Patent Application
20120063090
The disclosure relates generally to stacked die packages, and more particularly, to cooling mechanisms for stacked die packages.
Recently, three-dimensional integrated circuit (3D IC) packages or stacked die packages have provided a possible solution to traditional two-dimensional (2D) ICs in overcoming the interconnect scaling barrier and for improving performance. In stacked die packages, multiple dies are stacked together using vertical through silicon vias (TSVs) where longer wire connections and inter-die input/output (I/O) pads are eliminated. The overall performance is significantly improved with faster and more power efficient inter-core communication across multiple silicon layers.
As effective as 3D IC technology is, 3D IC technology faces critical thermal management challenges. When multiple dies are stacked vertically in a package, the thermal path for the dissipation of the heat generated by the dies is limited. Stacked die packages are typically encapsulated in a material that does not dissipate heat well, and if the heat dissipation problem is not addressed, the dies may overheat during operation, leading to possible problems with transistor performance and reliability. To address the heat dissipation problem, cooling systems that use thermal via and liquid micro channels have been proposed. However, such systems are complex and expensive to implement.
The features, aspects, and advantages of the disclosure will become more fully apparent from the following detailed description, appended claims, and accompanying drawings in which:
In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the present disclosure. However, one having an ordinary skill in the art will recognize that embodiments of the disclosure can be practiced without these specific details. In some instances, well-known structures and processes have not been described in detail to avoid unnecessarily obscuring embodiments of the present disclosure.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are merely intended for illustration.
Although
To address the heat dissipation problem in stacked die package 10, an approach according to an aspect of the present invention is to immerse dies A, B, C, and D in a cooling fluid. A volume of cooling fluid 60 is contained in housing 40, the housing 40 hermetically sealing dies A, B, C, and D from the environment or ambient. Cooling fluid 60 both cools and insulates dies A, B, C, and D. The cooling fluid 60 helps cool dies A, B, C, and D by absorbing heat generated by operating dies A, B, C, and D and drawing the heat away from the dies to the walls of housing 40 where the heat is then dissipated to the ambient.
Cooling fluid 60 can comprise a fluid or liquid. As an example, cooling fluid 60 can comprise a fluid such as oil, dielectric oil, water, a mixture of water and an anti-freeing agent, potassium formate, perfluorinate coolant, or the like. As a particular example, the cooling fluid 60 may comprise a non-electrically conductive liquid perfluorinate coolant such as those made by 3M™, including 3M's HFE-7100 coolant and similar such coolants.
In some embodiments, cooling fluid 60 comprises a two-phase liquid, such as which is commercially available from. One skilled in the art will understand that cooling fluid 60 may be any fluid capable of absorbing and releasing energy and may be in a fluid form, such as water, gas, oil, or a mixture thereof.
In operation a volume of cooling fluid 60 such as oil, for example heated by dies A, B, C, and D within housing 40 rises upwardly towards the top of housing 40. As the oil rises towards the top of the housing 40, upward flow is restricted and lateral flow occurs. Also, as heated oil cools, its density increases with a resultant downward flow aided by gravity. The downward flow is limited by the bottom of housing 40 consequently establishing a lateral flow to again bring the cooling fluid into engagement with the dies to begin the cycle anew. It is understood that the level of the cooling fluid should be maintained at a prescribed level as otherwise the cooling may be insufficient to lower the temperature of the operating dies.
The housing 40 defines the cooling fluid compartment and contains the cooling fluid 60. The housing 40 has a generally rectangular shape but other shapes are also contemplated; particularly, a shape or design capable of placing the cooling fluid 60 and dies A, B, C, and D in efficient heat exchange with one another. Housing 40 may be constructed of a material such as steel, aluminum, copper, silver, metal, silicon, or silicon carbide. Other materials, such as gold, though perhaps less cost effective than those already mentioned, are also thermally conductive to an adequate or even optimal degree and may also be used in certain embodiments.
To assist cooling of dies A, B, C, and D, in some embodiments an outside surface of housing 40 includes a plurality of radiators or fins 50 for heat dissipation. Fins 50 may be disposed on any or all of the outside surface(s) of housing 40. The fins 50 provide numerous surface areas for establishing heat transfer between the heated cooling fluid and the ambient air. Fins 50 may be elongated for efficient thermal energy transfer to the ambient and may be constructed of a material such as steel, aluminum, copper, silver, metal silicon, or silicon carbide. One skilled in the art will understand that fins 50 may be made from any material having a relatively high thermal conductivity. Although fins 50 as depicted in
The stacked die package 10 may also include a pressure release apparatus 65 in some embodiments. For convenience of illustration and ease of understanding, the pressure release apparatus 65 is shown in
In some embodiments, stacked die package 10 includes a deionizer 75 or an apparatus to deionize ions in the cooling fluid 60 that may be generated by the interaction between the cooling fluid 60 and components of the stacked die package 10, such as dies A, B, C, D, or bumps 30. If the ions are not deionized conductivity of cooling fluid 60 may increase causing shorts in one or more dies A, B, C, or D, thereby damaging them. One skilled in the art will appreciate how a deionizer is constructed and for convenience the details of such will not be described herein.
The teachings of the present disclosure of immersing stacked dies in a cooling fluid contained in a housing can also be applied to a multiple chip package.
Although cooling fluid circulation within housing 40 may be achieved by passive means as described above, in another embodiment of the present invention, an active pumping action with the use of a mechanical pump 80 is employed to circulate the cooling fluid.
In some embodiments, stacked die package 10 includes one or more barriers 96 disposed within the housing 40 of the stacked die package 10. Barriers 96 help direct the fluid flow A of cooling fluid 60, particularly to areas between two stacked dies, in the region of the bumps 30. Without barriers 96, a substantial amount of cooling fluid 60 may flow over the top of the top most die or around the sides of the dies as fluid flow will generally take the path of least resistance. One skilled in the art understands that barriers 96 may have any configuration or shape, so long as such shape or configuration directs fluid flow A substantially to regions between the dies (e.g., region of the bumps) and substantially blocks fluid flow over the top of the topmost die or around the sides of the stacked dies.
To further dissipate heat and enhance the cooling of cooling fluid 60, in another embodiment, a heat sink 70 is thermally coupled to conduit 85. Heat sink 70 draws heat from cooling fluid 60 to the ambient thereby cooling cooling fluid 60.
It is an advantage of the present invention to protect the dies in a stacked die package or chips and/or components in a multi-chip system package from excessive heat that would otherwise compromise the performance and/or reliability of the chips and/or components in these packages. It is another advantage that embodiments of the invention require minimal modifications to the current design for existing packages, is low cost and simple to implement. It is yet another advantage of the present invention that underfill materials are not needed between stacked dies (not including those dies that are disposed on a substrate or an interposer), unlike in conventional stacked die packages or multi-chip packages. It is contemplated that the cooling fluid system and method of the present disclosure can be used in any electronic packaging system, such as stacked chip package, multi-chip package, or stacked chip and multi-chip package that require a cooling fluid for cooling and/or heat prevention.
In the preceding detailed description, the present invention is described with reference to specifically exemplary embodiments thereof. It will, however, be evident that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the present disclosure. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that embodiments of the present disclosure are capable of using various other combinations and environments and are capable of changes or modifications within the scope of the invention as expressed herein.
