CROSS-REFERENCE TO RELATED APPLICATION

[0001] This PCT International Patent Application claims the benefit of U.S. Provisional Patent Application Serial No. 63/331,949, filed on April 18, 2022 and titled “Surface Mount Wicking Structure,” the entire disclosure of which is hereby incorporated by reference.

FIELD

[0002] The present disclosure relates generally to a heat sink for conveying heat from a heat source, such as an electronic component. More specifically, it relates to a heat sink having a porous wick structure.

BACKGROUND

[0003] Heat sinks are used to convey heat away from a heat source, such as an electronic device, to prevent the heat source and/or other components from being damaged due to excessive temperatures. One type of heat sink that is conventionally known is a heat pipe, which uses a refrigerant fluid that changes from a liquid to a gas at an evaporator to transmit heat from the heat source to a condenser, where heat exits as the refrigerant fluid condenses back to a liquid. Conventional heat pipes employ a wick to transfer the condensed refrigerant from the condenser back to the evaporator.

[0004] Additive manufacturing is used to manufacture parts in a series of steps by progressively adding material to the part being manufactured. One type of conventional additive manufacturing uses a heat source, such as a laser, to melt a source material, such as a metal powder. Typically, the source material is removed from areas where it is not melted. This allows parts to be made with a variety of complex shapes. [0005] Thermal dissipation in conventional 2-phase heat sinks is limited by the thermal resistance of the heatsink wall and other elements disposed between a heat source and a cooling means.

SUMMARY

[0006] In one embodiment of the invention, an electronic assembly is provided. The electronic assembly includes: a printed circuit board having a first surface and a second surface opposite the first surface; a heat-generating component disposed on the first surface of the printed circuit board; and a thermal wick assembly including a wick of liquid-permeable material and disposed on the second surface of the printed circuit board aligned with the heat-generating component and in thermal communication therewith.

[0007] In another embodiment of the invention, a method of forming an electronic assembly with a heat sink is provided. The method includes: depositing a wick of liquid-permeable material on a transferable substrate to form a thermal wick assembly; and attaching the thermal wick assembly on a surface of a printed circuit board opposite from and aligned with a heatgenerating component, and in thermal communication therewith.

[0008] In another embodiment of the invention, a method of forming an electronic assembly with a heat sink is provided. The method includes: forming a wick of liquid-permeable material directly on a surface of a printed circuit board by an additive manufacturing technique; and attaching a heat-generating component on an opposite surface of the printed circuit board opposite from and aligned with the wick of liquid-permeable material and in thermal communication therewith. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further details, features and advantages of designs of the invention result from the following description of embodiment examples in reference to the associated drawings.

[0010] FIG. 1 is a side cut-away view of a first electronic assembly, according to an aspect of the present disclosure;

[0011] FIG. 2 is a side cut-away view of a second electronic assembly, according to an aspect of the present disclosure;

[0012] FIG. 3 is a side cut-away view of a third electronic assembly, according to an aspect of the present disclosure;

[0013] FIG. 4 is a perspective view of a fourth electronic assembly, according to an aspect of the present disclosure;

[0014] FIG. 5 shows a flow chart listing steps in a second method of forming an electronic assembly with a heat sink; and

[0015] FIG. 6 shows a flow chart listing steps in a second method of forming an electronic assembly with a heat sink.

DETAILED DESCRIPTION

[0016] Recurring features are marked with identical reference numerals in the figures, in which example embodiments of an electronic assembly 20, 120, 220, 320 are disclosed.

[0017] The electronic assemblies 20, 120, 220, 320 of the present disclosure each reduce a distance between a heat source and a cooling device. Thus, thermal resistance is reduced and heat transfer is improved over conventional designs.

[0018] In some embodiments, an electronic assembly with a heat generating component, is attached to a porous wick/lattice structure or a conventional heatsink. In some embodiments, the porous wick/lattice structure is contained in a hollow heatsink filled with a 2-phase solution. In some embodiments, the porous wick/lattice structure is attached to a conventional heatsink, which is exposed to open environment for natural or forced convection heat exchange.

[0019] In some embodiments, the porous wick/lattice structure is mounted to a surface of a printed circuit board (PCB) and adhered thereto by a conventional surface mount processes on an opposite side of the heat generating component.

[0020] In some embodiments, the porous wick/lattice structure is fabricated by depositing wick/lattice structure on a transferable substrate that can be attached to the PCB assembly by conventional surface mount techniques.

