Patent Publication Number: US-2020281095-A1

Title: Systems and methods for using additive manufacturing for thermal management

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 14/592,387, filed Jan. 8, 2015, now allowed, which claims the benefit of U.S. Provisional Application No. 61/976,649, filed Apr. 8, 2014. 
    
    
     BACKGROUND 
     The operation of electronic devices requires satisfactory thermal management to ensure proper function. As the electronic devices become heated, the devices suffer from device degradation, functional failure, and lower lifespan. 
     For example, the capability of avionics electronics is determined by the computing processing ability of the system. Typically there are size and weight constraints for an avionics system. These systems are thermally limited such that, for a given volume, only a certain number of cores or processors can operate before thermal issues such as overheating occurs. Typically, processors are de-rated (up to 80%) to avoid overheating in high ambient temperature environments—drastically reducing capability. If the heat can be effectively removed from the system, more processing power, and ultimately more processing capability, is possible from the same volume and weight. 
     There are a number of conventional cooling methods such as fans and heatsinks that are currently used to remove heat from the electronic circuitry and maintain the operational temperature range for the electronics. Technological improvements have continued to increase the device density and reduce packaging while also increasing the computing power and functionality such that thermal management systems are a key operational element. In addition, certain applications have restrictions in the size and weight that limit the cooling capacity and therefore limit the processing power and functionality of the electronics. 
     Some improved advances include heat pipes and synthetic jet cooling. Heat pipes provide for some efficiency improvements in the thermal characteristics whereas synthetic jets essentially provide for improved reliability relative to fans. 
     System designers have increasingly recognized that the thermal management is a critical factor to the successful deployment of electronics and currently design assemblies and systems in order to optimize thermal performance. 
     The thermal path from the electronic component to the cold reservoir is limited by current technology. Certain conventional designs include the use of milled aluminum heat frames, composite materials for chassis and mounting electronics closer to the cold reservoir. Further aspects include integrating planar vapor chambers and linear heat pipes into a heat spreader structure. 
     What is needed to further enhance processing power and functionality is to improve the thermal performance. 
     SUMMARY 
     The thermal management system for electronics according to one example includes a heatframe, heat fins and/or heat exchanger, chassis portion and conformal slot portion integrally formed as a vapor chamber by 3D printing. In further embodiments, any 3D vapor chamber formed by the additive manufacturing processes as detailed herein is within the scope of the system. A further example includes a heat exchanger or cold plate that interfaces with the vapor chamber or chassis. In certain embodiments, the 3D vapor chamber has a 3D wick structure formed on internal surfaces. There can also be 3D support structures integrated into the 3D vapor chamber, wherein the support structures in one example facilitate the transfer of liquids and gas. 
     In one example, the vapor chambers are modular such that multiple chambers are coupled together to form a chassis. The chassis can include an input/output (I/O) interface that electrically connects the electronics on a circuit card to the external environment. 
     A further embodiment is a closed 3D vapor chamber having a heatframe with a component side and an opposing side with a vapor channel formed therebetween. There is at least one liquid receptacle on a first side end of the vapor channel, and typically a liquid receptacle on the opposing side end. A plurality of wick structures are interiorly disposed on at least some of the component side and the opposing side and heat fins and/or heat exchanger is disposed on an exterior of the 3D vapor chamber. 
     These and other aspects, features, and advantages of this disclosure will become apparent from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings. 
    
    
     
       DRAWINGS 
       Embodiments described herein will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1A  and  FIG. 1B  shows a conventional circuit card assembly with electronic components on a circuit card mated to a heat frame; 
         FIG. 2  is depicts the conventional circuit card assembly including the electronic circuit card, heat spreader, wedgelock, chassis and fins; 
         FIG. 3  shows a conventional chassis for housing circuit card assemblies; 
         FIG. 4  illustrates one embodiment of the present system that includes an integrated assembly providing thermal management for an electronic circuit card; 
         FIG. 5  shows the thermal flow path in a conventional chassis with attached circuit card assembly; 
         FIGS. 6A and 6B  depict the modular vapor chamber according to one embodiment; 
         FIG. 7  shows another embodiment of the modular vapor chamber with two circuit cards; 
         FIG. 8  is another example of the modular vapor chamber and various non-uniform wick structures; 
         FIG. 9A  shows another example of the modular vapor chamber having internal supports in accordance with another embodiment; 
         FIG. 9B  shows a modular vapor chamber embodiment with wick structures for enhanced support and fluid flow; 
         FIG. 9C  shows a modular vapor chamber embodiment with internal support structures that may also serve as feeder arteries for the liquid; 
         FIG. 10A-10G  depicts various embodiments of the structural characteristics for the internal supports for the 3D vapor chamber; 
         FIG. 11A-D  depicts several examples of the non-uniform wick structure; 
         FIG. 12A-12B  show modular vapor chamber embodiments with integrated hollow fins; 
         FIG. 13  shows thermal management system as a vertical assembly including several vapor chambers assemblies vertically assembled to form the chassis portion; 
         FIG. 14A-D  shows stacked modular vapor chambers and assembly into avionics system with I/O module; 
         FIG. 15  shows embodiment with enhanced convection using synthetic jets located in bottom tray and on top of I/O module; 
         FIG. 16A-C  shows modular vapor chamber in another embodiment that is integrated into the airframe skin; 
         FIG. 17A-C  shows modular vapor chambers in alternate stacking configurations; 
         FIG. 18  shows a thermal management system as a planar assembly including two or more of the vapor chambers planarly assembled to form the chassis portion; 
         FIG. 19A-C  shows various surface geometry of the 3D vapor chamber to envelop the circuit electronics including conformal, reverse-conformal and custom-conformal configurations; 
         FIG. 20  shows a thermal management system with a compartmentalized vapor chamber including several compartments partitioned within the same vapor chamber and adjacent to each other; and 
         FIG. 21A-F  is another example of the modular vapor chamber with complaint wall and wick structures. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments are described below in detail with reference to the accompanying drawings, where the same reference numerals denote the same parts throughout the drawings. Some of these embodiments may address the above and other needs. 
