ENABLING BARE DIE LIQUID COOLING FOR THE BARE DIE AND HOT SPOTS

Abstract

A liquid cooling device for a die including a support block supporting a plurality of substantially vertical channels transporting fluid to and from a bare die surface for heat removal. The device is mounted on top of a bare die using a frame or spring. In another embodiment, the device allows thermoelectric cooling of a dedicated fluid line.

Description

BACKGROUND

As processing power continually increases with advances in microprocessor technology, the heat that is produced increases. Many solutions seek to improve cooling of the die. Current micro-channel technology uses a thermal interface material (for example, TIM1) which is a major contributor to thermal resistance. Also the current micro-channel flow length and the heat capacity of the coolant (mass flow×specific heat) have the most significant impacts to thermal resistance. Often, the fluid boundary length is long. Another solution proposes to spray liquid over the die. However there are drawbacks to that implementation as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The claimed subject matter will be understood more fully from the detailed description given below and from the accompanying drawings of the disclosed embodiments which, however, should not be taken to limit the claimed subject matter to the specific embodiment(s) described, but are for explanation and understanding only.

FIG. 1 is a cross-sectional schematic diagram showing one embodiment.

FIG. 2 is an enlarged view showing fluid flow according to one embodiment, taken from View B of FIG. 1.

FIG. 3 is a top view of one embodiment.

FIG. 4 is a cross-sectional view of one embodiment, taken from line A-A of FIG. 1.

FIG. 5 is a cross-sectional schematic diagram showing one embodiment, including a dedicated fluid line.

FIG. 6 is a top view schematic diagram showing one embodiment, including a dedicated fluid line.

FIG. 7 is a cross-sectional schematic diagram showing one embodiment.

DETAILED DESCRIPTION

According to one embodiment, FIG. 1 shows a schematic of a liquid cooling device 10 including a support block 12 supporting cooling lines 14 in thermal communication with a bare die 16. The cooling lines 14 are configured to remove heat directly from the bare die 16 by transporting fluid to and from the surface of the bare die. By allowing direct contact between the fluid and the die, a cold plate is not required.

The liquid cooling device 10 may include a frame 18 coupling the support block 12 to a substrate 20 (for example, a semiconductor). The bare die is also coupled to the substrate 20 via solder balls and underfill material 22, attached to the bottom surface of the die. The bare die may also be coupled to the substrate using electrical connections, including soldered or conductive adhesive connections, or using other surface mount packaging technologies for integrated circuits.

The cooling lines 14 may be a singular, long, continuous line containing and circulating fluid in device 10. In one embodiment, the cooling lines include various segments of circulating fluid. These segments are broken down and named in this specification as an aid in describing the structure of one or more embodiments, and are not intended to be limiting. Further, the segments may be referred to in the singular or plural and are also not meant to be limited to that which is shown or described.

In one embodiment, the cooling lines may be closed-loop as fluid recycles in the device. In another embodiment, the cooling lines may be open-loop. Additional components such as heat exchangers and pumps may be coupled to the device and used to cool and circulate the fluid, respectively. Further, coolants with various heat capacities may be used as fluid for circulation in the cooling lines.

As shown in FIG. 1, the row of circles labeled 24 are referred to as “inlet pipes”, and the lower row of circles labeled 26 are referred to as “outlet pipes”. Both inlet pipes 24 and outlet pipes 26 are segments of the cooling lines 14, and the flow of the fluid through these pipes is perpendicular to the plane of the figure, as will be further described below. The inlet pipes may be positioned at a higher level than the fluid outlet pipes, such as shown in the figure. In one embodiment, the inlet pipes and the outlet pipes are positioned at the same height.

As the arrows indicate, fluid is transported downward from the inlet pipes 24 to the bare die 16 through a segment 28 referred to as an “inlet portion”. The fluid traveling upward from the bare die 16 to the outlet pipes 26 traverses a segment 30 referred to as an “outlet portion”. These two segments of inlet portions and outlet portions are also referred to as vertical channels.

It may be noted that in general, the flow of the fluid follows the direction of the arrows as indicated. In some locations or situations, the fluid flow may be non-uniform and deviate from the general direction of flow.

FIG. 1 further shows an area 32 in which a sealant may be used to fill in between the support block 12, bare die 16 and substrate 20. The sealant may include epoxy, neoprene, and other suitable materials to stop leaks, add structural support, and/or enable permanent attachment.

