Patent Publication Number: US-2023152369-A1

Title: Modular and adjustable thermal load test vehicle

Description:
BACKGROUND 
     Background and Relevant Art 
     Bespoke, high-density computing devices used for compute-heavy workloads (gaming, machine learning, etc.) include multiple processing devices or communication devices on a single chip. For example, a multi-chip module (MCM) can include a plurality of central processing unit cores, one or more graphical processing unit cores, memory pathways, other application specific integrated circuits, or combinations thereof. The components of the chip or MCM may produce different thermal flux and have different geometries, presenting challenges in designing thermal management systems to cool the chip or MCM. 
     BRIEF SUMMARY 
     In some embodiments, a device for simulating thermal loads includes a platform and a plurality of nodes supported by the platform. At least one node is a movable node connected to the platform by a movable stage to move the movable node relative to the platform. 
     In some embodiments, a device for simulating thermal loads includes a platform and a plurality of thermal nodes supported by the platform, at least one node of the plurality of thermal nodes. At least one of the thermal nodes is a configured to provide a thermal flux at a top surface. 
     In some embodiments, a device for simulating thermal loads includes a platform, a movable stage, a node, and a thermal source. The movable stage includes a first substage and a second substage. The first substage is movable relative to the second substage, and the second substage is coupled to the platform. The node is coupled to the first substage. The thermal source is connected to the node to transfer thermal energy between the thermal source and a top surface of the node. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter. 
     Additional features and advantages will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the teachings herein. Features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. Features of the present disclosure will become more fully apparent from the following description and appended claims or may be learned by the practice of the disclosure as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG.  1    is a perspective view of a thermal test vehicle (TTV), according to the present disclosure; 
         FIG.  2    is a perspective view of a node and movable stage, according to the present disclosure; 
         FIG.  3    is a perspective view of a TTV with movable and fixed nodes, according to the present disclosure; 
         FIG.  4    is a perspective view of a TTV with a plurality of movable nodes, according to the present disclosure; 
         FIG.  5 - 1    is a plan view of a multi-chip module; 
         FIG.  5 - 2    is a perspective view of a TTV simulating the MCM of  FIG.  5 - 1   , according to the present disclosure; 
         FIG.  6    is a cross-sectional side view of a thermal node, according to at least some embodiments of the present disclosure; 
         FIG.  7    is a perspective view of a fluid-thermally controlled thermal node, according to at least some embodiments of the present disclosure; 
         FIG.  8    is a side view of a TTV with a thermal management device positioned thereon, according to at least some embodiments of the present disclosure; and 
         FIG.  9    is a perspective view of a high-density array of thermal nodes, according to at least some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates generally to systems and methods for testing thermal management devices for chips and chip modules. More particularly, the present disclosure relates to systems and methods for simulating a chip or multi-chip module (MCM) design with a high degree of precision to allow engineers to test one or more thermal management solutions to control the thermal performance of the chip or MCM design. While allowing an engineer to test the chip or MCM design, a thermal test vehicle (TTV) according to the present disclosure may also include movable stages to precisely move the simulated chips or chip components to modify the chip or MCM design to evaluate how changes to the chip or MCM design affect the thermal profile or thermal performance of the simulated chip or MCM. 
     A plurality of movable nodes can be used to simulate the size, shape, position, thermal flux, and other properties of the components of a chip or MCM design. The components of the chip or MCM design may include a plurality of central processing unit (CPU) cores, one or more graphical processing unit (GPU) cores, memory pathways, other application specific integrated circuits (ASICs), or combinations thereof (hereinafter “chiplets”). 
     In some embodiments, a TTV according to the present disclosure includes a platform upon which at least one node is supported.  FIG.  1    illustrates a TTV  100  with a platform  102  that is a substantially flat surface upon which the nodes  104 - 1 ,  104 - 2  are positioned and supported to simulate the chiplets in the chip or MCM design. In some embodiments, the platform  102  is flat in at least one direction to within 100 microns. In some embodiments, the platform  102  is planar in two directions to within 100 microns. In some embodiments, the platform  102  is planar to within 30 microns. In at least one embodiment, the platform  102  is planar to within the positional precision of at least one movable stage  106  supporting a node  104 - 2 . 
     A node  104 - 1  may be directly coupled to the platform  102 , or a node  104 - 2  may be connected to the platform  102  by a movable stage  106  positioned therebetween. The node  104 - 2  may be coupled to a surface  108  of the movable stage  106 , and a base  110  of the movable stage  106  may be coupled to the platform  102  to allow precise movement of the node  104 - 2  relative to the platform  102 . 
