Failure Detection of BGA Transition Structures at High Frequencies

The purpose of this paper was to investigate the effect of thermal cycling on the high frequency behavior of a BGA transition structure. A broadband microwave BGA transition structure between a RF-PWB and a ceramic module was designed and fabricated. The stand-off height of the composite BGA solder joints was 500 mum. The BGA test modules mounted on the PWBs were exposed to thermal cycling testing over a temperature range of -40...+125 degC. To detect interconnection failures induced by cyclic thermal stresses, both DC resistance and scattering parameter measurements (45 MHz-25 GHz) were performed on the test assemblies at specific intervals. Parallel to the electrical measurements, crack propagation in the vicinity of the BGA transition structure was investigated using scanning acoustic microscopy (SAM). Moreover, scanning electron microscopy (SEM) was used to determine the failure mechanisms of the test assemblies. Degradation in the signal transmission characteristics was first observed at higher microwave frequencies as an increase in signal return loss (|S11|). As the thermal cycling test proceeded, the reflected signal loss became more significant and gradually became pronounced at lower microwave frequencies. Pure DC resistance measurements showed no indication on the degradation of the transition structure