Patent Document

BACKGROUND 
   Integrated circuits are fabricated on the surface of a semiconductor wafer in layers and later singulated into individual semiconductor devices, or “dies.” Since the material of a semiconductor wafer—commonly silicon—tends to be relatively fragile and brittle, dies are often packages in a protecting housing, or “package,” before the dies are interconnected with a circuit board. Packages may fall into any of a variety of package categories. Two such categories are exposed-die packages and non-leaded wirebond packages. 
     FIG. 1  shows a cross-sectional side view of an exposed-die package  100 , such as a PowerPad® package or a plastic package. The package  100  comprises a die  102  coupled to a leadframe die pad  104  of a leadframe  106  by way of a die attach material  103  (e.g., epoxy). The die  102  is electrically coupled to the leadframe  106  using bond wires  108 . The die  102 , the bond wires  108 , the die attach material  103  and portions of the leadframe  106  are encapsulated in a mold compound  110 . The leadframe  106  comprises a plurality of leads  112  that protrude from the mold compound  110 . At least some of the leads  112  may be electrically coupled to a circuit board  114 . In this way, electrical signals are transferred between the die  102  and the board  114 . Further, at least a portion of the die pad  104  is exposed from a surface  118  of the mold compound  110  and is in contact with the board  314 . As such, heat is transferred away from the die  102  and toward the board  114  by way of the die pad  104 . Thus, the board  114  acts as a heatsink for the package  100 . 
     FIG. 2  shows a cross-sectional side-view of an exemplary non-leaded wirebond package  200  (e.g., quad-flat no-lead package, small-outline no-lead package). The term “non-leaded” connotes a lack of leads protruding from the package  200 , as found in the package  100  of  FIG. 1 . The package  200  comprises a die  202  coupled to a leadframe die pad  204  of a leadframe  201  by way of a die attach material  203  (e.g., epoxy). The die  202  is electrically coupled to the leadframe  201  using bond wires  208 . The die  202 , the die attach material  203 , the bond wires  208  and portions of the leadframe  201  are encapsulated in a mold compound  210 . As previously mentioned, unlike the leaded package  100 , the non-leaded package  200  does not comprise any leads. Instead, the die  202  trades electrical signals with a circuit board  214  by way of peripheral portions  216  (“peripherals”) of the leadframe  201 . The peripherals  216  do not protrude from the mold compound  210  as do the leads  112  from the compound  110 ; instead, the peripherals  216  are exposed from a surface  218  of the mold compound  210 . The die pad  204  also may be exposed from the surface  218 . As such, because the die pad  204  is exposed from the surface  218  and is in contact with the board  214 , heat is transferred away from the die  202  and to the board  214  by way of the die pad  204 . Thus, the board  214  acts as a heatsink for the package  200 . 
   In some cases, circuit boards coupled to such packages (e.g., boards  114  and  214 ) may have a design flaw or some other limitation that prevents adequate heat dissipation away from the package. In such cases, a device containing the circuit board may overheat and either be destroyed or thrust into a state of thermal shutdown. Some packages may comprise heatsinks coupled to the package mold compound (e.g., mold compounds  210 ,  310 ) to help dissipate heat away from the package. However, package mold compounds usually do not have adequate levels of thermal conductivity to compensate for the overheating effect described above. 
   SUMMARY 
   The problems noted above are solved in large part by a heatsink apparatus and thermally-conductive intermediate material for dissipating heat in semiconductor packages. One exemplary embodiment may be a semiconductor package comprising a die adjacent a lead frame die pad, said lead frame die pad adapted to dissipate heat from the die. The package further comprises a thermally-conductive material abutting the die and a heatsink abutting the thermally-conductive material, said heatsink facing a direction opposite from the lead frame die pad. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which: 
       FIG. 1  shows an exposed-die package coupled to a circuit board; 
       FIG. 2  shows a non-leaded wirebond package coupled to a circuit board; 
       FIG. 3  shows an exposed-die package comprising a heatsink apparatus and intermediate material, in accordance with embodiments of the invention; 
       FIG. 4  shows a non-leaded wirebond package comprising a heatsink apparatus and intermediate material, in accordance with embodiments of the invention; 
       FIG. 5  shows a flow diagram of a process that may be used to implement the configurations of  FIGS. 3 and 4 , in accordance with embodiments of the invention; 
       FIGS. 6   a  and  6   b  show heatsink apparatus matrices that may be coupled to dies still on a semiconductor wafer, in accordance with embodiments of the invention; and 
       FIG. 6   c  shows a matrix from  FIG. 6   a  and/or  FIG. 6   b  coupling to dies still on a semiconductor wafer, in accordance with embodiments of the invention. 
   

   NOTATION AND NOMENCLATURE 
   Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
   DETAILED DESCRIPTION 
   The following discussion is directed to various embodiments of the invention. 
   Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
   Disclosed herein is a heatsink apparatus that may be incorporated into any of a variety of semiconductor packages to substantially enhance package thermal dissipation. Specifically, a thermally conductive heatsink apparatus is coupled to an interposer or some other intermediate material abutting a die in a package. The intermediate material is used to minimize mechanical stress caused by the die as a result of multiple thermal expansion rates in the die. Because the intermediate material also is thermally conductive, heat is transferred from the die to the heatsink apparatus by way of the intermediate material. In this way, heat is effectively dissipated from the package.  FIGS. 3 and 4  show the heatsink apparatus incorporated into an exposed-die package and a non-leaded wirebond package, respectively, although the heatsink apparatus may be used in any type of package (e.g., wirebond, flip-chip) to enhance heat dissipation. 