     The nodes  104 - 1 ,  104 - 2  and/or stages  106  may be coupled to the platform  102  through one or more connection mechanisms. For example, a platform  102  may include a plurality of holes that allow the nodes  104 - 1 ,  104 - 2  and/or stages  106  to be affixed to the platform  102 . In at least one example, a grid of holes may allow a movable stage  106  to be positioned at discrete, reproducible locations and orientations to recreate chip or MCM geometries. The holes may be threaded or unthreaded. In other examples, the platform  102  may include one or more slots, such as t-slots, to allow continuous movement and adjustment along known directions of the platform. In yet other examples, a grid of magnets in the platform  102  may apply an attractive and/or repulsive magnetic force to a node  104 - 1 ,  104 - 2  and/or stage  106  to retain and/or align the node  104 - 1 ,  104 - 2  and/or stage  106  on the platform  102 . 
     The nodes  104 - 1 ,  104 - 2  may be made of or include any thermally conductive material. In some embodiments, the nodes are made of or include copper, aluminum, iron, and other thermally conductive metals and alloys thereof. In some embodiments, the nodes include an electrically resistive material that allows the node to heat in response to an applied electrical current, thereby providing the thermal energy from the node itself. 
     The node may be coupled to the platform directly. In other examples, the node may be coupled to a stage that is coupled to the platform. Referring now to  FIG.  2   , the stage  206  may be a movable stage that allows precise adjustment of the position and/or orientation of the node  204  relative to the platform. A node  204  coupled to a movable stage  206  allows the movable node  204  to be positioned with a precision of less than 100 microns. For example, the movable stage  206  may have discrete positions with displacements less than 100 microns. In other examples, the movable stage  206  allows continual movements with less than 100 microns of backlash or free movement of the stage  206  and/or node  204  when positioned. In at least one example, the movable stage  206  has a precision of less than 30 microns. 
     In some embodiments, the stage provides movement in at least one axis, such as the z-direction normal to the surface of the platform. In some embodiments, the stage provides movement in at least three axes. For example, the stage may provide movement in the x-, y-, and z-directions relative to the surface of the platform.  FIG.  2    illustrates a movable stage  206  with three directional substages  212 - 1 ,  212 - 2 ,  212 - 3  that each provide movement in at least one direction. The node  204  is connected to a surface  208 , which is in turn connected to the first substage  212 - 1 . The first substage  212 - 1  provides movement in the z-direction. The first substage  212 - 1  is connected to the second substage  212 - 2 . The second substage  212 - 2  provides movement in the y-direction. The second substage  212 - 2  is connected to the third substage  212 - 3 . The third substage  212 - 3  provides movement in the x-direction. In other embodiments, the stage  206  may provide movement in more than three axes, such as translation in the x-, y-, and z-axes and rotation around the x-, y-, and z-axes. 
     The stage  206  may retain the selected position to within the precision tolerance as described herein (100 microns, 30 microns, etc.) when a force is applied to the stage. For example, the movable stage  206  may retain the selected position when a force of up to 100 Newtons (N) is applied to the stage. In some embodiments, a thermal interface material, such as a thermal paste, is applied to a top surface  214  of the node  204  when a thermal management device is connected to the node  204 . When the thermal management device, such as a cold plate or vapor chamber is positioned on the thermal interface material, a compressive force may be applied to compress the thermal interface material between the top surface  214  of the node  204  and the thermal management device to ensure a complete contact. The stage  206  may be stable to within the positional tolerance up to 100 N to prevent movement of the node  204  when the thermal management device is positioned. 
     As described herein, the node  204  may include a thermally conductive material to conduct heat between the top surface  214  of the node  204  and a thermal source. In some embodiments, the node  204  is a thermal node and includes the thermal source. For example, the node  204  may be or include a resistive heater. Applying an electric current to the resistive heater heats the thermal node  204 . A thermocouple positioned on the thermal node  204  at or near the top surface  214  allows a user to control the temperature of the top surface  214  by increasing or decreasing the applied current. 
     In other examples, the node  204  may be connected to a thermal source to control the temperature of the top surface  214  of the node  204 . In some embodiments, a thermal source is positioned in a recess or pocket  216  of the node  204  to apply or remove heat from the node  204 . In some examples, the thermal source is an insertable cartridge that includes a resistive heater. In some examples, the thermal source is a heated or cooled fluid that flows through a port in the node  204  to heat or cool the node material. In at least one embodiment, the thermal source is the stage  206 , which heats or cools the node  204  through a base of the node  204  coupled to the stage  206 . 
