An assessment of the thermal performance of the PBGA family

The plastic Ball Grid Array (PBGA) has generated significant interest as a cost effective packaging alternative for high I/O ULSI devices. This study assesses thermal performance of the PBGA family using the metric of power dissipation capability-“power rating” for IC packages. The metric chosen is the power dissipated for constraints of junction temperature (<105°C), and board temperature (<90°C), in low aspect ratio enclosures (portable products), as well as natural and forced air convection (~1.0 m/s) equipment operating conditions. The free and forced air conditions are typical of PC/workstation environments. Simulation studies using a finite difference based software for thermal performance of IC packages investigated the relative roles of package enhancements towards the thermal performance. Experimental data for the 106 PBGA in free air and portable radio mockup, and the 119 PBGA in free and forced air were used to validate the methodology. The study covers 68 to 324 pincount PBGAs and compares the performance with comparable pincount PQFPs (plastic Quad Flat Package) and other contemporary package styles. The study also addresses system level enhancements for extending the thermal performance of PBGAs for applications. The power dissipation for PBGAs in portable products is projected at 0.6 W. The power dissipation capability of the PBGA is projected to lie in the range 1.5-1.75 W in free and forced air environments. Coupling a motherboard ground plane to the package thermal vias and bumps allows performance enhancement to 2.8 W. A heat-sink attached PBGA allows heat dissipation in excess of 8 W in high end systems. The thermal performance of the PBGA is comparable to PQFP-even when no advantage is taken of the package thermal vias and bumps by the system. Furthermore, the performance of the PBGA compares well with CPGA, CQFP and the CBGA packages