Efficient heat spreading method and assembly for cooling integrated circuits - Patents.com

Abstract

The method may include attaching the integrated circuit to the printed circuit board in a first solder reflow process at a first reflow temperature. The method may include soldering a heat spreader to the integrated circuit in a second solder reflow process at a second reflow temperature, the second reflow temperature being lower than the first reflow temperature. The method may include attaching a cold plate to the heat spreader such that the thermally conductive material is positioned between the heat spreader and the cold plate. A related integrated circuit assembly is disclosed with a thermally conductive material, such as solder or liquid metal, positioned between the heat spreader and the integrated circuit. The thermally conductive material has a lower melting temperature than the solder on another surface of the integrated circuit.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application is a nonprovisional application and claims priority to U.S. Provisional Patent Application No. 63 / 301,003, filed January 19, 2022, and entitled “LOW TEMPERATURE SOLDERED HEAT SPREADER,” which is incorporated by reference in its entirety and for all purposes.

[0002] TECHNICAL FIELD This disclosure relates generally to cooling integrated circuits and methods for manufacturing integrated circuit assemblies. [Background technology]

[0003] Integrated circuits (ICs) can face the technical challenge of dissipating heat. ICs can use various cooling solutions to dissipate heat and achieve and / or maintain computing performance. Using solder to attach an IC to a cooling solution in an IC assembly can provide a desirable thermal conductivity. At the same time, solder can present technical challenges in the manufacture of IC assemblies. Summary of the Invention

[0004] Each of the claimed innovations has several aspects, no single aspect of which is solely responsible for its desirable attributes. Without limiting the scope of the claims, some prominent features of the disclosure will now be discussed briefly.

[0005] In some aspects, the technology described herein relates to a method for applying a cooling solution to one or more integrated circuit components, the method including attaching the integrated circuit to a printed circuit board in a first solder reflow process at a first reflow temperature, soldering a heat spreader to the integrated circuit in a second solder reflow process at a second reflow temperature, the second reflow temperature being lower than the first reflow temperature, and attaching the cold plate to the heat spreader such that a thermally conductive material is positioned between the heat spreader and the cold plate.

[0006] In some aspects, the techniques described herein relate to methods that further include applying an underfill material between the printed circuit board and the integrated circuit after the first solder reflow process and before the second reflow process.

[0007] In some aspects, the techniques described herein relate to methods where the second reflow temperature is below the glass transition temperature of the underfill material.

[0008] In some aspects, the techniques described herein relate to methods that further include depositing a gold film on at least one of the top surface of the integrated circuit or the bottom surface of the heat spreader prior to the second solder reflow process.

[0009] In some aspects, the techniques described herein relate to the manner in which the gold film is patterned.

[0010] In some aspects, the technology described herein relates to a method in which an integrated circuit includes an internal heat spreader.

[0011] In some aspects, the technology described herein relates to methods in which the integrated circuit is lidless.

[0012] In some aspects, the technology described herein relates to a method in which the heat spreader has a larger footprint than the integrated circuit.

[0013] In some aspects, the technology described herein relates to the manner in which the cold plate is electrically connected to ground.

[0014] In some aspects, the technology described herein relates to the manner in which the heat spreader is electrically connected to the cold plate.

[0015] In some aspects, the technology described herein relates to a method in which a printed circuit board includes a ground pad and a heat spreader is electrically connected to the ground pad.

[0016] In some aspects, the technology described herein provides an integrated circuit assembly with cooling for an integrated circuit, the integrated circuit assembly including a printed circuit board, an integrated circuit including a first surface and a second surface opposite the first surface, the second surface being soldered to the printed circuit board using solder, a heat spreader positioned such that a thermally conductive material is located between the heat spreader and the first surface of the integrated circuit, the thermally conductive material being electrically conductive, the thermally conductive material being solid at room temperature, and the thermally conductive material having a lower melting temperature than the solder, and a cooling plate attached to the heat spreader and in thermal communication with the heat spreader through the second thermally conductive material.

[0017] In some aspects, the technology described herein relates to an integrated circuit assembly in which the thermally conductive material includes a second solder.

[0018] In some aspects, the technology described herein relates to an integrated circuit assembly in which the thermally conductive material comprises a liquid metal.

[0019] In some aspects, the technology described herein relates to an integrated circuit assembly further including an underfill material positioned between the printed circuit board and the integrated circuit.

[0020] In some aspects, the technology described herein relates to integrated circuit assemblies in which the glass transition temperature of the underfill material is greater than the melting point of the solder.

[0021] In some aspects, the technology described herein relates to an integrated circuit assembly further including a gold film positioned between a first surface of the integrated circuit and the heat spreader.

[0022] In some aspects, the technology described herein relates to an integrated circuit assembly further including an adhesion layer positioned between the first surface of the integrated circuit and the gold film.

[0023] In some aspects, the technology described herein relates to an integrated circuit assembly in which the integrated circuit includes an internal heat spreader.

[0024] In some aspects, the technology described herein relates to an integrated circuit assembly in which the integrated circuit is lidless.

[0025] In some aspects, the technology described herein relates to an integrated circuit assembly further including a deformable conductor, the cooling plate being electrically grounded, the deformable conductor being positioned in contact between the heat spreader and the cooling plate, and the heat spreader and the cooling plate being electrically connected to each other via the deformable conductor.

[0026] In some aspects, the technology described herein relates to an integrated circuit assembly further including a deformable conductor, the printed circuit board including a ground pad, the deformable conductor being disposed in contact between the ground pad and the heat spreader, and the heat spreader and the ground pad being electrically connected to each other via the deformable conductor.

[0027] In some aspects, the technology described herein relates to an integrated circuit assembly with cooling for an integrated circuit, the integrated circuit assembly including a printed circuit board, an integrated circuit attached to the printed circuit board, a heat spreader soldered to the integrated circuit using solder, the solder having a reflow temperature below a glass transition temperature of an underfill material positioned between the printed circuit board and the integrated circuit, and a cooling plate positioned over the heat spreader and thermally coupled to the integrated circuit via a thermally conductive material.

