Abstract:
A semiconductor device package which includes a semiconductor package, a semiconductor device joined to the semiconductor package; and a lid to be placed over the semiconductor device and joined to the semiconductor package. The lid includes: a block of a first material having a first surface and a second surface, the second surface facing the semiconductor device, the block having perforations extending between the first surface and the second surface; inserts for filling the perforations, each of the inserts being made of a second material, at least one of the inserts protrudes beyond the second surface towards the semiconductor device; and a bonding material to bond the inserts to the block so that the at least one of the inserts protrudes beyond the second surface towards the semiconductor device. Also included is a method of assembling a semiconductor device package.

Description:
BACKGROUND 
     The present invention relates generally to integrated circuit heat dissipation devices, and, more particularly, to a semiconductor package lid that has high thermal conductivity inserts for alleviating thermal hot spots from semiconductor devices. 
     The semiconductor industry has seen tremendous technological advances in recent years that have permitted dramatic increases in circuit density and complexity, as well as equally dramatic increases in power consumption and package sizes. 
     Present semiconductor technology now permits single-chip and multi-chip microprocessors with many millions of transistors, operating at speeds of tens (or even hundreds) of MIPS (millions of instructions per second), to be packaged in relatively small, air-cooled semiconductor device packages. Because semiconductor devices (also referred to as microprocessors) and other related components are designed with increased capabilities and increased speed, additional heat is generated from these components. 
     As packaged units and semiconductor device sizes shrink, the amount of heat energy given off by a component for a given unit of surface area is also on the rise. The majority of the heat generated by a component, such as a semiconductor device for example, must be removed from the component in order to keep the component at an acceptable or target operating temperature. If the heat generated is not removed from the component, the heat produced can drive the temperature of the component to levels that may result in early failure of the component. 
     High end server products continue to improve system performance by using multi-core semiconductor devices. The high power densities in the core areas may generate local hot spots across the semiconductor device. Elevated temperatures impact the reliability and performance of the semiconductor device. The temperature in the semiconductor device including local hot spots in the semiconductor device cores must be managed to attain the desired reliability and performance. 
     BRIEF SUMMARY 
     The various advantages and purposes of the exemplary embodiments as described above and hereafter are achieved by providing, according to a first aspect of the exemplary embodiments, a semiconductor device package comprising: a semiconductor package; a semiconductor device joined to the semiconductor package; and a lid to be placed over the semiconductor device and joined to the semiconductor package, the lid comprising: a block of a first material having a first surface and a second surface, the second surface facing the semiconductor device, the block having a plurality of perforations extending between the first surface and the second surface; a plurality of inserts for filling the perforations, each of the inserts being made of a second material, at least one of the plurality of inserts protrudes beyond the second surface towards the semiconductor device; and a bonding material to bond the plurality of inserts to the block so that the at least one of the plurality of inserts protrudes beyond the second surface towards the semiconductor device. 
     According to a second aspect of the exemplary embodiments, there is provided a lid for a semiconductor device package comprising: a block of a first material having a first surface and a second surface, the second surface facing a semiconductor device, the block having a plurality of perforations extending between the first surface and the second surface; a plurality of inserts for filling the perforations, each of the inserts being made of a second material, at least one of the plurality of inserts protruding beyond the second surface; and a bonding material to bond the plurality of inserts to the block so that the at least one of the plurality of inserts protrudes beyond the second surface towards the semiconductor device. 
     According to a third aspect of the exemplary embodiments, there is provided a method of assembling a semiconductor device package comprising: obtaining a semiconductor package having a semiconductor device joined to the semiconductor package; obtaining a lid for the semiconductor device package comprising a block of a first material having a first surface and a second surface, the second surface facing the semiconductor device, the block having a plurality of perforations extending between the first surface and the second surface; positioning the lid on the semiconductor device and the semiconductor package; inserting a plurality of inserts into the perforations, each of the inserts being made of a second material, at least one of the plurality of inserts protrudes beyond the second surface so as to contact the semiconductor device; applying a bonding material to bond the plurality of inserts to the lid; applying a force to the lid and the at least one of the plurality of inserts so that the at least one insert maintains contact with the semiconductor device while the bonding material hardens; removing the force and separating the lid from the semiconductor device; applying a thermal interface material to the lid or the semiconductor device; positioning the lid on the semiconductor device and the semiconductor package; applying an adhesive material between the lid and the semiconductor package; applying a force to the lid to force the at least one of the plurality of inserts into the thermal interface material; and curing the adhesive material between the lid and the semiconductor package. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       The features of the exemplary embodiments believed to be novel and the elements characteristic of the exemplary embodiments are set forth with particularity in the appended claims. The Figures are for illustration purposes only and are not drawn to scale. The exemplary embodiments, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an isometric view showing a top view of a lid having inserts and a semiconductor package. 
