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22 SMT Magazine • April 2015 the appearance of the residues regardless of the reflow profile. However, it should be kept in mind that the flux residues in this study were exposed on the surface of the PCB as opposed to be- ing trapped under a component body or RF shield. An earlier work by the author shows that entrapment, somewhat regardless of peak temperature, can have a measurable negative effect of the SIR performance [2] . What is no- ticeable is the effect that a soak has on the SIR values. In all cases, except for the halogen- containing/255°C peak temperature scenario, the soak profile produced higher SIR values than its respective linear ramp profile. The re- sults also imply that a brief soak improves the SIR values more than a 10-degree increase in the peak temperature with a linear ramp pro- file. It is worth noting that the soak need not be not excessively long to create this improve- figure 22: Halogen-containing solder paste, 245°c peak temperature soak profile (run 2). figure 24: Halogen-free solder paste, 255°c peak temperature soak profile (run 2). figure 23: Halogen-free solder paste, 255°c peak temperature ramp profile (run 2). figure 25: Halogen-containing solder paste, 255°c peak temperature ramp profile (run 2). ElECTriCal rEliaBiliTy OF NO-ClEaN SOlDEr paSTE Flux rESiDuES continues FeAture