[0028] In some aspects, the technology described herein relates to an integrated circuit assembly further including one or more features of the integrated circuit assembly disclosed herein.

[0029] In some aspects, the technology described herein relates to an integrated circuit assembly with cooling for an integrated circuit, the integrated circuit assembly including a printed circuit board, an integrated circuit attached to the printed circuit board, a heat spreader soldered to the integrated circuit using solder, the solder having a reflow temperature below a reflow temperature of a second solder positioned between the printed circuit board and the integrated circuit, and a cooling plate positioned over the heat spreader and thermally coupled to the integrated circuit via a thermally conductive material.

[0030] For purposes of summarizing the disclosure, certain aspects, advantages, and novel features of the innovation are described herein. It is to be understood that not all such advantages may necessarily be achieved in accordance with any particular embodiment. Thus, the innovation may be embodied or implemented to achieve or optimize one advantage or group of advantages as taught herein, without necessarily achieving other advantages as may be taught or suggested herein. [Brief description of the drawings]

[0031] These and other features, aspects, and advantages of the present disclosure will be described with reference to drawings of certain embodiments, which are intended to illustrate, but not to limit, the disclosure, It is understood that the accompanying drawings, which are incorporated in and constitute a part of this specification, are for the purpose of illustrating the concepts disclosed herein and may not be to scale.

[0032] [Figure 1A] 1A-1C are schematic cross-sectional illustrations of cooling configurations for integrated circuits in accordance with some embodiments. [Figure 1B] 1A-1C are schematic cross-sectional illustrations of cooling configurations for integrated circuits in accordance with some embodiments. [Figure 1C] 1A-1C are schematic cross-sectional illustrations of cooling configurations for integrated circuits in accordance with some embodiments. [Figure 1D] 1A-1C are schematic cross-sectional illustrations of cooling configurations for integrated circuits in accordance with some embodiments.

[0033] [Figure 2A] FIG. 1 illustrates an example thermal characteristic of a particular cooling structure. [Figure 2B] FIG. 1 illustrates an example thermal characteristic of a particular cooling structure.

[0034] [Diagram 3] 1 is a flowchart illustrating an example process for manufacturing an integrated circuit assembly in accordance with some embodiments.

[0035] [Figure 4A-D] 1A-1C are schematic cross-sectional diagrams illustrating an integrated circuit assembly corresponding to a process for applying a cooling system to multiple integrated circuits, according to one embodiment.

[0036] [Figure 5A] FIG. 1 is a schematic illustrating a metal coating pattern according to some embodiments. [Figure 5B] FIG. 1 is a schematic illustrating a metal coating pattern according to some embodiments. [Figure 5C] FIG. 1 is a schematic illustrating a metal coating pattern according to some embodiments.

[0037] [Figure 6] FIG. 1 illustrates a schematic cross-section of a multi-component cooling system in accordance with some embodiments.

[0038] [Figure 7A] 1 illustrates a schematic cross-section of an integrated circuit cooling configuration using a liquid metal thermally conductive material in accordance with some embodiments. [Figure 7B] 1 illustrates a schematic cross-section of an integrated circuit cooling configuration using a liquid metal thermally conductive material in accordance with some embodiments.

[0039] [Figure 8A] 1A-1C are schematic cross-sectional illustrations of integrated circuit cooling configurations having a grounded heat spreader in accordance with some embodiments. [Figure 8B] 1A-1C are schematic cross-sectional illustrations of integrated circuit cooling configurations having a grounded heat spreader in accordance with some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The following detailed description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein may be embodied in many different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings, in which like reference numbers and / or terms may indicate identical or functionally similar elements. It should be understood that the elements illustrated in the figures are not necessarily drawn to scale. Furthermore, it should be understood that certain embodiments may include more elements than and / or a subset of the elements illustrated in the drawings. Furthermore, some embodiments may incorporate any suitable combination of features from two or more drawings.

[0041] Heat can present significant technical problems for integrated circuits (ICs). For example, excessive heat can lead to component damage, reduced lifetime, reduced reliability, or poor performance. In some ICs, high temperatures can cause the IC to automatically throttle performance. For example, systems on a chip (SOC), graphics processing units (GPUs), central processing units (CPUs), etc. may reduce operating frequencies in response to temperature increases above a certain level. In some cases, ICs may not be able to provide adequate performance due to thermal constraints. Thus, ICs can utilize various active and / or passive cooling solutions (e.g., fans, active liquid cooling, heat spreaders, cold plates, etc.) to dissipate heat from IC components and maintain performance. In some embodiments, the IC uses at least one cold plate for cooling. The cold plate can include fins. Fluid can flow through the cold plate for convective heat transfer.

[0042] ICs may have lids that act as built-in heat spreaders. These lids may face significant constraints that may limit their effectiveness. For example, built-in heat spreaders may be constrained by the overall dimensions of the IC package so that the heat spreader does not get in the way of other components and / or does not prevent the attachment of the IC to a Printed Circuit Board (PCB). The inclusion of active cooling or even more effective passive cooling may add complexity and expense that may not be desirable in various applications. For example, a built-in heat spreader without additional cooling may be sufficient for devices that perform only light tasks or operate in environments with sufficient airflow. However, such a cooling solution may not be sufficient under heavy loads and / or in environments where the ambient conditions are not favorable for passive cooling with a built-in heat spreader (e.g., due to poor airflow, high temperatures, etc.). Thus, when a built-in heat spreader is insufficient, an additional cooling solution is required. In some embodiments, an improved cooling solution may result in significantly higher performance, performance that can be sustained for a longer period of time, or both.

