Patent Publication Number: US-11656272-B1

Title: Test system with a thermal head comprising a plurality of adapters and one or more cold plates for independent control of zones

Description:
FIELD 
     The present disclosure relates to a test system comprising a thermal head capable of independently controlling a plurality of zones while testing a device. 
     BACKGROUND 
     Integrated circuit (IC) chips are typically fabricated with a plurality of identical copies on a semiconductor wafer. After wafer fabrication has been completed, the wafer may be cut or diced to separate the individual IC chips. These IC chips (also referred to as a device) may then be tested (referred to as a device under test (DUT)). The testing may involve electrical testing (burn-in tests, open- and short-circuit tests, device functional tests, system level tests, etc.), where the performance (e.g., functionality, speed, reliability, etc.) of an IC chip may be measured by a test system to determine whether the IC chip meets one or more performance metrics. For example, electrical test signals may be communicated to and/or from the IC chip to measure its performance. If an IC chip meets the performance metrics, then it may be assembled into a package. The package may be used for multiple purposes such as providing environmental protection and electrical contacts from the IC chip to a system board, among others. These packages may be tested. In some instances, the testing at the package level is similar to the testing at the chip level. 
     The performance of a DUT may be compared to a target performance, such as the performance of a reference device or another device, or according to a specification. One factor that may cause the performance of a DUT to deviate or fail prematurely while being tested may be its temperature. To ensure that any deviations in the performance of a DUT is not due to temperature, the DUT&#39;s temperature may be controlled during testing. It may be important that the temperature of the DUT remain constant and at a set point temperature (or within a given range). While under test, thermal energy may be exchanged between the DUT and components that are thermally coupled to it. A DUT&#39;s temperature may be controlled via a heatsink or cold plate that is thermally coupled to the DUT. Thermal coupling may occur when there is sufficient contact between the cold plate and the DUT and/or any intermediate layers. 
     Advances in technology, such as process nodes, have led to more difficult and expensive wafer fabrication. For example, technologies involving 9 nm or below may require extreme ultraviolet (EUV) fabrication techniques for critical mask layers. It may be difficult to design and fabricate advanced types of IC chips (e.g., system-on-chip (SOC) at the wafer level), particularly when a multitude of functions are involved. In some instances, different package designs may be developed or utilized. For example, a plurality of IC chips, a bare mix of IC chips, pre-packaged IC chips, etc., may be packaged together into a device. Different types of advanced packages, such as system-in-package (SiP), multi-chip module (MCM), stacked die, heterogeneous integration package, etc., have already been developed and are becoming more complex structurally and functionally. In some instances, the devices comprise an increasing number of components in the same size or more compact packaging, causing the components to be within close proximity to each other. The close proximity may make it difficult to control the temperatures of the components if not accounted for, as the temperature of a component may be affected by the temperature of a neighboring component. 
     Some of the devices (a chip or a package) may comprise a plurality of zones, where each zone may comprise one or more components (e.g., IC chips that are components in a package may each comprise a zone). For example, a complex SOC may comprise a plurality of components such as graphic processing unit (GPU) cores, a plurality of central processing unit (CPU) cores, and various interfaces and other functions, which are segmented into a plurality of zones in the device. In some instances, the components in a device under test may have different properties such as height, surface area, stacked vs. non-stacked, etc., and as such, a test system having a single adapter or a plurality of adapters with the same properties may not sufficiently thermally couple to the components (e.g., due to insufficient contact). In some instances, the components may dissipate different amounts of power while under testing conditions due to different functions of and/or tests being performed on the zones. It may be beneficial to keep the temperature of the components constant and at the same set point temperature (or within a given range) while the device is being tested. A test system may not account for the different amounts of power dissipation. What is needed is a test system capable of independent control of one or more properties (e.g., temperature, applied force, movement, etc.) for different components in a device or devices under test. What is needed is a test system capable of independently controlling components that are within close proximity to each other. 
     SUMMARY 
     Disclosed herein are thermal heads and corresponding test systems for independently controlling a plurality of zones (e.g., one or more components) while testing one or more devices under test. In some embodiments, a thermal head comprises a plurality of adapters, one or more heaters, and one or more thermal controllers for independently controlling temperatures of the components. For example, two components may have different set point temperatures. The thermal controllers may control the temperatures of the two components independently such that thermal control of one component does not affect the thermal control of the other component. At a given time, a first heater (thermally coupled to the first component) may be heating the first component, while the temperature of the second component may remain the same. In some embodiments, the thermal control is by way of one or more cold plates, and the thermal head comprises one or more cold plates. As one non-limiting example, at a given time, a first component is being cooled by a cold plate, whereas the second component is not. As yet another example, a third component may not be thermally coupled to a heater and/or cold plate. Embodiments of the disclosure include independent control of one or more forces using one or more force mechanisms. 
     A test system for testing one or more devices under test is disclosed. The test system comprises: a thermal head for controlling one or more temperatures of the one or more devices under test, the thermal head comprising: a plurality of adapters thermally coupled to one or more components of the one or more devices under test; and one or more heaters thermally coupled to the plurality of adapters and the one or more components of the one or more devices under test, wherein the one or more heaters are configured to heat the one or more components of the one or more devices under test; and one or more thermal controllers configured to independently control the one or more temperatures of the one or more components of the one or more devices under test. Additionally or alternatively, in some embodiments, at least two of the one or more components have different set point temperatures. Additionally or alternatively, in some embodiments, the one or more temperatures of the one or more components are independently controlled using different changes in temperature. Additionally or alternatively, in some embodiments, the one or more heaters comprise a first heater and a second heater and the one or more components comprise a first component and a second component, wherein the first heater is configured to heat the first component, and the second heater is configured to heat the second component. Additionally or alternatively, in some embodiments, the thermal head further comprises one or more temperature sensors configured to measure temperatures of the one or more heaters or the plurality of adapters, wherein the one or more thermal controllers control the one or more temperatures based on the measured temperatures. Additionally or alternatively, in some embodiments, an update frequency of the one or more thermal controllers for independently controlling the one or more temperatures of the one or more components is less than 200 microseconds. Additionally or alternatively, in some embodiments, the one or more heaters comprise a heater including at least two heating elements, wherein the thermal head further comprises: a thermal insulator located between the at least two heating elements. Additionally or alternatively, in some embodiments, the thermal insulator comprises a material having through-holes or trenches. Additionally or alternatively, in some embodiments, the thermal head further comprises: a thermal interface material located on at least one side of at least one of the one or more heaters. Additionally or alternatively, in some embodiments, the thermal head further comprises: a thermal interface material located on at least one side of at least one of the plurality of adapters. Additionally or alternatively, in some embodiments, the plurality of adapters comprises a first adapter thermally coupled to a first thermal interface material layer and a second adapter thermally coupled to a second thermal interface material layer, wherein a thermal resistance of the first thermal interface material layer is different from a thermal resistance of the second thermal interface material layer. Additionally or alternatively, in some embodiments, the first thermal interface material layer has a greater surface area than the second thermal interface material layer. Additionally or alternatively, in some embodiments, the second thermal interface material layer comprises openings or holes. Additionally or alternatively, in some embodiments, at least one of the one or more heaters contacts at least one of the one or more components. Additionally or alternatively, in some embodiments, at least one of the one or more heaters is attached to at least one of the plurality of adapters. Additionally or alternatively, in some embodiments, the at least one heater comprises a plurality of pins that allow the at least one heater to attach to the at least one adapter. Additionally or alternatively, in some embodiments, the plurality of pins is attached to the at least one adapter by soldering, welding, brazing, press fitting, or conductive adhesive. Additionally or alternatively, in some embodiments, a surface area of at least one of the one or more heaters is the same as a surface area of a corresponding adapter. Additionally or alternatively, in some embodiments, at least one of the one or more heaters and a corresponding adapter comprise mating alignment features for aligning the at least one heater and the corresponding adapter. Additionally or alternatively, in some embodiments, the one or more components of the one or more devices under test comprise a first component and a second component, and the plurality of adapters comprises a first adapter and a second adapter, wherein the first component is thermally coupled to the first adapter and the second component is thermally coupled to the second adapter. Additionally or alternatively, in some embodiments, the one or more thermal controllers control the one or more temperatures of the one or more components based on amounts of power from the one or more components. Additionally or alternatively, in some embodiments, the amounts of power from the one or more components comprise amounts of expected power dissipation. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more cold plates thermally coupled to at least one of the plurality of adapters, wherein the one or more cold plates are configured to cool the at least one adapter. Additionally or alternatively, in some embodiments, the one or more cold plates are independently controlled. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more force mechanisms configured to apply force to at least one of the one or more components. Additionally or alternatively, in some embodiments, the one or more force mechanisms are independently controlled. Additionally or alternatively, in some embodiments, at least two of the one or more components have different heights. Additionally or alternatively, in some embodiments, at least one of the plurality of adapters is thermally coupled to at least two of the one or more components. Additionally or alternatively, in some embodiments, each of the plurality of adapters is thermally coupled to a unique one of the one of the one or more components. Additionally or alternatively, in some embodiments, the one or more components are part of a single device under test. 
     A test system for testing one or more devices under test is disclosed. The test system comprises: a thermal head for controlling one or more temperatures of the one or more devices under test, the thermal head comprising: a plurality of adapters thermally coupled to one or more components of the one or more devices under test; and one or more cold plates thermally coupled to the plurality of adapters, wherein the one or more cold plates are configured to cool the plurality of adapters; and one or more thermal controllers configured to independently control the one or more temperatures of the one or more components of the one or more devices under test. Additionally or alternatively, in some embodiments, at least two of the one or more components have different set point temperatures. Additionally or alternatively, in some embodiments, the one or more temperatures of the one or more components are independently controlled using different changes in temperature. Additionally or alternatively, in some embodiments, the one or more cold plates comprise a first cold plate and a second cold plate, and the plurality of adapters comprise a first adapter and a second adapter, wherein the first cold plate is configured to cool the first adapter and the second cold plate configured to cool the second adapter. Additionally or alternatively, in some embodiments, at least two of the plurality of adapters are thermally coupled to the same cold plate. Additionally or alternatively, in some embodiments, at least one of the plurality of adapters contacts at least one of the one or more cold plates. Additionally or alternatively, in some embodiments, the at least one cold plate has a surface area that is the same as a surface area of the at least one adapter. Additionally or alternatively, in some embodiments, the one or more thermal controllers set, adjust, or maintain temperatures of the one or more cold plates by setting, adjusting, or maintaining a flow rate or temperature of a liquid or a gas associated with the one or more cold plates. Additionally or alternatively, in some embodiments, an update frequency of the one or more thermal controllers for independently controlling the one or more temperatures of the one or more components is less than 200 microseconds. Additionally or alternatively, in some embodiments, the thermal head further comprises: a thermal interface material located on at least one side of at least one of the one or more cold plates. Additionally or alternatively, in some embodiments, the thermal head further comprises: a thermal interface material located on at least one side of at least one of the plurality of adapters. Additionally or alternatively, in some embodiments, the plurality of adapters comprise a first adapter thermally coupled to a first thermal interface material layer and a second adapter thermally coupled to a second thermal interface material layer, wherein a thermal resistance of the first thermal interface material layer is different from a thermal resistance of the second thermal interface material layer. Additionally or alternatively, in some embodiments, the first thermal interface material layer has a greater surface area than the second thermal interface material layer. Additionally or alternatively, in some embodiments, the second thermal interface material layer comprises openings or holes. Additionally or alternatively, in some embodiments, the one or more components of the one or more devices under test comprise a first component and a second component and the plurality of adapters comprise a first adapter and a second adapter, wherein the first component is thermally coupled to the first adapter and the second component is thermally coupled to the second adapter. Additionally or alternatively, in some embodiments, the one or more thermal controllers control the one or more temperatures of the one or more components based on amounts of power from the one or more components. Additionally or alternatively, in some embodiments, the amounts of power from the one or more components comprise amounts of expected power dissipation. Additionally or alternatively, in some embodiments, at least two of the one or more components have different amounts of power dissipation. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more heaters thermally coupled to at least one of the one or more components, wherein the one or more heaters are configured to heat the at least one component. Additionally or alternatively, in some embodiments, the one or more heaters are independently controlled. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more force mechanisms configured to apply force to at least one of the one or more components. Additionally or alternatively, in some embodiments, the one or more force mechanisms are independently controlled. Additionally or alternatively, in some embodiments, the one or more force mechanisms contact at least one of the one or more cold plates. Additionally or alternatively, in some embodiments, at least one of the plurality of adapters is thermally coupled to at least two of the one or more components. Additionally or alternatively, in some embodiments, each of the plurality of adapters is thermally coupled to a unique one of the one of the one or more components. Additionally or alternatively, in some embodiments, the one or more components are part of a single device under test. 
