Thermal analysis of a flip chip ceramic ball grid array (CBGA) package

Abstract

The function of an electronic cooling package is to dissipate heat to ensure proper operation and reliability. The flip chip ball grid array package is probably the most suitable package for high-level thermal performance applications. A high thermal performance flip chip ceramic ball grid array (FC-CBGA) package with an aluminum silicon carbide (AlSiC) lid and one without lid were evaluated using the computational fluid dynamics (CFD) technique. This paper compares the thermal performance of a 35 × 35 mm FC-CBGA package with three different die sizes of 5 × 5 mm, 15 × 15 mm and 20 × 20 mm. The performance of a lid fitted with different heat sinks was investigated in standard JEDEC defined natural and in forced convection environments. Thermal measurements were performed using a functional application specific integrated circuit (ASIC) chip, in compliance with the JEDEC standards. Excellent agreement was found between the numerical results and the measured data. Improved thermal performance was observed with a lidded package as compared to the unlidded one. However, no significant improvement was observed between lidded and unlidded packages when fitted with a heat sink subjected to forced convection. This paper also discusses the package thermal budget estimate with and without heat sinks. Printed circuit board and package top surface temperature patterns were measured using an infrared thermal camera. The usefulness of the thermal characterization parameter is demonstrated in system level applications. Parametric studies were carried out to understand the effect of die size, radiation effect, gird size variations and airflow rate on die junction temperature and package thermal resistance. This study also incorporates the effects of substrate, lid, die and PCB temperatures for different die sizes in natural and forced convection environments.