Backward & Forward Compatibility
There are two differences between Pb-Free components and Sn/Pb components:
- The Pb-free soldering processes are done at a higher temperature range: Sn/Pb-soldering (215°C–240°C) vs Pb-free soldering (235°C–260°C).
- The soldering pastes used with Sn/Pb components have always been a formulation of Sn and Pb, typically eutectic 63%/37%; The Pb-Free soldering pastes have several formulations consisting of various combinations of Sn, Cu, Bi, Ag, and other.
Care has been taken to ensure that all components are solderable using the current Sn/Pb PCB assembly processes. This means that Pb-Free components can be integrated with Sn/Pb components whenever the assembly processes have not been converted to Pb-free. As a consequence, production assembly lines will not be affected by the use of Sn products and all stocks will be compatible with the various Sn/Pb solder assemblies and components.
Before September 2004, a universal standard for Pb-Free solderability testing had not been established. There were several Pb-Free assembly processes and components used with these processes prior to this time that were not tested to any Pb-Free solderability process. This includes Sn/Pb components. While most Pb-free solder pastes will be acceptable for Pb-Free products, the customer is cautioned to evaluate the Pb-Free pastes selected for production, particularly if the intent is to include Pb components.
Extensive testing performed to date ensures that Pb-free products will survive the Pb-free soldering temperatures. However, when customers convert their production line to Pb-free solder paste, many devices containing Pb will not survive the higher reflow temperature (235°C to 260°C) required for the Pb-free solder paste. This is because mold compounds and die attach materials designed to maintain the package's moisture sensitivity level must be changed. If a customer needs to use leaded parts with lead-free process, it is the customer's responsibility to make certain that Pb components are qualified to their Pb-free soldering process. This includes reflow temperature and solder paste.