Investigation of a novel leadframe treatment for “dry-pack free” packaging

The popcorn phenomenon in plastic surface mount packages is still widespread throughout the industry. One of the important factors identified to effectively eliminate the occurrence of this failure mode is adhesion. A novel adhesion-enhancing leadframe surface treatment is proposed as a solution to dry-pack free packaging of moisture sensitive surface mount devices. This paper discusses the use and characterization of an ultra-thin inorganic coating based on Zn-Cr chemistry to achieve level 1 for a highly moisture sensitive PQFP-160 package. The use of this coating led to a significant adhesion enhancement between the leadframe and moulding compound as well as superior adhesion retention characteristics when subjected to prolonged oxidising conditions at 280°C. The coating has a fibrous and acicular morphology and was estimated to be 90-120 Å by AES (Auger Electron Spectroscopy) depth profiling technique. X-ray Photoelectron Spectroscopy (XPS) analysis revealed that the Zn and Cr present in the coating are in the oxidised states and these species did not undergo compositional changes during wire bonding conditions