1. Field of the Invention
This invention relates in general to heatsink components, and in particular to an integrated venting, electromagnetic interference (EMI) shield and heatsink component for electronic equipment enclosures.
2. Description of Related Art
Modern computing systems generate significant heat within chassis enclosures and simultaneously generate EMI. As chip clock speeds, and power and circuit densities increase, heat generation by these components also increases, making cooling of the devices more difficult. To maintain reliable operation and data integrity for such systems, effective thermal management in the design is required.
At the same time, as clock and data speeds increase, the generation of EMI increases significantly. Worldwide regulatory rules require certification of electromagnetic compatibility (EMC) prior to shipment of systems.
Conventional methods of thermal management and EMI containment are often at odds in the design of chassis enclosures. To ensure designed performance and reliability, heat generated by active electronic and integrated circuit (IC) components is typically removed through convective heat transfer by forcing cooling air or other thermal carriers to flow past the active component surface. More effective heat removal can generally be achieved by having a higher airflow velocity flowing past the heat transfer surface. To further improve cooling capacity, extended heat transfer surfaces, such as a heatsink, may be attached to the component to increase the convective heat transfer from the component to the thermal carriers. Therefore, for a given exposed surface area and a fixed air moving device, the maximum cooling capacity can be achieved when the extended surface area is maximized and the airflow impedance offered by enclosure walls is minimized. As such, thermal management solutions employing air cooling technologies require venting panels with large number of ventilation apertures of substantial size or open designs in electronic chassis enclosures.
EMI containment, on the other hand, usually requires small apertures, or no openings at all in enclosure walls for effective EMI shielding, because ventilation apertures, when made of electrically conductive materials, behave as waveguide structures in electromagnetic terms. In general, electromagnetic waves propagate through a waveguide as long as the frequency of the wave is higher than the cutoff frequency of the waveguide. The geometry of the cross section of the waveguide determines the cutoff frequency of the waveguide. Below the cutoff frequency, electromagnetic waves do not propagate and are highly attenuated.
Further, the length of the waveguide structure determines the degree of attenuation of frequencies below the cutoff frequency. In practice, for rectangular waveguides, lengths greater than the widest portion of the waveguide are required to achieve desired attenuations. For circular waveguides, lengths greater than the diameter are usually required to provide needed attenuation. For waveguide structures of other cross sectional shapes, e.g., any closed polygon, the length is usually required to be longer than the widest cross sectional dimension. Therefore, apertures on enclosure walls, especially on the venting panels, can form an effective EMI barrier when the aperture size is so small that most frequencies associated with electromagnetic interference are below the cutoff frequency, and/or the aperture length is so deep that desired attenuation can be achieved.
Sample calculations for determining the cutoff frequency of a few common waveguides are as follows. For a circular cross-section waveguide, the cutoff frequency is determined by:             f      cutoff        =          1.841              2        ⁢                  xe2x80x83                ⁢        π        ⁢                  xe2x80x83                ⁢        a        ⁢                              ϵ            ⁢                          xe2x80x83                        ⁢            μ                                ,
where
fcutoff=cutoff frequency in Hertz,
a=diameter of the circular aperture in meters,
xcex5=permittivity of the media within the waveguide, and
xcexc=permeability of the media within the waveguide.
For a circular cross-section waveguide filled with air, the cutoff frequency is determined by:       f    cutoff    =                    5.523        xc3x97                  10          8                            2        ⁢                  xe2x80x83                ⁢        π        ⁢                  xe2x80x83                ⁢        a              ⁢          xe2x80x83        ⁢          Hz      .      
For a rectangular cross-section waveguide filled with air, the cutoff frequency is determined by:             f      cutoff        =                  1.5        xc3x97                  10          8                    b        ,
where
b=width of waveguide in meters, where the width of the waveguide is greater than the height of the waveguide.
An optimal solution to the cooling and EMI design problems must simultaneously address seemingly fundamental design conflicts between thermal management involving increasing heat dissipation and associated difficult thermal management design issues and EMI containment involving increasingly severe EMI radiation and agency certification design issues.
Moreover, packaging often requires extensive thermal and electromagnetic analysis to determine if electronic components within an enclosure will be adversely affected by the environment both inside and outside of the enclosure in which the components will be operating. For example, some components are very sensitive to EMI, and, as such, must be shielded. Similarly, because of dense packing and higher power outputs, cooling of certain high power electronic components may be best achieved if thermal interference created from heat removal of neighboring components can be minimized.
It can be seen, then, that there is a need in the art for components that can provide EMI containment and/or shielding while still providing adequate cooling or venting for heat generating components. Further, there is a need in the art for components that can provide the containment and/or shielding and cooling characteristics while maintaining low cost electronic enclosures.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses an EMI shielding heatsink with venting capabilities, comprising a heatsink block having at least one aperture, at least one thermal plate attached to at least one heat dissipating electronic component, and at least one thermal coupler thermally connecting the heatsink block and the thermal plate. The heatsink block comprises a thermally and electrically conductive material. The apertures are an integral part of the heatsink block, or are thermally and electrically coupled to the heatsink block, and allow a thermal carrier to pass from a first side of the heatsink block to a second side of the heatsink block The apertures are sized to prevent electromagnetic frequencies lower than the cutoff frequency associated with the aperture structure from passing through the apertures. The thermal plate is made of a thermally conductive material or device. The thermal coupler is made also of a thermally conductive material or device that thermally and mechanically connects the heatsink block to the thermal plate.
An object of the present invention is to provide components that can provide effective EMI shielding while still providing adequate cooling and venting for heat generating components. Another object of the present invention is to provide components that can provide the shielding and cooling characteristics while maintaining low cost electronic enclosures.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying detailed description, in which there is illustrated and described specific examples of a method, apparatus, and article of manufacture in accordance with the invention.