BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal conductive apparatus and, more particularly, to a thermal conductive apparatus having at least one micro-rough surface with plural nodules.
2. Description of the Prior Art
Referring to FIG. 1, a traditional thermal conductive apparatus 10 uses a metal cooling sheet 14 for heat dissipation since metal exhibits a high coefficient of thermal conductivity. However, most metals conduct not only heat but also electricity. If the traditional thermal conductive apparatus 10 includes a positive electrode (i.e., a first electrode 11) and a negative electrode (i.e., a second electrode 12), a dielectric layer 13 is required to be disposed between the electrodes 11 and 12 and the metal cooling sheet 14 to prevent a short circuit. The material of the dielectric layer 13 could be any material including dielectric such as quartz, silicon dioxide, Bakelite, or insulated plastics.
However, when applied to a heat-generating device (e.g., a light emitting diode or LED), the dielectric layer 13 cannot dissipate the heat efficiently and thus, the operating temperature of the heat-generating device increases. Consequently, the lifetime of the heat-generating device dramatically decreases or an issue of peeling occurs at the interface 131 between the first electrode 11, the second electrode 12, and the dielectric layer 13, and at the interface 132 between the dielectric layer 13 and the metal cooling sheet 14 due to poor bonding force caused by smooth contact surfaces after several thermal cycles. Finally, the heat conduction ability of the dielectric layer 13 is significantly degraded. In addition, the interfaces 131 and 132 lacking sufficient bonding force will cause damage to the traditional thermal conductive apparatus 10 and the heat-generating device carried thereon. SUMMARY OF THE INVENTION
The objective of the present invention is to provide a thermal conductive apparatus, which employ the interfaces, having at least one micro-rough surface, between two metal sheets and a polymer dielectric layer to exhibit high bonding strength and high heat dissipation efficiency. Accordingly, the thermal conductive apparatus of the present invention quickly reduces the operating temperature of a heat-generating device (e.g., an LED) carried thereon and the lifetime and reliability of the heat-generating device can both be enhanced.
In order to achieve the above objective, the present invention discloses a thermal conductive apparatus including a first electrode sheet, a second electrode sheet, a cooling sheet, and a polymer dielectric layer. Each of the first electrode sheet, the second electrode sheet, and the cooling sheet includes at least one micro-rough surface containing plural nodules. The nodules can be formed by electrodeposition. The polymer dielectric layer physically contacts the first electrode sheet and the second electrode sheet via the top surface thereof, and the cooling sheet via the bottom surface thereof. That is, the polymer dielectric layer is laminated between the first electrode sheet, the second electrode sheet and the cooling sheet in a physical contact manner. The polymer dielectric layer exhibits a coefficient of thermal conductivity above 1.0 W/mK, and the top and bottom surfaces thereof use micro-rough surfaces to physically contact the first and the second electrode sheets.
As for the manufacturing method of the thermal conductive apparatus of the present invention, first, a metal sheet and a cooling sheet are provided. Each of the metal sheet and the cooling sheet includes at least one micro-rough surface containing plural nodules. The nodules could be formed by electrodepositing. Second, a polymer dielectric layer is laminated between the metal sheet and the cooling sheet such that the at least one micro-rough surface physically contacts the top and bottom surfaces of the polymer dielectric layer. The polymer dielectric layer exhibits a coefficient of thermal conductivity above 1.0 W/mK. Third, the metal sheet is etched to form a first electrode sheet and a second electrode sheet that is electrically insulated from the first electrode sheet.
In addition, a first plating layer and a second plating layer are formed on the first electrode sheet and the second electrode sheet respectively to enhance the welding strength of the electrode sheets and to prevent oxidation on the first and the second electrode sheets. The structure including the above first plating layer, the second plating layer, the first electrode sheet, the second electrode sheet, the polymer dielectric layer, and the cooling sheet can be punched to form a thermal conductive apparatus with a specific shape.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described according to the appended drawing in which:
FIG. 1 is a traditional thermal conductive apparatus;
FIGS. 2-4 illustrate the manufacturing method of one embodiment of the thermal conductive apparatus of the present invention;
FIG. 5 illustrates another embodiment of the thermal conductive apparatus of the present invention; and
FIG. 6 illustrates a heat-generating device attached to the thermal conductive apparatus of FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
The following will describe the manufacturing method of the thermal conductive apparatus of the present invention in detail with accompanying figures.
Referring to FIG. 2, a metal sheet 21 and a cooling sheet 24 are provided. Each of the metal sheet 21 and the cooling sheet 24 includes at least one micro-rough surface 210 or 241. The micro-rough surfaces 210 and 241 are formed by electrodeposition and have plural nodules 250 thereon. The size distribution of the nodules ranges from 0.1 μm to 100 μm. The material of the metal sheet 21 is mainly copper, aluminum, or nickel. Other metals, alloys, or multi-layered composite metal (e.g., nickel-plated copper foil and rolled nickel-plated copper foil) can also be used for the metal sheet 21. The material of the cooling sheet 24 could be copper or aluminum.
