Patent Publication Number: US-2019189532-A1

Title: Integrated circuit package and fastener

Description:
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. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       For a more complete understanding of the apparatuses, systems and methods described herein, reference is now made to the following description taken in connection with the accompanying drawings in which: 
         FIG. 1A  is a perspective view of an integrated circuit package containing an integrated circuit suitable for use in exemplary embodiments; 
         FIG. 1B  is a perspective view of an integrated circuit package containing an integrated circuit suitable for use in exemplary embodiments; 
         FIG. 1C  is a schematic cross-sectional view of the integrated circuit package of  FIG. 1B ; 
         FIG. 1D  is a schematic cross-sectional view of a flip chip ball grid array integrated circuit package suitable for use in exemplary embodiments; 
         FIG. 2  is a cross-sectional illustration of a heat sink mounted on a board for dissipating heat from an integrated circuit package; 
         FIG. 3  is a cross-sectional illustration of an integrated circuit package fastened to a heat sink in accordance with exemplary embodiments; 
         FIG. 4  is an exploded perspective view of an integrated circuit package fastened to a heat sink in accordance with exemplary embodiments; 
         FIG. 5A  is a cross-sectional illustration of the integrated circuit package and heat sink shown in  FIG. 4  after fastening; 
         FIG. 5B  is a cross-sectional perspective illustration of the integrated circuit package and heat sink shown in  FIG. 4  after fastening; 
         FIG. 6A  is a cross-sectional illustration of an integrated circuit package and a heat sink; 
         FIG. 6B  is a cross-sectional illustration of an integrated circuit package fastened to a heat sink in accordance with exemplary embodiments; 
         FIG. 6C  is a cross-sectional illustration of an integrated circuit package fastened to a heat sink in accordance with exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the description and drawings, like reference numerals may refer to like elements throughout. 
       FIG. 1A  is a perspective view of an exemplary integrated circuit package  1 . The integrated circuit package  1  comprises a case  11 , which contains at least one integrated circuit comprising a die (not shown). The case  11  of the integrated circuit package  1  is configured to protect the integrated circuit from physical damage and corrosion. The case  11  of the integrated circuit package  1  comprises an upper surface  12   a  and a lower surface  12   b . The upper surface  12   a  and the lower surface  12   b  may be flat and arranged parallel to each other such that the upper surface  12   a  is opposite the lower surface  12   b . The case  11  may 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. 1A  shows the case  11  further comprising four side surfaces  13   a ,  13   b ,  13   c  and  13   d , each adjacent the upper surface  12   a  and the lower surface  12   b , however the case  11  may have more or fewer sides than this. A plurality of pins  14 , also known as legs, protrude from the sides  13   a ,  13   b ,  13   c  and  13   d  and extend downwards, away from the upper surface  12   a . The pins  14  may 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 package  1  is fastened to the board. The pins  14  may be soldered to the board. The pins  14  are configured to provide an electrical connection between the integrated circuit contained within the integrated circuit package  1  and one or more conductive components on the board. 
     The configuration of the pins  14  shown in  FIG. 1A  is by way of example only, and other known configurations may be used. For example, the plurality of pins  14  may extend from only two, opposite sides of the case  11  (such as for a dual in-line package). In other examples, the pins  14  may protrude from the lower surface  12   b  of the case  11 . The term pins  14  should be taken to also include similar connectors such as pads or balls, as used in a ball grid array, for example. 
       FIG. 1B  shows a ball grid array (BGA) integrated circuit package  1 . The integrated circuit package  1  of  FIG. 1B  is similar to the integrated circuit package  1  of  FIG. 1A , however here the plurality of pins  14  project from the lower surface  12   b  of the case  11 . The plurality of pins  14 , in this case comprising balls, are arranged in an array across the lower surface  12   b  of the case. As for the integrated circuit package  1  of  FIG. 1A , the pins  14  may be soldered to a board, and are configured to provide an electrical connection between the integrated circuit contained within the integrated circuit package  1  and one or more conductive components on the board. The ball grid array arrangement allows a higher density of pins  14  to be present on the integrated circuit package  1 . 
       FIG. 1C  shows a schematic cross-sectional view of the integrated circuit package  1  of  FIG. 1B , along the line X-X′ of  FIG. 1B , however the configuration will be similar for the integrated circuit package of  FIG. 1A . 