[0043] One additional cooling solution is a cold plate. A cold plate is typically attached to an IC using a thermal interface material (TIM). However, thermal interface materials can have high thermal impedance, for example, to many metals. A cold plate may be attached, for example, on top of an integrated heat spreader. The interface between the cold plate and the integrated heat spreader can limit cooling efficiency due to the relatively low thermal conductivity and high interfacial resistance of the TIM material located between the cold plate and the IC. This can be at least partially mitigated by using thermal pastes, thermal pads, and the like. A typical thermal paste utilizes a liquid carrier that contains a thermally conductive filler. The filler can include, for example, aluminum oxide, aluminum nitride, zinc oxide, and silver. Typically, thermal pastes have a thermal conductivity of a few W / m·K, for example, in the range of about 1 W / m·K to about 10 W / m·K.

[0044] Solder provides significantly higher thermal conductivity and lower interfacial impedance than typical TIMs. For example, solder may have a thermal conductivity of approximately 10 W / m·K, 20 W / m·K, 50 W / m·K, or even 80 W / m·K or more, depending on the solder's specific composition. However, using solder in place of a typical TIM, such as thermal paste or thermal pad, presents several technical challenges, as discussed below.

[0045] In the following description, the embodiments are described with reference to a single reflow process to attach components to a PCB and a second reflow process to attach a heat spreader to an IC. This is done for illustrative purposes only. Those skilled in the art should understand that multiple reflow processes may be used and the disclosure herein is not limited to only two reflow processes. For example, two, three, four, or more reflow processes may be employed prior to the reflow process to attach the heat spreader, and more than two reflow processes may be employed to attach the heat spreader. In a particular application, there may be two high-temperature reflows performed before the low-temperature solder reflow, including separate reflow processes to attach the IC to the top side of the PCB and to attach the IC to the bottom side of the PCB. Thus, the first and second reflow processes discussed herein are not necessarily the first and second reflow processes in a complete IC assembly method.

[0046] IC components may be attached to a PCB using a high temperature reflow process. For example, the reflow process may expose the PCB and components to temperatures well above 200 degrees Celsius. In certain embodiments, an underfill process may be employed. The use of underfill may add structure and reduce stresses that may cause the IC to crack and / or the solder joints to break when the IC is exposed to one or more of thermal stress, liquid drops, shock, vibration, and the like. While underfill materials may improve mechanical reliability and reduce stresses driven by thermal expansion coefficient mismatch, underfill materials may present challenges for soldered cooling solutions. In some applications, underfill materials may have a glass transition temperature lower than the solder reflow temperature of the soldered cooling solution. For example, underfill materials may have a glass transition temperature of 125 degrees Celsius, 155 degrees Celsius, and the like. At temperatures near the glass transition temperature or, depending on the material and application, above or below the glass transition temperature, the underfill can induce significant stress in the IC or lose its ability to harden the ball grid array as the structure of the underfill material changes and the material softens. The glass transition temperature of the underfill can constrain the processing temperature for subsequent processing steps, such as additional solder reflow steps.

[0047] Thus, using solder as part of a cooling system presents several challenges. Using solder to attach cooling components after an IC is attached to a PCB can cause problems associated with PCB reflow, underfill, or both. Soldering a heat sink during PCB reflow (e.g., when the IC component is attached to the PCB) can damage (e.g., crush) ball grid arrays used by many ICs, such as processors and SOCs. The thermal mass of the combined PCB and cooling plate can, in some circumstances, involve long reflow times due to heating a relatively large amount of material, which can result in reduced reliability or damage to the IC, PCB, or other components. Attaching cooling components prior to PCB reflow can present significant challenges later in the assembly process. For example, even lightweight cooling components can make it more difficult to place the components on the PCB for a variety of reasons, including increased weight and physical size.

[0048] If solder is used in the cooling system (e.g., to attach components and / or act as a thermal interface), there is an advantage to applying the solder after the PCB reflow process is completed. There may also be advantages to adding a relatively small or minimal thermal mass with the solder. Low temperature solder may be used in a secondary reflow process after PCB reflow, in which case the low temperature solder has a melting temperature below the melting point of the solder used in the PCB reflow. If underfill is used, the low temperature solder may advantageously have a melting temperature below the glass transition temperature of the underfill material to avoid potential damage resulting from stresses that may be particularly pronounced when the underfill material undergoes a glass transition.

[0049] In embodiments disclosed herein, the heat spreader is soldered to the integrated circuit (IC). This can reduce thermal mass compared to soldering a cold plate, thereby reducing the time the PCB and IC are exposed to high temperatures during additional reflow, reducing the potential for damage to the PCB, IC, etc. Additionally, in certain applications, adding less mass to the top of the IC can reduce the potential for damage to the IC's electrical interface (e.g., ball grid array). Attaching the heat spreader to the IC in a second reflow process can improve thermal performance. Additional cooling can also be implemented. Even in such cases, the benefits of soldering the heat spreader to the IC before thermally bonding the combined IC and heat spreader to additional cooling hardware can be realized. The TIM can be a thermal bottleneck. Thus, in some embodiments, performance can be improved by moving the thermal bottleneck further away from the heat source (e.g., the silicon die of the IC) relative to other designs, thereby reducing the impact of the bottleneck.

[0050] Some TIMs, especially those that achieve high thermal performance, are subjected to high pressure during manufacturing to achieve the most efficient heat transfer. However, if the TIM is applied directly to an integrated circuit chip, there is a risk that the application of high pressure may damage the IC. For example, if a cold plate is fastened directly to an IC (or the IC's built-in heat spreader) using fastening screws, the fastening screws may achieve high and / or optimal heat transfer. However, overtightening or uneven tightening of the screws may induce stresses in the IC that may crack the IC and / or lead to premature failure. By soldering the heat spreader to the IC, a high performance TIM may be applied between the heat spreader and the cold plate. In some applications, this interface may be subjected to high pressure without risk of damaging the IC components. The use of higher performance TIMs with higher compression is possible without compromising the electronics of the IC due to the compression that occurs between the heat spreader and the cold plate.

[0051] Improved thermal performance may be achieved in some embodiments by attaching the heat spreader to the IC using solder in a second reflow process. In some embodiments, higher performance may be achieved. For example, improved cooling may allow for increased operating power. With higher operating power, the integrated circuit may provide more computing power.

