Lead-free Tin Alloys as Substitutes for Tin-lead Alloy Plating

The use of lead and lead-components is prohibited or restricted for many applications. Presently there is therefore a discussion on the possibility to substitute lead as an alloying element in solder-alloys for electronic applications. The advantages for lead-containing tin-alloys as solder and solderable coating are for example low melting-point, effective prevention of whisker growth, low price and high availability. From the view of electrochemical deposition, the system is favoured because of the similarity of the standard potentials of both elements. It is therefore possible to deposit from acidic electrolytes without complexing agents any tin-lead ratio. Stable and mature processes are available for technical applications. In the search for lead-free solders these arguments must be considered. The electrolytic deposition of any alternative for tin-lead should be possible from systems which are non-hazardous to people or the environment. Taking account of the above mentioned arguments the paper describes initial experiments on the deposition of tin-bismuth-alloys. The eutectic Sn/Bi-alloy is already used as solder for special applications. By adjusting the Sn/Bi-ratio in the electrolyte. it is possible to deposit coatings, which have a similar range of melting point as known Sn/Pb-alloys. Preliminary results on solderability hardness and topography of different Sn/Bi-alloys are presented.