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June 2016 • SMT Magazine 109 SELECTING A SELECTIVE SOLDERING SYSTEM, PART 3 ty during the process with no voids in the final connection. 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 consider- ation for a complex machine such as a selec- tive soldering system and associated options is factory support, specifically training, software, upgrades and spare parts. SMT Next column: Programming for selective soldering Robert Voigt is VP of global sales at DDM Novastar Inc. To reach Voigt, click here. needs, and can also fabricate custom nozzles for special applications. Nitrogen inerting is an advisable and low- cost option on a selective soldering machine. Two systems are available: one that uses ni- trogen bottles which require replacement and recharging, and those that use a commercially available nitrogen generator. Some nitrogen systems incorporate a pre-heat stage which can also be used to activate the flux, performing two functions at once and eliminating the necessity of a separate flux pre-heater. Nitrogen improves soldering performance by assisting thermal capability and improving surface tension of the solder. Leaded solder is considerable more forgiving than lead-free in terms of oxidation, degradation and connec- tion quality, so nitrogen is not always needed in those cases. However, it is absolutely neces- sary for any application using lead-free solder. To ensure a good solder joint using lead-free, the nitrogen bubble protects the solder integri- Figure 3: Nozzle position with respect to board.