Methods of fabricating a composite carbon nanotube thermal interface device
Embodiments of a composite carbon nanotube structure comprising a number of carbon nanotubes disposed in a matrix comprised of a metal or a metal oxide. The composite carbon nanotube structures may be used as a thermal interface device in a packaged integrated circuit device.
This application is related to application Ser. No. ______, entitled “Method of Fabricating a Composite Carbon Nanotube Thermal Interface Device”, filed on even date herewith.
FIELD OF THE INVENTIONThe invention relates generally to the packaging of an integrated circuit die and, more particularly, to methods for manufacturing a composite carbon nanotube structure that may be used as a thermal interface device.
BACKGROUND OF THE INVENTIONIllustrated in
During operation of the IC device 100, heat generated by the die 110 can damage the die if this heat is not transferred away from the die or otherwise dissipated. To remove heat from the die 110, the die is ultimately coupled with a heat sink 170 via a number of thermally conductive components, including a first thermal interface 140, a heat spreader 150, and a second thermal interface 160. The first thermal interface 140 is coupled with an upper surface of the die 110, and this thermal interface conducts heat from the die and to the heat spreader 150. Heat spreader 150 conducts heat laterally within itself to “spread” the heat laterally outwards from the die 110, and the heat spreader 150 also conducts the heat to the second thermal interface 160. The second thermal interface 160 conducts the heat to heat sink 170, which transfers the heat to the ambient environment. Heat sink 170 may include a plurality of fins 172, or other similar features providing increased surface area, to facilitate convection of heat to the surrounding air. The IC device 100 may also include a seal element 180 to seal the die 110 from the operating environment.
The efficient removal of heat from the die 110 depends on the performance of the first and second thermal interfaces 140, 160, as well as the heat spreader 150. As the power dissipation of processing devices increases with each design generation, the thermal performance of these devices becomes even more critical. To efficiently conduct heat away from the die 110 and toward the heat sink 170, the first and second thermal interfaces 140, 160 should efficiently conduct heat in a transverse direction (see arrow 105).
At the first thermal interface, it is known to use a layer of thermal grease disposed between the die 110 and the heat spreader 150. Thermal greases are, however, unsuitable for high power—and, hence, high heat—applications, as these materials lack sufficient thermal conductivity to efficiently remove a substantial heat load. It is also known to use a layer of a low melting point metal alloy (e.g., a solder) as the first thermal interface 140. However, these low melting point alloys are difficult to apply in a thin, uniform layer on the die 110, and these materials may also exhibit low reliability. Examples of materials used at the second thermal interface include thermally conductive epoxies and other thermally conductive polymer materials.
Illustrated in
An example of a typical carbon nanotube 800 is shown in
Illustrated in
Referring now to block 210 in
The substrate 310 may comprise any suitable material upon which a composite carbon nanotube structure can be constructed, such as, for example, a silicon or a ceramic material. As noted above, in one embodiment, the composite carbon nanotube structure to be fabricated on the substrate 310 will ultimately be separated from the substrate. However, in other embodiments, the composite carbon nanotube structure is formed directly on a component, such as an integrated circuit die, a semiconductor wafer, a heat spreader, or a heat sink.
As set forth at block 220, a metal layer is deposited on the sacrificial layer. This is illustrated in
Referring to block 230, the metal layer is anodized to form a porous metal oxide layer. This is shown in
In
With reference still to
Returning now to
The selective deposition of the catalyst 350 may be achieved using either an electroplating process or an electroless plating process. In an electroplating process, no plating occurs on the exposed metal oxide surfaces within the pores 342 because sufficient electric current will not pass through the dielectric metal oxide. In an electroless plating process, the metal oxide material is not a catalytic material for the plating process, and the catalyst 350 does not build up on exposed metal oxide surfaces. For an electroplating process, the sacrificial layer 320 is comprised of an electrically conductive material and, for an electroless plating process, the sacrificial layer 320 is comprised of a suitable catalytic material (for the catalyst 350).
Referring now to block 260, carbon nanotubes are formed in the pores of the metal oxide layer. This is illustrated in
In one embodiment, as shown in
In the embodiments described above, carbon nanotubes 360 are grown within the pores 342 of a porous metal oxide layer 340. Metal oxides, such as Aluminum Oxide and oxides of other metals, are desirable because they can provide a regular and controlled pore structure. However, it should be understood that the disclosed embodiments are not limited to growth of carbon nanotubes in metal oxide materials. In further embodiments, carbon nanotubes may be grown in other porous substances (e.g., a porous polymer material).
