Treatment method after plating with Sn or Sn alloy

A treatment method after plating with Sn or an Sn alloy, comprising:

• performing plating with Sn or an Sn alloy;
• washing at least one of members used in a series of plating treatment steps with an acidic solution immediately after the plating with Sn or the Sn alloy, the acidic solution containing at least one kind selected from acids and salts thereof and having a pH of 5 or lower, wherein
• the acidic solution contains at least one complexing agent selected from the group consisting of gluconic acid, glycine, glucoheptonic acid, gluconolactone, glucoheptolactone, sorbic acid, and a salt thereof,
• the at least one of members is at least a conveyance tool for a substrate. repeating the plating and the washing 30 times, obtaining a surface coverage of the conveyance tool of 0% to 30%,
• wherein the surface coverage is a coverage of a surface of the conveyance tool with compound contaminations containing the Sn or the Sn alloy and is calculated by steps (i) to (iii):
• (i) observing by Field Emission Scanning Electron Microscopy the surface of the conveyance tool after repeating the plating and the washing 30 times;
• (ii) dividing an area of the surface into 4×5 squares such that a total number of squares is 20;
• and
• (iii) calculating the surface coverage according to equation (1):
• Surface coverage (%)=(Number of squares having the compound contaminations/Total number of squares)×100 (1).