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Publication numberUS20020023733 A1
Publication typeApplication
Application numberUS 09/981,952
Publication dateFeb 28, 2002
Filing dateOct 18, 2001
Priority dateDec 13, 1999
Publication number09981952, 981952, US 2002/0023733 A1, US 2002/023733 A1, US 20020023733 A1, US 20020023733A1, US 2002023733 A1, US 2002023733A1, US-A1-20020023733, US-A1-2002023733, US2002/0023733A1, US2002/023733A1, US20020023733 A1, US20020023733A1, US2002023733 A1, US2002023733A1
InventorsDavid Hall, Joe Fox
Original AssigneeHall David R., Fox Joe R.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
High-pressure high-temperature polycrystalline diamond heat spreader
US 20020023733 A1
Abstract
This invention presents a polycrystalline diamond heat spreader useful in electronic devices for transmitting thermal energy from a high-energy thermal source, such as an IC die, into a means for dissipating thermal energy, such as a heat sink. The heat spreader comprises a bondable material that forms in situ at high pressure and high temperature a low-impedance contact surface layer on at least one its major surfaces. The contact surface layer provides a means for chemically or metallurgically bonding the heat spreader to the IC die and or to the heat sink.
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Claims(18)
What is claimed:
1. A high-pressure high-temperature polycrystalline diamond heat spreader useful in electronic devices, comprising:
a. Discrete diamond crystals ranging in sizes from between 10μ and 3000μ intergrown into a unified matrix and bonded to a substrate by means of a high-pressure high-temperature sintering process;
b. The unified matrix having a major surface opposite the substrate;
c. The unified matrix further comprising at least one bondable material selected from the periodic table of elements consisting of Fe, Co, Ni, Pd, Pt, Cr, Mo, W, Nb, Ta, Hf, Zr, Ti, V, Al, Si, Ga, Au, Cd, Ag, An, Mg, Sn, and Ge, and compounds, carbides, and alloys thereof; and
d. The bondable material forming in situ, during the sintering process, a low-impedance, bondable contact-surface layer on at least a portion of the major surface opposite the substrate, said bondable surface being suitable for bonding said matrix to at least a portion of a high-energy thermal source.
2. The heat spreader of claim 1, wherein the bondable material does not exceed the weight of the diamond matrix.
3. The heat spreader of claim 1, wherein the bondable material does not exceed 20 weight-percent of the diamond matrix.
4. The heat spreader of claim 1, wherein the bondable material is in the form of a foil positioned adjacent the diamond crystals prior to being subjected to the high-pressure high-temperature sintering process.
5. The heat spreader of claim 1, wherein the bondable material is in the form of a powder positioned adjacent the diamond crystals prior to being subjected to the high-pressure high-temperature sintering process.
6. The heat spreader of claim 15, wherein the bondable material is intermixed with the discrete diamond crystals prior to being intergrown by the high-pressure high-temperature sintering process.
7. The heat spreader of claim 1, wherein the diamond crystals are coated with the bondable material prior to being subjected to the high-pressure high-temperature sintering process.
8. The heat spreader of claim 1, wherein the diamond crystals are sputter coated with the bondable material prior to being subject to the high-pressure high-temperature sintering process.
9. The heat spreader of claim 1, wherein the diamond crystals are coated with the bondable material using an ion implantation process prior to the sintering process.
10. The heat spreader of claim 1, wherein the diamond crystals are coated with the bondable material using a milling process.
11. The heat spreader of claim 1, wherein the substrate is adapted for bonding to a heat sink.
12. The heat spreader of claim 1, wherein the substrate is adapted for bonding to a thermal source.
13. The heat spreader of claim 1, wherein at least a portion of at least one major contact surface has low surface roughness.
14. The heat spreader of claim 1, wherein at least a portion of at least one major contact surface has a non-planar topography.
15. The heat spreader of claim 1, wherein at least a portion of the bondable surface has a non-planar topography.
16. The heat spreader of claim 1, wherein the bondable surface layer has a cross section of 1.5 mm, but preferably less than 0.25 mm, and more preferably less than 0.025 mm.
17. The heat spreader of claim 1, wherein at least a portion of one of the major contact surfaces are made to have high electrical resistance.
18. The heat spreader of claim 1, wherein the diamond matrix has a cross section greater than 1 mm.
Description
RELATED APPLICATIONS