       FIG.  3    illustrates an embodiment of a TTV  300  with a combination of nodes  304 - 1 ,  304 - 2 ,  304 - 3 ,  304 - 4  and stages  306 - 1 ,  306 - 2 ,  306 - 3 . In some embodiments, a TTV  300  according to the present disclosure includes a mix of node types and connections to the platform  302 . For example, a TTV  300  may include at least one node  304 - 4  coupled directly to the platform  302  and at least one node  304 - 1  coupled to a movable stage  304 - 1 . The movable node  304 - 1  is therefore adjustable relative to the fixed node  304 - 4  coupled directly to the platform  302 . In some embodiments, the TTV  300  includes at least one thermal node  304 - 2  to simulate a heat-generating component of a chip or MCM design and at least one node  304 - 3  that does not have a thermal source connected thereto. 
     In a particular example shown in  FIG.  4   , a TTV  400  may include at least four thermal nodes  404 - 1 ,  404 - 2 ,  404 - 3 ,  404 - 4  that allow the TTV  400  to simulate a MCM. As described herein, the thermal nodes  404 - 1 ,  404 - 2 ,  404 - 3 ,  404 - 4  may be movable via movable stages  406 - 1 ,  406 - 2 ,  406 - 3 ,  406 - 4  that allow the nodes  404 - 1 ,  404 - 2 ,  404 - 3 ,  404 - 4  to be precisely positioned relative to one another in at least one axis and simulate the topography and thermal load of chiplets of a MCM. For example, each node  404 - 1 ,  404 - 2 ,  404 - 3 ,  404 - 4  may be set such that each top surface  414 - 1 ,  414 - 2 ,  414 - 3 ,  414 - 4  is at a different temperature to simulate the heat generation of different processing cores or other computing components of the MCM. 
     In some embodiments, a node  404 - 1 ,  404 - 2 ,  404 - 3 ,  404 - 4  has a square or rectangular top surface  414 - 1 ,  414 - 2 ,  414 - 3 ,  414 - 4  to simulate the surface of a conventional processing core. In other embodiments, a node has a non-rectangular top surface that may allow for the simulate or other chiplets or portions of chiplets in non-conventional chip designs. For example, a node may have an octagonal top surface to simulate an octagonal processing core. In other examples, the top surface of the node may be triangular, trapezoidal, pentagonal, hexagonal, or other regular polygonal or irregular polygonal shapes, and may have one or more curved edge, such as at least a portion of a circle, an oval, or other curved shape. In at least one example, the top surface of the node is non-planar to simulate a convex or concave chiplet surface. 
     A plurality of nodes may be positioned adjacent to one another to simulate a single chiplet or processing core.  FIG.  5 - 1    is a plan view of an example of a MCM  518 . For example, some chiplets or processing cores  520  have a conventional rectilinear shape that is simulated through a single node with a rectangular top surface. Other chiplets or processing cores  520  have a non-rectilinear shape or have an area larger than a single node can simulate. For example, a GPU  522  may be larger than the plurality of processing cores  520  of the CPU. A control processor, memory interface  524 , or system agent  526  may have a different shape from the processing cores  520 . A plurality of nodes may combine to simulate the shape or size of a single chiplet or processing core  520 . In some embodiments, a first chiplet is simulated by a first node, while a second chiplet is simulated by a plurality of nodes with top surfaces positioned near or adjacent to one another. 
     Referring now to  FIG.  5 - 2   , a TTV  500  simulates the design and topography of the MCM  518  of  FIG.  5 - 1   . In some embodiments, a plurality of nodes  504  may be positioned with top surfaces  514  positioned near or adjacent to one another to simulate a thermal gradient within a single chiplet or processing core. For example, a GPU (such as the GPU  522  of  FIG.  5 - 1   ) may have a thermal gradient across a surface thereof during operation. The center of the GPU may operate at a higher temperature than the remainder of the GPU surface area. A plurality of nodes  504  can simulate the thermal gradient within the GPU by allowing a center node  528  at or near the center of the plurality of nodes  504  to be set to a higher temperature than other nodes  504  with top surfaces  514  near and/or adjacent to the center node  528 . The resulting different in temperatures of the top surfaces  514  of the nodes  504  can help simulate the thermal gradient in the GPU during operation to better test thermal management devices. 
