Lead (SnPb) PCB Assembly (SMD/SMT)

Typically, leaded solder is a mixture of tin and lead. Leaded PCB boards can withstand higher temperatures than lead-free boards, thus posing less of a thermal threat to the component and contain a lower flux percentage. Flux is the core inside the solder wire which provides good electrical contact and mechanical strength to the joint that is being soldered. The volume of flux in the solder material is a crucial parameter. The higher flux volume is usually desired to achieve a better connection and support to the component that is being soldered.

The lower flux volume is not desirable for lead-free soldering as it results in more difficulty to join the component terminal while soldering. In addition, after the solder cools it takes on a shinier appearance than lead-free solder, therefore it is easier to spot problems such as oxidation (which would dull the appearance). Finally, leaded solder is a cheaper alternative to lead-free and is overall easier to use.