Next, a polymer dielectric layer 23 is laminated between the metal sheet 21 and the cooling sheet 24 to form a multi-layered structure shown as FIG. 3. The micro-rough surfaces 210 and 241 physically contact the top and the bottom surfaces of the polymer dielectric layer 23, respectively, in which the nodules 250 of the micro-rough surfaces 210 and 241 are inserted into the polymer dielectric layer 23 to form mechanical interlocking. Therefore, considerably high bonding forces are generated between the metal sheet 21 and the polymer dielectric layer 23 and between the cooling sheet 24 and the polymer dielectric layer 23. The nodules 250 consist essentially of size ranging from 0.1 μm to 100 μm, protrude perpendicularly to a surface of the cooling sheet 24 and the metal sheet 21, and expand parallel to the surface of the cooling sheet 24 and the metal sheet 21 with a distance from 0.1 μm to 100 μm. As a result, even after the multi-layered structure undergoes several thermal cycles, it still exhibits strong and functional interfaces. Additionally, before laminating the polymer dielectric layer 23, an anti-oxidation layer could be formed on the micro-rough surfaces 210 and 241 by non-electrodeposition methods, such as electroplating, sputtering, spin-coating, solution coating, or powder coating to prevent oxidation, and thus maintain the bonding strength between the polymer dielectric layer 23, the metal sheet 21, and the cooling sheet 24. The material of the anti-oxidation layer is selected from nickel, chromium, zinc, silver, or an alloy thereof, with a coefficient of thermal conductivity above 1.0 W/mK. On the micro-rough surfaces 210 and 241, a chemical (e.g., silane as a coupling agent) could be applied, or a surface treatment (e.g., by plasma or corona) could be performed to improve the bonding strength and to achieve stable heat conduction.
The polymer dielectric layer 23 is formed by heating, blending, and rolling a polymer material mixed with at least one heat-conductive dielectric filler at a proper ratio, in which the polymer material is more easily processed and treated than metals or ceramic material, and the polymer material is a dielectric itself, and thus is suitable for a matrix of the polymer dielectric layer 23. Most polymer materials could be used as the matrix of the polymer dielectric layer 23, and they are not limited to the following: (1) rubber material (e.g., natural rubber, silicone, polybutene gel, SBS (Polystyrene-butadiene-styrene), or CTBN (carboxyl terminated butadiene acrylonitrile rubber)); (2) thermoplastics (e.g., epoxy, polyurethane, or polyester); and (3) thermosetting plastics (e.g., polyethylene, polyvinylidene fluoride, polypropylene, nylon, polyester, ABS (Acrylonitrile Butadiene Styrene) plastic, or copolymer thereof). The above thermosetting plastics could include a functional group such as an amino group, an acidic group, a halide group, an alcohol group, and an epoxide group. In regard to the heat-conductive dielectric filler, it could be selected from at least one material with a coefficient of thermal conductivity above 1.0 W/mK, preferably above 5.0 W/mK, particularly above 10.0 W/mK. The resistivity of the heat-conductive dielectric filler must be above 108 Ω-cm, preferably 1010 Ω-cm, particularly 1012 Ω-cm. The amount of the heat-conductive dielectric filler is in the range of 20%-90%, preferably 30%-80%, particularly 40%-70%, by volume of the polymer dielectric layer 23. Higher concentration of the heat-conductive dielectric filler results in higher heat conduction of the polymer dielectric layer 23. The heat-conductive dielectric filler is mainly selected from metal nitride such as aluminum oxide (Al2O3), aluminum nitride (AlN), or boron nitride (BN). Others, like metal oxides, metal borides, metallic salts, metal carbides, silicone compounds, and graphite, are also suitable for the heat-conductive dielectric filler. For a specific purpose, an antioxidant or a water repellent could be mixed into the heat-conductive dielectric filler as long as the coefficient of thermal conductivity thereof is above 1.0 W/mK.
In addition, the heat-conductive dielectric filler could exhibit various shapes, e.g., spherical, cubical, hexagonal, flake, polygonal, spiky, rod, coral, nodular, or filament. The particle size distribution of the heat-conductive dielectric filler ranges from 0.01 μm to 30 μm, preferably from 0.1 μm to 10 μm, and has an aspect ratio below 100.
Referring to FIG. 3, the multi-layered structure, which could be formed by plural polymer dielectric sub-layers, exhibits a total thickness ranging from 0.01 mm to 5 mm, preferably from 0.05 mm to 1 mm, particularly from 0.1 mm to 0.5 mm. Furthermore, the color of the polymer dielectric layer 23 mainly depends on that of the heat-conductive dielectric filler. Different color fillers, pigments or phosphors could be added to indicate the desired color. In general, the color desired in the light emitting diode is usually white.
