Patent Application
20090084931
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.
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.
According to one embodiment,
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
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.
Referring to
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
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
Referring back to
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
The liquid cooling device 90 may be similar in configuration to the embodiments shown in
Dedicated fluid line 92 is a fluid conduit separate from the cooling lines depicted in
At 120,
Similar to
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.
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.