     Heating a node can be done in one or more ways.  FIG.  6    is a cross-sectional side view of an embodiment of a node  604 . In a first example, a thermal cartridge  632  is inserted into a pocket  612  or recess in the node  604 . A power source is connected to the thermal cartridge  632  to apply a current to the thermal cartridge  632  and heat the thermal cartridge. The heat from the thermal cartridge is conducted through the material of the node toward a top surface of the node. 
     In some embodiments, the node  604  has one or more thermocouples  630 - 1 ,  630 - 2  affixed thereto, and the thermocouples  630 - 1 ,  630 - 2  may inform the power applied to the thermal cartridge  632 . For example, a high current may be applied to the thermal cartridge  632  until a first thermocouple  630 - 1  near the thermal cartridge  632  approaches a target temperature. The current may be reduced once the first thermocouple  630 - 1  near the thermal cartridge  632  approaches a target temperature and while a second thermocouple  630 - 2  near the top surface  614  measures the temperature of the node  604  near the top surface  614 . When the second thermocouple  630 - 2  near the top surface  614  approaches the target temperature, the power applied to the thermal cartridge  632  may be further reduced or stopped, allowing the heat from body of the node  604  to hold the top surface  614  and/or thermal interface material  636  at or near the target temperature. 
     In addition to the nominal temperature, the thermocouples  630 - 1 ,  630 - 2  can aid in measuring the thermal flux of the top surface  614  by determining how much thermal energy is in the node  604  at various positions relative to how much thermal energy is introduced to the node  604 . For example, a measurement made at the thermal cartridge  632  and a measurement made at the top surface  614  can allow the heat flux through the node  604  and, hence, at the top surface  614 , because the thermal conductivity of the node material is known and the distance between the thermal cartridge  632  and the top surface  614  is known. 
       FIG.  7    is a perspective view of a liquid-thermally controlled node  704 . While various forms of resistive heating have been described herein, other embodiments of nodes may be heated and/or cooled by a thermal fluid  740  flowed through a chamber  738  or port in the node  704 . In some embodiments, the flow rate and/or temperature of the thermal fluid  740  may be adjusted to heat and/or cool the node  704  to the target temperature. For example, during testing, the TTV may perform repeated runs simulating a MCM increasing in temperature under a computational load. The thermal fluid  740  may be hotter than the node  704  to increase the temperature of the node material and approach a target temperature at a top surface  714 . After the first run, a cold thermal fluid  740  may be flowed through the port and/or chamber  738  of the node  704  to cool the node  704  to a lower temperature, such as room temperature, below room temperature, or an elevated temperature above room temperature that is below the target operating temperature of the GPU being simulated. In at least one embodiment, both thermal fluids  740  and resistive heating may be used in combination. In at least one example, a resistive heater thermal cartridge may heat the node  704 , and a cool thermal fluid  740  may cool the node  704 . 
       FIG.  8    is a side view of an embodiment of a TTV  800  with a thermal management device  842  coupled thereto. In at least one example, a node  804  is a thermal node that uses integral resistance heating, such as applying an electric current through a copper alloy that causes the body of the thermal node  804  to heat. In some embodiments, a first contact  844 - 1  of the power source  832  is positioned at or near the top surface  814  and a second contact  844 - 2  is positioned at or near a base of the thermal node  804 . A thermal node  804  with a contact of the power source  834  at or near the top surface  814  may ensure the portion of the thermal node proximate the top surface  814  heats efficiently during application of current through the contacts. 
     A thermal interface material  836  is positioned between the top surface  814  of the node  804  and a thermal management device  842 . In some embodiments, the thermal management device  842  includes a cold plate. In some embodiments, the thermal management device  842  includes a vapor chamber. In some embodiments, the thermal management device  842  includes a Peltier cooler. In some embodiments, the thermal management device  842  includes a heat spreader. In some embodiments, the thermal management device  842  includes a heat pip. The thermal management device  842  may have a surface that is at least partially complementary to the topography of the top surfaces  814  of the plurality of nodes  804 . By accurately and precisely simulating the topography and thermal gradients of a new chip or MCM design, the thermal management device  842  can be tested and refined before the fabrication processes of the new chip or MCM design are complete. 
     Referring now to  FIG.  9   , while interchangeable and/or modular nodes are described herein, and the interchangeable and/or modular nodes may be selectively coupled to the platform and/or movable stages, still further MCM designs can be simulated using a TTV  900  with a high-density array  946  of small nodes  904 . For example, a plurality of pin-like nodes  904  (cylindrical, square, or other cross-sectional shapes) in a closely packed array  946  may allow for rapid construction of simulated topographies by selectively actuating or raising nodes  904 . For example, the surface area of a top surface  914  may be less than 4 mm 2 . In other examples, the surface area of a top surface  914  may be less than 2 mm 2 . In yet other examples, the surface area of a top surface  914  may be less than 1 mm 2 . By selectively raising some nodes  904  in the high-density array  946 , a cluster  948  of 100 nodes can simulate a 1 cm 2  processing core. 
