Humidity-Bias Driven Shorts in Multilayer Circuits: A Case Study in Failure Analysis

When a failure analysis (FA) involves a multiple layer structure separated by a polymeric material such as Benzocyclobutene (BCB), in a plastic package, it becomes a very challenging task to find out where the failure site is and how it failed. This is due to the fact that the chemical de-processing procedure removes BCB as well as the plastic molding compound. This paper outlines the studies carried out to determine the failure site and the root cause of the failure mechanism in a multilayer circuit and the steps taken to fix the problems. The methodology and results of this study are applicable to many other types of circuits.