Patent Publication Number: US-2023134978-A1

Title: Circuit card assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application Ser. No. 63/274,557, titled “CIRCUIT CARD ASSEMBLIES,” filed Nov. 2, 2021, incorporated herein by reference in its entirety and for all purposes. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to circuit card assemblies, and more particularly, circuit card assemblies comprising thermal management systems and methods, for management of transient thermal performance issues via use of integrated phase change modules. 
     BACKGROUND 
     Operation of electronic devices or assemblies requires proper thermal management and maintenance of electronic components (e.g., integrated circuits, circuit boards, circuit modules, processors, memory, disk drives, etc.). The electronic components typically generate heat during operation or are comprised of electronic components that generate heat. As the heat from the electronic device(s) builds, the electronic device or assembly may suffer from overheating, operational failure, degradation, other forms of thermal or mechanical stresses, or combinations thereof. 
     Such thermal stresses may be especially problematic or unmanageable for systems requiring (i) multiple electronic components, (ii) maximum processing or computing power, and/or (iii) specialized or harsh operating environments (e.g. aerospace, defense, extreme temperatures, high vibration, high altitudes, abrupt high-G/acceleration, hypersonic speed, etc.). These systems may suffer from transient thermal performance issues related to temperature fluctuations, intermittent power peaks, and temporary loss of cooling. Some examples include (1) exceeding junction temperature limits, resulting in significant computing performance (down-clocking or derating), (2) die temperature spikes/fluctuations, (3) non-functional heat pipe/liquid cooling (e.g. dryout), or a combination thereof. Failure to mitigate or resolve these transient thermal performance issues can lead to an inability to maintain electronic components in safe and reliable functioning conditions, which may cause or contribute to failures or performance degradations during normal or steady-state system operation. 
     Thus, there remains a need to provide alternative or improved circuit card assemblies having thermal management systems and methods that can provide more efficient cooling and/or heat dissipation, while minimizing temperature fluctuations during phase transition and/or mitigating or preventing decline of thermal performance during normal steady-state operating conditions. 
     SUMMARY 
     Aspects of the present invention are directed to circuit card assemblies comprising thermal management systems and methods. 
     In one exemplary aspect, there is provided a thermal management system for a heat source comprising at least one electronic component. The thermal management system comprises one or more phase change modules comprising phase change material for distributing and storing heat; a metal frame in thermal contact with the at least one electronic component and having at least one opening for receiving the one or more phase change modules; and a heat transfer apparatus in thermal contact with one or more of the at least one electronic component and the metal frame, the heat transfer apparatus providing a first heat transfer path. 
     In another exemplary aspect, there is provided a circuit card assembly. The circuit card assembly comprises a circuit board having at least one electronic component that generates heat; one or more phase change modules comprising phase change materials for distributing and storing heat; a metal frame coupled to the circuit board and in thermal contact with the at least one electronic component, the metal frame further having at least one opening for receiving the one or more phase change modules; and a heat transfer apparatus in thermal contact with one or more of the at least one electronic component and the metal frame, the heat transfer apparatus providing a first heat transfer path. 
     In another exemplary aspect, there is provided a method of manufacturing a circuit card assembly comprising at least one electronic component that generates heat. The method comprises (a) forming at least one opening in a metal frame for receiving the at least one electronic component; (b) forming at least one opening in the metal frame for receiving one or more phase change modules, the one or more phase change modules comprising phase change material for distributing and storing heat; (c) filling the at least one opening with the one or more phase change modules; and (d) attaching a metal layer over the at least one opening for containing the one or more phase change modules within the at least one opening of the metal frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings, with like elements having the same reference numerals. When a plurality of similar elements are present, a single reference numeral may be assigned to the plurality of similar elements with a small letter designation referring to specific elements. When referring to the elements collectively or to a non-specific one or more of the elements, the small letter designation may be omitted. In addition, according to common practice, the various features of the drawings are not drawn to scale unless otherwise indicated, and the dimensions of the various features may be expanded or reduced for clarity. Included in the drawings are the following figures: 
         FIG.  1    depicts an exemplary circuit card assembly. 
