Joint type · THT
Through-hole
Leaded parts through a plated barrel: fillets you can see, thermal mass you cannot.
- In this joint type
- 7/8
- Tip temperature span
- 330–400°C
- Dwell span
- 1.2–4.0s
- Scheduled ahead
- 1
| Technique | Tip | Tip °C | Dwell s | Flux | Alloy |
|---|---|---|---|---|---|
| Hook splice on stranded wire | conical 1.6 mm | 330 | 2.5 | ROL0 no-clean | Sn63Pb37 |
| Soldering a pad tied to an internal ground plane | chisel 3.2 mm | 400 | 4.0 | ROL1 mildly activated | SAC305 |
| Drag soldering a 0.1 in header | hoof 2.0 mm | 360 | 1.2 | ROL1 mildly activated | Sn63Pb37 |
| Diagnosing and repairing a cold joint | chisel 2.4 mm | 340 | 2.5 | ROL0 no-clean | SAC305 |
| Wick cleaning a through-hole pad without lifting it | knife 3.2 mm | 350 | 1.5 | RMA rosin mildly activated | Sn63Pb37 |
| Vacuum desoldering a through-hole part | chisel 3.2 mm | 380 | 3.0 | RMA rosin mildly activated | Sn63Pb37 |
| Through-hole fillet baseline | chisel 2.4 mm | 340 | 2.0 | ROL0 no-clean | SAC305 |
Hook splice on stranded wire
A hook splice is still the most reliable way to join two stranded wires by hand: it survives a pull test that a lap splice fails, and it keeps the joint thickness low enough to fit under heat shrink. The mechanic is simple - interlock the strands so the joint carries load in tension before any solder is applied.
Soldering a pad tied to an internal ground plane
A through-hole pad connected to an internal copper plane behaves like a heat sink with the thermal resistance of the board itself. The iron is not failing; the plane is pulling 8 to 12 watts out of the joint the moment contact is made. The fix is to add thermal mass and area, not to raise the temperature indefinitely.
Drag soldering a 0.1 in header
Drag soldering turns a 40-pin header from a two-minute job into a twelve-second job, but only if the tip carries a reservoir of molten alloy and the row is fluxed generously enough that the solder refuses to bridge. The technique works with Sn63Pb37 far better than with lead-free, because the eutectic alloy freezes 34 degrees lower and the tip can stay in contact without the joint stiffening under it.
Diagnosing and repairing a cold joint
A cold joint is not a joint with too little solder. It is a joint where the alloy froze while the surfaces underneath were still below wetting temperature, so the bond is mechanical contact rather than an intermetallic layer. Repair means removing the joint entirely, not adding solder on top of it.
Wick cleaning a through-hole pad without lifting it
Desoldering braid is the fastest way to clean a pad and the fastest way to destroy one. The difference is dwell time: braid that has already absorbed its fill stops conducting heat into the joint and starts conducting it into the adhesive, and the pad comes up with the braid.
Vacuum desoldering a through-hole part
A spring-loaded vacuum pump removes a through-hole joint in one pass when the alloy is fully molten and the nozzle seals against the pad. Most failed attempts share the same cause: the pump is fired while the alloy is still pasty, so it sucks a partial plug and leaves a ring of solder welded to the barrel wall.
Through-hole fillet baseline
The reference joint every other through-hole technique is measured against: a 1.0 mm hole, a 0.8 mm lead, a 2.6 mm annular pad and a concave fillet that wets to the top of the pad without climbing the lead. Get this one reproducible and 80% of hand-soldering defects stop appearing.