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2.1 Hand Soldering Foundations

Hand soldering remains oneessential offor therework, mostrepair, versatileand skillsspecialized inlow-volume electronicsassembly, manufacturing,managing bridgingtasks the gap betweenthat automated processes andcannot thesafely finetouch. detailsThe onlyreliability aof humanhand touch can manage. Its reliability, however,soldering comes not from intuition but from standardizing the tools, techniques, and environment so that every operator can achieve the same consistent result. By treating solderingit as a controlledcontrolled, repeatable process rather than an art,art. By standardizing tool selection, temperature settings, and the heat application sequence, manufacturers ensure joints that are not only electrically sound but also mechanicallymeet durable,mechanical safe,durability and repeatablestandards across shiftsall and products.operators.

2.1.1 WhatThe “good”Quality looksStandard

like

A successful hand-soldered joint must achieve the following characteristics within strict time constraints to prevent thermal damage to components and PCBs:

  • Shiny,Wetting and Fillet: The solder must form a shiny, concave fillet that smoothly wets both the pad and the component lead, noshowing pitsa orclean spikes.wetting angle of less than 60° (per IPC standards).
  • HeatTime in,Limit solder out(Dwell): The entire process—heating, feeding solder, and withdrawing the iron—must be completed within 2–4 seconds onfor SMD;SMT pads and 3–6 seconds onfor THT.THT pins.
  • Repeatability:Same The result frommust be consistent regardless of the operator, achieved through documented anyStandard operator,Work anyInstructions shift(SWI)—because tools, temps, and posture are standardized.
    .



2.1.2 PickTool Selection: Power and Recovery

The soldering station's thermal recovery rate is more critical than its static temperature. A high-power station (60–120 W) is required to maintain the rightset irontemperature when heat is rapidly transferred into large thermal masses (powere.g., &ground recovery)planes).

Feature

Why it mattersMandate

What to chooseRationale

Power / recoveryPower/Recovery

Holds temp when touching ground planes

60–120 W station with cartridge tips (fastheating element integrated).

Cartridge tips offer a faster thermal path)path, minimizing the dwell time required to achieve wetting.

Temperature controlControl

Consistent wetting without cooking flux

Digital setpoint,setpoint with sleep/boost modesmodes.

Ensures consistent temperature for wetting while protecting tips from oxidation during idle time.

ESD safeSafety

ESD-safeDon’t zaphandle, partstip, and bench mat, with verifiable earth bond.

GroundedPrevents tipelectrostatic &discharge handle;(ESD) verifieddamage earthto bondsensitive integrated circuits (ICs).

StandTip & spongeCare

SafetyPrimary +cleaning tip care

Weighted stand,with brass wool; (primary)secondary +cleaning with damp sponge (occasional)

Fume extraction

Keep lungs & optics clearsponge.

BenchBrass extractorwool orminimizes tip-vacthermal withshock HEPA/charcoaland tip erosion, extending tip life.

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



2.1.3 Tip shapesGeometry &and sizes (most defects start here)Application

PickTip shapeselection byis based on the pad and lead geometry to maximize the padcontact geometryarea; pickfor sizeefficient soheat thetransfer. Using a tip coversthat ~70–100%is oftoo small leads to long dwell times and potential pad width.lifting.

Shape

Use forCase

NotesSize Mandate

Chisel (favorite)Favorite)

Chips, gull-wings, THT pinspins.

Everyday tip; chooseChoose width ≈to cover ~70–100% of the pad width.

Hoof/Bevel

Drag soldersoldering finefine-pitch pitch;leads; feedapplying solder onto the back sideof large pads.

Holds a soldersmall “pool”;pool greatof withsolder, aiding flux flow and surface tension control.

Conical

Tight corners, jumpersjumpers.

EasyUse tosparingly; misuse—small contact area =requires slowcareful 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 areaapplication.

Tip careMaintenance:

  • KeepThe tip must be kept tinned (coated with a thin, shiny layer of solder) at all times; add a tiny solder bead when parking.
  • Clean with brass wool (quick jab), sponge onlytimes to removemaximize burnedthermal flux.
  • transfer efficiency. Use tip tinner to revive oxidized or dull tips; replace when pitted/eroded.tips.



2.1.4 TemperaturesTemperature thatControl work (and why)Thermal Safety

SolderTemperature meltsselection atis a temperature;balance wettingbetween happensthe slightlysolder's above,melting point and the need for a rapid wetting action, while avoiding damage happensto whenthe youPCB waitor therecomponent too long.body.

Alloy

Typical setpointSetpoint

WhenAction toif bump

WhenWetting tois back offSlow

Sn63/Pb37

315–350 °C

BigIncrease planes,tip postssize →or +apply preheat; only increase temp by 10–20 °C

If fluxfor brownsheavy fast or mask blistersplanes.

SAC305 (lead-free)Lead-Free)

340–380 °C

GroundSame pours,as lugsabove. →Lead-free +10–20requires °C

Ifhigher parts/plasticsthermal feelenergy “hot”due to touchits quickly

Low-temphigher Bi

260–300melting °C

Rare; be gentle

Very easy to overheat → keep lowpoint.

