Heat sink, heat sink assembly, and formation method of heat sink

Abstract

To provide a heat sink to maximize heat transfer.SOLUTION: A heat sink 12 includes a substrate 18 and a plurality of pin fins 20, the plurality of pin fins 20 include a first pin fin and a second pin fin, the first pin fin and the second pin fin have at least one different geometric characteristic, the first pin fin has a first end coupled to the substrate 18, a second end opposite the first end, a first portion, and a second portion, the first portion extends from the first end to the second portion, the first portion of the first pin fin has a first cross-sectional shape cut along the length of the pin fin, the second portion of the first pin fin has a second cross-sectional shape cut along the length of the pin fin, the first cross-sectional shape is selected from a predetermined list including an ellipse, a circle, and an airfoil, and the second cross-sectional shape is selected from the predetermined list and different from the first cross-sectional shape.SELECTED DRAWING: Figure 1

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of Provisional Patent Application No. 63 / 509602, filed June 22, 2023, and entitled “Non-Uniform Cross-Section Pin Fins for Enhanced Heat Transfer While Reducing Pressure Drop for Conjugate Heat Transfer in Inverters,” the contents of which are incorporated by reference in their entirety. [Technical field]

[0002] The present invention relates, for example, to heat sinks with pin fins having non-uniform cross-sections, heat sink assemblies, and methods of forming heat sinks. [Background technology]

[0003] Heat sinks are a conventional form of heat dissipation from heat-generating devices and include pin fins for dissipating heat, the pin fins having a uniform cross-section along their length. Summary of the Invention [Problem to be solved by the invention]

[0004] Pin fins may have an inverse relationship between heat transfer and pressure drop of the fluid passing between them; that is, increased heat transfer results in a larger pressure drop. A larger pressure drop reduces the fluid flow across the pin fin, thereby reducing heat transfer from the pin fin. Therefore, alternative pin fins may be required to maximize heat transfer. [Means for solving the problem]

[0005] In one general aspect, a heat sink includes a substrate and a plurality of pin fins, the plurality of pin fins including a first pin fin and a second pin fin. The first pin fin and the second pin fin have at least one different geometric characteristic. The first pin fin includes a first end coupled to the substrate, a second end opposite the first end, a first portion, and a second portion. The first portion extends from the first end to the second portion. The first portion of the first pin fin has a first cross-sectional shape cut along the length of the pin fin, and the second portion of the first pin fin has a second cross-sectional shape cut along the length of the pin fin. The first cross-sectional shape is selected from a predetermined list including an ellipse, a circle, and an airfoil, and the second cross-sectional shape is selected from the predetermined list and is different from the first cross-sectional shape.

[0006] In another general aspect, a heat sink assembly includes a substrate, a housing surrounding the substrate and containing a fluid, and a plurality of pin fins coupled to the substrate. The plurality of pin fins includes a first pin fin and a second pin fin. The first pin fin and the second pin fin have at least one distinct geometric characteristic. Each pin fin includes a first end coupled to the substrate, an opposing second end, a first portion, and a second portion. Each pin fin is spaced apart at the first end, and the first portion extends from the first end to the second portion. The first portion has a first cross-sectional shape cut along a length of the pin fin and the second portion has a second cross-sectional shape cut along a length of the pin fin. The second cross-sectional shape is an airfoil shape and the first cross-sectional shape is not an airfoil shape.

