Reliability assessment of a high CTE CBGA for high availability systems

Abstract

High availability network switches and routers employ high power dissipation ASICs that operate at near 100% utilization in a wide range of end-use environments. Ceramic ball grid array (CBGA) packages are typically employed to address these extreme thermal loading conditions. These ceramic packages exhibit a high coefficient of thermal expansion (CTE) differential when compared to the FR-4 printed circuit board. This large CTE mismatch results in a CBGA solder joint reliability that is significantly lower than that of a plastic ball grid array (PBGA) package. Various suppliers have developed high-CTE ceramic materials to be used as substrates for CBGA packaging. These high-CTE ceramic materials have a CTE that is more closely matched to that of FR-4, and hence, improves the solder joint reliability of the package when subject to thermal loading conditions encountered during field life. This study assessed the solder joint reliability of a CTE CBGA for use in a high availability network backbone router. A numerical technique based on fracture mechanics and energy methods was used to predict reliability under accelerated temperature cycling (ATC) conditions.