INTEGRATED CIRCUIT PACKAGE AND FASTENER

An apparatus is disclosed comprising an integrated circuit package, wherein the integrated circuit package comprises a case containing at least one integrated circuit and a fastener configured to fasten the case to a heat sink. A system comprising the apparatus and a heat sink, and a method comprising providing the apparatus and fastening a heat sink to the case of the apparatus are also disclosed.

FIELD

This specification relates generally to an integrated circuit package and fastener.

BACKGROUND

Integrated circuits (ICs) such as a System on a Chip (SoC) generate heat during operation. This heat may be dissipated to the surrounding environment through the provision of a heat sink. Manufacturing tolerances lead to the presence of a gap between the case of the package containing the integrated circuit and the heat sink. This gap may be filled with a thermal interface material (TIM), which enhances the thermal coupling between the integrated circuit package and the heat sink.

Heat generation in integrated circuits such as System on a Chip generally increases with the implantation of smaller line width processors and increased integration. This heat is dissipated to prevent the integrated circuit from overheating.

SUMMARY

According to a first aspect, there is provided an apparatus comprising an integrated circuit package, wherein the integrated circuit package comprises a case containing at least one integrated circuit and a fastener configured to fasten the case to a heat sink.

The fastener may be integrally formed with the case.

The fastener may be directly mounted on the case.

The fastener may be mounted on the case by an adhesive.

The fastener may comprise at least one screw configured to fasten the case to the heat sink.

The fastener may comprise a plurality of screws arranged adjacent a periphery of an upper surface of the case and configured to fasten the case to the heat sink.

The fastener may comprise at least one female screw thread configured to fasten the case to the heat sink.

The fastener may comprise at least one aperture, wherein the at least one aperture is configured to receive a screw to fasten the case to the heat sink.

The integrated circuit package may further comprise a lid, wherein the lid is mounted on the case, and wherein the lid comprises the fastener.

The fastener may comprise a plurality of apertures arranged around a periphery of the lid and configured to each receive a respective screw to fasten the case to the heat sink.

The lid may comprise a metal plate, a heat pipe or a vapour chamber.

The apparatus may further comprise a layer of thermal interface material between the case and the lid.

The integrated circuit may be a System on a Chip (SoC).

According to a second aspect, there is provided a system comprising an apparatus as disclosed herein and a heat sink fastened to the case of the apparatus using the fastener of the apparatus.

According to a third aspect, there is provided a method comprising providing an apparatus as disclosed herein and fastening a heat sink to the case of the apparatus using the fastener of the apparatus.

DETAILED DESCRIPTION

In the description and drawings, like reference numerals may refer to like elements throughout.

FIG. 1Ais a perspective view of an exemplary integrated circuit package1. The integrated circuit package1comprises a case11, which contains at least one integrated circuit comprising a die (not shown). The case11of the integrated circuit package1is configured to protect the integrated circuit from physical damage and corrosion. The case11of the integrated circuit package1comprises an upper surface12aand a lower surface12b. The upper surface12aand the lower surface12bmay be flat and arranged parallel to each other such that the upper surface12ais opposite the lower surface12b. The case11may be moulded around the integrated circuit, and may be made of plastic or ceramic, or other suitable materials exhibiting good thermal conductivity and strength.

FIG. 1Ashows the case11further comprising four side surfaces13a,13b,13cand13d, each adjacent the upper surface12aand the lower surface12b, however the case11may have more or fewer sides than this. A plurality of pins14, also known as legs, protrude from the sides13a,13b,13cand13dand extend downwards, away from the upper surface12a. The pins14may be made from metal and are configured to be mounted on a board such as a printed circuit board (not shown) such that the integrated circuit package1is fastened to the board. The pins14may be soldered to the board. The pins14are configured to provide an electrical connection between the integrated circuit contained within the integrated circuit package1and one or more conductive components on the board.

The configuration of the pins14shown inFIG. 1Ais by way of example only, and other known configurations may be used. For example, the plurality of pins14may extend from only two, opposite sides of the case11(such as for a dual in-line package). In other examples, the pins14may protrude from the lower surface12bof the case11. The term pins14should be taken to also include similar connectors such as pads or balls, as used in a ball grid array, for example.