     A test system for testing one or more devices under test is disclosed. The test system comprises: a thermal head for controlling one or more temperatures of the one or more devices under test, the thermal head comprising: a plurality of adapters thermally coupled to one or more components of the one or more devices under test; and one or more force mechanisms configured to apply one or more forces to the one or more components of the one or more devices under test; and a force controller configured to independently control the one or more forces applied to the one or more components of the one or more devices under test. Additionally or alternatively, in some embodiments, at least two of the one or more components are tested with different applied forces. Additionally or alternatively, in some embodiments, the one or more force mechanisms comprise one or more force applicators that apply the one or more forces to the one or more components. Additionally or alternatively, in some embodiments, the one or more force applicators comprise: a pneumatic or hydraulic cylinder, a pneumatic or hydraulic diaphragm, a stepper motor, a linear motor, a server motor, an electroactive polymer actuator, a shape memory alloy actuator, an electromagnetic actuator, a rotary motor, an electromechanical actuator, a piezoelectric actuator, or a voice coil. Additionally or alternatively, in some embodiments, the one or more force mechanisms comprise one or more pushers, wherein the one or more force applicators push the one or more pushers such that the one or more devices under test are moved toward a socket. Additionally or alternatively, in some embodiments, at least one of the one or more force mechanisms applies a force greater than 2 kgf. Additionally or alternatively, in some embodiments, the one or more force mechanisms comprise a first force mechanism and a second force mechanism, and the plurality of adapters comprises a first adapter and a second adapter, wherein the first force mechanism applies a first force to the first adapter and the second force mechanism applies a second force to the second adapter. Additionally or alternatively, in some embodiments, the one or more force mechanisms comprise one or more transducers configured to measure forces, wherein the force controller sets, adjusts, or maintains the one or more applied forces based on the measured forces. Additionally or alternatively, in some embodiments, the one or more force mechanisms comprise one or more force applicators, wherein the one or more force applicators are controlled based on differences between the measured forces and target forces. Additionally or alternatively, in some embodiments, the one or more transducers comprise: a pneumatic load cell, a hydraulic load cell, an inductive load cell, a capacitive load cell, a magnetorestrictive device, a strain gauge-based sensor, a force sensitive resistor, a thin film device, or a piezoelectric device. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more cold plates, wherein the one or more transducers contact the one or more cold plates. Additionally or alternatively, in some embodiments, at least one of the one or more force mechanisms comprises a spring. Additionally or alternatively, in some embodiments, at least one of the one or more force mechanisms comprises a piston, a ramp, and a roller, wherein movement of the piston causes movement of the ramp, which adjusts an amount of force applied by the roller. Additionally or alternatively, in some embodiments, at least one of the one or more force mechanisms comprises a cam and a roller, wherein rotation of the cam adjusts an amount of force applied by the roller. Additionally or alternatively, in some embodiments, at least one of the one or more forces is a variable force that is different at the beginning of the test and during the test, or during the test and at the end of the test. Additionally or alternatively, in some embodiments, at least one of the one or more forces is a fixed force that is the same at the beginning of the test and during the test, or during the test and at the end of the test. Additionally or alternatively, in some embodiments, at least one of the one or more force mechanisms applies force to at least two of the one or more components. Additionally or alternatively, in some embodiments, the test system further comprises: a testing force mechanism configured to move the one or more devices under test towards a socket for electrically coupling the one or more devices under test to the socket. Additionally or alternatively, in some embodiments, the testing force mechanism comprises a force applicator configured to apply a force greater than 10 kgf. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more heaters thermally coupled to at least one of the one or more components, wherein the one or more heaters are configured to heat the at least one component. Additionally or alternatively, in some embodiments, the one or more heaters are independently controlled. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more cold plates thermally coupled to at least one of the plurality of adapters, wherein the one or more cold plates are configured to cool the at least one adapter. Additionally or alternatively, in some embodiments, the one or more cold plates are independently controlled. Additionally or alternatively, in some embodiments, the one or more thermal controllers control the one or more temperatures of the one or more components based on amounts of power from the one or more components. Additionally or alternatively, in some embodiments, the amounts of power from the one or more components comprise amounts of expected power dissipation. Additionally or alternatively, in some embodiments, at least two of the one or more components have different amounts of power dissipation. Additionally or alternatively, in some embodiments, at least two of the one or more components have different heights. Additionally or alternatively, in some embodiments, at least one of the plurality of adapters is thermally coupled to at least two of the one or more components. Additionally or alternatively, in some embodiments, each of the plurality of adapters is thermally coupled to a unique one of the one of the one or more components. Additionally or alternatively, in some embodiments, the one or more components are part of a single device under test. 
     A test system for testing one or more devices under test is disclosed. The test system comprises: a thermal head for controlling one or more temperatures of the one or more devices under test, the thermal head comprising: a plurality of adapters thermally coupled to one or more components of the one or more devices under test, wherein the plurality of adapters comprises a first adapter and a second adapter, and movement of the first adapter is independent from movement of the second adapter; and a controller configured to independently control one or more properties of the plurality of adapters. Additionally or alternatively, in some embodiments, the one or more properties comprise temperature or force. Additionally or alternatively, in some embodiments, the plurality of adapters comprises a first adapter having a first height and a second adapter having a second height. Additionally or alternatively, in some embodiments, the plurality of adapters comprises a first adapter having a first thermal mass and a second adapter having a second thermal mass. Additionally or alternatively, in some embodiments, the plurality of adapters comprises a first adapter having a first surface area thermally coupled to a corresponding one or more components and a second adapter having a second surface area thermally coupled to corresponding one or more components. Additionally or alternatively, in some embodiments, at least two of the plurality of adapters are configured to thermally couple to the one or more components on the same side of a substrate of the one or more devices under test. Additionally or alternatively, in some embodiments, at least two of the plurality of adapters are configured to thermally couple to the one or more components on different sides of a substrate of the one or more devices under test. Additionally or alternatively, in some embodiments, the plurality of adapters comprises a first adapter nested within a second adapter. Additionally or alternatively, in some embodiments, the plurality of adapters comprises a first adapter and a second adapter, wherein the thermal head further comprises: a first heater thermally coupled to the first adapter and a second heater thermally coupled to the second adapter, wherein the first heater is nested within the second heater. Additionally or alternatively, in some embodiments, the plurality of adapters comprises a first adapter and a second adapter, wherein the thermal head further comprises: a first thermal interface material layer thermally coupled to the first adapter and a second thermal interface material layer thermally coupled to the second adapter, wherein the first thermal interface material layer is nested within the second thermal interface material layer. Additionally or alternatively, in some embodiments, the first adapter is thermally coupled to a first component and the second adapter is thermally coupled to a second component, and wherein movement of the second component is not independent from movement of the first component. Additionally or alternatively, in some embodiments, the one or more components comprise stacked components. Additionally or alternatively, in some embodiments, the first adapter is thermally coupled to a first component of the stacked components and the second adapter is thermally coupled to a second component of the stacked components, wherein a height of the first adapter is less than a height of the second adapter. Additionally or alternatively, in some embodiments, the first adapter is thermally coupled to a first component of the stacked components and the second adapter is thermally coupled to a second component of the stacked components, wherein a force applied by the first adapter is less than a force applied by the second adapter. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more heaters thermally coupled to at least one of the one or more components, wherein the one or more heaters are configured to heat the at least one component. Additionally or alternatively, in some embodiments, the one or more heaters comprise a first heater coupled to a first adapter and a second heater coupled to a second adapter, wherein movement of the first heater is independent from movement of the second heater. Additionally or alternatively, in some embodiments, at least one of the one or more heaters contacts at least one of the plurality of adapters. Additionally or alternatively, in some embodiments, the one or more heaters are independently controlled. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more cold plates thermally coupled to at least one of the plurality of adapters, wherein the one or more cold plates are configured to cool the at least one adapter. Additionally or alternatively, in some embodiments, the one or more cold plates comprise a first cold plate coupled to a first adapter and a second cold plate coupled to a second adapter, wherein movement of the first cold plate is independent from movement of the second cold plate. Additionally or alternatively, in some embodiments, at least one of the one or more cold plates contacts at least one of the plurality of adapters. Additionally or alternatively, in some embodiments, the one or more cold plates are independently controlled. Additionally or alternatively, in some embodiments, the thermal head further comprises: one or more force mechanisms configured to apply one or more forces to at least one of the one or more components. Additionally or alternatively, in some embodiments, the one or more force mechanisms are independently controlled. Additionally or alternatively, in some embodiments, at least two of the one or more components have different set point temperatures. Additionally or alternatively, in some embodiments, at least two of the one or more components have different amounts of power dissipation. Additionally or alternatively, in some embodiments, at least two of the one or more components are tested with different applied forces. Additionally or alternatively, in some embodiments, at least two of the one or more components have different heights. Additionally or alternatively, in some embodiments, at least one of the plurality of adapters is thermally coupled to at least two of the one or more components. Additionally or alternatively, in some embodiments, the one or more components are part of a single device under test. 
     It will be appreciated that any of the variations, aspects, features, and options described in view of the systems and methods apply equally to the methods and vice versa. It will also be clear that any one or more of the above variations, aspects, features, and options can be combined. It should be understood that the invention is not limited to the purposes mentioned above, but may also include other purposes, including those that can be recognized by one of ordinary skill in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1 A  illustrates a top view of an example chip comprising a plurality of zones. 
         FIG.  1 B  illustrates a block diagram of an example test system, according to some embodiments. 
         FIG.  2 A  illustrates a top view of an example device comprising a plurality of zones, according to some embodiments. 
         FIG.  2 B  illustrates a cross-sectional view of the device along line A-A, as drawn in  FIG.  2 A . 
         FIG.  2 C  illustrates a cross-sectional view of the device along line B-B, as drawn in  FIG.  2 A . 
         FIGS.  3 A- 3 C  illustrate cross-sectional views of an example thermal head comprising a plurality of adapters, according to some embodiments. 
         FIG.  4    illustrates a cross-sectional view of a portion of a thermal head, according to some embodiments. 
         FIG.  5 A  illustrate a cross-section diagram of an example heater, according to some embodiments. 
         FIG.  5 B  illustrates an example adapter comprising a hole that provides access to a pin, according to some embodiments. 
         FIGS.  6 A and  6 B  illustrate cross-section diagrams of an example cold plate, according to some embodiments. 
         FIG.  7 A  illustrates an example thermal interface material comprising openings or holes, according to some embodiments. 
         FIG.  7 B  illustrates an example liquid thermal interface material that is dispensed, according to some embodiments. 
         FIGS.  8 A and  8 B  illustrate top and cross-sectional views, respectively, of a device including stacked components, according to some embodiments. 
         FIG.  9 A  illustrates a top view of an example device comprising stacked components, according to some embodiments. 
         FIGS.  9 B and  9 C  illustrate cross-sectional views of a thermal head and device, along line B-B and A-A, respectively, as drawn in  FIG.  9 A . 
         FIGS.  10 A and  10 B  illustrate top and cross-sectional views, respectively, of an example device comprising components on a plurality of sides of a substrate, according to some embodiments. 
         FIG.  11    illustrates a cross-sectional view of a part of a test system comprising a thermal head and a device under test having components on a plurality of sides of a substrate, according to some embodiments. 
         FIG.  12 A  illustrates an example force mechanism comprising a piston and ramp, according to some embodiments of the disclosure. 
         FIG.  12 B  illustrates an example force mechanism comprising a cam-roller, according to some embodiments of the disclosure. 
         FIG.  13 A  illustrates a cross-sectional view of an example test system, according to some embodiments. 
         FIG.  13 B  illustrates a flowchart of an example method of operating the test system  1390 , according to some embodiments. 
         FIG.  14    illustrates an example active thermal control for a plurality of components of a device, according to some embodiments. 
         FIG.  15    illustrates an example thermal head and socket, according to some embodiments. 
