Abstract:
A method for coupling a heat slug to a lead frame, comprising aligning a heat slug and a lead frame depositing a material between the heat slug and the lead frame, and clamping together the heat slug and the lead frame.

Description:
BACKGROUND  
       [0001]     During a semiconductor packaging process, an integrated circuit (“IC”) is mounted inside a plastic mold compound (“package”). Various points on the IC are electrically connected to lead frames circumscribing the package using bond wires. In turn, the lead frames circumscribing the package are electrically connected to an application board, such as a printed circuit board (“PCB”). In this way, multiple electrical connections are established between the IC and the PCB. For example,  FIG. 1   a  shows a top view of an IC  100  electrically connected to lead frame  102  of a package  104  using bond wires  106 . The lead frame  102  is electrically connected to a PCB  108 , thereby establishing multiple electrical connections between the IC  100  and the PCB  108 .  
         [0002]     The IC  100  abuts a heat slug  200  that is used to conduct heat away from the IC  100  and out of the package  104 . During a packaging process, the heat slug  200  is coupled to the lead frame  102  using a riveting technique, wherein the heat slug  200  is punched through apertures  202  in the lead frame  102  and flattened on the opposite side of the lead frame  102 , as shown in  FIG. 1   b . In this way, the heat slug  200  is held abutting the lead frame  102 .  
         [0003]     However, this time-consuming riveting technique requires the use of a riveting machine, which adds to the cost of the manufacturing process. Furthermore, the mechanics of the riveting machine require the riveting process to be performed prior to package assembly. For this reason, during package assembly, the riveted lead frame  102  and heat slug  200  are fixed in place. Thus, the package  104  is limited in size and design flexibility.  
       SUMMARY  
       [0004]     The problems noted above are solved in large part by a clamping technique that couples a heat slug to a lead frame without the use of a clamping machine. One exemplary embodiment may be a method for coupling a heat slug to a lead frame, comprising aligning a heat slug and a lead frame, depositing a material between the heat slug and the lead frame, and clamping together the heat slug and the lead frame. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which:  
         [0006]      FIG. 1   a  shows a top vie of a printed circuit board (“PCB”) abutting a leaded package;  
         [0007]      FIG. 1   b  shows a cross sectional side view of a lead frame coupled to a heat slug using a riveting technique;  
         [0008]      FIGS. 2   a - 2   d  show a cross sectional side view of a lead frame and a heat slug coupled using the clamping technique, in accordance with embodiments of the invention;  
         [0009]      FIG. 3  shows a flow diagram of a process that may be used to implement the configurations of  FIGS. 2   a - 2   d , in accordance with embodiments of the invention;  
         [0010]      FIGS. 4   a - 4   d  show a cross sectional side view process flow of a lead frame and a heat slug coupled using the clamping technique, in accordance with embodiments of the invention;  
         [0011]      FIG. 5  shows a flow diagram of a process that may be used to implement the configurations of  FIGS. 4   a - 4   c , in accordance with embodiments of the invention;  
         [0012]      FIGS. 6   a - 6   c  show a cross sectional side view process flow of a lead frame and a heat slug coupled using the clamping technique, in accordance with embodiments of the invention; and  
         [0013]      FIG. 7  shows a flow diagram of a process that may be used to implement the configurations of  FIGS. 6   a - 6   c , in accordance with embodiments of the invention. 
     
    
     NOTATION AND NOMENCLATURE  
       [0014]     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  
       [0015]     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.  
         [0016]     Presented herein is a clamping technique that couples a heat slug to a lead frame without the use of a riveting machine.  FIGS. 2   a - 2   d  show a lead frame  102  being electrically coupled to a heat slug  200  using an exemplary embodiment of the clamping technique.  FIG. 3  shows a process that may be used to implement the configurations shown in  FIGS. 2   a - 2   d . Specifically,  FIG. 2   a  shows a lead frame  102  aligned adjacent a heat slug  200 . The lead frame  102  and the heat slug  200  are aligned by mating heat slug protrusions  201  and the apertures  202  (block  300 ). The heat slug  200  and the lead frame  102  are aligned to ensure compliance with design specifications. For example, design specifications may require that the heat slug  200  be positioned at a specific point in relation to the lead frame  102 . The heat slug protrusions  201  and the apertures  202  ensure that this positioning requirement is satisfied. The heat slug protrusions  201  and the apertures  202  preferably are substantially round in shape, although the protrusions  201  and the apertures  202  also may be any other suitable shape (e.g., rectangular, triangular).  
