Implement lead Free Wave Soldering

With the move toward lead-free electronic products, an increasing number of manufacturers are preparing to implement lead-free soldering processes in compliance with pending regulations. A great deal of effort has been placed on converting the reflow soldering process to lead-free due to the dominance of SMT components. Wave soldering must also be changed to lead free to avoid mixing of lead bearing and non-lead bearing alloys on the same assembly.

Implementing lead-free wave soldering involves more than replacing one solder alloy with another because no "drop-in" replacement strategy exists. A common notion is that one can simply switch from tin-lead (Sn Pb) to lead-free by dropping lead-free solder into an existing wave machine. Another general misunderstanding is that you need to buy a new wave machine for lead-free processing. Neither of these tactics is correct because there are alternative ways to minimize the cost of implementing lead-free wave soldering.
For lead-free wave soldering to be successful in a production environment, necessary changes to the entire process must be considered. The majority of lead-free solder alloys possess good solder ability but exhibit decreased wetting characteristics compared to tin lead solders. Since wetting is a critical factor affected by solder temperature, contact time, flux, use of nitrogen and wave configuration, changes are required that will affect the majority of machine parameters.

Introducing lead-free wave soldering generally involves two major process changes because lead-free alloys have a significantly higher tin content than tin lead solder and require higher processing temperatures. Many products will be converted to lead-free over a gradual phase-in, however numerous manufacturers are forging ahead by making their wave soldering machines lead-free compatible now.

It is common practice to change the characteristics of the laminar wave solder nozzle since a longer contact time may be required due to the lower wetting properties of lead-free alloys. Often the distance between the chip wave and laminar wave may be reduced to minimize any temperature drop between contact points. Increasing the length of the chip wave improves wetting while increasing the preheat output produces a similar effect. Reducing the fall height of the wave to decrease the distance of overflowing solder reduces the amount of dross with lead-free alloys.
Compared to tin-lead solder, most lead-free alloys oxidize more rapidly when the solder is liquid us due to their increased tin content. Tin oxide, consisting of tin-oxygen (SnO) and (SnO2), forms at a higher rate because of the higher processing temperature and results in more oxidation and dross. Nitrogen inserting of the solder pot is recommended and minimizes exposure of the liquid us solder to oxygen and decreases the amount of dross. Needless to say, reducing the rate of oxidation and the resulting dross build-up significantly improves the performance of the wave soldering process