FIG. 1Bshows a ball grid array (BGA) integrated circuit package1. The integrated circuit package1ofFIG. 1Bis similar to the integrated circuit package1ofFIG. 1A, however here the plurality of pins14project from the lower surface12bof the case11. The plurality of pins14, in this case comprising balls, are arranged in an array across the lower surface12bof the case. As for the integrated circuit package1ofFIG. 1A, the pins14may be soldered to a board, and are configured to provide an electrical connection between the integrated circuit contained within the integrated circuit package1and one or more conductive components on the board. The ball grid array arrangement allows a higher density of pins14to be present on the integrated circuit package1.

FIG. 1Cshows a schematic cross-sectional view of the integrated circuit package1ofFIG. 1B, along the line X-X′ ofFIG. 1B, however the configuration will be similar for the integrated circuit package ofFIG. 1A.

The integrated circuit comprises a die15, which is mounted on a substrate16and is electrically connected to the pins14by respective bond wires17.

The integrated circuit package1illustrated inFIG. 1Cis by shown by way of example, and other types and configurations of integrated circuit package1may be used with embodiments of the present disclosure. For example, the integrated circuit package1may be of a flip chip type, as illustrated inFIG. 1D.

FIG. 1Dshows an exemplary flip chip ball grid array package1suitable for use with the present disclosure. The general structure is similar to that shown inFIG. 1C. However in the flip chip package1shown inFIG. 1D, the die15is upside down relative to the die15shown inFIG. 1C, with the die15being electrically connected to the pins14(in this case the pins14being balls of a ball grid array) via solder balls18instead of bond wires17. The solder balls18are in a gap between the die15and a substrate16. The remainder of the gap may be at least partially filled with an underfill19, for example made from epoxy. The top of the die15may be covered by a lid such as a mould cap, forming the case11of the package1. Heat from the die15may therefore be dissipated directly to the lid. Instead of a mould, the lid may be a metal lid covering the die15, in some cases with a layer of thermal grease between the die15and metal lid.

During use, electrical energy supplied to the integrated circuit is converted into heat energy, which is dissipated through the case11of the integrated circuit package1to the outside. If the heat is not dissipated efficiently enough, there is a risk of the integrated circuit overheating. This may be a concern for System on Chip (SoC) integrated circuits, which comprise dense integration providing a computer on a single chip. Thus the heat output by a System on Chip may be high in comparison to simpler integrated circuits.

FIG. 2illustrates a current solution for dissipating heat from an integrated circuit using a heat sink20. An integrated circuit is contained within the integrated circuit package1. The package1is mounted on a board30such as a printed circuit board, for example by soldering or another known means. The package1is mounted such that the lower surface12bof the case11is adjacent an upper surface31of the board30.

The heat sink20may be mounted directly to the board30using screws32such that a lower surface21of the heat sink20is adjacent the upper surface12aof the case11of the integrated circuit package1. By mounting the heat sink20to the board30in this way, a gap35may be formed between the integrated circuit package1and the heat sink20, in this case between the upper surface12aof the case11of the integrated circuit package1and the lower surface21of the heat sink20. This gap35may be the result of tolerances in the dimensions of various components such as the board30, screws32, integrated circuit package1and heat sink20.

The size of the gap35may vary greatly with the tolerances of the board30, screws32, integrated circuit package1and heat sink20.

The gap35may be filled with air, which generally has lower thermal conductivity than the case11of the integrated circuit package1and heat sink20. The result is that heat transfer from the integrated circuit package1to the heat sink20via the gap35may be inefficient. A layer of thermal interface material (not shown) may therefore be used to fill the gap35to compensate for the tolerances. The thermal interface material is a thermally conductive material such as a thermal paste, and provides a thermal coupling between the case11of the integrated circuit package1and the heat sink20, in particular between the upper surface12aof the case11and the lower surface21of the heat sink20. Heat may therefore be more efficiently transferred between the integrated circuit package1and the heat sink20than if the gap were filled only with air.

