Influence of atmospheric exposure after surface activation on the low-temperature pressure bonding [TGP1] of aluminum/steel and copper/steel

The influence of atmospheric exposure on the low-temperature bonding of surface-activated aluminum, copper and mild steel sheets was studied in a high vacuum. The previous report showed that tight bonding was achieved in high vacuum with a surface activation bonding technique. However, a considerable amount of residual gases, such as water, hydrocarbons and carbon dioxide, remained in the atmosphere. Therefore the activated surface could immediately be contaminated with these gases. Bonding strengths were examined after exposure to various air pressures after surface activation. This decreased the bonding strength of Al after a threshold value of approximately 10(2) Pa(.)s was reached at various pressures. The bonding strength of Cu was decreased after an exposure of 10(0) Pa(.)s. XPS analysis revealed that the activated surface of Al was immediately oxidized by atmospheric exposure. However tight bonding was still attainable up to an exposure of 10(2) Pa(.)s. In contrast, the activated surface of Cu was not oxidized by atmospheric exposure, and only adsorption of residual gases was observed, but the bonding strength decreased with a smaller exposure compared with Al.