HEAT DISSIPATION STRUCTURE AND ELECTRONIC APPARATUS

A heat dissipation structure, for a semiconductor chip in which a die is provided on a surface of a substrate and an electric element is provided around the die, includes: a heat transfer plate thermally connected to a surface of the die; a liquid metal provided between the surface of the die and the heat transfer plate; and an insulating material covering the electric element. The heat transfer plate has a recessed portion in a location facing the electric element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2021-204268 filed on Dec. 26, 2021, the contents of which are hereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a heat dissipation structure for a semiconductor chip in which a die is provided on the surface of a substrate and an electric element is provided around the die, and an electronic apparatus.

BACKGROUND

Electronic apparatuses include semiconductor chips such as CPUs and GPUs. A CPU or a GPU is shaped to have a substrate which is a part to be mounted on a board and a rectangular die provided on the surface of the substrate. Small capacitors may be provided around the die on the surface of the substrate.

A semiconductor chip such as a CPU or a GPU is a heating element, and requires heat dissipation depending on its power consumption (especially when highly loaded). As a means of dissipating heat from the CPU or GPU, a heat dissipator such as a vapor chamber, a heat spreader, or a heat sink may be used, and brought into contact with the surface of the die to diffuse heat. A heat transfer plate may be interposed between the heat dissipator and the die. Grease or liquid metal having high thermal conductivity may be provided between the die and the heat dissipator or the heat transfer plate, in order to efficiently transfer heat (for example, Japanese Unexamined Patent Application Publication No. 2004-146819). Liquid metal has higher thermal conductivity than grease, and can effectively transfer heat from the die to the heat dissipator.

Liquid metal is electrically conductive, and may contain gallium as a main component and chemically react with solder. Since the liquid metal is liquid and has high fluidity, measures need to be taken to prevent the liquid metal from leaking out to the surrounding board and the like. Even in the case where the liquid metal flows out to the surroundings of the die, the liquid metal needs to be kept from coming into contact with electric elements such as capacitors around the die, because the liquid metal is electrically conductive and is likely to short-circuit the capacitors. In view of this, the electric elements provided on the substrate may be protected using an insulating adhesive.

A CPU die is lower than a GPU die in some cases. For such a CPU die, the gap between the substrate and the heat transfer plate is narrow. Since the adhesive has a certain height, a sufficient gap between the adhesive and the heat transfer plate cannot be secured or interference can occur.

One conceivable way of securing an appropriate gap between the adhesive and the heat transfer plate is to interpose a copper block or the like between the heat transfer plate and the CPU to thus raise the height. However, if the heat transfer plate and the copper block are soldered, there is a possibility that the solder chemically reacts with the liquid metal. Nickel-plating the copper block including the soldered part can prevent the chemical reaction, but causes a cost increase. Moreover, raising the height increases the thickness of the product, which is against the demand for thickness reduction in application to laptop PCs and the like.

SUMMARY

One or more embodiments of the present invention provides a heat dissipation structure and an electronic apparatus that enable effective heat dissipation of a semiconductor chip and can be produced at low costs.

A heat dissipation structure according to one or more embodiments of the present invention is a heat dissipation structure for a semiconductor chip in which a die is provided on a surface of a substrate and an electric element is provided around the die, the heat dissipation structure including: a heat transfer plate thermally connected to a surface of the die; a liquid metal provided between the surface of the die and the heat transfer plate; and an insulating material covering the electric element, wherein the heat transfer plate has a recessed portion in a location facing the electric element.

An electronic apparatus according to one or more embodiments of the present invention includes the heat dissipation structure and the semiconductor chip.

According to the above-described aspects of the present invention, the liquid metal is provided between the surface of the die and the heat transfer plate, so that the semiconductor chip can dissipate heat effectively. The heat transfer plate having the recessed portion is easy to manufacture, and can be produced at low costs.

The recessed portion may be a through hole, and the through hole may be closed with an insulating sheet. The through hole can be formed easily by punching or the like. The liquid metal is kept from entering the through hole closed with the sheet.

The recessed portion may be a bottomed hole. The bottomed hole can be formed easily by pressing or the like.

The heat dissipation structure may include an elastic material surrounding the die and sandwiched between the substrate and the heat transfer plate, and the elastic material may cover the electric element with the insulating material therebetween. Thus, the electric element is doubly protected by the insulating material and the elastic material.

The insulating material may be adhered to the substrate. Thus, the liquid metal is kept from approaching the electric element along the surface of the substrate, so that the electric element is protected more reliably.

