Abstract
An autocatalytic electroless tin plating process is necessary for the formation of a tin deposit layer on small connecting terminals of miniature electronic devices. Formulae using titanium（III）chloride as a reducing agent have been reported to date. However, the practical use of such a process has not been achieved because the poor catalytic activity of tin makes it difficult to form dense tin deposits at a satisfactory deposition rate.
Our newly developed formula for electroless tin deposition contains a germanium compound as a deposition accelerator. By adding the germanium compound to the plating bath, dense tin deposits comprising large crystal grains were obtained with increasing deposit thickness proportional to the plating time. The deposits have a double-layered structure comprising a tin-germanium underlayer and a tin upper layer. Presumably, the presence of tin and germanium mutually accelerates their deposition. The tin-germanium layer is formed initially, followed by the primary deposition of tin on the tin-germanium layer.
