Abstract
A new type of electroless tin plating bath has been applied in a disproportionation reaction of Sn (II) ion involving
2Sn(OH)3-→Sn+Sn(OH)62-
(Sn(II) Sn(0) Sn(IV))
In a previous paper, a Sn (II)-NaOH system bath (called a Na bath) was proposed. To develop a bath having higher plating rate, alkali hydroxide was replaced by KOH (a K bath) or LiOH (a Li bath).
Plating rates and the morphologies of deposits from the K and Li baths were compared with those from the Na bath.
The following results were obtained.
1. In terms of the width of the transparent stable region, the baths were in the order NaOH>KOH>LiOH, the same order as the solubility of the alkali hydroxides.
2. The K bath had the highest plating rate under the same conditions (Sn (II) 0.4M, KOH 5.2M, K3-citrate 0.5M, 80°C; 11.5μm/h).
3. Semibright compact deposits were obtained by simply lowering the temperature of the bath from 80°C to 60-75°C.
4. The plating and spontaneous decomposition reactions proceeded through disproportionation.