[0021] In some embodiments, the porous wick/lattice structure is directly fabricated on a (PCB) using an additive manufacturing (AM) method, such as selective laser sintering (SLS) or selective laser melting (SLM), although other AM techniques may be used.

[0022] FIG. 1 shows a first electronic assembly 20 that includes a heat-generating component 22, such as an electronic component mounted to a printed circuit board (PCB) 24. In some embodiments, and as shown in FIG. 1, the heat-generating component includes a surfacemounted electronic device. However, the heat-generating component may include another type of component, such as a through-hole mounted electronic device. The PCB 24 includes a first surface 26 and a second surface 28 opposite the first surface 26. The heat-generating component 22 is disposed on the first surface 26 of the PCB 24. The first electronic assembly 20 also includes a thermal wick assembly 40 disposed on the second surface 28 of the PCB 24, aligned with the heatgenerating component 22 and in thermal communication therewith.

[0023] The thermal wick assembly 40 of the first electronic assembly 20 shown in FIG. 1 is formed as a surface-mounted wick structure having a substrate 42 and a wick 44 of liquid- permeable material. The substrate may include a solid material having a high thermal conductance, such as metal. In some embodiments, the wick 44 may include unmelted or semi-melted source material used in an additive manufacturing process, such as granules of metal or another material that can be fused together in the additive manufacturing process. Alternatively or additionally, the wick 44 may include another material, such as an open-cell foam.

[0024] In some embodiments, the thermal wick assembly 40 is adhered to the second surface 28 of the PCB 24 by a surface mount processes. For example, solder 46, which may be deposited by a surface mount process, such as reflow soldering, may secure the substrate 42 of the thermal wick assembly 40 to the second surface 28 of the PCB 24.

[0025] The first electronic assembly 20 also includes plurality of thermal vias 30 which each include a metal material that extends between the first surface 26 and the second surface 28 of the PCB 24 for conducting heat from the heat-generating component 22 to the thermal wick assembly 40.

[0026] In some embodiments, and as shown in FIG. 1, the thermal wick assembly 40 is exposed to an open environment for natural or forced convection heat exchange. For example, heat may be transferred from heat-generating component 22 and to air within the wick 44. The air may transmit heat away from the wick 44 via convection currents or by a forced airflow, such as airflow directed by a fan or by movement of the first electronic assembly 20.

[0027] FIG. 2 shows side cut-away view of a second electronic assembly 120. The second electronic assembly 120 may be similar or identical to the first electronic assembly 20, but with a modified thermal wick assembly 140. The modified thermal wick assembly 140 includes the wick 44 being in physical and thermal contact with a copper layer 142 disposed on the second surface

28 of the PCB 24. The copper layer 142 may be an integral feature of the PCB 24, such as an electrically conductive layer thereof. Alternatively, the copper layer 142 may be affixed to the second surface 28 of the PCB 24 exclusively as part of the modified thermal wick assembly 140. The copper layer 142 may take the place of the substrate 42, which may be omitted from the modified thermal wick assembly 140.

[0028] FIG. 3 shows side cut-away view of a third electronic assembly 220. The third electronic assembly 220 may include similar or identical components as the first electronic assembly 20, but with the addition of a heatsink 50. Alternatively or additionally, the third electronic assembly 220 may include the modified thermal wick assembly 140. The heatsink 50 has a hollow construction with a solid wall 52 that surrounds the thermal wick assembly 40 or the modified thermal wick assembly 140. The heatsink 50 may be formed by additive manufacturing, although other manufacturing processes, such as casting and/or machining may be used. For example, the solid wall 52 may be formed by selectively melting a source material, such as a loose powder, using a concentrated heat source, such as a laser.

[0029] The heatsink 50 also includes a plurality of heat spreader fins 54 to provide a relatively large surface area for radiating heat. The heat spreader fins 54 may be formed as posts or as elongated fins, although they may take other forms. In some embodiments, the heat spreader fins 54 may be integrally formed with the solid wall 52 (e.g. by additive manufacturing or by another process), although the heat spreader fins 54 may be formed separately or independently.

