The design and characterisation of a high thermal efficiency leadframe with an integral heatspreader

The evolution, design, and characterization of a novel leadframe for plastic encapsulated devices are described, with details of its application in a 160-lead plastic quad flat pack. The challenges of putting a 400 mils square die dissipating 2.5 to 3 watts into this package were examined by finite difference analysis, and various arrangements of the leadframe were simulated until an optimum layout was derived. The leadframe was then refined in consultation with the frame manufacturers and device assemblers to achieve a solution which met all the manufacturability criteria. It was tested using a thermal test chip similar in size to the production chip, and its performance was compared with the options available. The test set-up used a miniature chamber in which the temperature was controlled by means of a bank of Peltier cells. The junction to ambient thermal resistance of the new design of leadframe was 28.6°C per watt, a reduction of almost 25% over the standard leadframe