Texture of electrodeposited tin layers and its influence on their corrosion behavior

• Grain orientation of Sn layers depends on current density and layer thickness.
• Corrosion of differently orientated tin layers does not depend on grain size.
• (3 2 1)/(2 2 0) texture prevents corrosion, while (1 1 2)/(1 0 1) texture enhances corrosion.
• Crystallographic model of tin surface may explain slow corrosion for (3 2 1)/(2 2 0).

Differences in the degree of corrosion of pure thin tin films electrodeposited on copper substrates were investigated in dependence on the layer thickness and the texture of the tin layers. The change of the preferred orientation of the tin layer deposited by applying different current densities was analyzed using X-ray diffraction. A graphical evaluation was used to determine the degree of corrosion after sample exposition to NaCl contaminations and humidity. Results show that a preferred orientation along the lattice planes (3 2 1) and (2 2 0) enhances the corrosion resistance of the tin layer by about one order of magnitude compared to a non-textured sample based on the corroded area. In contrast, a texture along (1 0 1) and (1 1 2) accelerates the oxidation of tin by a factor of about three to four compared with a randomly orientated specimen. The corrosion dependence on the preferred orientation decreases with increasing layer thickness. Moreover, scanning electron micrographs show no effect to the size of the tin grains on variations of the current density. In summary, changes in the process parameters of the electrodeposition lead to a variation of texture and thus modify the chemical and corrosion properties of the resulting tin layers. Consequently reliability properties like solderability or whisker growth in further applications depend on these parameters.

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