     The thermal management system in one example describes a thermal management device comprising a sealed vessel that contains a working fluid. A specially engineered internal structure within the sealed vessel interacts with the working fluid to enhance the transfer of heat energy. The vessel is of a conformal, reverse-conformal or custom-conformal shape as required by the specific application. One part of the internal structure includes fine structures engineered to provide strong capillary forces to the working fluid at locations where they are required. Other parts of the internal structure include fine structures engineered to transport the working fluid with minimal pressure drop while preventing interference with the vapor state of the working fluid. Additional support structures, as part of the internal structure act to internally support and strengthen the sealed vessel, and thereby to provide additional paths for fluid transport. Working components, usually electronic, that generate parasitic heat losses are thermally connected to the thermal management system. In effect, the thermal management system establishes a specially engineered thermal path between the electronic components and a cold reservoir and thereby transfers the heat from the components to the cold reservoir. 
       FIG. 1A  and  FIG. 1B  shows a conventional circuit card assembly with electronic components on a circuit card mated to a heat frame. Referring to  FIGS. 1A and 1B , a conventional circuit card  10  is shown in  FIG. 1A  with electronic components  20  that can include components such as processors that generate considerable heat. Referring to  FIG. 1B , in many applications the circuit card  10  is coupled to a heat spreader card  50  by flipping the circuit card  10  and securing it to the heat spreader  50  so the components  20  are proximate the heat spreader  50 . While this form of heat dissipation works to some degree, it can only dissipate a certain amount of heat generated by the components  20  and requires a large and bulky heat spreader  50 . As the processing capabilities have increased, the individual components have decreased in size and require even greater heat dissipation capabilities in a smaller space. 
       FIG. 2  depicts a conventional thermal management system  200  according to one example for an assembly (not shown). In such a conventional system, the components such as the heat frame or heat spreader  240  with wedgelock  250  and circuit card  210  coupled thereto are mated to the chassis frame  260  having fins  270 . In the state of the art, electronic components  220  are mounted to a component board  210  such as a printed circuit card/board (PCB). The components  220  typically have a thermal interface material (TIM)  230  to transfer the heat from the components  220  to the heatframe  240 , particularly since the components  220  may have different shape/size and the heatframe  240  is configured to allow for the highest component height. The heatframe  240  is typically constructed of a material such as aluminum to provide for efficient heat transfer of has a sufficient size to facilitate the heat transfer. 
     As noted in  FIG. 2 , components  220  generate heat that is conducted through TIM  230  to the heatframe  240 . The heatframe  240  further spreads the heat to the wedgelock  250 , to the chassis frame  260  and then to the fins  270 . Thus, the heat is finally dissipated to the environment and fins  270  are designed to be large enough to dissipate the expected heat from the electronic components. 
     In some cases, the heatframe  240  can be quite large in comparison to the circuit card  210 . The wedgelock  250  is used to seat the heatframe  240  (pre-assembled with the card  210 ) into the chassis frame  260  wherein the chassis frame  260  has a mating portion for the wedgelock  250 , for example a chassis groove, to receive the wedgelock  250 . The wedgelock  250 , in certain examples, is a cam operated device that serves to lock the heatframe  240  to the chassis frame  260 . Chassis frame  260  typically has fins  270  to allow for a greater surface area so the external environment that can include cooling air or liquid that removes the heat. 
       FIG. 3  shows a conventional chassis for housing circuit card assemblies. Referring to  FIG. 3 , a chassis frame  310  is shown having a number of chassis grooves  330  for seating a number of circuit cards  340  with the heat spreaders and electronics. The chassis frame  310  has a network of chassis fins  320  about the perimeter of the chassis frame to provide for heat transfer, which is typically on three sides, such as right, left, and top. When there are multiple cards in the chassis frame, there may be considerable heat generated by the individual cards such that other heat transfer features such as heatpipes and vapor chambers may be utilized. In this example, the electronic circuit card is coupled to the heat spreader card which is then inserted into the chassis frame via the grooves using the wedgelock to secure the card assembly to the chassis frame. 