[0001] Continuation in Part of U.S. application Ser. No. 09/460,105

Background of the Invention

[0002] This invention relates to a high-pressure high-temperature polycrystalline diamond material having high thermal conductivity useful in electronic devices for spreading the thermal energy produced by a high-density thermal source, such as an IC die, into a convective means for dissipating heat, such as a heat sink. More particularly, this invention relates to a polycrystalline diamond heat spreader that has a low-impedance layer of bondable material on at least one of its major surfaces that is economically formed in situ during the high pressure and high temperature process. The bondable layer on the heat spreader provides a means for intimately coupling with the IC die and or the heat sink.

[0003] The continued development of high-speed electronic devices, such as IC dies, produces increasing heat densities in such devices that are destructive to the device, itself. Currently these densities exceed 200,000 w/m2, or roughly the equivalent of the heat density on the sun's surface. Thermal management, or the dissipation of the thermal energy in such devices, has become a major technological hurdle for manufacturers; in fact, the efficient dissipation of thermal energy is more and more becoming a major impediment to the further development of such devices.

[0004] The non-abrasive and thermal properties of a high-pressure high-temperature polycrystalline diamond make it an ideal material for use in a thermal management system for dissipating thermal energy.

[0005] First of all, high-pressure high-temperature polycrystalline diamond is the most economical form of man-made diamond, costing less than {fraction (1/20)}th the cost of any other form of diamond material. Second, it is a mature product whose production has been known in the art for nearly 50 years. It is produced from natural or synthetic discrete diamond crystals that may vary in size and are typically mounted onto metal carbide subtrate. A known catalyst material of up to approximately 30% by volume is provided by either mixing it with the diamond or by infiltration from the metal binder used in the carbide substrate. The catalyst may also be provided by a combination of mixing and infiltration. This assembly is sealed inside a refractory metal can and loaded inside a reaction vessel well known in the art. The reaction vessel is inserted into a high-pressure high-temperature press apparatus also known in the art and taken to pressure and temperature regions where diamond is thermodynamically stable. Under these conditions the catalyst melts and infiltrates, or sweeps through, the diamond mass, resulting in diamond-to-diamond bonding, or intergrowth. The result is a matrix of polycrystalline diamond material that possesses the combined properties of its catalyst material and its natural or synthetic diamond constituents: strong, rigid, high in thermal conductivity, low in thermal capacity, black in color, and it has a coefficient of thermal expansion compatible with that of silicon.

[0006] Next, high-pressure high-temperature polycrystalline diamond may be manufactured into a variety of configurations by either performing the substrate or by using standard machine shop art. For example, by varying the interfacial surface of the metal carbide substrate onto which the discrete diamond crystals are mounted, the shape and surface topography of the diamond matrix may take on planar and non-planar shapes. These shapes may be further modified to achieve multiple configurations and surfaces having low surface roughness, which adds to the versatility of this form of polycrystalline diamond. Furthermore, polycrystalline diamond may be made electrically resistive by either chemically or mechanically removing its residual catalytic content.

[0007] The objective of a thermal management system is to take the heat away from the thermal source as quickly as possible and deliver it to a convective means for dissipation into the atmosphere. An obstacle common in any thermal management system is the thermal resistance of the materials being used and the contact surface, or junction, thermal resistance arising where such materials are joined. High-pressure high-temperature polycrystalline diamond has the lowest thermal resistance, or highest thermal conductivity, of any material, except in some cases diamond itself. However, in the chain of materials used to transmit heat from the thermal source and ultimately into the atmosphere, even where polycrystalline diamond is used, it has been found that thermal resistance at the junctions may be higher than the thermal resistance of all the other elements in the thermal chain. Thus contact surface resistance must be reduced in order to take full advantage diamond's high thermal conductivity in a thermal management system.

