Failure analysis of intermittent pin-to-pin short caused by phosphorous particle in molding compound

Many "intermittent pin-to-pin short" cases have occurred in LSI packages that are processed with a molding compound containing phosphorus as a flame-retardant. The failure always occurred after a few months to one year of usage, but all stress methods that have been tried seem unable to accelerate the failure before field usage. The paper describes an experimental investigation into ways of detecting phosphorous particles. Two kinds of phosphorous particles were seen in the device. A broken coating one formed an acid solution pool and caused a spider shaped growth of copper particles. It also formed a shorting path that resulted in the intermittent pin-to-pin short. The large copper particle that coexisted with phosphorous particles is the body of the spider. Soft X-ray can reveal large and medium particles near the failed pin. Focused ion beam (FIB) using passive voltage contrast (PVC) can reveal the spider shape that forms shorting path. EDS mapping provides not only the shorting path but also materials information.