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96 SMT Magazine • August 2016 large row of connectors/leads not in close prox- imity to SMD components could use a wide nozzle to swipe (or wave) the entire row at once. On the other hand, a small area situated near an SMD would require a very small nozzle to avoid disturbing the surface mount device. There are myriads of standard nozzle designs for performing dips and drags, and they are lim- ited only by your imagination or the complex- ity of the board. Selective gives you many ways to tackle a soldering routine, so you want to think about the sequence, the nozzle configura- tions you use, and the best way to save process- ing time. It may make sense to buy a custom nozzle if you have a high volume board with a unique profile. After all, nozzles aren't very ex- pensive and they last quite a long time. Jet nozzles attack the board at about the same angle (7°) as a wave machine does 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. Wettable nozzles provide finer accuracy than jet type which makes them 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. 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. Think about the Future Perhaps you're considering the acquisition of a selective solder machine for a specific new project, or you're a contract assembly shop ex- panding your offerings to handle custom con- figurations. Look beyond the immediate future and think about how your needs may grow. Some selective manufacturers can offer a base machine that allows for the addition of future modules to expand your capabilities. But some don't, so be sure to ask. Additional modules can come in a number of formats, allowing you to double or triple your production throughput. You may be able to get them combined in pairs to perform two opera- tions on the same lead, or get separate modules that only perform a single fluxing, preheat, or solder operation. Beyond modules, some manufacturers offer automatic conveyors which allow the operator to stage boards and feed them automatically when a previous board is complete. This allows one operator to perform multiple functions rather than keeping his attention on a single machine. SELECTING A SELECTIVE SOLDERING SYSTEM, PART 5 Figure 2: A wide variety of nozzle types and shapes can be used for the most efficient process. Figure 3: A wettable nozzle on an inline selective soldering machine.