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Changing to a silver-based solder (typically alloys of tin, silver and copper) is definitely a cost issue for a relatively low-value item like a can. I did in fact do work in this area several years ago and found that specially formulated epoxy adhesives and polyamide hot melts were two serious candidates to replace solders. Polyamide hot melts are quite difficult to handle, requiring application temperatures of 400 deg F and higher, but give outstanding adhesion to tin-plated steel. The epoxies proved valuable in that they were very resistant to most paint-related or automotive chemicals, with the exception of methylene chloride (which subsequently has been phased out of almost all such products).