Thermal characteristics of single and multi-layer high performance PQFP packages

Using experimental and computational techniques, it is shown that significant reduction in the package thermal resistance can be achieved by using a multilayer lead frame structure for medium and high lead count plastic quad flat pack (PQFP) packages. The thermal resistance of the 132 lead PQFP is reduced by 38% and 43% with copper and alloy 42 lead frames, respectively, under natural convection. A three-dimensional finite-element thermal model is constructed and correlated with the experimental data. Using this model, it is demonstrated that the contribution of the low thermal conductivity insulating adhesive tape to the overall thermal resistance is about 1 (°C/W). In addition, increasing the power and ground plane thicknesses from 6 to 10 mils results in only about 1.5 (°C/W) improvement in the junction-to-ambient thermal resistance. The thermal model is used to compare the thermal characteristics of the single-layer and multilayer PQFPs with copper and alloy 42 lead frames in the multicomponent board environment. The comparison indicates that the thermal resistance of the multilayer/alloy 42 lead frame PQFPs approach the thermal resistance of the multilayer/copper lead frame packages as the board temperature rises above the ambient temperature as a result of board heating. These packages will have similar thermal performance if the board temperature rises about 70 (°C) above the ambient