[0030] The heatsink 50 defines an internal space 56 that contains the thermal wick assembly 40. The internal space 56 is bounded by the solid wall 52. In some embodiments, and as shown in FIG. 3, the internal space 56 is at least partially bounded by the PCB 24. In some embodiments, and as shown in FIG. 3, the internal space 56 may extend into the heat spreader fins

54. Alternatively, the heat spreader fins may be solid and/or isolated from the internal space 56. The heatsink 50 may transfer heat to an ambient atmosphere by any means such as radiation, conduction, and/or convection.

[0031] In some embodiments, the third electronic assembly 220 further includes a coolant fluid 58 disposed in the internal space 56. In some embodiments, the coolant fluid 58 may include a refrigerant material, which may also be called a 2-phase solution, and which is configured to change between a liquid phase and a vapor phase to convey heat away from the thermal wick assembly 40. The refrigerant material may boil, or change between a liquid phase and a vapor phase to convey heat from the from the thermal wick assembly 40 and to the solid wall 52. For example, the refrigerant material may boil within the wick 44 and travel in the vapor phase to an interior surface of the solid wall 52. At or near the solid wall 52, the refrigerant material may condense back to the liquid phase to transmit heat to the solid wall 52, where it may be subsequently conducted out of the heatsink 50.

[0032] In some embodiments, and as shown in FIG. 3, a sealant material 60, such as caulk or epoxy is disposed between the heatsink 50 and the PCB 24 to form a seal therebetween for containing the coolant fluid 58 within the internal space 56.

[0033] FIG. 4 is a perspective view of a fourth electronic assembly 320 that includes a common substrate 324 with a plurality of different thermal wick assemblies 340 disposed thereupon. FIG. 4 may show the thermal wick assemblies 340 in a state of manufacturing, such as using an additive manufacturing process. In some embodiments, each of the thermal wick assemblies 340 may be cut or otherwise separated with a corresponding portion of the common substrate 324 to form a plurality of the thermal wick assemblies 40, each having a single substrate 42 and wick 44. Alternatively or additionally, a thermal wick sub-structure may be formed having a single substrate 42 with two or more of the wicks 44 for attachment to the PCB 24 with the two or more wicks 44 each being aligned with a corresponding heat-generating component 22.

[0034] FIG. 5 shows a flow chart listing steps in a first method 400 of forming an electronic assembly with a heat sink. As can be appreciated in light of the disclosure, the order of operation within the first method 400 is not limited to the sequential execution as illustrated in FIG. 5, but may be performed in one or more varying orders as applicable and in accordance with the present disclosure. The first method 400 includes depositing, at step 402, a wick 44 of liquid-permeable material on a transferable substrate 42 to form a thermal wick assembly 40.

[0035] The first method 400 also includes attaching, at step 404, the thermal wick assembly 40 on a surface of a printed circuit board opposite from and aligned with a heat-generating component, and in thermal communication with the heat-generating component via the printed circuit board, with the printed circuit board conducting a substantial amount of heat from the heatgenerating component to the wick of liquid-permeable material. The substantial amount of heat may include a majority of the heat produced by the heat-generating component. However, the substantial amount of heat may vary depending on a particular application or set of conditions. In some embodiments, step 404 includes attaching the thermal wick assembly on the surface of the printed circuit board includes using a surface mounting technique, such as a reflow soldering process.

[0036] FIG. 6 shows a flow chart listing steps in a second method 500 of forming an electronic assembly with a heat sink. As can be appreciated in light of the disclosure, the order of operation within the second method 500 is not limited to the sequential execution as illustrated in FIG. 6, but may be performed in one or more varying orders as applicable and in accordance with the present disclosure. [0037] The second method 500 includes forming, at step 502, a wick of liquid-permeable material directly on a surface of a printed circuit board by an additive manufacturing technique. In some embodiments, the additive manufacturing technique includes selective laser sintering (SLS). Alternatively or additionally, the additive manufacturing technique may include selective laser melting (SLM).

[0038] The second method 500 also includes attaching, at step 504, a heat-generating component on an opposite surface of the printed circuit board opposite from and aligned with the wick of liquid-permeable material and in thermal communication with the wick of liquid- permeable material via the printed circuit board, with the printed circuit board conducting a substantial amount of heat from the heat-generating component to the wick of liquid-permeable material. The substantial amount of heat may include a majority of the heat produced by the heatgenerating component. However, the substantial amount of heat may vary depending on a particular application or set of conditions. In some embodiments, step 504 includes attaching the heat-generating component on the opposite surface of the printed circuit board includes using a surface mounting technique, such as a reflow soldering process.

[0039] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.