         FIG.  2    is an exploded view of the circuit card assembly shown in  FIG.  1     
         FIG.  3    depicts a portion of the circuit card assembly shown in  FIG.  1   . 
         FIGS.  4 A- 4 D  depict the stages formed from an exemplary method of manufacturing the portion of the circuit card assembly shown in  FIG.  3   . 
         FIG.  5    is a flow diagram showing the method steps used in stages shown in  FIGS.  4 A- 4 D . 
         FIG.  6 A  depicts an exemplary thermal management system, showing an exemplary heat transfer apparatus providing a heat transfer path during a period of reduced heat dissipation or cooling. 
         FIG.  6 B  depicts the thermal management system shown in  FIG.  6 A , showing another heat transfer path during a period of standard steady-state heat dissipation or cooling. 
         FIG.  7 A- 7 B  depict another embodiment of an exemplary heat transfer apparatus. 
         FIG.  8    depicts another embodiment of an exemplary heat transfer apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     The thermal management systems disclosed herein are usable for electronic components associated with circuit card assemblies (CCA), including for CCA used in specialized or harsh operating environments (e.g. aerospace, defense, extreme temperatures, high vibration, high altitudes, abrupt high-G/acceleration, hypersonic speed, etc.). While the thermal management systems are described herein with respect to electronic components associated with circuit card assemblies (CCA), it will be understood that the invention is not so limited. To the contrary, aspects of the present invention are usable in applications or products in which it is desirable to manage or stabilize the thermal energy (heat or temperature) of electronic components. 
     As used herein, the term “circuit card assembly” comprises electronic components or other electronics units that generate heat (of varying degrees) or require heat dissipation or cooling. In an exemplary embodiment, a circuit card assembly may comprise semiconductor products, such as field-programmable gate array (FPGA) sets, central processing units (CPU), and graphics processing units (GPU). In another exemplary embodiment, a circuit card assembly may comprise a circuit board having high power semiconductor products, processors, or other electrical components with the circuit board coupled to a heat frame. The term “heat frame” may include any electronic housing, unit, housing, frame, rack, compartment adapted to house, contain, or enclose (partially or entirely; fixed or removable) circuit boards and/or electronic components. 
     With reference to the drawings,  FIGS.  1  and  2    illustrate an exemplary circuit card assembly, such as a circuit card assembly  100 . In general, circuit card assembly  100  includes at least one electronic component  104 , a heat transfer apparatus  106 , and one or more phase change modules  108 . In an exemplary embodiment, circuit card assembly  100  comprises a circuit board  102  having at least one component that generates heat, such as electronic component  104 . Coupled to the circuit board  102  is a metal frame  110 , which is positioned in circuit card assembly  100 , such that metal frame  110  is in thermal contact with electronic component  104 . To this end, metal frame  110  may have a size, shape, and/or surface contours configured to correspond to one or more components of circuit card assembly  100 , such as heat transfer apparatus  106  and electronic component  104 . Further, metal frame  110  may comprise metal having a satisfactory heat or thermal conductivity, such as aluminum, copper, or alloys thereof (e.g. aluminum or copper alloys). 
     Metal frame  110  further includes at least one opening  112  (e.g. a pocket) for receiving one or more phase change modules  108 . Phase change modules  108  comprise phase change material for distributing and storing heat generated by electronic component  104 . In an exemplary embodiment, phase change modules  108  are configured for distributing and storing heat during a period of reduced heat dissipation or cooling. This period of reduced heat dissipation or cooling may be due to operating conditions such as high altitude, high acceleration, hypersonic speed, intermittent computing power, or a combination thereof. 
