Thermal sensitivity analysis for the 119 PBGA-a framework for rapid prototyping

New package prototyping is often a sequential process where the chip and system parameters are specified first, then the package design is initiated. A reduction in overall cycle time can be affected if the events occur simultaneously. This study proposes a methodology for addressing this issue. The method is outlined in the context of prototyping the 119 plastic ball grid array (PBGA) package thermal performance. The parameters influencing performance are system, device, or package based. Ranges for the "yet-to-be-fixed" parameters are determined and factorial analyses are used to yield approximate linear models with interactions for package performance. Once the device and system parameters are "fixed", the linear equations are solved simultaneously with junction and board temperature constraints to yield a design options map for package layout. The prototyping sequence for the PBGA results in substrate thermal conductivity, mother board thermal conductivity, mother board load, and heat sink attachment as the set of "variable" parameters-with other parameters being "fixed". The design options map gives the minimum substrate thermal conductivity needed to meet the thermal performance specification for a particular set of parameters. The substrate specification is further related to physical attributes required of the package in terms of thermal vias, thermal bumps and metal layers. These results are generically applicable to the PBGA family. A 119 PBGA package enclosing a 2 W chip requires a minimum substrate thermal conductivity of 0.03 W/cm-/spl deg/C to meet the junction temperature constraint for high performance workstation environments. Results of the performance prediction are further verified by a composite finite element simulation and experimental validation with prototypes. The design options map can be recreated without any additional simulation studies in the event any change in the "fixed" parameters occurs. The methodology described allows anticipation of design options in the "dynamic" environment of prototyping, and implementation of optimized package designs to meet performance under multiple customer environments.