[0008] The reduction of contact surface resistance may be achieved by intimately coupling the polycrystalline diamond heat spreader to the thermal source and or to the heat sink. However, in the past, intimately coupling with diamond has been an expensive and difficult obstacle since standard bonding materials are reluctant to wet diamond due to its chemical inertness. This obstacle is overcome by this invention by providing a polycrystalline diamond material that has a bondable contact surface of low thermal impedance, economically formed in situ at high pressure and high temperature on at least one surface of the polycrystalline diamond heat spreader.

SUMMARY OF THE INVENTION

[0009] This invention presents a polycrystalline diamond heat spreader for use in electronic devices having low thermal impedance and bondable contact surfaces that are formed in situ during the high-pressure high-temperature process. Polycrystalline diamond of this invention is produced by the high-pressure high-temperature sintering method from discrete natural or synthetic diamond crystals ranging in sizes from between 10μ to 3000μ that are intergrown into a unified matrix. Because polycrystalline diamond is produced from discrete crystals that are mounted on a substrate, by varying the shape of the substrate's interfacial surface, the polycrystalline diamond matrix may be pre-configured having a variety of planar and non-planar surface topographies. Furthermore, the polycrystalline diamond of this invention is black in color, strong and rigid, and may be made having high electrical resistance, low surface roughness, high thermal conductivity, low thermal capacity, and a coefficient of thermal expansion compatible with silicon. Therefore, it is well suited to be bonded adjacent to the silicon IC as well as to the heat sink. Moreover, the inter-crystalline intergrowth of polycrystalline diamond provides an uninterrupted, low-impedance thermal path for transmitting heat between the heat source and the sink.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a perspective diagram of a heat spreader of the present invention having a bondable layer on at least one major surface.

[0011]FIG. 2 is a sectioned representation of a non-planar heat spreader having a convex profile.

[0012]FIG. 3 is a sectioned representation of a non-planar heat spreader having an interrupted surface profile.

[0013]FIG. 4 is a diagram of polycrystalline diamond intergrown by the high-pressure high-temperature sintering method depicting thermal paths through the matrix.

[0014]FIG. 5 is a cross-section diagram of the polycrystalline diamond heat spreader positioned between an electronic heat source and the means for dissipating thermal energy.

DETAILED DESCRIPTION OF THE INVENTION

[0015] This invention presents a high-pressure high-temperature polycrystalline diamond heat spreader for use in electronic devices having high thermal conductivity and comprising a bondable contact surface opposite the substrate having low thermal impedance that is economically formed in situ during the high-pressure high-temperature sintering process. The bondable contact surface permits bonding of the heat spreader to a thermal source or to a heat sink. The contact surface may also be made to be planar or non-planar, to have low surface roughness, and to have high electrical resistance.

[0016] Thermal energy is transmitted in diamond faster than in any other material at ambient temperatures. Heat is transmitted through a metal by electron transport and through a crystal, such as diamond, by phonon, or acoustic, transport. In either case there is some thermal resistance. Also, where materials are joined in a thermal chain, intimate coupling of materials is necessary in order to reduce junction thermal resistance and maximize thermal energy transmission. Studies have shown that thermal resistance is highest at the contact surfaces, or junctions, where materials are joined together, making contact surface resistance as significant a consideration in the thermal chain as the actual thermal conductivity of the materials themselves. This phenomenon is equally applicable among the discrete diamond crystals within the matrix of polycrystalline diamond.

[0017] Since polycrystalline diamond is produced from discrete natural or synthetic diamond crystals, each crystal boundary is potentially a thermal barrier. However, when the diamond crystals are intergrown at high pressure and high temperature their boundaries are intimately merged creating an uninterrupted thermal path through the material. Therefore, the more thorough the diamond-to-diamond bonding, or intergrowth, the more efficiently polycrystalline diamond is capable of conducting thermal energy.