Referring to FIG. 2, an enlarged view showing fluid flow according to one embodiment, taker from View B of FIG. 1, is shown at 40. Referring in particular to vertical channel 42, the fluid travels downward through the inlet portion 28, contacts the bare die surface 44 to remove heat, and travels upward through the outlet portion 30, as described above. The vertical channel further includes a heat transfer region 46 connecting the inlet portion 28 with the outlet portion 30 and routing the fluid so that it transitions from a downward direction to an upward direction.

In describing one or more embodiments, there are references to orientation and direction. It should be understood that these references are used to aid in understanding the relationships between components and fluid flow, and are not meant to be limiting in any way. For example, vertical channels do not necessarily need to be oriented vertically, such as the case with a closed system where the flow will be pressurized.

The fluid traversing vertical channel 42 contacts an area 48 on the surface of the bare die and removes heat from that area. Additional vertical channels adjacent to vertical channel 42, such as 50 and 52, may each be in thermal contact with a respective surface area on the bare die. In one embodiment, the entire bare die surface may be covered with vertical channels for cooling of the entire die. Alternatively, only select regions are covered with vertical channels.

The vertical channels may include walls dividing the fluid flow to reduce the fluid boundary length. In one embodiment, a vertical channel shares a wall with an adjacent vertical channel. For example, vertical channel 42 shares one wall 54 with vertical channel 50 and one wall 56 with vertical channel 52. These common walls extend from the outlet pipe to the surface of the bare die.

Another type of wall is referred to as a separation wall which is in the vertical channel for separating the fluid traveling to the bare die from the fluid traveling away from the bare die. As shown, separation wall 58 does not extend all the way down to the bare die, but instead leaves a gap between the end of the separation wall and the bare die surface, thus allowing room for the fluid to flow from the inlet portion to the outlet portion. As the fluid goes around the separation wall, from the inlet portion into the heat transfer region and up the outlet portion such as indicated by the arrows, the fluid removes heat from the bare die.

In this exemplary embodiment, the walls are less than 10 μm in thickness. The wall thickness may also be greater than 10 μm depending on other device parameters. The walls may be pressed onto the die surface. They may also be fastened using an adhesive or other method. Walls may be temporarily affixed on or permanently attached to the bare die surface.

The configuration described above brings about a short heat transfer region length and the flow over the bare die surface results in thin thermal and hydrodynamic boundary layers. This condition yields very high local heat transfer coefficients, indicating that thermal communication between the bare die and the fluid is good, enabling efficient cooling.

A simulation was performed using a computational fluid dynamics software program called Icepak, made by ANSYS, Inc. of Canonsburg, Pa., to determine the feasibility of obtaining high heat transfer coefficients in a configuration similar to the one described above. For exemplary purposes, the channel dimensions were set to 50 μm×50 m with a separation plate 10 μm thick. The equivalent heat flux was 100 W/cm² and the inlet velocity 1 m/s. The results showed a pressure drop of approximately 60 kPa, well within the capability of a gear pump (thus the boundary conditions were realistic). The resulting heat transfer coefficient variation was on the average over 100,000 W/cm², which may be equivalent or better than that of the current macro or micro channels.

Turning to FIG. 3, a top view of one embodiment is shown at 70. In accordance with the figure and similar to the embodiment of FIG. 1, the support block 12 holds segments of the cooling lines, specifically the vertical channels (not visible), which are capable of transporting fluid from the inlet pipes 24 down to the bare die and back up to exit at the outlet pipes 26. In one embodiment, the cooling lines further include an inlet manifold 72 that delivers fluid to all of the inlet pipes 24 and an outlet manifold 74 that receives fluid from all of the outlet pipes 26.

In this exemplary embodiment, the inlet pipes 24 and the outlet pipes 26 alternate in a parallel configuration. As the flow of fluid in the inlet pipes 24 heads toward the general direction of the outlet manifold 74, the inlet portions 28 of the vertical channels are fed, as will be more apparent below. After entering the inlet portions, the flow traverses the outlet portions of the vertical channels and feeds the outlet pipes, where the flow is toward the general direction of the outlet manifold.

Typically, the cooling lines on an inlet side (top) of the liquid cooling device will start off cool and after thermal communication with the bare die surface, the cooling lines on an outlet side (bottom) of the device will be warmer. Fluid collecting in the outlet manifold is generally significantly warmer than the fluid entering the inlet manifold. Generally, in a closed system, fluid exiting the outlet manifold 74 may be routed to a heat exchanger or other heat removal device (not shown) before the fluid recycles and reenters the inlet manifold 72.

