Thermal and Thermomechanical Modelling of Ball Grid Array Packages

Abstract

Ball grid array is a promising packaging technology. To exploit its benefits, a good knowleldge of its thermal and thermomechanical behaviour is mandatory.

Ball grid array allow to a higher silicon to printed circuit board (PCB) area ratio, sometimes increasing dramatically the power density at the package level. Elevated die temperature can degrade reliability and moreover decrease electrical performance (e.g CMOS applications).

Thermal analysis of package’s structure and printed circuit board stackup are performed for a better understanding of the importance of the constitutive elements of the package allowing to an enhanced thermal coupling of both parts for cost effective thermal management.

The reliability of the solder balls is a key concern. Fatigue failure, induced by the thermal expansion mismatch between the package and the FR4 board, is one aspect of pellicular importance. The plastic strains within the solder alloy computed in the finite elements analysis are used as inputs in the Engelmaier equation to estimate the fatigue life of the assembly.