The thickness of the layer of thermal interface material depends on the magnitude of the tolerances and the type of thermal interface material used. The thickness of the layer of thermal interface material should be selected so that it fills the gap35without exerting too much stress on the package1or board30.

The thermal resistance of the gap35may be reduced by selecting a thermal interface material with a higher thermal conductivity or by trying to minimise the tolerances. However, as heat generation has increased with the increased miniaturisation of integrated circuits, the development of more thermally conductive thermal interface materials has not necessarily kept pace. Furthermore, highly thermally conductive thermal interface materials tend to be harder, so they may need a larger gap35to operate and to minimise compression stress on components of the board30.

FIG. 3illustrates an apparatus according to exemplary embodiments.

The apparatus comprises an integrated circuit package1, which comprises a case11containing at least one integrated circuit, as described in relation toFIG. 1A,FIG. 1B,FIG. 1C, andFIG. 1D. The package1may be mounted on a board30such as a printed circuit board, for example by soldering or another known method.

The integrated circuit package1also comprises a fastener40. The fastener40is configured to fasten the case11of the integrated circuit package1to a heat sink20. The case11is fastened to the heat sink20such that they are attached together, and hence the integrated circuit package1and heat sink20are attached together. Heat can therefore be transferred from the integrated circuit to the heat sink20, via the case11.

In some examples, the fastener40may be configured to fasten the case11to the heat sink20reversibly, such that the case11and heat sink20may be unfastened at a later stage. In other examples, the fastener40may be configured to fasten the case11to the heat sink20permanently, such that the case11and heat sink20cannot be unfastened using reasonable force.

The fastener40may be configured to mechanically cooperate with a corresponding feature of the heat sink20so that the case11is fastened to the heat sink20.

FIG. 3shows the fastener40fastening the case11to the heat sink20.

The fastener40may be integrally formed with the case11. For example, the fastener40may be integrally formed during manufacture of the case11, such as during a moulding process.

The fastener40may be mounted on the case11, for example on the upper surface12aof the case11or a side surface13a,13b,13cand13dof the case11. For example, the fastener40may be attached to the case11by an adhesive such as glue or resin, or by welding.

FIG. 3shows the fastener40comprising a plurality of screws41a,41b. Each screw41a,41bis configured to mechanically cooperate with a corresponding fastener25of the heat sink20such that the case11and heat sink20are fastened together. For example, each screw41a,41bmay couple with a corresponding female thread contained within an aperture26a,26bof the heat sink20, as shown inFIG. 3. In other examples, each screw41a,41bmay be configured to pass through a corresponding aperture26a,26bof the heat sink20before mechanically cooperating with a nut (not shown) on the other side of the heat sink20.

In the example shown inFIG. 3, the case11of the integrated circuit package1comprises a plurality of apertures42a,42bcorresponding to the plurality of screws41a,41b. Each screw41a,41bpasses through a respective aperture42a,42bof the case11followed by a respective aperture26a,26bof the heat sink20until a head of the screw41a,41bcontacts part of the case11adjacent the aperture42a,42b. In some examples, the screws41a,41bmay pass through corresponding apertures (not shown) in the board30.

The fastener40may be configured to couple the case11to the heat sink20such that a surface of the case11(i.e. the upper surface12a) contacts a surface of the heat sink20(i.e. the lower surface21). In some examples, a layer of thermal interface material (not shown) may be provided between the lower surface21of the heat sink20and the upper surface12aof the case11, such that thermal coupling between the case11and the heat sink20is increased.

Although not shown inFIG. 3, a lid50may be mounted to the upper surface12aof the case11as described later with reference toFIG. 4. A layer of thermal interface material may be provided between the lid50and the upper surface12aof the case11, to thermally couple the lid50to the case11. A layer of thermal interface material may also be provided between the lid50and the lower surface21of the heat sink20, to thermally couple the lid50to the heat sink20.

The fastener40may comprise at least one screw41a,41bor at least one female screw thread. Although screws41a,41bhave been discussed as the exemplary fastener40in relation toFIG. 3, other suitable means could be used as the fastener40instead. For example, the fastener40could comprise one or more clips, locks, rivets, latches or the like.