     The integrated circuit comprises a die  15 , which is mounted on a substrate  16  and is electrically connected to the pins  14  by respective bond wires  17 . 
     The integrated circuit package  1  illustrated in  FIG. 1C  is by shown by way of example, and other types and configurations of integrated circuit package  1  may be used with embodiments of the present disclosure. For example, the integrated circuit package  1  may be of a flip chip type, as illustrated in  FIG. 1D . 
       FIG. 1D  shows an exemplary flip chip ball grid array package  1  suitable for use with the present disclosure. The general structure is similar to that shown in  FIG. 1C . However in the flip chip package  1  shown in  FIG. 1D , the die  15  is upside down relative to the die  15  shown in  FIG. 1C , with the die  15  being electrically connected to the pins  14  (in this case the pins  14  being balls of a ball grid array) via solder balls  18  instead of bond wires  17 . The solder balls  18  are in a gap between the die  15  and a substrate  16 . The remainder of the gap may be at least partially filled with an underfill  19 , for example made from epoxy. The top of the die  15  may be covered by a lid such as a mould cap, forming the case  11  of the package  1 . Heat from the die  15  may therefore be dissipated directly to the lid. Instead of a mould, the lid may be a metal lid covering the die  15 , in some cases with a layer of thermal grease between the die  15  and metal lid. 
     During use, electrical energy supplied to the integrated circuit is converted into heat energy, which is dissipated through the case  11  of the integrated circuit package  1  to 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. 2  illustrates a current solution for dissipating heat from an integrated circuit using a heat sink  20 . An integrated circuit is contained within the integrated circuit package  1 . The package  1  is mounted on a board  30  such as a printed circuit board, for example by soldering or another known means. The package  1  is mounted such that the lower surface  12   b  of the case  11  is adjacent an upper surface  31  of the board  30 . 
     The heat sink  20  may be mounted directly to the board  30  using screws  32  such that a lower surface  21  of the heat sink  20  is adjacent the upper surface  12   a  of the case  11  of the integrated circuit package  1 . By mounting the heat sink  20  to the board  30  in this way, a gap  35  may be formed between the integrated circuit package  1  and the heat sink  20 , in this case between the upper surface  12   a  of the case  11  of the integrated circuit package  1  and the lower surface  21  of the heat sink  20 . This gap  35  may be the result of tolerances in the dimensions of various components such as the board  30 , screws  32 , integrated circuit package  1  and heat sink  20 . 
     The size of the gap  35  may vary greatly with the tolerances of the board  30 , screws  32 , integrated circuit package  1  and heat sink  20 . 
     The gap  35  may be filled with air, which generally has lower thermal conductivity than the case  11  of the integrated circuit package  1  and heat sink  20 . The result is that heat transfer from the integrated circuit package  1  to the heat sink  20  via the gap  35  may be inefficient. A layer of thermal interface material (not shown) may therefore be used to fill the gap  35  to 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 case  11  of the integrated circuit package  1  and the heat sink  20 , in particular between the upper surface  12   a  of the case  11  and the lower surface  21  of the heat sink  20 . Heat may therefore be more efficiently transferred between the integrated circuit package  1  and the heat sink  20  than 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 gap  35  without exerting too much stress on the package  1  or board  30 . 
     The thermal resistance of the gap  35  may 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 gap  35  to operate and to minimise compression stress on components of the board  30 . 
       FIG. 3  illustrates an apparatus according to exemplary embodiments. 
     The apparatus comprises an integrated circuit package  1 , which comprises a case  11  containing at least one integrated circuit, as described in relation to  FIG. 1A ,  FIG. 1B ,  FIG. 1C , and  FIG. 1D . The package  1  may be mounted on a board  30  such as a printed circuit board, for example by soldering or another known method. 
     The integrated circuit package  1  also comprises a fastener  40 . The fastener  40  is configured to fasten the case  11  of the integrated circuit package  1  to a heat sink  20 . The case  11  is fastened to the heat sink  20  such that they are attached together, and hence the integrated circuit package  1  and heat sink  20  are attached together. Heat can therefore be transferred from the integrated circuit to the heat sink  20 , via the case  11 . 