As set forth at block 270, the metal oxide matrix with carbon nanotubes is separated from the substrate to form a free-standing composite carbon nanotube structure. This is shown in
In a further embodiment, as set forth at block 280 in
Illustrated in
Referring now to block 510 in
Note that, in
For electroplating, the plating solution 680 comprises metal ions (of the metal to be plated on substrate 610) and an electrolyte, such as sulfuric acid (H2SO4) or a base such as KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide). The metal to be plated may comprise, by way of example, Tin (Sn), Indium (In), Copper (Cu), Nickel (Ni), Cobalt (Co), Iron (Fe), Cadmium (Cd), Chromium (Cr), Ruthenium (Ru), Rhodium (Rh), Rhenium (Re), Antimony (Sb), Bismuth (Bi), Platinum (Pt), Gold (Au), Silver (Ag), Zinc (Zn), Palladium (Pd), Manganese (Mn), or alloys thereof. In another embodiment, the plating solution 680 further comprises a complexing agent to complex ions in the plating solution in order to change their solubility and oxidation/reduction potential. For example, for Cobalt metal ions, citric acid can be used as the complexing agent to make the Cobalt ions soluble in a basic (high pH) solution. In a further embodiment, the plating solution 680 also includes one or more additives to regulate the material properties of the plated metal (e.g., polyethylene glycol or di-sulfides to regulate grain size).
For electroless plating, the plating solution comprises metal ions (again, of the metal to be plated on substrate 610), one or more complexing agents, and one or more reducing agents. As set forth previously, the metal to be plated may comprise Tin, Indium, Copper, Nickel, Cobalt, Iron, Cadmium, Chromium, Ruthenium, Rhodium, Rhenium, Antimony, Bismuth, Platinum, Gold, Silver, Zinc, Palladium, Manganese, or alloys thereof. Also as noted above, a complexing agent comprises a substance to complex ions in the plating solution in order to change their solubility and oxidation/reduction potential (see example above). The reducing agent (or agents) comprises any substance that will supply electrons to the plating bath 680 during the plating process, including formaldehyde, hypophosphite, dimethyl amine borane, or hydrazine hydrate. In another embodiment, the plating solution 680 also includes a substance to adjust the pH of the plating solution. In a further embodiment, the plating solution also includes one or more additives to regulate the properties of the deposited metal, as described above.
Referring next to block 520, a layer of metal is plated on the substrate, wherein this metal layer includes carbon nanotubes from the plating bath. This is illustrated in
The metal layer 620 may be deposited on the substrate using an electroplating process or an electroless plating process. For electroplating, in one embodiment, a seed layer may first be deposited on the substrate 610 prior to deposition of the metal layer 620. This is shown in
In one alternative embodiment, as set forth at block 530 in
In another embodiment, where the substrate 610 comprises a sacrificial substrate, the metal matrix layer 620 with carbon nanotubes 690 is separated from the substrate, as denoted at block 540. This is shown in
In a further embodiment, the free-standing composite carbon nanotube structure 600 is attached to another component (e.g., a die, a heat spreader, a heat sink, etc.). This is illustrated in
An IC device having a thermal interface comprising a free-standing composite CNT structure—e.g., the packaged IC device 301 of
Referring to
Coupled with bus 705 is a processing device (or devices) 710. The processing device 710 may comprise any suitable processing device or system, including a microprocessor, a network processor, an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA), or similar device. In one embodiment, the processing device 710 comprises an IC device including a free-standing composite CNT structure (e.g., packaged IC device 301 having thermal interface devices 300a, 300b, or packaged IC device 601 having thermal interface devices 600a, 600b). However, it should be understood that the disclosed thermal interface devices comprising a composite CNT structure may find use in other types of IC devices (e.g., memory devices).
Computer system 700 also includes system memory 720 coupled with bus 705, the system memory 720 comprising, for example, any suitable type of random access memory (e.g., dynamic random access memory, or DRAM). During operation of computer system 700 an operating system 724, as well as other programs 728, may be resident in the system memory 720. Computer system 700 may further include a read-only memory (ROM) 730 coupled with the bus 705. During operation, the ROM 730 may store temporary instructions and variables for processing device 710, and ROM 730 may also have resident thereon a system BIOS (Basic Input/Output System). The computer system 700 may also include a storage device 740 coupled with the bus 705. The storage device 740 comprises any suitable non-volatile memory—such as, for example, a hard disk drive—and the operating system 724 and other programs 728 may be stored in the storage device 740. Further, a device 750 for accessing removable storage media (e.g., a floppy disk drive or CD ROM drive) may be coupled with bus 705.
The computer system 700 may include one or more input devices 760 coupled with the bus 705. Common input devices 760 include keyboards, pointing devices such as a mouse, and scanners or other data entry devices. One or more output devices 770 may also be coupled with the bus 705. Common output devices 770 include video monitors, printing devices, and audio output devices (e.g., a sound card and speakers). Computer system 700 further comprises a network interface 780 coupled with bus 705. The network interface 780 comprises any suitable hardware, software, or combination of hardware and software capable of coupling the computer system 700 with a network (or networks) 790.