A gap may be formed between the insulating material and the die. Thus, the leaked liquid metal is stored in the gap and prevented from further spreading accidentally.

The semiconductor chip may be a CPU mounted on a board, and the electric element may be a capacitor.

The insulating material may be an ultraviolet curable coating material. The insulating material can be formed easily using such a coating material.

According to the above-described aspects of the present invention, the liquid metal is provided between the surface of the die and the heat transfer plate, so that the semiconductor chip can dissipate heat effectively. The heat transfer plate having the recessed portion is easy to manufacture, and can be produced at low costs.

DETAILED DESCRIPTION

Embodiments of the present invention will be described in detail below, with reference to the drawings. Note that the present invention is not limited to these embodiments.

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

The electronic apparatus12is, for example, a laptop PC, a desktop PC, a tablet terminal, or a smartphone, and includes a central processing unit (CPU)14. The CPU14performs high-speed computation and thus generates heat accordingly, so that heat dissipation is needed. The electronic apparatus12includes a vapor chamber16as a heat dissipation means for the CPU14. The electronic apparatus12may include a graphics processing unit (GPU), besides the CPU14. Although the heat dissipation structures10,10A, and10B described below are used for the CPU14as an example, these heat dissipation structures are also usable for other semiconductor chips such as a GPU.

The vapor chamber16is a plate-shaped member obtained by joining the edges of two metal plates (e.g. copper plates) to form a closed space inside, and can diffuse heat with high efficiency by the phase change of a working fluid enclosed in the closed space. A wick that delivers the condensed working fluid by capillary action is located in the closed space of the vapor chamber16.

Two substantially parallel heat pipes18are provided in the vapor chamber16. The heat pipes18have their ends connected to a fan20. Each heat pipe18is a thin flat metal pipe having a closed space formed inside, in which a working fluid is enclosed. A wick is located in the heat pipe18, as in the vapor chamber16.

The heat dissipation means for the heating element such as the CPU14is not limited to the vapor chamber16, and various heat dissipators are applicable. Examples of heat dissipators include metal plates with high thermal conductivity such as copper and aluminum, graphite plates, heat lanes, and heat sinks.

FIG.2is a perspective view of the CPU14. The components of the heat dissipation structure10are omitted inFIG.2. The top and bottom of the heat dissipation structure10are not limited in a state in which the heat dissipation structure10is incorporated in the electronic apparatus12and used, and the heat dissipation structure10may be, for example, upside down.

The CPU14includes a substrate22and a die24. The substrate22is a thin plate-shaped portion mounted on a board26, and is rectangular in a plan view. The die24is a portion including an arithmetic circuit, and slightly protrudes from the surface of the substrate22. The die24has a rectangular shape smaller than that of the substrate22in a plan view, and is located approximately at the center of the surface of the substrate22. The CPU14is one of the components that generate the most heat in the electronic apparatus12, and the die24in particular generates heat.

A plurality of small capacitors (electric elements)28are provided on the surface of the substrate22. Several capacitors28are located relatively close to the die24, and many capacitors28are arranged along one edge22aof the substrate22. The capacitors28arranged along the edge22aare also referred to as capacitors28a. The height of the capacitors28is lower than that of the die24.

FIG.3is a schematic cross-sectional side view of the heat dissipation structure10according to one or more embodiments.FIG.4is a perspective view of a heat transfer plate30according to one or more embodiments.FIG.5is a schematic plan view illustrating the positional relationship of components in the heat dissipation structure10according to one or more embodiments. InFIG.5, the vapor chamber16and the board26are omitted, and each component is illustrated in solid lines regardless of whether it is located in front of or behind another component.

The heat dissipation structure10includes the vapor chamber16, the heat transfer plate30thermally connected to the vapor chamber16, a liquid metal32provided between the surface of the die24and the heat transfer plate30, an insulating material34covering the capacitors28, and an elastic material36provided between the substrate22and the heat transfer plate30. The heat transfer plate30is thermally connected to the surface of the die24via the liquid metal32.

The liquid metal32is basically a metal that is liquid at room temperature, but is liquid at temperatures in a normal use state in which the CPU14is in operation. The liquid metal32is metal, and therefore has excellent thermal conductivity and electrical conductivity. For example, the liquid metal32is mainly made of gallium.

The insulating material34is, for example, an ultraviolet curable coating material, and is formed in a film shape. The coating material is applied so as to cover the capacitors28and then irradiated with ultraviolet rays to cure and form the insulating material34. The insulating material34can be easily formed using such an ultraviolet curable coating material. The insulating material34may be any other insulating adhesive or the like.

