| Decreasing thermal contact resistance at a material interface -> Monitor Keywords |
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  Decreasing thermal contact resistance at a material interfaceRelated Patent Categories: Metal Working, Method Of Mechanical Manufacture, Heat Exchanger Or Boiler MakingThe Patent Description & Claims data below is from USPTO Patent Application 20070169345. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a division of U.S. patent application Ser. No. 10/306,108 (Attorney Docket No. 042390.P13014) filed Nov. 26, 2002, entitled "DECREASING THERMAL CONTACT RESISTANCE AT A MATERIAL INTERFACE." FIELD OF THE INVENTION [0002] Embodiments of the invention relate generally to the field of thermal contact resistance and more specifically to creating chemical bonds between the mating parts of a heat sink. BACKGROUND INFORMATION [0003] Solid materials, such as copper or aluminum, generally conduct heat more efficiently than do gases such as air. The thermal conductivity of a material describes the materials ability to conduct heat. Pure copper has a thermal conductivity of 386 Watts/meter degree centigrade (W/m .degree. C.) at zero degrees centigrade. Air has a thermal conductivity of 0.024 W/m .degree. C. When two solid pieces of material are mated together by means of mechanical bonding, entrapped voids exist at the mating surface, which require heat to flow through a combination of smoothly contacting parts of the surface and across the entrapped voids. In the region of the voids, the heat transfer is affected by the thermal conductivity of the entrapped gas, or lack thereof, depending on the particular design of the mating surface. In the region of the contacting surfaces the heat transfer is governed more closely by the thermal conductivity of the solid materials. [0004] FIG. 1 illustrates, at 100, an existing heat source/sink assembly where three materials are joined together. With reference to FIG. 1, a heat source 102 is mated with an interface material 106. The interface material 106 is mated to a heat sink 104 by means of mechanical bonding. The mechanical bonding results in entrapped voids and a resulting gap as indicated by 150. A heat flow 110 is in the direction from the heat source 102 to the heat sink 104 along a temperature gradient where a temperature profile decreases in the direction of the arrow. The interface material 106 has a thickness 108. The thermal resistance of a material is inversely proportional to the thermal conductivity. A material with a high conduction coefficient, such as copper described above has a low thermal resistance. A gas, such as air described above has a high thermal resistance. At the interface of two materials joined together by mechanical bonding, thermal contact resistance exists. [0005] FIG. 2 is a plot 200 of thermal resistance 204 verses interface material thickness 202. A linear variation of thermal resistance 206 with material thickness 202 indicates a non-zero thermal resistance R.sub.C 208 when the material thickness is zero at 210 (contact resistance). Existing heat transfer assemblies, such as the one shown in FIG. 1, exhibit the contact resistance shown in FIG. 2 at 208 and 210. Contact resistance has the undesirable effect of reducing the amount of heat transferred from the heat source 102 to the heat sink 104 in FIG. 1. [0006] At a molecular level, the contacting surfaces are actually very far apart due to the mechanical bonding. FIG. 3 illustrates, at 150, an atomic level view of an existing heat source/surface material interface. A distribution of heat source surface molecules is shown at 304. Heat source surface molecules 304 are representative of the atomic scale existing on the surface 112 from FIG. 1. A distribution of interface surface molecules is shown at 302. The interface surface molecules 302 are representative of those molecules existing on the surface 114 in FIG. 1. [0007] Valence shells 310, of the heat source surface molecules 304, are shown as concentric circles with their respective atomic nuclei. Similarly, valence shells 308, of the interface surface molecules 302, are shown as concentric circles with their respective atomic nuclei. In between the heat source surface and the interface material surface are voids 312 defined by a gap 306. The gap 306 prevents the valence shells 308 from contacting the valence shells 310. The transfer of heat is impeded by the gap 308 and the voids 312 since the thermally excited heat source surface molecules 304 are not in molecular contact with the interface material-surface molecules 302. The thermal contact resistance results from the voids and resulting gap between the materials. [0008] Existing heat transfer assemblies rely on mechanical bonds at the mating surfaces of adjacent material. Referring again to FIG. 1, typically, the interface material 106 is softer than either the heat source 102 or the heat sink 104. Mechanical bonding is achieved when the softer interface material 106 is pressed into the irregularities in the surface 112 of the heat source 102 and the surface 118 of the heat sink 104. Over time, and through use, the mechanical bonds can weaken and break. The already high thermal resistance 206 (FIG. 2) between the components 102, 106, and 104 of the hest transfer assembly 100 increases. This increase in thermal resistance results in a higher operating temperature for heat source 102. Adverse effects on an attached electronic device (not shown) are realized and the life expectancy of the associated system is jeopardized. BRIEF DESCRIPTION OF THE DRAWINGS [0009] The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. The invention is illustrated by way of example and is not limited in the figures of the accompanying drawings, in which like references indicate similar elements. [0010] FIG. 1 is a diagram illustrating a typical conventional heat source/sink assembly. [0011] FIG. 2 is a graph illustrating thermal resistance as a function of interface material thickness. [0012] FIG. 3 is a diagram illustrating an atomic level view of the heat source/surface material interface depicted in FIG. 1. [0013] FIG. 4 is a flow chart illustrating a method directed to forming a chemical bond at the surface/surface contact within a heat sink, according to one embodiment of the present invention. [0014] FIG. 5 is a diagram illustrating a heat source/sink assembly with chemical bonding between materials, according to one embodiment of the present invention. [0015] FIG. 6 is a diagram illustrating an atomic level view of chemical bonding at the heat source/surface material interface depicted in FIG. 5. DETAILED DESCRIPTION [0016] In the following detailed description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order to not obscure the understanding of this description. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the invention is defined only by the appended claims. [0017] Within a heat sink assembly according to embodiments of the present invention, the interface material is chemically bonded to both the heat source material and the heat sink material, thereby lowering the contact resistance formerly existing there between. The chemical bonding achieved between the respective materials can be, for example, ionic, covalent or metallic bonds, depending on the characteristic of the materials used to make the heat source, the interface material, and the heat sink. In other embodiments, other types of bonds may be used such as, for example, polar, non-polar, hydrogen bonds, dipole-dipole, ion-dipole, and van der Waals bonds. In some embodiments, more than one type of bond may be formed in an interface (e.g., the interface between the interface material and the heat sink or between the interface material and the heat source). [0018] In embodiments in which a metal and a non-metal are used for the interface material and one of the adjacent layers (i.e., either the heat source or the heat sink), an ionic bond can be formed between the interface material and the adjacent layer. [0019] In embodiments in which a non-metal is used for both the interface material and an adjacent layer, a covalent bond can be formed between the interface material and the adjacent layer. Continue reading... Full patent description for Decreasing thermal contact resistance at a material interface Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Decreasing thermal contact resistance at a material interface patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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