HEAT SINK, HEAT SINK ASSEMBLY, AND METHODS OF FORMING A 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 Improving 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 to heat sinks, heat sink assemblies, and methods of forming heat sinks, for example, with pin fins having non-uniform cross-sections. [Background technology]

[0003] Heat sinks are a conventional form of heat dissipation from heat-generating devices and include pin fins for dissipating heat, with 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 can have an inverse relationship between heat transfer and the 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 fins, thereby reducing heat transfer from the pin fins. 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 having at least one different geometric feature, the first pin fin having a first end coupled to the substrate, a second end opposite the first end, Extending from the first enda first part, and Extending from the second end The first pin fin has a first cross-sectional shape cut along the length of the pin fin, and the second pin fin has a second cross-sectional shape cut along the length of the pin fin. The first cross-sectional shape may be an ellipse, a circle, Or rectangular , the second cross-sectional shape is It is an airfoil .

[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 different geometric characteristic. Each pin fin has a first end coupled to the substrate, a second end coupled to the substrate, and a third end coupled to the first end. a first end and a second end on the opposite side, Extending from the first end a first part, and Extending from the second end Each pin fin includes a second portion. On the substrate, they are spaced apart The first section has a first cross-sectional shape cut along the length of the pin fin, and the second section has a second cross-sectional shape cut along the length of the pin fin. The second cross-sectional shape is an airfoil, and the first cross-sectional shape is oval, circular, or rectangular .

[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 having at least one different geometric feature, each pin fin having a first end coupled to the substrate, a second end opposite the first end, Extending from the first end a first part, and Extending from the second end The first portion extends from the first end to the second portion. No. The first portion of one pin is a non-streamlined body, and the second portion of the first pin is a streamlined body. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a heat sink assembly according to 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. 1 is a cross-sectional view of a pin fin of a heat sink assembly according to one or more embodiments of the present disclosure. [Figure 3] 1 shows 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 INVENTION

[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 plurality 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, or steel. 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 for the heat sink 12 to be used in natural convection mode without the use of a pump, fan, or the like, in which case the heat sink 12 rejects heat into stagnant air.

[0010] Each of the 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. The pin fins 20 are spaced apart such that rows of the pin fins 20 are arranged longitudinally along the substrate 18, and each row of the pin fins 20 is spaced apart from other rows of the pin fins 20 in a lateral direction transverse to the longitudinal direction. The rows of the pin fins 20 may be staggered such that the geometric center of one pin fin 20 is adjacent to the spacing between adjacent pin fins 20 in an adjacent row in the lateral direction. In some embodiments, the pin fins 20 may have non-uniform spacing, where some pin fins 20 are spaced apart at different distances and / or are staggered.

[0011] Referring now to FIGS. 2A and 2B , the pin fins 20 may have non-uniform cross-sections, 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 can be measured by an axis A extending 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 can have any feasible shape for heat transfer, such as a circle, an ellipse, an airfoil, or a rectangle. As used herein, an ellipse may include a circle. As shown in FIGS. 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 previously mentioned, the first cross-sectional shape may be another shape other than 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 other than 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 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 fins 20 are depicted as having a non-uniform cross-section, it is contemplated and possible for only a portion of the pin fins 20 to have a non-uniform cross-section, with the remaining pin fins 20 having a uniform cross-section. In further embodiments, the pin fins 20 can include first and second pin fins having different geometric characteristics. The different geometric characteristics can include different shape characteristics, overall heights, different cross-sectional heights, any combination thereof, etc.

[0013] The first portion 28 can include a first aft side 40 and a first leading side 42, and the second portion 30 can include a second aft side 44 and a second leading side 46. The second aft side 44 can overlap the first aft side 40, with the second aft side 44 being thinner than the first aft side 40. The second leading side 46 can overlap the first leading side 42, with the second leading side 46 being wider than the first leading side 42. The second aft side 44 of the airfoil can terminate in a tip, or end 48, or can be rounded. The tip of the second aft side 44 can 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, as shown in FIG. 1 , the second aft side 44 is oriented downstream of the fluid flow F.

