Flux needles 15G, 16G, 18G: dosing without flooding the board
Choose a flux needle by viscosity and dose size. The higher the G number, the thinner the needle: 18G (1.02 mm bore) for drops and small SMD, 16G (1.37 mm) as an all-rounder for gel flux, 15G (1.50 mm) for thick pastes. All screw onto a syringe or dispenser with a Luer Lock thread.
Without a needle, flux comes out of the syringe as a sausage and half of it lands where it shouldn’t. A dispensing needle gives a dose you can see and control: a dot on a pad, a line along the leads — and the board stays clean.
Which needle to choose
| Needle | Bore / outer | Best for |
|---|---|---|
| 18G | 1.02 / 1.2 mm | drop dispensing, small SMD, tight spots |
| 16G | 1.37 / 1.6 mm | gel flux, thinner pastes — all-rounder |
| 15G | 1.50 / 1.8 mm | thicker pastes, medium-viscosity glues and sealants |
What to push with
The needle screws onto a Luer Lock syringe. You can dispense with:
- a plunger — it comes with Flusenko flux paste, while Amtech RMA-223-UV without a plunger suits you if you already have one;
- a dispenser — the piston dispenser gives smooth flow and even doses, and your hands don’t tire on big jobs.
Dispensing without waste
- Screw the needle on fully so flux doesn’t leak along the thread.
- Push the first drop onto a tissue to clear the air.
- Apply flux before heating: a thin line or a dot on each pad.
- After work, pull the plunger back slightly so flux doesn’t ooze, and put the cap on.
Flusenko’s tip. Cold gel flux is stiff. If the plunger is hard to push, hold the syringe in your hand or near a warm lamp for a few minutes — the flux softens and doses come out more even.
Caring for needles
Steel-tube needles last a long time unless left full of flux for weeks: dried gel clogs the bore. Remove the needle after work and keep the syringe capped. Keep a spare 18G — it clogs first.
Needles, fluxes and a dispenser come together in the “Flux dispensing” kit.
FAQ
What does “G” in the needle name mean?
It’s the gauge: the higher the number, the thinner the needle. 18G is thinner than 16G, and 16G is thinner than 15G.
Will the needles fit my syringe?
If the syringe or dispenser has a Luer Lock thread, yes. It’s the standard fitting on flux syringes.
The needle is clogged — what now?
Warm it with a hot-air gun or warm water and push the flux through with the plunger. If that fails, replace it — needles are cheap.