[0007] In yet another general aspect, a heat sink includes a substrate and a plurality of pin fins, the plurality of pin fins including a first pin fin and a second pin fin. The first pin fin and the second pin fin have at least one different geometric characteristic. Each pin fin includes a first end coupled to the substrate, a second end opposite the first end, a first portion, and a second portion. The first portion extends from the first end to the second portion. The plurality of pin fins includes a first pin and a second pin, the first portion of the first pin being a non-streamlined body and the second portion of the first pin being a streamlined body. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a heat sink assembly in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 2 is a perspective view of a pin fin of the heat sink assembly of FIG. 1 in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 2 is a cross-sectional view of a pin fin of a heat sink assembly in accordance with one or more embodiments of the present disclosure. [Diagram 3] 1 illustrates a flowchart of a method for forming a heat sink in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Referring initially to FIG. 1, a heat sink 12 assembly 10 is shown. The heat sink 12 assembly 10 includes a heat sink 12 attached to a device 14 to dissipate heat accumulated in the device 14. The device 14 may be any device 14 capable of generating heat, such as a computer component, more specifically an inverter pin card. The heat sink 12 assembly 10 may further include a housing 16 that surrounds the heat sink 12 and contains a fluid in which the heat sink 12 is immersed. The heat sink 12 may include a substrate 18 and a number of pin fins 20 coupled to the substrate 18. The substrate 18 may be formed of any material capable of transferring heat from the device 14, such as copper, aluminum, steel, etc. The heat sink 12 assembly 10 may include a pump 22 configured to direct a fluid flow F through the housing 16 and across the pin fins 20 of the heat sink 12. The pump 22 may circulate the fluid through the housing 16, where the fluid flow F moves in a single direction across the pin fins 20. The fluid flows from one end of the housing 16 to the opposite end of the housing 16 and is then circulated through tubes or other means to move the fluid back to the other end of the housing 16. In some embodiments, the fluid may be air, in which case the pump 22 is a fan that circulates air across the pin fins 20 in an open environment. However, it is contemplated and possible that the heat sink 12 may be used in natural convection without the use of a pump, fan, or the like, in which case the heat sink 12 rejects heat to stagnant air.

[0010] The plurality of pin fins 20 may include a first end 24 coupled to the substrate 18, an opposing second end 26, a first portion 28, a second portion 30, and a transition section 32 at a boundary 34 between the first portion 28 and the second portion 30. Each pin fin 20 is spaced apart such that rows of pin fins 20 are arranged along a longitudinal direction along the substrate 18, and each row of pin fins 20 is spaced apart from other rows of pin fins 20 along a lateral direction transverse to the longitudinal direction. The rows of pin fins 20 may be staggered such that the geometric center of one of the pin fins 20 is adjacent to the spacing between adjacent pin fins 20 in the lateral adjacent rows. In some embodiments, the pin fins 20 may have non-uniform spacing, where some pin fins 20 are spaced apart and / or staggered at different distances.

[0011] 2A and 2B, the pin fins 20 may have a non-uniform cross-section, where the first portion 28 of each pin fin 20 has a first cross-sectional shape and the second portion 30 has a second cross-sectional shape that is different from the first cross-sectional shape. Each cross-sectional shape is taken along the length of the pin fin, where the length may be measured by an axis A that extends through the first end 24, the second end 26, and the geometric center of the pin fin. It is conceivable and possible for the pin fin 20 to have more than two different cross-sectional shapes, such as three, four, or more than four. Each portion may have any feasible shape for heat transfer, such as a circle, an ellipse, an airfoil, a rectangle, etc. As used herein, an ellipse may include a circle. As shown in FIG. 2A and 2B, the first portion 28 extends from the first end 24 to the second portion 30, where the first cross-sectional shape is an ellipse and the second cross-sectional shape is an airfoil. As mentioned above, the first cross-sectional shape may be another shape that is not an airfoil. It is also conceivable and possible for the first cross-sectional shape to be an airfoil and the second cross-sectional shape to be another shape that is not an airfoil. In further embodiments, the cross-sectional shapes may include streamlined bodies and non-streamlined bodies, where a streamlined body has a shape with a drag coefficient below a predetermined threshold and a non-streamlined body has a shape with a drag coefficient equal to or greater than the predetermined threshold. In some embodiments, the predetermined threshold is the drag coefficient of the ellipse measured in the direction of flow along the length of the ellipse, where the length of the ellipse is the longest portion of the ellipse that is oriented upstream. Examples of shapes that are streamlined bodies include airfoils and flat disks with their thinnest side oriented upstream. Examples of shapes that are non-streamlined bodies include flat disks, circles, ellipses, etc. with their longest side oriented upstream.

[0012] Although the pin fin 20 is depicted as having a non-uniform cross-section, it is contemplated and possible for only a portion of the pin fin 20 to have a non-uniform cross-section, with the remaining pin fin 20 having a uniform cross-section. In further embodiments, the pin fin 20 can include a first pin fin and a second pin fin having different geometric characteristics. The different geometric characteristics can include different shape characteristics, overall heights, different cross-sectional heights, any combination thereof, and the like.

