We have investigated the characteristics and formation mechanism of tarnish on tin plated copper and copper alloy strips for electrical and electronic parts.
Further more, we have also researched the elimination method of tarnish. The main results obtained are summarized as follows:
1) It was found that tarnish was a kind of tin oxide formed through the action of oxygen and humidity in the air. It was also revealed that the oxygen bearing layer of tarnished surface was thicker than that of normal surface. Thus, it is supposed that the “yellow” appearance of tarnish is due to the thickening of oxygen bearing layer of tarnished surface.
2) The contact resistivity and surface roughness of tarnished surface were not inferior to that of normal surface.
3) The solderability of tarnished surface was not so good as that of normal surface when nonactive flux was used. But differences in solderability were not observed with active flux.
4) To eliminate tarnish, chemical methods, especially the pickling method, were found much effective.