An electrical-circuit assembly includes an electrical-device and a heat-sink. The heat-sink has a base having a first-surface and a second-surface. The first-surface is in thermal communication with the electrical-device. The heat sink also has a lid having a third-surface and a fourth-surface. The third-surface faces toward the second-surface. The heat sink also has side-walls disposed between the base and the lid extending from the second-surface to the third-surface. The base, the lid, and the side-walls define a cavity. The heat sink also has a porous-structure extending from the second-surface toward the third-surface terminating a portion of the distance between the second-surface and the third-surface thereby defining a void between the porous-structure and the third-surface. The base, the side-walls, and the porous-structure are integrally formed of a common material. The porous-structure is characterized as having a contiguous-porosity network. The heat sink also has a heat-transfer-fluid disposed within the cavity.

TECHNICAL FIELD OF INVENTION

This disclosure generally relates to an electrical-circuit assembly, and more particularly relates to an electrical-circuit assembly with a heat-sink.

DETAILED DESCRIPTION

FIG. 1illustrates is a section view of an electrical-circuit assembly10, hereafter referred to as the assembly10. As will be described in more detail below, the assembly10is an improvement on previous electrical-circuit-assemblies because the assembly10passively cools an electrical-device12. As used herein, the term “passively” means that no mechanical pump or fan mechanism is used to cool the assembly, that would typically require an external power source, add cost, and increase a package-size.

The assembly10includes the electrical-device12. The electrical-device12may be any electrical-device12that may benefit from cooling (i.e. heat removal) during operation, including, but not limited to, capacitors, resistors, inductors, amplifiers, micro-processors, etc., or any combination thereof, as will be recognized by one skilled in the art. The electrical-device12may include printed-circuit-boards formed of epoxy-resins, polyimide-resins, and/or ceramics. The electrical-device12may be a vehicle-controller, such as that used for controlling an autonomous-vehicle, which typically generates more heat than a typical vehicle-controller, due to the increased microprocessor demands required for autonomous driving.

The assembly10also includes a heat-sink14operable to remove heat from the electrical-device12. The heat-sink14includes a base16having a first-surface18and a second-surface20opposite the first-surface18. The base16may be formed of any material that is heat-conducting. In the example illustrated inFIG. 1, the base16is formed of an aluminum-alloy that is die-cast. The first-surface18of the base16is in thermal communication with the electrical-device12. That is, the first-surface18provides a path for heat to be conducted away from the electrical-device12.

The heat-sink14also includes a lid22having a third-surface24and a fourth-surface26opposite the third-surface24. In the example illustrated inFIG. 1the lid22is formed of an aluminum-alloy that is die-cast. The lid22is arranged so the third-surface24faces toward the second-surface20. The lid22may be attached to the base16by any method to preferably form a hermetic-seal, including welding, soldering, adhesives, etc., and in the example illustrated inFIG. 1, the lid22is friction stir welded to the base16forming a metallurgical bond.

The heat-sink14also includes side-walls28disposed between the base16and the lid22extending from the second-surface20to the third-surface24and define a perimeter of the heat-sink14. The base16, the lid22, and the side-walls28cooperate to define a cavity30.

The heat-sink14also includes a porous-structure32extending from the second-surface20toward the third-surface24. The porous-structure32terminates (i.e. ends, stops, etc.) a portion of a distance between the second-surface20and the third-surface24thereby defining a void34between the porous-structure32and the third-surface24. That is, the porous-structure32does not completely fill the cavity30and leaves the void34between the porous-structure32and the third-surface24. The base16, the side-walls28, and the porous-structure32are integrally formed of a common material (e.g. die-cast aluminum-alloy). That is, the base16, the side-walls28, and the porous-structure32are formed as one unit during the die-casting process and are not formed as a result of welding separate die-case components together, or sintering powdered metals to create the porous-structure32. The porous-structure32is characterized as having a contiguous-porosity network. That is, fluidic communication exists throughout the entire porous-structure32enabling a flow of fluids through the porous-structure32. In contrast, the second-surface20, the side-walls28, and the third-surface24inhibit the flow of fluid through their respective sections. The porous-structure32is formed by controlling porosity in the base16during the die-casting process, as will be appreciated by those skilled in the art of die-casting. The porous-structure32defines an exposed-surface36that faces the third-surface24. The exposed-surface36is created by removing a portion of a surface-skin, formed during die-casting, from the base16by mechanical and/or chemical processing. A depth38of the porous-structure32is in a range from about 1.0 millimeters to about 4.0 millimeters. The porous-structure32is characterized by a percent-porosity40in a range from about 48-percent to about 74-percent.