       FIG. 4  illustrates one embodiment of the present system that includes an integrated thermal management system for an electronic circuit card, wherein the integrated system is manufactured by additive manufacturing. As used herein, additive manufacturing refers to processing techniques such as 3D printing, rapid prototyping (RP), direct digital manufacturing (DDM), selective laser melting (SLM), electron beam melting (EBM), and direct metal laser melting (DMLM). 
     Referring again to  FIG. 4 , the integrated thermal management card assembly  400  in this example includes a heatframe  440 , fins  470 , card mounting portion  460  and chassis mounting portion  450  that are integrally formed as a unitary thermal management structure  480 . In this example, the card mounting portion  460  integrally formed with the heatframe  440  removes the need for the wedgelock mating of the conventional assembly of  FIG. 2 . The card mounting portion  460  retains the printed circuit card  410  such as by friction fit and/or tongue and groove. The chassis mounting portion  450  is employed as part of the chassis architecture that is also used to seat circuit cards inserted in slots or channels. As part of ruggedizing this architecture, the mounting portion  450  ensures a friction fit in the chassis, so that the circuit cards do not shake loose from the backplane. It also provides pressure between the bottom of the card or heat frame and the chassis wall, thus creating a good thermal bond. In the depicted chassis architecture, the traditional wedgelock is superfluous as the elements are integrally formed and do not insert cards in slots, but stacks circuit cards as slices that are then retained to the I/O module via fasteners, thereby eliminating the traditional wedgelock. 
     In one example the heatframe  440  is a vapor chamber and the printed circuit card  410  with the accompanying components  420  are coupled to the vapor chamber. The printed circuit card  410  engages the heatframe  440  that is configured to receive the printed circuit card  410 . In one example, the heatframe  440  includes a tongue and groove feature that follows the sides of the circuit card  410 . The heatframe  440 , in one example, is designed for the printed circuit card  410  and the accompanying heat generating component  420  such that the heatframe  440  is designed to be in close proximity to the components  420  on at least one side. In such an example, the thermal interface material is not required or can be minimized. 
     According to one embodiment, a further feature of the vapor chamber implementation is a reduction in the Electromagnetic Interference (EMI) of the assembly  480  which allows mating multiple assemblies while providing strong attenuation for EMI generated by the electronics or present in the external environment. 
     In addition, the heatframe  440  in one example is designed to be in close proximity for conductive coupling with not only the upper surface or top of the component  420  but in some examples on one or more sides of the component  420 . The ability to effectuate heat transfer over a greater surface area of the components  420  greatly enhances the thermal management capabilities of the structure  480 . In one example the heatframe  440  is conductively coupled to the top surface and at least one side surface of the component  420 . As used herein, conductively coupled refers to being in direct, indirect or close proximity to a component such that heat transfer can occur. For the indirect contact, a material such as a thermal interface material can be utilized. 
     Thermal performance estimates using thermal resistance of the exemplary thermal management systems illustrated in  FIGS. 4 and 6-18  with the 3D manufactured vapor chambers indicate they are superior to today&#39;s state of the art systems. 
       FIG. 5  shows the thermal flow path in a conventional chassis unit with attached circuit card assembly. Specifically,  FIG. 5  is a cut away side perspective and depicts a conventional chassis unit  510  for a circuit card  520  having components  530  of varying size and shape and is secured to the chassis frame  565  by a wedgelock  560 . The thermal flow path in a conventional chassis unit  510  comprising thermal interface material (TIM)  535 , heatframe  550 , wedgelocks  560  and chassis  565  with attached circuit card assembly. TIM  535  is typically used to conduct heat from the components  530  to the heat frame  550 . At least some of the heat is conveyed by conduction  580  through the heat frame  550  to the chassis frame  565  and finally to the heat fins  570  and dissipated to the environment. The wedgelock  560  typically provides a mechanical camming mechanism that provides mechanical pressure forcing the heat frame  550  into intimate contact with at least one side of the groove in the chassis wall, ensuring mechanical retention of the heat frame  550  in the chassis unit  510  and acceptable thermal contact between the mating surfaces. The wedgelock  560  mechanism occupies space in the chassis wall and causes it to be thicker than it would otherwise be, increasing the size and weight of the overall chassis  510 . 