[0018] Another aspect of high thermal conductivity that the applicants have discovered is that the lower the concentration of nitrogen in the diamond and the larger the crystal size, the more conductive the thoroughly intergrown polycrystalline diamond seems to be. The applicants believe that this may be due to fewer defects in the crystal lattice that affect phonon transport and to the actual reduction of crystalline surface area, and thus the boundaries, within the polycrystalline diamond matrix. Natural or synthetic diamond is suitable for this invention, but synthetic diamond having controlled growth characteristics and low nitrogen content is preferred. The applicants have found that by mixing large crystals, say up to 3000μ, having low nitrogen content into a matrix of smaller crystals, say greater than 10μ, higher thermal conductivity has been achieved. Another benefit from using larger crystals is that the matrix may be made thicker, which also contributes to the spreading capacity of the heat spreader. By using large diamond crystals in the matrix, a heat spreader having at least a cross section of 19 mm×at least 4 mm may be achieved. This is especially important as heat densities continue to increase.

[0019] Like other forms of diamond, high-pressure high-temperature polycrystalline diamond is chemically inert and, therefore, difficult to bond to other materials. This invention overcomes this obstacle by providing an economical bondable surface integral to the matrix that is formed in situ during the high-pressure high-temperature sintering process.

[0020] The key ingredient is the formation of a layer of bondable material on the surface of the heat spreader. The formation of that surface is the distinguishing feature of the invention. Contrary to prior art products where the aim is to consume all of the catalyst in the process, the present invention seeks to pool the excess catalyst, or other bondable material on the surface opposite the substrate, and to use that layer as a bondable surface.

[0021] Since diamond is chemically inert, it resists chemical adhesion to another material, making it difficult to obtain the intimate contact required for efficient thermal transfer. Polycrystalline diamond (PCD) is a product that exhibits diamond crystals bonded together using a metal catalyst, and the finished product contains some metal at interstitial sites on the surface, but it is desirable that the presence of metal in the product be kept to a minimum. Therefore, normally the interstitial material is insufficient for a competent bond. The object of this invention, then, is to produce a PCD product that has an intimate layer of bondable material on at least one major surface. Such a bondable surface may be composed of the catalyst material, itself, or the material may be inert to the process.

[0022] A product according to the present invention may be produced by obtaining a known quantity of a mixture of diamond fine powders, on the order of from about 10μ to about 3000μ in size, a known catalyst, such as cobalt, a cemented metal carbide substrate, such as tungsten carbide, and a bondable material, such as copper. Other materials that may be considered as the bondable are: Fe, Co, Ni, Pd, Pt, Cr, Mo, W, Nb, Ta, Hf, Zr, Ti, V, Al, Si, Ga, In, Au, Cd, Ag, An, Mg, Sn, Ge or compounds, carbides, or alloys thereof. The cobalt catalyst may be supplied by infiltration from the tungsten carbide substrate, although a slight amount of cobalt may be mixed into the diamond power to complement the infiltrating catalyst. If the catalyst is supplied by intermixing with the diamond powder, it usually does not exceed 50 weight-percent of the diamond powder and in most cases is less than 30 weight-percent, The copper, or other bonding material, may be in foil or powder form in an amount not to exceed the weight of the diamond matrix. The bondable material may be less than 20 weight-percent of the diamond mixture, as long as it is sufficient to produce the bondable surface. The specific weight percent of bonding material used in the process will depend upon the specific application: the grain size of the diamond powders, the thickness of the diamond matrix desired, the type of bonding material and type of surface to which it will be bonded, and the processing conditions of time, temperature, pressure are determinative of the amount material that must be used. When a foil is used, it should be between about 0.002″ to 0.050″ inches thick. The foil is laid in the bottom of a refractory metal container and the diamond mixture is then placed on top of the foil. When a powder is used, it, too, is spread in the bottom of the container. The powder may also be intermixed with the diamond mixture. A tungsten carbide disk, or substrate, is then placed on top of the diamond mixture. These components are then compacted together inside the container and hermetically sealed from contamination. The metal container is then placed inside a reaction vessel known in the art, and the assembly is inserted into an ultra high-pressure high-temperature press apparatus. The press is activated and the diamond mixture, substrate, and bondable material are taken to conditions where diamond is thermodynamically stable. The specific parameters of the process are apparatus dependent. That is to say, that there are several styles of HPHT presses in use today and each style is distinguishable by its design, method of operation, and its mechanical and hydraulic systems. Generally, however, the process will take approximately 2 to 45 minutes. In every style of press, the reaction vessel appropriate for the style of press being used, which includes a resistance heating mechanism, is exposed to conditions of pressure and temperature of approximately 50 to 70 Kilobars and between about 1200°-1500° C., respectively. Under such conditions, the catalyst in the substrate melts and a portion of it infiltrates the diamond mixture causing the diamond crystals to chemically bond to one another in a process known as intergrowth. The copper foil also melts and back infiltrates a thin layer of the mixture providing a intimate bond with the diamond matrix.

