A new tool development for the thermal design and quick performance evaluation of FBGA devices

Due to rising thermal concerns from increasing power densities and industry demands for shorter development cycle times, we have developed quick solutions to assess the thermal performance of the FBGA package, one of the most widespread package options. We have designed a user friendly tool that provides a quick estimation of the junction to ambient thermal resistance of the FBGA package under JEDEC test conditions (JESD 51-2 and JESD 51-6). Results can be obtained within minutes by a click of a button after the simple entry of key package and environmental data. The tool significantly reduces the time for thermal evaluation; from hours or days needed to conduct full Computational Fluid Dynamics (CFD) simulations, to minutes by using the tool. It can also be used for upfront thermal design as it is able to assess the thermal impact due to changes in various package factors such as package size, die size, presence of solder balls under the die area, number and thickness of substrate metallized layers, total substrate thickness and number of thermal vias under the die area. The tool is also able to assess the impact due to changes in wind speed up to 1m/s and test board including both the 1S0P and 2S2P JEDEC PCB. With these features, the tool can be used to quickly estimate if the package specifications meet the desired thermal requirement, and if it fails to meet the requirement, rapidly identify potential package thermal design options. The formulation of the tool was challenging due to large number of factors involved such as the individual package components, environmental parameters and test boards. The complexity was further exacerbated by the complicated interactions between these factors and their impact on thermal performance. A systematic approach was thus designed to tackle these challenges. The formulation begun by the analysis of a large database of CFD simulation studies that were conducted for FBGA production devices. Using Design of Experiments (DOE), - - additional identified CFD simulations were conducted for a comprehensive assessment of all the factors. Experimental measurements were conducted using selected FBGA production devices under JEDEC still air and forced convection conditions on both 1S0P and 2S2P test boards. CFD simulation results of the selected test vehicles shows excellent agreement with the experimental studies with less than 10% deviations. From the extensive list of package and environmental parameters, key factors with significant thermal impact were identified through DOE and analysis of customized partial factorial results. It is found that the package size, die size, presence of solder balls under the die area and the substrate thermal conductivity are the key package factors with significant impact on the FBGA thermal performance. The FBGA thermal performance was then expressed as a function of these factors. Next, to verify that the key trends are well captured, the tool was then subjected to rigorous testing by comparison with both Computational Fluid Dynamics (CFD) simulation results and experimental measurements. Comparison of results shows that the discrepancies are within 15% under a specified applicable range, with more than 75% of the test results having less than 10% deviations. This paper presents the approach used in the formulation of the tool and the valuable insights on the FBGA package structure and thermal performance thus obtained.