         FIG.  16    illustrates a block diagram of an exemplary computer used for one or more controllers, according to embodiments of the disclosure. 
     
    
    
     It will be appreciated that any of the variations, aspects, features, and options described in view of the systems apply equally to the methods and vice versa. It will also be clear that any one or more of the above variations, aspects, features, and options can be combined. 
     DETAILED DESCRIPTION 
     Disclosed herein are thermal heads and corresponding test systems for independently controlling a plurality of zones (e.g., one or more components) while testing one or more devices under test. In some embodiments, a thermal head comprises a plurality of adapters, one or more heaters, and one or more thermal controllers for independently controlling temperatures of the components. For example, two components may have different set point temperatures. The thermal controllers may control the temperatures of the two components independently such that thermal control of one component does not affect the thermal control of the other component. At a given time, a first heater (thermally coupled to the first component) may be heating the first component, while the temperature of the second component may remain the same. In some embodiments, the thermal control is by way of one or more cold plates, and the thermal head comprises one or more cold plates. As one non-limiting example, at a given time, a first component is being cooled by a cold plate, whereas the second component is not. As yet another example, a third component may not be thermally coupled to a heater and/or cold plate. Embodiments of the disclosure include independent control of one or more forces using one or more force mechanisms. Embodiments of the disclosure further include methods for operation thereof. 
     The following description is presented to enable a person of ordinary skill in the art to make and use various embodiments. Descriptions of specific devices, techniques, and applications are provided only as examples. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to a person of ordinary skill in the art that the described examples may be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be taken as limiting. Various modifications in the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described herein and shown, but are to be accorded the scope consistent with the claims. 
     Various techniques and process flow steps will be described in detail with reference to examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to a person of ordinary skill in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein. 
     In the following description of examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples. 
     The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combination of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will also be understood that the term “same,” when used in this specification, refers to the stated feature as being identical or within a certain range (e.g., 1%, 5%, etc.) from identical. 
     Some of the devices may comprise a plurality of zones, where each zone may comprise one or more components (e.g., IC chips in a package or functional blocks in a chip).  FIG.  1 A  illustrates a top view of an example chip comprising a plurality of zones. Device  100  may comprise zones  117 A,  117 B,  117 C,  117 D,  119 A,  119 B, and  119 C. For example, a complex SOC device may comprise a plurality of graphic processing unit (GPU) cores, a plurality of central processing unit (CPU) cores, and various interfaces and other functions, where zones  119 A,  119 B, and  119 C may be high-power zones (e.g., comprising GPU and/or CPU cores), and zones  117 A,  117 B,  117 C, and  117 D may be low-power zones (e.g., comprising memory, transceivers, etc.). A zone may comprise one or more components. In some embodiments, at least two zones of a device may dissipate different amounts of power while under testing conditions due to different functions of and/or tests being performed on the zones. It may be beneficial to keep the temperature of one or more zones constant and at one or more set point temperatures (or within a given range) while the device is being tested. 
     A zone may comprise one or more components, such as zone  117 A comprising one component, and zone  119 C comprising at least two components. One or more components may be part of a single device (as shown in the figure), or alternatively, part of a plurality of devices under test (not shown in the figure). 
       FIG.  1 B  illustrates a block diagram of an example test system, according to some embodiments. Test system  190  may comprise a thermal head  150 , a controller  158 , a socket  121 , and a tester  141 . The thermal head  150  may be configured to thermally control the device under test  100 . The thermal head  150  may comprise one or more of: an adapter  130 , a heater  156 , a cold plate  162 , or a force mechanism  132 . The adapter  130  may be configured to allow thermal energy to transfer to and/or from thermally-coupled components. For example, the adapter  130  may allow thermal energy (e.g., heat) to transfer from the heater  156  located on the bottom side of the adapter  130  to the cold plate  162  located on the top side of the adapter  130 . The heater  156  may be configured to raise the temperature (e.g., heat) of the device  100 , and the cold plate  162  may be configured to lower the temperature (e.g., cool) of the device  100 . The thermal head&#39;s ability and speed at thermally controlling the temperature of the device  100  may depend on the thermal coupling between its components and the device  100 . 
     The force mechanism  132  may be configured to apply a force to the device  100  to enhance the thermal coupling between the thermal head  150  and the device  100 . The controller  158  may be configured to send one or more signals to the thermal head  150  to control one or more of its components. For example, the controller  158  may send a current or voltage signal to the heater  156  to cause it to heat the device  100 . As another example, the controller  158  may send a current or voltage signal to a valve metering the flow inside the cold plate  162  or associated chiller to cause it to cool down the device  100 . Additionally or alternatively, the controller  158  may send a current or voltage signal to cause the force mechanism  132  to apply more or less force to the thermal head  150 , thereby improving the thermal coupling between the thermal head  150  and the device  100  without damaging it. As one non-limiting example, the thermal controller may be a field-programmable gate array (FGPA)-based proportional-integral-derivative (PID) controller. 
     The socket  121  may be configured to electrically couple power connections and/or test signals from the tester  141  to the device  100 , or from the device  100  to the tester  141 . The tester  141  may send test signals and/or receive response signals for determining the performance of the device  100 . In some embodiments, the tester  141  may monitor the power being supplied to one or more of: the DUT, a component, or zones of the DUT. Although the figure illustrates the test system  190  as comprising one or more components, embodiments of the disclosure may include additional components, or one or more components may not be included. Additionally or alternatively, although one configuration of the test system is shown, embodiments of the disclosure may comprise other configurations such as the thermal head comprising an additional adapter located on the bottom side of the device  100 . 
     Example Thermal Head Comprising a Plurality of Adapters 
       FIG.  2 A  illustrates a top view of an example device comprising a plurality of zones, according to some embodiments. Device  200  may comprise a plurality of components, such as component  202 A, component  202 B, and components  203 A-H mounted on a substrate  210 . The device  200  may comprise one or more high-power components (e.g., components  202 ), one or more low-power components (e.g., components  203 ), or a combination thereof. In some embodiments, the device  200  may comprise any type of component (e.g., chips or packages); non-limiting examples include logic, RF, analog, digital, power, diodes (e.g., light emitting diodes (LEDs)), sensors (e.g., image sensors), microelectromechanical systems (MEMS), integrated passive devices (IPDs), power management units or integrated circuits (PMUs, PMICs), etc. Additionally or alternatively, the device  200  may comprise other types of components including, but not limited to, resistors, capacitors, inductor, transistors, etc. 
     As one non-limiting example, the device  200  may be a SiP device used for high performance computing (HPC) applications. Component  202 A and component  202 B may be processor chips (e.g., CPU and/or GPU chips) surrounded by dynamic random access memory (DRAM) chips, for example. The memory chips may be individual chips, packaged chips, through-silicon via (TSV) stacked chips (e.g., high bandwidth memory (HBM) devices), or the like. In some embodiments, one or more components may be located in close proximity to one or more other components. For example, memory chips may be placed close to the processor chips to reduce signal delays and noise in the memory to processor interconnections, improving overall performance due to, e.g., higher transfer speeds and reduced latency. The close proximity may cause the temperature from one component to affect the temperature of another component. 
       FIG.  2 B  illustrates a cross-sectional view of the device  200  along line A-A, as drawn in  FIG.  2 A . Line A-A may be drawn through components  202 B,  203 D, and  203 H. The components  202 B,  203 D, and  203 H may be mounted on and connected to the substrate  210  by way of interconnects  206 . In some embodiments, the components in a device  200  may be on a single layer of the substrate  210 . In some embodiments, the interconnects  206  may be component interconnects, such as solder balls, copper pillar bumps, C4 (controlled collapse chip connection) bumps, gold bumps, wire bonding, or conductive adhesive, as non-limiting examples. The interconnects  206  may allow the components to be mechanically and/or electrically connected to the substrate  210 . The substrate  210  may comprise any type of material, such as laminate. In some embodiments, the substrate  210  may comprise one or more layers of: conductive traces, conductive plane layers, dielectric layers, or a combination thereof. One or more vias may be used to connect conductive layers. The layer(s) and/or vias may be formed using a printed circuit board process. Embodiments of the disclosure may include other materials (e.g., ceramic, silicon, glass, molding compound, etc.) for creating the substrate  210 . 
     The components  202 / 203  and interconnects  206  may be located on the top side of the substrate  210 , and interconnects  216  may be located on the bottom side of the substrate  210 . In some embodiments, no components may be located on the bottom side of the substrate  210 . The interconnects  216  may be, for example, used to electrically couple the device  200  to a board. The board may be a test board, when the device  200  is being tested, or a system board, when the device is being used in a final product. When coupled to a test board, the interconnects  216  may electrically couple to a socket used to send test signals between a tester and the device  200 . The interconnects  216  may be solder balls, pins, leads, pads on the substrate  210 , or other forms of interconnects. 
     As one non-limiting example, the test board may send one or more test (input) signals to the device  200  and/or may receive one or more output signals from the device  200 . The test signal(s) may have a predetermined pattern. The output signal(s) may represent the electrical characteristics of the device  200  in response to applying the test signal(s) to the device  200  while being tested. In some embodiments, the testing may be performed using multiple sets of input and output signals, while operating the device  200  under the same or different conditions (e.g., different temperatures). 
       FIG.  2 C  illustrates a cross-sectional view of the device  200  along line B-B, as drawn in  FIG.  2 A . Line B-B may be drawn through components  202 A and  202 B. In some embodiments, as shown in the figure, two or more components (e.g., chips or packages) may have different heights due to, e.g., different designs and/or manufacturing variations. For example, component  202 A may be shorter than component  202 B, resulting in a height difference  220 . In some embodiments, the height difference  220  may be due to differences in the types of components. For example, memory chip  203 A may be taller than processor chip  202 A. As another example, high-power chip  202 B may be taller than high-power chip  202 A. It is also contemplated that in instances where components  202 A and  202 B have the same height, they may be located at different planes after assembly to the substrate  210  due to differences in final solder size during assembly (e.g., differences in solder ball compression during soldering). 
     If the height differences of the components in the device  200  are not accounted for, the test system may not be able to adequately control the testing conditions of the components of the device  100 . For example, the test system may have an adapter or associated heater that contacts the top of component  202 B, but not the top of component  202 A, due to the height difference  220 . As a result, the test system may be thermally coupled to the component  202 B, but may not be adequately thermally coupled to the component  202 A. Such lack of thermal coupling may cause performance problems when testing the component  202 A. Example test systems of the disclosure are capable of simultaneously testing different components in one or more devices under test having different set point temperatures. The thermal control of the different components is such that they have temperatures within a tolerance (such as 1%, 5%, etc.) from respective set point temperatures without compromising the performance of the components. Additionally or alternatively, the test systems of the disclosure are able to test device(s) comprising multiple components having different heights at a given time without compromising thermal performance. 
     Although  FIGS.  2 A- 2 C  illustrate two components with eight other components located along the sides of a substrate, embodiments of the disclosure may include any number and/or arrangement of components. Additionally or alternatively, the components in a device may be arranged in any manner not shown in the figure. 
     Embodiments of the disclosure may include a test system comprising a thermal head configured to thermally control one or more devices under test.  FIGS.  3 A- 3 B  illustrates cross-sectional views of an example thermal head comprising a plurality of adapters, according to some embodiments. The thermal head  350  may be configured to test one or more devices. The device may comprise component  302 A, component  302 B, component  303 A, component  303 D, substrate  310 , interconnects  306 , and interconnects  316 , which may have one or more properties similar to component  202 A,  202 B,  203 A,  203 D, substrate  210 , interconnects  206 , or interconnects  216 , respectively. 
     The thermal head  350  may comprise a plurality of adapters  330 A- 330 D. Adapters  330 B and  330 C may be located at the inner regions of the thermal head  350 , and the adapters  330 A and  330 D may be located at the outer regions of the thermal head  350 . Each adapter  330  may be thermally coupled to a corresponding component of the device. In some embodiments, one or more (e.g., each) adapters may be thermally coupled to one component. In some embodiments, a first adapter may be thermally coupled to a first component, and a second adapter may be thermally coupled to a second component. Adapter  330 A may be thermally coupled to component  303 A, adapter  330 B may be thermally coupled to component  302 A, adapter  330 C may be thermally coupled to component  302 B, and adapter  330 D may be thermally coupled to component  303 D. In some embodiments, the number of adapters used for testing a device may be the same as the number of components in a device. In some embodiments, at least one adapter may be thermally coupled to one or more (e.g., at least two) components. For example, an adapter may be thermally coupled to a first component and a second component. In some embodiments, the number of adapters used for testing a device may be less than the number of components in a device. 