Referring to FIG. 4, the metal sheet 21 is separated to form a first electrode sheet 211 and a second electrode sheet 212 by etching or precision carving, in which the first and the second electrode sheets 211 and 212 are electrically insulated from each other. The first electrode sheet 211 includes a first micro-rough surface 2101 contacting the polymer dielectric layer 23, and the second electrode sheet 212 includes a second micro-rough surface 2102 contacting the polymer dielectric layer 23. The first electrode sheet 211 and the second electrode sheet 212 connect a power source and a heat-generating device (e.g., a light emitting diode, not shown) to form a conductive circuit loop. Finally, the thermal conductive apparatus 20 of the present invention is formed. The cooling sheet 24 with a thickness above 0.03 mm (preferably from 0.07 mm to 5.0 mm, particularly from 0.1 mm to 1.0 mm) is desired to achieve the purposes of high heat conduction and stiff structure. The cooling sheet 24 includes a third micro-rough surface 240, by which the cooling sheet 24 is bound to the polymer dielectric layer 23. The material of the cooling sheet 24 is a metal having high heat conduction ability such as aluminum, copper, magnesium, or an alloy thereof. To prevent oxidation of the surface of the cooling sheet 24 at high temperature, a layer of nickel, zinc, chromium, tin, silver or gold could be plated thereon. In another embodiment, a bottom-cooling sheet (not shown) is welded under the cooling sheet 24 by solder reflow or spot welding to enhance heat dissipation ability. The material of the bottom-cooling sheet could be metal, ceramic, or other heat-conductive material.
In another embodiment, the multi-layered structure of FIG. 3, including the metal sheet 21, the polymer dielectric layer 23, and the cooling sheet 24, is processed by etching, drilling, thermal forming, and punching to form a recess portion (like the space between the first and the second electrode sheets 211 and 212 in FIG. 4) in the multi-layered structure. The recess portion is the place ready for the connection of the electrode sheets or for the heat-generating device and filled with phosphors. In addition, if the material of the bottom-cooling sheet is metal, the surface thereof could be processed by CNC (computer numerical control) drilling, CNC punching or etching to form a three-dimensional hollow where the metal sheet 21, the polymer dielectric layer 23, and the heat-generating device can be inserted. A rough surface could be formed in the three-dimensional hollow to generate a stronger bonding force with the polymer dielectric layer 23. Also, a nickel layer or a gold layer could be plated on the surface of the three-dimensional hollow to ease the bonding between the bottom of the heat-generating device and the polymer dielectric layer 23.
The material of the bottom-cooling sheet is not limited to metal and can be any material with high heat dissipation rate.
FIG. 5 illustrates another embodiment of the thermal conductive apparatus of the present invention, which is based on the thermal conductive apparatus 20 in FIG. 4. The first plating layer 221 and the second plating layer 222 are formed on the first electrode sheet 211 and the second electrode sheet 212, respectively, by electroplating or sputtering. The materials of the first and the second plating layers 221 and 222 is selected from the group consisting of gold, silver, copper, tin, zinc, and chromium. The first and second plating layers 221 and 222 not only improve the welding strength between the electrode sheets 211 and 212 and the heat-generating device but also protect the electrode sheets 211 and 212 from oxidation. Thus, a thermal conductive apparatus 20′, capable of carrying a heat-generating device, is formed. Then, a heat-generating device 30 (e.g., an LED chip, refer to FIG. 6) with specific functions is placed on the thermal conductive apparatus 20′ and metal wires 31 and 32 (or metal sheets) are soldered to the first plating layer 221 and the second plating layer 222, respectively. Referring to FIG. 6, the first and the second plating layers 221 and 222 are connected to the positive and the negative terminals of a power source to form a conductive circuit loop of a high heat-dissipating electronic device 40. In addition, a layer of a heat sink compound 33 could be placed between the heat-generating device 30 and the polymer dielectric layer 23 to enhance the bonding strength there between. In some specific applications, the thermal conductive apparatus 20′ of FIG. 5 is cut to a specific shape by punching, wafer dicing, or curved cutting.
Referring back to FIG. 4, the interfaces between the cooling sheet 24, the first electrode sheet 211, the second electrode sheet 212 and the polymer dielectric layer 23 include the micro-rough surfaces 2101, 2102 and 240. Note that, in practice, not every interface includes a micro-rough surface but the interfaces including at least one micro-rough surface will improve the bonding strength and heat conduction effect to a certain degree.
When the thermal conductive apparatus of the present invention is applied to a heat-generating device (e.g., light emitting diode), similar to the configuration in FIG. 6, the heat generated by the heat-generating device can be conducted through the thermal conductive apparatus to the environment and reach a thermal equilibrium. That is, the operation of the heat-generating device maintains a certain temperature by efficient heat dissipation provided by the thermal conductive device. Thus, damage to the heat-generating device is avoided. In addition, since the thermal conductive device undergoes several thermal cycles in normal operation, the micro-rough surfaces with nodules provide sufficient bonding strength to prevent the electrode sheets, the cooling sheet and the polymer dielectric layer from separating. Therefore, the thermal conductive apparatus of the present invention can achieve the expected objective of providing a thermal conductive apparatus with high bonding strength and high heat dissipation efficiency to improve the lifetime and reliability of the heat-generating device carried thereon.
The devices and features of this invention have been sufficiently described in the above examples and descriptions. It should be understood that any modifications or changes without departing from the spirit of the invention are intended to be covered in the protection scope of the invention.
Patent Application
20070137835
