Abstract:
Numerous embodiments of a heat spreader, comprised of a plurality of downset legs, which provides a simple and lower cost method of forming a heat spreader as compared to conventional methods are disclosed, as well as novel apparatus and methods for attaching the heat spreader to a substrate and a secondary device to the heat spreader, are disclosed.

Description:
BACKGROUND  
         [0001]    1. Field  
           [0002]    This disclosure relates generally to microelectronic technology, and more specifically, to apparatus used for heat dissipation in a microelectronic package and methods of fabricating the same.  
           [0003]    2. Background Information  
           [0004]    Recently, there has been rapid development in microelectronic technology and, as a result, microelectronic components are becoming smaller and circuitry within microelectronic components is becoming increasingly dense. As the circuit density increases, heat generation typically increases as well. Thus, heat dissipation is becoming more critical as the technology develops.  
           [0005]    Various techniques may typically be used to remove or dissipate heat generated by a microelectronic component, which may also be referred to as a microelectronic die. These techniques may include passive or active solutions. One such technique, which may be classified as a passive solution, involves the use of a mass of conductive material in thermal contact with a microelectronic die. This mass of conductive material may alternatively be referred to as a slug, heat spreader, or integrated heat spreader (IHS). One of the primary purposes of a heat spreader is to spread, or absorb and dissipate the heat generated by a microelectronic die. This may at least in part eliminate “hot spots” within the microelectronic die.  
           [0006]    A heat spreader may achieve thermal contact with a microelectronic die by use of a thermally conductive material, such as a thermal interface material (TIM) disposed therebetween. Typical thermal interface materials may include, for example, thermally conductive gels, grease or solders. Heat spreaders are typically constructed of a thermally conductive material such as aluminum, electrolytically plated copper, copper alloy, or ceramic, for example.  
           [0007]    Referring now to the figures, where like elements are recited with like designations, there is illustrated numerous embodiments of a microelectronic package. FIGS. 4 and 5 are alternative views of one example of a microelectronic package  200 . As is well known, a microelectronic package may comprise at least one microelectronic die  206 , coupled to a heat spreader and a substrate  202 , such as a printed circuit board (PCB). Package  200  comprises a microelectronic die  206  (see FIG. 4), coupled to a substrate  202 , which may also be referred to as a substrate carrier. Secondary electronic components such as capacitors (not shown) may be attached to the substrate  202  as well. Typically, the microelectronic die  206  is attached to one side of the substrate  202 , and attachment may be by means of a plurality of solder balls or solder bump connections  210  (see FIG. 4), although alternative attachment methods exist. The package  200  further comprises a mass of thermally conductive material, or heat spreader  204 . Heat spreader  204  may be formed out of a suitable conductive material such as copper, aluminum, or carbon composites, although alternative materials exist. In package  200 , the heat spreader  204  is typically in thermal contact with the microelectronic die  206  by means of a thermal interface material  208  (see FIG. 4). A contiguous lip  212  may be formed on the heat spreader  204 , and may span around the microelectronic die  206 . This lip  212  may serve as an attachment point for the heat spreader  204  to attach to the substrate  202 , as well as to provide structural support for the body of the heat spreader  204 . Additionally, the heat spreader  204  may provide structural support for the entire package  200 , and may, for example, reduce or prevent warpage of the substrate  202 . However, this substantially contiguous lip  212  typically does not contribute significantly to heat dissipation, and may add weight and cost to a device package. Additionally, the processes used to manufacture the substantially contiguous lip  212  of a heat spreader  204  may result in a greater variation in flatness of the top side  205  of a heat spreader, which may affect thermal performance due at least in part to a reduced contact surface area between the top side  205  of the heat spreader and a secondary device such as a heat sink. Heat spreader  204  may be attached to substrate  202  by using solder, sealants, or other types of adhesive materials, shown generally by attachment material  214 , although alternative attachment methods exist. Heat spreaders, such as heat spreader  204 , are typically attached to the substrate  202  by using a sealant  214 , which substantially fills the gap between the heat spreader  204  and the substrate  202 , and forms a completely enclosed cavity. In operation, heat is typically conducted from the microelectronic die  206  through the thermal interface material  208  to the heat spreader  204  by heat conduction. A vent hole  218  (see FIG. 5) may be formed in the heat spreader, and may provide pressure relief inside the package. A heat sink, such as a folded fin or an extruded pin heat sink, for example (not shown) may be attached to the top side  205  of the heat spreader  204 , and in operation, heat is transferred from the heat spreader  204  to the heat sink, and convective heat transfer primarily transfers heat from the heat sink to the surrounding air. Heat sinks are typically attached to a heat spreader  204  by use of an adhesive material, or a mechanical attachment mechanism. Thermal performance may be affected by the method used to attach a heat sink, and depending on which method of attachment is used, such methods may result in heat sinks having a reduced heat transfer capability.  
