Effect of RF Plasma Ion Etching on Low Temperature Pressure Bonding Strength in Aluminum-Steel and Copper-Steel Systems

Low temperature pressure bonding tests were carried out by surface activated bonding technique. The experiments were made in a high vacuum range from 1×10-4 to 10-3 Pa by using commercially supplied aluminum (1050), copper (C1100) and mild steel (SPC3) sheets. As the surface activating treatment, RF plasma ion etching was employed. The effects of bonding pressure and RF plasma ion etching on bonding strength were investigated. It was revealed that the tightly bonding could successfully be achieved at low temperature (335 K) when the metal surfaces were sufficiently activated by RF plasma ion etching. The bonding strengths of activated specimens were increased with increase of loading pressure. In the case of aluminum, more than 495 MPa of loading, the fracture the bonding interface was not observed by peeling test but the aluminum plate was fractured itself. For the copper bonding, more than 750 MPa of loading was sufficient enough to achieve tight bonding. The bonding pressure required to achieve tight bonding was about 3-4 times of yielding strength. However the bonding could slightly achieve by loading those of pressure without surface activating treatment. The bonding strengths were increased with the increase of the amount of RF ion etching treatment. The amount of RF ion etching for surface activation could be estimated by XPS depth-profile analysis.