A method for depositing a whisker resistant tin-based coating layer on a surface of a copper substrate, the method comprising: contacting the surface of the copper substrate with an immersion tin plating composition comprising: a source of Sn 2+ ions sufficient to provide a concentration of Sn 2+ ions between 5 g/L and 20 g/L; a source of Ag + ions sufficient to provide a concentration of Ag + ions between 10 ppm and 24 ppm; a source of sulfur-based complexing agent for tinions and copper-ions sufficient to provide a concentration of sulfur-based complexing agent between 60 g/L and 120 g/L, said sulfur-based complexing agent being capable of reversing the relative EMF potentials of copper and tin; a source of hypophosphite ion sufficient to provide a concentration of hypophosphite ion between 30 g/L and 100 g/L; in addition to the source of hypophosphite, a source of anti-oxidant sufficient to provide a concentration of anti-oxidant between 30 g/L and 110 g/L; a source of pyrrolidone sufficient to provide a concentration of pyrrolidone of at least 12 g/L; and an acid in a concentration sufficient to lower the pH of the composition between 0 and 5, wherein the tin-based coating comprises at least 80 wt% Sn. contacting the surface of the copper substrate with an immersion tin plating composition comprising: a source of Sn 2+ ions sufficient to provide a concentration of Sn 2+ ions between 5 g/L and 20 g/L; a source of Ag + ions sufficient to provide a concentration of Ag + ions between 10 ppm and 24 ppm; a source of sulfur-based complexing agent for tinions and copper-ions sufficient to provide a concentration of sulfur-based complexing agent between 60 g/L and 120 g/L, said sulfur-based complexing agent being capable of reversing the relative EMF potentials of copper and tin; a source of hypophosphite ion sufficient to provide a concentration of hypophosphite ion between 30 g/L and 100 g/L; in addition to the source of hypophosphite, a source of anti-oxidant sufficient to provide a concentration of anti-oxidant between 30 g/L and 110 g/L; a source of pyrrolidone sufficient to provide a concentration of pyrrolidone of at least 12 g/L; and an acid in a concentration sufficient to lower the pH of the composition between 0 and 5, wherein the tin-based coating comprises at least 80 wt% Sn. a source of Sn 2+ ions sufficient to provide a concentration of Sn 2+ ions between 5 g/L and 20 g/L; a source of Ag + ions sufficient to provide a concentration of Ag + ions between 10 ppm and 24 ppm; a source of sulfur-based complexing agent for tinions and copper-ions sufficient to provide a concentration of sulfur-based complexing agent between 60 g/L and 120 g/L, said sulfur-based complexing agent being capable of reversing the relative EMF potentials of copper and tin; a source of hypophosphite ion sufficient to provide a concentration of hypophosphite ion between 30 g/L and 100 g/L; in addition to the source of hypophosphite, a source of anti-oxidant sufficient to provide a concentration of anti-oxidant between 30 g/L and 110 g/L; a source of pyrrolidone sufficient to provide a concentration of pyrrolidone of at least 12 g/L; and an acid in a concentration sufficient to lower the pH of the composition between 0 and 5, wherein the tin-based coating comprises at least 80 wt% Sn.