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November 2015 • SMT Magazine 75 or more. Actual machine specifications depend on board size and throughput requirements. They can cost from $10,000 to $80,000, de- pending on the features and options. Most are available in a lower cost, bench-top model or can be purchased with a stand for a simple free-standing unit. • Pros: Good ROI, controllability over the solder process; repeatable; very little operator learning curve • Cons: Cost is higher than prior methods, but it is the lowest cost per board method; Wave will take up larger footprints on the shop floor Selective Selective is a special type of soldering which is used for a mixed technology incorporating SMT and through-hole where obstructions on the board prevent use of other through-hole methods. Selective conducts auto-fluxing, pre- heat and selective soldering of each component via a small nozzle tip rather than a large wave. Pre-programmed software positions the nozzle at the board precisely at the joint contact via an X-Y movement of either the board or the solder nozzle. Selective is the only good way to solder through-hole components on boards where other components already installed create ob- structions that would prevent a wave system, sMT quIck TIps SeLeCTING A THroUGH-HoLe SoLDerING SySTem, PArT 1 figure 4: cost-effective automatic single wave benchtop solder system. figure 3: example of transport fingers in a wave soldering system. note the waterfall of hot solder that makes contact with the board components.