[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 eliminate the step, where the cross-sectional shape gradually changes shape to eliminate the step. For example, the first cross-sectional shape may change from elliptical to airfoil-shaped 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 airfoil-shaped to elliptical 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 somewhere 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-shaped 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 multiple pin fins 20 is at the boundary 34 between the first portion 28 and the second portion 30. The transition section 32 includes portions of each of the first portion 28 and the second portion 30, and 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, the second portion 30 may be 70% of the height of the pin fin, and the transition section 32 may be 10% of the height of the pin fin, with half of the height of the transition section 32 included in the first portion 28 and the other half of the height of the transition section 32 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, for example, 20% and 80% for the first portion, 10% and 90% for the second portion, etc. The proportions of the first and second portions of the pin fins 20 may vary depending on the position of the pin fin 20. For example, a pin fin 20 located upstream may have a first portion that occupies 20% of the height of the pin fin 20, and a pin fin 20 located downstream 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 shape 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. While 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] Referring to FIG. 3 , a flowchart of a method 300 for forming the heat sink 12 assembly 10 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 and second portions 28 and 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 and second portions 28, 30 of the pin fin 20 are formed with a step at the boundary 34 between the first and second portions 28, 30, the method 300 may include a step 306 that includes blending the boundary 34 between the first and second portions 28, 30 of the pin fin to remove the step defined by the boundary 34. The boundary 34 may be blended by welding, grinding, polishing, or other methods of smoothing the edges of a metal structure.

[0017] Referring to FIGS. 1-3 , during operation, the presence of the pin fins 20 reduces the pressure of the fluid flowing across the pin fins 20, which in turn reduces the fluid flow rate across the downstream pin fins 20. The reduced fluid flow rate reduces 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 coefficients. For example, an elliptical cross-section increases the heat transfer coefficient and increases the pressure drop compared to an airfoil-shaped cross-section. Therefore, 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 coefficient compared to an airfoil-shaped cross-section. Furthermore, using an airfoil-shaped 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 cross-section, thereby maximizing the heat transfer coefficient of the pin fin 20 compared to a pin fin with a uniform cross-section.

[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 different 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 the length of the pin fin, and the second portion of the first pin fin having a second cross-sectional shape cut along the 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 the 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 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 pin fin is adjacent to the spacing between adjacent pin fins in adjacent rows in the lateral direction.

[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 a trailing side, the leading side being larger than the trailing 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 first pin fins and second pin fins, the first pin fin and the second pin fin having at least one different geometric characteristic, each pin fin having a first end coupled to the substrate, an opposite 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 the length of the pin fin, the second portion having 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 not being an airfoil.

[0026] 8. The heat sink assembly of clause 7, wherein the airfoil has a leading side and a trailing side, the leading side being larger than the trailing 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 clause 7, wherein the first cross-sectional shape is an oval or a circle.

[0029] 11. The heat sink assembly of clause 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 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 pin fin is adjacent to the spacing between adjacent pin fins in the lateral adjacent rows.

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

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

[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 different 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 clause 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. A heat sink as described in 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 the 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 clause 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 clause 22, further comprising forming the substrate by an additive manufacturing process, wherein the first portion is bonded to the substrate by an additive manufacturing process.

[0042] 24. The method of clause 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 to the second portion.

[0044] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and that other embodiments may take various alternative forms. The figures are not necessarily to scale, and certain features may be exaggerated or reduced in size to show details of particular components. Therefore, specific structural and functional details disclosed herein should not be construed 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 shown and described with reference to any figure can be combined with features shown in one or more other figures to produce embodiments not explicitly shown or described. The combinations of illustrated features provide representative embodiments for typical applications. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be desirable in particular applications or implementations.

[0045] As used herein, the singular forms "a," "an," and "the" (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] While exemplary embodiments have been described above, these embodiments are not intended to describe all possible forms encompassed by the claims. It should 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 noted above, features of various embodiments can be combined to form additional embodiments of the invention not explicitly described or shown. While various embodiments have been described as advantageous or preferable 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, depending on the particular application and implementation, may be compromised 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 particular 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 extending from the first end, and a second portion extending from the second end; a first portion of the first pin fin having a first cross-sectional shape cut along the length of the pin fin, and a second portion of the first pin fin having a second cross-sectional shape cut along the length of the pin fin; The heat sink, wherein the first cross-sectional shape is an ellipse, a circle, or a rectangle, and the second cross-sectional shape is an airfoil.

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 the length of the pin fin.

3. 2. The heat sink of claim 1, 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 pin fin is adjacent to a spacing between adjacent pin fins in an adjacent row in the lateral direction.

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 a trailing side, the leading side being larger than the trailing 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, a second end opposite the first end, a first portion extending from the first end, and a second portion extending from the second end; Each pin fin is spaced apart on the substrate; A heat sink assembly, wherein the first portion has a first cross-sectional shape cut along the length of the pin fin, 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 an ellipse, a circle, or a rectangle.

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 oval 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 elliptical to airfoil-shaped along the length of the pin fin.

12. 8. The heat sink assembly of claim 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 pin fin is adjacent to the spacing between adjacent pin fins in the laterally adjacent rows.

13. The heat sink assembly of claim 7 , wherein the first portion has 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 extending from the first end, and a second portion extending from the second end; 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 having a drag coefficient below a predetermined threshold, and a non-streamlined body is a shape having a drag coefficient above a predetermined threshold.

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

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