         FIG. 2  is an isometric view showing a bottom view of the lid in  FIG. 1 . 
         FIG. 3A  is a cross sectional view of an assembled semiconductor module having a lid with thermally conductive inserts. 
         FIG. 3B  is a cross sectional view of an assembled semiconductor module having a lid with thermally conductive inserts similar to  FIG. 3A  but also including a lid adhesive, thermal interface materials and a cold plate. 
         FIG. 4  is an isometric view of the lid and semiconductor package in a fixture in preparation for setting the height of the inserts with respect to the chip surface on the semiconductor package. 
         FIG. 5  is an exploded view of the lid, semiconductor package and fixture of  FIG. 4 . 
         FIG. 6  is a process flow for lid and insert bonding of the semiconductor module of  FIG. 3A . 
         FIG. 7  is a process flow for module capping assembly of the semiconductor module of  FIG. 3B . 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments integrate highly conductive insert material into an existing heat spreading lid (hereafter just lid). The insert may be made from a highly conductive material such as but not limited to graphite, copper or chemically vapor deposited (CVD) diamond. The insert position in the lid may be tailored so as to be positioned directly over hot spot locations. The thermal Interface material (TIM) bondline thickness (BLT) (i.e., the thickness of the thermal interface material between the insert and the semiconductor device) may also be minimized at the hot spot locations so as to conform to the semiconductor device surface to provide better thermal performance. There may be a thermal improvement of about 2° C. in the semiconductor device hot spot area as compared to assemblies without the inserts in the lid. 
     The exemplary embodiments may also be ideal for semiconductor devices on organic packaging because the inserts may also compensate for the warpage induced interface variation in TIM BLT. 
     Referring to the Figures in more detail, and particularly referring to  FIG. 1 , there is shown an exploded view of a semiconductor module  10  according to the exemplary embodiments. The semiconductor module  10  may include a semiconductor package  12  which may be a ceramic or nonceramic material such as an organic package. The exemplary embodiments may be applicable to any type of packaging suitable for supporting and electrically connecting to a semiconductor device. 
     On semiconductor package  12  may be one or more semiconductor devices  14 , electrically and physically connected to the semiconductor package  12 . In  FIG. 1 , for purposes of illustration and not limitation, there is shown one semiconductor device  14 . 
     Assembled above semiconductor device  14  may be a lid  16 . The lid  16  may typically be made from a thermally conductive material such as copper or a copper alloy. Pure copper (99.9% copper) is most preferred for its high thermal conductivity. The lid  16  may have at least one perforation  18  extending entirely through the lid  16 . For purposes of illustration and not limitation, lid  16  shown in  FIG. 1  may have six perforations  18 . Within each perforation  18  may be situated an insert  20 . 
     Inserts  20  may be made from a high thermally conductive material such as but not limited to graphite, copper or CVD diamond. The graphite may be, for example, orthotropic pyrolytic graphite. Even though the lid  16  and insert  20  may both be made from copper, the improved design of the lid  16  may lead to improved removal of heat from the semiconductor device  14  due to the reduced bondline thickness of the thermal interface material. 
     The semiconductor device  14  may be a multi-core semiconductor device. Each of the cores may lead to hot spots which may require an insert  20 . For example, the semiconductor device  14  illustrated in  FIG. 1  may be a six core semiconductor device having six hot spots requiring six inserts  20 . The number of inserts  20  need not exactly correspond with the number of cores since one or more of the cores may be disabled for one reason or another. Moreover, in semiconductor devices  14  having cores close to each other, a single insert may be used to cover one or more of the cores. While one semiconductor device  14  is shown in  FIG. 1 , there may be more than one semiconductor device  14  and each one of the semiconductor devices  14  may require one or more inserts  20 . 
     The inserts  20  may be sized to fit the core area or core areas of the semiconductor device  14 . For example, for a semiconductor device having a size of 29.8 mm by 25.6 mm, the inserts  20  may have a size of 4 mm by 4 mm with a thickness of 2.6 mm. 
       FIG. 1  shows the lid  16  from the top. The bottom of the lid  16  is shown in  FIG. 2 . The lid  16  may have a recess  22  that is sized to fit over the one or more semiconductor devices that may be joined to the semiconductor package  12 . As can also be seen in  FIG. 2 , the perforations  18  for receiving the inserts  20  extend entirely through the lid  16  and most preferably, the inserts  20  protrude passed the bottom surface  26  of the lid. 