     By being thermally coupled, the temperature of an adapter may affect the temperature of a corresponding thermally-coupled component. In some embodiments, two or more adapters may be thermally independent from one another such that the temperature of one adapter and/or its corresponding thermally-coupled component may not affect the temperature of another adapter and/or its corresponding thermally-coupled component. For example, the adapter  330 B may be thermally independent from the adapter  330 C, resulting in the temperatures of the adapters and/or corresponding thermally-coupled components not affecting each other. In some embodiments, the adapters and/or thermally-coupled components may be independently controlled, such as independently thermally controlled. 
     The independent control may comprise one or more of: independent thermal control (e.g., using independent adapters, independent heaters, independent flow control, independent heat sinks, and/or independent cold plates), or independent force control (e.g., using independent force mechanisms). In this manner, the test system may provide different thermal control for different components of a device. 
     One or more properties of one or more adapters may be such that different properties (e.g., heights) of the components may be accounted for such that the heat transfer between a thermal head and a component may not be compromised due to, e.g., the size of the component. For example, one or more properties (e.g., size, force, etc.) of the adapter  330 B may be different than one or more properties of the adapter  330 C to account for the height difference between the component  302 A and the component  302 B. In some embodiments, the size (e.g., height) of an adapter and/or associated components may be related (e.g., inversely proportional) to the size of the corresponding thermally-coupled component. As one non-limiting example, the height of adapter  330 C may be taller (compared to the adapter  330 B) due to component  302 B being shorter (compared to the component  302 A). 
     In some embodiments, first adapter  330 B may have a first height and second adapter  330 C may have a second height. This difference in height may account for height differences between corresponding components of the device(s) under test. In some embodiments, first adapter  330 B may have a first thermal mass and second adapter  330 C may have a second thermal mass. The difference in thermal mass may account for differences in thermal masses between corresponding heaters. In some embodiments, first adapter  330 B may have a first surface area, and second adapter  330 C may have a second area. This difference in surface area may account for differences in surface area between corresponding components of the device(s) under test, or differences in thermal interface material (TIM) layers. The adapters may have other differences, such as different thermal conductivities, widths, etc. In some embodiments, differences in the adapters may lead to heating or cooling the components by different amounts. 
     The multiple-adapter thermal head of the disclosure comprises a monolithic adapter that is thermally coupled to components of a device under test. The monolithic adapter may be made of a continuous material. In some instances, the monolithic thermal head may comprise a monolithic cold plate, a monolithic heater, and/or a plurality of large-sized heaters (greater than 900 mm 2 , as one non-limiting example). An example adapter is described in more detail below. 
     As shown in the figure, the thermal head  350  may include one or more heaters  356  thermally coupled to one or more adapters and one or more components of one or more devices under test. For example, the adapter  330 B may be thermally coupled to a heater  356 B, and the adapter  330 C may be thermally coupled to a heater  356 C. The first heater  356 B may be configured to heat the first component  302 A, and the second heater  356 C may be configured to heat the second component  302 B. In some embodiments, two or more heaters  356  may be thermally independent from each other such that the thermal control of one and/or its corresponding thermally-coupled component may not affect the thermal control of another heater  356  and/or its corresponding thermally-coupled component. In some embodiments, one or more (e.g., each) adapters may be thermally coupled to a unique heater. In some embodiments, one or more adapters, such as the adapter  330 A shown in  FIG.  3 A , may not be thermally coupled to a heater. Example heaters are discussed in more detail below. 
     A heater may be located close to a corresponding thermally-coupled component so that the delay between the change in temperature of the heater and the change in temperature of the device may be minimized. In some embodiments, at least one heater may be located adjacent to (e.g., contacts) at least one component, or an intermediate layer (e.g., a TIM layer) that contacts the component. In some embodiments, at least one heater may be located adjacent to (e.g., contacts) at least one adapter. The at least one heater and the at least one adapter may comprise mating alignment features for aligning the two together. Any misalignments may reduce the amount of thermal coupling between the heater and the adapter. Example mating alignment features may include, but are not limited to, protrusions on one surface and mating indents on another surface, or the perimeter shape of one element (e.g., the heater) and a corresponding recess or outline in the adapter or a retainer. 
     Embodiments of the disclosure may include a heater comprising a plurality of (e.g., at least two) heating elements that are spatially separated and thermally isolated using a thermal insulator between the heating elements. In some embodiments, a thermal insulator (e.g., a thermal insulating material or air) may be located between at least two heating elements to prevent or reduce thermal coupling between them. Example thermal insulating materials may include, but are not limited to, materials having low thermal conductivity (e.g., polymers, plastics), materials having a high void content (e.g., foam materials, mineral wool), air, vacuum, or the like. In some embodiments, the thermal insulating material may comprise through-holes or trenches for increased thermal isolation. 
     In some embodiments, a heater  356  may be a small-sized heater (less than 500 mm 2 , as one non-limiting example). Small-sized heaters may have increased complexity and/or manufacturing yields compared to large-sized heaters. Small-sized heaters may also be easier to control due to their lower thermal mass, particularly suitable for maintaining a device at or within a certain range from a set point temperature. In addition to being easier to control, small-sized heaters may operate faster (in terms of temperature change), making thermal control of a device under test more stable and accurate. In some embodiments, the size of a heater may be based on the size of the component that it is thermally coupled to. For example, a device under test may comprise a plurality of components having different sizes, such as large-sized components and small-sized components, and the corresponding test system may comprise a plurality of heaters having different sizes, such as large-sized heaters and small-sized heaters. In some embodiments, the surface areas of the device and heater that contact each other may be the same. An intermediate layer such as a TIM layer may also have the same surface area. 
     Additionally or alternatively, one or more TIM layers  322  may be used to enhance thermal coupling between an adapter and a corresponding component of the thermal head or DUT. In some embodiments, a TIM layer  322  may be located on at least one side of an adapter and/or a heater. The TIM layer  322  may be located between an adapter and a device (such as TIM layer  322 A located between adapter  330 A and component  303 A), between a heater and a device (such as TIM layer  322 B located between heater  356 B and component  302 A), or between an adapter and a heater (such as TIM layer  332 C located between adapter  330 C and heater  356 C). Additionally or alternatively, in some embodiments, a TIM layer may be located between an adapter and a heater, and the same or a different TIM may be located between the heater and a device (e.g., a TIM layer on both sides of the heater). In some embodiments, different TIM layers may have different properties. For example, the thermal resistance of the TIM layer  322 B may be different from the thermal resistance of the TIM layer  322 C. Example TIM layers are discussed in more detail below. 
     In some embodiments, one or more properties of the heater and/or TIM may be configured to account for different sized components such that the heat transfer between a heater (or an adapter) and a component may not be compromised due to the size of the component. Returning back to the previous example of component  302 A being taller than component  302 B, in some embodiments, the height of the heater  356 B and/or TIM layer  322 B may be less than the height of the heater  356 C and/or TIM layer  322 C. 
     Embodiments of the disclosure may further include one or more force mechanisms  332 A or  332 B to move a corresponding adapter closer to a thermally-coupled component. Example force mechanisms may include, but are not limited to, a spring, a lever coupled to a force applicator, or a force applicator. In some embodiments, the force mechanism  332  may apply a force onto one side of the adapter to move the other side closer to the surface of the TIM layer  322  and/or component. In some embodiments, movement of a first adapter is independent from movement of a second adapter; for example, movement of adapter  330 B may not cause movement of adapter  330 C, and therefore movement of heater  356 B may be independent from movement of heater  356 C. As one non-limiting example, the independent movement of the adapters may account for any height differences (e.g., due to manufacturing tolerances). Embodiments of the disclosure comprise test systems capable of independently controlling the forces on different components. 
     The disclosed thermal head may comprise one or more controllers. One example controller is a thermal controller configured to control one or more heaters. A thermal controller may send one or more signals to a given heater including, but not limited to, sending different signals to different heaters such that they are independently controlled. For example, a first signal sent to the first heater  356 B may adjust its temperature without affecting the second heater  356 C. In some embodiments, at least two components may be tested at different temperatures during a given test operation, and corresponding controllers and heaters may operate independently to maintain the components at those respective temperatures. For example, a first controller and corresponding heater  356 B may operate to insure the first component  302 A is at a first temperature, while a second controller and corresponding heater  356 C may operate to insure the second component  302 B is at a second temperature. 
     In some embodiments, at least two components and corresponding heaters  356  may have different changes in temperature. The at least two components may have different power dissipation levels, for example, and as a result, different changes in temperature. For example, the first component  302 A may dissipate a first power level, and the second component  302 B may dissipate a second power level. The first heater  356 B may operate at a first change in temperature corresponding to the first power level, while the second heater  356 C may operate at a second change in temperature corresponding to the second power level. Additionally or alternatively, the thermal controller may control the temperature(s) based on power dissipated from the component(s) of one or more devices under test. 
     In some embodiments, two or more adapters may be thermally dependent, such that they are thermally coupled together. Two or more adapters (e.g., adapters  330 A and  330 D) may be coupled to the same inputs from the thermal controller. For example, the components  303 A and  303 D may be low-power memory chips or packages arranged in a row of four, such as shown by the arrangement of components  203 A- 203 D on the left side of  FIG.  2 A  or components  203 E- 203 H on the right side. A single adapter or a plurality of adapters may be thermally coupled to plurality of components. In some embodiments, the plurality of adapters and/or the plurality of components may have the same height. 
     Additionally or alternatively, the controller may comprise a force controller configured to send a plurality of signals to the thermal head to independently control one or more forces applied to one or more components. The force controller may send one or more signals to a given force mechanism, such as sending different signals to different force mechanisms to control the force applied by a given adapter. As one non-limiting example, a force controller may cause a first force to be applied to a first adapter  330 B and a second force to be applied to a second adapter  330 C. For example, the force controller may apply a larger force to a component having a larger surface area compared to a component having a small surface area. In some instances, the pressure on the larger surface area component may be the same as the pressure on the smaller surface area component. 
     In some embodiments, the thermal head  350  may comprise one or more cold plates configured to lower the temperature of one or more of: one or more adapters, one or more components, or the device.  FIG.  3 B  illustrates an example thermal head comprising a cold plate  362 . In some embodiments, at least two of the plurality of adapters may be thermally coupled to the same cold plate, such as adapter  330 B and  330 C being thermally coupled to cold plate  362 . Thermal energy may be transferred to/from the cold plate  362  to the adapter  330 B and/or adapter  330 C. The cold plate  362  may be located on the top side of one or more adapters  330 , and one or more heaters  356  may be located on the bottom side of the adapter(s)  330 . In some embodiments, the cold plate  362  can cool components  303 A and/or  303 D by, e.g., contacting at least a part of the force mechanisms  332 A and/or  332 B. 
     In some embodiments, the thermal head  350  may comprise a plurality of cold plates, such as shown in  FIG.  3 C . At least two cold plates may be thermally independent from one another. Cold plate  362 B may be thermally coupled to the adapter  330 B, and the cold plate  362 C may be thermally coupled to the adapter  330 C. The thermal control of the cold plate  362 B may not affect the temperature and/or thermal control of the cold plate  362 C and vice versa, for example. 
     In some embodiments, movement of cold plate  362 B may be independent from movement of cold plate  362 C. The amount of force applied may depend on the properties of the corresponding component, heater, TIM, adapter, or a combination thereof. More force may be applied when a corresponding component has a larger surface area, for example. Example force mechanisms are discussed in more detail below. 
     In some embodiments, at least two components and corresponding cold plates  362  may have different changes in temperature due to, e.g., having different power dissipation levels. For example, the first component  302 A may dissipate a first power level, and the second component  302 B may dissipate a second power level. The first cold plate  362 B may operate with a first temperature corresponding to the first power level, while the second cold plate  362 C may operate with a second temperature corresponding to the second power level. Additionally or alternatively, the cold plates  362 B and  362 C may operate at different temperatures, such as when the corresponding components are tested at different temperatures. 
