Is copper or nickel flashing a must for good solderability of tin plated steel

A. I think the principal problem is the brighteners in the tin bath. I think an alkaline tin is easier to solder than a bright acid tin.

A. If you want solderability, use a matte tin. Organic brighteners in really bright tin make soldering a bitch. Solder as soon as possible after plate. One month old tin plate is a lot harder to solder than 1 week old, even in matte. Can you switch to a more aggressive flux or will that cause even worse problems. I did an experiment on recycling wire connecters that had been on the shelf for aver 3 years. Unfortunately, I do not have the records of it.

A. The best way to solder tinplate is to use alkaline tin that has been flow melted. Acid tin will be more likely to have brighteners added and this will make the wettability of the surface quite poor. The "art" to soldering is to have a good wettable surface and hence a low contact angle between the molten solder and the tinplate. Try using a good flux with the solder, or better still, don't let the tinplate age as it develops a tenacious tin oxide layer that must be removed. This can be done by giving it a quick alkaline etch. If the soldering is in a non critical area, try giving it a scrub with mild abrasive.

A. In tin plating if you would like good solderablity you need to keep as little brighteners out and also thin deposits .0001"" or lower. If you need thicker deposits you might want to look at tin/lead deposits.