       FIG. 3A  is a cross-section of  FIG. 1  in the direction of arrows  3 - 3  in  FIG. 1 .  FIG. 3B  shows the module  10  fully assembled. A problem with organic semiconductor packages is that the semiconductor package  12  may be cambered (i.e., not flat) which causes semiconductor device  14  to also be cambered so that good thermal contact and a uniform gap between the lid  16  and semiconductor device  14  may not be possible. The camber shown in  FIG. 3A  is somewhat exaggerated for the purpose of illustration but it can be seen that the lid  16  without the inserts  20  would only make good thermal contact with the semiconductor device  14  with a thin gap in the center of the semiconductor device  14  and not at the corners of the semiconductor device  14  due to a larger gap. The gap between the lid  16  and semiconductor device  14  at the corners of the semiconductor device  14  is larger than at the center of the semiconductor device  14  which causes poor thermal performance. Even with the presence of a thermal interface material, the lid  16  without the inserts  20  may not have a uniform thin gap and therefore not make good thermal contact with the semiconductor device  14 . 
     Lid  16  contains the six inserts  20 , three of which are shown as inserts  20 A,  20 B,  20 C. Again, six inserts in lid  16  is just for the purpose of illustration and not limitation and in practice, there may be more or less than six inserts. At least one of the inserts  20 A,  20 B,  20 C may protrude from the bottom surface  26  of the lid  16  to compensate for the camber of semiconductor package  12 . For purposes of illustration and not limitation, each of the inserts  20 A,  20 B,  20 C may protrude beyond the surface  26  of the lid  16  by a different amount. There will usually be at least one insert  20  that protrudes beyond the surface  26  of the lid  16 . Moreover, the inserts  20  may not extend beyond the upper surface  27  of the lid  16 . Typically, camber may result in a distortion of about 100 μm so that at least one of the inserts  20  in general may need to extend from the bottom surface  26  about the same amount to compensate for the camber. Because the inserts  20 A,  20 B,  20 C compensate for the different height of the semiconductor device  14  due to the camber of the semiconductor package  12 , there will be a uniform bondline thickness of the thermal interface material  24  (shown in  FIG. 3B ) at each insert  20 A,  20 B,  20 C at each hot spot. 
     Once the inserts  20  have been assembled in lid  16  by a process to be described hereafter, the inserts  20  may be bonded to the lid  16  by a bonding material  28  to hold the inserts  20  rigidly in place. The bonding material  28  may be, for example, an adhesive or more preferably a solder. The adhesive may be a silver-filled adhesive or silver-filled epoxy so that it has good thermal conductivity. Most preferred is to use a solder because of better thermal conductivity which is desirable to conduct heat between the inserts  20  and the lid  16 . Lead-free solders are preferred such as SAC  305  comprising tin (Sn), silver (Ag) and copper (Cu). If the inserts  20  are made from one of the nonmetallic materials mentioned above, it may be desirable to coat the inserts  20  with a material such as nickel, chrome or gold so that the solder may adhere better to the insert  20 . 
     In another assembly process, shown completed in  FIG. 3B , thermal interface material  24  may be applied to the semiconductor device  14  and the lid  16  may be bonded to the semiconductor package  12  by an adhesive  30 . 
     In various exemplary embodiments, there may be a heat spreader  32  in addition to the lid  16 . To maintain good thermal contact between the heat spreader  32  and the lid  16 , there may be a second thermal interface material  34 . 
     The fully assembled module with thermal interface material  24 , lid adhesive  30 , heat spreader  32  and thermal interface material  34  is shown in  FIG. 3B . 
     Referring now to  FIG. 4 , there is shown the module  10  in a fixture  40  by which the inserts  20  may be adjusted in the lid  16  and then bonded to the lid  16 . 
       FIG. 5  is an exploded isometric view of the fixture  40  shown in  FIG. 4 . 
