Plastic packaging of microelectronic circuit devices

Thermally conductive heat transfer bodies are included in plastic packages to extend from the die pad and/or circuit chip to or near the surface of the package. Leakage is prevented by encapsulating the heat transfer body in a thin film of plastic and/or by arranging the interface between metal and plastic to be elongated and convoluted. The heat transfer body is attached to the die pad and/or lead frame to stabilize the body during molding and to aid in thermal communication between the chip and the heat transfer body. Air cavities and EMI shielding are provided by caps secured to the lead frames.