     To facilitate and/or manage this distribution and/or storage of heat from electronic component  104 , circuit card assembly  100  includes heat transfer apparatus  106 . In an exemplary embodiment, heat transfer apparatus  106  is comprised of at least one heat pipe  118  ( FIG.  2   ). Heat pipe  118  is positioned relative to electronic component  104  and metal frame  110 , such that heat pipe  118  is in thermal contact with one or more of electronic components  104  and metal frame  110 . In this configuration, heat pipe  118  provides a heat transfer path  114  for the heat generated by electronic component  104 . In an exemplary embodiment, heat transfer path  114  is provided during the period of reduced heat dissipation or cooling. Further, heat transfer path  114  may be different from another heat transfer path  116  during a period of standard/normal steady-state heat dissipation or cooling. 
     In another exemplary embodiment, heat transfer apparatus  106  is comprised of at least one heat spreader  142 , such as a metal (e.g. copper or copper alloy) plate ( FIG.  2   ). Heat spreader  142  is positioned relative to electronic component  104  and metal frame  110 , such that heat spreader  142  is in thermal contact with one or more electronic components  104  and metal frame  110 . In this configuration, heat spreader  142  provides a heat transfer path  144  for the heat generated by the CCA or components thereof, such as electronic component  104 . In an exemplary embodiment, heat transfer path  144  is provided during the period of reduced heat dissipation or cooling. Further, heat transfer path  144  may be different from another heat transfer path during a period of standard/normal steady-state heat dissipation or cooling, such as heat transfer path  116 . 
     In yet another exemplary embodiment, heat spreader  142  is additionally or optionally comprised of an oscillating heat pipe  136  ( FIG.  8   ) embedded therein. At least one oscillating heat pipe  136  is positioned relative to one or more of electronic component  104  and metal frame  110 , such that oscillating heat pipe  136  is in thermal contact with one or more of electronic components  104  and metal frame  110 . In this configuration, oscillating heat pipe  136  provides a heat transfer path, such as heat transfer path  144 , for the heat generated by electronic component  104 . In an exemplary embodiment, the heat transfer path  144  is provided during the period of reduced heat dissipation or cooling. Further, the heat transfer path  144  may be different from another heat transfer path during a period of standard/normal steady-state heat dissipation or cooling, such as heat transfer path  116 . 
     Referring now to  FIGS.  2  and  3   , an exemplary heat pipe  118  is disposed adjacent to metal frame  110 , such that phase change modules  108  embedded in metal frame  110  may be disposed above (as shown by arrow  140   a  in  FIG.  3   ), below (as shown by arrow  140   b  in  FIG.  3   ), or on one or more sides (as shown by arrow  140   c ) of heat pipe  118 . Desirably, at least one opening or pocket  112  of metal frame  110  may be defined in metal frame  110  Opening or pocket  112  is configured to receive a respective phase change module  108 , such that opening or pocket  112  has a size and shape sufficient to receive a respective phase change module  108 . 
     Still further, in this configuration, phase change modules  108  may be in thermal contact with electronic component  104  because as is illustrated in  FIG.  3   , phase change modules  108  embedded in metal frame  110  may be disposed above (as shown by arrow  140   a  in  FIG.  3   ), below (as shown by arrow  140   b  in  FIG.  3   ), and/or on one or more sides (as shown by arrow  140   c  in  FIG.  3   ) of at least one pocket  124 . At least one pocket  124  of metal frame  110  is configured for respectively receiving a component of circuit card assembly  100  that generates heat, such as electronic component  104 . 
     Desirably, embedding phase change modules  108  within a portion of metal frame  110 , such that phase change modules  108  are in thermal contact with one or more of metal frame  110  and electronic component  104 , as described above, allows for improved management of transient thermal performance issues (as will be discussed below). Further, embedding a phase change material like that used in phase change modules  108  within a portion of metal frame  110  does not interfere with operation of heat pipe  118  (which provides heat transfer path  116 ) during normal steady-state conditions. 
