Comparison of Cl effect on Au-Al and Cu-Al HTS and bHAST wire bond reliability performance

Wire bond industry is transitioning from Au (gold) bonding wire to Cu (copper) bonding wire, due to the high cost of Au and comparatively much lower cost and good electricity conductivity of Cu. Whilst Cu is less reliable than Au. Cu is susceptible to corrosion especially under the presence of moisture and Cl (chloride). In this work, Au and Cu wires were ball bonded to Al pad and molded with EMC (epoxy mold compound) with different ranges of Cl. Cl was purposely added into EMC to trigger the failure. All EMC samples were prepared with pH range of 5 - 7. Reliability tests bHAST (biased highly accelerated stress test) and HTS (high temperature storage test) were conducted. The results showed that under dry condition, Cl was not easy to attack the wire bond, and failure did not occur unless high content of Cl (up to 500ppm) was present. On the contrary, under humid environment, even several ppm content of Cl would cause failure of Cu-Al wire bond. By comparison, under humid environment, as Au-Al wire bond formed corrosion products which locked the Cl, therefore Cl could not repeatedly serve as a catalyst. Au-Al failure occurred only with high ppm content of Cl (up to 500ppm). In addition, it is found that Cl will promote the Au-Al IMC growth in HTS and bHAST.