Patent ID: 12238897

DETAILED DESCRIPTION

The following describes embodiments of a heat dissipation structure, a method for manufacturing a heat dissipation structure, and an electronic apparatus according to the present invention in details, with reference to the drawings. The present invention is not limited to the following embodiments.

FIG.1is an exploded perspective view partially illustrating a heat dissipation structure10and a portable information apparatus12according to one or more embodiments of the present invention.

The portable information apparatus (electronic apparatus)12may be a laptop PC, a tablet terminal, or a smartphone, for example, which includes a graphics processing unit (GPU)14. The heat dissipation structure10may be used for the portable information apparatus12, and it can also be applied to other electronic apparatuses such as stationary desktop computers. The GPU14is a semiconductor chip capable of real-time image processing. The GPU14, which generates a considerable amount of heat due to the high-speed calculation, requires heat dissipation. The portable information apparatus12includes a vapor chamber (heat dissipator)16for heat dissipation from the GPU14.

The vapor chamber16has a plate-like shape and includes two metal plates (e.g., copper plates) that are joined at their peripheral edges to define a closed space inside the plates. The vapor chamber16diffuses heat efficiently through the phase change of working fluid enclosed in the closed space. In the closed space of the vapor chamber16, a wick is provided, which sends the condensed working fluid by capillarity.

The vapor chamber16is provided with substantially parallel two heat pipes18, and the ends of these heat pipes18are connected to a fan20. The heat pipes18each include a flattened thin metal pipe, inside of which a closed space is defined, and working fluid is enclosed in the closed space. Like the vapor chamber16, the heat pipes18are provided with a wick.

Various heat dissipators other than the vapor chamber16may be used for heat dissipation from heat-generating elements such as the GPU14. Heat dissipators include, for example, metal plates with high thermal conductivity such as copper and aluminum, graphite plates, heatlanes, and heat sinks.

FIG.2is a perspective view of the GPU14.FIG.2omits the components of the heat dissipation structure10. The GPU14has a substrate22and a die (electric component)24. The substrate22is a thin plate-like portion mounted on a board26, and has a rectangular shape in plan view. The die24is a part including an arithmetic circuit, and slightly protrudes from the upper surface of the substrate22. The die24has a rectangular shape smaller than the substrate22in plan view, and is located substantially in the center of the upper surface of the substrate22. The GPU14is one of the components that generate the most heat in the portable information apparatus12, and the die24in particular generates heat. In other words, the die24is one of the electric components that generates the most heat in the portable information apparatus12. The portable information apparatus12also includes a central processing unit (CPU). Like the GPU, the CPU has a substrate and a die, and the heat dissipation structure10can be used for the CPU. The heat dissipation structure10is also applicable to heat dissipation from semiconductor chips other than the GPU14and the CPU, or other heat-generating electric components.

On the upper surface of the substrate22, many small capacitors28are arranged to surround the die24. These capacitors28are arranged on the four sides of the die24in one lines or in two lines at some locations. These capacitors28are located relatively close to the die24. The height of the capacitors28is lower than the die24.

FIG.3is a schematic cross-sectional side view of the heat dissipation structure10according to one or more embodiments of the present invention. The heat dissipation structure10has the vapor chamber16described above and a mesh (porous material)30placed between the vapor chamber16and the surface of the die24. The mesh30is impregnated with liquid metal (heat-transfer fluid)32.

The liquid metal32is essentially metal that is liquid at room temperatures, and it may be liquid at least at the temperatures of normal use where the board26of the portable information apparatus12is energized and the GPU14is in operation. The liquid metal32, which is metal, has excellent thermal conductivity and electrical conductivity. Also, the liquid metal32, which is liquid, has fluidity.

Essentially the entire width of the mesh30is impregnated with the liquid metal32, so that the liquid metal32comes in contact with the surfaces of the die24and the vapor chamber16, establishing a good thermal connection between them. Essentially the entire surface of the mesh30is impregnated with the liquid metal32, and under some conditions, some portions of the mesh30(e.g., the edges) may not be impregnated to keep room for absorbing an extra amount.

The mesh30has a rectangular shape that is the same as or slightly larger than the surface of the die24to cover the surface of the die24. The mesh30may have some small holes depending on the heat generation distribution in the die24, and the holes may serve as a liquid reservoir for the liquid metal32.

