Selective Cu Surface Activation for Cu-Sn Thermocompression 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 regent. From the data obtained by changing the compression temperature and time, we assumed that the activating effect of the deposition on Cu was induced by lowering the reaction temperature with Sn. Since the deposition was not observed on other materials including silicon based and organic polymer based dielectrics, we believe this technology is promising to simplify the chip let manufacturing process especially in future high-density interconnection systems.