Methods for transfer molding encapsulation of a semiconductor die with attached heat sink

Abstract

A semiconductor device includes a heat sink adjacent to a die. A dam is positioned at the peripheral edges of the heat sink. During a transfer molding process, the dam serves two purposes. First, the dam prevents damage to the mold. Second, the dam prevents encapsulant packaging compound material from flowing onto the heat sink. The dam may be a gasket. The dam may also be a burr created by, for example, stamping the bottom of the heat sink. The dam may include copper, polyamides, and leadlock tape. The dam may be permanently connected to the heat sink or removed following packaging. The dam may be removed mechanically, through the use of heat, or during an electrolytic deflash cycle.

What is claimed is:  
     
         1 . A transfer molding method for packaging a plurality of semiconductor device assemblies at the same time, each semiconductor device assembly having a semiconductor die having a plurality of bond pads thereon and having a portion thereof attached to a portion of a lead frame having a plurality of leads, at least one bond pad of the plurality of bond pads of the semiconductor die connected to at least one lead of the plurality of leads of the lead frame, comprising: 
 forming a heat sink having a top surface and a bottom surface, each top and bottom surface having peripheral edges therearound for each semiconductor die;    forming a substantially continuously formed protruding edge from the heat sink at the peripheral edges of the bottom surface of the heat sink for each semiconductor die;    positioning the top surface of each heat sink adjacent to each semiconductor die having the plurality of bond pads thereon;    placing the each heat sink and each semiconductor die of each semiconductor device assembly of said plurality of semiconductor device assemblies in a transfer molding apparatus having the protruding edge formed at the peripheral edges of the bottom surface of each heat sink in contact with a portion of the transfer molding apparatus; and    removing a dam from adjacent to a surface of each heat sink following an encapsulation of each semiconductor die and the heat sink.    
     
     
         2 . The method of  claim 1 , wherein the protruding edge is removed with heat.  
     
     
         3 . The method of  claim 1 , wherein the protruding edge is removed during an electrolytic deflash cycle.  
     
     
         4 . A method of packaging a plurality of semiconductor device assemblies, each semiconductor device assembly having a semiconductor die having a plurality of bond pads thereon and having a portion thereof attached to a portion of a lead frame having a plurality of leads, at least one bond pad of the plurality of bond pads of the semiconductor die connected to at least one lead of the plurality of leads of the lead frame, comprising: 
 forming a dam adjacent a periphery of a heat sink for each semiconductor die, each dam formed from material of the heat sink, the dam protruding from edge portions of the periphery of the heat sink;    positioning the heat sink adjacent each semiconductor die;    positioning the dam, heat sink, and each semiconductor die in a transfer molding apparatus having the dam contacting a portion of the transfer molding apparatus for encapsulating a plurality of semiconductor device assemblies;    encapsulating each semiconductor die and each heat sink in molding material in the transfer molding apparatus; and    removing the dam from adjacent to a surface of the heat sink following the encapsulation of each semiconductor die and each heat sink in the molding material in the transfer molding apparatus.    
     
     
         5 . A method of packaging a semiconductor device assembly of a plurality of semiconductor device assemblies, each semiconductor device assembly having a semiconductor die having a plurality of bond pads thereon and having a portion thereof attached to a portion of a lead frame having a plurality of leads, at least one bond pad of the plurality of bond pads of the semiconductor die connected to at least one lead of the plurality of leads of the lead frame, comprising: 
 providing a heat sink for each semiconductor die;    forming a dam adjacent a periphery of the heat sink for each semiconductor die, each dam formed from a material thereof, the dam configured as a protruding edge portion of the periphery of the heat sink;    positioning the heat sink adjacent to the semiconductor die;    positioning the lead frame, the semiconductor die, the heat sink, and the dam in a transfer molding apparatus in a plurality of semiconductor device assemblies, each dam contacting a portion of the transfer molding apparatus;    encapsulating a portion of the portion of the lead frame, the semiconductor die, and the heat sink in molding material in the transfer molding apparatus for each semiconductor device assembly of a plurality semiconductor device assemblies; and    removing the dam from adjacent to a surface of the heat sink following the encapsulation of each semiconductor die and the heat sink in the molding material in the transfer molding apparatus.