     In some embodiments, each of the nodes  904  is raised independently of the surrounding nodes  904 , allowing each to be raised by a different amount. The cluster of nodes may simulate a non-planar surface of a chiplet or processing core, such as a convex or concave surface. In a particular example, a cluster of 100 nodes can simulate an convex oval 1 cm 2  processing core. In at least another example, a cluster of  200  nodes can simulate a semicircular processing core with each node set to a different target temperature to simulate a thermal gradient across the processing core. In some embodiments, the nodes of the high-density array are actuated (e.g., raised) by an electromagnet. In other embodiments, nodes of the high-density array are actuated hydraulically, mechanically, or by positioned a solid block underneath the array to force the nodes upward. A high-density array can allow for the simulation of unconventional chiplet shapes and designs while also allowing rapid recreation of many different MCM designs. 
     In at least one embodiment, a TTV according to the present disclosure allows for the shapes, sizes, positions, temperatures, and thermal fluxes of the components of a chip or MCM to be replicated. Thermal management devices can be developed, tested, and refined without first developing the expensive and complex fabrication of the proposed chip or MCM. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure relates generally to systems and methods for testing thermal management devices for chips and chip modules. More particularly, the present disclosure relates to systems and methods for simulating a chip or multi-chip module (MCM) design with a high degree of precision to allow engineers to test one or more thermal management solutions to control the thermal performance of the chip or MCM design. While allowing an engineer to test the chip or MCM design, a thermal test vehicle (TTV) according to the present disclosure may also include movable stages to precisely move the simulated chips or chip components to modify the chip or MCM design to evaluate how changes to the chip or MCM design affect the thermal profile or thermal performance of the simulated chip or MCM. 
     A plurality of movable nodes can be used to simulate the size, shape, position, thermal flux, and other properties of the components of a chip or MCM design. The components of the chip or MCM design may include a plurality of central processing unit (CPU) cores, one or more graphical processing unit (GPU) cores, memory pathways, other application specific integrated circuits (ASICs), or combinations thereof (hereinafter “chiplets”). 
     In some embodiments, a TTV according to the present disclosure includes a platform upon which at least one node is supported. The platform is a substantially flat surface upon which the nodes are positioned and supported to simulate the chiplets in the chip or MCM design. In some embodiments, the platform is flat in at least one direction to within 100 microns. In some embodiments, the platform is planar in two directions to within 100 microns. In some embodiments, the platform is planar to within 30 microns. In at least one embodiment, the platform is planar to within the positional precision of at least one movable stage supporting a node. 
     A node may be directly coupled to the platform, or a node may be connected to the platform by a movable stage positioned therebetween. The node may be coupled to a surface of the movable stage, and a base of the movable stage may be coupled to the platform to allow precise movement of the node relative to the platform. 
     The nodes and/or stages may be coupled to the platform through one or more connection mechanisms. For example, a platform may include a plurality of holes that allow the nodes and/or stages to be affixed to the platform. In at least one example, a grid of holes may allow a movable stage to be positioned at discrete, reproducible locations and orientations to recreate chip or MCM geometries. The holes may be threaded or unthreaded. In other examples, the platform may include one or more slots, such as t-slots, to allow continuous movement and adjustment along known directions of the platform. In yet other examples, a grid of magnets in the platform may apply an attractive and/or repulsive magnetic force to a node or stage to retain and/or align the node or stage on the platform. 
     The nodes may be made of or include any thermally conductive material. IN some embodiments, the nodes are made of or include copper, aluminum, iron, and other thermally conductive metals and alloys thereof. In some embodiments, the nodes include an electrically resistive material that allows the node to heat in response to an applied electrical current, thereby providing the thermal energy from the node itself. 
     The node may be coupled to the platform directly. In other examples, the node may be coupled to a stage that is coupled to the platform. The stage may be a movable stage that allows precise adjustment of the position and/or orientation of the node relative to the platform. A node coupled to a movable stage allows the movable node to be positioned with a precision of less than 100 microns. For example, the movable stage may have discrete positions with displacements less than 100 microns. In other examples, the movable stage allows continual movements with less than 100 microns of backlash or free movement of the stage and/or node when positioned. In at least one example, the movable stage has a precision of less than 30 microns. 