[0013] The first portion 28 may include a first aft side 40 and a first leading side 42, and the second portion 30 may include a second aft side 44 and a second leading side 46. The second aft side 44 may overlap the first aft side 40, the second aft side 44 being thinner than the first aft side 40. The second leading side 46 may overlap the first leading side 42, the second leading side 46 being wider than the first leading side 42. The second aft side 44 of the airfoil may terminate in a tip, or end 48, or may be rounded. The tip of the second aft side 44 may be oriented within the housing 16 such that the fluid flow F through the housing 16 contacts the second leading side 46 before contacting the second aft side 44. In other words, the second aft side 44 is directed downstream of the fluid flow F, as shown in FIG. 1.

[0014] The different cross-sectional shapes of the first portion 28 and the second portion 30 may form or define a step below the second portion 30 and above the first portion 28. This section of the pin fin 20 may be blended to remove the step, where the cross-sectional shape gradually changes shape to remove the step. For example, the first cross-sectional shape may change from an ellipse toward an airfoil along the length of the pin fin 20 as the first portion 28 extends toward the second portion 30. Similarly, the second cross-sectional shape may change from an airfoil toward an ellipse along the length of the pin fin 20 as the second portion 30 extends toward the first portion 28. As a result, each of the first portion 28 and the second portion 30 may have a modified shape near the boundary 34, where the modified shape is between an airfoil and an ellipse. The second portion 30 near the boundary 34 may have an airfoil-shaped elliptical shape that is primarily an airfoil shape, and the first portion 28 near the boundary 34 may have an airfoil-shaped elliptical shape that is primarily an elliptical shape. This area around the boundary 34 may be referred to as the transition section 32, where the transition section 32 of the plurality of pin fins 20 is at the boundary 34 between the first portion 28 and the second portion 30. The transition section 32 may include portions of each of the first portion 28 and the second portion 30, where the transition section 32 may be a percentage of the height of each pin fin. For example, the first portion 28 may be 30% of the height of the pin fin and the second portion 30 may be 70% of the height of the pin fin, where half of the height of the transition section 32 is included in the first portion 28 and the other half of the height of the transition section 32 is included in the second portion 30. It is conceivable and possible for the first portion 28 and the second portion 30 to include different percentages of the height of the pin fin, e.g., 20% first portion and 80% second portion, 10% first portion and 90% second portion, etc. The ratio of the first portion to the second portion of the pin fin 20 may vary depending on the position of the pin fin 20. For example, a pin fin 20 disposed on the upstream side may have a first portion that occupies 20% of the height of the pin fin 20, and a pin fin 20 disposed on the downstream side may have a first portion that occupies 30% of the height of the pin fin 20.As a further example, a pin fin 20 located between an upstream pin fin 20 and a downstream pin fin 20 may have a first portion that occupies 25% of the height of the pin fin 20. The height of the first portion may gradually change from the upstream side to the downstream side.

[0015] The transition section 32 transitions from an elliptical to an airfoil shape along the length of the pin fin 20, providing a transition cross-section that blends the elliptical shape of the first portion 28 with the airfoil shape of the second portion 30. Although specific height percentages are given, it is contemplated and possible that the first portion 28 and the second portion 30 may comprise different height percentages of the pin fin 20, such as 40% for the first portion 28 and 60% for the second portion 30. In further embodiments, the transition section 32 may be any workable percentage of the pin fin 20, such as 1%, 5%, 15%, 20%, or any percentage therebetween. The height of the transition section 32 depends on the manufacturing method, which is described in more detail below. It is also contemplated and possible that the pin fin 20 does not include the transition section 32, and a step is defined by the difference in cross-sectional shape at the boundary between the first portion 28 and the second portion 30.

[0016] 3, a flow chart of a method 300 of forming the assembly 10 of the heat sink 12 is shown. In step 302, the method 300 may include forming a substrate 18, a first portion 28 of the pin fin 20, and a second portion 30 of the pin fin 20. The substrate 18 and the pin fin 20 may be formed by any known process, such as additive manufacturing, casting, extrusion, etc. In step 304, the method 300 may include bonding the first portion 28 of the pin fin 20 to the second portion 30 of the pin fin 20, and bonding the first end 24 of the first portion 28 to the substrate 18. The first portion 28 and second portion 30 of the pin fin 20 and the substrate 18 may be bonded by known processes, such as welding, or may be formed together during an additive manufacturing process or casting. In some embodiments where the first portion 28 and the second portion 30 of the pin fin 20 are formed with a step at the interface 34 between the first portion 28 and the second portion 30, the method 300 may include a step 306 that includes blending the interface 34 between the first portion 28 and the second portion 30 of the pin fin to remove the step defined by the interface 34. The interface 34 may be blended by welding, grinding, polishing, or other methods of smoothing the edges of a metal structure.