         [0017]     The lead frame  102  then is held abutting the heat slug  200  with one or more clamps  250  (block  301 ). As shown in  FIG. 2   b , solder wires  252  are used to deposit solder into the apertures  202  (block  302 ). Heating the lead frame  102  and the heat slug  200  causes the solder to melt and fill the apertures  202 . Although spaces between the heat slug  200  and the lead frame  102  are substantially narrow, a capillary effect causes the melted solder to flow between the heat slug  200  and the lead frame  102 , thereby electrically coupling the lead frame  102  and the heat slug  200 , as shown in  FIG. 2   c  (block  304 ). The clamps then may be removed, as shown in  FIG. 2   d  (block  306 ). The IC  100  (not shown) optionally may be coupled to the heat slug  200  using solder from the solder wires.  
         [0018]      FIGS. 4   a - 4   d  show the lead frame  102  being electrically coupled to the heat slug  200  by way of another embodiment of the clamping technique mentioned above.  FIG. 5  shows a process that may be used to implement the configurations shown in  FIGS. 4   a - 4   d . Referring to  FIGS. 4   a - 4   d  and  5 , the process may begin by printing or otherwise depositing solder paste  240  on at least one of a surface  402  of the heat slug  200  or a surface  400  of the lead frame  102  (block  500 ), as shown in  FIG. 4   a . The lead frame  102  then is aligned adjacent the heat slug  200  using the heat slug protrusions  201  and the apertures  202  (block  501 ), as shown in  FIG. 4   b . As previously mentioned, the lead frame  102  and the heat slug  200  are aligned to ensure compliance with design specifications. The heat slug protrusions  201  and the apertures  202  preferably are substantially round in shape, although the scope of disclosure is not limited to this shape and comprises rectangular, triangular and other suitable shapes and sizes. The lead frame  102  then is held abutting the heat slug  200  with one or more clamps  250  (block  502 ), as shown in  FIG. 4   c . The IC  100  ( FIG. 1   a ) may be coupled to the heat slug  200  using the solder paste. The solder is first heated until molten (block  503 ). After the solder paste cools and the lead frame  102  is firmly coupled to the heatsink  200 , the clamps  250  may be removed (block  504 ), as shown in  FIG. 4   d.    
         [0019]      FIGS. 6   a - 6   c  show the lead frame  102  being mechanically and/or electrically coupled to the heat slug  200  by way of yet another embodiment of the clamping technique mentioned above.  FIG. 7  shows a process that may be used to implement the configurations of  FIGS. 6   a - 6   c . Specifically, the process may begin by depositing liquid die attach material  699  or film die attach material  699  on either a surface  400  of the lead frame  102  or a surface  402  of the heat slug  200  (block  700 ). The lead frame  102  then is aligned with the heat slug  200  using heat slug protrusions  201  and the apertures  202  (block  701 ), as shown in  FIG. 6   a . As mentioned above, the heat slug  200  is aligned with the lead frame  102  to ensure proper compliance with design specifications. The heat slug protrusions  201  and/or the apertures  202  may be substantially round, rectangular, or any other suitable shape. The lead frame  102  subsequently is held abutting the heat slug  200  with one or more clamps  250  (block  702 ), as shown in  FIG. 6   b . The IC  100  (not shown) optionally may be coupled to the heat slug  200  using the die attach material. As shown in block  704 , the die attach material then is optionally cured until dry (e.g., using a curing oven) and then the clamps  250  are removed, as shown in  FIG. 6   c  (block  706 ). A die also may be coupled to the heatsink  200  during this process.  
         [0020]     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. It is intended that the following claims be interpreted to embrace all such variations and modifications.