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April 2016 • SMT Magazine 73 to control the wave height, and its smallest di- ameter is 3 mm. It costs more than jet wave and requires daily maintenance. Check references Remember to consult a variety of machine providers, talk to the manufacturers themselves if possible, and get references to contact before making a purchase. An important consideration for a complex machine such as a wave soldering system and associated options is factory sup- port, specifically training, software, upgrades and spare parts. Next chapter: Selective Solder Fluxing Tech- nologies. SMT robert Voigt is VP of global sales at DDM novastar Inc. To reach Voigt, click here. sElEcTinG a sElEcTivE soldErinG sYsTEm, ParT 1 The spray type is gener- ally faster, has been time- tested over many years of service, and has higher sol- ids flux capability. Down- sides to spray are: more flux residue, more mainte- nance and more wear parts may need replacing. Microdrop fluxing is more accurate, provides better hole filling, leaves little residue and is general- ly maintenance free. How- ever, it costs more, runs a bit slower and is more com- plicated to program. Preheating Technology Preheating minimizes thermal shock before sol- dering. Preheat systems can be integral with the se- lective soldering machine or offered as an optional module. Quick IR, area IR, and area quartz techniques are available, and can be employed on both the bottom and the top of the board. Area quartz is usually specified for thick boards. IR provides quick response and is gradient controllable, whereas some form of convection delivers a lower gradient but a more uniform heat transfer quality. A combination of the two may be used for high thermal mass applications. Soldering Technology There are three common types of soldering technologies available: jet wave, wettable noz- zles, and hybrid (mini-wave and dip combina- tion). Jet wave is similar to wave soldering in that it's directional and has the same benefits as wave. Its smallest solder diameter is 4 mm, it requires minimal maintenance, and it is fairly low cost. Wettable nozzles solder in every direction, 360°, or in either the x or y direction. It is easy Figure 3: Some of the soldering nozzles that are typically used in the selective soldering process.