Patent Application
20080296757
1. Field of the Present Invention
The present invention generally relates to a fluid spreader, and more particularly, to a fluid spreader that has at least one channel or protrusion to decrease the thickness of the fluid located between one or more areas of the fluid spreader and a second component or multiple secondary components.
2. Description of the Related Art
A Thermal Interface Material (referred to as TIM), which is defined as a material with better thermal conductivity than air, has been commonly used to fill between surfaces of semiconductors and heat sinks or heat spreaders, in order to increase thermal transfer efficiency. The TIM has many forms. The most common one for IC packaging or electronics assembly is a white-colored paste or thermal grease, such as silicone oil with aluminum oxide, zinc oxide, or boron nitride filler particles.
As the operational speed of Integrated Circuits (ICs) gets faster or the number of circuits increase, or the IC power level increases, the heat generated from the IC increases significantly. For better heat dissipation, it is required that the TIM should have high thermal conductivity, minimal thickness, small or preferably no voids in the TIM and at the interface thereof, and good adhesion between IC chip and heat sink and/or heat spreader. The same is true of TIM materials used in the cooling or heating of other systems—whether they are based on ICs, electronic modules, or other electronic or non-electronic heat or cold-generating devices.
Typically, the heat sinks consist of a plate with one or more flat surfaces and an array of protruded fins to enlarge the surface area contacting with the air or other heat transfer fluid, and therefore increasing the heat dissipation rate. If the heat transfer fluid is a liquid then the heat transfer structure is often referred to as a cold plate. If the heat transfer structure's purpose is mainly to provide good heat transfer from a small area heat or cold source (e.g. an IC chip as a heat source) by conduction to a larger area then the heat transfer structure is often referred to as a heat spreader. The concepts discussed herein can be equally applied to heat spreaders, cold plates and heat sinks, vapor chambers and the like. The heat transfer structures are usually made of aluminum or copper due to their good thermal conductivity of 237 and 401 W/mK, respectively. However, a great decrease of the thermal transfer efficiency between the heat transfer structures and the IC chips or other heat or cold sources occurs due to unsmooth contact areas there between. The TIMs are used to mediate between the heat transfer structures and the heat or cold sources or components to cure such an insufficiency.
Roughness of a contact surface will more or less affect the contact area at the interface of the TIM and the heat transfer surfaces, no matter how flat the surface is. In a conventional flat heat transfer structure, if voids exist at the interface of TIM and the heat transfer structure, the heat transfer efficiency will reduce due to the decreased contact surface between the heat transfer structure and TIM. Furthermore, the thickness of TIM also significantly affects the heat transfer efficiency between TIM and the heat transfer surfaces. The thinner the TIM the better the heat transfer efficiency. The TIM is typically the most significant thermal resistance that affects the heat transfer from the heat or cold source to the heat transfer structure—often accounting for 50% to 70% of that thermal resistance. This is due to the fact that the thermal conductivity of the TIM materials is so low (typically in the range of 1 to 4 W/mK) or 2 orders of magnitude lower than aluminum or copper.
Therefore, there is a need of a fluid spreader such as a heat transfer structure in semiconductor IC and other fields, which has improved heat transfer efficiency for TIM.
It is one object of the invention to provide a fluid spreader that increases the contact area to the fluid (TIM or other fluid).
It is another object of the invention to provide a fluid spreader that helps fluid to flow through channels formed on its surface in a predetermined direction.
It is still another object of the invention to provide a fluid spreader that reduces the thickness of TIM or fluid between the spreader and a secondary component or components (e.g. a heat source (such as a chip in a semiconductor package) or cold source) so as to increase the heat transfer from the heat or cold source to the spreader or to derive some other benefit by way of the reduced fluid thickness.
It is yet another object of the invention to provide a fluid spreader that improves the flow of fluid or TIM between the spreader and a secondary component or components such that the force applied to the fluid spreader to promote that fluid flow is substantially reduced in comparison to a fluid spreader or heat transfer structure without channels or protrusions.
In order to achieve the above and other objectives, the fluid spreader of the invention includes a first surface, wherein the first surface has at least one channel that extends to the outer periphery of the first surface.
In one embodiment of the invention, at least two channels are formed parallel or non-parallel to one another, configured in symmetrical or asymmetrical manner and arranged in equal or different intervals. Channels in this embodiment may also be arranged in radial patterns extending outward from the interior of the fluid spreader.
