Four checks, in order
When a selective solder nozzle stops wetting, the usual response is to raise the pot temperature or replace the nozzle. Both are expensive ways to discover that the cause was flux residue. Work through these four before ordering a spare:
- Surface condition — oxidation or burnt flux on the wetting surface
- Cleanliness — residue inside the orifice and on the outside of the tip
- Orifice geometry — a rounded or chipped edge changes the solder column
- Machine condition — pot temperature, nitrogen atmosphere and pump stability
Oxidation and flux residue
The nozzle has to be wetted by the solder for a stable column to form. An oxidised surface repels it, and burnt flux baked onto the outside of the tip does the same. A disciplined cleaning interval at the correct temperature does more for wetting than any parameter change.
Residue inside the orifice is harder to see and shows up as an uneven column or a slight sideways skew. If a clean nozzle produces a straight column on a test run and the production nozzle does not, the difference is internal residue or wear, not the pump.
Orifice wear
| Symptom | Likely cause | First action |
|---|---|---|
| Column will not form at startup | Oxidised surface | Clean and re-tin the wetting surface |
| Column skews or pulses | Residue or a chipped orifice edge | Inspect the orifice under magnification |
| Wetting fine but joint is inconsistent | Pot temperature, flux quantity or board preheat | Check machine parameters, not the nozzle |
| Nozzle wets but wears out quickly | Abrasive cleaning or aggressive flux | Review cleaning tools and flux chemistry |
A rounded orifice edge is the point at which cleaning stops helping. The column geometry is set by that edge; once it is worn, the nozzle should be re-lapped or replaced.
When it is the machine, and when it is not
Pump wear, pot temperature drift and a weak nitrogen atmosphere all produce real faults — but they affect every nozzle on the machine, not just one. If one station is failing and the others are stable, start with the nozzle. If all of them changed together, look at the machine.
We machine selective, point and slot nozzles in conical and slotted profiles and lap the orifice edge after grinding. If you are seeing a wear pattern that does not match the table above, send a photograph of the nozzle and the joint; the geometry is often the answer.
