Achieving accurate thermal characterization using a CFD code: a case study of PLCC packages

Achieving component-level thermal characterization using computational fluid dynamics (CFD) is assessed using a case study approach. The FLOTHERM code is used to simulate the thermal performance of three plastic-based components (68-lead and 84-lead Plastic Leaded Chip Carriers or PLCCs and a 164-lead Plastic Quad Flat Pack or PQFP) under forced air cooling conditions. Predictions of thermal resistance are compared to experimental measurements. One aspect of the work is to use results from a single situation (84-PLCC and an approach air velocity of 1.5 m/sec) to develop a set of “modeling guidelines”. These modeling guidelines are then be applied to the other components and flow conditions (0.76 to 3.05 m/sec) to test their validity. Guideline parameters include near component flow field nodalization, geometric detail in representing conduction paths and code user options such as turbulent flow models. The average deviation of predicted versus measured values of junction to ambient thermal resistance (θ_ja) was 7.5% using the derived guidelines. An additional component design sensitivity investigated was the effect of the introduction of a heat spreading “heat post” in the high temperature regions of the 164-PQFP