     In  FIGS. 6A and 6B , embodiments of the present system as a modular vapor system  600  are illustrated. The depiction in  FIG. 6A  shows a modular vapor chamber  600  that is custom designed to the circuit card  610  and having heat fins  670  to dissipate heat from the electronic components  620 . The electronic components  620  reside on at least one surface of a circuit card  610  that engages the heatframe  625 . The heatframe  625  in this example is designed to conform to the electronic components  620  to be in close proximity to the components  620  in order to efficiently remove heat from the components  620 . The heatframe  625  is configured so the interior component side of the heatframe  625  is sized and shaped about the components  620  for optimal thermal transfer. In one example the circuit card  610  has components  620  on both sides and the heatframe  625  on both sides. 
     Referring to  FIG. 6B , a three dimensional (3D) vapor channel chamber  600  for a circuit card  610  is depicted in a cut away side perspective view. The modular vapor chamber  600  has a component side  680  that in this example is custom designed to conform to the heat generating components  620  and optimize heat transfer by being in close proximity to the components. In one example the component side  680  is configured to conduct heat from at least one surface of the components  620 , in particular those that generate the most heat. In another example, the component side  680  is configured to conduct heat from more than one surface of the components  620  such as the component top surface and one or more side surfaces. In one embodiment, coupled to the component side  680  is a wick structure  650  that helps to direct liquid towards the heated components  620  such as from the receptacle  690  located near the sides. The liquid is converted to vapor by the heated components  620 , wherein the vapor absorbs the heat and moves outwards towards the receptacles  690  where the vapor is converted back into liquid. The receptacles  690  provide for further heat transfer such that heat from the vapor is removed and turns into liquid. 
     In one example the modular vapor assembly  600  is integrally formed with the wick structure  650 , the component side  680  and the upper side  675  with the vapor chamber formed therebetween and having receptacles  690  on both sides. The distance between the component side  680  and the opposing upper side  675  of the heatframe  625  is typically at least 0.5 mm and can be further optimized for the required heat transfer to allow for the liquid to move along the wick surface from the receptacles  690  and for the vapor to return to the receptacles  690 . In this example there are no internal supports. The integral structure includes the mounting features to mate with the circuit card  610 . 
     Referring to  FIG. 7 , a cut away side view perspective shows one embodiment of the present system  700  that includes an integral three dimensional (3D) vapor chamber assembly  725  disposed between two circuit cards  710 . The two circuit cards  710  each include a number of components  720 , wherein the cards can be identical cards having the same components or different components and layout. The vapor chamber assembly  725  includes two component side surfaces  780  with wick structures  750  that form a vapor channel therebetween. In one example the modular vapor assembly  725  is integrally formed with the wick structure  750  and the vapor chamber  725  formed between the two circuit cards  710  have receptacles  790  on both sides. In this example there are no internal supports. Further, the integral structure includes the mounting features to mate with the circuit cards  710 . 
       FIG. 8  is an example of a thin modular vapor chamber  810  with various non-uniform wick structures. In  FIG. 8  the vapor chamber assembly in this embodiment illustrates a thin vapor chamber  810  with the wick structures  830  and/or  840  formed on the component side of the vapor chamber. In one example the wick is a non-uniform wick in a thickness direction  830 . In a further example the wick is a non-uniform wick in the thickness and planar directions  840 . As used herein, the “thickness” refers to dimensions normal to local vapor chamber casing and “planar” refers to dimensions parallel to local vapor chamber casing. 
       FIG. 9A  shows another example of the modular vapor chamber having internal supports.  FIG. 9B  shows the modular vapor chamber embodiment with off-plane wick structures for enhanced support and fluid flow. Referring to  FIGS. 9A and 9B , the modular vapor assembly  900  is depicted showing internal supports or posts  990  that can be used to enhance stiffness and increase the liquid return. In this example, the modular vapor assembly  900  includes the modular vapor chamber  930  with one or more posts  990  that add greater stiffness to the assembly. A further aspect of the supports  990  is to increase the liquid transport by means or capillary action. The circuit card  910  includes electronic components  920  that generate heat that is conveyed to the vapor chamber  930  due to the close proximity to at least one side of the vapor chamber  930 . The heat from the component  920  converts the liquid in the vapor chamber  930  to vapor that is then conveyed to the receptacles  980  and converted to liquid. The liquid is transported by the wick structure  985  that is formed on the component side of the vapor chamber  930 . The posts  990  in this example are integrally formed wick structures that provide further capability to transport the liquid. 
       FIG. 9C  shows another embodiment of the modular vapor chamber embodiment  935  with internal support structures  995  that may also serve as feeder arteries for the working liquid. The components  920  generate heat that is transferred to the vapor chamber  935  which causes evaporation of the liquid in the wick structures  985  and converts the liquid to vapor that travels above the wick structures  985  to the receptacles. The internal support structures  995  in one example resemble bridge trusses or other bio-inspired structures for the vapor chamber case for high strength and low weight. Typically, the thickness of the vapor chamber case is 100-150 microns. However, using support structures such as  995 , the vapor chamber case and the wick features can be made thinner, especially in proximity of the hot components and enhanced fins to decrease the thermal resistance. The wick structure and the support structures in one example are integrally formed by 3D printing or other additive manufacturing processes. 
