Patent Application
20080057333
Referring to
The method of fabricating the heat dissipation substrate 20 is described as follows. The feeding temperature of a batch-type blender (HAAKE-600P) is set to be 20° C. higher than the melting point (Tm) of the material, and the pre-mixed materials of the thermally conductive polymer dielectric insulating layer 23 are added, and raw materials are placed in a steel cup and uniformly stirred with a measuring spoon. Initially, the rotation speed of the batch-type blender is 40 rpm, and 3 minutes later, the rotation speed is increased to 70 rpm. The materials are blended for 15 minutes and then taken out, thereby forming a heat-dissipating composite material.
The heat-dissipating composite material is put into a mould in a longitudinally symmetrical manner. The mould uses a steel plate as an outer layer and has a thickness in the middle of, for example, 0.15 mm. Teflon mold release cloths are disposed on the upper and lower sides of the mould, respectively. First, the heat-dissipating composite material is pre-heated for 5 minutes, and then pressed for 15 minutes under a pressure of 150 kg/cm2 and a temperature equal to the blending temperature. Afterwards, a heat dissipation sheet of a thickness of 0.15 mm is formed.
The first metal layer 21 and the second metal layer 22 are disposed on the upper and lower sides of the heat dissipation sheet and then pressed again, pre-heated for 5 minutes, and then pressed for 5 minutes under a pressure of 150 kg/cm2 and a temperature equal to the blending temperature, so as to form the heat dissipation substrate 20, in which the thermally conductive polymer dielectric insulating layer 23 is in the middle and the first metal layer 21 and the second metal layer 22 are respectively attached onto the upper and lower sides of the polymer dielectric insulating layer 23.
Table 1 shows experimental results of the tension and withstand voltage test of different roughness of metal layers. The thermally conductive polymer dielectric insulating layer 23 uses polyvinylidene fluoride (PVDF) with the melting point of 165° C. as a base material, and thermally conductive fillers Al2O3 and AlN are dispersed in the PVDF, wherein the volume percentages of the two are 60% and 45%, respectively. In this embodiment, the thickness of the thermally conductive polymer material layer 23 is smaller than 0.3 mm. The adhesion test is performed according to JIS C6481 specification for testing the peeling strength of the interfaces.
As shown in Table 1, the surface roughness (Rz) of the Comp. case is in a range of 3.0-4.5, and is lower than those in the Examples 1 to 7. The adhesion of the Comparative Example case is 7.5 N/cm, which is far less than those of the Examples 1 to 7. It is obvious that a larger roughness can increase peeling strength between the thermally conductive polymer dielectric insulating layer and the first and second metal layers. Moreover, all experimental cases can pass the withstand voltage test of 5 kV or at least higher than 3 kV, and the thermal conductivity is larger than 1.0 W/m·K.
Table 2 shows a test comparison table of different types of high polymers.
The experimental cases 1 and 2 use PVDF and PETFE (Tefzel™) as polymeric base materials, respectively, and the thermally conductive filler is Al2O3. The polymers in the Comparative Examples 1 and 2 are selected from HDPE and EPOXY without fluorine. In the Examples and Comparative Examples, the volume percentages of the polymers and the thermally conductive filler are 40% and 60%, respectively, and the copper foils having the same roughness Rz in the range of 7.0-9.0 are used as the first metal layer and the second metal layer.
The Comparative Example of EPOXY comprises liquid EPOXY, Novolac resin, dicyandiamide, urea catalyst, and Al2O3. The liquid EPOXY selects Model DER331 of Dow Chemical Company, the Novolac resin selects Model DER438 of Dow Chemical Company, the dicyandiamide selects Dyhard 100S of Degussa Fine Chemicals, and the urea catalyst selects Dyhard UR500 of Degussa Fine Chemicals. The Al2O3 has a grain size in the range of 5-45 μm, and is manufactured by Denki Kagaku Kogyo Kabushiki Kaisya.