[0052] 1A and 1B are illustrations of an integrated circuit assembly with cooling according to some embodiments. In FIG. 1A and 1B, a PCB 101 has an IC 102 mounted thereon. In some embodiments, the IC 102 may be mounted to the PCB 101 using a ball grid array 108. The ball grid array 108 may include a plurality of solder balls. An underfill 109 may be disposed between the PCB 101 and the IC 102. The IC 102 may be an Application Specific Integrated Circuit (ASIC). The IC 102 may be a relatively high power IC. The IC 102 may include a semiconductor die, such as a silicon die. On top of the IC 102 is a heat spreader 104 attached to the IC 102 using low temperature solder 103. The heat spreader 104 is thermally connected to a cooling plate 106 via a TIM 105. The TIM 105 may be any suitable material for a thermal interface, such as thermal paste or a thermal pad.

[0053] As illustrated in FIG. 1A, in some embodiments, the cold plate 106 can be secured to the PCB by one or more anchor bolts 107. FIG. 1A illustrates an embodiment in which the anchor bolts 107 extend into the heat spreader 104 but do not emerge from the heat spreader 104. In some implementations, the anchor bolts 107 can extend into the cold plate 106 but do not emerge from the cold plate 106. In some other implementations, the anchor bolts 107 can extend through the cold plate 106. In such implementations, nuts can be secured to the anchor bolts 107 at the top exposed surface of the cold plate 106. In some implementations, it may be desirable to not have the anchor bolts 107 extend beyond the heat spreader 104 to reduce or limit the weight placed on the ball grid array 108 during reflow. In some embodiments, the cold plate 106 and the heat spreader 104 can be affixed to one another after the low temperature solder 103 is reflowed. This reduces the possibility of the ball grid array 108 being crushed while the cooling plate 106 and heat spreader 104 are affixed together. Any other suitable fasteners may be implemented in place of or in addition to the anchor bolts 107.

[0054] FIG. 1B depicts an alternative "floating" implementation. In FIG. 1B, the IC 102, solder 103, and heater spreader 104 are electrically and mechanically connected to the PCB 101 by a ball grid array 108, and underfill 109 can provide additional mechanical and / or thermal integrity. In contrast to anchor bolts 107 in FIG. 1A, anchor bolts 110 in FIG. 1B may not extend into the cold plate 106. Instead, anchor bolts 110 can extend into the heat spreader 104 that is soldered to the IC 102 via solder 103. Bolts 111 can be used to affix the cold plate 106 to the heat spreader 104. An embodiment such as that shown in FIG. 1B can allow the cold plate 106 to be clamped against the heat spreader 104 to compress the TIM 105, reducing the risk of damage to the IC 102 and / or PCB 101 compared to the example shown in FIG. 1A. Instead of or in addition to the bolts 110 and / or 111, any other suitable fasteners may be implemented.

[0055] 1C and 1D illustrate an embodiment similar to FIGS. 1A and 1B, respectively, except that a spring is included. In FIG. 1C, a spring 112 is placed around the anchor bolt 107 such that when the anchor bolt 107 is tightened, the spring 112 is compressed between the head of the anchor bolt 107 and the PCB 101. Similarly, in FIG. 1D, a spring 112 is placed around the anchor bolt 110 such that when the anchor bolt 110 is tightened, the spring 112 is compressed. The spring 112 can absorb force and control pressure on the IC 102 and other components. Without the spring 112, it can be difficult to control the force on the IC 102 when the anchor bolt 107 or 110 is tightened, which can result in damage to the IC 102, especially if the anchor bolt 107 or 110 is not tightened evenly.

[0056] In some embodiments, the solder 103 can instead be another thermally conductive material (e.g., a thermal pad, thermal paste, a curable thermally conductive material, etc.). Embodiments such as those shown in Figures 1B and / or 1D can provide significant improvements over conventional designs known to those skilled in the art. For example, while the interface between the IC 102 and the heat spreader 104 can be of a conventional thermally conductive material, the embodiments shown in Figures 1B and / or 1D can be used to reduce the thermal resistance of the thermal interface layer because the thermally conductive material can be compressed to a thinner thickness than would normally occur using a more conventional fixed gap design, and / or the presence of voids, air pockets, etc. can be reduced.

[0057] While the figures herein depict the use of screws or bolts to affix the cooling plate to the PCB and / or heat spreader (optionally using springs), and to attach the heat spreader and ICs to the PCB, it should be understood that other approaches are possible. For example, instead of screws or bolts, clips or other suitable hardware could be used to affix components together.

[0058] 1A-1D depict exemplary embodiments in which the integrated circuit is soldered to the PCB using a ball grid array, other surface mount techniques may alternatively or additionally be used, hi some embodiments, the integrated circuit may be attached to the PCB using sockets and pins.

[0059] The integrated circuit assembly of FIGS. 1A-1D can be advantageous for several reasons. For example, the heat spreader 104 can be significantly larger than the built-in heat spreader of the IC 102. The heat spreader 104 has a larger footprint than the IC 102. The heat spreader 104 may be, for example, two or four times larger than the surface area of ​​the built-in heat spreader of the IC 102. Thus, heat generated by the IC 102 can be transferred to the heat spreader 104 and spread over a relatively large surface area before encountering the relatively lower thermal conductivity of the TIM 105. Because the heat has already been carried away from the IC 102 and spread over a larger area, the thermal performance of the TIM 105 has less impact on the performance of the IC 102 than certain other designs with a TIM between the IC and the heat spreader. For example, the heat flux of the heat spreader 104 may be 3 / 4, 1 / 2, or even less than the heat flux in the IC 102. For example, the heat flux is about 25 W / cm 2 to about 10 W / cm 2 It is possible that the