[0023] Although the copper is not a catalyst for diamond intergrowth, it does not completely block the infiltrating cobalt and does not completely prohibit intergrowth. A powder layer acts much the same way as the copper foil. The advantage of the copper foil is found in its ease of handling. When the copper powder is intermixed with the diamond mixture, the melted copper is swept from the diamond matrix by the infiltrating cobalt and allowed pool on the opposing surface. Some of the copper is allowed to remain in the matrix in order to strengthen the bond between the diamond and the copper layer. In these three examples, the objective is to provide a layer of bondable material on the major surface. The reaction vessel is then cooled and returned to atmospheric conditions and removed from the press.

[0024] Depending upon the type of bonding material used, the diamonds at the interface between the bonding material are not unaffected by the presence of the non-catalytic material may exhibit a less competent pattern of intergrowth. Notwithstanding the presence of the non-catalytic material, the copper layer is intimately bonded to the diamond and creates a surface to which a thermal source or heat sink may be attached.

[0025] An examination of the finished product reveals that the diamond has intimately bonded to the substrate and the copper is bonded to the diamond, forming a surface to which the thermal components may be bonded. It is desirable that the layer of bondable material be approximately between 0.002″ to 0.020″ thick. The examination also reveals that the catalyst metal has collected at interstitial sites throughout the matrix. These pools of catalyst are less thermally conductive than the path formed by the intergrown diamond, and, therefore, it is preferred to control the amount of residual catalyst in the final product. Although, copper is used in this example, other bondable materials as described herein may be beneficially used.

[0026] The infiltrating cobalt may also form a bondable layer. This may be achieved by altering the grain size of the diamond powder, the amount of cobalt in the mixture, and the processing parameters. Generally, the finer the diamond powder the more difficult it is to infiltrate and the larger volume of catalyst required. However, finer crystal sizes produce a more thermally conductive part since the diamond matrix may be made denser. Therefore, a balance must be achieved between particle size and volume of catalyst used in the process. Also by accelerating the process so that the melting temperature of the catalyst is reached in a shorter period of time encourages swifter infiltration and promotes pooling of the catalyst on the opposing surface.

[0027] The heat spreader of the present invention may be made to have high electrical resistance. Diamond is not electrically conductive; it is the residual metal catalyst in the PCD that produces electrical conductivity. Therefore, in order to make the heat spreader electrically resistive, it is necessary to remove the residual metal from the diamond matrix. This is usually accomplished by acid leaching in boiling aqua regia. The surface not infiltrated with bondable material may be made more resistive by masking off the bondable layer to protect it from acid, or by partial immersion of the unbound layer into the acid. As the metal is dissolved in the acid, the remaining diamond matrix becomes electrically resistive. It is not necessary to remove all the metal as long as there is a contiguous layer free of metal in the diamond matrix. Even with the catalyst metal substantially removed, the diamond matrix remains intact because the diamond crystals are bonded, intergrown, together.

