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108 SMT Magazine • June 2016 off and helping to preserve solder quality. For this reason, a wettable solder can move in every direction, 360°, or in either the x or y direction, and it is easy to control the bubble height. This combination provides maximum flexibility for a large variety of boards. Wettable nozzles provide finer accuracy than jet type which makes it better suited to connections in close proximity to SMDs. It also produces less oxidation because there's less con- tact with air. For this reason, wettable nozzles are also best suited for lead-free solder which tends to be more vulnerable to oxidation. • Pros: Provides pinpoint accuracy for high- est connection integrity on densely populated boards • Cons: Costs more than jet wave and re- quires daily maintenance to prevent clogging Custom nozzle capabilities can be made to cover very large areas of a circuit board in a single pass while masking SMD components to speed production. Contract manufacturers who assemble a wide variety of board configurations should make sure the machine they're investigating can accommodate both types of nozzles and/ or custom/hybrid configurations if they think they are ever going to need them. Which is better: moving the board or the nozzle? Jet wave nozzles can only attack the board in a single direction, much like wave machines. The design of wettable nozzles permits a flat an- gle of attack, so the board or the solder pot can move in any direction. Whether you choose a machine that moves the board or the nozzle depends entirely on your process application and the most efficient means to achieve it while retaining as much flexibility for other applica- tions as possible. Most machine manufactur- ers can recommend the best situation for your SELECTING A SELECTIVE SOLDERING SYSTEM, PART 3 Figure 2: Example of a wettable nozzle.

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