     Turning now to  FIGS.  4 A- 4 D and  5   , an exemplary method of manufacturing a portion of circuit card assembly  100 , such as method  500 , is disclosed. Details of method  500  are set forth below with respect to the elements of exemplary circuit card assembly  100 . In particular, method  500  comprises steps for embedding phase change modules  108  within metal frame  110 , as was described above. 
     Specifically, as illustrated in  FIGS.  4 A- 4 D  and the flow diagram in  FIG.  5   , method  500  comprises a step  510  of forming at least one opening in a metal frame, such as opening or pocket  124  in metal frame  110 , for receiving electronic component  104 . Still further, in an exemplary embodiment, method  500  also includes a step of forming at least one groove  126  ( FIG.  4 A ) in metal frame  110  for contacting a surface of a heat transfer apparatus, such as heat transfer apparatus  106 . 
     Groove  126  is formed, such that heat transfer apparatus  106  comprising heat pipe  118  is in thermal contact with electronic components  104  and/or metal frame  110 . Specifically, groove  126  is formed, such that heat pipe  118  is disposed at least partially within groove  126 . In this configuration, heat transfer apparatus  106  comprising heat pipe  118  provides a first heat transfer path, such as path  114 . In an exemplary embodiment, path  114  is used during a period of reduced heat dissipation or cooling. Additionally or optionally, first heat transfer path  114  is different from a second heat transfer path, such as path  116  (as shown in  FIG.  6 B ), which is provided during a period of standard/normal steady-state heat dissipation or cooling. 
     The heat transfer path during steady-state operation, such as path  116 , provides a generally higher thermal conduction path through heat pipe  118 , relative to other components of circuit card assembly  100 , for example. In general, heat pipes are two-phase heat transfer devices that utilize evaporation and condensation of working fluid to outperform any solid/metal heat conduction. For example, heat pipes can usually achieve higher thermal conductivity than copper. Accordingly, heat pipe  118 , through which path  116  is provided, performs essentially as a thermal superconductor, such that negligible heat is transferred along other thermal paths. Thus, heat pipe  118  is the dominant/primary heat transfer path during normal steady-state operation. 
     However, during a period of reduced/loss of cooling or heat dissipation, heat pipe  118  may become less effective due to condensation loss or dryout, for example. In an exemplary embodiment, this period of reduced heat dissipation or cooling may be due to operating conditions such as high altitude, high gravitational force (G-force), high acceleration, hypersonic speed, intermittent peaks of computing power usage, or a combination thereof. During this period of reduced heat dissipation or cooling, temperature starts to increase and heat pipe  118 , through which path  116  is provided, becomes less effective. Thus, in such an embodiment, heat pipe  118  becomes a secondary heat transfer path (i.e. no longer the dominant or primary heat transfer path). Accordingly, a heat transfer or thermal path that is different from path  116 , such as heat path  114 , becomes the dominant or primary heat transfer path. Phase change modules  108  are desirably located along heat transfer path  114  in order to distribute and/or store heat. Thus, path  114  becomes the dominant or primary heat transfer path at predetermined melting points when phase change modules  108  start to absorb heat, while maintaining their temperature constant for a certain period of time. In this way, temperature fluctuations during phase transitions are minimized and/or declines of thermal performance during steady-state conditions are mitigated or prevented, such that circuit card assemblies  100  comprising electronic component  104  can be maintained in reliable working condition. 
     As illustrated in  FIG.  4 B  and the flow diagram in  FIG.  5   , method  500  also includes a step  520  of forming at least one opening  112  in metal frame  110  for receiving phase change modules  108 . In an exemplary embodiment of circuit card assembly  100 , opening  112  of metal frame  110  comprises a T-shaped pocket. The opening  112  may include a pair of ledges  128  to receive a portion of metal layer  130 . 
     As stated above, phase change modules  108  comprise phase change material for distributing and storing heat from electronic component  104 . In an exemplary embodiment, phase change modules  108  are configured to distribute and store heat away from at least electronic component  104  during the period of reduced heat dissipation or cooling. 
