CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This PCT International Patent Application claims the benefit of and priority to U. S.

Provisional Patent Application Serial No. 63/192,307 filed on May 24, 2021, and titled “Printed Circuit Board Assembly With Integrated 2-Phase Heat Sink,” the entire disclosure of which is hereby incorporated by reference.

FIELD

[0002] The present disclosure relates generally to an electronic assembly including a heat sink for conveying heat from a printed circuit board including a heat source.

BACKGROUND

[0003] Heat skinks 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 skink 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. SUMMARY

[0005] An electronic assembly is provided. The electronic assembly comprises a heat sink including a shell of liquid tight material defining an open face and a porous wick containing a cooling fluid. The electronic assembly also comprises a printed circuit board (PCB) including a heat source and covering the open face of the first heat sink and contacting the porous wick. The first heat sink is configured to cause the cooling fluid to migrate through the porous wick between the shell and the PCB and to change from a liquid to a gas phase to convey the heat from the heat source to the shell.

BRIEF DESCRIPTION OF THE DRAWINGS

[0001] Further details, features and advantages of designs of the invention result from the following description of embodiment examples in reference to the associated drawings.

[0002] FIG. 1 shows a side cut-away view of a first electronic assembly of the present disclosure.

[0003] FIG. 2 shows a side cut-away view of a second electronic assembly of the present disclosure.

[0004] FIG. 3 shows a side cut-away view of a third electronic assembly of the present disclosure.

[0005] FIG. 4 shows a side cut-away view of a fourth electronic assembly of the present disclosure.

DETAILED DESCRIPTION

[0006] Recurring features are marked with identical reference numerals in the figures, in which example embodiments of electronic assemblies 20, 120, 220, 320 are disclosed. FIG. 1 shows a side cut-away view of a first electronic assembly 20 that includes a first heat sink 22 and a printed circuit board (PCB) 24. The first heat sink 22 includes a shell 30 of liquid tight material defining an open face 32 and a porous wick 34 containing a cooling fluid (not shown). The cooling fluid may include a liquid partially filling the shell 30 of the first heat sink 22. In some embodiments, the porous wick 34 may not completely fill the shell 30. For example, and as shown in FIG. 1, the porous wick 34 may be disposed adjacent to the shell 30 for a depth that is approximately consistent. The porous wick 34 may define one or more cavities 35 within the first heat sink 22.

[0007] In some embodiments, the porous wick 34 may include material melted or partially melted by additive manufacturing. For example, the porous wick 34 may include a partially sintered powder having a relatively high porosity. In some embodiments, the shell 30 includes the same material as the porous wick 34. The shell 30 may be formed to have a porosity that is lesser than a porosity of the porous wick 34. For example, the shell 30 may include the same powder that has been more fully sintered to form the shell 30 with a very low porosity, making the shell 30 liquid tight. The shell 30 may be formed by additive manufacturing, such as selective laser sintering (SRS).

[0008] The PCB 24 includes a heat source 50. The PCB also includes a planar substrate

52 covering the open face 32 and contacting the porous wick 34 of the first heat sink 22 for transmitting heat away from the heat source 50 and to the first heat sink 22. The planar substrate 52 of the PCB 24 may include a metal core with a conductive layer 54 disposed thereupon for conducting electrical current between electrical components on the PCB 24. The conductive layer 54 may include, for example, copper, although other electrically conductive materials may be used. The PCB 24 also includes an electrical insulator 56 disposed between the planar substrate 52 and the conductive layer 54. This electrical insulator 56 may include a layer of an adhesive material. The electrical insulator 56 may be used, especially where the planar substrate 52 includes an electrically conducive material, such as metal.

[0009] The heat source 50 may include an electronic device 52, such as a microprocessor or a power electronic device, disposed on the conductive layer 54 of the PCB 24. Additionally or alternatively, the heat source 50 may include one or more portions of the conductive layer 54, particularly in high-current applications where the conductive layer 54, itself, generates heat by resistive heating.

[0010] A cooler 58 may be disposed over the heat source 50 opposite from the first heat sink 22 for removing heat from the heat source 50. The cooler 58 may include, for example, another heat sink, a liquid cooling block for circulating a cooling fluid, and/or a heat pipe for conveying heat to a location away from the heat source 50.

[0011] The first heat sink 22 is configured to cause the cooling fluid to migrate through the porous wick 34 between the shell 30 and the PCB 24 and to change from a liquid to a gas to convey the heat from the heat source 50 to the shell 30, where the heat can be dissipated by warming air outside of the first heat sink 22.

