Silicon precipitate nodules on BiCMOS processing

Qualification failures on a BiCMOS product were found to be caused by a metal bridge between a signal line and a power supply bus at an array of vias. Additional metal protrusions were discovered at other via array sites. The protrusions were found to be caused by silicon precipitate nodules which were identified by de-processing, SEM (Scanning Electron Microscopy), and EDX (Energy Dispersive X-ray). Short term containment consisted of a temporary design rule change. Corrective actions have been pursued which includes lower temperature passivation, sintering after passivation, and a conversion from AlCuSi to AlCu.