Enhancement of thermal performance of a PBGA (plastic ball grid array) is often accomplished by embedding metal layers in the substrate and the inclusion of a copper spreader in the mold compound. The thermal effectiveness of the substrate planes in spreading the heat is frequently compromised by the necessity to separate the various voltages on the power plane and the required clearance regions around the electrical vias. Determining the appropriate effective conductivity has frequently been addressed by engineering judgment. Detailed simulation of the entire package, inclusive of structural detail in all the substrate planes, is very time consuming and inefficient. In the paper, the determination of the effective conductivity is accomplished with a simplified finite element representation of each metal layer capturing the connectivity of the traces or the metal patterns in the planes. The appropriate conductivities are then used in a detailed CFD model. The two stage process was chosen to model the performance of the thermally enhanced PBGA with and without a copper spreader placed at the top of the mold compound. A test case of a 516 27×27 mm PBGA was used. The model results are compared against experimental measurements. The CFD model was used to determine the performance with heat sinks in natural and forced convection environments and the results compared to experimental measurements.

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