What is selective soldering?
Selective soldering is a soldering process for through-hole (THT) components in which a small solder nozzle travels to exactly the joints that are to be soldered. Wave soldering, by contrast, runs the entire underside of the board over a solder wave. Selective soldering therefore allows through-hole components to be soldered on assemblies that are already SMD-populated and would not survive a wave.
Wave, selective, hand: where the line runs
Wave soldering is fast, but it heats the whole underside and needs a masking pallet as soon as sensitive components are in the way. Hand soldering is arbitrarily flexible, but slow and dependent on the individual doing it. Selective soldering sits between them: reproducible like a machine process, precise like hand soldering, and slower than the wave, because the nozzle visits every joint one at a time.
When selective soldering is the right choice
On mixed-technology assemblies with few through-hole parts, on double-sided assemblies, where temperature-sensitive components sit near the joints, at tight pitches where a wave would bridge, and everywhere a masking pallet would cost more than the longer process time.
What actually drives the process time
Not the number of components, but the path of the nozzle: how many joints there are and where they sit, the travel between them, the dwell time per joint, plus preheating and flux application. Two assemblies with the same component count can differ substantially in selective soldering time if the joints are distributed differently across the board. This is exactly why a flat surcharge per through-hole component regularly misleads.
Where this shows up in PCBoffer
PCBoffer computes selective soldering time from geometry: the position of the through-hole joints comes out of the fabrication data, from which the nozzle path, the dwell time per joint and the travel between them follow. No per-component surcharge. The same path can be emitted as an NC program for the machine.
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