     The thermal controller may be configured to control one or more heaters (as discussed above), one or more cold plates, or both. To control the cold plate(s), the thermal controller may send one or more signals to one or more flow control valves associated with each cold plate. In instances where the thermal head comprises at least two cold plates, the thermal controller may send one signal to one cold plate&#39;s flow valve without affecting the flow through another cold plate&#39;s valve (independent flow control). The cold plate and associated thermally-coupled components (adapter, heater, component, etc.) may be thermally isolated from other (e.g., neighboring) cold plates and associated thermally-coupled components. In some embodiments, a thermal insulator (e.g., a thermal insulating material or air) may be disposed between neighboring cold plates. 
     The properties of a cold plate  362  may be based on the properties of a thermally-coupled adapter  330 . For example, the surface area of the cold plate  362  (that contacts the adapter) may be the same as the surface area of the adapter  330  (the top side of the adapter that contacts the cold plate). As discussed in more detail below, a cold plate  362  may comprise one or more cooling channels that a liquid or gas may flow through. The flow rate and/or temperature of the liquid or gas may affect the cooling abilities of the cold plate  362 . 
     Example Thermal Head 
     Embodiments of the disclosure may include one or more thermal heads with the properties as described herein. For purposes of simplifying the descriptions, some of the figures may illustrate some, but not all, portions of the disclosed thermal heads. A portion of a thermal head, comprising an adapter, will now be described, but the thermal head may include other portions not disclosed or in combination with the disclosures herein.  FIG.  4    illustrates a cross-sectional view of a portion of a thermal head, according to some embodiments. The thermal head  450  is configured to thermally control a component  402  mounted on a substrate  410 . Although the figure illustrates a single adapter  430  and single component  402  on a single substrate  410 , embodiments of the disclosure may include any number of components (e.g., 2, 3, 4, 5, 10, etc.), any type of components (e.g., high-power chips, low-power chips, passive components, etc.), and any number of substrates. 
     When testing a device, it may be difficult, but important, to control the temperature of the device while being tested. In some instances, thermal control may require heating or cooling one or more components of the device at a rapid rate so that the component(s) may reach the set point temperature quickly and the temperature remains constant during the test. 
     The adapter  430  may comprise a continuous piece of thermally-conductive material. For example, the adapter  430  may comprise a metal such as copper, aluminum, silver, or a metal matrix composite (copper-diamond, aluminum-diamond, copper-graphite, aluminum-graphite, etc.). One or more properties (e.g., thermal mass, height, surface area, etc.) may be based on the set point temperature and/or the properties of the thermally-coupled heater and/or cold plate. 
     In some embodiments, the thermal head  450  may comprise a heater  456 . The heater  456  may be configured to apply heat to the component  402 . In some embodiments, the heater  456  may increase the temperature of the component  402  when, e.g., the component power is low and/or when its temperature is lower than the set point temperature of the component  402 . The heater  456  may be any type of heater including, but not limited to, a solid-state device (e.g., comprising a ceramic body with one or more resistive traces), a cartridge heater in a thermally-conductive body, a thermoelectric device (TED), a silicon-based semiconductor device, etc. In some embodiments, the heater  456  may have a low thermal mass. In some embodiments, the thermal mass of the heater  456  may be less than the thermal mass of the adapter  430 , the cold plate  462 , or both. In some embodiments, the thermal mass of the heater  456  may be at least 5 times lower than the thermal mass of the adapter  430 . In some embodiments, the thermal mass of the heater  456  may be at least 10 times lower than the thermal mass of the adapter  430 . The thermal mass of the heater  456  may affect its responsivity, temperature ramp rate, and conductive heat transfer, e.g., through the heater  456 , adapter  430 , cold plate  462 , or a combination thereof. 
     Additionally or alternatively, the thermal head  450  may comprise cold plate  462 . The cold plate  462  may be configured to cool the adapter  430 , which may thereby cool the heater  456  and/or component  402 . When the heater  456  is off, the cooled adapter  430  may cool the heater  456 . The cold plate  462  may include one or more cooling channels  469 , which may circulate liquid or gas to cool the cold plate  462 . Example liquids may include, but are not limited to, water, a heat transfer fluid, a refrigerant coolant, a gas, etc. In some embodiments, one or more other cooling mechanisms may be used to cool the cold plate  462 , such as a thermo-electric cooler (TEC) (as one non-limiting example). The TEC may cool the cold plate  462  below the temperature of a fluid circulating through the cold plate  462 , for example. As another (non-limiting) example, a chiller or a radiator may be used to cool the temperature of the fluid. 
     The adapter  430  may be configured to thermally couple to the component  402 . Better thermal coupling may lead to better thermal control. In some embodiments, thermal coupling may occur by way of the adapter  430  making contact with the component  402  and/or using one or more intermediate layers to facilitate heat transfer between the adapter  430  and the component  402 . TIM layers  422  are example intermediate layers. 
     In some embodiments, one or more TIM layers  422  may be located between one or more components of the thermal head  450 . A TIM layer  422  may be used to reduce thermal resistance, thereby enhancing the thermal coupling. For example, one TIM layer  422  may be located between the adapter  430  and the heater  456 , and/or one TIM layer  422  may be located between the heater  456  and the component  402 . As another example, a TIM layer  422  may be located between the cold plate  462  and the adapter  430  (not shown). In some instances, a TIM layer may be excluded, and instead, the cold plate  462  and adapter  430  may be one continuous material (e.g., a cold plate with one or more adapters machined out of its surface). A TIM layer may comprise one or more of: a thermal grease (e.g., oil or other material comprising embedded thermally-conductive particles such as metal particles or ceramic particles), a liquid material (e.g., glycol, water), a carbon material, a metallic malleable material (e.g., a low-melting point material such as indium, tin, or a combination of materials such as a thermally conductive elastomeric pad with an aluminum foil cover layer), a thermally conductive elastomeric pad, or the like. 
     In some embodiments, thermal coupling between the adapter  430  and the component  402  may be improved when there is a force applied to components of the thermal head  450  and/or the component  402 , making better contact. The thermal resistance between the adapter  430  and the component  402  may be related to the amount of applied force. The applied force may also impact the contact between socket contactors and interconnects  416  (which the test system uses to electrically connect to the component). Additionally or alternatively, the applied force may help prevent or reduce the component  402  and/or substrate  410  from unwanted warping, which may lead to defects. 
     Embodiments of the disclosure may include other types of intermediate layers including, but not limited to, bumps, posts, or other contacts over the surface of the adapter, cold plate, and/or heater to increase or decrease thermal coupling. The number, size, density, and/or pattern of the bumps, posts, or contacts may be configured such that a target thermal resistance between an adapter and a heater, an adapter and a cold plate, or a heater and a component may be obtained. In some embodiments, the thermal resistance may be configured according to the type of component or device. For example, the test system for a low-power component may be configured with high thermal resistance. A low-power heater may be used for thermal control, and due to the high thermal resistance, may be able to easily heat up the low-power component. 
     The thermal head  450  may further comprise one or more temperature sensors to measure the temperature of the adapter  430 , heater  456 , or cold plate  462 . The measured temperature may be used by the thermal controller to set, adjust, or maintain the temperature of the adapter  430 , heater  456 , and/or cold plate  462 . The measured temperature may be compared to a set point temperature, and the signals sent to the controller may be updated accordingly to minimize the difference between the measured temperature and the set point temperature. Setting, adjusting, or maintaining the temperature of the heater  456  may comprise setting, adjusting, or maintaining the current or voltage from the thermal controller to the heater  456 . Setting, adjusting, or maintaining the temperature of the cold plate  462  may comprise setting, adjusting, or maintaining the flow rate or temperature of the liquid or gas associated with the cold plate  462 . In some embodiments, the update frequency of the thermal controller for controlling the temperatures is less than 200 microseconds. 
     An example method for controlling the temperature of a component includes, but is not limited to, setting or adjusting the temperature based on whether the measured temperature (e.g., heater temperature) is above or below the set point temperature (or set point temperature range). If the measured temperature is above the set point temperature, the thermal controller reduces the amount of power to the heater. If the measured temperature is below the set point temperature, then the thermal controller increases the amount of power to the heater. In some embodiments, the heater may be configured for a specific power output of the thermal controller. As one example, the thermal controller is capable of powering the heater with up to 500 W using 100 V, where the heater generates 500 W with a 100 V supply (e.g., for the set point temperature or across the set point temperature range). In some embodiments, the heater may be configured for the corresponding component, such as the heater having an output power that is greater than the output power of the component. For example, a 30 W heater may be used to heat a 10 W component, while a 300 W heater may be used to heat a 100 W component. The lower the thermal mass of the heater, the more effective the heater  456  becomes in increasing the temperature of the component  402  quickly. In some embodiments, the thermal controller separately sets or adjusts different temperatures of the thermal head. For example, the controller sets or adjusts a DUT temperature, an adapter temperature, a cold plate temperature, etc. 
     Example Heater 
       FIG.  5 A  illustrate a cross-section diagram of an example heater, according to some embodiments of the disclosure. The figure illustrates one surface  558  of the heater  556 , which contacts an adapter  530  or one or more TIM layers (which would be located between the surface of the heater  556  and the adapter  530 ). Another surface  559  of the heater  556  may contact a component of the DUT or a TIM layer (which would be located between the surface  559  of the heater  556  and a component of the DUT). 
     In some embodiments, the heater  556  may comprise a plurality of heater pins, one or more heating elements, one or more measurement traces, or a combination thereof. Some of the plurality of pins  551  (including pins  551 A and  551 B),  553  (including pins  553 A and  553 B),  555  (including pins  555 A and  555 B), and  557  (including pins  557 A and  557 B) may be pins used to carry electrical current into and out of the heater  556 . In some embodiments, the pins  551 ,  553 ,  555 , and/or  557  may be attached to one or more pads (not shown) on the heater  556 . Example methods for attaching the heater pins to the pads include, but are not limited to, brazing, soldering, gluing (e.g., using electrically-conductive epoxy), etc. As shown in the figure, one or more insulating layers  566  may insulate the pins  551 ,  553 ,  555 , and  557  from the adapter  530 , e.g., to prevent electrical shorts. The insulating layers  566  may be located around the heater pins, and/or between the heater pins and the adapter  530 . The insulating layers  566  may comprise one or more of: plastic, rubber, ceramic, or another dielectric. In some embodiments, an insulating layer  566  may be a hollow polytetrafluoroethylene (PTFE) tube with an inner diameter sized for the diameter of a heater pin and an outer diameter configured to fit into clearance holes in the body of the adapter  530 . 
     Although  FIG.  5 A  illustrates a single row of six heater pins, embodiments of the disclosure may comprise any configuration and number of heater pins, such as a single row of heater pins arranged around the perimeter of the surface of the heater, two heater pins in a row on one side of the heater, 10 or more heater pins in a row, 4 pins in two rows on two sides of the heater, or the like. In some embodiments, the plurality of heater pins may occupy less than 10%, 30%, 50%, etc. of the surface  558  of the heater  556 . In some embodiments, the inner region of the surface  558  of the heater  556  may exclude heater pins to allow the heater  556  to make contact with the adapter  530  at the inner region. 
     The heating elements  563  and  565  may be used to generate heat for the heater  556 . In some embodiments, the heating elements  563  and  565  may comprise resistors and/or resistive traces. The total area of thermal control by the heater  556  may depend on the properties of the heating elements  563  and  565 . For example, the heating elements  563  and  565  may be formed on separate layers within the body of the heater  556 , where one or more resistive traces of the heating element may be formed on a plurality of layers so that a target resistance within a target area of the heater  556  may be obtained. In some embodiments, the heating elements  563  and  565  may be located closer to the adapter  530  than the ground plane  567  and measurement trace  561 . 
     In some embodiments, each zone of the thermal head may comprise one or more heating elements and a measurement trace  561 . In some embodiments, any number of heating elements and measurement traces may be associated with a zone, depending on the power requirements of the zone and power limitations of the heating elements. In some embodiments, the total area of thermal control may be the same as the total surface area of the heater  556 . Alternatively, the total area of thermal control may be less (e.g., 20%) than the total surface area of the heater  556 . A heating element may be located throughout a large percentage (e.g., 80% or more) of the surface of the heater  556 , or certain zone(s) of the heater  556 . In some embodiments, one or more first heating elements may be associated with one or more first zones, and one or more second heating elements may be associated with one or more second zones. As one non-limiting example, the first heating elements and first zones may be high-power heating elements and high-power zones, respectively, while the second heating elements and second zones may be low-power heating elements and low-power zones, respectively. 
