Evacuated core circuit board

Abstract

An evacuated core circuit board (10) for dissipating heat from a heat generating electronic component, the evacuated core circuit board comprising: at least one circuit layer (12) to which the heat generating electronic component (14) is electronically coupled; a base layer (16) a comprising a body structure (19) having a substantially hollow interior (20); and a dielectric layer (18) provided between at least a portion of the circuit layer (12) and the base layer (16), wherein the hollow interior (20) is at least partially evacuated.

Claims

1. An evacuated core circuit board for dissipating heat from a heat generating electronic component, the evacuated core circuit board comprising: at least one circuit layer to which the heat generating electronic component is electronically coupled; a base layer a comprising a body structure having a substantially hollow interior, which is sealed; and a dielectric layer provided between at least a portion of the circuit layer and the base layer, wherein the hollow interior is at least partially evacuated and wherein the inner surface of the hollow interior may be treated with a surface treatment material wherein the surface treatment material is nanoparticulate.

2. An evacuated core circuit board according to claim 1, where the body structure is a unitary plate-like structure defined by substantially opposed top and a bottom faces.

3. An evacuated core circuit board according to claim 2, wherein the top and bottom faces are substantially evenly spaced apart to define the hollow interior of the body structure.

4. An evacuated core circuit board according to claim 2, wherein the top and bottom faces are substantially evenly spaced apart over a substantial portion of their interior surface area.

5. An evacuated core circuit board according to claim 1, wherein the hollow interior contains air which has been partially evacuated.

6. An evacuated core circuit board according to claim 1, wherein the hollow interior contains a phase change material at a reduced atmosphere.

7. An evacuated core circuit board according to claim 1, wherein the heat generating electronic component is an light emitting diode (LED) light.

8. An evacuated core circuit board according to claim 1, further comprising a bonding agent layer between the circuit layer and the base layer for bonding the circuit layer to the base layer.

9. An evacuated core circuit board according to claim 1, wherein the base layer forms part of the circuit layer.

10. An evacuated core circuit board according to claim 9, wherein the surface of the base layer is deposited with sections of conductive layers and dielectric layers.

11. An evacuated core circuit board according to claim 9, wherein the dielectric layer is applied to the surface of the conductive layer and portions are etched away to reveal conductive portions.

12. An evacuated core circuit board according to claim 1, wherein the surface treatment material has a high Debye temperature.

13. An evacuated core circuit board according to claim 1, wherein the internal surface treatment material has a Debye temperature of at least 600 k.

14. An evacuated core circuit board according to claim 1, wherein the surface treatment material is any one or more of carbon, beryllium, sapphire, titanium dioxide, titanium nitride, titanium carbonate, hafnium diboride, zirconium diboride, titanium diboride, scandium nitride, vanadium carbide, chromium, ruthenium, silicone and calcium carbonate.

15. An evacuated core circuit board according to claim 1, wherein the mean particle size of the surface treatment material is about 1 to 40 nm.

16. An evacuated core circuit board according to claim 2, wherein the top face and bottom face are provided with a featured surface.

17. An evacuated core circuit board according to claim 16, wherein the featured surface comprises a number of surface area maximising corrugations.

18. An evacuated core circuit board according to claim 17, wherein the corrugations extend across the surface of the unitary body in a direction offset from a latitudinal axis of the unitary body.

19. A LED lamp array, the lamp array comprising: one or more LEDs arranged on the evacuated core circuit board of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

(2) FIG. 1 is a cross sectional view of an evacuated core circuit board in accordance with a first aspect of the present invention;

(3) FIG. 2 is side view drawing of the evacuated core circuit board in accordance with the first aspect of the present invention;

(4) FIG. 3 is an upper perspective drawing of the evacuated core circuit board in accordance with the first aspect of the present invention; and

(5) FIG. 4 is a graphical representation of the results of Example 1.

DESCRIPTION OF EMBODIMENTS

(6) In FIGS. 1 to 3 there is shown an evacuated core circuit board 10 in accordance with the present invention. The evacuated core circuit board 10 comprises a circuit layer 12 to which a heat generating electronic component, for example a LED 14 is electronically coupled to. The evacuated core circuit board 10 further comprises a base layer 16. A dielectric layer 18 is provided between at least a portion of the circuit layer 12 and the base layer 16. The dielectric layer 18 is electrically insulating, to prevent the shorting of the LED 14. As shown in FIG. 1, at least one part of the LED can be directly bonded to the base layer. Alternatively, the LED may be bonded to the circuit layer which is on or in the dielectric layer.

(7) The base layer 16 comprising a body structure 19 with a substantially hollow interior 20. The substantially hollow interior 20 is coated with a surface coating (not shown). The base layer 16 is constructed of a unitary plate like structure with a top face 22 and bottom face 24.

(8) It is well understood that the heat may propagate by way of conduction, convection or radiation. Typical heat transfer methods used in electronics rely on conduction to remove heat from the heat source. In this arrangement, the speed at which the heat can be removed from the heat source is limited by the speed at which heats conducts through the solid. It is understood by the applicant that by providing the body structure 19 with a hollow interior, that at least a portion of the heat generated by the heat source may be transferred by way of radiation through the hollow interior 20. As would be understood by person skilled in the art, the speed at which heat propagates by way of radiation is much faster than that of conduction.

(9) The difficulty faced in the design of a hollow interior 20 that demonstrates a suitably high rate of radiation is to increase the amount of heat that is emitted from the solid surface into the hollow interior, such that its speed competes with conduction through the solid.