The mesh30may be made of woven wire or a plate material with a large number of holes etched into it. Although the mesh30may be made of a resin material, for example, the mesh30made of a metal material will have a suitable heat transfer performance. When the mesh30is made of a metal material, a nickel material (including an alloy containing nickel as a main component) or a copper or aluminum material plated with nickel may be used. That is, the mesh30may be made of a nickel material at least on the surface. This can prevent the alteration by the liquid metal32. The mesh30made of a nickel material omits the plating process. The mesh30made of a copper or aluminum material plated with nickel has favorable thermal conductivity.

The mesh30may be replaced by other porous materials that can be impregnated with liquid metal32, such as sponges or other foams. A porous material in the present application refers to a material that can be impregnated with a heat-transfer fluid such as the liquid metal32, regardless of resin, metal, or the like. The sponge as a porous material may be either resin or metal (like a metal scourer). The porous material in the present application may be either an elastic body or a rigid body.

The vapor chamber16is essentially placed in parallel with the surface of the die24. As long as the vapor chamber16may be placed so as to come in contact with the entire surface of the mesh30(or the sponge), the vapor chamber16may be slightly non-parallel (substantially parallel) due to slight elastic deformation or uneven thickness of the mesh30.FIG.3does not illustrate a single layer of the liquid metal32because the mesh30is impregnated with the liquid metal32. Microscopically, the layer of the liquid metal32may exist between the die24and the mesh30, or between the die24and the vapor chamber16.

These heat dissipation structure10and portable information apparatus12have favorable heat transfer performance because the die24and the vapor chamber16are thermally connected by the liquid metal32, with which the mesh30is impregnated. While the portable information apparatus12is carried and moved, it may be subjected to vibrations or shocks, so that pressure is applied to the liquid metal32repeatedly from the die24and vapor chamber16. Although having fluidity, the liquid metal32, with which the mesh30is impregnated, keeps impregnation due to the wettability with the mesh30and other factors, and thus it does not leak into the surroundings.

For this reason, an appropriate amount of the liquid metal32is held between the die24and the vapor chamber16, thus preventing deterioration of heat transfer performance. This also prevents the liquid metal32from touching the capacitors28and other electric components mounted on the board26.

The liquid metal32essentially does not touch the capacitors28, meaning that no insulating material34(illustrated in the imaginary lines inFIG.3) is required to cover the capacitors28. The liquid metal32essentially does not touch the electric components mounted on the board26, meaning that no sponge wall36(illustrated in the imaginary lines inFIG.3) is required to surround the four sides of the substrate22. In other words, the heat dissipation structure10does not require any insulating material34such as adhesive or sponge wall36, thereby reducing the number of parts and assembly man-hours. For some design conditions or considering unforeseen circumstances, the heat dissipation structure10may include the insulating material34, the sponge wall36, or the like.

The inventor conducted an experiment to compare a heat dissipation structure where not only the liquid metal32but also the mesh30is interposed between the die24and the vapor chamber16as in the heat dissipation structure10, with a heat dissipation structure where only the liquid metal32is interposed. The experiment showed no significant difference in heat transfer performance between them, confirming that the heat dissipation structure10has good heat transfer performance.

The experiment conducted by the inventor also shows that certain large vibrations and shocks caused the leakage of liquid metal32and a decrease in heat transfer performance in the structure with only the liquid metal32interposed, while no significant change was observed in the heat dissipation structure10before and after the experiment. This confirms that the heat dissipation structure10kept good performance.

The inventor also conducted a similar experiment for the structure where only heat-transfer grease, not liquid metal32, was interposed between the die24and the vapor chamber16. Although heat-transfer grease has lower fluidity than the liquid metal32, it leaked somewhat and some deterioration was found in heat transfer performance. That is, a leakage from between the die24and the vapor chamber16due to vibrations is not a phenomenon unique to the liquid metal32, but this is a phenomenon common to all heat-transfer fluids. The porous material of the heat dissipation structure10according to one or more embodiments may be impregnated with a heat-transfer fluid including heat-transfer grease, from which an effect of preventing the leakage can be obtained. The heat transfer fluid in the present application means not only liquid but also semi-solid and viscous substances having fluidity, and includes grease, oil compound, and the like. The material, thickness and diameter of the micropores of the porous material may be selected in accordance with the viscosity, fluidity, wettability, and other properties of the heat transfer fluid used for impregnation.

Next the following describes a method for manufacturing the heat dissipation structure10.FIG.4is a flowchart of the method for manufacturing the heat dissipation structure10.FIG.5is a schematic cross-sectional side view illustrating the placing step.FIG.6is a schematic cross-sectional view illustrating the holding step. This manufacturing method of the heat dissipation structure10assumes that the GPU14is already mounted on the board26prior to the steps illustrated inFIG.4. The board26may be assembled to the chassis of the portable information apparatus12, or may be in a state before assembly.