     As illustrated in  FIG.  4 C  and the flow diagram in  FIG.  5   , method  500  further comprises a step  530  of filling opening or pocket  112  with phase change modules  108 . Pocket  112  is filled with phase change modules  108 , such that embedded phase change modules  108  in metal frame  110  are disposed above (as shown by arrow  140   a  in  FIG.  3   ), below (as shown by arrow  140   b  in  FIG.  3   ), and/or on one or more sides (as shown by arrow  140   c  in  FIG.  3   ) of heat pipe  118 . 
     As shown in  FIG.  4 D  and the flow diagram in  FIG.  5   , method  500  also includes a step  540  of attaching metal layer  130  over pocket  112  for containing phase change modules  108  within pocket  112  of metal frame  110 . Specifically, metal layer  130  may act as a lid or cover configured for engagement with ledges  128  of pocket  112  ( FIG.  4 B ). Still further, in an exemplary embodiment, metal layer  130  may comprise copper and may be disposed over pocket  112  of metal frame  110  by soldering, brazing, welding or thermal epoxy. 
     Referring now to  FIGS.  6 A- 6 B , as circuit card assembly  100  becomes heated or undergoes other forms of thermal stresses, circuit card assembly  100  may require management of the thermal performance to remain within operating parameters/specifications. In an exemplary embodiment, exemplary thermal management system  200  comprising phase change modules  108  that are integrated within metal frame  110  and/or heat transfer apparatus  106 , serves to perform that management function. Thermal management system  200  is discussed further below and with reference to the components of circuit card assembly  100 . 
     In an exemplary embodiment, thermal management system  200  is configured to manage a heat source comprising at least one electronic component, such as electronic component  104 . Thermal management system  200  comprises phase change modules, such as phase change modules  108  discussed above. Phase change modules  108  comprise phase change material for distributing and/or storing heat from electronic component  104 . Metal frame, such as metal frame  110  is in thermal contact with electronic component  104 . Metal frame  110  includes at least one opening, such as pocket  112 , for receiving phase change modules  108 . A heat transfer apparatus, such as heat transfer apparatus  106 , is also in thermal contact with electronic component  104  and/or metal frame  110 . Heat transfer apparatus  106  is configured for providing a first heat transfer path. Additional details of the individual components of thermal management system  200  and operation thereof are discussed below. 
     Metal frame  110  may comprise a metal having a satisfactory heat or thermal conductivity, such as aluminum, copper, or alloys thereof (e.g. aluminum or copper alloys). In an exemplary embodiment, opening  112  of metal frame  110  may comprise a pocket, such as a T-shaped pocket having a pair of ledges  128  (as shown in  FIG.  4 B ) to receive a lid or cover, such as metal layer  130 . Metal layer  130  may comprise metal, such as copper, and may be disposed over at least one opening  112  by soldering, brazing, welding or thermal epoxy. 
     Phase change modules  108  is configured for distributing and/or storing heat during a period of reduced heat dissipation or cooling. This period of reduced heat dissipation or cooling may arise because of or in relation to operating conditions comprising high altitude, high acceleration, hypersonic speed, intermittent computing power, or a combination thereof. Such operating conditions may lead to transient thermal issues that require management of heat from electronic component  104  via thermal management system  200 . 
     To achieve this, thermal management system  200  includes heat pipe  118 . Heat pipe  118  is disposed adjacent metal frame  110 , such that phase change modules  108  embedded in metal frame  110  are disposed above (as shown by arrow  140   a  in  FIG.  3   ), below (as shown by arrow  140   b  in  FIG.  3   ), and/or on one or more sides (as shown by arrow  140   c  in  FIG.  3   ) of heat pipe  118 . In an exemplary embodiment, heat pipe  118  is configured to provide a first heat transfer path  114  during the period of reduced heat dissipation or cooling ( FIG.  6 A ). Further, the first heat transfer path  114  may be different from a second heat transfer path  116 , which is provided by heat transfer apparatus  106  during a period of standard steady-state heat dissipation or cooling ( FIG.  6 B ). Details of the first transfer path  114  and second transfer path  116  are now discussed below. 
