Title: Electrically isolated heat sink lead frame for plastic encapsulated semiconductor assemblies

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Abstract: An improved lead frame having an electrically isolated heat sink portion is provided for the manufacture of high heat dissipating semiconductor devices. A large heat sink metallic portion having an exposed surface has plastic encapsulating material partially disposed thereabout such that associated semiconductor device leads are correctly positioned with respect to the heat sink metallic portion but are electrically isolated from it. A semiconductor chip is mounted directly on the heat sink metallic portion such that high heat dissipation is obtained. The lead frame provides for a plurality of metallic heat sink portions joined to a corresponding plurality of semiconductor device lead portions. Joining means positioned in the frame between adjacent metallic heat sink portions and correspondingly between successive semiconductor device lead portions are attached to each other to hold the respective portions of the lead frame in proper relationship to each other during the assembly process. These joining means are removed after plastic encapsulation thereby making it possible to electrically isolate the metallic heat sink portion from the semiconductor device lead portion. The use of this type composite lead frame structure where the metallic heat sink portion is joined to the device lead frame structure allows great versatility in types of material and types of fabrication steps used to provide a semiconductor device while the particular joining means used make it possible to obtain these advantages while still maintaining an electrically isolated heat sink.


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