     In some examples, the fastener  40  may be configured to fasten the case  11  to the heat sink  20  reversibly, such that the case  11  and heat sink  20  may be unfastened at a later stage. In other examples, the fastener  40  may be configured to fasten the case  11  to the heat sink  20  permanently, such that the case  11  and heat sink  20  cannot be unfastened using reasonable force. 
     The fastener  40  may be configured to mechanically cooperate with a corresponding feature of the heat sink  20  so that the case  11  is fastened to the heat sink  20 . 
       FIG. 3  shows the fastener  40  fastening the case  11  to the heat sink  20 . 
     The fastener  40  may be integrally formed with the case  11 . For example, the fastener  40  may be integrally formed during manufacture of the case  11 , such as during a moulding process. 
     The fastener  40  may be mounted on the case  11 , for example on the upper surface  12   a  of the case  11  or a side surface  13   a ,  13   b ,  13   c  and  13   d  of the case  11 . For example, the fastener  40  may be attached to the case  11  by an adhesive such as glue or resin, or by welding. 
       FIG. 3  shows the fastener  40  comprising a plurality of screws  41   a ,  41   b . Each screw  41   a ,  41   b  is configured to mechanically cooperate with a corresponding fastener  25  of the heat sink  20  such that the case  11  and heat sink  20  are fastened together. For example, each screw  41   a ,  41   b  may couple with a corresponding female thread contained within an aperture  26   a ,  26   b  of the heat sink  20 , as shown in  FIG. 3 . In other examples, each screw  41   a ,  41   b  may be configured to pass through a corresponding aperture  26   a ,  26   b  of the heat sink  20  before mechanically cooperating with a nut (not shown) on the other side of the heat sink  20 . 
     In the example shown in  FIG. 3 , the case  11  of the integrated circuit package  1  comprises a plurality of apertures  42   a ,  42   b  corresponding to the plurality of screws  41   a ,  41   b . Each screw  41   a ,  41   b  passes through a respective aperture  42   a ,  42   b  of the case  11  followed by a respective aperture  26   a ,  26   b  of the heat sink  20  until a head of the screw  41   a ,  41   b  contacts part of the case  11  adjacent the aperture  42   a ,  42   b . In some examples, the screws  41   a ,  41   b  may pass through corresponding apertures (not shown) in the board  30 . 
     The fastener  40  may be configured to couple the case  11  to the heat sink  20  such that a surface of the case  11  (i.e. the upper surface  12   a ) contacts a surface of the heat sink  20  (i.e. the lower surface  21 ). In some examples, a layer of thermal interface material (not shown) may be provided between the lower surface  21  of the heat sink  20  and the upper surface  12   a  of the case  11 , such that thermal coupling between the case  11  and the heat sink  20  is increased. 
     Although not shown in  FIG. 3 , a lid  50  may be mounted to the upper surface  12   a  of the case  11  as described later with reference to  FIG. 4 . A layer of thermal interface material may be provided between the lid  50  and the upper surface  12   a  of the case  11 , to thermally couple the lid  50  to the case  11 . A layer of thermal interface material may also be provided between the lid  50  and the lower surface  21  of the heat sink  20 , to thermally couple the lid  50  to the heat sink  20 . 
     The fastener  40  may comprise at least one screw  41   a ,  41   b  or at least one female screw thread. Although screws  41   a ,  41   b  have been discussed as the exemplary fastener  40  in relation to  FIG. 3 , other suitable means could be used as the fastener  40  instead. For example, the fastener  40  could comprise one or more clips, locks, rivets, latches or the like. 
     The fastener  40  is configured to mechanically cooperate with a corresponding fastener  25  of the heat sink  20  such that the case  11  is fastened to the heat sink  20 . For example where the fastener  40  comprises one or more screws  41   a ,  41   b , each screw  41   a ,  41   b  is configured to mechanically cooperate with a corresponding female screw thread of the heat sink  20 . Where the fastener  40  comprises a female screw thread, the female screw thread is configured to mechanically cooperate with a screw of the heat sink  20 . 
     Fastening the case  11 , and hence the integrated circuit package  1 , to the heat sink  20  using the fastener  40  may reduce the tolerances between the heat sink  20  and integrated circuit package  1  and may reduce the gap  35  between the heat sink  20  and case  11 . The dissipation of heat from the case  11  to the heat sink  20  may be improved. A thin layer of thermal interface material may be provided between the upper surface  12   a  of the case  11  and the lower surface  21  of the heat sink  20 . 
       FIG. 3  shows that the heat sink  20  is also coupled to the board  30  by a plurality of screws  32 , or other coupling means. However, this is optional, and the heat sink  20  does not need to be directly coupled to the board  30 . 