[0060] 2A and 2B illustrate thermal characteristics of a cooling structure. FIG. 2A shows thermal characteristics that may be exhibited by a cooling structure not formed with the low temperature soldered heat spreader disclosed herein. In these figures, the height of the components of the stack is proportional to the temperature rise of each component. The combined height of each stack is proportional to the combined temperature rise of the individual stacks. In FIG. 2A, the die is in thermal contact with the lid through a first TIM, and the lid is in thermal contact with the heat spreader through a second TIM. A cold plate, which may include convective liquid and / or cooling fins, is then placed on top of and in thermal contact with the heat spreader. FIG. 2B depicts thermal characteristics that may be exhibited by a cooling structure formed in accordance with the disclosure herein. In FIG. 2B, the die is in thermal contact with the lid through a first TIM, and the lid is soldered to the heat spreader. The heat spreader is then in thermal contact with the cold plate, which may include convective liquid and / or cooling fins, through a second TIM. As shown in Figure 2A, the second TIM may contribute most to the temperature rise when the TIM is placed between the lid and the heat spreader. In Figure 2B, when the heat spreader is soldered to the lid and the second TIM is placed between the heat spreader and a cold plate (which may include, for example, convection liquid and / or cooling fins), the contribution of the second TIM to the temperature rise is significantly reduced, resulting in a reduced overall temperature rise.

[0061] FIG. 3 is a flow chart illustrating an exemplary process 300 for forming a soldered cooling assembly, according to some embodiments. In block 302, a first reflow process may be performed to solder one or more integrated circuit chips to a printed circuit board. In block 304, an underfill process may be performed to encapsulate the bottom side of the one or more IC chips. It should be understood that in some embodiments, an underfill process may not be performed. In block 306, a second reflow process may be performed to solder at least one heat spreader to at least one IC of the one or more ICs. In some embodiments, all of the ICs of the IC assembly may have heat spreaders soldered thereto. However, in other embodiments, only some of the ICs may have heat spreaders soldered thereto, and the top surfaces of the other ICs may remain exposed. For example, a heat spreader may be soldered to relatively high-power components, but not to relatively low-power components. A thermally conductive material, such as a pad or paste, may be applied to at least one heat spreader and any exposed ICs in block 308. In block 310, a cold plate may be affixed over one or more exposed ICs and / or heat spreaders and may contact the ICs and / or heat spreaders via the thermally conductive material.

[0062] 4A-4D illustrate cross-sectional views of an integrated circuit assembly corresponding to a process for applying a cooling system to multiple integrated circuits, according to one embodiment. In FIG. 4A, ICs 102 and 113 are attached to PCB 101. ICs 102 and 113 can be attached to PCB 101 using a high temperature reflow process. Although not illustrated in FIG. 4A-4D, high temperature solder from the high temperature reflow process can attach ICs 102 and 113 to PCB 101. IC 102 can be a relatively high power integrated circuit. IC 102 can be, for example, a high power application specific integrated circuit, a system on a chip, a power IC, etc. IC 102 can be a packaged integrated circuit that can include an internal heat spreader (e.g., a lid). In some embodiments, IC 102 can be lidless. IC 113 can include, for example, dynamic random access memory (DRAM) and / or other components that generate less heat relative to IC 102.

[0063] In FIG. 4B, the heat spreader 104 is affixed to the IC 102 using low temperature solder 103. As illustrated in FIG. 2B, the heat spreader may not be soldered to the low power IC 113. The heat spreader 104 is attached to the IC 102 using a low temperature reflow process that is lower than the high temperature reflow process. The low temperature reflow process may be performed at a temperature lower than the glass transition temperature of the underfill material. The low temperature reflow process may be performed at a temperature lower than 160 degrees Celsius in certain applications. The heat spreader may be precisely positioned (e.g., within tolerances) and / or compressed to ensure proper contact. In some applications, the heat spreader 104 may be secured to the IC 102 to keep the heat spreader 104 in place during the low temperature reflow process. For example, in some applications, a force (e.g., a downward force toward the IC 102) may be applied to keep the heat spreader 104 in place. In some applications, no force may be applied. For example, the heat spreader 104 may be significantly heavy such that external forces are ineffective or limited.

[0064] In Figure 4C, the TIM 105 is applied to the top of the ICs 113 and to the top of the heat spreader 104. In Figure 4D, a cold plate 106 is affixed and placed in contact with the TIM 105 on top of the ICs 113 and the heat spreader 104. The cold plate 106 may be attached to the PCB 101 using one or more anchor bolts 107. As illustrated, the anchor bolts 107 pass through the heat spreader 104. The anchor bolts do not pass through the heat spreader in some other applications.

[0065] 5A-5C are illustrations of metal coating patterns according to some embodiments. In some embodiments, the coating may be applied to a surface of an IC (e.g., on an integrated heat spreader) and / or to a heat spreader, such as heat spreader 104 of FIGS. 1A-1D and / or 4B-4D or heat spreader 709 of FIGS. 7A-7B and 8A-8B. In some embodiments, the heat spreader may comprise copper, plated aluminum, anodized aluminum, another suitable material, or any suitable combination thereof. For example, the heat spreader may comprise copper. In some embodiments, the heat spreader may comprise nickel-plated copper. It may be important that the joint between the IC and the heat spreader is robust. Thus, in some embodiments, a metallization layer, such as, for example, a gold coating, may be used to improve the reliability of the joint. For example, the top surface of IC 102, the bottom surface of heat spreader 104, or both may be coated with a metallization layer, such as a gold film, which may be about 50 nm thick or more, such as in the range of about 50 nm thick to about 100 nm thick. The metallization layer may be deposited using immersion, thermal evaporation, electron beam evaporation, or other suitable deposition process.

[0066] In a particular embodiment, the gold film may be deposited on the lid of an IC having an integrated heat spreader. In some other embodiments, the IC may comprise a lidless package with an exposed die. Those skilled in the art will appreciate that the embodiments described herein are applicable to lidded and lidless ICs. A metallization layer, such as a gold film, may be applied to the exposed die surface to enable soldering of an external heat spreader, such as heat spreader 104. Heat spreader 104 may then be soldered to an IC 102 that does not have an integrated heat spreader (e.g., a lid). In a particular embodiment, the metallization layer may comprise a single layer, such as, for example, a single gold layer. In some other embodiments, the metallization layer may comprise multiple layers. For example, the metallization layer may comprise a chromium adhesion layer (or other suitable adhesion layer material, such as tungsten, niobium, or titanium) and a gold layer.

