Copper wire bonded package characterization and reliability for QFN package from iNEMI collaborative project

The iNEMI Cu Wire Reliability Project Team has performed reliability tests on a copper wire bonded QFN (Quad Flat No-Lead) package to assess its long term reliability. Bare copper (Cu) and Palladium coated Cu (Pd/Cu) bonding wires were used with a low chlorine mold compound as test vehicles using 5 DOE legs comparing wire type and process conditions. Five HAST (Highly Accelerated Stress Test) conditions with fixed bias voltage, varying temperature and humidity, and one condition of HTS (High Temperature Storage) and TC (Temperature Cycling) were used for the reliability test. The TC test resulted in no failures for all segments up to 3000 cycles; however, different results were obtained from HAST. The packages were tested for a longer time to achieve failures. With longer times and cycles, the bare Cu package was found to fail due to oxidation around the bonded ball area and Cu/Pd packages failed due to the Pd distribution pattern in the bonded ball. A humidity level of 55%RH was sufficient to affect the oxidation of the bare Cu wire but to a lesser degree than at 85%RH.