1. Field of the Present Invention
The present invention is in the field of integrated circuits and, more particularly to integrated circuits that use heat dissipation hardware.
2. History of Related Art
Mobile processors including notebook and desktop computers have historically used a thermal interface pad to participate in the heat transfer process. Thermal interface pads are characterized by a one-sided adhesive, which makes it relatively easy to apply and to remove the thermal solution. A drawback is that the thermal interface pad has poor thermal conductivity. As the maximum designed thermal power of CPUs has increased, this pad has proven to be insufficient for most applications.
The inadequacy of thermal interface pads as a heat transfer mechanism forced mobile processing device manufacturers to employ thermal greases or “phase change” materials that had been in use on desktops machines and server-class computers for some time. Standard phase change materials are typically a polymer/carrier filled with a thermally conductive filler, which changes from a solid to a high-viscosity liquid (or semi-solid) state at a certain transition temperature typically in the range of 50 to 70° C. These materials conform well to irregular surfaces and have wetting properties similar to thermal greases, which significantly reduces the contact resistance at the different interfaces. Due to this composite structure, phase change materials are able to withstand mechanical forces during shock and vibration, protecting the die or component from mechanical damage. When heated to the transition temperature, the material significantly softens to a near liquid-like physical state in which the thermally conductive material slightly expands in volume. This volumetric expansion forces the more thermally conductive material to flow into and replace the microscopic air gaps present in between the heat sink and electronic component. With the air gaps filled between the thermal surfaces, a high degree of wetting of the two surfaces minimizes the contact resistance.
Unfortunately, phase change materials and thermal greases are difficult to use in a manufacturing environment. Specifically, the quasi-liquid characteristics of phase change materials and thermal greases are sensitive to any gradient in the pressure applied to the film. Typically, the phase change material is situated between a thermal interface such as the bottom of a heat sink, a fan sink assembly, a vapor chamber, or a heat spreader (with or without heat pipes) surface and an upper surface of the device itself. In either case, maintaining a uniformly thick film is important and difficult. It is important to ensure the best heat transfer characteristics possible and thereby improve device performance, reliability, and lifetime. It would be desirable, therefore, to implement an integrated circuit assembly that permitted the use of these advanced heat transfer materials and addressed the difficulty of maintaining a uniform thickness inherent with these materials.
The objective identified above is achieved according to the present invention by an integrated circuit assembly that includes an integrated circuit overlying a printed circuit board and a thermal solution interface such as a fan sink or a heat pipe overlying the integrated circuit. The lower surface of the thermal solution interface has a plurality of spacer structures to enforce a uniform displacement between the lower surface and an underlying surface contacted by the spacers. A heat transfer material, such as a thermal phase change material or a thermal grease, is positioned between the thermal solution interface and the underlying surface contacted by the spacers. The assembly may include a socket connected to the printed circuit board into which the integrated circuit is inserted. The integrated circuit may include a thermally conductive heat spreader attached to its upper surface such that the spacers contact an upper surface of the heat spreader. In other embodiments, the heat transfer material directly contacts an upper surface of the integrated circuit die. The spacers likely enforce a uniform displacement in the range of approximately 0.001 to 0.005 (dependent on ideal properties of the interface material) inches. The spacers may be configured as a set of substantially hemispherical protrusions or a set of substantially parallel elongated ridge protrusions.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description presented herein are not intended to limit the invention to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
Generally speaking, the present invention is concerned with an integrated circuit assembly that employs semi-liquid heat transfer materials such as thermal grease and/or phase change materials. The semi-liquid material is formed between a pair of surfaces of the assembly. At least one of the surfaces includes spacer structures formed thereon. The spacer structures are preferably of a uniform dimension and, in one embodiment, are hemispherical. The presence of the spacer structures positioned across the face of the surface enforces a uniform separation between the two plates between which the phase change material is present. Any gradient in pressure across the face of the surface will not result in a heat transfer material thickness gradient or non-uniformity. By maintaining a uniformly thick phase change material across a heat transfer interface of an integrated circuit, the invention beneficially improves the heat transfer properties of the integrated circuit by eliminating localized “hot spots” that may occur when portions of the heat transfer material are thinner than others.
Turning now to the drawings,
A heat spreader 108 is shown as attached to an upper surface of integrated circuit 106. Heat spreader 108 (also referred to as an integrated circuit cap) is preferably a thermally conductive material that facilitates the transfer of heat from integrated circuit 106. A preferred implementation of heat spreader 108 is made of copper. A thermal paste or grease 111 is likely placed between heat spreader 108 and an upper surface of integrated circuit 106 to further enhance the efficiency of heat transfer.
A thermal solution interface 114 is shown as resting on an upper surface of heat spreader 108. Interface 114 may comprise the lower portion of a heat sink or fan sink assembly that is attached to printed circuit board 102. In the preferred implementation, thermal interface 114 is secured from above using a spring force (not shown) or other securing mechanism (such as a set of screws), to maintain the thermal interface in proximity to the underlying integrated circuit 106.
In the depicted embodiment, thermal solution interface includes a plurality of spacers 112 formed on the surface of interface 114. As depicted in the bottom view of
Returning to
Referring to
The embodiment of assembly 100 depicted in
An even lower profile is achieved with the integrated circuit assembly 500 depicted in
It will be apparent to those skilled in the art having the benefit of this disclosure that the present invention contemplates a mechanism for maintaining a uniform dimension of a thermal interface material in an integrated circuit assembly. It is understood that the forms of the invention shown and described in the detailed description and the drawings are to be taken merely as presently preferred examples. It is intended that the following claims be interpreted broadly to embrace all the variations of the preferred embodiments disclosed.