Referring to FIG. 4, a cross-sectional view of one embodiment taken from line A-A of FIG. 1 is shown at 80. (It is noted that this embodiment slightly differs from that of FIG. 1.) Looking up toward the top from the cross-section, the frame 18 surrounds the support block 12 which supports a grid 82 of vertical channels. As described above and shown in the figure, one or more vertical channels include an inlet portion routing fluid to the die and an outlet portion routing fluid away after contacting the die. As depicted in FIG. 4, for example, as fluid is circulating, the fluid flows through the inlet portion 28 (out of the page) to the outlet portion 30 (into the page) at vertical channel 42. Adjacent to vertical channel 42 on the left side is vertical channel 50, and on the right side is vertical channel 52. As seen from FIGS. 1-4, fluid in vertical channels 50, 42, and 52 are delivered by different inlet pipes and the fluid exit via different outlet pipes. In the columns (up and down, referenced to the page) of vertical channels, fluid is supplied by the same inlet pipes and is returned to the same outlet pipes, that is, each column of squares is tied to the same inlet pipe or outlet pipe.

Referring back to FIG. 4, the squares cross-sections as indicated by the grid 82 correspond to individualized bare die surface areas. As mentioned above, the vertical channels separate flow to ensure small boundary length for the fluid as it flows by the bare die surface areas.

Although the vertical channels are shown to have square cross-sections, the channels may be individual tubes and may have circular or other shaped cross-sections. The vertical channels may also be arranged in a different pattern and not necessarily in a grid configuration. For example, certain areas of the die may not need cooling, therefore walls and vertical channels are not needed in those areas.

Referring to FIG. 5, one embodiment for a liquid cooling device 90 provides a separate dedicated fluid line 92 for isolating a hot spot 94. Hot spots are known areas on the bare die in need of extra heat dissipation or higher rate of heat dissipation. It may be useful to identify the hot spots and target them for more efficient cooling of the die.

The liquid cooling device 90 may be similar in configuration to the embodiments shown in FIGS. 1-4. A support block 96 is configured to support a system of cooling lines 98 and may be mounted to a bare die 100 and substrate 102 via a frame 104. The die and the substrate are coupled by solder balls and underfill material 106. The support block may be attached to the substrate and leaks may be prevented by application of epoxy at 108. Cooling lines 98 include segments such as inlet pipes carrying fluid to inlet portions of vertical channels and to heat transfer regions where the fluid touches the surface of the bare die and removes heat. The cooling lines further include outlet portions of vertical channels to remove the heated fluid and join with outlet pipes that take the fluid away from the die.

Dedicated fluid line 92 is a fluid conduit separate from the cooling lines depicted in FIGS. 1-5. As seen from FIG. 5, this fluid line is dedicated to transporting fluid to and from the hot spot 94. The dedicated fluid line has a vertical channel through which fluid can reach the hot spot and remove heat. Dedicated fluid line 92 further includes an inlet line 110 routing fluid to the vertical channel and an outlet line 112 routing fluid away from the vertical channel.

At 120, FIG. 6 shows a top view of one embodiment including a dedicated fluid line 122. The embodiment may include a thermoelectric cooling (TEC) device 124 for cooling the fluid that circulates throughout the dedicated fluid line. Circulation of fluid in the dedicated fluid line may be driven by a pump. The dedicated fluid line may also be coupled to other components such as heat exchangers.

Similar to FIGS. 1-5, the embodiment may include a support block 126 supporting a grid configuration (not visible, under inlet pipes 128 and outlet pipes 130) capable of separating fluid flow and for cooling surface areas of the bare die that are not considered hot spots. In this embodiment, there may be two inlet manifolds 132 to deliver fluid to the inlet pipes. The outlet pipes connect to an outlet manifold 134. Although only one dedicated fluid line is shown, additional hot spots may be isolated and additional fluid lines may be dedicated to cooling those hot spots.

The dedicated fluid line 122 further includes an inlet line 136 transporting fluid to the die. The inlet line 136 passes by a cold side 138 of TEC device 124 and cooling the fluid inside. The dedicated fluid line 122 further includes an outlet line 140 transporting fluid to the die. The outlet line 140 passes by a hot side 142 of TEC device 124 and the fluid in the outlet line cools the hot side of the TEC device.

The cooling fluid used in the dedicated fluid line may be different from that of the cooling lines 98. For example, a lubricant-water solution may be used in the dedicated fluid line while water is used in the cooling lines. Further, the cooling fluid may be subcooled by the TEC device. The temperature, flow speed, dimensions, etc. of the dedicated fluid line may also differ from the parameters used for the cooling lines.

It should be noted that the cooling lines may include segments that also may vary depending on size of the bare die and other device parameters. For example, the number of vertical channels, inlet pipes, outlet pipes, inlet manifold, and outlet manifold may vary depending on the number of dedicated fluid lines. The segments may vary by diameter, length, thickness of material, connectivity, etc.