     As shown in  FIG.  6 A , circuit card assembly  100  includes electronic component  104 . Electronic component  104  generates heat, thereby requiring thermal management to reduce or eliminate the risk of operational failure and/or other undesirable effects of thermal stresses. The cooling of or dissipation of this heat from electronic component  104  during the period of reduced heat dissipation or cooling is indicated by first heat transfer path  114 . As explained above, cooling or heat dissipation of electronic component  104  is provided by path  114  because heat pipe  118  provides generally higher thermal conductivity relative to other components of circuit card assembly  100 . Such path  114  is indirectly or directly determined by at least the position and configuration of phase change modules  108  relative to one or more of metal frame  110 , electronic component  104 , and heat apparatus  106 . In the exemplary embodiment shown in  FIG.  6 A , heat from electronic component  104  is distributed and/or stored (via path  114 ) through heat pipe  118  and through metal frame  110  having embedded phase change modules  108 . 
     In contrast, as illustrated in  FIG.  6 B , cooling or heat dissipation of electronic component  104  during the period of standard/normal steady-state heat dissipation or cooling is indicated by second heat transfer path  116 . Second heat transfer path  116  is different from first heat transfer path  114 , at least because heat transfer path  116  indicates heat from electronic component  104  is distributed/dissipated or stored through heat pipe  118  during standard/normal steady-state conditions. Thus, heat transfer path  114  involving use of phase change modules  108  replaces heat transfer path  116  along heat pipe  118  as the primary or dominant heat transfer path during the period of reduced heat dissipation or cooling. In this way, inclusion of phase change modules  108  in thermal management system  200  of circuit card assembly  100  has a neutral effect on or at least does not negatively affect normal/standard steady-state heat dissipation or cooling. Thus, first heat transfer path  114  provides an added advantage to thermal management of circuit card assembly  100 . Further, thermal management system  200  comprising first heat transfer path  114  and second heat transfer path  116  provides more efficient cooling and/or heat dissipation because path  114  is configured to minimize temperature fluctuations during phase transition and path  116  is configured to mitigate or prevent decline of thermal performance during normal steady-state operating conditions. 
     Referring now to  FIGS.  7 A- 7 B , another exemplary embodiment of thermal management system  200  additionally or optionally comprises heat spreader  142  and phase change modules  108  embedded therein. Heat spreader  142  is positioned relative to electronic component  104  (as shown in  FIGS.  6 A- 6 B ) and metal frame  110 , such that heat spreader  142  is in thermal contact with electronic component  104  and/or metal frame  110 . In this configuration, heat spreader  142  provides a heat transfer path  144  for the heat generated by electronic component  104 . In an exemplary embodiment, heat transfer path  144  is provided during the period of reduced heat dissipation or cooling ( FIG.  6 A ). Further, heat transfer path  144  may be different from another heat transfer path during a period of standard/normal steady-state heat dissipation or cooling, such as heat transfer path  116  ( FIG.  6 B ). 
     In an exemplary embodiment, as illustrated in  FIG.  7 B , heat spreader  142  is configured to distribute heat from a local heat source. The local heat source may comprise electronic component  104 . Electronic component  104  may be disposed adjacent heat spreader  142 , such that heat from electronic component  104  is provided in a centrally located region  152  of heat spreader  142 . In this way, heat spreader  142  distributes heat from central region  152  and throughout an area defined by heat spreader  142 . The heat distribution rate may be impacted by a heat sink surface (having a predetermined heat transfer coefficient) disposed on the opposite side of heat spreader  142 . 
