Thermal interface apparatus, systems, and methods

An apparatus and system, may include a thermal interface material comprised of an array of carbon nanotubes and a buffer layer disposed between the thermal interface material and one of a die or a heat spreader. In some embodiments the carbon nanotubes may be formed above a buffer layer formed above a surface of the heat spreader.

TECHNICAL FIELD

The subject matter relates generally to apparatus, systems, and methods used to assist in transferring heat from one element or body, such as a circuit, to another, such as a heat sink.

BACKGROUND INFORMATION

Electronic components, such as integrated circuits, may be assembled into component packages by physically and electrically coupling them to a substrate. During operation, the package may generate heat which can be dissipated to help maintain the circuitry at a desired temperature. Heat sinks, including heat spreaders, may be coupled to the package using a suitable thermal interface to assist in transferring heat from the package to the heat sink.

DETAILED DESCRIPTION

In the following detailed description of various embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that compositional, structural, and logical substitutions and changes may be made without departing from the scope of this disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

Examples and embodiments merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The following description is, therefore, not to be taken in a limiting sense.

FIG. 1is a cross section view of an apparatus10according to various embodiments. Apparatus10includes a package substrate12, a die14and a thermal management aid such as a heat sink or an integral heat spreader16which is mounted adjacent the die14and separated from it by a gap.

The substrate of die14is typically made of silicon and has frontside and backside surfaces. The die14also has an integrated circuit20and solder bump contacts22on the frontside surface. The contacts22connect with contact pads (not shown) on the upper surface of package substrate12. In some embodiments, the contacts22are manufactured according to a commonly used controlled collapse chip connect (C4) process.

In use, electric signals and power are provided to the integrated circuit20. Operation of the integrated circuit20causes heating of die14. Heat is transferred from the integrated circuit20through the substrate of die14to the heat spreader16through a thermal interface material24interposed in the gap between them.

InFIG. 1, the heat spreader16includes a top plate17and supporting side walls19. In some embodiments the side walls19completely surround the die14. In one embodiment the heat spreader16is coupled to a further heat sink (not shown) which may or may not be actively cooled.

In some embodiments, the thermal interface material24comprises an array25of either densely packed multi-walled or single walled carbon nanotubes or a combination of both single and double walled nanotubes. In some embodiments, either the heat spreader16or a lower surface thereof, is formed of, or coated with, a high thermal conductivity metal (and its alloys) such as molybdenum or copper, semiconductor material such as silicon or compounds as SiC (silicon carbide). In some embodiments the buffer layer consists of a film selected from the group consisting of Cr, Mo, Ti. W. SiC and TiC.

In some embodiments, a first layer26is deposited on the surface of the heat spreader16prior to growing the array of carbon nanotubes25in order to prevent a chemical reaction at the surface of the substrate of heat spreader16between the heat spreader surface material and reactive gases which may be used to support the growth of the nanotubes in either a thermal or plasma assisted chemical vapor deposition (CVD) method. When grown by the CVD process, some of the carbon nanotubes of the array of nanotubes25are aligned with a substantial number of the carbon nanotubes oriented substantially perpendicular to the surface of heat spreader16.

Carbon nanotubes have a coefficient of thermal conductivity along their longitudinal axis which is relatively high relative to the conductivity orthogonal to the longitudinal axis. The thermal conductivity of carbon nanotubes along their longitudinal axes is substantially higher than that of other materials used for thermal intermediates. The thermal conductivity of multi-walled nanotubes is about 3000 to 4000 W/m-K and theoretically about 6000 W/m-K for single walled nanotubes.

In some embodiments, a catalyst is applied to either the surface of the heat spreader16or as a separate layer of layer26. In some embodiments such catalysts include metals such as nickel, iron and cobalt which are selected to improve the efficiency of the deposition process.

