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In the previous two chapters on selective soldering, we covered the different applications well-suited to this technology, and the various types of fluxing methods available. In this column, we’ll cover the common types of soldering technologies available, plus nitrogen inerting systems.
It’s important to remember that selective soldering does not necessarily replace a wave machine, because wave soldering is still the most efficient method of processing boards with only through-hole components. But selective is essential for a mixed technology board, and depending on the nozzle type used, can replicate the wave technique in a compact way.
Jet (or wave) soldering is similar to wave in that it’s uni-directional and provides the same benefits as wave. Its smallest solder diameter is 4 mm, it requires minimal maintenance, and it is fairly low cost. The nozzle type you use will depend on the make-up of the board and the location of SMDs on that board.
For instance, a fairly large row of connectors/leads not in close proximity to SMD components could use a wide nozzle to swipe (or wave) the entire row at once. A small area closed situated to an SMD would require a very small nozzle to avoid disturbing the surface mount device.
Jet nozzles attack the board at about the same angle (7°) as a wave machine and can deliver a high volume of solder using a tapered tip which guides solder roll-off in one direction returning unused solder back to the pot from its trailing edge. In this scenario, the direction of travel (board or nozzle) is very important.
Jet nozzles are long-lasting and usually cost only a few hundred dollars. Some boards can benefit from a custom nozzle to solder an area as quickly as possible in a dip or drag process, or even a min-wave.
• Pros: Many nozzle types, including custom configurations, can be used for most efficient speed and high quality, if the board population permits it
• Cons: Boards (or solder pot) can only move in one direction making programming a little more complex
Editor's Note: This article originally appeared in the June 2016 issue of SMT Magazine.