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December 2015 • SMT Magazine 85 all components only for a very short time, then exits the wave. The solder pot size is determined by wave size, the smallest holding around 100 lbs. of sol- der for a 7–8" wave width, up to 2,400 lbs. of solder for a 24" wide wave. Since solder is costly, the size of the machine contributes to the cost of operation. Also, solder running in a hot wave is susceptible to oxidation and depletion so all these factors add cost. Inerting the area with nitrogen at the point of contact will produce a better quality joint and eliminate the possibility of a cold solder joint or oxidation. Nitrogen also helps to cut down on dross, which is defined as solder that builds up enough oxidation or flux residue to render the solder useless, somewhat like slag. Contact on the component by the solder wave only takes place in seconds and once passed, cools almost immediately. Flux systems There are two common types of fluxing sys- tems are available: • Foam: A bath or pot that is usually as wide as the wave. The flux is poured into the flux pot, and an aerator in the pot creates foam which is applied to the thru-hole component and board. • Spray: A high pressure container holds flux which is sprayed on the board by an oscil- lating spray head to cover all the components and the entire board. Foam fluxing tends to be less expensive and easier to maintain than spray. The downside is that this will cause evaporation if it's not con- tained, and the flux will degrade more quickly. Foam systems are low cost to operate, and easy to use and maintain. sMT QuiCk TiPs SeLecTInG A WAVe SoLDerInG SySTem, PArT 2 Figure 2: Benchtop wave solder system. Figure 3: Foam fluxer.