Rule:Rules: If a joint does not wet cleanly within 4 seconds (SMD) or 6 seconds (THT) at the set temperature, stop. The problem is not temperature, but insufficient contact area, oxide contamination, or lack of preheat. Raising the temperature excessively leads to flux burnout and pad damage.

    2.1.5 Hand Soldering Technique

    The technique must follow a clear sequence to ensure proper intermetallic bond formation: clean, apply heat, add solder, remove heat, remove solder.

    1. Preparation:Use Clean the pad/lead area if using liquid flux.
    2. Heat Application: Place the clean, tinned tip to simultaneously touch the lowest temp that wets in 2–4 s.
    3. 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, reflowand the tackedlead. 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; waitWait a beat (1–2 seconds) for heat to soak.
  2. Solder Feed: Feed wire solder to the joint interface (the opposite side of the jointiron), (not directly onto the tip) until a concave fillet forms and wicks through.
  3. Withdraw solder, theniron tip. TargetThe 3–6solder sshould total.
flow

Tellsinstantly 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; bringtoward the work to your eyes, not your neck to the work.heat.
  • BoardWetting support:and Withdrawal: use a vise or frame; don’t fight springy panels.
  • Hand spacing: pencil grip nearOnce the tipjoint foris control;complete (concave fillet formed), withdraw the solder feedwire, handand relaxed.
  • Fume:then extractorinstantly 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 towithdraw the touch,iron nottip. cooking).Total time must be contained within the dwell limits.



2.1.96 Common defectsDefects →and smallestReliable reliable fixFixes

Symptom

Likely causeCause

First fixReliable Fix

Dull/grainyGrainy jointJoint

LowInsufficient tempheat or(cold oxide;joint); oxidized finish; cooked fluxflux.

FreshApply flux;fresh flux; clean tip; reflow joint at +10 °C; clean tip & reflowC.

Solder balling/splatter

Dirty board; wet flux boiling

Clean site; longer preheat; reduce temp 10 °C

Bridge (SMD)

Too much solder;solder noadded; fluxtip pathremoved too quickly.

FluxFlood +with flux; drag a clean chisel tip alongacross leads;the useleads to remove excess solder.

THT No Top Fill

Hole clearance too tight; large ground plane acting as heat sink.

Apply solder wickpreheat gentlyto the board bottom (80–120 °C); increase tip size.

Lifted padPad

OverheatExcessive dwell time; prying or prymechanical stress while hotsolder is liquid.

Lower temp;temperature; biggeruse larger tip (faster)for faster transfer); letallow the joint to cool completely before movingapplying mechanical stress.

That's an excellent point. The section dedicated to the training drill for new operators is crucial because it bridges theoretical knowledge (the handbook content) with practical execution, which is a key mandate for a robust manufacturing environment.

I excluded it in the previous rewrite because it wasn't explicitly structured as a main section, but it is highly valuable for the target audience (managers and engineers focused on training and standardization). I will ensure the concept of a mandatory, standardized training drill is integrated back into the "Hand Soldering Foundations" chapter.

Here is the revised section covering the essential training drill, framed as a standardized proficiency check.

2.1.7 Proficiency Check and Training Drill

Hand soldering proficiency requires a clear standard that operators must meet before working on live product. This is achieved through a standardized, measurable drill that verifies controlled application of heat and proper technique.

  • The Mandate: Every new operator must pass a timed drill on a designated training coupon (a small PCB board with test pads). This coupon must include high-risk features like fine-pitch SMT, standard chip passives, and heavy THT pins.
  • The Metric: The operator is measured on two criteria:
    1. Time Compliance: Completing the sequence (heating, soldering, cleaning) within the specified dwell limits (e.g., 4 seconds for SMT, 6 seconds for THT).
    2. Quality Compliance: Achieving IPC-A-610 Class 2 or 3 acceptance criteria for fillet formation, wetting angle, and cleanliness (no cold joints, no excessive flux residue).
  • Verification: The soldered coupon is submitted for a formal Visual Inspection and logged as the operator's proficiency record. Failure requires immediate, focused re-training on the specific technique or defect type.

Final Checklist: Hand Soldering Quality Control

Mandate

Setup Check

Technique Check

ESD Control

ESD wrist strap checked and grounded; all tools are ESD safe.

Only touch the component body/lead with ESD-safe tweezers/tools.

Tip Health

Tip type and size match the required pad geometry; tip is freshly tinned.

Use brass wool for cleaning; replace tip when pitted or dull.

Temperature

Temperature set to the lowest viable heat to wet the alloy in 2–4 seconds (SMD).

If wetting is slow, add flux or preheat the board; do not just increase iron temperature.

THT noDwell top fillLimit

PreheaterTight hole;is coldused planefor dense/heavy copper boards.

PreheatTotal board;heat largerapplication chisel;time addlimited flux;to if3–6 chronicseconds →per enlargeTHT hole next revpin.

ICQuality won’t alignGate

Standard Work Instruction (SWI)Tack tooand big;IPC noacceptance thirdcriteria handare posted and followed.

TinyJoint tack;must usedisplay tweezersa &concave magnificationfillet and full wetting angle.



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



Conclusion: Establishing disciplined practices for iron selection, tip care, temperature control, ergonomics, and inspection transforms soldering from a variable skill into a predictable process. When executed this way, hand soldering delivers fast, clean, and repeatable joints that protect product quality and production efficiency.

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