FIGS. 2A-2Billustrate portions of the base16within the cavity30before the surface-skin is removed. In one embodiment, the portion of the base16within the cavity30is cast with a planar-surface (not shown). In another embodiment (seeFIG. 2A), the portion of the base16within the cavity30is cast with ribs42forming an undulating-surface, wherein when the surface-skin is removed the exposed-surface36is characterized as having undulations44. In yet another embodiment (seeFIG. 2B), dimples46(i.e. depressions, embossments, etc.) are cast into the portion of the base16within the cavity30to create the undulating-surface and may increase the heat conduction in a direction normal to the second-surface20. Other structures may be formed in the base16within the cavity30by bead-blasting or other means that also create undulations44in the exposed-surface36.

FIG. 3is a table that illustrates an example of a preferred pore-size-distribution that may be developed in the porous-structure32based on a rate-of-casting, entrained gas, and other casting parameters that will be appreciated by those in the art. A pore diameter range and the number of pores in the respective range are listed.

Referring back toFIG. 1, the assembly10also includes a heat-transfer-fluid48disposed within the cavity30and occupies a portion of the cavity30(i.e. the cavity30is not completely filled with the heat-transfer-fluid48). The heat-transfer-fluid48may be any heat-transfer-fluid48with a boiling-point suited to the thermal environment of the application. In the example illustrated inFIG. 1, the heat-transfer-fluid48is acetone. In other applications a mixture of water and ethylene glycol may be used for the heat-transfer-fluid48. The heat-transfer-fluid48is heated by the second-surface20from the heat conducted away from the electrical-device12. The heat-transfer-fluid48evaporates, transports across the porous-structure32and across the void34in the cavity30, and condenses on the third-surface24thereby distributing the heat over the third-surface24. The condensed heat-transfer-fluid48returns to the porous-structure32that acts as a wicking-plane to direct the liquid heat-transfer-fluid48back to the desired heat producing location (e.g. the locations of greatest heat conduction from the electrical-device12). This closed-system (i.e. sealed system) is beneficial because it does not require the heat-transfer-fluid48to be replenished, or transferred into and/or out of the cavity30. Experimentation by the inventors indicates that the heat-transfer capability of the assembly10as describe above is in excess of 40,000 Watts/meter-Kelvin (40,000 W/mK), compared to only 140 W/mK for a typical solid aluminum-heat-sink.

Referring again toFIG. 1, the fourth-surface26is configured to dissipate the heat generated by the electrical-device12to a surrounding environment50, and in one embodiment includes cooling-fins52extending beyond the fourth-surface26.

Accordingly, an electrical-circuit-assembly10(the assembly10is provided. The assembly10is an improvement over other electrical-circuit-assemblies because the assembly10passively transfers heat away from the electrical-device12at a greater rate than the typical solid aluminum-heat-sink.

While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. “One or more” includes a function being performed by one element, a function being performed by more than one element, e.g., in a distributed fashion, several functions being performed by one element, several functions being performed by several elements, or any combination of the above. It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first contact could be termed a second contact, and, similarly, a second contact could be termed a first contact, without departing from the scope of the various described embodiments. The first contact and the second contact are both contacts, but they are not the same contact. The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “if” is, optionally, construed to mean “when” or “upon” or “in response to determining” or “in response to detecting,” depending on the context. Similarly, the phrase “if it is determined” or “if [a stated condition or event] is detected” is, optionally, construed to mean “upon determining” or “in response to determining” or “upon detecting [the stated condition or event]” or “in response to detecting [the stated condition or event],” depending on the context.