Abstract:
Provided is an enclosure for encapsulating one or more printed circuit boards (PCBs) configured for having electronic devices mounted thereon. The enclosure includes a main chassis body including a bottom portion and an outer wall including connectable panels for encasing the main chassis body. The enclosure also includes a top portion configured for completing a seal between the main chassis body and the outer wall, wherein one of the PCBs forms one of the connectable panels.

Description:
I. FIELD OF INVENTION 
     The present invention is related to cooling hermetical encapsulated electronics. More specifically, the present invention is related to efficiently cooling electronic devices hermetically encapsulated within a sealed enclosure. 
     II. BACKGROUND OF THE INVENTION 
     As the footprint of electronic components continues to decrease, enabling greater numbers of components to be placed on a printed circuit board (PCB), efficiently dissipating heat produced by the components becomes more challenging. This problem is amplified as even more of these PCBs are housed within a single enclosure, or chassis. 
     Traditionally, air is used as the catalyst for dissipating heat and cooling the electronic components electronics within the enclosure. But as the performance demands of these electronic components continues to increase, the traditional heat dissipating approaches become more inefficient and less effective. This ineffectiveness is particularly true in instances where the chassis is sealed, which is most often the case where the chassis is used as a line replaceable units (LRU). 
     LRUs are used primarily as modular components on aircraft and typically contain aircraft electronics. Usually, these enclosures are not sealed. Cooling air streams through the enclosure in order to remove heat generated by the electronics inside the enclosure. These LRU&#39;s are widely used, for example, in military aircraft applications. The Aeronautical Radio, Incorporated (ARINC) 600 standards specification defines rack and panel sizes, weights, connectors, mounting positions, cooling features, and other characteristics associated with aircraft LRU&#39;s. Also, available air mass, according to the size of the LRU, is specified. The air mass is used to cool the electronic devices inside the LRU.  FIG. 1 , for example, is an illustration of an ARINC 600 LRU enclosure  100 , in which embodiments of the present invention may be practiced. 
     In  FIG. 1 , the ARINC 600 enclosure includes a front panel  102  and a rear panel  104 . As noted above, air masses can be used to cool electronic devices mounted on a printed circuit board (PCB) inside the enclosure  100 . The ARINC 600 standards specification also governs drilled holes in a defined area at the bottom of the enclosure  100  (not shown) and drilled holes  106  at a top of the enclosure  100 . 
     During operation, for example, cooling air can be injected into a bottom air inlet area and will stream through the enclosure  100 , through the drilled holes  106 , and out of the enclosure  100 . This process of streaming air through the enclosure  100  removes heat from the electronic devices. This streaming air, however, exposes the electronic devices to an outer, potentially harmful, external environment. This external environment can be detrimental to the operation and reliability of the electronic devices. 
     For example, filtering of the external air could be deficient such that as the streaming air comes into contact with the electronic devices, the devices can be damaged. Salt filled air, for example, can have a corrosive effect on the electronics. There are many other disadvantages to the cooling mechanics of the conventional ARINC 600 LRU enclosure  100 . 
     An additional disadvantage is that the streaming air must be filtered to a certain level in order to prevent a sandblasting effect on the electronic devices. Also, in the case of eruption of fire inside the LRU enclosure  100 , smoke will be distributed along the cooling paths, permitting the fire to expand to other areas within the enclosure  100 . These disadvantages can significantly impact performance, reduce the mean time between failure (MTBF) of the electronic devices, and decrease their reliability. 
     III. SUMMARY OF EMBODIMENTS OF THE INVENTION 
     Given the aforementioned deficiencies, a need exists for improved techniques for cooling electronic devices mounted on PCBs within sealed LRU enclosure. More specifically, a need exists for improved cooling techniques for an ARINC 600 enclosure having encapsulated electronic devices. 