The fastener40is configured to mechanically cooperate with a corresponding fastener25of the heat sink20such that the case11is fastened to the heat sink20. For example where the fastener40comprises one or more screws41a,41b, each screw41a,41bis configured to mechanically cooperate with a corresponding female screw thread of the heat sink20. Where the fastener40comprises a female screw thread, the female screw thread is configured to mechanically cooperate with a screw of the heat sink20.

Fastening the case11, and hence the integrated circuit package1, to the heat sink20using the fastener40may reduce the tolerances between the heat sink20and integrated circuit package1and may reduce the gap35between the heat sink20and case11. The dissipation of heat from the case11to the heat sink20may be improved. A thin layer of thermal interface material may be provided between the upper surface12aof the case11and the lower surface21of the heat sink20.

FIG. 3shows that the heat sink20is also coupled to the board30by a plurality of screws32, or other coupling means. However, this is optional, and the heat sink20does not need to be directly coupled to the board30.

FIG. 4is an exploded view of an apparatus according to exemplary embodiments. As discussed in relation toFIG. 3, the apparatus comprises an integrated circuit package1, which itself comprises a case11containing at least one integrated circuit. The package1may be configured to be mounted on the board30, for example by soldering or another known method, such that a lower surface12bof the case11is adjacent an upper surface31of the board30.

FIG. 4shows the apparatus further comprising a lid50, as discussed previously in relation toFIG. 3. The lid50is configured to be mounted adjacent the upper surface12aof the case11such that a surface of the lid50is parallel to the upper surface12aof the case11. The lid50is thermally conductive and is configured to dissipate heat from the case11. The dissipated heat is transferred from the case11to the heat sink20via the lid50.

The lid50may comprise a plate made from a metal such as aluminium or copper, or a thermally conductive composite. For example, aluminium may be chosen for low power applications while copper may be chosen for moderate power applications. In some examples, the lid50may comprise a heat pipe, such as a micro heat pipe, or a vapour chamber. A heat pipe or vapour chamber may be chosen for high power applications. In some examples, the lid50may be configured to circulate cooling liquid.

The lid50may be directly coupled to the case11. For example, the lid50may be mounted to the upper surface12aof the case11using an adhesive such as glue. A layer of thermal interface material may be provided between the lid50and the upper surface12aof the case11, to thermally couple the lid50to the case11. The lid50may be mounted on the case11before the integrated circuit package1is fastened to the heat sink20.

FIG. 4shows the lid50comprising a plurality of apertures51a,b,c,dconfigured to each receive a respective screw41a,b,c,d. In this example four screws41a,b,c,dand four respective apertures51a,b,c,dare shown, however another number of screws41a,b,c,dand respective apertures51a,b,c,dmay be used.FIG. 4shows the apertures51a,b,c,dare arranged adjacent a periphery53of the lid, and hence adjacent a periphery of the upper surface12aof the case11. This ensures a secure coupling between the case11and the heat sink20once the heat sink20is installed, with a good tolerance.

A lower surface21of the heat sink20is arranged adjacent an upper surface54of the lid50—the opposite surface of the lid50to the case11. The heat sink20is fastened to the case11by the screws41a,b,c,dand apertures51a,b,c,d. That is, each screw41a,b,c,dis configured to pass through a respective aperture33a,b,c,din the board30, followed by a respective aperture51a,b,c,dof the lid50, followed by a respective aperture26a,b,c,din the lower surface21of the heat sink20. Each aperture26a,b,c,din the heat sink20comprises a female thread (not shown) configured to engage with the male thread of a respective screw41a,b,c,d. Thus, when each screw41a,b,c,dis screwed into the respective aperture26a,b,c,dof the heat sink20, the screw41a,b,c,dis held in place by the female thread.

The heat sink20shown inFIG. 4is a straight fin heat sink comprising a plurality of fins27extending perpendicularly from an upper surface28of the heat sink20, opposite the lower surface21of the heat sink20. However, this heat sink20is shown by way of example only, and other types of heat sink20may be used instead, such as pin heat sinks and flared fin heat sinks.

A layer of thermal interface material may be provided between the lower surface21of the heat sink20and the upper surface12aof the case11.

