Abstract:
The present invention is directed toward systems, packages, and methods for providing improved thermal performance in such packages and systems. Embodiments of the invention include a semiconductor integrated circuit (IC) package having a substrate with a heat spreader mounted on the substrate. An IC die is mounted to the heat spreader such that the heat spreader lies in between the die and the substrate. The invention is also directed to a heat spreader plate useable in a semiconductor package. The heat spreader plate comprises a plate comprised of thermally conductive material suitable for attachment to a packaging substrate wherein the plate includes openings for exposing electrical bonding surfaces of a packaging substrate when the heater spreader plate is mounted on the packaging substrate. Such openings enable wirebonding between the exposed electrical bonding surfaces of the substrate and an integrated circuit die to complete construction of a package including the heatspreader.

Description:
TECHNICAL FIELD 
   The invention described herein relates generally to semiconductor device packaging. In particular, the invention relates to a semiconductor device package that constructed such that a heat spreader is advantageously positioned between the chip substrate and the semiconductor die thereby increasing the thermal cooling properties of the package. 
   BACKGROUND 
   Heat spreaders are generally used in integrated circuit device packages. One such integrated circuit device package  100  is shown in the simplified schematic illustration of  FIG. 1 . The depicted package  100  is a ball grid array type package. In  FIG. 1 , there is a substrate  10  onto which an integrated circuit device (also referred to herein as an IC die or chip)  12  is mounted. The die  12  is commonly attached to a front side surface of the substrate  10 . Commonly this means attachment to a front side die attach pad  11  with an epoxy material  13 . The depicted substrate  10  includes copper conducting structures  11  (for example, bonding pads, bonding rings, bond fingers, and the like) that comprise electrical connections in the package  100 . These wires  14  are connected to rows of bond pads on the die by ball bonds  15 . Thus, the electrical connections of the die  12  are electrically connected to selected conducting structures  11  using the bonding wires  14 . The die  12  is encapsulated with a molding material  17 . Additionally, a heat spreader  18  is adhered (commonly using epoxy) to the front side surface of the substrate  10  to protect the die  12  and to spread the heat generated by the die  12  over a larger area. Importantly, in conventional packages the heat spreader  18  is attached to the top of the package. Thus, heat generated by the die  12  passes through the encapsulating layer  17  to thermally communicate with the heat spreader  18 . 
   In many conventional applications such an arrangement has proved satisfactory. However, with the increasing circuit density within dies  12  arises a need for more connections from the die  12  to the substrate  10 . The depicted configuration uses two rows  1 , 2  of die mounted bond pads to connect with the various conducting structures  11  of the substrate  12 . It is becoming common to use three row implementations and newer packages will use four or more rows. With each added row comes the necessity to increase the height h of the layer of encapsulating molding material  17  to sufficiently protect the wires  14 . As this height h increases the heat dissipation effectiveness of the heatspreader  18  decreases due to increasing distance away from the die. Additionally, as the processing power of modern semiconductor devices increases, such devices can perform more operations per second. With this increasing speed comes increasing heat. Thus, among other things, there is a need for systems and methods that can improve the thermal performance of the package. semiconductor package and methods for its fabrication are disclosed. 
   In general, the present invention is directed toward systems, packages, and methods for providing improved cooling in such packages and systems. 
   One embodiment of the invention comprises a semiconductor integrated circuit (IC) package. The package includes a packaging substrate with a heat spreader mounted on a first side of the substrate. An integrated circuit die is mounted to the heat spreader such that the die is in thermal communication with the heat spreader and such that the heat spreader lies in between the die and the substrate. 
   In another embodiment, a heat spreader plate for use in a semiconductor package is disclosed. The heat spreader plate comprises a plate comprised of thermally conductive material suitable for attachment to a packaging substrate. The plate includes openings configured to expose electrical bonding surfaces of a packaging substrate when the heat spreader plate is mounted on the packaging substrate. Such openings enable wirebonding between the exposed electrical bonding surfaces of the substrate and a integrated circuit die. 
   Other aspects and advantages of the invention will become apparent from the following detailed description and accompanying drawings which illustrate, by way of example, aspects of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following detailed description will be more readily understood in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a simplified schematic cross section view of a portion of a conventional integrated circuit package used to package semiconductor IC chips. 
       FIG. 2A  is simplified cross-sectional view of a semiconductor package embodiment having a heat spreader interposed between a packaging substrate and a semiconductor die in accordance with an embodiment of the invention. 