       FIG. 10A-10G  depicts various embodiments and structural characteristics for the internal supports for the 3D vapor chambers described herein. The internal supports are used, for example, to maintain the shape of the vapor chamber and the dimensions for the vapor and liquid transport. While certain embodiments shown herein depict the vapor chamber having a wick structure on only one side of the vapor chamber,  FIG. 10A  shows the vapor chamber  1005  has two component sides  1010  and two porous wick portions  1020  that are on opposing sides and with a vapor space  1030  therebetween. Such an embodiment would be used when there are circuit cards with components (not shown) coupled on either side and conductively coupled to the vapor chamber component sides  1010  and with the vapor space  1030  disposed therebetween. 
     The vapor chamber in a further embodiment includes internal supports that are fabricated via the 3D printing process in numerous designs, number, shapes and sizes such as shown in  FIG. 10B-10G . In one example, the supports comprise one or more solid internal support structures with braces  1045  that can be perpendicular within the vapor chamber case or angled. Another example includes having solid internal support structures  1055  that are curved or have a curved portion. In other embodiments, the internal supports  1065 ,  1075  include liquid feeder arteries to facilitate the liquid transport. For example, the internal supports can be porous structures that can be straight  1065  or curved  1075 . Operationally, the supports should be designed such that the vapor chambers can withstand atmospheric pressure at any point of time. Specifically, the vapor chambers should neither break down under high atmospheric pressure nor implode under low atmospheric pressure. Further, the supports should be designed such that the vapor chambers do not affect the overall desired stiffness or rigidity of the chassis assembly. 
     Various shapes for solid internal supports are shown in  FIG. 10B-10D . Referring to  FIG. 10B , the internal support and brace  1045  are straight structures that are internally coupled between the opposite surfaces of the vapor chamber  1040 . In  FIG. 10C , the solid internal support structures are angled or curved  1055 .  FIG. 10D  shows an internal support structure  1050  without the brace. The internal support in one example is positioned proximate the heated component(s), sometimes referred to as the pocket. In another example shown in  FIG. 10  E, the solid internal support structure includes a vascular or root system for efficient spreading of force/loads and/or liquid. 
       FIGS. 10F and 10G  depict internal support and liquid feeder arteries. The support structures in these examples are porous and allow for liquid and/or air to pass through the structure within the vapor chamber.  FIG. 10F  shows straight porous internal support structures while  FIG. 10G  illustrates angled or curved internal support structures. 
     The number of the internal supports may be dependent upon the design criteria and factors include the required support for the vapor chamber case and the thermal properties of the various supports. The size and shape for the internal supports also depends upon the design criteria and thermal/mechanical requirements. Whenever the supports are desired only for lending structural strength to the vapor chamber, solid supports are used. On the other hand, when the supports are desired additionally for enhanced cooling of the electronic components, wick structure is used. 
     According to one embodiment, there are various wick structures that are employed with the vapor chamber assemblies. In one example the wick structures are formed from additive manufacturing processes such as 3D printing. The wick structures can be uniform or non-uniform wick structures in multiple directions. According to one embodiment, the wick structures are deployed within the internal space of the vapor chamber and also serve as internal support structures. 
       FIG. 11A-D  depicts several examples of the non-uniform wick structure. Specifically,  FIG. 11A  shows a perspective view of a non-uniform wick structure  1140  in the thickness direction (z direction). In  FIG. 11B , the non-uniform wick structure  1150  in the thickness direction shows the pores  1160 ,  1165  which in this example has larger size pores  1160  proximate the component side of the vapor chamber for transporting liquid. The pores  1165  on the vapor side are of a smaller pore size and transport the vapor to receptacles in the vapor chamber. The pores in these examples are round or curved spaces, wherein the curved wick structure allows for 3D printing in any orientation that allows for non-planar vapor chambers. 
     Referring to  FIG. 11C , the non-uniform wick structure  1170  is shown in the thickness and in-plane direction (x-y direction). In  FIG. 11D  the non-uniform wick structure  1180  shows further examples of the larger pores  1190  on the liquid transport side and smaller pores  1195  on the vapor transport side. 
     The structures shown in  FIG. 11A-11D  are one example of a class of geometries by 3D printing in almost any orientation and straightforward transitions from larger to smaller pores and vice-versa. The one example shown is for circular cylindrical “bore-holes” along the three axes. It is to be noted that, apart from the cut planes, there are no straight surfaces in this pore-scale geometry. This attribute is used for build-orientation of independent non-uniform wick structures. The figures show non-uniform wick structures built on a planar surface, but a further embodiment provides for deforming these wick structures to follow a curved 3D surface that in one example has a large radius of curvature relative to the thickness of the wick structure layer. These representative wick structures  1140 ,  1150 ,  1170 ,  1180  that are 3D printed can be built in numerous orientations, unlike posts or braces, because it is built with curves or arc portions. For example, large overhangs cannot be effectively printed without support structures, and these wick structures allow for internal build supports that can be integrated with the inner surfaces, namely the vapor side and the casing side of the vapor chamber. 
