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106 SMT Magazine • June 2016 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 col- umn, we'll cover the common types of solder- ing technologies available, plus nitrogen inert- ing systems. Soldering Technologies 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 de- pending on the nozzle type used, can replicate the wave technique in a compact way. Nozzle Types 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 de- liver 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 cus- tom configurations, can be used for most effi- cient speed and high quality, if the board popu- lation permits it • Cons: Boards (or solder pot) can only move in one direction making programming a little more complex Wettable nozzles create a uniform bubble by virtue of the surface tension of the solder. Excess solder rolls off around the entire surface of the nozzle, rather than in a single direction, thus producing less turbulence from solder roll- by Robert Voigt DDM NOVASTAR Selecting a Selective Soldering System, Part 3 SMT QUICK-TIPS Figure 1: Example of typical jet nozzle.

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