In another embodiment of the invention, the channel has a convex, semi-circle, V-shaped or other non-rectangular profile.
In still another embodiment of the invention, the channel includes surface textures or protrusions, such as serrated edges, on internal sidewalls or the floor of the channel. These features can be used to affect the flow of the fluid through the channels (e.g. making flow easy in one direction and difficult in another direction).
In another embodiment of the invention the fluid spreader comprises a first surface and a second surface or multiple secondary surfaces, with the first surface and at least one of the secondary surfaces also having channel features as described elsewhere in this invention. In some embodiments the fluid spreader will have a first surface with at lease one channel and a second surface opposite to the first surface that also has at least one channel. In other embodiments the fluid spreader will have a first surface with at least one channel and several secondary surfaces orthogonal to the first surface also with at least one channel (e.g. a cube with channels on multiple faces). In yet other embodiments the first and secondary surfaces are not flat and their relationship to each other may be of varying geometry.
In another embodiment of the invention the channels on the first and secondary surfaces may be of radically different scale (e.g. 150 um to 300 um channel width on one surface and 300 um to 1000 um channel width on another surface) to better match to the properties of the fluid or TIM in contact with each surface.
In yet another embodiment of the invention, there may be on one surface several areas or patches of channels with different scale, orientation or other unique features described elsewhere in this invention, to allow fluid flow to be affected in different ways relative to the patch the fluid is flowing through.
In another embodiment of the invention there could be two or more different types of fluids or thermal interface materials used in different areas on the surface with channels, such as a low flow fluid in the central portion of the surface and a high flow, low viscosity fluid on the peripheral portions of the surface.
In another embodiment of the invention the channels may be so wide as to create distinct pedestals or protrusions on the surface of the fluid spreader. These pedestals or protrusions can be preferentially located to correspond to hot spots, cold spots or other specific areas on the mating component (e.g. electronic component or IC chip) to preferentially affect the properties of the fluid or the fluid interaction with the components and fluid spreader in that location. For example, protrusions on the fluid spreader could decrease the TIM thickness local to those protrusions and those protrusions could correspond to hot spots on an IC chip—the thinner TIM material improving the heat transfer between those hot spots and the fluid spreader/heat transfer structure and preferentially cooling those hot spots more effectively in comparison to a heat transfer structure without protrusions.
In another embodiment of the invention the first surface could have areas of several different levels or planes—in order to affect the fluid thickness and flow between two or more corresponding components. For example, the fluid spreader could have sections at three distinct levels to contact three separate ICs on a multi-chip module or System-in-Package.
In a further embodiment of the invention fluid spreaders or components with channels formed in them to affect fluid flow and thickness can be arranged opposed to one another, thereby further reducing the fluid or TIM thickness between those two opposed surfaces.
In another embodiment of the invention the surface has not only channels, but also reservoirs (sections of the surface with higher geometric volume than the channels) that can be used to store excess fluid flow or can be used as a source of fluid to flow into the channels.
In another embodiment of the invention the channels are fully terminated within the periphery of the fluid spreader; specifically the channels do not extend out to the periphery. In this case, since the channels have no direct outlet for the fluid or TIM flow, the amount of fluid or TIM material must be controlled such that the material flows easily within the channels and between the surface of the fluid spreader and the component.
Furthermore, the invention also provides a semiconductor package including at least a fluid spreader, a semiconductor chip and a TIM layer between the fluid spreader and the chip, wherein the fluid spreader has a plurality of channels on a first surface thereof with varying widths along the whole channel. The fluid spreader is a heat transfer structure.
To provide a further understanding of the present invention, the following detailed description illustrates embodiments and examples of the present invention, this detailed description being provided only for illustration of the present invention.
Wherever possible in the following description, like reference numerals will refer to like elements and parts unless otherwise illustrated.
The invention relates to a flow spreader with channels that can guide a fluid flow through the channels while minimizing fluid voids generated at any interfaces and while minimizing the thickness of the fluid between the opposing surfaces of the fluid spreader and another object. The term “fluid” hereafter refers to any fluid that inherently flows at room temperature or becomes flowable at some operation temperature, melting temperature or some other defined temperature without respect to any limit to the viscosity of the fluid.