The elastic material36has a rectangular shape slightly larger than that of the substrate22, and protrudes slightly from the substrate22. A rectangular hole36ais formed approximately at the center of the elastic material36. The elastic material36is sandwiched between the substrate22and the heat transfer plate30. In one or more embodiments, however, the part of the elastic material36covering the capacitors28aalong the edge22aof the substrate22(seeFIG.5) is not in contact with the heat transfer plate30. The die24is fitted in the rectangular hole36a. A small gap38is secured between the die24and the hole wall of the rectangular hole36a. The elastic material36is adhered and fixed to the surface of the substrate22by adhesive tape40of the same shape in a plan view. The elastic material36is slightly higher than the die24in a natural state without external force, and is appropriately compressed by the heat transfer plate30in an assembled state of the heat dissipation structure10. For example, the elastic material36is made of an insulating material such as a sponge material. The elastic material36is a material that does not absorb the liquid metal32. The elastic material36is provided with a pull tab37(see FIG.5) for removal.

The heat transfer plate30is made of a material having excellent heat transference, and is, for example, a copper plate. The heat transfer plate30has a thickness of about 0.3 mm to 2 mm, for example. The heat transfer plate30has substantially the same rectangular shape and area as the substrate22, but is shaped so as not to face the capacitors28aalong the edge22aof the substrate22(seeFIG.5). Hence, the heat transfer plate30and the capacitors28ado not interfere with each other.

The heat transfer plate30is fixed to the vapor chamber16by soldering or the like. The heat transfer plate30may be subjected to surface treatment such as nickel plating. The heat transfer plate30has through holes (recessed portions)30aand30bin the locations facing the capacitors28. The through hole30ais located facing one capacitor28, and has a relatively small area corresponding to one capacitor28. The through hole30bis located facing two adjacent capacitors28, and has a relatively large area corresponding to two capacitors28.

The through holes30aand30bare covered with sheets33aand33brespectively. The sheets33aand33bare insulating, elastic, and flexible. The sheet33ahas an area suitable for covering the through hole30a. The sheet33bhas an area suitable for covering the through hole30b, and is slightly larger than the sheet33a. The sheets33aand33bare rectangular or circular, for example. The sheets33aand33bare not made of any special material and are inexpensive. Attaching the sheets33aand33bso as to cover the through holes30aand30bis a simple operation that can be easily performed even by an unskilled worker and can be automated.

An appropriate amount of the liquid metal32is applied to the top surface of the die24in the assembly stage of the heat dissipation structure10. The vapor chamber16and the heat transfer plate30are then placed, as a result of which the liquid metal32is pressed by the heat transfer plate30and spreads evenly over the surface of the die24, thus filling the gap between the die24and the heat transfer plate30. Since the liquid metal32is liquid, the liquid metal32has fluidity and spreads sufficiently when pressed by the heat transfer plate30. Accordingly, at the microlevel, the heat transfer plate30and the die24are in direct contact with each other in some parts, and the liquid metal32fills the small gaps in the other parts. This allows efficient thermal conduction between the die24and the heat transfer plate30, and can improve the heat dissipation of the CPU14.

The height H0of the die24is lower in the CPU14than in a GPU or the like in some cases. In such a case, the gap between the substrate22and the heat transfer plate30is narrow. Since the insulating material34has a certain height H1, a sufficient gap between the insulating material34and the heat transfer plate30cannot be secured or interference can occur with the conventional technology.

In the heat dissipation structure10and the electronic apparatus12according to one or more embodiments, on the other hand, the heat transfer plate30has the through holes30aand30bas recessed portions in the locations facing the capacitors28so as to provide escape spaces. Thus, the insulating material34covering the capacitors28can be prevented from interfering with the heat transfer plate30, and also the elastic material36can be interposed therebetween. The term “recessed portion” herein denotes a portion that is recessed from the surface regardless of whether it is a through hole or a bottomed hole. The through holes30aand30bare covered with the sheets33aand33b, but the heat transfer plate30itself has recessed portions. Since the sheet bodies have high flexibility and elasticity, the function of the through holes30aand30bas escape spaces can be maintained.