[0028] Another, method of producing a bondable layer on the heat spreader matrix of the present invention is by intermixing with the diamond crystals a bondable material selected from the periodic table of elements consisting of Fe, Co, Ni, Pd, Pt, Cr, Mo, W, Nb, Ta, Hf, Zr, Ti, V, Al, Si, Ga, In, Au, Cd, Ag, An, Mg, Sn, Ge or compounds, carbides, or alloys thereof prior to high-pressure high-temperature processing. The intermixing may be accomplished either by mixing, milling, or coating the discrete crystals by such standard art processes as sputter coating, ion implantation, or physical or chemical vapor deposition. During the high-pressure high-temperature sintering process, the bondable material is also swept through the matrix by the infiltrating catalyst and accumulates, or pools, in a layer near or on the opposite surface of the heat spreader. The thickness of this bondable layer need only be sufficient to form an acceptable bond and may vary depending on the volume of bondable material in the matrix and is desirably about 1 mm, preferably 0.25 mm, or more preferably 0.025 mm. After processing, the bondable material may be machined to a desired configuration and thickness, and to remove surface asperities. A thin bondable layer is preferred over a thick bondable layer because thermal impedance is proportional to the width of the junction between the heat spreader and the IC die or the heat sink.

[0029] Another method of producing the bondable layer on the heat spreader of this invention is by positioning the bondable material, either as a powder or as a solid foil or sheet, adjacent to the diamond crystals prior to high-pressure high-temperature processing. Then as the temperature increases, the bondable material melts and infiltrates the diamond mass, combining with the sweeping catalyst material and becoming integral to the heat spreader.

[0030] Additionally, even the metal carbide substrate on which the diamond crystals are mounted may be used in some cases as the bondable layer. In the high-pressure high-temperature sintering process the metal carbide substrate also becomes intimately bonded to the diamond mass. After processing the metal carbide substrate may be ground or lapped thin—also producing a bondable surface on one side of the heat spreader.

[0031] In applications where the heat spreader is mounted adjacent the IC die, it may be desirable to make the heat spreader electrically resistive. Diamond is electrically non-conductive. But, the residual catalyst material in the matrix of polycrystalline diamond causes it to be electrically conductive. Electrical resistance may be achieved, however, by either chemically or mechanically removing at least a portion of the residual catalyst material from at least a portion of the surface adjacent the heat source, creating an insulating layer of diamond. Using this method a substantial portion of the catalyst also may be removed from the entire matrix if so required. The applicants have found that where there is thorough diamond intergrowth the removal of the residual catalyst material from the matrix does not significantly compromise the structural integrity of the heat spreader.

[0032]FIG. 1 is a perspective illustration of a heat spreader of the present invention. It depicts a matrix (15) of high-pressure high-temperature polycrystalline diamond that is naturally black in color. The black color is an added intrinsic benefit for the heat spreader application; the back color enhances the thermal absorption. The heat spreader has bondable material layers (11 and 1) on each of its major contact surfaces that permit intimate attachment of the heat spreader to a thermal source as well as to a heat sink. According to the present invention, these bondable contact surfaces are economically produced in situ during the high-pressure high-temperature process and are integral to the polycrystalline diamond matrix. Each contact surface may be composed of different materials. For example, the junction layer (11) may be produced by lapping or grinding the metal carbide substrate to a thin layer, while the junction layer (1) may be produced by providing the bondable material in the form of a powder of sheet positioned adjacent the diamond matrix. Another method may be to sandwich the diamond crystals between two metal carbide substrates, and after processing, by then lapping or grinding both sides of the heat spreader to produce the bondable surface. These contact surfaces may be further modified by standard machine shop art of lapping and grinding in order to remove asperities and achieve low surface roughness and high flatness. Although the configuration shown is a right cylinder, different prismatic configurations not shown are also producible and intended within the scope of the present invention.

[0033]FIG. 2 is a section illustration of a heat spreader of the present invention depicting the metal carbide substrate (17) intimately bonded to the polycrystalline diamond matrix (23). Bondable material is shown in high concentration layers along the major contact surfaces (21 and 25) of the heat spreader. The metal carbide substrate (17) may be reduced to a thin contact surface (19) by employing standard machine shop art, or it may be removed altogether exposing the junction surface (21) for bonding either to the thermal source or the heat sink. As described earlier in this application, the bondable material depicted in high concentrations along the junction surfaces (21 and 25) may be provided by intermixing, by coating the diamond crystals, or by positioning a powder or sheet of the bondable material adjacent the diamond prior to high-pressure high-temperature processing. The major contact surfaces at 19 and 21 are depicted having a non-planar, convex profile. Though not shown, other non-planar profiles are intended within the scope of this invention, such as concave, conical, truncated conical, and hemispherical.