[0017] 1-3, during operation, the presence of the pin fins 20 reduces the pressure of the fluid flowing across the pin fins 20, which reduces the fluid flow rate across the downstream pin fins 20. The reduced fluid flow rate reduces the amount of heat transfer across the pin fins 20 (e.g., the downstream pin fins 20). The cross-sectional profile of the pin fins 20 results in different pressure drops and heat transfer rates. For example, an elliptical cross-section will have a higher heat transfer rate and a higher pressure drop than an airfoil cross-section. Thus, placing the elliptical cross-section portion of the pin fin 20 in the low velocity region of the fluid flow F near the substrate 18 can minimize the pressure drop of the fluid flow while improving the heat transfer rate compared to an airfoil shape. Additionally, using an airfoil cross-section in the high velocity region of the fluid flow F away from the substrate 18 can reduce the pressure drop and maximize the fluid flow rate compared to an elliptical shape, maximizing the heat transfer rate of the pin fins 20 compared to a uniform cross-section pin fin.

[0018] This disclosure may be further defined by the following clauses:

[0019] 1. A heat sink comprising: a substrate; and a plurality of pin fins, the plurality of pin fins including a first pin fin and a second pin fin, the first pin fin and the second pin fin having at least one distinct geometric characteristic, the first pin fin having a first end coupled to the substrate, a second end opposite the first end, a first portion, and a second portion, the first portion extending from the first end to the second portion, the first portion of the first pin fin having a first cross-sectional shape cut along a length of the pin fin, the second portion of the first pin fin having a second cross-sectional shape cut along a length of the pin fin, the first cross-sectional shape being selected from a predetermined list comprising an ellipse, a circle, and an airfoil, and the second cross-sectional shape being selected from the predetermined list and different from the first cross-sectional shape.

[0020] 2. A heat sink as described in clause 1, wherein at least one of the first pin fin and the second pin fin has a transition section at a boundary between the first portion and the second portion, the transition section having a transition cross-section that changes from the first cross-sectional shape to the second cross-sectional shape along the length of the pin fin.

[0021] 3. A heat sink as described in clause 1, wherein the pin fins are arranged in rows of pin fins along the longitudinal direction, each row of pin fins spaced apart from other rows of pin fins along the lateral direction, and the rows of pin fins are staggered such that the center of one of the pin fins is adjacent to the spacing between adjacent pin fins in the lateral adjacent rows.

[0022] 4. The heat sink of clause 1, wherein the first portion has at least 10% of the height of the pin fins.

[0023] 5. The heat sink of clause 1, wherein the second cross-sectional shape is an airfoil having a leading side and an aft side, the leading side being larger than the aft side.

[0024] 6. The heat sink of clause 5, wherein the first cross-sectional shape is an ellipse or a circle.

[0025] 7. A heat sink assembly comprising: a substrate; a housing surrounding the substrate and containing a fluid; and a plurality of pin fins coupled to the substrate, the plurality of pin fins including a first pin fin and a second pin fin, the first pin fin and the second pin fin having at least one distinct geometric characteristic, each pin fin having a first end coupled to the substrate, an opposing second end, a first portion, and a second portion, each pin fin being spaced apart at the first end, the first portion extending from the first end to the second portion, the first portion having a first cross-sectional shape cut along a length of the pin fin, the second portion having a second cross-sectional shape cut along a length of the pin fin, the second cross-sectional shape being an airfoil, and the first cross-sectional shape being non-airfoil.

[0026] 8. The heat sink assembly of clause 7, wherein the airfoil has a leading side and an aft side, the leading side being larger than the aft side.

[0027] 9. The heat sink assembly of clause 8, further comprising a pump configured to direct a flow of fluid through the housing, the leading side of the airfoil being oriented upstream of the flow of fluid.

[0028] 10. The heat sink assembly of claim 7, wherein the first cross-sectional shape is an ellipse or a circle.

[0029] 11. A heat sink assembly as described in clause 7, wherein each pin fin has a transition section at a boundary between the first and second portions, the transition section having a transition cross-section that changes from elliptical to airfoil-shaped along the length of the pin fin.

[0030] 12. A heat sink assembly as described in clause 7, wherein the plurality of pin fins are arranged in rows of pin fins along the longitudinal direction, each row of pin fins spaced apart from other rows of pin fins along the lateral direction, and the rows of pin fins are staggered such that the center of one of the pin fins is adjacent to the spacing between adjacent pin fins in the lateral adjacent rows.