The through holes30aand30bare covered with the sheets33aand33b. Accordingly, even in the case where the liquid metal32leaks out from the gap between the die24and the heat transfer plate30, the liquid metal32is kept from entering the through holes30aand30b, and the solder as the connecting portion between the heat transfer plate30and the vapor chamber16is protected. The elastic material36comes into contact with the sheets33aand33band may press the sheets33aand33blightly, but the sheets33aand33bare typically elastic and flexible and deform appropriately. Moreover, the elastic material36itself is elastic, too, so that no excessive external force is exerted on the insulating member34and the capacitors28.

The capacitors28are doubly insulated by the insulating material34and the elastic material36, and protected from the leaked liquid metal32. Even in the case where the insulating material34and the elastic material36near the capacitors28peel off and the capacitors28come into contact with the sheets33aand33b, a short circuit with the heat transfer plate30is prevented because the sheets33aand33bhave insulating property. Since the insulating material34is adhered to the substrate22with the adhesive tape40, the liquid metal32is kept from approaching the capacitors28along the surface of the substrate22, and therefore the capacitors28are protected more reliably. In addition, the gap38is secured between the insulating material34and the die24, so that the leaked liquid metal32is stored in the gap38and is prevented from further spreading accidentally.

The through holes30aand30bof the heat transfer plate30can be formed easily by punching or the like at low costs. Moreover, the through holes30aand30bcan be formed at the same time as cutting out the external shape by punching or the like in the manufacturing process of the heat transfer plate30, with it being possible to further reduce the manufacturing costs. By making only the center part of the heat transfer plate30as the contact portion with the die24slightly thick and making the other peripheral part of the heat transfer plate30thin, a relatively large gap with the insulating material34can be secured to thus avoid interference. However, reducing the thickness of the whole peripheral part of the heat transfer plate30which is a thin plate requires precision and needs CNC processing and the like, which increases the number of manufacturing steps and increases the costs. Forming the through holes30aand30bin the heat transfer plate30as in one or more embodiments, on the other hand, is low in cost.

FIG.6is a schematic cross-sectional side view of a heat dissipation structure10A according to one or more embodiments of the present invention.FIG.7is a perspective view of a heat transfer plate50in one or more embodiments. The heat dissipation structure10A includes the heat transfer plate50instead of the heat transfer plate30in the heat dissipation structure10.

The heat transfer plate50has the same size, shape, and material as the heat transfer plate30, but differs from the heat transfer plate30in that the through holes30aand30bare replaced with bottomed holes (recessed portions)50aand50bwith an appropriate depth. The bottomed hole50ahas the same position and the same area as the through hole30a. The bottomed hole50bhas the same position and the same area as the through hole30b. The heat transfer plate50is not provided with the sheets33aand33b.

In the heat dissipation structure10A, the heat transfer plate50has the bottomed holes50aand50bas recessed portions in the locations facing the capacitors28. Thus, the insulating material34covering the capacitors28can be prevented from interfering with the heat transfer plate50, and also the elastic material36can be interposed therebetween. The elastic material36enters the bottomed holes50aand50band may come into contact with their bottom surfaces. However, since the bottomed holes50aand50bhave an appropriate depth, compression is not significant, and no excessive external force is exerted on the insulating member34and the capacitors28. The bottomed holes50aand50bcan be formed easily, for example, by pressing the heat transfer plate50. An insulating coating may be provided on the bottom surface of each of the bottomed holes50aand50b.

FIG.8is a schematic cross-sectional side view of a heat dissipation structure10B according to one or more embodiments of the present invention. The heat dissipation structure10B includes an elastic material60instead of the elastic material36in the heat dissipation structure10. The elastic material60has the same outer edge shape, thickness, and material as the elastic material36, but differs from the elastic material36in that the rectangular hole36ais replaced with a rectangular hole60ahaving a larger area. The rectangular hole60ais formed slightly smaller than the outer edges of the heat transfer plate30. That is, the elastic material60is compressed on all four sides by the part along the outer edges of the heat transfer plate30, and does not exist at the capacitors28, the through holes30aand30b, and the sheets33aand33b. Thus, depending on the design conditions, the elastic material60is provided along the outer edges of the heat transfer plate30and surrounds at least the die24. This prevents the liquid metal32from leaking out to the surrounding board26and the like. The heat transfer plate30in the heat dissipation structure10B may be replaced with the heat transfer plate50(seeFIG.7).

Depending on the design conditions, the heat transfer plate30or50may be omitted and the vapor chamber16may be thermally connected to the die24via the liquid metal32in each embodiment. That is, the vapor chamber16itself may be used as a heat transfer plate for the die24.

The present invention is not limited to the embodiments described above, and changes can be made freely without departing from the gist of the present invention.

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