Investigation of Al-induced electroless Sn film deposition on Cu substrate

Smooth, shiny and homogeneous tin and tin boride films have been deposited on the copper (Cu) substrates using aluminium (Al) induced electroless process. These coatings were prepared by introducing Al as a prime reducing agent. The galvanic couple between Cu-Al initiates the metal reduction reaction from a bath without traditional reducing agent and additives. Additionally sodium borohydride as a chemical reducing agent was also added for codeposition of boron. This study was conducted in the temperature range of 30 to 95 degrees C, though improved deposit morphology was found only above 80 degrees C. The optimum geometric area ratio between the substrate and Al foil surfaces was found to be 0.5. X-ray diffraction analysis confirmed the polycrystalline tetragonal structure of the deposit and crystallite size was found similar to 25 nm. The electrochemical measurement showed that the coupled Al can shift the Cu substrate potential negatively which enhances the rate of reduction reaction. The polarization measurements indicated the validation of mix potential theory, particularly for the tin deposition process.