Failure analysis on corrosion induced Cu-Al bond failures

The failure analysis from the manufacturer could not fully explain the Cu-Al bond open and drift issues in some plastic encapsulated microcircuits. For further investigation, an insight analysis containing chemical deprocessing, cross-sectioning and mechanical opening was performed to define the root cause. Several new findings were observed to support a reasonable cause. The corrosion reaction of intermetallic compounds (IMC) with Cl ions participating was responsible for the anodic bond open failures, cracks grew at the interfaces of Cu ball and IMC, and the re-deposition of Cu ball corrosion resulted in leakage current and drift faults. The results prove that Cu-Al bond is sensitive to H2O and Cl, which play a role as catalysis, and the corrosion tend to happen more easily in anode with bias.