Selective Cu Surface Activation for Cu-Sn Thermocompression Microbump Bonding Without Flux Deposition

We have developed a Cu selective wet chemical treatment that can deposit an activating compound only on Cu surface. With this treatment, thermocompression bonding (TCB) between Cu and Sn can be performed without applying a flux agent. From the data obtained by changing the flow gas of the plasma pretreatments for SnAg microbump chip side, we assumed that the activating effect of the deposition on Cu surface was not prevented by Sn oxide layer formed by O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> plasma. Therefore, the plasma pretreatments for SnAg bumps were preferred to be combined with the chemical treatment, which worked as a cleaning step of the bump surface and they can improve the bonding quality of TCB.