Improvement of electrical conductivity of Cu/Ag glue joints by discharge cleaning

Abstract

A study of different methods for cleaning copper components to improve electrical conductivity of Cu/Ag glue joints is presented. Copper samples were cleaned with three different methods: (i) wet chemical cleaning with tetrachloroethylene, (ii) discharge cleaning with an oxygen plasma, and (iii) subsequent discharge cleaning with oxygen and hydrogen plasmas. Discharge cleaning was performed in a low-pressure weakly-ionized plasma created with a RF generator of the output power of 200 W and the frequency of 27.12 MHz. The concentration of impurities on the copper surface was determined by Auger electron spectroscopy (AES) depth profiling. Cleaning with oxygen plasma caused effective removal of organic impurities, but the oxygen concentration on the surface was increased. Additional cleaning with hydrogen plasma effectively reduced the oxide film, so the copper surface became virtually free of any impurities. The electrical resistance of the joints between the components treated by different methods showed that the contact resistance is decreased with increasing copper surface cleanliness.