Soldering 101

Soldering is one of those “small” skills that unlocks a lot of building: sensors, keyboards, robots, repairs, and prototypes. This guide stays visual-first (every concept has a photo), but adds the missing beginner details that prevent burnt boards, cold joints, and headaches.

The one rule that fixes 80% of mistakes:
Heat the metals first, then feed solder into the joint (not onto the tip).

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0) Before you start: what “good” looks like (and what “bad” looks like)

What you’re aiming for

• Solder flows like a tiny shiny “fillet” (a smooth ramp) between pad and lead/wire.
• You can still see the shape of the wire/lead underneath—not a giant blob.
• The joint is still while cooling (no “wiggle” during solidification).

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1) Set up safely (for lungs, eyes, and your PCB)

1A) Copy a real teaching bench setup (lighting + stable work + organization)

Do this every time:

• Work on a steady table (no lap soldering).
• Add bright light (desk lamp + magnifier if you have one).
• Put the iron in a proper stand on a heat-resistant mat.
• Keep flammables away (paper towels, alcohol bottle, plastic bags).

1B) Fume safety (the “invisible beginner mistake”)

Even if you can’t smell much, soldering produces flux fumes. Use ventilation that captures fumes near the joint.

A simple “good enough” airflow setup:

• Put a small fume extractor or fan behind the joint so it pulls smoke away from your breathing zone.
• Aim for gentle airflow—strong wind can cool the joint and blow tiny parts away.

1C) Eye + burn + hand safety (quick checklist)

• Wear safety glasses. Solder can spit (especially while rework/desoldering).
• Treat the iron like a small welding torch:
  • Never set it down on the table—always in the stand.
  • Keep the cord routed so you can’t snag it.
• Keep a heat-proof place to drop hot parts (ceramic tile or silicone mat).
• Wash hands after soldering—especially if you use leaded solder.

1D) Board safety (ESD) for sensitive electronics

Not every project needs ESD protection, but it’s cheap insurance for modern ICs.

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2) Tools that actually matter (and why)

Must-have

• Temperature-controlled soldering iron (or a quality fixed-temp iron).
• Stand + heat-resistant mat (non-negotiable).
• Brass wool (preferred) or a damp sponge to clean the tip.
• Electronics solder (rosin/flux core).
• Flux (pen or small tub). Flux is the “easy mode” button.
• Helping hands / PCB holder so nothing moves while cooling.
• Flush cutters for trimming leads.
• Isopropyl alcohol + swabs/brush for cleanup.

Strongly recommended for beginners

• Good lighting + magnification (your eyes can’t fix what they can’t see).
• Tweezers (especially for small parts).

For “board health” and clean wiring

• Heat gun for heat-shrink tubing (cleaner and safer than a lighter).
• Desoldering tools (wick and/or pump) for fixing mistakes.

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3) Prep the iron: clean + tin the tip (the “secret sauce”)

This is the biggest quality lever beginners ignore. A dirty, oxidized tip won’t transfer heat well—then you stay on the pad longer, which damages the PCB.

3A) Clean the tip

Best practice:

• Wipe quickly, don’t “scrub the life out of it.”
• If you’re using a sponge: damp, not dripping.

3B) Tin the tip (coat it with solder)

Tinning rhythm (do this constantly):

1. Heat the iron.
2. Clean the tip (brass wool/sponge).
3. Add a small amount of solder so the tip looks shiny.
4. Solder a joint.
5. Clean + re-tin every few joints or whenever it looks dull.

Board health tip: If your joint takes longer than a few seconds to melt, don’t “camp” on the pad.
Stop, clean/tin the tip, add flux, and try again with better contact.

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4) The core motion: “touch both metals, feed solder, freeze”

Watch the motion first (animation)

Step-by-step photos (exact placement)

Tiny pro details that prevent failures

• Use the flat face of the tip (more contact area = faster heat).
• Add flux if solder doesn’t want to wet/flow.
• Don’t blow on the joint. Let it cool naturally.

