抄録
Pb-Sn-Cu alloy plating from fluoborate baths has been carried out by the constant current method (CCM) and the pulse current method (PCM). It has been found from polarization measurements that the existence of Pb2+ in the plating bath decreases the limiting current density of copper deposition. The copper content in plated layers made by CCM qualitatively corresponded with the limiting current density of copper deposition. In the case of PCM, the copper content in the plated layer reached a maximum at a frequency of about 10Hz. During the PCM off-time, a layer of high copper content was formed at the electrode surface by a Pb+Cu2+→Pb2++Cu replacement reaction. This is the chief distinction of PCM. The tin content of the plated layer did not change with current density in CCM and increased with the addition of hydroquinone to the plating bath. The preferred orientation of lead in plated layers obtained by CCM using a bath containing gelatin and hydroquinone was (220) plane, but this was not recognized for PCM except in the case of low duty ratios. Plating layers having a compact, smooth sureface morphology were prepared by PCM at a low frequency and a duty ratio of about 0.5.