     The heating elements  563  and  565  may be configured to generate heat using, e.g., resistors. The heating elements may be electrically coupled to heater pins such that power via a current or voltage signal can be applied to the heater pins to turn on the corresponding heating elements. Power applied to pins  553 A and  553 B may cause the electrically-coupled heating element  563  to turn on and generate heat, and power applied to pins  555 A and  555 B may cause the electrically-coupled heating element  565  to turn on and generate heat. In some embodiments, the number of heating elements and/or heating element layers may be increased to increase the overall power output from the heater  556  at a given voltage. For example, a heater  556  may comprise five heating elements, each configured to generate 200 W at 200 VDC, thereby generating a total output power of 1000 W. 
     In some embodiments, the heater  556  may comprise a plurality of heating zones. In some embodiments, the heater  556  may comprise one or more insulating mechanisms to insulate two or more heaters or heating zones from each other. One example insulating mechanism comprises through-holes or trenches in the body of the heater at location(s) between the heating elements and edge(s) of the heating zones. Another example insulating mechanism comprises using different adapters for different zones, such as one or more first adapters and associated heaters for a first heating zone, and one or more second adapters and associated heaters for a second heating zone. 
     The measurement trace(s)  561  may be used for measuring the temperature of one or more surfaces (e.g., the surface  559  that contacts a component or an intermediate TIM layer) of the heater  556 . The measurement trace  561  may be located within the body of the heater  556 . The measurement trace  561  may be located close to the surface  559 , for example. In some embodiments, the measurement trace  561  may be a trace with a certain temperature coefficient of resistance such that its resistance can be correlated to a temperature reading, this type of device is also referred to as a resistance temperature detector (RTD). 
     In some embodiments, after manufacturing the heater  556 , resistances of the measurement trace  561  can be measured at different temperatures to generate pre-determined calibration information such as a calibration curve, calibration table, or associated relationships (between resistance and temperature). The pre-determined calibration information may be stored in, e.g., a non-volatile memory chip or coded into a 1D or 2D code (e.g., a linear barcode or 2D matrix barcode) or stored remotely in a database. The pre-determined calibration information may be used by a controller to determine the temperature of a heater or heat zone and use that knowledge to control one or more resistors (e.g., resistor  563  or resistor  565 ) included in the heater for thermal control of a corresponding zone. 
     In some embodiments, a measurement trace  561  may be coated with a dielectric. The thickness of the dielectric may depend on the physical construction and limitations of the heater  556 . In some embodiments, the dielectric may have a thickness less than 2 mm. In some embodiments, the dielectric may have a thickness less than 0.4 mm. The measurement trace  561  may be located throughout the surface  559  of the heater  556  that contacts a component or intermediate layer (e.g., a TIM layer that contacts the component). For example, the area in which the measurement trace  561  is located may be the same as the area in which another heating element (e.g., resistor  563  or resistor  565 ) is located, although these may be on different layers in the heater. 
     While some of the plurality of pins may be used to carry electrical current for heating, others may be used for shielding. Pins  557 A and  557 B, shown in  FIG.  5 A , may be electrically coupled to a ground plane  567  for electromagnetic interference (EMI) shielding. The ground plane  567  may be grounded, providing an electrical ground path to the heater  556  during testing. During testing, the heaters may be turned on and off in rapid succession, at high voltages and currents, which can generate electrical noise that can potentially interfere with the testing circuitry or measurements. Shielding the heater elements with a ground plane  567  that covers them may reduce or eliminate the unwanted electrical noise. In some embodiments, the pins  557 A and  557 B may be electrically coupled to an adapter. For example, as shown in the adapter illustrated in  FIG.  5 B , the adapter  530  comprises a hole  525  that provides access to the pin  557 A and/or pin  557 B. The hole  525  may expose ground pin  523  that may be attached to an adapter  530  by being, e.g., soldered, spot welded, brazed, glued (e.g., using an electrically-conductive adhesive), etc. In some embodiments, the pin  557 A and/or pin  557 B may be attached to the adapter  530  by, e.g., soldering. Having both the adapter  530  and ground plane  567  grounded improves the shielding of the heater elements compared to having only the ground plane  567  grounded. In the case where both the adapter  530  and ground plane  567  are grounded, there is an effective shield formed both above and below the heater elements. 
     In some embodiments, the adapter may include a retainer  571 . The retainer  571  may be configured as a mechanical attachment for attaching (e.g., requiring a tool for removal) the heater  556  to the adapter  530 . This mechanical attachment facilitates thermal coupling between the heater  556  and the adapter  530 . Example mechanism attachments include, but are not limited to, clamps, screws, retains, or the like. As shown in the figure, the retainer  571  may be located within the body of the adapter  530 , allowing the heater  556  and adapter  530  to have any sizes for surface areas, including the same-sized surface area (as one non-limiting example). With the size of the adapter being the same or substantially the same as the size of the corresponding component, the disclosed test systems are able to quickly change the temperature of the component due to, e.g., the thermal mass of the adapter. In some embodiments, the hole  525  in the adapter  530  provides access to one or more pins, such as pins  557 A and  557 B. 
     Additionally or alternatively, the retainer  571  may be configured for electrically coupling the adapter  530  to one or more ground pins  523 . The ground pin  523  may be flexible ground pins, for example, that allow the heater  556  and adapter  530  to expand at different rates. The heater  556  and adapter  530  may have different coefficients of thermal expansion, allowing the two to expand and contract at different rates with temperature changes without undue stress or strain on either component and while maintaining good thermal contact between the adapter  530  and the heater  556 . 
     In some embodiments, the heater is attached (e.g., requires a tool for removal) to the adapter. An attached heater results in better thermal coupling between the adapter, heater, and/or any intermediate layers. Without attaching the heater, any movement in the adapter and/or intermediate layers may limit how quickly heat can transfer from the heater to the adapter and/or corresponding component. 
     Referring back to  FIG.  5 A , the ground plane  567  may be a solid ground plane or a perforated ground plane (the size of the perforations may be configured based on desired EMI frequencies). In some embodiments, the area of the ground plane  567  may be greater than or equal to the area of the heating elements. In some embodiments, the area of the ground plane may be at least 80%, 85%, 90%, 95%, etc. of the area of the surface of heater  556 . The ground plane  567  may be located within a certain depth from the surface of the heater  556  (that contacts a component or an intermediate layer), such as (but not limited to) less than 1.5 mm, less than 1 mm, less than 0.6 mm, etc. 
     Although not shown in the figure, the heater  556  may comprise a plurality of dielectric layers, a plurality of conductive layers, and/or a plurality of conductive vias for making electrical connections between the plurality of conductive layers. In some embodiments, the outer surfaces of the heater may comprise a protection layer (e.g., a dielectric such as ceramic) to protect the conductive layers located within the heater  556 . 
     Example Cold Plate 
       FIGS.  6 A and  6 B  illustrate cross-section diagrams of an example cold plate, according to some embodiments of the disclosure. The cold plate  662  may be oriented such that its bottom surface  691  is located closest to a corresponding heater or adapter. The cold plate  662  comprises a cavity with an inlet and outlet for coolant  671  to circulate through the cooling channels  669 . The cavity may be formed by a top plate  673  and a bottom plate  675 . The cold plate  662  comprises a plurality of fins  663 . In some embodiments, the plurality of fins  663  may comprise fins that are long, rectangular fins or rounded pin fins. The plurality of fins  663  may be integrated into the bottom plate  675  and top plate  673 . In some embodiments, the plurality of fins  663  may be oriented perpendicular from the top plate  673  and/or bottom plate  675 . The plurality of fins  663  are used to increase the surface area that contacts the coolant  671  that flows through the cold plate  662 , thereby providing more effective heat transfer from the cold plate  662  to the coolant  671 . 
     Example Thermal Interface Material (TIM) Layers 
     The test system disclosed herein may use one or more TIM layers. A TIM layer may affect the thermal resistance between an adapter and a heater, an adapter and a cold plate, an adapter and a component, or a heater and a component. A TIM layer may be selected based on one or more properties of the thermal head, adapter, heater, cold plate, a component on the device under test, etc. The thermal resistance may be adjusted by configuring the thickness of the TIM layer and/or its thermal conductivity, for example. Additionally or alternatively, the surface area of a TIM layer may be adjusted by including one or more openings or holes  727 , as shown in  FIG.  7 A . The thermal resistance of the TIM layer  722  may be configured based on size and/or number of openings or holes  727 . In some embodiments, the TIM layers  722  in a thermal head may be different, e.g., a first TIM layer may have a greater surface area than a second TIM layer. 
     In some embodiments, the TIM layer  722  may be configured based on the properties of the associated component and/or zone. For example, a high thermal resistance TIM layer may be used for a low-power component. In some embodiments, the properties of the TIM layers may be different for different components and/or zones of a device. 
     The TIM layer  722  may be formed using any technique, such as dispensing a liquid TIM  722  on a component or device, as shown in the example of  FIG.  7 B . Using a liquid TIM may help minimize gaps between an adapter and a component, for example, which may reduce the thermal resistance between the two; although other types of TIM materials may be included, such as a solid TIM material, a paste TIM material, or a grease TIM material. A reduced thermal resistance may be beneficial in instances, such as when an adapter does not comprise a heater, when an adapter is used only for cooling, when an adapter is used for adjusting the temperature of a high-power component, or when an adapter comprises a heater and is used for both heating and cooling, among others. 
     A liquid TIM may be dispensed on the component(s) or device prior to testing and then removed after testing has been completed. To determine whether the dispensed liquid TIM meets target properties (e.g., amount, location, thickness, etc. of the dispensed TIM), one or more techniques may be employed to inspect the dispensed liquid TIM, such as a machine vision system that visually inspects and compares it to one or more pre-determined criteria, or a system that tests its thermal resistance value. Based on whether or not the dispensed TIMs meet one or more target properties, the test system may proceed with performing the test (dispensed TIM qualifies), or create an alert (dispensed TIM does not qualify). In this manner, a device may be tested only when the TIM properties do not affect the testing of the device, ensuring that the testing results accurately represent the performance of the device. Too much dispensed liquid TIM may overflow onto one or more components and may adversely affect it during testing (e.g., if the liquid TIM is electrically conductive), or could pose a reliability issue for the device (e.g., if the liquid TIM induces corrosion or other deleterious effects). Too little TIM may lead to high thermal resistance(s), causing problems with the testing such as being able to maintain the component at a set point temperature. In some instances, if no TIM was dispensed and a high power is applied to the component, the component may fail due to thermally-induced catastrophic failure. 
     Example Thermal Head for a Device Comprising Stacked Components 
     Embodiments of the disclosure may comprise other types of devices, such as a device that may comprise one or more stacked components.  FIGS.  8 A and  8 B  illustrate top and cross-sectional views, respectively, of a device including stacked components, according to some embodiments. The device  800  may include a plurality of components, such as component  802 B, component  802 T, and components  803 A-H mounted on a substrate  810 . One or more components may be stacked on one or more other components, such as component  802 T being a top component stacked on a bottom component  802 B. In some embodiments, the footprint of component  802 T may be smaller than the footprint of component  802 B. Component  802 B may be a high-power component, for example. In some embodiments, the stacked components  802 B and  802 T may be coupled together using, e.g., one or more interconnects  818  such as one or more of: TSVs, microbumps, or the like. In some embodiments, components  803 A-H may be auxiliary components. 
     As one non-limiting example, the component  802 T may be a cache memory chip, and the component  802 B may be a processor chip, where the component  802 T may be stacked on the component  802 B. In such an arrangement, the component  802 T may be a standalone chip (e.g., a chip capable of operating independently) that provides a higher memory capacity than an internal cache in the processor chip itself. Stacking a cache chip  802 T on top of the processor chip  802 B may reduce interconnect length, thereby increasing read/write speeds and reducing latency. In some embodiments, the component  802 B may be a high-power component, and the component  802 T may be a low-power component. 
     Device  800  may further include substrate  810 , interconnects  806 , and interconnects  816 , where one or more of: the substrate  810 , interconnects  806 , or interconnects  816  have properties similar to corresponding substrate  210 , interconnects  206 , or interconnects  216 , respectively. As shown in  FIG.  8 B , there may be one or more height differences among the stacked components (comprising components  802 T and  802 B) and other components  803 C and  803 G in device  800 . 
