2.1 Hand Soldering Foundations
Iron selection, tips, temperatures, and ergonomics for repeatable joints.
Hand soldering
isremains one of the most reliableversatile whenskills in electronics manufacturing, bridging the rightgap between automated processes and the fine details only a human touch can manage. Its reliability, however, comes not from intuition but from standardizing the tools, tips, temperatures,techniques, and postureenvironment workso together to makethat every jointoperator can achieve the same,same noconsistent matterresult. whoBy 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, handtreating soldering becomesas a controlled process insteadrather ofthan an art—fast,art, repeatable,manufacturers ensure joints that are not only electrically sound but also mechanically durable, safe, 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)
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.
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.
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
2.1.6 Technique: heat first, solder second
SMD (chips & gull-wings)
- Tin one pad lightly.
- Place part, reflow the tacked pad, align, then solder the opposite side.
- For gull-wings, flood with flux, set hoof/chisel at lead + pad, feed a small, steady solder stream; the tip pulls solder along.
- Clean up bridges with flux + clean chisel (no solder feed), or a knife swipe.
THT
- Touch lead and pad together with the tip; wait a beat for heat to soak.
- Feed solder to the opposite side of the joint (not the tip) until a concave fillet forms and wicks through.
- 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
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