[0067] In some embodiments, voids at the interface between the IC 102 and the heat spreader 104 may significantly affect thermal performance, reliability of the interface, or both. In some embodiments, a vacuum reflow process may be used to reduce the presence of voids. In some embodiments, the gold film may be patterned to reduce the formation of voids. For example, the gold film may be patterned to provide channels for air and / or other gases to escape during the reflow process. FIGS. 5A-5C illustrate different patterns that may be used to reduce the formation of voids at the interface. In some embodiments, the center of the IC may be the primary heat source, and therefore the pattern may not be hollow in that area to increase or maximize heat transfer. The pattern may be symmetrical about a central axis. It should be understood that in some embodiments, other patterns may be preferred. For example, in some embodiments, a SOC may have an area with a CPU core, another area with a GPU core, and another area with a modem or other communication function. In some applications, it may be preferred to have a solid thin film area over the CPU core or GPU core, etc., depending on the layout of the IC and the functions performed by the IC.

[0068] FIG. 6 is an illustration of a multi-component integrated circuit assembly with a cooling system according to some embodiments. In FIG. 6, two high-power ICs 102 and two low-power ICs 113 are attached to a single PCB 101. A heat spreader 104 is soldered to the high-power IC 102 using low-temperature solder 103. The heat spreader 104 and the low-power ICs 113 are in thermal contact with a single cold plate 106 via a thermally conductive material 105. In some embodiments, it may be advantageous to have multiple components in thermal contact with a single cold plate. For example, using a single cold plate for multiple components may reduce cooling costs and weight, may allow the cold plate to be significantly larger than would be possible if each component had its own cold plate, or both. However, technical problems may be encountered when using a single large cold plate for multiple components. Due to manufacturing tolerances, different components may be at different heights from the PCB, and the heights may vary from circuit board to circuit board and from IC to IC. Thus, using a thick layer (e.g., about 500 μm) of thermally conductive material may ensure that all components are in good thermal contact with the cold plate. However, because conventional thermally conductive materials tend to be relatively poor thermal conductors compared to, for example, solder, a thick layer of TIM may result in poorer heat transfer performance, thus reducing the maximum operating performance of the integrated circuit. By moving the TIM away from the high-power integrated circuits, it is possible to accommodate manufacturing variances using a relatively thick TIM layer, which may lead to improved performance, while increasing the efficiency of heat transfer from the high-power integrated circuits. It should be understood that other configurations are possible. For example, in some embodiments, there may be a different number of high-power ICs 102 and low-power ICs 113. In some embodiments, there may be no low-power ICs.

[0069] Although some embodiments discuss low-temperature solder positioned between the heat spreader and the cold plate, alternatively or additionally, any suitable thermally conductive material with a relatively higher thermal conductivity and lower melting point than the high-temperature solder that attaches the IC and the PCB can be used. For example, a liquid metal with a melting temperature below about 50 degrees Celsius and a relatively low thermal resistance during operation of the IC can be used in place of the low-temperature solder. Such a thermally conductive material can be electrically conductive. Such a thermally conductive material can include a metal. Such a thermally conductive material can be solid at room temperature. An exemplary embodiment with a liquid metal as a thermally conductive material positioned between the heat spreader and the cold plate is discussed with reference to FIGS. 7A and 7B.

[0070] 7A and 7B are illustrations of an exemplary integrated circuit assembly with cooling according to some embodiments. In some embodiments, a floating heat spreader can be affixed to the chip using foam, O-ring gaskets, or the like to form a sealed volume, which can enable the use of liquid metal as the thermally conductive material. For example, the liquid metal thermally conductive material can include an indium-based material, a gallium-based material, or another metallic material that melts at a relatively low temperature, such as some bismuth or tin alloys. A liquid metal thermally conductive material can be desirable because it can have a relatively high thermal conductivity. For example, a liquid metal thermally conductive material can have a thermal conductivity of about 20 W / m·K to about 80 W / m·K, such as about 20 W / m·K to about 50 W / m·K, or more. Typically, such materials can have a melting temperature below about 50 degrees Celsius and thus can be liquid during operation of the integrated circuit. Therefore, it can be important to confine the liquid metal thermally conductive material to keep it from spreading to undesired locations.

[0071] FIG. 7A illustrates a floating design that can be implemented on a lidded integrated circuit. As shown in FIG. 7A, a substrate 702 can be affixed to a PCB 701. The substrate 702 and the PCB 701 can be electrically and mechanically joined by a ball grid array 703. The ball grid array 703 can include high temperature solder balls. In some embodiments, an underfill can be used between the substrate 702 and the PCB 701. The IC 704 can be mechanically and electrically attached to the substrate 702 via a second ball grid array 705. In some embodiments, an underfill can be present between the substrate 702 and the IC 704. A thermally conductive material 706 can be formed on top of the IC 704 and can enable thermal communication between the IC 704 and the lid 707. A second thermally conductive material 708 can be formed on top of the lid 707, and a heat spreader 709 can be disposed on top of the lid 707 and the second thermally conductive material 708. The second thermally conductive material 708 can be a liquid metal thermally conductive material. The second thermally conductive material 708 has a lower melting temperature than the high temperature solder balls of the ball grid array 703. The lid 707 and the heat spreader 709 can define a cavity 710 that is sealed using an O-ring gasket 711. Although an O-ring gasket is depicted in FIG. 7A, it is understood that other forms of rings or gaskets can be used to seal the cavity 710. The cavity can include one or more overflow trenches 712 in the heat spreader 709 that can hold excess liquid. By ensuring that liquid does not leak from the cavity 710, shorting of any electronics that may be exposed to the liquid can be avoided. The heat spreader 709 can be in thermal communication with a cold plate 714 through the thermally conductive material 713. Anchor bolts 715 can be threaded through the PCB 701 and into the heat spreader 709 to provide mechanical stability. As discussed above with reference to FIGS. 1C and 1D, the use of springs 716 can help reduce and / or prevent damage that may occur due to even torque rotation of anchor bolts 715.

