Challenges in copper 2nd bond quality on nickel palladium leadframe

Nickel-palladium (NiPd) based lead finishes has been one of the options for lead-free electronics. Currently there are different types of NiPd finish in the industry like NiPdAuAg, NiPdAu and rough NiPdAuAg. These preplated lead frame finishes while eliminate the need for plating after assembly/encapsulation, it also has a few challenges especially on the 2nd bond wire bond quality. This is especially obvious when Cu wire bond was introduced. This paper will provide some insight, compare the 2nd bond performance when using Cu wire on both Ag plated frame and NiPd frame. It was observed that stitch pull strength for Cu wire bonding on rough uppf lead frame generally lower than the Ag plated Cu lead frame and percentage of Cu remain after stitch pull for rought µppf lead frame is lesser than the Ag plated lead frame. The different results possible due to different lead frame plating materials, plating thickness and hardness.