(10) As would be understood by a person skilled in the art, when the temperature of a body is greater than absolute zero, inter-atomic collisions cause the kinetic energy of the atoms or molecules to change. This results in charge-acceleration and/or dipole oscillation which produces electromagnetic radiation.

(11) Without wishing to be bound by theory, the applicant understands that emissivity of a material is dependent on a number of factors. These factors include the material's chemical composition and physical structure, the temperature of the material, the Debye temperature of the material and associated phonon oscillation rates, the angle of passage of these oscillations, and finally the polarization of that material. These factors similarly affect the absorption of radiation. The fine tuning of any one of these factors may be used to improve the emission and absorption of heat by way of radiation.

(12) The inventors have discovered that materials with a high Debye temperature or a low specific heat per mole more readily emit and absorb radiation. Without wishing to be bound by theory, this is understood to be due to the atomic structure of the material and the high rate of oscillation of particles at temperature.

(13) As it is the dipole oscillation which produces radiation, emission of radiation can only occur at the surface of a material. Additionally, radiation can only occur once every dipole oscillation. Therefore, it is advantageous to use materials with high phonon oscillation rates and to maximise surface area. Without wishing to be bound by theory, the inventors have discovered that by coating the inner surface of the hollow interior with a surface coating that comprises crystalline nanoparticles in the size range of about 1 to 40 nm the surface area and transmission speed may be increased. By increasing the emitting and absorbing surfaces area, heat transfer is also increased. Additionally, particle size may also be inversely proportional to the materials heat transfer speed. Materials need to be chosen carefully as their particle size will influence structure and Debye temperature.

(14) The rate of the dipole oscillation dictates the emission wavelength, with the oscillation rate dictated by the phonon oscillation rate. Materials that can handle high rates of oscillation will permit more transfer. Ideally, the accepting material will have a similar wavelength and phonon oscillation to the emitting material and should subsequently be matched. This is understood to provide the maximum heat transfer through the hollow interior 22.

(15) In the embodiment shown in FIGS. 1 to 3, the body structure 19 is plate-like, though it is envisaged that the shape may be adapted to the particular heat source. For example, the body structure 19 may be sized and shaped for use with mobile telephones or within laptops and personal computers.

(16) Where the heat generating electronic component has its own heat slug 26, the heat slug is directly reflowed to the base layer through a hole in the dielectric layer 18.

(17) Both the top face 22 and the bottom face 24 are provided with a series of corrugations along their surfaces. In the embodiment shown in FIGS. 2 and 3, the directions of the corrugations are offset 45 degrees from the lateral axis of the base layer 16. The corrugations of the top face 22 and the bottom face 24 are offset by 90 degrees.

(18) The hollow interior 20 is evacuated by way of an evacuation tube 28. Once the hollow interior has been evacuated, the evacuation tube 28 is sealed in order to maintain a vacuum therein.

(19) By both increasing the efficiency and managing the extraneous thermal energy of the of the LED light source, the Applicant has been able to improve the overall performance of an LED lamp. In this manner, the maximum visible light may be utilised from the LED, whilst extraneous energy is removed from the LED lamp.

Example 1

(20) As discussed previously, the Inventors have identified that the use of the metal core circuit board for dissipating heat from a LED light source. The difficulty faced in the manufacture of the LED lamps is that whilst higher currents result in higher light levels from the LED light source, it also increases the operating temperature of the LED. This increase in operating temperature also reduces the efficiency of LED light sources. Typical conductive heat sinks only allow the current to be increased to a certain point before the LED efficiency is affected as a result of heat generation. To compare the metal core circuit board of the present invention to typical heat sinks, series of test were performed which compared the effect that increased current had on a single 1 watt LED on the metal core circuit board of the present invention against an identical single 1 watt LED cooled by industry standard heat sinking technology. The base layer of the metal core circuit board was constructed of 99.98% pure copper which has been pressed into a unitary plate-like structure defined by substantially opposed top and a bottom faces. The hollow interior was coated in surface treatment material comprised of Nanoparticles within the size range of about 1 to 40 nm, the materials were elemental or molecular in nature and included sapphire nanoparticles, carbon nanoparticles, titanium nitride nanoparticles, and calcium carbonate nanoparticles. It is understood by the Inventors that multiple nanoparticle elements or molecules can be used. The materials were mixed in even quantities with approximately 50 mg of material being injected within the chamber and evenly coating the surface. Following coating, the chamber was evacuated and sealed. A single LED was solder to the circuit layer.

(21) Each single 1 watt LED had a specified run current of 0.35 A. The increase in current through each LED was made over a number of steps, with each step in current being maintained for 5 minutes before increasing the current to the next step. The results of the test are shown in FIG. 4.

(22) As can be seen from FIG. 4, at 0.35 A the lux is quite similar between the two products. There then is a rapid divergence at 2 run current. At 3 to 4 run current there is a thermal cascade where the heat the LED is producing causes the light levels to drop even though more power is being supplied.

(23) Whilst Example 1 demonstrated the advantages of the evacuated core circuit board of the present invention with respect to a single LED light, this effect is compounded in commercial uses of LED lights. In an attempt to increase light output, commercial manufacturers place more LEDs on their boards to compensate for lower light output at lower operating current. Typical commercial LED light can have up to nine LEDs on a single board. As identified by the inventors, light output is proportionate to the temperature and it understood that the temperature of the LED junction and ultimately the speed of heat transfer through the heatsink plays and important factor in overall light output. In the aforementioned commercial example, there are nine separate LEDs which each contribute to the overall heat and therefor the overall light efficiency. By improving the capabilities of the heatsink, the inventors have discovered that more light will be produced with a higher reliability, using less LEDs.

(24) Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, formulations and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.