[0072] Although FIG. 7A illustrates an embodiment with a lidded IC, a similar structure can be used with a lidless IC, for example, as shown in FIG. 7B. Unlike FIG. 7A, the embodiment shown in FIG. 7B does not include a lid 707. Instead, the heat spreader 709 can be in thermal communication with the IC 704 through a second thermally conductive material 708, which can be a liquid metal thermally conductive material. In FIG. 7B, the heat spreader 709 and the substrate 702 can form a cavity 718. The cavity 718 can be sealed by a gasket 717, which can be, for example, a rubber gasket, a foam gasket, or the like. It should be understood that a lidded IC can also be used in an assembly similar to that shown in FIG. 7B. For example, if the lid of the lidded IC does not extend to the edge of the substrate, the heat spreader and the substrate can be used to form a sealed cavity similar to that shown in FIG. 7B.

[0073] In some assemblies, the heat spreader may be electrically grounded. Various techniques may be used to ground the heat spreader. For example, in some embodiments, the cold plate may be grounded, and the heat spreader may be grounded through the cold plate. In some embodiments, the heat spreader may be grounded through the PCB.

[0074] 8A is an illustration of an exemplary embodiment in which the heat spreader 709 is in electrical communication with the cold plate 714 through a conductive gasket 719. The heat spreader 709 may be electrically connected to the cold plate through any suitable electrical connection, such as conductive foam, a conductive O-ring, a conductive spring, or another deformable conductor. The cold plate 714 may be connected to ground.

[0075] In some embodiments, for example as shown in FIG. 8B , the cold plate 714 may not be connected to ground, and instead the heat spreader 709 may be grounded through the PCB 701. The conductive spring fingers 720 may electrically connect the heat spreader 709 to the PCB 701. The conductive spring fingers 720 may deform as the anchor bolts 715 are tightened and the heat spreader 709 approaches the PCB 701. The conductive spring fingers 720 may contact one or more ground pads (not shown) on the PCB 701. Any other suitable conductive structure for electrically connecting the cold plate 714 to the PCB 701 may be implemented instead of or in addition to the conductive spring fingers 720.

[0076] Although Figures 8A and 8B illustrate an assembly similar to that shown in Figures 7A and 7B, it should be understood that in other embodiments, such as, but not limited to, the embodiments illustrated in Figures 1A-1D and 6, a grounded heat spreader can be implemented.

[0077] The integrated circuit assemblies disclosed herein can be implemented in a variety of contexts. For example, such integrated circuit assemblies can be used in automotive electronics, such as electronics for autonomous driving and / or driver assistance features. The integrated circuit assemblies disclosed herein can be implemented in any suitable system that can benefit from the cooling provided by such systems. For example, high performance computing and / or computationally intensive applications, such as neural network processing, machine learning, artificial intelligence training, etc., can benefit from the cooling provided by the integrated circuit assemblies disclosed herein. Additional Embodiments

[0078] In the foregoing specification, the present disclosure has been described with reference to specific embodiments. It will be apparent, however, that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present disclosure. The specification and drawings are therefore to be regarded in an illustrative rather than a restrictive sense.

[0079] Indeed, while the present disclosure is in the context of certain embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and / or uses of the present invention and its equivalents. In addition, while several variations of the embodiments have been shown and described in detail, other modifications that are within the scope of the present disclosure will be readily apparent to those skilled in the art based on the present disclosure. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the present disclosure. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another to form various forms of the embodiments disclosed herein. Any of the methods disclosed herein need not be performed in the order recited. It is therefore not intended that the scope of the present disclosure should be limited by the specific embodiments described above.

[0080] It should be understood that the systems and methods of the present disclosure each have several innovative aspects, no single aspect of which is solely responsible for or requires the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and subcombinations are intended to be included within the scope of the present disclosure.

[0081] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although features may be described above as acting in a particular combination and may even initially be claimed as such, one or more features from the claimed combination may in some cases be excluded from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination. No single feature or group of features is necessary or essential to any embodiment.

[0082] It should be understood that conditional language used herein, particularly "can," "could," "might," "may," "eg," and the like, is generally intended to convey that certain embodiments include certain features, elements, and / or steps, but not other embodiments, unless specifically stated otherwise or understood otherwise within the context in which it is used. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required by one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps are included or should be performed in any particular embodiment, with or without authorial input or direction. Terms such as "comprising," "including," "having," and the like are synonymous and are used in an inclusive and open-ended manner and do not exclude additional elements, features, acts, operations, and the like. In addition, the term "or" is used in an inclusive sense (and not an exclusive sense), so that, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. In addition, the articles "a," "an," and "the" used in this application and the accompanying claims should be interpreted to mean "one or more" or "at least one," unless otherwise specified. Similarly, although operations may be depicted in the figures in a particular order, it should be recognized that such operations need not be performed in the particular order shown, or in sequential order, or that all illustrated operations need not be performed to achieve desirable results. Additionally, the figures may generally depict another exemplary process in the form of a flow chart. However, other operations not depicted may be incorporated into the generally illustrated exemplary methods and processes.For example, one or more additional operations may be performed before, after, simultaneously with, or during any of the illustrated operations. Additionally, the order of operations may be rearranged or changed in other embodiments. In certain circumstances, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0083] Furthermore, the methods and devices described herein may be susceptible to various modifications and alternative forms, specific examples of which are shown in the drawings and described in detail herein. However, it should be understood that the disclosure is not limited to the specific forms or methods disclosed, but rather, the disclosure encompasses all modifications, equivalents, and alternatives that are included within the spirit and scope of the various implementations described and the appended claims. Furthermore, any particular feature, aspect, method, property, characteristic, quality, attribute, element, etc., disclosed herein in connection with an implementation or embodiment can also be used in all other implementations or embodiments described herein. Any method disclosed herein need not be performed in the order listed. The methods disclosed herein may include certain actions performed by a practitioner. However, the methods may also include any third-party instructions of those actions, either explicitly or implicitly. The ranges disclosed herein also encompass any and all overlapping ranges, subranges, and combinations thereof. Language such as "up to," "at least," "greater than," "less than," "between" is inclusive of the recited numbers. Numbers preceded by terms such as "about" or "approximately" are inclusive of the recited numbers and should be interpreted based on the context (e.g., as precisely as reasonably possible under the circumstances, e.g., ±5%, ±10%, ±15%, etc.). Phrases preceded by terms such as "substantially" are inclusive of the recited numbers and should be interpreted based on the context (e.g., as much as reasonably possible under the circumstances). For example, "substantially constant" includes "constant." Unless otherwise specified, all measurements are made at standard conditions, including temperature and pressure.

