System level mechanical shock reliability of BGA packages: Experimental and numerical analysis

The demand for large form factor Flip Chip Ball Grid Array (FCBGA) package has been increasing to meet the growing needs of high bandwidth network traffic. It is also well known that FCBGA packages are sensitive to external mechanical shock. The dynamic performance of electronics under mechanical loading, such as bending and shock conditions, has been an important factor in the quality and reliability of these large body size packages. Meanwhile, the trend towards miniaturization and increased functional density has resulted in decreasing I/O pitch and increasing power. The high power dissipation in turn has resulted in the use of much heavier heatsinks fabricated from copper in lieu of aluminum. Heavier copper heatsinks increase the likelihood of package failure in mechanical shock environments. Consequently, optimization of heatsink design and attachment methods is necessary to minimize the effect of mechanical shock during impact on FCBGA solder interconnections. In this paper, three-dimensional Finite Element (FE) models have been developed to study the impact of different heatsink attachment methodologies. The structural damping coefficients based on the total weight of heatsink and backing plate have been derived, with which an excellent correlation has been achieved of the principal strain time histories on the PCB near the package corner between the model predictions and experimental results under different shock conditions. The models developed with this methodology enable board designers, thermal engineers, manufacturing and packaging teams to optimize the package, board and heatsink design and build a mechanically reliable product.