           [0008]    Heat spreaders, such as the one shown in FIGS. 4 and 5, are typically formed from a series of stamping processes, in a multistage manufacturing environment. These stamping processes typically result in a relatively low yield range in the production of heat spreaders, due, at least in part, to the processes used for forming heat spreaders. Additionally, the processes may result in a significant variation in flatness of the top surface  205  of a heat spreader  204 , which, as explained previously, may increase the resistance of the package and reduce thermal efficiency. Additionally, the processes as described may affect bond line thickness  207  (see FIG. 4). Bond line thickness  207 , or BLT, as is well known, is the distance from the top of a microelectronic die  206  to the bottom of a heat spreader  204  in the assembled microelectronic package  200 . In addition to controlling or maintaining a BLT, there is typically a need to control the height of a second level attachment such as a heat sink, which may be a heat sink such as the types previously described. A greater variation in flatness may make dimensional control of this second level attachment device difficult. This design may additionally result in more costly and/or less effective attachment techniques for both the attachment of the heat spreader  204  to substrate  202 , or the attachment of one or more devices such as a heat sink to the heat spreader  204 . A need exists for an improved heat spreader design, which addresses at least some of these manufacturing and thermal performance concerns. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. The claimed subject matter, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 is a cross sectional diagram of one embodiment of the claimed subject matter.  
         [0011]    [0011]FIG. 2 is an obtuse plan view of one embodiment of the claimed subject matter.  
         [0012]    [0012]FIG. 3 a  is an obtuse plan view of one embodiment of the claimed subject matter.  
         [0013]    [0013]FIG. 3 b  is an obtuse plan view of one embodiment of the claimed subject matter.  
         [0014]    [0014]FIG. 4 is a cross sectional diagram of a prior art processor package with IHS.  
         [0015]    [0015]FIG. 5 is an obtuse plan view of a prior art processor package with IHS.  
         [0016]    [0016]FIG. 6 is a computing system, which may be used with at least one embodiment of the claimed subject matter.  