     The adapters of the thermal head may be configured such that heat transfer between an adapter (and/or heater and/or cold plate) and stacked components may not be compromised.  FIG.  9 A  illustrates a top view of an example device comprising stacked components, according to some embodiments. The device may comprise components  903 A- 903 H. Additionally, the device  900  may comprise at least one stacked component, which includes component  902 T stacked on component  902 B. Device  900  may have one or more properties (e.g., comprising interconnects to electrically couple components to a substrate, interconnects to electrically couple a substrate to a test system, etc.) similar to device  100 ,  200 ,  800 , or a combination thereof. 
       FIGS.  9 B and  9 C  illustrate cross-sectional views of a thermal head  950  and device, along line B-B and A-A, respectively, as drawn in  FIG.  9 A . Thermal head  950  may comprise a first adapter  930 B and/or a first heater  956 B that are thermally coupled to a first component (e.g., one component  902 B and/or lower portion of the stacked components) and a second adapter  930 C and/or second heater  956 T thermally coupled to a second component (e.g., component  902 T and/or upper portion of the stacked components). 
     The test system may comprise a thermal head  950 . The thermal head  950  may comprise plurality of adapters including, but not limited to, adapters  930 A- 930 D. One or more adapters, such as adapters  930 A- 930 D may have one or more properties similar to other adapters disclosed herein, such as adapters  330 A- 330 D. For example, the adapter  930 A may not be thermally-coupled to a heater. As another example, the adapter  930 D may transfer force to a component applied by way of a spring or other force mechanism  932 F. The adapter  930 D may additionally or alternatively be contacting a TIM layer  922 F, located between the adapter  930 D and the component  903 F. 
     In some embodiments, one or more adapters may be thermally coupled to a first portion of the stacked components. For example, adapter  930 B may be thermally coupled to a component  902 B or a portion of a component  902 B of the stacked components. The thermal coupling may comprise one or more corresponding thermally-coupled components as making contact. For example, the adapter  930 B may be thermally coupled to a heater  956 B and a TIM  922 B. The adapter  930 B may contact the heater  956 B, for example. The TIM  922 B may contact a portion of the component  902 B, such as its outer region (e.g., outer perimeter). 
     Adapter  930 C may be thermally coupled to another component (e.g., component  902 T) or another portion of the stacked components. The adapter  930 C may be thermally coupled to a heater  956 T and a TIM  922 C, where the TIM  922 C may contact the top surface of the component  902 T. In some embodiments, the first adapter  930 C may be nested (fully or partially) within the second adapter  930 B. The second adapter  930 B may surround a plurality (two or more, such as four) sides of the first adapter  930 C. The first adapter  930 C and second adapter  930 B may be thermally coupled, for example. 
     In some embodiments, the corresponding first heater  956 T may be nested within the second heater  956 B. The second heater  956 B may surround a plurality (e.g., two or four) sides of the first heater  956 B. Similarly, the first TIM layer  922 C may be nested within the second TIM layer  922 B. In some embodiments, as shown in the figure, a TIM layer  922 C may be located between the components of the stacked components. 
     In some embodiments, the second adapter  930 C may be located in a hollow portion of and surrounded by the first adapter  930 B. In some embodiments, the first adapter  930 B, the corresponding heater  956 B, and/or the corresponding TIM  922 B may contact most (e.g., more than 50%) of the top surface of the component  902 B. 
     In some embodiments, thermal control of the first component  902 B in the stacked components and/or its thermally-coupled (first) adapter  930 B may be independent from thermal control of the second component  902 T in the stacked components and/or its thermally-coupled (second) adapter  930 C. In some embodiments, separate control signals may be transmitted to the corresponding heaters, cold plates, and/or force mechanisms. 
     The different adapters, heaters, and/or TIM layers for different portions of the stacked components may be configured accordingly. For example, the force applied by the adapter  930 C to both components in the stack (component  902 B and component  902 T) may be at least partially transferred as force applied to the bottom component (component  902 B). The adapters may apply force to different regions of component  902 B, so in some embodiments, the force applied by adapter  930 C may be less than the force applied by the adapter  930 B. As another example, the top component  902 T may a memory chip and the bottom component  902 B may be a processor. The heater  956 T for the top component  902 T may be less powerful than the heater  956 B for the bottom component  902 B. Additionally or alternatively, the adapter  930 C (contacting the top component  902 T, or an intermediate layer such as the heater  956 T and/or TIM  922 C) has a lower conductivity, smaller contact area, and/or higher TIM resistance compared to the adapter  930 B (contacting the bottom component  902 B). 
     One or more (e.g., each) of the adapters, heaters, cold plates, and/or TIM layers disclosed herein of a given device may account for differences in the properties of the corresponding components, such as different heights of the components and/or arrangement of components. In the example shown in  FIGS.  9 A- 9 C , adapter  930 A, adapter  930 D, adapter  930 E, and adapter  930 F (and/or corresponding heaters, cold plates, TIM layers, or a combination thereof) may account for the height(s) of component  903 B, component  903 F, component  903 C, and component  903 G, respectively, and any associated TIM layers and/or interconnects. The adapter  930 B, heater  956 B, and/or TIM layer  922 B may account for the height of component  902 B and any associated TIM layers and/or interconnects. The adapter  930 C, heater  956 T, and/or TIM layer  922 C may account for the total height of components  902 B and  902 T and any associated TIM layers and/or interconnects. One or more force mechanisms may be used to move a corresponding adapter, heater, and/or cold plate closer to a thermally-coupled component. For example, the thermal head  950  may comprise a spring  932 B that moves adapter  930 A closer to the component  903 B and a spring  932 F that moves adapter  930 D and TIM  922 F closer to the component  903 F. Other force mechanisms may be used including, but not limited to, a lever, a force applicator, or the like. 
     Example Thermal Head for a Device Comprising Components on a Plurality of Sides of a Substrate 
     In some embodiments, a device under test may include component(s) and/or package(s) located on a plurality of sides of a substrate, such as device  1000  including components  1002 A and  1002 B located on the top side of the substrate  1010 , and component  1002 C located on the bottom side of the substrate  1010 , as shown in the top and cross-sectional views of  FIGS.  10 A and  10 B , respectively. The top view of  FIG.  10 A  illustrates the outline of component  1002 C (located on the bottom side of the substrate  1010 ). As shown in the figures, in some embodiments, the component  1002 C may be located at different regions of the substrate  1010  along the x- and y-axes than the components  1002 A and  1002 B. In some embodiments, high-power component(s) may be located on one side of the substrate  1010  and low-power component(s) on the other side. Interconnects  1006  may be component or package interconnects that mount the components to the substrate  1010 . For example, interconnects  1006 A may mount the component  1002 A to the top surface of the substrate  1010 , interconnects  1006 B may mount the component  1002 B to the top surface of the substrate  1010 , and interconnects  1006 C may mount the component  1002 C to the bottom surface of the substrate  1010 . In some embodiments, the device  1000  may include interconnects  1016  to electrically couple the device  1000  to a board. The board may be a test board with a socket that engages the DUT (when the device  1000  is being tested) or a system board (when the device is being used in a package). 
     Although the figures illustrate chips, packages, or other components as mounted on the surface of a substrate, embodiments of the disclosure may comprise one or more components that are partially or fully enclosed within the substrate. For example, the device under test may be an embedded die or fan-out wafer-level type of package. 
       FIG.  11    illustrates a cross-sectional view of a part of a test system comprising a thermal head and a DUT having components on a plurality of sides of a substrate, according to some embodiments. The device may comprise components  1102 A and  1102 B located on the top side of substrate  1110  and component  1102 C located on the bottom side. The thermal head may comprise a plurality of adapters  1130 A,  1130 B, and  1130 C for independent control of components  1102 A,  1102 B, and  1102 C, respectively. 
     In some embodiments, the thermal head may comprise one or more adapters configured to thermally couple to corresponding components from a plurality of sides of a substrate. The adapters  1130 A and  1130 B are configured to thermally couple from the top side of the substrate  1110 , and the adapter  1130 C is configured to couple from the bottom side of the substrate  1110 . In some embodiments, the thermal coupling and/or contact of the adapters to the plurality of sides of the substrate may occur simultaneously. 
     Additionally or alternatively, the test system  1190  may comprise one or more mechanisms for electrically coupling to send and/or receive test signals from the device. A socket body  1170  may comprise test contact pins  1172 , which may contact and/or electrically couple to the interconnects  1116  of the device. The properties of the adapters  1130 A,  1130 B, and  1130 C may have similar properties to the adapters discussed herein. 
     Embodiments of the disclosure may include any of the properties including those described herein, such as (but not limited to) the device comprising additional components not shown in the figure, one or more adapters thermally coupled to a plurality of components, using a passive or active temperature control, using a passive or active force mechanism, etc. 
     Example Force Mechanisms 
     One (non-limiting) example force mechanism may comprise a piston.  FIG.  12 A  illustrates an example piston, according to some embodiments of the disclosure. The thermal head may comprise the force mechanism, an adapter  1230 , a cold plate  1262 , and a heater  1256 . 
     A piston  1243  is coupled to a ramp  1204  and a roller  1205 . The piston  1243  may move in accordance with the amount of applied force. For example, movement of the piston  1243  to the right along the x-axis causes the ramp  1204  to move, applying a greater amount of force on the roller  1205 , which then applies a greater amount of force on the top of the thermal head may then cause an applied force to the component  1202 . The amount of applied force may be measured by a transducer  1239 . 
     In some embodiments, the piston  1243  and at least a portion of the ramp  1204  may be located off to the side of the thermal head, creating an overall shorter profile than if the force applicator were located on top of the thermal head. The piston  1243 , ramp  1204 , and/or roller  1205  may be used and exchanged for a certain type of component, such as a specific SiP DUT where a greater amount of force is desired (e.g., a high pin-count or ball-count SiP). The specific SiP DUT may be tested without having to change the rest of the test system by removing any other force mechanism and replacing it. The other force mechanism may be attached or detached using screws, bolts, or attachment means. 
     Another example force mechanism comprises a cam-roller, such as the one shown in  FIG.  12 B . The cam-roller comprises a cam  1207 A and a roller  1207 B. The cam  1207 A rotates in a certain direction, such as clockwise, where the rotation of the cam adjusts the amount of force to be applied via the roller  1207 B in the z-direction. 
     In some embodiments, at least one force applied by the force mechanism(s) may be a variable force, wherein the variable force may be different at the beginning of a test (right when testing begins) and during the test, or during the test and at the end of the test (right when testing ends). In some embodiments, the variable force may be force that has been adjusted during the test. In some embodiments, the at least one force may be a fixed force that is the same at the beginning of the test and during the test, or during the test and at the end of the test. Embodiments may include other types of force mechanisms; example force mechanisms are discussed below. 
     Example Test Systems 
       FIG.  13 A  illustrates a cross-sectional view of an example test system, according to some embodiments. The test system  1390  may comprise a thermal head and a socket. The device may comprise a plurality of components  1302 ,  1303 A, and  1303 B mounted on a substrate  1310 . The substrate  1310  may comprise interconnects  1316  to electrically couple to a tester (not shown). The socket comprises a socket body  1318  comprising test contact pins  1317 . Movement of the socket body  1318  towards the device or movement of the device towards the socket body  1318  may cause the test contact pins  1317  to electrically couple to the interconnects  1316 . 
     One of the force mechanisms included in the test system  1390  may comprise a pusher  1331  and force applicator  1333  for electrically coupling the device to the test contact pins  1317  of the test system  1390  for testing (e.g., sending and/or receiving electrical signals from the tester to the device). The force applicator  1333  pushes the pusher  1331 , which then pushes one or more unpopulated portions of the substrate  1310  of the device towards the socket body  1318  and corresponding test contact pins  1317 . The force applicator  1333  can be any type of device that applies a force including, but not limited to, a pneumatic or hydraulic cylinder, a pneumatic or hydraulic diaphragm, a stepper motor, a linear motor, a server motor, an electroactive polymer actuator, a shape memory alloy actuator, an electromagnetic actuator, a rotary motor, an electromechanical actuator, a piezoelectric actuator, a voice coil, or other active force application device. The force applicator  1333  may apply a force between 5-300 kgf, including any force in between. 
