Lead frame for plastic encapsulated semiconductor assemblies

摘要

An improved lead frame is provided for the manufacture of high heat dissipating semiconductor devices having a large heat sink metallic portion exposed with plastic encapsulating material partially disposed thereabout. A semiconductor unit is mounted directly on the heat sink such that high heat dissipation is obtained. The lead frame provides for pairs of metallic heat sink portions joined to a interdigitated center lead frame portion such that the interdigitation of the semiconductor device leads associated with each of the opposed heat sink portions provides for a high density lead frame structure from which a minimum of material must be removed in the fabrication process. The center lead frame portion comprises two parallel interconnecting rails or tie bars which provide a dual function in that they provide a mold stop for subsequent plastic encapsulation fabrication steps while simultaneously providing a support for alignment hole means which provide indexing of the lead frame and associated opposed heat sink portions through various automated manufacturing steps. The use of a composite lead frame structure wherein the metallic heat sink portion is joined to the center lead frame structure allows great versatility in the types of material and the types of fabrication steps used to provide a semiconductor device thus allowing manufacture at greatly reduced cost.