US Patent 7221042 Leadframe designs for integrated circuit plastic packages

The specification describes a plastic cavity package design for high power transistor packages in which the leadframe is formed of a composite of materials. This allows the portions of the leadframe that require strength to be formed of a high strength material, e.g. steel, while the paddle portion of the leadframe is formed of a high thermal conductivity material, e.g. copper. This composite leadframe optimizes thermal and mechanical performance at low cost. In the preferred embodiment the leadframe is provided with a center cutout, where the die is attached. A copper insert is assembled in the cutout. The copper insert provides an effective heat sink, while the remainder of the leadframe provides the desired mechanical strength.