[0034]FIG. 3 is another section illustration of the present invention depicting an application where the metal carbide substrate (27) is attached to the diamond matrix (31) at an interrupted interfacial surface (29) having a layer of bondable material (30) along the interface. This sample is also provided with a bondable layer (33) on the opposite major contact surface of the heat spreader. The interrupted profile of the interface (29) may be the result of grooves in either a parallel or radial pattern along the surface of the diamond matrix. Or it may be the result of discrete protrusions, such as nodes, projecting above the spreader's major contact surface. Additionally, these configurations may be combined with the non-planar profile of FIG. 2 to present a complex non-planar profile that greatly increases the versatility of this invention. The added surface created by the non-planar configurations enhances the means of attachment and the spreading capacity of the polycrystalline diamond.

[0035]FIG. 4 is a magnified section illustration of the high-pressure high-temperature polycrystalline diamond matrix of the present invention. High-pressure high-temperature polycrystalline diamond is composed of discrete diamond crystals that are chemically intergrown at high pressure and high temperature in the presence of a metal catalyst. In this illustration, intergrown diamond crystals (37) are vaguely bordered at interstitial sites (41) by residual metal catalyst. The intergrown structure of the matrix creates an uninterrupted thermal path (39) for transmitting heat from the thermal source to the heat sink. Since diamond has low thermal capacity, heat accumulation in the matrix is slight and quickly transmitted into the heat sink. The accumulation of bondable material (35) along the major contact surfaces of the heat spreader, according to the present invention, provides a low-impedance junction to both the heat source and the heat sink. The residual metal catalyst, which is electrically conductive, may be removed from the contact surfaces of the matrix, or from the matrix itself, by chemical or mechanical means in order to produce an insulating medium. The removal of the residual metal catalyst does not significantly affect the structural integrity of the matrix. The matrix of the present invention is strong, rigid, and thermally compatible with both the silicon of the IC die and the ceramic or metal composition of the heat sink, reducing the likelihood that the thermal cycling of the IC will result failure of the heat spreader or the die.

[0036]FIG. 5 is a section illustration of a heat spreader of the present invention incorporated into a thermal management system. The heat spreader (53) is mounted onto a circuit board (49) positioned between the IC die (47) and the heat sink (43). The heat spreader of the present invention is intimately bonded to the heat sink and the IC die along its major contact surfaces using the bondable material layers (45) of the present invention. Low thermal impedance is achieved at the junctions by maintaining the bonding layer sufficiently thin so as to reduce contact surface thermal resistance. As the computer IC is cycled hot spots (51) develop on the surface of the die. The thermal energy radiating from the die is quickly spread across the surface of the die and transmitted into the heat spreader. Since the heat spreader has low thermal capacity, heat does not accumulate in the spreader itself, but is quickly conducted into the high thermal capacity heat sink and convectively transmitted into the atmosphere or other high capacity medium. Adaptations of this design are obvious to those skilled in the art and are included within the scope of this invention although not depicted. For example, a free flowing or jetted fluid or cryogenic thermal management system may be substituted for the heat sink shown. Also, heat pipes or cooling fluid conduits (55 and 57) may be added to the heat spreader or the heat sink in order to increase the thermal differential, adding to the efficiency of the system. Or, the heat spreader may be positioned on both sides of the IC die to further enhance dissipation of thermal energy.

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Classifications
U.S. Classification165/80.3, 257/E23.111, 257/E23.098, 165/185
International ClassificationH01L23/473, F28F13/00, H01L23/373
Cooperative ClassificationH01L2924/0002, F28F2255/18, F28F13/00, H01L23/473, H01L2924/3011, H01L23/3732, F28F2013/005
European ClassificationH01L23/473, H01L23/373D, F28F13/00
Legal Events
DateCodeEventDescription
Jul 15, 2015ASAssignment
Owner name: NOVATEK IP, LLC, UTAH
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:HALL, DAVID R.;REEL/FRAME:036109/0109
Effective date: 20150715