[0084] As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items, including single members. By way of example, "at least one of A, B, or C" is intended to cover A, B, C, A and B, A and C, B and C, and A, B, and C. Connecting language such as "at least one of X, Y, and Z" is otherwise understood in the context in which it is generally used to convey that an item, term, etc. may be at least one of X, Y, or Z, unless specifically stated otherwise. Thus, such connecting language is generally not intended to imply that a particular embodiment requires that at least one of X, at least one of Y, and at least one of Z, respectively, be present. Headings provided herein, if any, are for convenience only and do not necessarily affect the scope or meaning of the devices and methods disclosed herein.

[0085] Thus, the claims are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the present disclosure, the principles and novel features disclosed herein.

Claims

1. 1. A method for applying a cooling solution to one or more integrated circuit components, comprising: attaching the integrated circuit to a printed circuit board in a first solder reflow process at a first reflow temperature; soldering a heat spreader to the integrated circuit in a second solder reflow process at a second reflow temperature, the second reflow temperature being lower than the first reflow temperature; and attaching the cold plate to the heat spreader such that a thermally conductive material is positioned between the heat spreader and the cold plate.

2. 10. The method of claim 1, further comprising applying an underfill material between the printed circuit board and the integrated circuit after the first solder reflow process and before the second reflow process.

3. The method of claim 2 , wherein the second reflow temperature is below a glass transition temperature of the underfill material.

4. 10. The method of claim 1, further comprising depositing a gold film on at least one of a top surface of the integrated circuit or a bottom surface of the heat spreader prior to the second solder reflow process.

5. The method of claim 4 , wherein the gold film is patterned.

6. The method of claim 1 , wherein the integrated circuit comprises an internal heat spreader.

7. The method of claim 1 , wherein the integrated circuit is lidless.

8. The method of claim 1 , wherein the heat spreader has a footprint larger than the integrated circuit.

9. The method of claim 1 , wherein the cold plate is electrically connected to ground.

10. The method of claim 9 , wherein the heat spreader is electrically connected to the cold plate.

11. The method of claim 1 , wherein the printed circuit board comprises a ground pad, and the heat spreader is electrically connected to the ground pad.

12. 1. An integrated circuit assembly with cooling for an integrated circuit, comprising: A printed circuit board; an integrated circuit having a first surface and a second surface opposite the first surface, the second surface being soldered to the printed circuit board using solder; a heat spreader positioned such that a thermally conductive material is located between the heat spreader and a first surface of the integrated circuit, the thermally conductive material being electrically conductive, the thermally conductive material being solid at room temperature, and the thermally conductive material having a lower melting temperature than the solder; a cold plate attached to the heat spreader and in thermal communication with the heat spreader through a second thermally conductive material.

13. 13. The integrated circuit assembly of claim 12, wherein the thermally conductive material comprises a second solder.

14. The integrated circuit assembly of claim 12 , wherein the thermally conductive material comprises a liquid metal.

15. The integrated circuit assembly of claim 12 further comprising an underfill material positioned between the printed circuit board and the integrated circuit.

16. 16. The integrated circuit assembly of claim 15, wherein the glass transition temperature of the underfill material is greater than the melting point of the solder.

17. 13. The integrated circuit assembly of claim 12, further comprising a gold film positioned between the first surface of the integrated circuit and the heat spreader.

18. 20. The integrated circuit assembly of claim 17, further comprising an adhesion layer positioned between the first surface of the integrated circuit and the gold film.

19. The integrated circuit assembly of claim 12 , wherein the integrated circuit comprises an internal heat spreader.

20. The integrated circuit assembly of claim 12 , wherein the integrated circuit is lidless.

21. Further comprising a deformable conductor; The cooling plate is electrically grounded; the deformable conductor is positioned in contact between the heat spreader and the cold plate; The integrated circuit assembly of claim 12 , wherein the heat spreader and the cold plate are electrically connected to each other via the deformable conductor.

22. Further comprising a deformable conductor; the printed circuit board includes a ground pad; the deformable conductor is disposed between and in contact with the ground pad and the heat spreader; 13. The integrated circuit assembly of claim 12, wherein the heat spreader and the ground pad are electrically connected to each other via the deformable conductor.

23. 1. An integrated circuit assembly with cooling for an integrated circuit, comprising: A printed circuit board; an integrated circuit mounted on the printed circuit board; a heat spreader soldered to the integrated circuit using solder, the solder having a reflow temperature below a glass transition temperature of an underfill material positioned between the printed circuit board and the integrated circuit; a cold plate positioned over the heat spreader and thermally coupled to the integrated circuit via a thermally conductive material.

24. 1. An integrated circuit assembly with cooling for an integrated circuit, comprising: A printed circuit board; an integrated circuit mounted on the printed circuit board; a heat spreader soldered to the integrated circuit using solder, the solder having a reflow temperature below a reflow temperature of a second solder positioned between the printed circuit board and the integrated circuit; a cold plate positioned over the heat spreader and thermally coupled to the integrated circuit via a thermally conductive material.

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