[0031] 13. The heat sink assembly of claim 7, wherein the first portion has at least 10% of the height of the pin fins.

[0032] 14. The heat sink assembly of claim 13, wherein the first portion comprises between 10% and 40% of the height of the pin fin.

[0033] 15. The heat sink assembly of clause 7, wherein the different geometric feature is a cross-sectional shape of the first pin fin and the second pin fin.

[0034] 16. A heat sink comprising: a substrate; and a plurality of pin fins, the plurality of pin fins including a first pin fin and a second pin fin, the first pin fin and the second pin fin having at least one distinct geometric characteristic, each pin fin having a first end coupled to the substrate, a second end opposite the first end, a first portion, and a second portion, the first portion extending from the first end to the second portion, the plurality of pin fins including the first pin fin and the second pin fin, the first portion of the first pin fin being a non-streamlined body, and the second portion of the first pin fin being a streamlined body.

[0035] 17. The heat sink of claim 16, wherein the streamlined body is an airfoil.

[0036] 18. The heat sink of clause 16, wherein the non-streamlined body is an ellipse or a circle.

[0037] 19. The heat sink of clause 16, wherein a streamlined body is a shape having a drag coefficient below a predetermined threshold and a non-streamlined body is a shape having a drag coefficient above a predetermined threshold.

[0038] 20. The heat sink of clause 19, wherein the predetermined threshold is the drag coefficient of the ellipse or circle measured in the flow direction along the length of the ellipse or circle.

[0039] 21. Forming a first portion of a pin fin, the first portion having a first cross-sectional shape cut along a length of the pin fin, the first cross-sectional shape being elliptical; forming a second portion of the pin fin, the second portion having a second cross-sectional shape cut along a length of the pin fin, the second cross-sectional shape being an airfoil; A method of forming a heat sink comprising: bonding a first portion of a pin fin to a second portion of a pin fin.

[0040] 22. The method of claim 21, wherein each of the first and second portions of the pin fin is formed by an additive manufacturing process, and the first and second portions are joined by an additive manufacturing process.

[0041] 23. The method of claim 22, further comprising forming a substrate by an additive manufacturing process, and wherein the first portion is bonded to the substrate by an additive manufacturing process.

[0042] 24. The method of claim 21, further comprising blending a boundary between the first and second portions of the pin fin to remove a step defined by the boundary.

[0043] 25. The method of clause 21, further comprising bonding a first end of the first portion to the substrate, and a second end of the first portion being bonded to the second portion.

[0044] An embodiment of the present disclosure is described herein. However, it should be understood that the disclosed embodiment is merely an example, and other embodiments may take various alternative forms. The figures are not necessarily to scale, and some features may be exaggerated or reduced in order to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art how to utilize the embodiments in various ways. As will be understood by those skilled in the art, various features illustrated and described with reference to any figure can be combined with features shown in one or more other figures to produce an embodiment not explicitly illustrated or described. The combination of the illustrated features provides a representative embodiment for a typical application. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be desirable in a particular application or implementation.

[0045] As used herein, the singular forms (definite and indefinite articles) refer to both the singular and the plural, unless the context clearly indicates otherwise. By way of example, a "processor" programmed to perform various functions may refer to one processor programmed to perform each and every function, or to multiple processors collectively programmed to perform each of the various functions.

[0046] Although exemplary embodiments have been described above, these embodiments are not intended to describe all possible forms encompassed by the claims. It is to be understood that the terms used herein are terms of description rather than limitation, and that various modifications are possible without departing from the spirit and scope of the disclosure. As mentioned above, features of various embodiments can be combined to form further embodiments of the invention not expressly described or illustrated. Although various embodiments have been described as advantageous or preferred over other embodiments or prior art implementations with respect to one or more desirable characteristics, those skilled in the art will recognize that one or more characteristics or characteristics may be compromised depending on the particular application and implementation to achieve the desired overall system attributes. These attributes include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, and the like. Thus, to the extent that any embodiment is described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the disclosure and may be desirable for certain applications.