     
    
     DETAILED DESCRIPTION  
       [0017]    [0017]FIGS. 1 and 2 show two different views of a microelectronic package  300 , which may address at least some of the previously described manufacturing and thermal performance concerns. The microelectronic package  300  is comprised of a heat spreader  110 , which comprises a body  101  with a plurality of downset legs  112 ,  114  and  116  (see FIG. 2) formed thereon, a substrate  102 , and a microelectronic die  106  (see FIG. 2). The present embodiment is shown depicting a plurality of downset legs  112 ,  114  and  116 , although the claimed subject matter is not limited to any particular number of downset legs. One or more of the downset legs  112 ,  114  or  116  may be formed to be downset from the heat spreader body bottom surface  118  (see FIG. 1) by a particular distance  142  (see FIG. 2), which may form a cavity  120  between the one or more downset legs  112 ,  114  and  116  and the body bottom surface  118 . The offset distance  142  may be approximately as deep as the thickness of microelectronic die  106 , for example. A notch  140  may be formed between the top surface  138  of the heat spreader body  101  and one or more heat spreader sides  128 , and may be formed from one or more of the forming processes described hereinafter. Additionally, while downset legs  112 ,  114  and  116  are shown formed on the corners of the heat spreader  110 , it will be understood that the plurality of downset legs  112 ,  114  or  116  may be formed on other areas of the heat spreader  110 , and they are not limited to formation on the corners. Referring now to FIG. 1, the plurality of downset legs  112 ,  114  and  116 , in this embodiment, provide an offset of the bottom body surface  118  of the heat spreader  110  to the substrate  102 . This offset  118  forms a cavity  120  in the heat spreader  110 . The depth of the cavity  120  may be less than or equal to the thickness of microelectronic die  106 , but the claimed subject matter is not so limited, and may, for example, be greater than the thickness of the microelectronic die  106 . Heat spreader  110  may be attached to a substrate  102 , and may be attached by using an attachment material  134  (see FIG. 2), such as a sealant/polymer, which may be applied to at least a portion of the bottom surface  136  of one or more downset legs  112 ,  114  or  116 , although the claimed subject matter is not limited in this respect. When the heat spreader  110  is attached to the substrate  102 , the downset legs  112 ,  114 , and  116  may form a non-contiguous lip  144  around the microelectronic die  106 . In one embodiment, this non-contiguous lip may eliminate or reduce the need for a vent hole such as vent hole  218  of FIG. 5, which, as stated previously, serves the primary purpose of providing pressure relief inside the package. Additionally, one or more of the discontinuities in the non-contiguous lip  144  of heat spreader  110  may serve as attachment locations for secondary devices, as will be explained in more detail later. Attachment of the heat spreader  110  to the substrate  102  may be by any number of methods, including but not limited to pressing, application of epoxy, soldering, or any suitable method, but the claimed subject matter is not limited in this respect. Additionally, mechanical attachment devices, such as generic mechanical attachment device  122  (see FIG. 2), may be used to attach the heat spreader  110  to the substrate  102 , and will be described in more detail later. The top surface  138  of the heat spreader  110  may be substantially planar in one embodiment, but the claimed subject matter is not limited in this respect.  
         [0018]    The heat spreader as shown in FIGS.  1  and/or  2 , for example, may be formed by use of one or more cold forming processes, such as, for example, one or more stamping processes, although the claimed subject matter is not limited in this respect. As is well known, a stamping process may use a slug of material and then stamp out features or dimensions from a slug of material. In one embodiment, a stamping process may be used to stamp down one or more downset legs  112 ,  114  and  116 , to provide a heat spreader  110  as described. It will, of course, be understood that the claimed subject matter is not limited to any particular process for forming the heat spreader  110  as shown and described, but any suitable method for forming a heat spreader  110  is within the scope of the claimed subject matter. Additionally, the material used to form a heat spreader  110  as shown and described may be any number of materials, and the claimed subject matter is not limited to any particular material or category of materials. There are pluralities of methods, which may be used to form one or more of the heat spreaders  110  as claimed and described. These methods include, for example, stamping, machining, progressive manufacturing, laser cutting, or injection molding, although the claimed subject matter is not limited to any particular method but any method of manufacture capable of producing the heat spreader  110  as claimed and described are within the scope of the claimed subject matter. One such method of forming a heat spreader  110  comprises starting with a mass of material, or slug, and cutting or machining it to a set of dimensions. A subsequent step in the manufacture would comprise one or more stamping processes, which would form the plurality of downset legs  112 ,  114 , and  116 . This stamping process may for notch  140  in the vicinity of a formed downset leg. This process may be a single step, or may be a series of steps, and the claimed subject matter is not limited to any particular manufacturing process or series of steps.  