   In particular,  FIG. 3  shows an exposed die package  300  comprising a chip (i.e., die)  302  electrically coupled to a leadframe  304  by way of bond wires  306 . The die  302  is physically coupled to a leadframe die pad  298  of the leadframe  304  by way of a die attach material  308  (e.g., solder, epoxy). The die  302  may be electrically coupled to a circuit board  311  by way of bond wires  301  and leads  296 . An intermediate material  310  abuts the die  302  and a heatsink apparatus  312  abuts the intermediate material  310 . The intermediate material  310  may be any of a variety of thermally conductive materials, such as an interposer (e.g., adhesive heat conductive tape), a liquid die attach, film die attach, solder alloy, or mold die attach. The heatsink apparatus  312  may be metal (e.g., copper), thermally-conductive plastic or any other suitably thermally conductive material. The die  302 , the die attach material  308 , the intermediate material  310 , and portions of the lead frame  304  and the heatsink apparatus  312  may be encapsulated in and protected by a mold compound  303 . Because there exists little thermal resistance between the die  302  and the heatsink apparatus  312  (i.e., the intermediate material  310  is thermally conductive), the heatsink apparatus  312  may prevent a device containing the package  300  and/or the circuit board  311  from overheating, being thrust into thermal shutdown, or otherwise becoming damaged. 
     FIG. 4  shows yet another exemplary embodiment of the heatsink apparatus described above. Specifically,  FIG. 4  shows a non-leaded wirebond package  400  (e.g., a quad-flat no-lead or small-outline no-lead package) comprising a die  402  electrically coupled to a circuit board  411  by way of a leadframe  404  and bond wires  406 . The die  402  is physically coupled to a leadframe die pad  403  of the leadframe  404  by way of a die attach material  408  (e.g., epoxy). An intermediate material  410  abuts the die  402  and a heatsink apparatus  412  abuts the intermediate material  410 . The intermediate material  410  may be any of a variety of thermally conductive materials, such as an interposer (e.g., adhesive heat conductive tape), a liquid die attach, a film die attach, solder alloy, or a mold die attach. The heatsink apparatus  412  may be a metal (e.g., copper), a thermally-conductive plastic or any other such material. The die  402 , the die attach material  408 , the intermediate material  410 , and portions of the lead frame  404  and the heatsink apparatus  412  may be encapsulated in and protected by a mold compound  420 . Because there exists little thermal resistance between the die  402  and the heatsink apparatus  412  (i.e., the intermediate material  410  is thermally conductive), the heatsink apparatus  412  may prevent a device containing the package  400  and the circuit board  411  from overheating, being thrust into thermal shutdown, or otherwise becoming damaged. 
   A heatsink apparatus may be incorporated into a package using any of a variety of techniques, depending on the intermediate materials used to couple the heatsink apparatus to the package die.  FIG. 5  shows one exemplary process that may be used to implement a heatsink apparatus and intermediate material into any type of package. The process may be begun by depositing thermally-conductive material (“intermediate material”) onto a suitable surface of a heatsink apparatus and/or a package die (block  500 ). As mentioned above, the intermediate material may be any suitable, thermally-conductive material, such as liquid die attach, film die attach, an interposer (e.g., adhesive heat conductive tape), or a mold compound, although the scope of disclosure is not limited to these materials. The process then may be continued by coupling the heatsink apparatus to the package die, with the intermediate material sandwiched therebetween (block  502 ). In this way, heat may be dissipated from the chip to the heatsink by way of the intermediate material. In cases where the intermediate material is a mold compound, the process comprises the optional step of holding together the heatsink apparatus and the die using a vacuum, clamps, or other suitable tool until the mold compound is cured (block  504 ). The process may further be continued by depositing a mold compound into the package (block  506 ). The process may be completed by curing the mold compound (block  508 ). This process may be performed in any order, and one or more steps may be removed. 
   In many cases, the process of  FIG. 5  may be used to couple a heatsink apparatus to a die that has already been singulated from a semiconductor wafer or leadframe strip. However, the process of  FIG. 5  also may be used in situations where the dies have not yet been singulated from a semiconductor wafer or leadframe/substrate strip. In these cases, multiple heatsink apparatuses may simultaneously be coupled to multiple package dies (i.e., the process of  FIG. 5  may be performed en masse on several dies of a wafer or leadframe/substrate strip). These multiple heatsink apparatuses may be coupled to multiple dies on a wafer or leadframe/substrate strip by arranging the apparatuses in a matrix pattern to match the pattern of the dies on the wafer. Although the scope of disclosure is not limited to any particular pattern, two exemplary patterns are shown in  FIGS. 6   a  and  6   b.    
     FIGS. 6   a  and  6   b  each show a top-down view of a matrix  600 ,  602  comprising multiple heatsink apparatuses  604 ,  606 , respectively. Each matrix  600 ,  602  comprises multiple apertures  601  fixed between at least some of the heatsink apparatuses  604 ,  606 . The apertures  601  may be of any shape, such as a substantially rectangular shape or a cross shape. In at least some embodiments, a matrix may comprise singulation lines to aid in die separation, such as singulation lines  610  on the matrix  600 . As shown in  FIG. 6   c , a matrix  600  (or matrix  602 ) may be coupled to a wafer  608  comprising multiple dies  615 . The apparatuses  604  of the matrix  600  may be coupled to the dies  615  of the wafer  608  using the process of  FIG. 5 . The apertures  601  may be used to deposit a mold compound onto the dies  615 . After the mold compound has been cured, the wafer  608  may be singulated such that at least some of the dies  615  are separated from each other. 
   The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, while the above embodiments illustrates the heatsink apparatus incorporated into an exposed-die package and a non-leaded wirebond package, the heatsink apparatus also may be used in any other type of package to enhance heat dissipation. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Technology Category: h