       FIG. 12A-12B  show modular vapor chamber embodiments with integrated hollow fins. As shown in  FIGS. 12A and 12B , the modular vapor chamber  1210  is shown according to yet another example. In this example, the vapor chamber fins  1220  are hollow vapor chamber fins, thereby permitting a greater surface area for heat transport. The large condenser surface area associated with the fins  1220  dramatically decreases the contribution of the condensation thermal resistance (temperature drop) in the thermal resistance chain. In another embodiment, the hollow fins may be replaced by other heat exchange mechanisms such as an integral fluid heat exchanger or a cold plate interface coupled to the system. 
       FIG. 13  shows a thermal management system for electronics  1300  as a stacked assembly, including several vapor chambers assemblies  1330 ,  1340 , and  1350  with or without circuit cards and assembled along with chassis case portions such as an upper and lower chassis mount to form the chassis  1300 . Referring again to  FIG. 13 , the modular stacked assembly  1300  includes multiple modular vapor chamber assemblies  1310 ,  1330 ,  1340 , and  1350 , each configured to be stacked together to form the larger unit. In one example the circuit card assemblies  1320  are coupled to respective modular vapor chamber assemblies which are then combined into the chassis  1300 . As previously described the circuit cards can be coupled to the vapor chamber assemblies such as by friction fit or other securing mechanisms. The modular vapor chamber assembly units  1330 ,  1340 , and  1350  including any corresponding circuit cards  1320  are secured to each other by fastening mechanisms such as bolts. There can be any number of modular vapor chamber assemblies and circuit cards stacked together and secured as a unitary assembly. The outermost portions of the modular stacked assembly may or may not be coupled to circuit cards and may be used for packaging and securing the assemblies and circuit cards. 
       FIG. 14A-D  shows an example of forming the stacked modular vapor chambers and corresponding circuit cards assembled into an avionics system  1400  with corresponding input output modules  1410 . Referring to  FIG. 14A , a further depiction of the stacked modular vapor chambers is illustrated with circuit cards  1440  coupled to both sides of a vapor chamber  1430  forming a vapor chamber sandwich  1450 . The sandwich  1450  shows the vapor chamber  1430  disposed between the electronic circuit cards  1440 . As shown in  FIG. 14B , the modular vapor chamber sandwich  1450  can be stacked with other modular vapor chamber sandwich units and secured to each other to form a modular electronic assembly  1420 . In  FIG. 14C , the modular electronic assembly  1420  is electrically coupled to a backplane or input/output modules  1410 , forming the final assembly  1400  as depicted in  FIG. 14D . 
     As detailed herein, one of the unique attributes of the present system is a 3D vapor chamber having non-uniform wick structures. A further aspect is the collection of individual vapor chambers to form a modular chassis, wherein the circuit cards are aligned and the vapor chambers are stacked to reduce the EMI by isolating the individual vapor chambers. 
     Other features of the modular chassis stack relate to the mechanical architecture. For example, the ability to configure a chassis with a variable number of ‘slots’ depending on the application, the use of an integral base plate/air mover (such as synthetic jets or fan). A further aspect employs a separable I/O module that is customized to the application and environmental requirements. 
     For example,  FIG. 15  shows an embodiment of the thermal management system for an electronic assembly  1500  with enhanced convection using synthetic jets  1550  located in at least one of the lower tray  1540  and upper tray  1530  of electronic assembly  1500 . In this example the upper tray has fins and considerable access to the external environment for increased air flow. The synthetic jets  1550  are added to augment the airflow and enhance free convection. The I/O connectors  1510 ,  1520  in this example include cut-outs for external air flow such as from turbines or fans. 
       FIG. 16A-C  shows a modular vapor chamber  1600  in another embodiment that is integrated into an airframe  1640 . Referring to  FIG. 16A , the individual vapor chambers  1610 ,  1620  and  1630  in the shapes and with structural supports for the intended application are shown along with the exterior heat fins.  FIG. 16B  illustrates the modular vapor chambers assembled into a circular unitary thermal management assembly  1600 .  FIG. 16C  shows the thermal management assembly  1600  configured to enable various applications such as deployment in an unmanned aerial vehicle  1640 . 
       FIG. 17A-C  shows thermal management assemblies with different stacking configurations of the modular vapor chambers. Referring to  FIG. 17A , there are several modular vapor chambers  1710 ,  1720 ,  1730  and  1740  with circuit cards coupled to the chambers that are shaped and sized to form the thermal management assembly  1750  of  FIG. 17B . The circuit cards for the modular vapor chambers  1720 ,  1730  are stacked along the length of the thermal management assembly  1750  with exterior fins encircling the assembly  1750  for dissipating the heat.  FIG. 17C  shows a thermal management assembly  1700  with modular vapor chambers having circuit cards radially disposed in a circular form allowing for heat dissipation on all the exterior surfaces. 
