Question: Is it true we can use lead-free solder to remove leaded solder on our soldering iron tips? I seem to remember we were shown how to flood the tip with lead-free solder three times, wiping clean after each flooding, to remove any lead residue before soldering a lead-free solder joint. Is this something we can say we do as a company to explain how we switch from leaded to lead-free soldering without having seperate solder tips exclusive to lead-free applications? Also, how much cross contamination are we actually getting using the same sponge for lead and lead-free? Must we have a sponge available for both?
Answer: All great questions. This concept has been talked about since the lead-free process was introduced 1984. The allowable amount is less than .1% of lead in lead-free solders.
Can you clean them as you suggest, the answer is yes. We don’t recommend it as this is an inconsistent process and the operators will not be fastidious to make sure they do it every time. We’ve promoted the separation of both processes to prevent contamination, separate solder iron tips and sponges. You mention cross contamination and how much of it can happen by using the sponges for both processes. The issue is the imbedded solder in the sponge that can be transferred and secondly the fluxes being used with lead free are more aggressive and melt at higher temperature, so there are issues with the transfer of these fluxes to the old leaded process and contaminating that process with these new fluxes.
The other issue is proving you do not have any lead cross contamination in your lead free product. As a manufacturer of products you have the responsibility to provide to the customer with Material Declaration Sheets identifying the materials in your product and the amounts of each of these materials in your process as defined by the Directives. This includes all the components you buy including the boards, components and wires, which includes the insulation, where lead is used in the coloration of the insulation.
So to quickly answer your question, we recommend complete separation from both processes to prevent the cross contamination and this forces the operators to pay more attention to the significance of keeping the materials separate.