The effect of the oxidation of Cu-base leadframe on the interface adhesion between Cu metal and epoxy molding compound

Abstract

Low temperature oxidation of a Cu-base leadframe has been made to investigate the effect of Cu oxidation on the adhesion of Cu-base leadframe (Cu L/F) to epoxy molding compounds (EMC). In contrast to previous studies, the existence of small amount of cupric oxide (CuO) was observed next to the Cu/sub 2/O, confirming the oxide layer structure of Cu/Cu/sub 2/O/CuO/air. It was shown that the early stage of oxidation improved the adhesion strength between EMC and Cu leadframe. Furthermore the optimum copper oxide thickness required for the maximum pull strength ranged from 20 nm to 30 nm. The high pull strength was presumably due to the increase of surface wettability and mechanical interlocking effects resulting from oxidation. The Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) studies on the Cu L/F and EMC surface after pull test indicated that failure modes before the maximum adhesion were a mixture of the adhesive failure between Cu/sub 2/O and CuO interface plus the EMC cohesive failure. After the maximum adhesion, the failure modes changed to the adhesive failure of Cu/Cu/sub 2/O interface as the copper oxide thickness further increased.