[0012] As shown in FIG. 1, the first heat sink 22 includes a base portion 60 adjacent to the open face 32 and a radiator portion 62 spaced apart from the open face 32. The radiator portion 62 may include the shell 30 defining a plurality of fins 64, each providing an increased surface for transmitting the heat from the cooling fluid to the ambient air. The fins may be formed as rods or as elongated strips. However, it should be appreciated that the fins may have any configuration. One or more of the fins 64 may contain the porous wick 34, as shown in FIG. 1. Alternatively or additionally, one or more of the fins 64 may be hollow and/or solid. One or more of the cavities 35 may extend into a corresponding one of the fins 64. [0013] The first electronic assembly 20 shown in FIG. 1 also includes a fastener 70 extending through or around the PCB 24 and configured to secure the PCB 24 onto the first heat sink 24. The fastener 70 may include comprises a screw or a bolt extending through the PCB 24 and into a corresponding lug 72 in the first heat sink 22. However, the fastener 70 may take other forms, such as a clip or clamp that holds the PCB 24 onto the first heat sink 22. The lug 72 may be formed of the same material as the porous wick 34. For example, the material may be further sintered or otherwise formed into a more rigid form to provide the lug 72 with additional mechanical strength for engaging and retaining the fastener 70. A fastener seal 74 is disposed between the first heat sink 22 and the PCB 24 and adjacent to the fastener 70, forming a liquid- tight seal therebetween. The fastener seal 74 may cover the lug 72, as shown in FIG. 1. The fastener 70 may extend through the fastener seal 74.

[0014] The first heat sink 22 also includes a rim 76 extending around at least a portion of a periphery of the open face 32. In some embodiments, and as shown in FIG. 1, the rim 76 extends parallel to the PCB 24. The rim 76 may be integrally formed with the shell 30. For example, the rim 76 may be formed by additive manufacturing, such as selective laser sintering (SRS). A peripheral gasket 78 is disposed between the rim 76 and the PCB 24, forming a liquid-tight seal therebetween.

[0015] FIG. 2 shows a side cut-away view of a second electronic assembly 120 of the present disclosure. The second electronic assembly 120 may be similar or identical to the first electronic assembly 20, except for a few changes shown in the drawings and/or described herein. The second electronic assembly 120 includes a second PCB 124 having a flexible substrate 152 in place of the planar substrate 52 in the PCB 24 of the first electronic assembly 20. The flexible substrate 152 may have a lesser thickness than the planar substrate 52, although the flexible substrate 152 may have any suitable thickness. The second electronic assembly 120 also includes a second heat sink 122, which may be similar or identical to the first heat sink 22 of the first electronic assembly 20.

[0016] FIG. 3 shows a side cut-away view of a third electronic assembly 220. The third electronic assembly 220 may be similar or identical to the first electronic assembly 20 and/or the second electronic assembly 120, except for a few changes shown in the drawings and/or described herein.

[0017] The third electronic assembly 220 includes a third heat sink 222 and a third PCB

224. The third heat sink 222 may be similar to the first heat sink 22 of the first electronic assembly 20, except with the addition of a first pin 170 and a second pin 180 each extending outwardly from the third heat sink 222 perpendicular to and beyond the open face 32 and extending through the third PCB 224 for securing the third PCB 224 with the third heat sink 222. The first pin 170 may be attached to a lug 72 in the third heat sink 222. For example, the first pin 170 may be integrally formed with the lug 72, although the first pin 170 may be welded or otherwise attached to the lug 72. The second pin 180 may be attached to a rim 76 of the third heat sink 222. For example, the second pin 180 may be integrally formed with the rim 76, although the second pin 180 may be welded or otherwise attached to the rim 76. One or both of the pins 170, 180 may serve another purpose, such as for providing an electrical grounding connection between the third PCB 224 and the third heat sink 222 and/or for attachment of other devices or items, such as one or more wires, a mounting bracket, or a housing to cover the third PCB 224.

[0018] In some embodiments, either or both of the first pin 170 and/or the second pin 180 may be formed as a stud having external threads. In some embodiments, a first solder joint 172 may join the first pin 170 to the third PCB 224. Additionally or alternatively, a second solder joint 182 may join the second pin 180 to the third PCB 224.

[0019] FIG. 4 shows a side cut-away view of a fourth electronic assembly 320. The fourth electronic assembly 320 may be similar or identical to one or more of the other electronic assemblies 20, 120, 220 except for a few changes shown in the drawings and/or described herein. [0020] The fourth electronic assembly 320 includes a fourth heat sink 322 and a fourth

PCB 324. The fourth heat sink 322 may be similar to the first heat sink 22 of the first electronic assembly 20. The fourth heat sink 322 includes an extended rim 376 in place of the rim 76 of the first heat sink 22. The extended rim 376 may include a curved top surface 378, although the extended rim 376 may have any configuration.

[0021] As shown in FIG. 4, the fourth heat sink 322 also includes a peripheral wall 380 that extends from the extended rim 376 perpendicularly to the open face 32 and around an edge of the fourth PCB 324. The peripheral wall 380 and the extended rim 376 may together define a channel 382 for receiving a peripheral gasket 384 forming a liquid tight seal between the fourth heat sink 322 and an edge 326 of the fourth PCB 324.

[0022] In some embodiments, and as shown on FIG. 4, the edge 326 of the fourth PCB 324 is pressed and formed into the channel 382 to form the liquid tight seal between the fourth heat sink 322 and the edge 326 of the fourth PCB 324.

[0023] In some embodiments, and as shown on FIG. 4, a peripheral seal 384, such as an

O-ring, is disposed over the fourth PCB 324 and adjacent to or within the channel 382. The peripheral seal 384 may include a resilient material, such as rubber. Alternatively or additionally, the peripheral seal 384 may include a rigid material, such as metal, for securing the fourth PCB 324 tightly to the fourth heat sink 322. [0024] 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.