In step S1(impregnation step) ofFIG.4, the mesh30is impregnated with an appropriate amount of liquid metal32. For impregnation, the mesh30may be immersed in a bath of the liquid metal32, or the liquid metal32may be applied to the mesh30. Although the liquid metal32may be difficult to permeate the mesh30for impregnation, the mesh30at this step is easy to handle because it is a single piece prior to assembly into the heat dissipation structure10. Also, the six faces of the mesh30, including the top, bottom, front, back, left, and right, are open, making it easy for the liquid metal32to permeate for impregnation. The mesh30is a single piece at this step, and thus the operator can inspect it visually or by a prescribed method to see if the mesh30is properly impregnated with the liquid metal32.

In step S2, the surface of the die24is cleaned and an appropriate amount of liquid metal32is applied thereto. The liquid metal32essentially is applied to the entire surface of the die24. Step S2may be performed at any timing prior to the next step S3.FIG.5illustrates the liquid metal32applied to the surface of the die24with the bold line.

As illustrated inFIG.5, in step S3(placing step), the mesh30impregnated with liquid metal32is placed on the surface of the die24. In this step, the liquid metal32applied to the die24and the liquid metal32, with which the mesh30is impregnated, are mixed. This ensures that the liquid metal32, with which the mesh30is impregnated, will be in contact with the surface of the die24. Depending on conditions, for example, when the liquid metal32and the surface of the die24have good wettability, the preliminary step S2may be omitted.

In step S4, the surface of the vapor chamber16is cleaned and an appropriate amount of liquid metal32is further applied thereto. The liquid metal32is applied to the portion of the vapor chamber16that is to be in contact with the mesh30. In one or more embodiments, the portion to which the liquid metal32is applied is nickel-plated in advance. Step S4may be performed at any timing prior to the next step S5.FIG.6illustrates the liquid metal32applied to the surface of the vapor chamber16with the bold line.

As illustrated inFIG.6, in step S5(holding step), the vapor chamber16is brought into contact with the mesh30, so that the mesh30is held between the vapor chamber16and the die24. The vapor chamber16is fixed to the board26and the chassis with screws or the like (seeFIG.1).

In this step, the liquid metal32applied to the vapor chamber16and the liquid metal32, with which the mesh30is impregnated, are mixed. This ensures that the liquid metal32, with which the mesh30is impregnated, will be in contact with the surface of the vapor chamber16. Depending on conditions, for example, when the liquid metal32and the surface of the vapor chamber16have good wettability, the preliminary step S4may be omitted.

Before this step, the mesh30is pre-impregnated with the liquid metal32, meaning that there is no need to impregnate the mesh30deeply with the liquid metal32on the surface of the die24by step S2and the liquid metal32on the surface of the vapor chamber16by step S4. Therefore, at this step, it is not necessary to press the vapor chamber16hard against the mesh30and press the die24for a long time for impregnation. If the mesh30were impregnated with the liquid metal32in this step, the mesh30would be covered with the vapor chamber16, making it difficult to inspect the impregnation. In contrast, inspection will be easy if the impregnation is performed in step S1beforehand.

FIG.7is a schematic cross-sectional view of a step in a manufacturing method that is a modified example of the heat dissipation structure10. In this method, the periphery of the mesh30not impregnated with the liquid metal32is fixed to the vapor chamber16, and this mesh30is brought into contact with the die24as it is. In this case, the mesh30is fixed to the vapor chamber16by soldering or caulking at its peripheral fixed portion38.

In this method, one face of the mesh30is blocked by the vapor chamber16. Thus, the fixed portion38may be provided intermittently rather than all the way around the mesh30to keep open spaces and help the air inside exhausted before impregnating the mesh30with the liquid metal32on the surface of the die24.

To promote impregnation of the mesh30with the liquid metal32on the surface of the die24, the following steps may be conducted: the vapor chamber16and the mesh30are pressed against the die24hard with a certain amount of force; the vapor chamber16and the mesh30are pressed against the die24for some length of time; and the pressing force of the vapor chamber16and mesh30may be varied over time. The fixed portion38has the effect of preventing the liquid metal32, with which the mesh30is impregnated, from leaking out to the surroundings. The manufacturing method illustrated inFIGS.4to7also is applicable when sponge is used as the porous material or when grease is used as the heat-transfer fluid.

Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.

DESCRIPTION OF SYMBOLS

10heat dissipation structure12portable information apparatus (electronic apparatus)16vapor chamber (heat dissipator)22substrate24die (electric component)28capacitor30mesh (porous material)32liquid metal (heat-transfer fluid)