       FIG. 2B  is simplified plan view of a heat spreader plate embodiment placed on a packaging substrate in accordance with the principles of the invention. 
       FIGS. 3A and 3B  are simplified cross-sectional views of additional semiconductor package embodiments constructed in accordance with the principles of the invention. 
     It is to be understood that in the drawings like reference numerals designate like structural elements. Also, it is understood that the depictions in the Figures are not necessarily to scale. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments set forth hereinbelow are to be taken as illustrative rather than limiting. It should be readily apparent to those of ordinary skill in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the invention. 
   In the following detailed description, semiconductor device package embodiments will be disclosed. In particular, the depicted structures depict package embodiments having heat spreaders attached to the package between the substrate and the die. Such packages provide improved heat dissipation performance relative to conventional packages. Additionally, embodiments of the invention include packages configured such that the heat spreader includes cooling fins to increase thermal performance. And also includes embodiments that have portions of the heatspreader extending to the edge of the package thereby having an edge portion capable of radiating heat thereby dissipating heat from the package. Such package configurations demonstrate superior thermal properties relative to conventional packages. 
     FIG. 2A  depicts one embodiment of a semiconductor package  200  constructed in accordance with the principles of the invention. The depicted embodiment is a simplified cross-section view of a package embodiments constructed in accordance with the principles of the invention. The depicted embodiment includes a substrate  210  constructed in accordance with the principles of the invention. In the depicted embodiment, the substrate  210  comprises a standard PBGA (plastic ball grid array) substrate. Typically, such substrates  210  include a core  202  sandwiched between two or more metallization layers. For example, metallization layers  203 ,  203 ′ which also typically include layers of solder mask  204 ,  204 ′. Commonly, the core  202  is formed of fiber material suspended in a cured BT (bismaleimide triazine) resin material. This core  202  is then treated to form metallization layers  203 ,  203 ′. Commonly, copper materials or coated copper materials are used. However, other conductive materials can be used. Solder mask layers  204 ,  204 ′ can then be formed over portions of the metallization layers  203 ,  203 ′. Such substrates  210  are commonly very thin, on the order of about 0.50–0.60 mm thick. Additionally, the metallization layers  203 ,  203 ′ can be used to define electrical bonding surfaces including bonding rings, bonding pads, bond fingers (as well as many other different types of electrical connections used in semiconductor packaging). Additionally, solder balls  205  are attached to a backside surface of the substrate  201  to facilitate the physical and electrical connection of the package  200  to a system board (e.g., a motherboard). Methods used for constructing such substrates  210  are known to those having ordinary skill in the art. 
   Insulating layers  204 ,  204 ′ can be formed over portions of the metallization layers  203 ,  203 ′ to provide electrical insulation between various portions of metallization layers  203 ,  203 ′ and also to provide electrical insulation from other layers formed over top of the metallization layers  203 ,  203 ′. One commonly used material for forming insulating layers  204 ,  204 ′ is solder mask material. It is to be noted that the front side metallization layers  203  can be electrically connected with backside metallization layers  203  using via structures  206 . 
   In accordance with an embodiment of the invention, a thermally conductive heat spreader plate  208  is then attached to the substrate  210 . This heat spreader plate  208  is attached to a front side surface of the substrate  210 . Typically such attachment is accomplished using any one of a number of suitable adhesives. In one example, epoxy materials can be used. In one embodiment, the heat spreader plate  208  is formed of copper or other thermally conductive material. Embodiments of a heat spreader  208  can be layered. For example, a copper heat spreader  208  having a nickel layer plated on a top surface can be employed. Also, embodiments of the heat spreader  208  can be of many thicknesses. For example, thicknesses in the range of about 6–25 mil are typically suitable. In one implementation a heat spreader  208  of about 12 mils thickness is employed. 
   An integrated circuit (IC) die  212  is attached to a front side surface of the heat spreader plate  208 . Commonly, such attachment is accomplished using an adhesive (e.g., epoxy)  213 . Thermally, conductive adhesives are particularly suitable (although not required) for die attachment. Thus, a very thin adhesive layer is now all that lies between the die  212  and heat spreader  208 . This configuration significantly improves the thermal performance of the package relative to conventional configurations. As with conventional embodiments, the die  212  is electrically connected to selected electrical bonding surfaces formed by the metallization layers  203 ,  203 ′. Such electrical connections are typically established using bonding wires  214  (which can also connect to underlying metallization layers  203 ′ using conducting vias  206  that penetrate through the substrate  210 ). The die  212  and bonding wires  214  are encapsulated using a mold cap  217  made of molding material that protects and seals the inner components of the package  200 . Such molding materials are commercially available and well known in the art. 