Note that the primary objective to reduce the thickness of the TIM (the thickness between the heat or cold source and the heat transfer structure) has analogs in other applications and fields. For example, the structures that will be described in the present invention, could be used in any application where the intent is to reduce the thickness of a fluid interface material (for example between a piston and cylinder, or shaft and bushing, or lens assemblies, or any other application that can be appreciated by someone skilled in the art). In these cases the fluid interface material's primary purpose may not be for heat transfer but for some other purpose (e.g. a lubricant such as grease or oil, a dielectric fluid to affect electromagnetic properties or other). Such a fluid interface could also be useful to minimize bond line thicknesses for many different types of joining applications—whether the joining process is accomplished by use of adhesives or glues, or by soldering or brazing materials, or other joining materials that fall under our broad nomenclature of fluid. These materials may or may not be a liquid or paste material at room temperature and in some cases would only become a flowable liquid at some elevated temperature.
In the case that the fluid is a TIM, a TIM used in contact with a heat transfer structure includes various materials such as thermal greases, phase change materials, thermal adhesives, thermally conductive compounds, solders, liquid metals, braze alloys, thermally conductive elastomers, thermally conductive adhesive tapes, and thermally conductive pads. All those TIMs are flowable at room temperature or at operation temperatures with different viscosities. Other fluids that are relevant to the invention are lubricants such as oils and greases, joining materials such as adhesives, soldering alloys, brazing alloys and the like, and any other fluid that would benefit an application by a reduction in that fluids thickness.
Smooth internal sidewalls of the channels help reduce the friction between the flowing fluid and the fluid spreader, and to fill the fluid completely up in the channels. Furthermore, smaller contact area between the fluid and spreader due to the varying width of channel improves the heat transfer to the spreader. In addition, the configuration of channels in the fluid spreader contributes to the reduction of the fluid thickness that shortens the distance between the first surface and a second component or components surface(s) and therefore significantly enhances heat transfer and other properties.
In the case that the fluid spreader is a heat transfer structure, it needs not only to reduce the thickness of the fluid between a first surface of the heat transfer structure and a component or device, but also to completely fill up all the channels on the first surface of the heat transfer structure with the fluid. That is, it is preferable not to form any voids at the interfaces of the channels and the fluid, especially around intersections of sidewalls and bottoms of the channels. Therefore, with a given channel, the bottom profile of the channel is preferable gradually changed.
The fluid is flowable at room temperature, operation temperature or some other temperature and the flow speed is determined by its viscosity. In order to help the fluid flow along a preferred direction in the channels 15, some surface textures or surface features can be added to the internal sidewalls of the channels 15 to guide elements of the fluid flow near the internal sidewalls in the on-going direction, as shown in
In some embodiments, the fluid spreader has a first surface with at lease one channel and a second surface opposite to the first surface that also has at least one channel. Each channel extends to an outer periphery of its corresponding surface, which has at least one of the surface features as defined above. The channels can be formed parallel or non-parallel to one another. If the channels are formed parallels, they are arranged at equal or different intervals. Channels in this embodiment may also be arranged in radial patterns extending outward from the interior of the fluid spreader. Alternatively, channels can be fully terminated within the periphery of the fluid spreader; specifically the channels do not extend out to the periphery. In other embodiments, the fluid spreader has a first surface with at least one channel and several secondary surfaces orthogonal to the first surface also with at least one channel (e.g. a cube with channels on multiple faces). Each channel extends to an outer periphery of its corresponding surface, which has at least one of the surface features as defined above. Channels in this embodiment may also be arranged in radial patterns extending outward from the interior of the fluid spreader. Alternatively, channels can be fully terminated within the periphery of the fluid spreader; specifically the channels do not extend out to the periphery. Furthermore, channels in this embodiment could extend out to the periphery on one or more surfaces of the fluid spreader and would not extend out the periphery on one or more separate surfaces. In yet other embodiments, the fluid spreader has a first and several secondary surfaces, all of which are not flat and their relationship to each other may be of varying geometry. Each channel extends to an outer periphery of its corresponding surface, which has at least one of the surface features as defined above. Channels in this embodiment may also be arranged in radial patterns extending outward from the interior of the fluid spreader. Alternatively, channels can be fully terminated within the periphery of the fluid spreader; specifically the channels do not extend out to the periphery.
