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2.1 Hand Soldering Foundations

Iron selection, tips, temperatures, and ergonomics for repeatable joints.

Hand soldering is most reliable when the right tools, tips, temperatures, and posture work together to make every joint the same, no matter who holds the iron. A well-chosen station with fast heat recovery, ESD safety, and fume extraction keeps conditions consistent, while tip shape and size ensure quick wetting without damage. The goal is to heat pad and lead together, feed solder to the joint—not the tip—and finish in a few seconds for a smooth, shiny fillet. Preheat and flux help stubborn pads fill without raising temperature too far, and dwell limits prevent lifted pads or cooked parts. With standardized setups, inspection points, and operator drills, hand soldering becomes a controlled process instead of an art—fast, repeatable, and safe.

2.1.1 What “good” looks like

  • Shiny, concave fillet that wets pad and lead, no pits or spikes.
  • Heat in, solder out within 2–4 seconds on SMD; 3–6 seconds on THT.
  • Same result from any operator, any shift—because tools, temps, and posture are standardized.



2.1.2 Pick the right iron (power & recovery)

Feature

Why it matters

What to choose

Power / recovery

Holds temp when touching ground planes

60–120 W station with cartridge tips (fast thermal path)

Temperature control

Consistent wetting without cooking flux

Digital setpoint, sleep/boost modes

ESD safe

Don’t zap parts

Grounded tip & handle; verified earth bond

Stand & sponge

Safety + tip care

Weighted stand, brass wool (primary) + damp sponge (occasional)

Fume extraction

Keep lungs & optics clear

Bench extractor or tip-vac with HEPA/charcoal

Cartridge-style stations recover heat faster at lower setpoints → less pad risk.



2.1.3 Tip shapes & sizes (most defects start here)

Pick shape by pad geometry; pick size so the tip covers ~70–100% of pad width.

Shape

Use for

Notes

Chisel (favorite)

Chips, gull-wings, THT pins

Everyday tip; choose width ≈ pad

Hoof/Bevel

Drag solder fine pitch; feed solder on back side

Holds a solder “pool”; great with flux

Conical

Tight corners, jumpers

Easy to misuse—small contact area = slow heat

Knife

Tall pins near plastic; slicing bridges

Light touch; avoid scraping mask

Micro-chisel

0402–0603 chips

Don’t go too tiny; you still need contact area

Tip care

  • Keep tinned at all times; add a tiny solder bead when parking.
  • Clean with brass wool (quick jab), sponge only to remove burned flux.
  • Use tip tinner to revive dull tips; replace when pitted/eroded.



2.1.4 Temperatures that work (and why)

Solder melts at a temperature; wetting happens slightly above, and damage happens when you wait there too long.

Alloy

Typical setpoint

When to bump

When to back off

Sn63/Pb37

315–350 °C

Big planes, posts → +10–20 °C

If flux browns fast or mask blisters

SAC305 (lead-free)

340–380 °C

Ground pours, lugs → +10–20 °C

If parts/plastics feel “hot” to touch quickly

Low-temp Bi

260–300 °C

Rare; be gentle

Very easy to overheat → keep low

Rules:

  • Use the lowest temp that wets in 2–4 s.
  • If you need more than 6–8 s on THT at sane temp → change tip size or preheat, not +50 °C.



2.1.5 Wire solder, flux & helpers

Item

Choose

Why

Wire diameter

0.3–0.5 mm for SMD; 0.8–1.0 mm for THT

Feed control without blobs

Flux core

No-clean, halide-free

Leaves benign residue; less cleaning

Extra flux

Pen/gel (no-clean)

Improves wetting & drag soldering

Preheater

Small plate or hot air at 80–120 °C

Cuts dwell on planes & big parts

Tweezers

Fine, ESD; one straight, one curved

Control & alignment

Magnification

3–10× + bright, diffuse light

See wetting angle & bridges



2.1.6 Technique: heat first, solder second

SMD (chips & gull-wings)

  1. Tin one pad lightly.
  2. Place part, reflow the tacked pad, align, then solder the opposite side.
  3. For gull-wings, flood with flux, set hoof/chisel at lead + pad, feed a small, steady solder stream; the tip pulls solder along.
  4. Clean up bridges with flux + clean chisel (no solder feed), or a knife swipe.

