Effects of plating parameters on the Au-Sn co-electrodepositon for flip chip-LED bumps

Abstract

The Au-Sn alloy was successfully pulse electrodeposited in a new non-cyanide and non-toxic stable electroplating bath which basically was composed of Au compound and tin sulfate (SnS04). The composition and morphology of electrodeposited Au-Sn alloy were investigated in terms of current density, temperature and pH value in the developed bath. It was possible to control tin content in the electrodeposits by means of current density. Au-Sn alloy with Sn concentration of about 20 to 45 at.% was deposited at peak current density ranging from 3 mA/cm 2 to 45 mAzcm". Although the microstructure and surface morphology of the electrodeposits were influenced by the peak current density, dense and smooth Au-Sn films with fine grain had been electroplated at different current density. With increasing pH value, the tin content in the alloy was obviously increased from about 10 to 45 at.%. When the pH value was greater than 8.5, the deposits became porous and incompact mainly owing to the hydrogen evolution reaction during plating. With increasing temperature, the tin content was slightly changed, however, the grain size became bigger and the films had a tendency towards coarser because of the rapid consumption of metallic ions. Therefore, it can be concluded that the optimum condition of pH value for electroplating of Au-Sn alloys was ranging from 7.5 to 8 and that of temperature was 35 to 45°C.

Microstructure evolution of Au/SnSb-CuNiAg/(Au)Ni during high temperature aging

“…The high thermal conductivity of Au-Sn (57 W/mC) makes it particularly useful for bonding high-power devices that demand good heat dissipation. The eutectic Au-Sn alloy (Au-20 Wt.% Sn) is broadly used in optoelectronic industries of military products (Pan et al, 2011). However, Au80Sn20 is expensive and has a limited plastic deformation range (Yoon et al, 2007a(Yoon et al, , 2007b(Yoon et al, , 2008Tsai et al, 2006;Kim and Lee, 2006;Chromik et al, 2005;Kim et al, 2005;Yoon et al, 2007aYoon et al, , 2007b.…”

Study on Co-Electrodeposition Mechanism of Au-30at.%Sn Eutectic in Non-Cyanide Bath by Electrochemical Methods

“…To solve this problem, a number of attempts have been made to develop non-cyanide Au-Sn electroplating baths. [12][13][14] Up to now, the electrodeposition technology of Au-Sn alloys has not yet fully developed due to the large gap in standard electrochemical reduction potentials between Au and Sn ions. Complexing agents can reduce the deposition potential difference between the desired metal ions to a great extent, which is the key factor in realizing co-deposition of Au-Sn.…”