     In some embodiments, the stage provides movement in at least one axis, such as the z-direction normal to the surface of the platform. In some embodiments, the stage provides movement in at least three axes. For example, the stage may provide movement in the x-, y-, and z-directions relative to the surface of the platform. In other embodiments, the stage may provide movement in more than three axes, such as translation in the x-, y-, and z-axes and rotation around the x-, y-, and z-axes. 
     The stage may retain the selected position to within the precision tolerance as described herein (100 microns, 30 microns, etc.) when a force is applied to the stage. For example, the movable stage may retain the selected position when a force of up to 100 Newtons (N) is applied to the stage. In some embodiments, a thermal interface material, such as a thermal paste, is applied to a top surface of the node when a thermal management device is connected to the node. When the thermal management device, such as a cold plate or vapor chamber is positioned on the thermal interface material, a compressive force may be applied to compress the thermal interface material between the top surface of the node and the thermal management device to ensure a complete contact. The stage may be stable to within the positional tolerance up to 100 N to prevent movement of the node when the thermal management device is positioned. 
     As described herein, the node may include a thermally conductive material to conduct heat between the top surface of the node and a thermal source. In some embodiments, the node is a thermal node and includes the thermal source. For example, the node may be or include a resistive heater. Applying an electric current to the resistive heater heats the thermal node. A thermocouple positioned on the thermal node at or near the top surface allows a user to control the temperature of the top surface by increasing or decreasing the applied current. 
     In other examples, the node may be connected to a thermal source to control the temperature of the top surface of the node. In some embodiments, a thermal source is positioned in a recess or pocket of the node to apply or remove heat from the node. In some examples, the thermal source is an insertable cartridge that includes a resistive heater. In some examples, the thermal source is a heated or cooled fluid that flows through a port in the node to heat or cool the node material. In at least one embodiment, the thermal source is the stage, which heats or cools the node through a base of the node coupled to the stage. 
     In some embodiments, a TTV according to the present disclosure includes a mix of node types and connections to the platform. For example, a TTV may include at least one node coupled directly to the platform and at least one node coupled to a movable stage. The movable node is therefore adjustable relative to the fixed node coupled directly to the platform. In some embodiments, the TTV includes at least one thermal node to simulate a heat-generating component of a chip or MCM design and at least one node that does not have a thermal source connected thereto. 
     In a particular example, a TTV may include at least four thermal nodes that allow the TTV to simulate a MCM. As described herein, the thermal nodes may be movable via movable stages that allow the nodes to be precisely positioned relative to one another in at least one axis and simulate the topography and thermal load of chiplets of an MCM. For example, each node may be set such that each top surface is at a different temperature to simulate the heat generation of different processing cores or other computing components of the MCM. 
     In some embodiments, a node has a square or rectangular top surface to simulate the surface of a conventional processing core. In other embodiments, a node has a non-rectangular surface that may allow for the simulate or other chiplets or portions of chiplets in non-conventional chip designs. For example, a node may have an octagonal top surface to simulate an octagonal processing core. In other examples, the top surface of the node may be triangular, trapezoidal, pentagonal, hexagonal, or other regular polygonal or irregular polygonal shapes, and may have one or more curved edge, such as at least a portion of a circle, an oval, or other curved shape. In at least one example, the top surface of the node is non-planar to simulate a convex or concave chiplet surface. 
     A plurality of nodes may be positioned adjacent to one another to simulate a single chiplet or processing core. For example, some chiplets or processing cores have a conventional rectilinear shape that is simulated through a single node with a rectangular top surface. Other chiplets or processing cores have a non-rectilinear shape or have an area larger than a single node can simulate. For example, a GPU may be larger than the plurality of processing cores of the CPU. A control processor, memory interface, or system agent may have a different shape from the processing cores. A plurality of nodes may combine to simulate the shape or size of a single chiplet or processing core. In some embodiments, a first chiplet is simulated by a first node, while a second chiplet is simulated by a plurality of nodes with top surfaces positioned near or adjacent to one another. 
     In some embodiments, a plurality of nodes may be positioned with top surfaces positioned near or adjacent to one another to simulate a thermal gradient within a single chiplet or processing core. For example, a GPU may have a thermal gradient across a surface thereof during operation. The center of the GPU may operate at a higher temperature than the remainder of the GPU surface area. A plurality of nodes can simulate the thermal gradient within the GPU by allowing a center node at or near the center of the plurality of nodes to be set to a higher temperature than other nodes with top surfaces near and/or adjacent to the center node. The resulting different in temperatures of the top surfaces of the nodes can help simulate the thermal gradient in the GPU during operation to better test thermal management devices. 
