Effect of the microstructure of copper oxide on the adhesion behavior of epoxy/copper leadframe joints

The thermal oxidation of copper leadframe was carried out at 175 degreesC a nd the adhesion behavior of the epoxy/copper leadframe joint was analyzed b y investigating the microstructure changes of copper oxide with the thermal oxidation time of copper. The peel strength increased sharply at an early stage of oxidation (similar to 20 min) followed by a slight increase. After further oxidation (120 min), the peel strength showed a slight decrease. T he contact angles of water and diiodomethane decreased sharply at an early stage of oxidation with negligible change afterwards. As the oxidation time increased, X-ray photoelectron spectroscopy (XPS) results revealed that th e chemical composition of copper oxide had changed (Cu/Cu2O --> Cu2O --> Cu O); this change improved the wettability of the copper surface, which affec ted the peel strength. Increase of the surface roughness of copper oxide, i nvestigated by scanning electron microscopy (SEM) and atomic force microsco py (AFM), causes the epoxy resin and copper oxide to undergo mechanical int erlocking, which increases the peel strength. Failure analysis by SEM and X PS indicated that failure was largely in the copper oxide, and the amount o f copper oxide on the peeled epoxy increased as the oxidation time increase d, due to the weak mechanical strength of the oxide layer. However, a small portion of the epoxy resin was also fractured during the failure process, regardless of the oxidation time. Consequently, fracture proceeded mainly i n the copper oxide close to the epoxy resin/copper oxide interface.