FIG. 7 shows the exemplary embodiment of FIG. 5 with an alternate mounting method at 150. The embodiment includes a frame 152 for attachment to the substrate 102. A spring 154 is attached to the frame 152 and the support block 96. The spring is used to ensure that the vertical channels do not damage the die. There may be additional springs (in addition to the two shown in the figure) distributed around the die, between the bottom of the support block 96 and on top of the frame 152. In this embodiment, instead of epoxy, O-rings 156 may be used as a sealant. Standoffs 158 may be used as a spacer to offer additional structural support to the die 100.

In one embodiment, although the spring 154 is shown attached to frame 152, the frame is not required, and the spring may be directly attached to the substrate. Further, the spring may include any type of suitable spring and is not limited to the coil spring as pictured.

It is appreciated that the liquid cooling device has been explained with reference to one or more exemplary embodiments, and that the device is not limited to the specific details given above. References in the specification made to other embodiments fall within the scope of the claimed subject matter.

Any reference to device may include a component, circuit, module, or any such mechanism in which the device can achieve the purpose or description as indicated by the modifier preceding the device. However, the component, circuit, module, or any such mechanism is not necessarily a specific limitation to the device.

Reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the disclosed subject matter. The various appearances of “an embodiment,” “one embodiment,” or “some embodiments” are not necessarily all referring to the same embodiments.

If the specification states a component, feature, structure, or characteristic “may”, “might”, or “could” be included, that particular component, feature, structure, or characteristic is not required to be included. If the specification or claim refers to “a” or “an” element, that does not mean there is only one of the element. If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.

Those skilled in the art having the benefit of this disclosure will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present claimed subject matter. Indeed, the claimed subject matter is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define such scope and variations.

Claims

1. A liquid cooling device for a die, the device comprising:

a plurality of substantially vertical channels transporting fluid to and from a bare die surface, one or more of the channels comprising: an inlet portion transporting fluid to the bare die surface, an outlet portion adjacent to the inlet portion and transporting fluid away from the bare die surface, and a heat transfer region located between the inlet portion and the outlet portion, wherein fluid flowing through the heat transfer region directly contacts the bare die surface and removes heat from the bare die surface;

a support block capable of supporting the channels; and

a mechanism capable of attaching the support block to a substrate,

wherein a plurality of the channels are adjacent to each other.

2. The liquid cooling device of claim 1 further comprising one or more inlet pipes transporting fluid to the channels and one or more outlet pipes transporting fluid away from the channels.

3. The liquid cooling device of claim 2 wherein the inlet pipes are substantially parallel to the outlet pipes.

4. The liquid cooling device of claim 1 wherein the inlet portion and the outlet portion are separated by a wall.

5. The liquid cooling device of claim 1 wherein the heat transfer region is selectively positioned on the bare die surface.

6. The liquid cooling device of claim 5 wherein the heat transfer region is placed over a hot spot on the die.

7. The liquid cooling device of claim 1 wherein the channels cover a substantial area of the bare die surface.

8. The liquid cooling device of claim 1 wherein the channels are configured into a grid to separate flow.

9. The liquid cooling device of claim 1 wherein the mechanism comprises a spring coupling the support block to the substrate.

10. The liquid cooling device of claim 1 wherein the mechanism comprises epoxy for permanent attachment.

11. The liquid cooling device of claim 1 further comprising a thermoelectric cooling (TEC) device thermally coupled to one or more of the channels.

12. A liquid cooling device for a die, the device comprising:

a plurality of substantially vertical channels transporting fluid to and from a bare die surface, one or more of the channels comprising: an inlet portion transporting fluid to the bare die surface, an outlet portion adjacent to the inlet portion and transporting fluid away from the bare die surface, and a heat transfer region located between the inlet portion and the outlet portion, wherein fluid flowing through the heat transfer region directly contacts the bare die surface and removes heat from the bare die surface;

a support block capable of supporting the channels and coupling to a substrate; and

a dedicated fluid line routing fluid to a hot spot on the bare die surface.

13. The liquid cooling device of claim 12 wherein the dedicated fluid line is routed over a thermoelectric cooling (TEC) device.

14. The liquid cooling device of claim 13 wherein an outlet line of the dedicated fluid line is routed over a hot side of the TEC device and an inlet line of the dedicated fluid line is routed over a cold side of the TEC device.

15. The liquid cooling device of claim 12 wherein the dedicated fluid line comprises a vertical channel with a heat transfer region above the hot spot.