Acidic plating bath and additives for electrodeposition of bright tin

A primary tin plating brightening additive, comprising:

• a substituted naphthalene carboxaldehyde of the following general formula:
• ##STR7## where O is oxygen and where A is selected from the class consisting of hydrogen, hydroxy alkyl, polyalkoxy and 3-sulfopropyl, said alkyl containing from 2 to 8 carbon atoms, said polyalkoxy containing from 2 or 3 carbon atoms in the repeating unit wherein the number of repeating units ranges from 2 to about 40 per molecule, and said 3-sulfopropyl compound having the formula --CH.sub.2 CH.sub.2 CH.sub.2 SO.sub.3 Z where Z is selected from the class consisting of hydrogen, Group 1A, and Group 2A of the Periodic Table, including from 1 to about 97 percent of at least one alpha unsaturated compound selected from the group consisting of carboxylic acids, amides, and esters for producing bright electrodeposits of tin from an aqueous acid plating bath.