It should be understood that the computer system 700 illustrated in
Embodiments of a methods 200, 500 for fabricating composite carbon nanotube structures 300, 600—as well as embodiments of a thermal interface device comprising such a composite CNT structure—having been herein described, those of ordinary skill in the art will appreciate the advantages of the disclosed embodiments. The disclosed composite CNT structures provides high thermal conductivity, high mechanical strength, and good chemical stability. Further, these composite CNT structures may be fabricated to a very thin and uniform thickness. Also, the disclosed composite CNT structures may be fabricated using well known, low cost methods (e.g., CVD, PECVD, electroplating, electroless plating, sputtering, etc.), and their fabrication and use as thermal interface devices is compatible with existing assembly and process conditions.
The foregoing detailed description and accompanying drawings are only illustrative and not restrictive. They have been provided primarily for a clear and comprehensive understanding of the disclosed embodiments and no unnecessary limitations are to be understood therefrom. Numerous additions, deletions, and modifications to the embodiments described herein, as well as alternative arrangements, may be devised by those skilled in the art without departing from the spirit of the disclosed embodiments and the scope of the appended claims.
Claims
1-38. (canceled)
39. A method comprising:
- disposing a substrate in a plating bath including a plating solution, the plating solution including ions of a metal and carbon nanotubes; and
- forming a layer of the metal on the substrate, the metal layer including a number of the carbon nanotubes.
40. The method of claim 39, wherein the metal comprises one of tin, indium, copper, nickel, cobalt, iron, cadmium, chromium, ruthenium, rhodium, rhenium, antimony, bismuth, platinum, gold, silver, zinc, palladium, and manganese.
41. The method of claim 39, wherein the carbon nanotubes comprise up to approximately 20 percent by weight of the plating solution.
42. The method of claim 39, wherein the metal layer is formed by electroplating.
43. The method of claim 42, wherein the plating solution further comprises a complexing agent.
44. The method of claim 42, wherein the plating solution further comprises an additive to regulate a property of the metal layer.
45. The method of claim 44, wherein the additive comprises polyethylene glycol or a di-sulfide.
46. The method of claim 42, further comprising depositing a seed layer on the substrate prior to forming the metal layer.
47. The method of claim 39, wherein the metal layer is formed by electroless plating.
48. The method of claim 47, wherein the plating solution further comprises a complexing agent and a reducing agent.
49. The method of claim 48, wherein the reducing agent comprises one of formaldehyde, hypophosphite, dimethyl amine borane, and hydrazine hydrate.
50. The method of claim 47, wherein the plating solution further comprises a substance to adjust a pH of the plating solution.
51. The method of claim 47, wherein the plating solution further comprises an additive to regulate a property of the metal layer.
52. The method of claim 51, wherein the additive comprises one of polyethylene glycol and a di-sulfide.
53. The method of claim 47, further comprising depositing a catalyst on the substrate prior to forming the metal layer.
54. The method of claim 47, further comprising heating the plating solution in the plating bath.
55. The method of claim 39, further comprising applying an electric field across the metal layer to align the carbon nanotubes in the metal layer.
56. The method of claim 55, wherein the carbon nanotubes are aligned substantially perpendicular to a surface of the substrate.
57. The method of claim 39, wherein the substrate comprises a semiconductor wafer, an integrated circuit die, a heat spreader, or a heat sink.
58. The method of claim 39, further comprising separating the metal layer including the carbon nanotubes from the substrate to form a free-standing composite carbon nanotube (CNT) structure.
59. The method of claim 58, further comprising attaching the composite CNT structure to a component.
60. The method of claim 59, wherein the component comprises a semiconductor wafer, an integrated circuit die, a heat spreader, or a heat sink.
61. The method of claim 59, wherein attaching the composite CNT structure to the component comprises:
- depositing a layer of a low melting point metal alloy on a surface of the composite CNT structure; and
- attaching the composite CNT structure to the component using the layer of low melting point metal alloy.
62. The method of claim 61, wherein the low melting point metal alloy comprises a solder.
63. The method of claim 58, wherein the composite CNT structure has a thickness in a range of approximately 2 μm to 20 μm.
64-76. (canceled)
Type: Application
Filed: Jan 9, 2009
Publication Date: Sep 10, 2009
Inventor: Valery M. Dubin (Portland, OR)
Application Number: 12/319,626
International Classification: B05D 3/06 (20060101); C25D 3/02 (20060101); C25D 3/30 (20060101); C25D 3/46 (20060101); C25D 3/38 (20060101); C25D 3/12 (20060101); C25D 3/26 (20060101); C25D 3/04 (20060101); C25D 3/50 (20060101); C25D 3/54 (20060101); C25D 3/48 (20060101); C25D 3/22 (20060101); C25D 3/10 (20060101); C25D 3/32 (20060101); B05D 1/18 (20060101); B29C 41/42 (20060101); B29C 45/14 (20060101);