     In some embodiments, the test system may comprise a transducer  1329  that measures the force being applied by the force applicator  1333  in real-time (while the force is being applied). The transducer  1329  can generate one or more force measurement signals used as feedback for a controller communicating to the force applicator  1333  to adjust the force applied such that a target force is met. The transducer  1329  can comprise a pneumatic load cell, a hydraulic load cell, an inductive load cell, a capacitive load cell, a magnetorestrictive device, a strain gauge-based sensor, a force sensitive resistor, a thin film device, a piezoelectric device, or the like. Although the figure illustrates the transducer  1329  as having a width that is the same as the pusher  1331 , embodiments of the disclosure may include a transducer  1329  that has a width smaller than the width of the pusher  1331 . In some embodiments, the test system  1390  may comprise one or more springs (not shown) that may be used to return the pusher  1331 , transducer  1329 , and/or force applicator  1333  to a home position when the force applicator  1333  is not applying a force. Additionally, in some embodiments, the test system  1390  may comprise a home sensor (not shown) used to indicate when the pusher  1331 , transducer  1329 , and/or force applicator  1333  are in the home position. The home position may be the position where the pusher  1331 , transducer  1329 , and/or force applicator  1333  are located the furthest away from the thermal head and/or not applying a force to it, for example. 
     Another force mechanism in the test system  1390  may comprise a force mechanism included in a thermal head. The thermal head force mechanism may comprise a force applicator  1343  for thermally coupling the device to the thermal head for thermal control of one or more components of a device under test. The force applicator  1343  may apply force to a cold plate  1362  and/or an adapter  1330 C of the thermal head. The force applicator  1343  can be any type of device that applies a force including, but not limited to, a pneumatic or hydraulic cylinder, pneumatic or hydraulic diaphragm, stepper motor, linear motor, server motor, voice coil, or other active force application device. The force applicator  1343  can apply a force including, but not limited to, between 1 kgf, 2 kgf, 100 kgf, 300 kgf, or 500 kgf. The thermal head may comprise a transducer  1339  (e.g., load cell, strain gauge-based sensor, force sensitive resistor, thin film device, piezoelectric device, or the like) that measures the force being applied by the force applicator  1343  in real-time and generates one or more force measurements signals used as feedback for a controller communicating to the force applicator  1343  to adjust the applied force to meet a target force. The force applicator  1343  may have any width, for example, the same width or smaller than the width of the adapter  1330 . 
     As shown with the example of  FIG.  13 A , embodiments of the disclosure may comprise active thermal control, passive thermal control, active force control, passive force control, or a combination thereof. Active thermal control may be used to set or change the temperature of one or more components of a device to a set point temperature (or within a given range). The active thermal control may comprise a heater  1356 , adapter  1330 C, and/or a cold plate  1362 , which change the temperature of one or more components in a device based on a thermal controller. A temperature sensor may be included for measuring the temperature of the device under test, where the measured temperature may be used as feedback by the thermal controller, heater  1356 , and/or cold plate  1362 . 
     Additionally or alternatively, the test system  1390  may comprise passive thermal control. Passive thermal control may allow one or more components in a device to change its temperature using, e.g., heat transfer. The passive thermal control may comprise one or more adapters  1330 A and  1330 B, which may transfer (e.g., exchange) thermal energy with one or more thermally-coupled components  1303 A and  1303 B, respectively. In some embodiments, the passive thermal control may allow the temperature of a thermally-coupled component to reach the temperature of the adapter  1330 . The adapters  1330 A and  1330 B may contact the components  1303 A and  1303 B, respectively. In some embodiments, the adapters  1330 A and  1330 B (for passive thermal control) may not be thermally coupled to a heater. In some embodiments, one or more adapters  1330 A and/or  1330 B may not be thermally coupled to a cold plate  1362  or may be thermally coupled to a cold plate  1362  that does not include cooling channels for circulation of a cooling material. 
     Embodiments of the disclosure may include both active and passive thermal control. For example, as shown in the figure, the test system may comprise one or more adapters  1330 A and  1330 B for passive thermal control and one or more adapters, such as adapter  1330 C, for active thermal control. In some embodiments, active thermal control may be used for components that have temperature set points or specific requirements, while passive thermal control may be used for other types of components (e.g., low-power components, components that do not have specific test temperature requirements, components whose performance is not sensitive to temperature, etc.). 
     Additionally or alternatively, any type of thermal control may be combined with any type of force control. For example, one or more adapters, such as adapters  1330 A and  1330 B for passive thermal control may be combined with passive force control, such as a spring, bellows, elastomer, or the like. As another example, a force applicator  1343  for active force control may be combined with a heater  1356  for active thermal control. 
     In some embodiments, different amounts of control may be used to account for different temperature set points or requirements, different component heights, different arrangements, etc. 
       FIG.  13 B  illustrates a flowchart of an example method of operating the test system  1390 , according to some embodiments. Process  1370  comprises step  1372  where the test system  1390  sets the temperature of the thermal head to one or more set point temperatures. The ramp rate of the temperature may be as fast as possible or may be predetermined, for example. In step  1374 , the test system places the device to be tested in a socket. The temperature of the thermal head may reach the one or more set point temperatures before or after the device is placed in the socket. 
     In step  1376 , a first force may be applied to the device for electrically coupling the device to the socket. A transducer may measure the amount of force applied. If the measured force does not meet a threshold force, then the test system may cease process  1370 . Otherwise, in step  1378 , a second force may be applied to the device in order to bring the adapter(s)/heater(s)/TIM(s) in contact with the individual chips, e.g., the force need to thermally couple the thermal head to the device. A transducer measures the amount of force applied to the device, and ends the process if it does not meet a threshold force. 
     If the amount of first force and the amount of second force applied to the device meet their respective threshold forces, then the test system  1390  starts device testing (step  1380 ). In some embodiments, the test system  1390  starts device testing in response to a start-of-test signal transmitted from one or more controllers (e.g., a handler, a thermal controller). During the test, the test system  1390  may optionally send one or more signals to the controller to change modes and/or set point temperature(s) (step  1382 ). Example modes may comprise, but are not limited to, measuring the heater temperature, measuring the DUT temperature, etc. The mode may be changed in accordance with the examples of the disclosure. 
     In step  1384 , the test system  1390  completes the device testing and sends an end-of-test signal to the controller(s). The second force applied on the device may be removed (step  1386 ), and then the first force applied on the device may be removed (step  1388 ). In some embodiments, process  1370  may not proceed to step  1388  until the test system  1390  verifies that the second force applied on the device has been removed (in step  1386 ). In some embodiments, process  1370  may not proceed to step  1390  until the test system  1390  verifies that the first force applied on the device has been removed (in step  1388 ). In step  1390 , the device may be removed from the socket. One or more steps of process  1370  may be repeated, e.g., to test other devices. 
     Embodiments of the disclosure may comprise active thermal control for a plurality of components of a device, as shown in  FIG.  14   . The test system  1490  may comprise a thermal head and a socket. In some embodiments, the thermal head comprises a force mechanism. The force mechanism (e.g., pusher  1431 , transducer  1429 , force applicator  1433 , force applicator  1443 , transducer  1439 , etc.) and socket (comprising socket body  1418  and test contact pins  1417 ) may have one or more properties similar to the force mechanisms and socket discussed herein (e.g., described in the context of  FIGS.  13  and  15   ). The device may comprise a plurality of components  1403 ,  1402 A, and  1402 B mounted on a substrate  1410 . The substrate  1410  may comprise interconnects  1416  for receiving and/or transmitting test signals to and/or from a tester. 
     The test system  1490  may comprise a plurality of adapters  1430 A and  1430 B thermally coupled to component  1402 A and component  1402 B, respectively. The plurality of adapters  1430  may be thermally coupled to different heaters  1456 ; adapter  1430 A is thermally coupled to heater  1456 A, while adapter  1430 B is thermally coupled to heater  1456 B. The plurality of adapters  1430  may be thermally coupled to different cold plates  1462 ; adapter  1430 A is thermally coupled to cold plate  1462 A, while adapter  1430 B is thermally coupled to cold plate  1462 B. A thermal controller may be configured to independently control the temperatures of the component  1402 A and component  1402 B by way of the respective adapter  1430 A or  1430 B, heater  1456 A or  1456 B, and/or cold plate  1462 A or  1462 B. These may be two non-limiting examples of active thermal control. 
     Embodiments of the disclosure may further comprise passive thermal control. The thermal energy dissipated from the component  1403  may be allowed to transfer (e.g., dissipate) heat to adapter  1430 C. 
     Additionally or alternatively, the thermal head of  FIG.  14    may comprise both active and passive force control. For active force control, a force applicator  1443  applies force to the adapters  1430 A and  1430 B, which then applies force to components  1402 A and  1402 B. The amount of force applied, as measured by the transducer  1439 , may be controlled by a controller that determines the force to be applied by the force applicator  1443 . In some embodiments, the force control may not be independent for each adapter or component, such as the force applicator  1443  applying force to at least two adapters and/or components. 
     Embodiments of the disclosure my further comprise passive force control. The spring  1432 A may apply a force to the adapter  1430 C, which then applies force to the component  1403 . The amount of force applied may not be adjustable and may be based on the properties of the spring  1432 A. 
     Embodiments of the disclosure may comprise active force control for a plurality of components, according to some embodiments of the disclosure. The test system  1590  of  FIG.  15    may comprise a thermal head and a socket. The force mechanisms (e.g., pusher  1531 , transducer  1529 , force applicator  1533 , force applicators  1543 A and  1543 B, transducer  1539 A and  1539 B), other parts of the thermal head (e.g., cold plates  1562 A and  1562 B, adapters  1530 A,  1530 B, and  1530 C, heaters  1556 A and  1556 B), socket (comprising socket body  1518  and test contact pins  1517 ), and parts of the device (e.g., interconnects  1516 , components  1502 A,  1502 B, and  1503 , substrate  1510 ) may have one or more properties similar to the force mechanisms, parts of the socket, and parts of the device discussed herein (e.g., described in the context of  FIGS.  13 A and  14   ). 
     Example Controller 
     As discussed above, one or more controllers may be used for the test systems and/or thermal heads of the disclosures.  FIG.  16    illustrates a block diagram of an exemplary computer  1602  used for one or more controllers, according to embodiments of the disclosure. The computer may be a machine, within which a set of instructions, causes the machine to perform any one of the methodologies discussed herein, may be executed, according to embodiments of the disclosure. In some embodiments, the machine can operate as a standalone device or may be connected (e.g., networked) to other machines. In a networked configuration, the machine may operate in the capacity of a server or a client machine in a server-client network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine can be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a cellular telephone, a web appliance, a network router, a switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. A mobile device may include an antenna, a chip for sending and receiving radio frequency transmissions and wireless communications, and a keyboard. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one of the methodologies discussed herein. 
     The exemplary computer  1602  includes a processor  1604  (e.g., a central processing unit (CPU), a graphics processing unit (GPU), or both), a memory  1606  (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM), etc.), and a static memory  1608  (e.g., static random access memory (SRAM), etc.), which can communicate with each other via a bus  1610 . 
     The computer  1602  may further include a video display  1612  (e.g., a liquid crystal display (LCD) or light emitting diode (LED) display). The computer  1602  also includes an alpha-numeric input device  1614  (e.g., a keyboard), a cursor control device  1616  (e.g., a mouse), a disk drive unit  1618 , a signal generation device, a network interface device  1622 , and one or more wireless interface devices. 
     The computer  1602  may also include other inputs and outputs, including digital I/O and/or analog I/O. For example, the inputs and outputs may communicate with external devices, such as chillers, pressure controllers, force controllers, flow value controllers, etc., using any type of communication protocol. 
     The drive unit  1618  includes a machine-readable medium  1620  on which is stored one or more sets of instructions  1624  (e.g., software) embodying any one or more of the methodologies or functions described herein. The software may also reside, completely or at least partially, within the main memory  1606  and/or within the processor  1604  during execution thereof by the computer  1602 , the main memory  1606  and the processor  1604  also constituting machine-readable media. The software may further be transmitted or received over a network via the network interface device  1622  and/or a wireless device. 
     While the machine-readable medium  1620  is shown in an exemplary embodiment to be a single medium, the term “machine-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable medium” shall also be taken to include any medium that is capable of storing, encoding, or carrying a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present invention. The term “machine-readable medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical and magnetic media, and carrier wave signals. 
     Although examples of this disclosure have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of examples of this disclosure as defined by the appended claims.