SPEEDY EVALUATION METHOD FOR UNIFORM COVERING PROPERTY OF SN LAID ON PB-SN ALLOY PLATING LAYER

摘要

PURPOSE: To speedily evaluate the uniform covering property of Sn on turn plating by measuring the current flowing, while applying anode-polarization to an Sn plating layer on a turn plated steel plate in an acetic acid soda or acetic acid potassium solution. ;CONSTITUTION: A sample in which Sn is laid on a turn plated steel plate is cut in its approximate size and impregnated in acetate solution, a constant electric potential is applied thereto by means of a potentiostat, and the flowing current is measured. If the uniform covering property of Sn plating on the turn plating is high, the current is stabilized by approx. 20 seconds, and hardly changes thereafter. If the uniform covering property of Sn is low, the floating current continues to increase immediately after application of the voltage. This event can be estimated because pin holes existing in the Sn plated layer expand during the process in which Pb is anode-dissolved. Here, the current valve after 3 to 5 minutes is read and assumed as the scale of evaluation in order to quantitatively measure the uniform covering property of Sn. Thereby, the evaluation for which the period of 2 weeks to 3 months has been required conventionally can be shortened significantly.;COPYRIGHT: (C)1996,JPO