The EPOXY is prepared according to the following steps. First, 50 phr of DER331 and 50 phr of DEN438 are mixed in a resin kettle at a temperature of 80° C. till becoming a homogeneous solution. Then, 10 phr of Dyhard 100S and 3 phr of Dyhard UR300 are added in the resin kettle and further mixed for 20 minutes at a temperature of 80° C. Subsequently, 570 phr of the Al2O3 filler are added into the resin kettle and mixed till the filler is completely dispersed in the resin to form a resin slurry. The gas contained in the resin slurry is removed in a vacuum for 30 minutes. Then, the resin slurry is placed on a copper foil surface, and another copper foil is laid on the surface of the resin slurry, thereby forming a copper foil/resin slurry/copper foil composite structure. The copper foil/resin slurry/copper foil composite structure is placed in a metal frame with a thickness of 3 mm. A rubber roller is used to flatten the copper foil surface. The composite structure together with the metal frame is placed in a furnace at a temperature of 130° C. to be pre-cured for 1 hour. Then, the composite structure together with the metal frame is placed in a vacuum hot press machine with a vacuum degree of 10 torr and a pressure of 50 kg/cm2 in order to be further cured for 1 hour at 150° C. The composite structure is cooled to be lower than 50° C. at a pressure of 50 kg/cm2 and is removed from the hot press machine.
The test substrates used in the PVDF and PETFE experimental cases and the HDPE and EPOXY Comparative cases have passed the following tests.
1. Flexibility: an 1 cm wide test specimen is bent 180 degree along the exterior circumference of a metal rod which has a diameter of 5 mm, and the surface of the test specimen should has neither ruptures nor cracks.
2. Peel Strength Test: a 180 degree T-peel strength measurement is applied to the test specimen (1.0 cm×12 cm) by clamping the upper and lower metal foil at one end of the specimen, and testing the sample under a constant tensile speed of 3 cm/min in a tensile testing machine.
3. Dielectric Strength (insulation withstanding voltage) Test: it is a withstanding voltage test using Kikusui Model TOS5101 Withstanding Voltage Tester by applying 1 kV on the upper and lower electrodes of the 1″ diameter specimen for 30 seconds and applying a step increase 0.5 kV for each consecutive tests until the applied voltage exceeds the withstanding voltage of the insulation layer of the specimen.
As shown in Table 2, the Example 1 and Example 2 cases of the fluorine-containing polymers PVDF and PETFE have superior flexibility, and pass the withstanding voltage test since these two could withstand a voltage higher than 5 kV. On the contrary, the Comparative Example 1 using HDPE as the polymer passes the flexibility test, however, fails the withstanding voltage test since the HDPE system could only withstand a voltage lower than 2 kV, which is obviously lower than those in the Example 1 and Example 2. Comparative Example 2 using EPOXY as the polymer passes the withstanding voltage test, however, fails the flexibility test.
Furthermore, the fluorine-containing materials such as PVDF and PETFE are not easily caught on fire and do not support combustion (meeting UL 94 V-0), and are much more suitable for safety applications in comparison with HDPE or EPOXY.
The volume percentages of the fluorine-containing polymer and the thermally conductive filler can be adjusted to some extent and still have the same characteristics. The volume percentage of the fluorine-containing polymer is preferably in the range of 30-60%; the volume percentage of the thermally conductive filler is in the range of 40-70%, and more preferably in the range of 45-65%.
In addition to the aforementioned materials, the thermally conductive high molecular polymer can be selected from the group of poly(tetrafluoroethylene) (PTFE), tetrafluoroethylene-hexafluoro-propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), perfluoroalkoxy modified tetrafluoroethylenes (PFA), poly(chlorotri-fluorotetrafluoroethylene (PCTFE), vinylidene fluoride-tetrafluoroethylene copolymer (VF-2-TFE), poly(vinylidene fluoride), tetrafluoroethylene-perfluorodioxole copolymers, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-perfluoromethylvinylether with cure site monomer terpolymer.
The thermally conductive filler can be nitride and oxide, wherein the nitride includes zirconium nitride (ZrN), boron nitride (BN), aluminum nitride (AlN), and silicon nitride (SiN) and the oxide includes aluminum oxide (Al2O3), magnesium oxide (MgO), zinc oxide (ZnO), and titanium dioxide (TiO2).
Furthermore, in order to be used in the high power light-emitting devices such as LEDs, the first metal layer 21 carrying the LED device 10 can be made of copper so as to fabricate a relevant circuit of the LED device 10 thereon. The second metal layer 22 on the bottom can be made of copper, aluminum, or an alloy thereof.
The heat dissipation substrate of the present invention has the advantages of high thermal conductivity, high withstanding voltage, high tensile strength, and flexibility, so that it can be applied in an LED module for illumination to dissipate heat. Furthermore, the heat dissipation substrate can further be used in more compact size portable devices, e.g., a notebook or a mobile phone, in which higher efficiency of heat dissipation is required.
The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 095131947 | Aug 2006 | TW | national |