     Heating a node can be done in one or more ways. In a first example, a thermal cartridge is inserted into a pocket or recess in the node. A power source is connected to the thermal cartridge to apply a current to the thermal cartridge and heat the thermal cartridge. The heat from the thermal cartridge is conducted through the material of the node toward a top surface of the node. 
     In some embodiments, the node has one or more thermocouples affixed thereto, and the thermocouples may inform the power applied to the thermal cartridge. For example, a high current may be applied to the thermal cartridge until a first thermocouple near the thermal cartridge approaches a target temperature. The current may be reduced once the first thermocouple near the thermal cartridge approaches a target temperature and while a second thermocouple near the top surface measures the temperature of the node near the top surface. When the second thermocouple near the top surface approaches the target temperature, the power applied to the thermal cartridge may be further reduced or stopped, allowing the heat from body of the node to hold the top surface at or near the target temperature. 
     In addition to the nominal temperature, the thermocouples can aid in measuring the thermal flux of the top surface by determining how much thermal energy is in the node at various positions relative to how much thermal energy is introduced to the node. For example, a measurement made at the thermal cartridge and a measurement made at the top surface can allow the heat flux through the node and, hence, at the top surface, because the thermal conductivity of the node material is known and the distance between the thermal cartridge and the top surface is known. 
     While various forms of resistive heating have been described herein, other embodiments of nodes may be heated and/or cooled by a thermal fluid flowed through a chamber or port in the node. In some embodiments, the flow rate and/or temperature of the thermal fluid may be adjusted to heat and/or cool the node to the target temperature. For example, during testing, the TTV may perform repeated runs simulating a MCM increasing in temperature under a computational load. The thermal fluid may be hotter than the node to increase the temperature of the node material and approach a target temperature at a top surface. After the first run, a cold thermal fluid may be flowed through the port and/or chamber of the node to cool the node to a lower temperature, such as room temperature, below room temperature, or an elevated temperature above room temperature that is below the target operating temperature of the GPU being simulated. In at least one embodiment, both thermal fluids and resistive heating may be used in combination. In at least one example, a resistive heater thermal cartridge may heat the node, and a cool thermal fluid may cool the node. 
     In at least one example, the node is a thermal node that uses integral resistance heating, such as applying an electric current through a copper alloy that causes the body of the thermal node to heat. In some embodiments, a first contact of the power source is positioned at or near the top surface and a second contact is positioned at or near a base of the thermal node. A thermal node with a contact of the power source at or near the top surface may ensure the portion of the thermal node proximate the top surface heats efficiently during application of current through the contacts. 
     A thermal interface material is positioned between the top surface of the node and a thermal management device. In some embodiments, the thermal management device includes a cold plate. In some embodiments, the thermal management device includes a vapor chamber. In some embodiments, the thermal management device includes a Peltier cooler. In some embodiments, the thermal management device includes a heat spreader. In some embodiments, the thermal management device includes a heat pip. The thermal management device may have a surface that is at least partially complementary to the topography of the top surfaces of the plurality of nodes. By accurately and precisely simulating the topography and thermal gradients of a new chip or MCM design, the thermal management device can be tested and refined before the fabrication processes of the new chip or MCM design are complete. 
     While interchangeable and/or modular nodes are described herein, and the interchangeable and/or modular nodes may be selectively coupled to the platform and/or movable stages, still further MCM designs can be simulated using a high-density array of small nodes. For example, a plurality of pin-like nodes (cylindrical, square, or other cross-sectional shapes) in a closely packed array may allow for rapid construction of simulated topographies by selectively actuating or raising nodes. For example, the surface area of a top surface may be less than 4 mm 2 . In other examples, the surface area of a top surface may be less than 2 mm 2 . In yet other examples, the surface area of a top surface may be less than 1 mm 2 . By selectively raising some nodes in the high-density array, a cluster of 100 nodes can simulate a 1 cm 2  processing core. 
     In some embodiments, each of the nodes is raised independently of the surrounding nodes, allowing each to be raised by a different amount. The cluster of nodes may simulate a non-planar surface of a chiplet or processing core, such as a convex or concave surface. In a particular example, a cluster of 100 nodes can simulate an convex oval 1 cm 2  processing core. In at least another example, a cluster of 200 nodes can simulate a semicircular processing core with each node set to a different target temperature to simulate a thermal gradient across the processing core. In some embodiments, the nodes of the high-density array are actuated (e.g., raised) by an electromagnet. In other embodiments, nodes of the high-density array are actuated hydraulically, mechanically, or by positioned a solid block underneath the array to force the nodes upward. A high-density array can allow for the simulation of unconventional chiplet shapes and designs while also allowing rapid recreation of many different MCM designs. 