       FIG. 18  shows a thermal management system  1800  as a planar assembly such as circular, square or rectangular, including two or more partitioned vapor chambers  1810 ,  1820 ,  1830  and  1840  planarly assembled to form the chassis of the system  1800 . Referring again to  FIG. 18 , the assembled thermal management system  1800  has a heatframe that includes a number of partitioned modules/vapor chambers  1810 ,  1820 ,  1830  and  1840  from a planar perspective. In one example, a typical heatframe unit is replaced by several vapor chambers  1810 ,  1820 ,  1830  and  1840  arranged in a planar manner coupling the vapor chambers with respective circuit cards and assembled to provide thermal and structural support to the thermal management system  1800 . In this configuration, even if one of the vapor chambers  1810 ,  1820 ,  1830  and  1840  is punctured, the other vapor chambers keep supporting and cooling the electronics. Such a system structure supports redundancy and critical mission initiatives. 
       FIG. 19A-C  shows various surface geometries of the 3D vapor chamber to envelop circuit electronics including conformal, reverse-conformal and custom-conformal configurations. In one example, the distance or gap between the electronic components and the component side of the vapor chamber is 5-12 microns. In  FIG. 19A , the thermal management structure  1910  is customized such that the component surface geometry of the 3D vapor chamber  1915  is approximately conformal to the circuit card  1920  and components  1925  in maintaining the vapor chamber in close proximity to the components  1925  for efficient heat transfer. In one example the component side of the vapor chamber provide conductive coupling on the top surface of the components and one or more sides of the components. 
     In  FIG. 19B , the thermal management structure  1940  is customized such that the surface side of the 3D vapor chamber  1945  is reverse-conformal to the circuit card  1950  and components  1955  in keeping with design criteria for integration in the chassis with other cards. In such configurations, the vapor chamber case lifts down and reaches out to the electronic components  1955 . This arrangement in certain applications aids in capillary transport of the liquids through the wick structures. 
     In one further example shown in  FIG. 19C , the thermal management structure  1960  is customized such that the surface side of the 3D vapor chamber  1965  is custom-fit to the circuit card  1970  and components  1975  to increase the heat transfer and optimize the cross section coverage of the components  1975  by the vapor chamber  1965  and particularly the components that generate the most heat. 
     In each of these examples of the thermal management systems  1910 ,  1940  and  1960 , the ability to customize the surface geometry of the 3D vapor chambers  1915 ,  1945  and  1965  to the circuit card components optimizes the thermal management and allows for higher density of components and components with greater temperatures. The circuit cards  1920 ,  1950  and  1970  and components  1925 ,  1955  and  1975  in one example have a standard layout such that multiple boards can be accommodated by a single heatframe design. In addition, the integral design of corresponding mounting features (not shown) into their respective heatframes (not shown) allows for improved mating with the boards  1920 ,  1950  and  1970 , thereby eliminating the conventional wedgelock. Furthermore, the ability to integrally design the fins (not shown) and chassis (not shown) to the heatframes (not shown) allows for customization for the intended heat dissipation for specific circuit cards and components. A result of the thermal management structures  1910 ,  1940  and  1960  that allows for smaller heatframes when thermal characteristics are not high and for larger heatframes and fins for components that generate more heat. According to one example, the 3D vapor chambers  1915 ,  1945  and  1965  in the integral thermal management structures  1910 ,  1940  and  1960  are made using additive manufacturing technology such as 3D printing. 
       FIG. 20  shows an alternative configuration of the compartmentalization of the vapor chamber in a horizontal plane. Referring to  FIG. 20 , such a thermal management system  2000  includes a larger, compartmentalized vapor chamber  2010 . The bigger vapor chamber  2010  is divided into several compartments  2020 ,  2030 ,  2040 ,  2050  and so on using partitions  2060 ,  2070  and so on. The compartments  2020 ,  2030 ,  2040 ,  2050  may be equal or unequal in size depending on the design purpose. Further, each of the compartments  2020 ,  2030 ,  2040 ,  2050  may be designed to serve/cool the specific electronics coupled to the respective vapor chambers. The compartmentalization of the vapor chambers allows at least some of the vapor chambers to function if one or more compartments are compromised. At the same time, the compartments  2020 ,  2030 ,  2040 ,  2050  share common boundary walls and are unified by the structural integrity and rigidity of the bigger vapor chamber  2010 . 
