A novel coupling agent based on Zn-Cr chemistry for enhanced moulding compound to leadframe adhesion and improved popcorn resistance

A novel leadframe surface treatment is proposed as a popcorn solution for moisture sensitive surface mount devices. In this paper, we demonstrated the use of an ultrathin Zn-Cr (A2) coating on a Cu leadframe to achieve level 1 for a highly moisture sensitive PQFP-16O package. Marked improvement in moulding compound/leadframe adhesion and superior adhesion retention when subjected to prolonged oxidising conditions at 280/spl deg/C were distinct features of this coating system. The A2-layer has a fibrous acicular morphology and was estimated to be 90-120 /spl Aring/ by AES (Auger electron spectroscopy) depth profiling. X-ray photoelectron spectroscopy (XPS) analysis revealed that the Zn and Cr present in the coating were in the oxidised states, and these species did not undergo compositional changes during wire bonding. The wire bondability issues surrounding A2-treated leadframes can be rectified by various potential methods of producing wire bondable leadframes.