After the prepared thermal interface material24has been formed on either the heat spreader16or, alternatively on layer26which was previously applied to the heat spreader substrate, the structure24is then thermally coupled to the backside surface of the die14. The thermal coupling is improved by orienting the free ends of the nanotubes to engage the backside of silicon die18. In some embodiments the coupling is directly to the backside of die14and in other embodiments the coupling is to a layer30on die14.

In some embodiments, spacers28are inserted between die14and heat spreader16to define a minimum gap width. On such spacer is shown in the detail view ofFIG. 2. In some embodiment multiple spacers28may be distributed about the perimeter of thermal interface material24.

If the height h of the spacers28is less than the thickness of thermal interface material24by a predetermined amount when the die and the heat spreader are forced together during assembly until they both contact spacers28, a controlled bias force is applied between the free ends of some carbon nanotubes of the array of carbon nanotubes25and the backside surface of die14to provide a good thermal contact.

In some embodiments, a surface of the heat spreader is formed from a material having a hardness substantially less than that of the nanotubes and free ends27of at least some of the carbon nanotubes26project from the array of carbon nanotubes24to embed them in the surface26of the heat spreader16as shown in the detail2B which is not to scale. In some embodiments the surface is a coating26.

By increasing the difference between the thickness of the thermal interface material24and the height of the gap defined by spacer28, the bias force for the junction between thermal intermediate24and die14can be controllably increased when a sufficient loading force is applied to the heat spreader16to have the spacer28engage both the surface of both heat spreader16and die14. By controlling the loading force and limiting it to a predetermined maximum force, the array of nanotubes25of the thermal interface material24will be deformed elastically by the bias force so that the highly conductive longitudinally oriented carbon nanotubes remain intact while they establish a highly conductive path between the die and heat spreader.

In some embodiments. the free ends of some of the individual nanotubes of the array of carbon nanotubes in the array of nanotubes25in thermal interface material24make generally perpendicular contact with the entire surface of die substrate18. This also allows the thermal interface material24to efficiently engage the entire surface of die14even if it is not perfectly smooth.

Substantial alignment of the longitudinal axes of many nanotubes of the of the array of carbon nanotubes25so that they are substantially perpendicular to the surface of die14provides a thermal path with direct, low thermal resistance between the surface of die14and heat spreader16.

In some embodiments, free ends of the carbon nanotubes of the carbon nanotube array of the thermal interface material may contact a layer30. In some embodiments, layer30is a metal film of gold or silver or other suitable metal or alloy having high thermal conductivity and which may be readily deposited on the surface of die substrate18. Layer30provides a reduced thermal resistance thermal coupling between the surface of die14and the carbon nanotubes of thermal interface material24.

In some embodiments, at least some of the carbon nanotubes of the thermal interface material24are coated or partially coated with gold, silver, platinum or other suitable metals or alloys by physical deposition or sputtering methods which are known. Such metal coated nanotubes may further reduce the contact thermal resistance between nanotubes of the thermal interface material24and either the surface of die14or the buffer30on the surface of die14.

Some embodiments include a number of methods. For example,FIG. 3is a flow chart illustrating several methods according to various embodiments. Thus, a method311may (optionally) begin at block321with coupling a heat source to a first surface of an array of substantially aligned carbon nanotubes and interposing a layer between at least one of either a heat source or a heat sink and at least one of either the first or a second surface of the array of carbon nanotubes in a block325. The method may include bonding another surface of the heat source to a substrate in block327.

In some embodiments block321of method311may also include forming a layer on the heat source and growing the array of substantially aligned carbon nanotubes on the layer.

In some embodiments block325of method311may also include applying an adhesion promoting layer between the heat sink and the array of carbon nanotubes.

FIG. 4is a flow chart of a method411illustrating several methods according to various embodiments. Thus, a method411may (optionally) begin at block421with growing an array of substantially aligned carbon nanotubes from a surface of a die and contacting the surface of a heat sink with free ends of some of the carbon nanotubes of the array of carbon nanotubes in block423.

In some embodiments method411also comprises forming an adhesion layer on the surface of the die according to block423.