         [0019]    [0019]FIG. 3 a  comprises a plan view of a microelectronic package in accordance with another embodiment of the claimed subject matter. In this embodiment, the heat spreader  110  has a plurality of holes or voids, such as  124  and  126 , located in the vicinity of the downset legs  112 ,  114  and  116 . Holes  124  and  126  are configured to receive one or more pins, bolts, or similar devices such as generic mechanical attachment device  122 , for example. These one or more attachment devices  122  may be coupled to substrate  102 , although the claimed subject matter is not limited in this respect. Additionally, these one or more attachment devices  122  may be attached to a secondary device such as a heat sink or a temperature-testing device (not shown) which may be configured to be attached to heat spreader  110 , for example. The present embodiment of the claimed subject matter is not limited to any particular type of mechanical attachment device and may include, for example pins, screws, bolts or rivets, and any type of mechanical attachment device that may be adapted to be inserted in voids  124  and/or  126 . Additionally, one or more types of adhesives known in the art may be used to attach one or more secondary components (not shown) to the heat spreader  110 . It will additionally be understood that alternative configurations or methods to attach one or more secondary components to the heat spreader  110  are in accordance with the claimed subject matter. Additionally, a plurality of pins, or other mechanical attachment devices (not shown), may be formed on the heat spreader  110 , and may be configured to receive one or more secondary components such as a heat sink (not shown). These one or more attachment devices may be configured to pass through the heat spreader  110 , or through the heat spreader  110  and substrate  102 .  
         [0020]    In yet another alternative embodiment, FIG. 3 b  shows a clip configuration, including clips  130  and  132 , although the claimed subject matter is not limited to any particular number of or location of clips. Clips  130  and  132 , in this embodiment, may be coupled to the substrate  102 , and clipped to the top surfaces of downset legs  112  and  114 , although this is just one possible embodiment of a clip attachment, and the claimed subject matter is not so limited. These one or more clips  130  and  132  may be alternatively be attached to the heat spreader  110 , and configured to be coupled to a substrate  102  when microelectronic assembly  510  is assembled. Additionally, one or more of the downset legs  112 ,  114  and  116  may be configured to receive one or more clips such as  130  and  132 . These one or more clips may be attached to a secondary component such as a heat sink (not shown), although the claimed subject matter is not limited in this respect. It will, of course, be understood that many such attachment devices or methods exist that are in accordance with at least one embodiment of the claimed subject matter.  
         [0021]    For purposes of clarity, the claimed subject matter is described primarily in the context of utilization with an integrated circuit flip chip configuration, packaged with a substrate and heat spreader as shown in the accompanying figures. However, it will be understood that the claimed subject matter is not limited to just this particular configuration, and the claimed subject matter is applicable to other types of microelectronic packages. For example, microelectronic packages in accordance with the claimed subject matter may include packages with varying form factors, such as, for example, pin grid array, ball grid array, ball grid array with pinned interposers and wire bonding, although, again, these are just examples, and the claimed subject matter is not limited in this respect.  
         [0022]    One or more of the foregoing embodiments of a microelectronic package may be utilized in a computing system, such as computing system  600  of FIG. 6. Computing system  600  is comprised of at least one processor (not shown), a data storage system (not shown), at least one input device such as keyboard  604 , and at least one output device such as monitor  602 , for example. System  600  includes a processor that processes data signals, and may comprise, for example, a PENTIUM®III or PENTIUM® 4 microprocessor, available from Intel® Corporation.  
         [0023]    Computing system  600  comprises a keyboard  604 , and may include other user input devices such as a mouse  606 , for example. Computing system  600  may utilize one or more microelectronic packages such as described in one or more of the foregoing embodiments. For purposes of this application, a computing system embodying components in accordance with the claimed subject matter may include any system that utilizes a microelectronic package, which may include, for example, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), or a microprocessor.  
         [0024]    While certain features of the claimed subject matter have been illustrated as described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such embodiments and changes as fall within the true spirit of the claimed subject matter. Additionally, in the preceding detailed description, numerous specific details were set forth in order to provide a thorough understanding of the claimed subject matter. However, it will be understood by those skilled in the art that the claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the claimed subject matter.