THT

  1. Touch lead and pad together with the tip; wait a beat for heat to soak.
  2. Feed solder to the opposite side of the joint (not the tip) until a concave fillet forms and wicks through.
  3. Withdraw solder, then tip. Target 3–6 s total.

Tells of a good joint

  • Fillet is concave, smooth; wetting angle < 60°.
  • For THT, see a small, shiny crown on top side.



2.1.7 Ergonomics & ESD (make good joints easy)

  • Posture: forearms supported, wrist neutral; bring the work to your eyes, not your neck to the work.
  • Board support: use a vise or frame; don’t fight springy panels.
  • Hand spacing: pencil grip near the tip for control; solder feed hand relaxed.
  • Fume: extractor nozzle 5–10 cm from joint, angled.
  • ESD: mat grounded, wrist strap checked; ESD-safe tools only.



2.1.8 Dwell limits & preheat cues

  • SMD pad: aim 2–4 s; if not wetting by 4 s, stop → more flux, larger tip, or preheat.
  • THT pad: aim 3–6 s; if not filling by 8 s, stop → preheat or add thermals next spin.
  • Preheat target on stubborn planes: board surface 80–120 °C (warm to the touch, not cooking).



2.1.9 Common defects → smallest reliable fix

Symptom

Likely cause

First fix

Dull/grainy joint

Low temp or oxide; cooked flux

Fresh flux; +10 °C; clean tip & reflow

Solder balling/splatter

Dirty board; wet flux boiling

Clean site; longer preheat; reduce temp 10 °C

Bridge (SMD)

Too much solder; no flux path

Flux + drag a clean chisel along leads; use solder wick gently

Lifted pad

Overheat or pry while hot

Lower temp; bigger tip (faster); let cool before moving

THT no top fill

Tight hole; cold plane

Preheat board; larger chisel; add flux; if chronic → enlarge hole next rev

IC won’t align

Tack too big; no third hand

Tiny tack; use tweezers & magnification



2.1.10 Standard work (how we make it repeatable)

Record on the traveler or WI:

  • Station ID, iron model, tip part no., set temp, solder alloy/Ø, flux type.
  • For each operation: photos of “good” joints and “limit” examples (IPC class).
  • Inspection points (what gets checked, under what magnification).
  • Time limit per joint (SMD/THT), and the stop-escalate rule.


2.1.11 First Article & training drills

FA on a new product/technique

  • Solder 5 samples of each joint type (chip, gull-wing corner, one header pin).
  • Inspect under 7–10×, record: wetting, bridges, top-fill, cosmetic.
  • Lock temp/tip if all pass within dwell targets; else adjust and repeat.

Drills for new operators (1–2 hours)

  • 20× 0603 chips (tack + opposite pad).
  • 10× SOT-223 tab + legs (flux control).
  • One 0.5 mm QFP (drag with bevel tip).
  • 10× THT pins on a header (opposite-side feed, top-fill).
  • Pass when all meet time and cosmetic targets.



2.1.12 Safety & housekeeping

  • Leaded solder? Wash hands before food; keep food away from bench.
  • Hot tips look like cold tips—use stand; don’t park irons on mats.
  • Keep wire clippings contained; vac the bench; no loose whiskers near BGAs.
  • Tip sleep after 30–60 s idle; power down at breaks.



2.1.13 Pocket checklists

Before you start

  • ESD strap green; extractor on
  • Tip type/size correct; tip freshly tinned
  • Temp set for alloy; preheater on if heavy copper
  • Solder wire Ø and flux pen ready; good light & magnification

Each joint

  • Heat pad + lead together
  • Feed solder to the joint, not the tip
  • Pull solder, then tip; check fillet in 2–4 s (SMD) / 3–6 s (THT)

If it misbehaves

  • Add flux; clean & re-tin tip
  • Bigger tip or tiny preheat boost
  • Stop if >8 s on THT—change approach



Bottom line: repeatable hand soldering is power + tip + posture. Use a station with real thermal recovery, pick a tip that fits the pad, run the lowest temp that wets fast, and work comfortably with flux, light, and extraction. Keep tips tinned, joints quick, and records clear—your results will look the same on Monday morning and Friday night.


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