Wearout reliability study of Cu and Au wires used in flash memory fine line BGA package

Bond reliability at a Cu wire bond under a humid environment is a major concern in replacing Au wires. Conventional bare Cu bonding wires, in general, are more susceptible to moisture corrosion compared to Au and PdCu wires. This paper discusses the wearout reliability performance of two wires used in flash fineline BGA package. Weibull plots for two wire legs have been used to calculate the survival hours and cycles at 0.10% failure rate & its t₅₀ life. The bond reliability of PdCu and Au wires are compared in the reliability testing of uHAST (unbiased HAST), biased HAST and component level temperature cycling. The lifetimes for two wire types in extended reliability stresses are calculated respectively. Moisture resistance is significantly greater for Au wire. An insulating layer is formed at the bond interface for PdCu wire after extended unbiased and biased HAST hours and induces resistive opens. Corrosion induced deterioration would be the root cause of failure for both Cu wires. The Cu ball bond corrosion is a chemical reaction of Cu-Al IMC (Intermetallic Compound) and halogens (Cl^-) from molding compound under moisture environment. Failure mechanism has been proposed and discussed in this paper.