       FIG. 21A-F  are other examples of the modular vapor chamber with compliant wall and wick structures. Referring to  FIG. 21A , the modular vapor chamber  2100  includes wall (vapor chamber case)  2110  and wick structures  2130  and  2140 . As for the wall  2110 , it conforms to the top of the electronic components represented by an angled rectangle  2120 . The rectangle  2120  is typically angled/slanted because the electronic components are “tipped” relative to PCB due to manufacturing tolerances and thus may have a non-horizontal top-profile. Operationally, the vapor chamber case  2110  needs to adapt to the angled top-profile and at least that area of the vapor chamber case wall is made compliant. Exaggerated representation of ridges  2115  in the vapor chamber case  2110  enable the desired compliance without plastic deformation. In other examples, in addition to the wall  2110 , the wick structures  2140  associated with the compliant part of the wall  2110  are also made compliant. Referring to  FIG. 21A  once more,  2130  refers to the plurality of wick structures that are rigid/non-compliant and  2140  to the plurality of wick structures that are compliant. By construction, the wick structures in area  2130  are typically connected to each other internally whereas the wick structures in area  2140  are unconnected. There are various ways these complaint parts of the vapor chamber case  2110  and the wick structures  2140  can be permuted and combined as described below. 
       FIG. 21B  represents an example of the modular vapor chamber with wick structures  2140  having uniform pore size all through and the structure posts  2145  positioned at relatively uniform distance from each other.  FIG. 21C  represents an example of the modular vapor chamber with wick structures  2140  having small pores near the top, large pores near the vapor chamber case. In such a configuration, the structure posts  2155  are positioned such that there are relatively smaller gaps through the structures at the top and larger gaps at the bottom.  FIG. 21D  represents an example of the modular vapor chamber with wick structures  2140  having large pores near top and small pores near the vapor chamber case. In such a configuration, the structure posts  2165  are positioned such that there are relatively larger gaps through the structures at the top and smaller gaps at the bottom. Further, referring to  FIG. 21E , in the vapor chamber case  2170 , compliant and unconnected wick structures  2175  are localized only to the component area. Furthermore, referring to  FIG. 21F , unconnected wick structures line the whole vapor chamber case  2180  including the unconnected wick structures  2185  making the whole vapor chamber case  2180  compliant. 
     In operation, according to one embodiment, the thermal management system includes a vapor chamber having a vapor chamber case with a component side and an opposing vapor side, internal wick structures disposed on at least the component side, internal working fluid, and additional internal support structures. The system in one example is made as a single unitary structure, wherein the case, wick structures, and internal support structures are integrally formed during formation by 3D printing or other Additive Manufacturing process. The working fluid is typically added to the internal structure until the wick is saturated, then the outer case is sealed. This filling process introduces the working fluid into the case. In certain examples, some of the fluid will be in the liquid state, while some may be in the vapor state. When one part of the thermal management system is thermally connected to a cold reservoir, and another part to a heat source such as electronic components, heat is conducted from the heat source, through adjacent vessel envelope wall, and into the adjacent wick structure which is saturated with liquid. This addition of heat causes the liquid phase of the working fluid to boil into the vapor phase within the vessel. The process is similar to that of an operating heat pipe. 
     In one embodiment, the wick structure is engineered such that very fine features are present near the heat source, thus increasing the strength of the capillary force. However, the fine structures have a high fluid resistance. Therefore, the wick structure between the cold reservoir and heat source is engineered as a coarse structure with smooth features that minimize the fluid resistance. The fine and coarse structures are engineered to maximize the rate of fluid transport, and thus the optimal amount of heat can be transferred. 
     In another embodiment, the wick structure between the cold reservoir and heat source includes finer structures close to the vapor gap, and coarser structures close to the vessel wall. The finer structures prevent the liquid phase of the working fluid passing through the wick from interacting with the vapor phase of the working fluid passing through the vapor space in the opposite direction. The coarser structures near the vessel wall allow the liquid to pass through the wick with minimal pressure drop. In one example, the thermal path from the electronic component to the cold reservoir is enhanced by transporting the working fluid (any mix of liquid and vapor) contained within the vapor chamber by means of capillary action through any combination of the wick structure and the internal support structure to dissipate heat from the heatframe. 
     The assembly in one example enhances the thermal capability and the entire structure is fabricated using additive manufacturing technology to allow for complex geometries that are conformal to the components. Although the figures indicate “pockets” for the hot components, in one exemplary embodiment the vapor chamber case “conforms” to the hot components via “pockets”, “planes”, or “posts”, as needed. According to one example the wick structure is non-uniform wick oriented in the thickness direction. In another example the wick structure is a non-uniform wick having a thickness and planar directions. 
     In a thermal management system for circuit cards in a chassis, the components have parasitic heat losses that thermally coupled to the device. These losses are removed in order to maintain a proper operating environment for the electronics. In one example the present system moves the heat from the component such as to cold sink reservoirs, thus maintaining the component at low temperature. 
     The present systems reduce the thermal resistance of this thermal path while maintaining or lowering the weight of the system. Certain technical advantages of the present system include lower weight, lower thermal resistance, unlimited shapes and form factors, unitary single piece construction. Commercial advantages include custom designs, lower price, and more capability and greater thermal elements in the same volume. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments, they are by no means limiting and are merely exemplary. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. 
     Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.