Do lead free solder joints always look dull?

Fortunately, the answer is no. In general, the lead free soldering materials do exhibit a less than brilliant finish. This is due to several factors: First, higher amounts of flux in the solder material. More material has an affect on appearance, particularly in a no clean since that increased material is destined to remain on the board ~ unless it is cleaned thoroughly. Second, the higher processing temperatures can cause these increased residue levels to darken after reflow ~ unless they are cleaned thoroughly. Third, the new lead free alloys seem to exhibit cosmetic darkening when processed outside their recommended processing profile. Unfortunately cleaning can’t fix everything!

So how might an engineer avoid those dull solder joints? Implement a modern cleaning process, using modern cleaning materials. The top of the line materials on the market the past year or two generally are effective on lead free solders, except. There is always an exception. Except, they generally will need to be run at higher operating parameters. Perhaps a higher concentration for aqueous products, a higher temperature for aqueous of semi-aqueous products, or a longer exposure time for any cleaning process. Each of these choices may be undesirable for a number of reasons, and fortunately, the cleaning industry has responded with new products, designed from the ground up to address these lead free challenges at the process condition users have been accustomed to for many years. Just tune into the newest technology, review the reams data generated on scores of soldering materials, and sleep easy as this process delivers the beautiful solder joints the industry requires.