     Fixture  40  includes a base plate  42  upon which module  10  and lid  16  may be positioned. The module  10  and lid  16  are properly aligned to the base plate  42  by locator frame  44 . Locator frame  44  may be secured to the base plate  42  by threaded fasteners  46 . Inserts  20  (not shown in  FIGS. 4 and 5 ) may be placed in perforations  18  of lid  16 . Bonding material  28  (not shown in  FIGS. 4 and 5 ) may also be applied at this time. Thereafter, load housing  48  may be affixed to the base plate  42  by threaded fasteners  50 . Within load housing  48  are threaded ball-nose spring plungers  52  which are threaded into the load housing  48 . These threaded ball-nose spring plungers  52  contact inserts  20 . A load spring  54  may apply a force to at least partially flatten out the camber from module  10 . For example, application of the load spring  54  may reduce the camber of the module  10  from about 250 μm to 100 μm but does not entirely eliminate the camber. Threaded ball-nose spring plungers  52  are threaded against the inserts  20  until the inserts  20  make contact with the semiconductor device  14 . A force of approximately 2 to 3 pounds is applied by each of the plungers  52  to the semiconductor device  14 . At this juncture, the fixture  40 , module  10  and lid  16  with inserts  20  are heated to a sufficient temperature so that the bonding material  28  is either reflowed if the bonding material is solder or cured if the bonding material is an adhesive. After cooling down, the module  10  and lid  16  with inserts  20  may be removed from the fixture  40 . The inserts  20  are now set in lid  16 . 
     The lid  16  may now be assembled to semiconductor package  12  with thermal interface material  24  and lid adhesive  30 . Fixture  40  may be used to assemble the lid  16  with inserts  20  to the semiconductor package  12  but without application of the load by plungers  52 . Either the plungers  52  may be backed out of the load housing  48  or a load housing  48  may be substituted that does not have the plungers  52 . The fixture  40  with the assembled module  10  may be heated to a predetermined temperature to cure the lid adhesive  30 . The predetermined temperature for the lid adhesive cure process is less than the melting point of the solder bonding material  28 . 
     The exemplary embodiments may be practiced with a process as described with respect to  FIGS. 6 and 7 . The reference numbers that follow refer back to the corresponding elements in  FIGS. 1 to 5 .  FIG. 6  describes the lid and insert bonding process while  FIG. 7  describes the module capping assembly process. 
     The lid and insert bonding process begins by obtaining a module  10  of a semiconductor package  12  and a semiconductor device  14  conventionally joined to the semiconductor package  12 , box  62 . The semiconductor device  14  may be conventionally underfilled with an underfill material if required. 
     A lid is obtained, box  64 , such as lid  16  described previously and shown in detail in  FIGS. 1 and 2 . The lid  16  should have the perforations  18  suitable for receiving the inserts  20 . 
     The lid  16  is positioned on the module  10 , box  66 , inserts are placed in the perforations of the lid, box  68 , and then a bonding material may be dispensed to the inserts, box  70 . 
     The assembly of module  10 , lid  16 , inserts  20  and bonding material  28  may be placed on the base plate  42  of fixture  40  followed by the locator frame  44  secured by fasteners  46 , load housing  48  secured by fasteners  50 , and plungers  52 . A suitable load may be applied by load spring  54 , box  72 , to hold the lid  16  firmly against the semiconductor package  12  which may also partly remove the camber of the module  10 . Inserts  20  may then be pushed until contact is made with the semiconductor device  14 . Approximately 2 to 3 pounds of force may be applied by the plungers  52  to the semiconductor device  14  through application of the load spring  54 . The fixture  40 , module  10  and lid  16  with inserts  20  are heated to a suitable temperature to cure the adhesive or reflow the solder, whichever is used as the bonding material for the inserts  20 . 
     The load applied by the lid load spring  54  is removed and the lid  16  with bonded inserts  20  is removed from the fixture  40  along with the module  10 , box  74 . 
     Referring now to  FIG. 7 , for module capping assembly, the lid  16  with bonded inserts  20  is assembled to semiconductor package  12 . Conventional thermal interface material  24  may be applied to the semiconductor device  14 , box  76 . 
     An adhesive  30  may be dispensed between the lid  16  and semiconductor package  12  and then the lid  16  with bonded inserts  20  may be placed on the semiconductor package  12  and semiconductor chip  14 , box  78 . A load of about 40 to 50 pounds (depending on the size of the semiconductor device) may be applied to the lid  16  so that the inserts  20  are pressed into the thermal interface material  24  and a uniform bondline thickness of the thermal interface material is obtained, box  80 . The adhesive  30  may be conventionally cured, box  82 . 
     The module capping assembly described in  FIG. 7  may use the fixture  40  described in  FIGS. 4 and 5  but without the load applied by the plungers  52  as described earlier. 
     It is noted that with the present exemplary embodiments, a bondline thickness at the center of the semiconductor device and at the corner of the semiconductor device may each be about 15 μm. Previously, the best bondline thickness of the thermal interface material that could be obtained was about 15 μm at the center of the semiconductor device and about 35-40 μm at the corner of the semiconductor device. 
     It will be apparent to those skilled in the art having regard to this disclosure that other modifications of the exemplary embodiments beyond those embodiments specifically described here may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.