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5) Through-hole soldering (headers, resistors, LED leads)

Fast workflow that protects pads:

1. Insert the part fully (or to the intended height).
2. Slightly bend leads so the part doesn’t fall out.
3. Add flux (optional, but makes everything easier).
4. Heat pad + lead together.
5. Feed solder into the joint.
6. Remove solder, remove iron.
7. Trim leads after cooling.

Board health tip: If a pad starts to look like it’s lifting or the solder mask is discoloring, stop and let it cool. Too much dwell time is the #1 cause of lifted pads.

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6) Wires: strip → twist → tin → join → strain relief

Wire soldering is where beginners accidentally build “fragile art.” You want mechanical strength + solder.

The “wire tinning” trick (makes joining easy)

• Strip the wire.
• Twist strands so they stay together.
• Add flux.
• Heat the wire and feed solder until the strands look “silvered” (not a fat blob).

Add strain relief (don’t rely on solder as glue)

• Use heat-shrink tubing over the joint when possible.
• Tie down wires with a zip tie or anchor point so movement doesn’t stress the joint.

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7) Heat gun (and when NOT to use one)

A heat gun is perfect for heat-shrink and some rework tasks—but it’s not a substitute for a controlled soldering iron on most PCB joints.

Heat gun best practices (human + board safety)

• Keep the nozzle moving (avoid scorching).
• Use the lowest heat that shrinks tubing smoothly.
• Don’t aim at the PCB for long—uncontrolled heating can warp plastics, loosen connectors, or damage components.

If you need hot air for electronics rework: a hot-air rework station is safer than a generic paint-stripper heat gun because it gives you temperature and airflow control.

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8) Inspection: spot the common failures fast

8A) Cold joint (weak connection)

Fix: add flux, reheat until it flows, optionally add a touch of fresh solder, then let it cool without movement.

8B) A clean “wetted” joint example

8C) Quick inspection checklist (30 seconds)

• Any bridges between pins? (especially ICs/headers)
• Any joints that look dull/grainy?
• Any joints shaped like a ball sitting on top? (often not wetted)
• Any pads discolored or lifting?

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9) Desoldering & rework (how to fix mistakes without wrecking pads)

Rework is where boards get damaged. The goal is short heat contact + lots of flux.

9A) Solder wick (desoldering braid)

Pro rework trick: add flux to the wick (or to the joint) before heating—wick works way better.

9B) “Save the pad” rules (board health)

• Don’t keep reheating the same pad nonstop. Heat → attempt → cool → repeat, instead of cooking it.
• If solder won’t melt quickly:
  • clean and re-tin tip
  • add flux
  • use a slightly larger tip face for better heat transfer

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10) Surface-mount (SMD) preview (so you recognize it)

You can learn SMD as a beginner—start with bigger sizes (like 0805) before tiny parts.

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11) Finish cleanly (reliability + looks)

• Inspect under bright light (and magnification if possible).
• Clean flux residue if you used rosin or water-soluble flux:
  • swab/brush with isopropyl alcohol
  • dry fully before power
• Park the iron in its stand, then unplug.

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Practice plan: 30 minutes to “I can solder”

Round 1 — motion practice (no board stress)

• Twist two scrap wires together and solder until you get three smooth joints in a row.

Round 2 — through-hole basics

• Solder a header pin onto a spare PCB or perfboard.
• Aim for consistent joints without blobs.

Round 3 — “fixing your own mistakes”

• Intentionally make a bad joint.
• Then fix it with flux + reheat, and clean it up.

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Quick printable cheat sheet

Before soldering

• Light + stable bench
• Ventilation / fume capture
• Tip clean + tinned

During soldering

• Heat pad + lead together
• Feed solder into the joint
• Remove solder, then iron
• Don’t move while cooling

After soldering

• Inspect (bridges? cold joints?)
• Clean residue as needed
• Unplug and store safely

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• 2024 1
• 2022 2
• 2019 1

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