       FIG. 4  is an exploded view of an apparatus according to exemplary embodiments. As discussed in relation to  FIG. 3 , the apparatus comprises an integrated circuit package  1 , which itself comprises a case  11  containing at least one integrated circuit. The package  1  may be configured to be mounted on the board  30 , for example by soldering or another known method, such that a lower surface  12   b  of the case  11  is adjacent an upper surface  31  of the board  30 . 
       FIG. 4  shows the apparatus further comprising a lid  50 , as discussed previously in relation to  FIG. 3 . The lid  50  is configured to be mounted adjacent the upper surface  12   a  of the case  11  such that a surface of the lid  50  is parallel to the upper surface  12   a  of the case  11 . The lid  50  is thermally conductive and is configured to dissipate heat from the case  11 . The dissipated heat is transferred from the case  11  to the heat sink  20  via the lid  50 . 
     The lid  50  may 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 lid  50  may 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 lid  50  may be configured to circulate cooling liquid. 
     The lid  50  may be directly coupled to the case  11 . For example, the lid  50  may be mounted to the upper surface  12   a  of the case  11  using an adhesive such as glue. A layer of thermal interface material may be provided between the lid  50  and the upper surface  12   a  of the case  11 , to thermally couple the lid  50  to the case  11 . The lid  50  may be mounted on the case  11  before the integrated circuit package  1  is fastened to the heat sink  20 . 
       FIG. 4  shows the lid  50  comprising a plurality of apertures  51   a,b,c,d  configured to each receive a respective screw  41   a,b,c,d . In this example four screws  41   a,b,c,d  and four respective apertures  51   a,b,c,d  are shown, however another number of screws  41   a,b,c,d  and respective apertures  51   a,b,c,d  may be used.  FIG. 4  shows the apertures  51   a,b,c,d  are arranged adjacent a periphery  53  of the lid, and hence adjacent a periphery of the upper surface  12   a  of the case  11 . This ensures a secure coupling between the case  11  and the heat sink  20  once the heat sink  20  is installed, with a good tolerance. 
     A lower surface  21  of the heat sink  20  is arranged adjacent an upper surface  54  of the lid  50 —the opposite surface of the lid  50  to the case  11 . The heat sink  20  is fastened to the case  11  by the screws  41   a,b,c,d  and apertures  51   a,b,c,d . That is, each screw  41   a,b,c,d  is configured to pass through a respective aperture  33   a,b,c,d  in the board  30 , followed by a respective aperture  51   a,b,c,d  of the lid  50 , followed by a respective aperture  26   a,b,c,d  in the lower surface  21  of the heat sink  20 . Each aperture  26   a,b,c,d  in the heat sink  20  comprises a female thread (not shown) configured to engage with the male thread of a respective screw  41   a,b,c,d . Thus, when each screw  41   a,b,c,d  is screwed into the respective aperture  26   a,b,c,d  of the heat sink  20 , the screw  41   a,b,c,d  is held in place by the female thread. 
     The heat sink  20  shown in  FIG. 4  is a straight fin heat sink comprising a plurality of fins  27  extending perpendicularly from an upper surface  28  of the heat sink  20 , opposite the lower surface  21  of the heat sink  20 . However, this heat sink  20  is shown by way of example only, and other types of heat sink  20  may 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 surface  21  of the heat sink  20  and the upper surface  12   a  of the case  11 . 
       FIGS. 5A and 5B  respectively show side-view cut-outs and perspective view cut-outs of the apparatus of  FIG. 4  once the heat sink  20 , lid  50  and board  30  have been fastened together by the screws  41   a,b,c,d.    
     Again, although screws  41   a,b,c,d  have been discussed as the exemplary fastener  40  in relation to  FIGS. 4, 5A and 5B , a different fastener  40  could be used instead. For example, the fastener  40  could comprise one or more clips, locks, rivets, latches or the like. 
       FIGS. 6A, 6B and 6C  illustrate the thermal benefit of example embodiments of the present application. 
       FIG. 6A  shows a prior art example of an integrated circuit package  1  and a heat sink  20 . An integrated circuit package  1  is mounted on a board  30  A lid  50  may be located between the upper surface  12   a  of the case  11  of the integrated circuit package  1  and the lower surface  21  of the heat sink  20 . A first layer of thermal interface material  61  may be provided in the gap  66  between the upper surface  12   a  of the case  11  and the lid  50 . The heat sink  20  is arranged such that a lower surface  21  of the heat sink  20  is adjacent an upper surface of the lid  50 . A second layer of thermal interface material  62  may be provided in the gap  67  between the heat sink  20  and the lid  50 . The thermal interface material of the first layer  61  and the second layer  62  may be the same type of thermal interface material or different types of thermal interface material. 
     The thermal resistance R TIM  of a thermal interface layer may be derived using the following equation: 
     