   It should be noted that in the depicted embodiment the heat spreader  208  extends past the edge of the mold cap  217  to form an exposed rim portion  218 . This edge portion  218  can improve thermal performance by radiating heat into the ambient environment. However, the inventors point out that edge of the mold cap  217  can extend all the way to the end of the substrate  210 . Such embodiments still fall within the intended scope of the invention although there is no exposed rim portion of the embodiments where the heat spreader  208 . 
     FIG. 2B  is a plan view showing an embodiment of heat spreader  208  which can be mounted onto a substrate in accordance with the principles of the invention. The heat spreader  208  includes a plurality of cutouts  220  that are openings in the heat spreader. The depicted heat spreader  208  is shown mounted on a substrate having a plurality of electrical bonding surfaces exposed. Such electrical bonding surfaces include bonding fingers  224 , bonding rings  225 , bonding pads  226 , and other related electrical contact structures. These electrical bonding surfaces are situated in the cutouts  220  to facilitate wire bonding with a die. The dashed lines  228  correspond to a bonding locality for attaching a die onto the heat spreader  208 . 
   Another embodiment is depicted in the simplified cross-section view of  FIG. 3A  which show a substrate  310  embodiment upon which an integrated circuit die  312  is mounted. In the depicted embodiment, the substrate  310  comprises, for example, a standard two level PBGA (plastic ball grid array) substrate. As explained previously, such substrates  310  typically include metallization layers, vias, and backside solder balls. The die  312  is wire bonded  314  to electrical bonding surfaces of the substrate  310 . In the depicted embodiment, cooling fins  301  are added to the exposed rim portion  318  of the heat spreader  308 . Such cooling fins  301  are generally thin strips of thermally conductive material in thermal communication with the heat spreader  308 . Such fins  301  can enhance the cooling properties of the heat spreader  308 . The inventors also contemplate embodiments where the fins are encapsulated by the mold cap. 
   Another embodiment is depicted in the simplified cross-section view of  FIG. 3B  which show a substrate  310  embodiment upon which an integrated circuit die  312  is mounted. In the depicted embodiment, the substrate  310  comprises, for example, a standard two level PBGA (plastic ball grid array) substrate. As explained previously, such substrates  310  typically include metallization layers, vias, and backside solder balls. The die  312  is wire bonded  314  to electrical bonding surfaces of the substrate  310 . As with other embodiments, a heat spreader  308  is mounted between the die  312  and the substrate  310 . Additionally, in the depicted embodiment, a second (or top) heat spreader  308   t  can be added over the mold cap  317 . Additionally, the second heat spreader  308   t  can be in thermal contact with the exposed rim portion of the heat spreader  308  located at the outer portion  318  of the substrate. Typically, this is accomplished by positioning the second heat spreader  308   t  in physical contact with the heat spreader  308 . For example, solder can be used to adhere the second heat spreader  308   t  to the heat spreader  308  In other embodiments, the second heat spreader  308   t  is not in thermal communication with or physical contact with the heat spreader  308 . 
   The present invention has been particularly shown and described with respect to certain preferred embodiments and specific features thereof. However, it should be noted that the above-described embodiments are intended to describe the principles of the invention, not limit its scope. Therefore, as is readily apparent to those of ordinary skill in the art, various changes and modifications in form and detail may be made without departing from the spirit and scope of the invention as set forth in the appended claims. Other embodiments and variations to the depicted embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims. In particular, it is contemplated by the inventors that cooling fins can be attached to the portions of the heat spreader internal to the mold cap to enhance the thermal properties of the package. Although only a few configurations are expressly disclosed herein, it should be appreciated by anyone having ordinary skill in the art that, using the teachings disclosed herein, many different package support configurations can be implemented and still fall within the scope of the claims. Further, reference in the claims to an element in the singular is not intended to mean “one and only one” unless explicitly stated, but rather, “one or more”. Furthermore, the embodiments illustratively disclosed herein can be practiced without any element which is not specifically disclosed herein.