J. A. Roepsch, Raytheon, McKinney, TX

Summary: Two case studies will be discussed in which root failure cause was related to process issues at the supplier. Contamination on raw PWBs resulted in poor solderability at the package level. In the first case study, a photoresist material used to protect the solder on one side of the board as the other side was being etched was not completely being removed. A plasma clean was sufficient in cleaning the photoresist from the solder allowing boards in stock to be used. The board supplier changed processes on future builds by etching both sides of the board simultaneously eliminating the need for the photoresist. No future failures were identified after this process change. The second case study also was a failure initiating at the supplier. Material was trapped in vias due to their small feature size, later leaching out onto the board surface. The source of the carbonate material was never fully understood but could be isolated to the supplier. Once the vias were filled by the supplier, future failures were no longer identified. A rework process involving 10% HCl was carried out on failed CCAs improving the solderability with replacement BGAs.