       
         
           
             
               R 
               TIM 
             
             = 
             
               t 
               kA 
             
           
         
       
     
     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. 6B  shows an apparatus in accordance with example embodiments. As for  FIG. 6A , the integrated circuit package  1  is mounted on a board  30  A lid  50  is mounted on the case  11  of the integrated circuit package  1  such that a lower surface  55  of the lid  50  is adjacent an upper surface  12   a  of the case  11 . A first layer of thermal interface material  61  may be provided in the gap  66  between the upper surface  12   a  of the case  11  and the lower surface  55  of the lid  50 . The first layer of thermal interface material  61  may have the same thickness t 2  as the thickness t 1  of the first layer of thermal interface material  61  shown in  FIG. 6A , or a smaller thickness. In some examples, there may be no interface material  61  provided in the gap  66  between the upper surface  12   a  of the case  11  and the lower surface  55  of the lid  50 . 
     However, unlike  FIG. 6A ,  FIG. 6B  shows that the heat sink  20  is fastened to the lid  20  by a fastener  40 , in this case a plurality of screws  41   a,b . A second layer of thermal interface material  62  may still be provided in the gap  67  between the heat sink  20  and the lid  50 , however the thickness t 3  of the second layer of thermal interface material  62  may now be smaller than the thickness t 4  of the second layer of thermal interface material  62  shown in  FIG. 6A . The result is that R TIM  may be reduced in  FIG. 6B  as compared to  FIG. 6A . 
       FIG. 6C  is similar to  FIG. 6B , however here the lid  55  may also contact upper surface  31  of the circuit board  30 , in a similar manner as shown in  FIGS. 5A and 5B . The screws  41   a,b  pass through the circuit board  30  in a similar manner as shown in  FIGS. 4A and 4B , followed by respective apertures  51   a,b  in the lid  50  and apertures  26   a,b  in the heat sink  20 , to fasten the case to a heat sink. RTIM may be further reduced by increasing the cross sectional area A of the lid  50 , in particular the lower surface  55  of the lid  50 , or by using a highly thermally conductive lid  50  such as a lid  50  comprising 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 sink  20  to the case  11  of the apparatus using the fastener  40  of the apparatus. For example, the method may involve screwing the heat sink  20  to the case  11  using one or more screws  52  such that the heat sink  20  is fastened to the case  11 , and hence the integrated circuit package  1 . 
     According to examples, there is also provided a system comprising an apparatus as previously discussed and a heat sink  20  fastened to the case  11  of the apparatus using the fastener  40  of 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.