     Heat distribution rate decreases as distance from the local heat source increases, because of increased thermal resistance. In an exemplary embodiment, heat spreader  142  has a square geometry (as shown in  FIG.  7 B ), such that four corners  150  are located at the farthest distance from centrally located region  152 . Thus, the rate of heat distribution is the lowest at four corners  150 , thereby making a heat transfer path through one or more or four corners  150  generally less effective heat transfer regions/paths (and therefore having lower temperature) of the heat spreader  142 . It should be understood however that heat spreader  142  is not limited to a square geometry. Heat spreader  142  may include at least one location along an exterior periphery that represent(s) the farthest distance(s) from centrally located region  152  of heat spreader  142 . In another exemplary embodiment, heat spreader  142  may be have a rectangular or circular geometry and phase change modules  108  can be encapsulated (as shown in  FIG.  7 A ) along an exterior periphery of heat spreader  142  (e.g. along a peripheral rim of a circular heat spreader  142 ). One skilled in the art would understand from the description herein that other geometries (regular or irregular) of heat spreader  142  may depend on the design of circuit card assembly  100 , or components thereof (e.g. electronic component  104 ). 
     In the exemplary embodiment shown in  FIG.  7 A , phase change module  108  can be encapsulated in at least one of four corners  150 , where openings or pockets  156  are formed. In an exemplary embodiment, metal layer  130  may be disposed over pockets  156  for containing phase change modules  108  within pockets  156 . Specifically, metal layer  130  may act as a lid or cover. Still further, in an exemplary embodiment, metal layer  130  may comprise copper and may be disposed over pockets  156  by soldering, brazing, welding or thermal epoxy. Integration of phase change modules  108  in at least one of four corners  150  does not adversely impact or at least has a neutral effect on the thermal performance of at least one heat spreader  142  during steady-state operating conditions. This is because as stated above, heat spreader  142  is less effective in terms of heat distribution rate in locations that are the farthest from the local heat source (center). 
     During a period of reduced cooling and/or heat dissipation period, heat spreader  142  becomes less effective (i.e. due to operating conditions such as high altitude, high gravitational force (G-force), high acceleration, hypersonic speed, intermittent peaks of computing power usage, or a combination thereof) and temperature starts to increase. Thus, another heat transfer or thermal path that is different from the heat transfer path through centrally located region  152  of heat spreader  142  becomes the primary or dominant heat transfer path, e.g. heat path  144  ( FIG.  6 A ). Phase change modules  108  are located along this path  144 . Phase change modules  108  encapsulated within heat spreader  142  start to absorb heat while keeping their temperature constant for a certain period of time. In this way, temperature fluctuations during phase transition are minimized. Additionally or optionally, decline of thermal performance during steady-state conditions are mitigated or prevented because phase change modules  108  are integrated in location(s) that are the farthest from the local heat source (center) and so less effective in heat dissipation or distribution during steady-state conditions. 
       FIG.  8    shows another exemplary embodiment of thermal management system  200 , in which an oscillating heat pipe, such as heat pipe  136 , is embedded in heat spreader  142 . As shown in  FIG.  8   , oscillating heat pipe  136  comprises a first plurality of channels  132  forming a first channel pattern, e.g. serpentine channel pattern. Oscillating heat pipe  136  further comprises a second plurality of channels  134  forming a second channel pattern, e.g. a serpentine channel pattern, such that the second channel pattern is formed in spaces of oscillating heat pipe  136  that are unoccupied by the first channel pattern formed by first plurality of channels  132 . Material of phase change modules  108  is configured to be distributed via second plurality of channels  134  of oscillating heat pipe  136 . Such distribution may be activated during the period of reduced heat dissipation or cooling. In this configuration, second plurality of channels  134  containing a phase change material like that used in phase change modules  108  do not interfere with first plurality of channels  132  containing working fluid for heat dissipation and/or cooling during normal steady-state conditions. Thus, integration of phase change material into oscillating heat pipe  136  and/or heat spreader  142  does not undesirably impact or at least has a neutral effect on heat dissipation and/or cooling during normal steady-state conditions. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.