heat sink .

Different structural requirements may arise leading to the use of one of the above structures or foils. In other words, the wire mesh structure of Figure 2 and the foil structure of Figure 3 may be selectively used for different reasons. For example, the wire mesh supported interface structure 200 of FIG. 2 is beneficial when there is high pressure between the heat sink and the chip. The interfacial gap is controlled to be twice the thickness of the wire. Therefore, the molten interfacial alloy is rarely squeezed out due to pressure. Structure 200 can be fabricated in such a way to provide more or less pressure as desired. The foil 300 of FIG. 3 can be used in situations where greater flexibility of the foil is desired, since obviously the foil can be made in a less rigid way than the structure 200 of FIG. 2 .

In this way, by proposing a structure and a method for bridging the gap between the chip and the heat sink by the low-melting alloy even when the low-melting alloy does not wet the chip and the heat sink, the present invention solves problems in microprocessing. problem of poor wetting inherent in the low melting temperature alloy interface between the chip and the heat sink.

While the preferred embodiment of the invention has been described, it will be understood by those skilled in the art that various modifications and enhancements, now and in the future, may be made to the invention which fall within the scope of the appended claims. These claims should be considered to retain the proper protection for the invention first described.

Claims (20)

1. device that is used to form hot interface, described hot interface is included in first structure that embeds in the acolite, the alloy of described fusing can not be easy to react with the material of described first structure, first structure of described embedding and the alloy of described fusing can put on the interface and not form bonded interface by solid form, but at the device duration of work by form this heat of linkage interface by the heat that device shed.

2. according to the device of claim 1, wherein said first structure has the aperture.

3. according to the device of claim 2, wherein said first structure is metallized.

4. according to the device of claim 3, wherein said first structure is a silk screen.

5. according to the device of claim 3, wherein said first structure is a rigidity, and the level of its rigidity and surface apertures is optionally proportional.

6. according to the device of claim 1, wherein said structure is used for providing thermal bonding between the heat sink and chip of semiconductor device.

7. according to the device of claim 6, the size of wherein said structure can change according to the size selectivity ground of described chip.

8. according to the device of claim 7, wherein at described chip with describedly arrange described alloy embedded structure with solid form between heat sink, and described heat sink work will be melted described alloy and be formed desired hot interface.

9. according to the device of claim 3, wherein said alloy is applied to all sides of described structure.

10. according to the device of claim 9, wherein said alloy is applied to all sides of the described structure that comprises between the aperture.

11. according to the device of claim 9, the thickness of wherein said alloy embedded structure depends on the amount of the alloy that described structure side is applied.

12. according to the device of claim 9, wherein said alloy is sputtered on all sides of described structure.

13. according to the device of claim 9, wherein said alloy is splashed to the wherein both sides of the described structure at hot interface to be formed at least.

14. according to the device of claim 9, wherein use physics or chemical vapor deposition technology with described alloy deposition on described structure.

15. device that is used to form thermal bonding, described thermal bonding is included in metal forming embedded in the acolite, the alloy of described fusing can not be easy to react with described paper tinsel, the paper tinsel of described embedding and the alloy of described fusing can apply and not form bonded interface by solid form, but only just form this interface after the heat of formed heat radiation during applying proper device operation.

16. according to the device of claim 15, wherein said paper tinsel is used for providing thermal bonding between the heat sink and chip of semiconductor device.

17. according to the device of claim 16, the size of wherein said paper tinsel can change according to the size selectivity ground of described chip.

18. according to the device of claim 17, wherein said alloy embed paper tinsel with solid form be arranged in described chip and described heat sink between, and described heat sink work will be melted described alloy and be formed desired hot interface.

19. according to the device of claim 18, wherein said alloy is applied to all sides of described paper tinsel.

20. a method that is used for forming in computing environment hot interface in semiconductor device, comprising: metal structure is embedded in the acolite, and the alloy of described fusing can not be easy to react with described structure; Be arranged in heat sink with solid form the structure of described embedding and chip between, only make after the described alloy of heat fusing that sheds from described chip during the proper device operation, to form this hot interface and bonding.