In another embodiment of the invention the channels on the first and secondary surfaces may be of radically different scale (e.g. 150 um to 300 um channel width on one surface and 300 um to 1000 um channel width on another surface) to better match to the properties of the fluid in contact with each surface. Channels in this embodiment may also be arranged in radial patterns extending outward from the interior of the fluid spreader. Alternatively, channels can be fully terminated within the periphery of the fluid spreader; specifically the channels do not extend out to the periphery. In yet another embodiment of the invention, there may be on one surface several areas or patches of channels with different scale, orientation or other unique features described elsewhere in this invention, to allow fluid flow to be affected in different ways relative to the patch the fluid is flowing through.
In another embodiment of the invention there could be two or more different types of fluid interface materials used in different areas on the surface with channels, such as a low flow fluid in the central portion of the surface and a high flow, low viscosity fluid on the peripheral portions of the surface. Channels in this embodiment may also be arranged in radial patterns extending outward from the interior of the fluid spreader. Alternatively, channels can be fully terminated within the periphery of the fluid spreader; specifically the channels do not extend out to the periphery.
In another embodiment of the invention the first surface could have areas of several different levels or planes—in order to affect the fluid thickness and flow between two or more corresponding components. For example, the fluid spreader could have sections at three distinct levels to contact three separate ICs on a multi-chip module or System-in-Package.
The process includes steps of flattening the part of the fluid spreader surface that includes the channels after sintering by coining or stamping or by flattening by eliminating material from the surface by machining, grinding, polishing or other material removal methods. The process optionally includes a step of altering the geometry of the channels of the fluid spreader by etching, plating, or coating.
According to another embodiment of the invention, a process to make a fluid spreader with channels as described is provided. The process is performed by at least one of powder metallurgy, pressing and sintering of a suitable material such as copper. The process includes steps of flattening the part including the fluid spreader surface that has the channels after sintering; or altering the surface width or profile of the channels. The step of flattening the part including the channel surface can be achieved by coining, stamping, polishing, grinding or lightly machining. The step of altering the surface width or profile of the channel is achieved etching, plating or coating.
According to still another embodiment of the invention, a process to make a fluid spreader with channels as described is provided. The process performs machining, stamping, forging, etching or casting on two or more non-parallel surfaces or a continuously curvilinear surface of the channels. The continuously curvilinear surface can be a face of a cube for example.
In all above embodiments, an area can be further provided in the middle of the fluid spreader, or in one or other locations that are advantageous, for access by a vacuum pick-up head used in the assembly process. The spreader is picked up and placed onto the IC package and chip by a semi-automatic or fully automatic pick and place machine. This pick-up area meets the need of a flat area for the vacuum pick-up nozzle of the automatic pick and place machine. This pick-up area would be needed for any heat spreader with grooves/channels on the outside surface for TIM application.
In all embodiments of the invention, the channels on each face or surface can be of different scale, orientation or other features.
An assembly of two or more fluid spreader as described opposing faces or surfaces with channels is further provided. In some embodiments, the protrusions or pedestals of the fluid spreaders partially or completely correspond to one another to form appropriate-sized reservoirs between two of the fluid spreaders of the assembly. In other embodiments, the channels of the fluid spreaders partially or completely correspond to one another to form appropriate-sized reservoirs between two of the fluid spreaders of the assembly. The reservoirs can receive appropriate volume of the fluid filled there between. This assembly thereby makes the fluids go to the very minimum thickness possible and some benefits can be derived by way of reduced fluid thickness
In view of foregoing, the present invention offers advantages over the prior art as follows. With a given amount of fluid (such as a TIM fluid), the thickness of the fluid between the first surface of the fluid spreader and the adjoining component or device (e.g. chip in a semiconductor IC package) is reduced and thereby the heat transfer efficiency (or other property that benefits from a thinner fluid layer) is improved. This design of fluid spreader is not just for thermal dissipation purpose in electronic field, but also can be applied to other fields that need to guide the fluid to flow through the channels to achieve the thinnest fluid layer possible.
With the use of the fluid spreader according to the invention, the flow of fluid or TIM between the spreader and a secondary component or components improves such that the force applied to the fluid spreader to promote that fluid flow is substantially reduced in comparison to a fluid spreader or heat transfer structure without channels or protrusions. It should be apparent to those skilled in the art that the above description is only illustrative of specific embodiments and examples of the present invention. The present invention should therefore cover various modifications and variations made to the herein-described structure and operations of the present invention, provided they fall within the scope of the present invention as defined in the following appended claims.
