BGA Interconnection Reliability in Mirrored Module Configurations

Interconnection dimensions are becoming more important due to electrical signal timing requirements and stray effects, such as unwanted inductance, leading to increasingly denser packaging. One way to shorten the signal path is to use mirrored structures, where the components are placed on opposite sides of the printed circuit board (PCB). This paper presents thermal cycling test (TCT) results in a temperature interval from -40 degrees C to + 125 degrees C and simulation results of plastic ball grid array components mounted on one side [single side (SS) configuration] and in different mirrored configurations on a PCB. Anand's constitutive model is used in the finite-element analysis software to calculate dissipated creep energy densities in the interconnections. Field lifetimes of the presented cases were also calculated on the basis of the dissipated creep energy densities and TCT data. In addition, supporting microscopic studies were done. The single-sided configuration had a longer lifetime than the mirrored configurations with components on opposite sides. The mirrored configurations had adverse simulated creep energies and TCT lifetimes, compared with the single-sided configuration. The simulations proved that the flexibility of the mirrored structures was hindered, thus increasing stress levels in critical interconnections.