In some embodiments method411also comprises forming an adhesion layer on some of the carbon nanotubes of the array of carbon nanotubes according to block425.

FIG. 5is a flow chart of a method511illustrating several methods according to various embodiments. Thus, a method511may (optionally) begin at block521with coupling a heat sink to a first surface of an array of carbon nanotubes and, in block523, applying an adhesion promoting coating to at least one of either the surface of a heat source or some of the carbon nanotubes of the array of carbon nanotubes. In some embodiments method511also comprises coupling the heat source to a second surface of the array of carbon nanotubes in block525,

In some embodiments applying an adhesion promoting coating to the surface of the heat source of block523comprises applying a metal.

In some embodiments applying an adhesion promoting coating to some of the carbon nanotubes of block523comprises sputtering a metal coating on the carbon nanotubes.

In some embodiments applying an adhesion layer to the heat sink of block523comprises applying a chemical adhesion promoting layer.

FIG. 6is a depiction of a computing system according to an embodiment. One or more of the embodiments of apparatus with one or more dies having a thermal intermediate with a thermal interface layer and a buffer layer interposed between the die and a heat spreader may be used in a computing system such as a computing system600ofFIG. 6. The computing system600includes at least one processor (not pictured), which is enclosed in a microelectronic device package610, a data storage system612, at least one input device such as a keyboard614, and at least one output device such as a monitor616, for example. In some embodiments' the data storage system612is a memory device such as a dynamic random access device. The computing system600includes a processor that processes data signals, and may include, for example, a microprocessor available from Intel Corporation. In addition to the keyboard614, an embodiment of the computing system includes a further user input device such as a mouse618, for example.

For the purposes of this disclosure, a computing system600embodying components in accordance with the claimed subject matter may include any system that utilizes a microelectronic device package, which may include, for example, a data storage device such as dynamic random access memory, polymer memory, flash memory and phase change memory. The microelectronic device package can also include a die that contains a digital signal processor (DSP), a micro-controller, an application specific integrated circuit (ASIC), or a microprocessor.

Embodiments set forth in this disclosure can be applied to devices and apparatus other than a traditional computer. For example, a die can be packaged with an embodiment of the thermal interface material and buffer layer, and placed in a portable device such as a wireless communicator or a hand held device such as a personal data assistant or the like. Another example is a die that can be coupled to a heat sink with an embodiment of the thermal interface material and buffer layer and placed in a dirigible craft such as an automobile, a watercraft, an aircraft or a spacecraft.

The apparatus10, substrate12, die14, heat spreader16, integrated circuit20, solder bumps22thermal interface material24and layers26and30, spacer28and aligned nanotube array24may all be characterized as “modules” herein. Such modules may include hardware circuitry, and/or a processor and/or memory circuits, software program modules and objects, and/or firmware, and combinations thereof, as desired by the architect of the apparatus10and system600, and as appropriate for particular implementations of various embodiments. For example, such modules may be included in a system operations simulation package, such as a software electrical signal simulation package, a power usage and distribution simulation package, a thermo-mechanical stress simulation package, a power/heat dissipation simulation package, and/or a combination of software and hardware used to simulate the operation of various potential embodiments.

It should also be understood that the apparatus and systems of various embodiments can be used in applications other than for coupling and heat transfer between dice and heat sinks, and thus, these embodiments are not to be so limited. The illustrations of apparatus10and system600are intended to provide a general understanding of the elements and structure of various embodiments, and they are not intended to serve as a complete description of all the features of compositions, apparatus, and systems that might make use of the elements and structures described herein.

Applications that may include the novel apparatus and systems of various embodiments include electronic circuitry used in high-speed computers, communication and signal processing circuitry, data transceivers, modems, processor modules, embedded processors, and application-specific modules, including multilayer, multi-chip modules. Such apparatus and systems may further be included as sub-components within a variety of electronic systems, such as televisions, cellular telephones, personal computers, workstations, radios, video players, vehicles, and others.