FIGS. 5A and 5Brespectively show side-view cut-outs and perspective view cut-outs of the apparatus ofFIG. 4once the heat sink20, lid50and board30have been fastened together by the screws41a,b,c,d.

Again, although screws41a,b,c,dhave been discussed as the exemplary fastener40in relation toFIGS. 4, 5A and 5B, a different fastener40could be used instead. For example, the fastener40could comprise one or more clips, locks, rivets, latches or the like.

FIGS. 6A, 6B and 6Cillustrate the thermal benefit of example embodiments of the present application.

FIG. 6Ashows a prior art example of an integrated circuit package1and a heat sink20. An integrated circuit package1is mounted on a board30A lid50may be located between the upper surface12aof the case11of the integrated circuit package1and the lower surface21of the heat sink20. A first layer of thermal interface material61may be provided in the gap66between the upper surface12aof the case11and the lid50. The heat sink20is arranged such that a lower surface21of the heat sink20is adjacent an upper surface of the lid50. A second layer of thermal interface material62may be provided in the gap67between the heat sink20and the lid50. The thermal interface material of the first layer61and the second layer62may be the same type of thermal interface material or different types of thermal interface material.

The thermal resistance RTIMof a thermal interface layer may be derived using the following equation:

where t is the thickness of the thermal interface layer, A is the cross sectional area of the thermal interface layer, and k is the thermal conductivity of the thermal interface layer.

FIG. 6Bshows an apparatus in accordance with example embodiments. As forFIG. 6A, the integrated circuit package1is mounted on a board30A lid50is mounted on the case11of the integrated circuit package1such that a lower surface55of the lid50is adjacent an upper surface12aof the case11. A first layer of thermal interface material61may be provided in the gap66between the upper surface12aof the case11and the lower surface55of the lid50. The first layer of thermal interface material61may have the same thickness t2as the thickness t1of the first layer of thermal interface material61shown inFIG. 6A, or a smaller thickness. In some examples, there may be no interface material61provided in the gap66between the upper surface12aof the case11and the lower surface55of the lid50.

However, unlikeFIG. 6A,FIG. 6Bshows that the heat sink20is fastened to the lid20by a fastener40, in this case a plurality of screws41a,b. A second layer of thermal interface material62may still be provided in the gap67between the heat sink20and the lid50, however the thickness t3of the second layer of thermal interface material62may now be smaller than the thickness t4of the second layer of thermal interface material62shown inFIG. 6A. The result is that RTIMmay be reduced inFIG. 6Bas compared toFIG. 6A.

FIG. 6Cis similar toFIG. 6B, however here the lid55may also contact upper surface31of the circuit board30, in a similar manner as shown inFIGS. 5A and 5B. The screws41a,bpass through the circuit board30in a similar manner as shown inFIGS. 4A and 4B, followed by respective apertures51a,bin the lid50and apertures26a,bin the heat sink20, to fasten the case to a heat sink. RTIM may be further reduced by increasing the cross sectional area A of the lid50, in particular the lower surface55of the lid50, or by using a highly thermally conductive lid50such as a lid50comprising a micro channel heat pipe or vapour chamber.

According to examples, there is also provided a method comprising providing an apparatus as discussed previously, and fastening a heat sink20to the case11of the apparatus using the fastener40of the apparatus. For example, the method may involve screwing the heat sink20to the case11using one or more screws52such that the heat sink20is fastened to the case11, and hence the integrated circuit package1.

According to examples, there is also provided a system comprising an apparatus as previously discussed and a heat sink20fastened to the case11of the apparatus using the fastener40of the apparatus.

Some exemplary devices which may use a System on a Chip (SoC) include smartphones, televisions, games consoles, and personal computers, including desktops, laptops and tablets. These devices may comprise an apparatus or system as described herein.

It will be appreciated that the above described example embodiments are purely illustrative and are not limiting on the scope of the invention. Other variations and modifications will be apparent to persons skilled in the art upon reading the present application.

Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or any generalization thereof and during the prosecution of the present application or of any application derived therefrom, new claims may be formulated to cover any such features and/or combination of such features.