     In at least one embodiment, a TTV according to the present disclosure allows for the shapes, sizes, positions, temperatures, and thermal fluxes of the components of a chip or MCM to be replicated. Thermal management devices can be developed, tested, and refined without first developing the expensive and complex fabrication of the proposed chip or MCM. 
     The present disclosure relates to systems and methods for testing thermal management devices according to at least the examples provided in the sections below: 
     [A1] In some embodiments, a device for simulating thermal loads includes a platform and a plurality of nodes supported by the platform. At least one node is a movable node connected to the platform by a movable stage to move the movable node relative to the platform. 
     [A2] In some embodiments, at least node of the plurality of nodes of [A1] is a thermal node. The thermal node is configured to provide thermal energy at a top surface of the thermal post. 
     [A3] In some embodiments, the thermal node of [A2] is connected to a thermal source and conducts thermal energy to or from the top surface. 
     [A4] In some embodiments, the thermal node of [A2] is a thermal source. 
     [A5] In some embodiments, the movable stage of any of [A1] through [A4] moves the movable node in a z-direction relative to the platform. 
     [A6] In some embodiments, the movable stage of any of [A1] through [A5] moves the movable node in at least three axes relative to the platform. 
     [A7] In some embodiments, the movable stage of any of [A1] through [A6] moves the movable node with a precision less than 100 microns relative to the platform. 
     [A8] In some embodiments, the plurality of nodes of any of [A1] through [A7] includes at least 4 nodes. 
     [A9] In some embodiments, the at least 4 nodes of [A8] are each movable nodes that are independently movable by at least 4 movable stages. 
     [A10] In some embodiments, a first movable node of the plurality of nodes of any of [A1] through [A9] is coupled to and movable relative to the platform by a first movable stage, and a second movable node of the plurality of nodes of any of [A1] through [A9] is coupled to and movable relative to the platform by a second movable stage. 
     [A11] In some embodiments, a first thermal node of the plurality of nodes of any of [A1] through [A10] is configured to provide a first thermal flux at a first top surface of the first thermal post, and a second thermal node of the plurality of nodes of any of [A1] through [A10] is configured to provide a second thermal flux at a second top surface of the second thermal post. 
     [A12] In some embodiments, the first thermal flux of [A11] is different from the second thermal flux. 
     [A13] In some embodiments, the first top surface of [A11] has a different area than the second top surface. 
     [A14] In some embodiments, the device of any of [A1] through [A13] includes a heat sink in contact with a top surface of at least two nodes of the plurality of nodes. 
     [A15] In some embodiments, the device of any of [A1] through [A13] a vapor chamber in contact with a top surface of at least two nodes of the plurality of nodes. 
     [B1] In some embodiments, a device for simulating thermal loads includes a platform and a plurality of thermal nodes supported by the platform, at least one node of the plurality of thermal nodes. At least one of the thermal nodes is a configured to provide a thermal flux at a top surface. 
     [B2] In some embodiments, a first top surface of a first thermal node of the plurality of thermal nodes of [B1] is adjacent to a second top surface of a second thermal node of the plurality of thermal nodes of [B1] and the first top surface and second top surface are configured to simulate at least a portion of a chiplet. 
     [B3] In some embodiments, a first thermal flux of the first thermal node of [B2] is different from the second thermal flux of the second thermal node. 
     [B4] In some embodiments, a surface area of at least two of the thermal nodes of the plurality of thermal nodes of [B2] have a top surface area of less than 4 mm 2 . 
     [C1] In some embodiments, a device for simulating thermal loads includes a platform, a movable stage, a node, and a thermal source. The movable stage includes a first substage and a second substage. The first substage is movable relative to the second substage, and the second substage is coupled to the platform. The node is coupled to the first substage. The thermal source is connected to the node to transfer thermal energy between the thermal source and a top surface of the node. 
     The articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements in the preceding descriptions. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value. 
     A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims. 
     It should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “front” and “back” or “top” and “bottom” or “left” and “right” are merely descriptive of the relative position or movement of the related elements. 
     The present disclosure may be embodied in other specific forms without departing from its characteristics. The described embodiments are to be considered as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.