     An embodiment of the present invention includes an enclosure for encapsulating one or more PCBs configured for having electronic devices mounted thereon. The enclosure includes a main chassis body including a bottom portion and an outer wall including connectable panels for encasing the main chassis body. The enclosure also includes a top portion configured for completing a seal between the main chassis body and the outer wall, wherein one of the PCBs forms one of the connectable panels. 
     Embodiments of the present invention provide an LRU enclosure constructed in accordance with ARINC 600 specification standards. The enclosure includes inlet air streams throughout the enclosure to a top portion, and out of the enclosure. Heat dissipated from the electronic devices mounted on PCBs within the LRU will be removed via the inlet air streams. At least one of the panels of the enclosure is formed from one of the PCBs. Electronic devices mounted on this one PCB are encapsulated within the LRU enclosure. 
     Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. 
    
    
     
       IV. BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention. 
         FIG. 1  is an illustration of an ARINC 600 enclosure in which embodiments of the present invention may be practiced. 
         FIG. 2  is an expanded view of the conventional ARINC 600 enclosure illustrated in  FIG. 1 . 
         FIG. 3  is an illustration of a sealable enclosure  300  constructed in accordance with embodiments of the present invention. 
         FIG. 4  is a cross-sectional view of an interior portion of the enclosure illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the present invention is described herein with illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility. 
     As used in this application, the terms “component”, “module”, “system”, “interface”, or the like are generally intended to refer to a computer-related entity, either hardware, a combination of hardware and software, software, or software in execution. For example, a component may be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and/or a computer. 
       FIG. 2  is an expanded view  200  of the conventional ARINC 600 enclosure  100  illustrated in  FIG. 1 . In  FIG. 2 , the LRU enclosure  100  includes a main chassis body  202  having a bottom panel portion  204  and a top panel portion  206 . The enclosure  100  also includes a wall portion including side panels  208 ,  210 ,  212 , and  214 . PCBs  216 , affixed to the main chassis body  202 , include electronic devices (not shown) that, among other things, produce and dissipate heat. 
     During operation, heat is removed when cool air is injected via inlets in the bottom portion  204  through the enclosure  100  and out of the LRU via the holes  106  in the top portion  206 . As noted above, several features of the LRU enclosure  100  render its cooling capabilities as being deficient in many instances. One of the most significant disadvantages is that electronic devices mounted on the PCBs  216  are directly exposed to air from an external environment, which streams and circulates around the electronic devices. 
       FIG. 3  is an illustration of a sealable enclosure  300  constructed in accordance with embodiments of the present invention. During operation, an exterior portion of the enclosure  300 , viewable in  FIG. 3 , will be in contact with an external environment (e.g., outside world). Electronic devices, mounted on PCBs, are hermetically encapsulated inside the enclosure  300 . 
     The idea of the enclosure  300  is that the encapsulated electronics can be cooled with air in accordance with the ARINC 600 standards while the electronics are encapsulated—without the electronic devices being exposed to air from the external environment. 
     By way of example, the enclosure  300  can achieve an IP65, IP66, and IP67 Titans rating and can achieve valve pressures in accordance with the ARINC 600 standards. Valves are used in enclosures, such as the enclosure  300 , to facilitate decompression. Tightness of the seal can be achieved through the use of gaskets and sealed screws. 
     The enclosure  300  includes a main body  301 , top and bottom panel portions  302  and  304 , respectively, along with side panel portions  306 ,  308 ,  310 , and  312 . The side panel portions  306  and  308  include fins (e.g., heat sinks)  314  and  316 , respectively. The side panel portion  312  is formed of an input/output (IO) PCB configured for mounting electronic devices. 
     By way of example, and not limitation, the top  302 , bottom  304 , and side panel portions  306 ,  308 ,  310 , and  312  can be hermetically sealed. In this example, the I/O PCB  312  serves as a backplane and is an integral component of the sealing process. The electronic devices can be mounted on one side of the PCB  312 . In the exemplary enclosure  300  of  FIG. 3 , a connector  318  is mounted on the other side of the PCB  312 . 