Claims

1. A substrate; a plurality of pin fins; the plurality of pin fins includes a first pin fin and a second pin fin, the first pin fin and the second pin fin having at least one different geometric characteristic; the first pin fin has a first end coupled to the substrate, a second end opposite the first end, a first portion, and a second portion; The first portion extends from the first end to the second portion; a first portion of the first pin fin having a first cross-sectional shape cut along a length of the pin fin, and a second portion of the first pin fin having a second cross-sectional shape cut along a length of the pin fin; A heat sink, wherein a first cross-sectional shape is selected from a predetermined list including an ellipse, a circle, and an airfoil, and a second cross-sectional shape is selected from the predetermined list and is different from the first cross-sectional shape.

2. 2. The heat sink of claim 1, wherein at least one of the first pin fin and the second pin fin has a transition section at a boundary between the first portion and the second portion, the transition section having a transition cross-section that changes from the first cross-sectional shape to the second cross-sectional shape along a length of the pin fin.

3. 2. The heat sink of claim 1, wherein the pin fins are arranged in rows of pin fins along the longitudinal direction, each row of pin fins spaced apart from other rows of pin fins along the lateral direction, and the rows of pin fins are staggered such that a center of one of the pin fins is adjacent a spacing between adjacent pin fins in a laterally adjacent row.

4. The heat sink of claim 1 , wherein the first portion has a height of at least 10% of the height of the pin fins.

5. The heat sink of claim 1 , wherein the second cross-sectional shape is an airfoil having a leading side and an aft side, the leading side being larger than the aft side.

6. The heat sink of claim 5 , wherein the first cross-sectional shape is an ellipse or a circle.

7. A substrate; a housing that surrounds the substrate and contains a fluid; a plurality of pin fins coupled to the substrate; The plurality of pin fins includes a first pin fin and a second pin fin, the first pin fin and the second pin fin having at least one different geometric characteristic; Each pin fin has a first end coupled to the substrate, an opposing second end, a first portion, and a second portion; Each pin fin is spaced apart at a first end, the first portion extending from the first end to a second portion; A heat sink assembly, wherein the first portion has a first cross-sectional shape cut along the length of the pin fin and the second portion has a second cross-sectional shape cut along the length of the pin fin, the second cross-sectional shape being an airfoil and the first cross-sectional shape being non-airfoil.

8. The heat sink assembly of claim 7 , wherein the airfoil has a leading side and a trailing side, the leading side being larger than the trailing side.

9. The heat sink assembly of claim 8 , further comprising a pump configured to direct a flow of fluid through the housing, the leading side of the airfoil being oriented upstream of the flow of fluid.

10. The heat sink assembly of claim 7 , wherein the first cross-sectional shape is an ellipse or a circle.

11. 8. The heat sink assembly of claim 7, wherein each pin fin has a transition section at a boundary between the first portion and the second portion, the transition section having a transition cross-section that changes from an elliptical shape to an airfoil shape along the length of the pin fin.

12. 8. The heat sink assembly of claim 7, wherein the pin fins are arranged in rows of pin fins along the longitudinal direction, each row of pin fins spaced apart from other rows of pin fins along the lateral direction, and the rows of pin fins are staggered such that a center of one of the pin fins is adjacent a spacing between adjacent pin fins in a laterally adjacent row.

13. The heat sink assembly of claim 7 , wherein the first portion has a height of at least 10% of the height of the pin fin.

14. The heat sink assembly of claim 13 , wherein the first portion comprises between 10% and 40% of the height of the pin fin.

15. The heat sink assembly of claim 7 , wherein the different geometric feature is a cross-sectional shape of the first pin fin and the second pin fin.

16. A substrate; a plurality of pin fins; The plurality of pin fins includes a first pin fin and a second pin fin, the first pin fin and the second pin fin having at least one different geometric characteristic; Each pin fin has a first end coupled to the substrate, a second end opposite the first end, a first portion, and a second portion; The first portion extends from the first end to the second portion; the plurality of pin fins includes a first pin fin and a second pin fin; The heat sink, wherein a first portion of the first pin fin is a non-streamlined body and a second portion of the first pin fin is a streamlined body.

17. The heat sink of claim 16 , wherein the streamlined body is an airfoil.

18. The heat sink of claim 16 , wherein the non-streamlined body is an ellipse or a circle.

19. 17. The heat sink of claim 16, wherein a streamlined body is a shape that has a drag coefficient below a predetermined threshold and a non-streamlined body is a shape that has a drag coefficient above a predetermined threshold.

20. 20. The heat sink of claim 19, wherein the predetermined threshold is a drag coefficient of the ellipse measured in a flow direction along the length of the ellipse.

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