     In the enclosure  300 , the electronic devices are encapsulated within the main body  301 . To facilitate cooling, air can stream around the main body  301 , which can be covered by simple sheet metal external enclosure (illustrated in  FIG. 4 ). As the air streams, it also blows across the heat sinks  314  and  316 , facilitating the transfer of heat from the heat sinks  314  at  316  into the cooling air via a convection process. 
     The simple sheet metal will have openings at top and bottom sections according to the ARINC 600 specification standard. As cooling air streams in through the bottom and streams along the side on the heat sinks  314  and  316  of the main body  301 , the heat sinks  314  and  316  absorb and evacuate the produced by the electronic devices. The cooling air can then be evacuated out of the top and bottom of the sheet metal external enclosure. In this manner, the electronic devices are never directly exposed to the cooling air. 
     Electronics are encapsulated within the main body  301  of the enclosure  300  (i.e., inner enclosure). The heat produced by the electronic devices is absorbed by the heat sinks  314  at  316  by heat conduction. A more detailed explanation of the cooling of the encapsulated portion of the main body  301  is provided below. 
       FIG. 4  is a cross-sectional view of an interior portion  400  of the enclosure  300 . In accordance with the ARINC 600 specification, cooling air, represented by arrows  402 , enters at the bottom of the external enclosure  401  and streams around  403  the encapsulated main body  301 . The cooling air, after being heated by the electronic devices, exits  404  the outer enclosure  401  at a desired outlet location in accordance with the ARINC 600 specification. 
     In the manner above, the cooling air evacuates the heat along the side panels  306  and  308  of the main body  301 , thus removing it from electronic devices, such as a computer module  406  and a power supply  407 . The computer module  406  and the power supply  407  are never exposed to the cooling air. The heat is transported along the side walls of the main body  301 , being absorbed by the cooling air via heat convection, and transported into the outer enclosure  401 . 
     Embodiments of the present invention offer a more reliable cooling enclosure having a lower MTBF using conduction cooling, which is a more efficient cooling process. With respect to the ARINC 600 specification, with different PCBs having different heat sinks, the air streams through the heat sinks. In this scenario, one heat sink, for example, closest to the cooling air, can have a larger pressure drop. 
     The ARINC 600 specification also defines a pressure drop across the LRU which must remain within specified limits. This requirement tours that the cooling air is equally distributed across the LRUs, which are generally installed parallel to each other. By way of example, once the pressure drops across the enclosure  301 , it can be adjusted to equalize any changes related to heat produced by the internal electronic devices. As noted above, valves can be used as a mechanism for controlling and facilitating the different pressure drops, pressure levels, and decompression. 
     The valves, in essence, equalize the different pressure environments. The ability to accommodate different pressure levels enables the LRU&#39;s to be used at sufficiently high altitudes without the risk of destruction due, for example, to explosions because of over pressure. 
     Referring back to  FIG. 3 , the backplane PCB  312  is used to form one of the side panels of the enclosure  301 . The connector  318  is attached to the PCB  312  and provides connectivity for power, as well as accommodating the input and output of processor signals. In the case of aircraft, for example, the electronics to the aircraft are transferred through the connector  318 . 
     Since the backplane PCB  312  can be removable, a variety of gaskets can be used to facilitate a tight seal. On example of an efficient type gasket is to have an O-ring configured for placement in a groove. The O-ring and the groove can be pressed into place. The use of an O-ring is merely one approach to attaching the backplane PCB  312  and forming a tight seal. The O-ring, or other suitable sealing technique, can ensure that the seal between the PCB  312  and the rest of the enclosure  300  will be devoid of any holes. Screws, with sealing material, can be used as an added measure. Using this approach, the PCB  312  can be used to actually form the seal. In conventional ARINC 600 LRUs, for example, a separate plate is used as a side panel to form the seal. 
     CONCLUSION 
     It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.