Soldering 101

Soldering is a small skill that opens up a lot: sensors, keyboards, robots, repairs and prototypes. This guide shows each step with a photo and covers the details that save beginners from burnt boards and joints that don’t hold.

If you remember one thing

Heat the metal parts first, then feed solder into the joint. Not onto the tip of the iron.

What a good joint looks like

Good: smooth and shiny, solder has flowed into the joint. Photo: Wikimedia Commons

Bad: dull and lumpy, sitting on top instead of flowing in. Photo: Wikimedia Commons

A good joint has three things:

• The solder forms a small, shiny ramp between the pad and the wire or lead.
• You can still see the shape of the lead under the solder. It isn’t buried in a blob.
• Nothing moved while it cooled.

Set up safely

The bench

A steady surface, a clear bench, good light and tools within reach. Photo: Wikimedia Commons

Every time:

• Work on a steady table, never on your lap.
• Use bright light, and a magnifier if you have one.
• Keep the iron in a proper stand, on a heat-resistant mat.
• Keep paper towels, alcohol and plastic bags away from the iron.

Fumes

You might not smell much, but the flux in solder gives off fumes. Pull them away from your face, close to where you work.

A fume extractor behind the work pulls the smoke away from you. Photo: Wikimedia Commons

A small extractor or fan behind the joint is enough. Keep the airflow gentle: a strong draft cools the joint and blows small parts away.

Eyes, burns and hands

• Wear safety glasses. Solder can spit, especially when you desolder.
• The iron always goes back in the stand, never on the table.
• Route the cable so you can’t catch it with your arm.
• Have a heat-proof spot, like a ceramic tile, to drop hot parts on.
• Wash your hands afterwards, especially with leaded solder.

Static (ESD)

Not every project needs it, but an anti-static strap is cheap and protects modern chips.

Clip the strap to a grounded point, like an ESD mat. Photo: Wikimedia Commons

The tools that matter

A few tools used well beat a big kit used at random. Photo: Wikimedia Commons

You need:

• A temperature-controlled iron, or a good fixed-temperature one
• A stand and a heat-resistant mat
• Brass wool, or a damp sponge, to clean the tip
• Electronics solder with a rosin (flux) core
• Extra flux, as a pen or a small tub. It makes everything easier.
• Helping hands or a PCB holder, so nothing moves while it cools
• Flush cutters to trim leads
• Isopropyl alcohol and a brush to clean up

Worth having: a magnifier, tweezers for small parts, desoldering wick or a pump for mistakes, and a heat gun for heat-shrink tubing.

Clean and tin the tip

Beginners skip this the most, and it matters the most. A dirty, oxidised tip passes heat badly, so you hold it on the pad longer, and that’s what damages boards.

A quick wipe removes the oxide. A clean tip heats faster. Photo: Wikimedia Commons

Wipe it quickly. If you use a sponge, it should be damp, not dripping.

Tinning: a thin coat of solder keeps the tip shiny. Photo: Wikimedia Commons

Repeat this rhythm all the time:

1. Heat the iron.
2. Clean the tip.
3. Melt a little solder on it, so it looks shiny.
4. Solder a joint.
5. Clean and re-tin every few joints, or whenever the tip looks dull.

Don’t keep the iron on the pad

If the solder takes more than a few seconds to melt, stop. Clean and tin the tip, add flux, and try again with better contact.

The basic motion

The iron heats the joint, solder goes into the joint, then everything holds still. Animation: Wikimedia Commons

1. Position: touch the iron to the pad and the lead at the same time.

   

   Both metals heat together. Photo: Wikimedia Commons

2. Feed: touch the solder where the hot metals meet and let it flow. Don’t push.

   

   The solder melts on the joint, not on the iron. Photo: Wikimedia Commons

3. Finish: take the solder away first, then the iron. Hold still while it cools.

   

   Solder away, then iron away. Photo: Wikimedia Commons

A few details that help:

• Use the flat face of the tip. More contact means faster heat.
• If the solder won’t flow, add flux.
• Don’t blow on the joint. Let it cool by itself.

Through-hole parts

Headers, resistors, LEDs: anything with legs that go through the board.

Heat pad and lead, feed solder, trim the lead. Photo: Wikimedia Commons

1. Push the part in fully, or to the height you want.
2. Bend the leads slightly so it doesn’t fall out.
3. Add flux if you have it.
4. Heat the pad and the lead together.
5. Feed solder into the joint.
6. Remove the solder, then the iron.
7. Trim the leads once it’s cool.

Watch the pad

If the pad starts to lift or the board around it changes colour, stop and let it cool. Holding the iron too long is the most common way to lift a pad.

Wires

With wires you want a joint that is mechanically strong as well as soldered.

Smooth flow is good. Bubbles and a rough surface usually mean too much heat or movement. Photo: Wikimedia Commons

Tin the wires first. Strip them, twist the strands, add flux, then heat the wire and feed solder until the strands look silver. No blobs. Two tinned wires join in a second.

Add strain relief. Solder isn’t glue. Put heat-shrink tubing over the joint, and tie the wire down so movement doesn’t pull on the joint.

Heat guns

A heat gun is great for heat-shrink tubing, but it doesn’t replace the iron on board joints.

What a heat gun is for: heat-shrink. Photo: Wikimedia Commons

• Keep the nozzle moving.
• Use the lowest heat that shrinks the tubing.
• Don’t point it at the board for long. It can warp plastic, loosen connectors and damage parts.

For hot-air rework on electronics, use a hot-air rework station. Unlike a paint-stripping heat gun, it lets you set the temperature and airflow.

Check your work

Cold joints

A cold joint: dull, grainy, crusty. Photo: Wikimedia Commons

Fix: add flux, reheat until it flows, add a little fresh solder if needed, and let it cool without moving.

A healthy joint

Smooth, with clean edges and no spikes or balls. Photo: Wikimedia Commons

A 30-second check

• Any bridges between pins, especially on chips and headers?
• Any dull or grainy joints?
• Any joints that look like a ball sitting on top?
• Any pads that are discoloured or lifting?

Fixing mistakes

Boards get damaged during rework more than anywhere else. Keep heat contact short and use plenty of flux.

Add flux, add fresh solder if needed, remove it cleanly, solder again. Photo: Wikimedia Commons

Solder wick

Lay the braid on the solder, press the iron on top, lift both straight up. Photo: Wikimedia Commons

Put flux on the wick before you heat it. It soaks up solder much better.

Save the pad

• Don’t keep heating the same pad. Heat, try, let it cool, try again.
• If the solder won’t melt quickly: clean and tin the tip, add flux, or use a bigger tip.

A first look at SMD

You can learn surface-mount parts as a beginner. Start with larger sizes like 0805 before the tiny ones.

Tack one side, line it up, then solder the other side with flux. Photo: Wikimedia Commons

Finish cleanly

• Inspect under bright light, magnified if you can.
• Clean flux residue with isopropyl alcohol and a brush, and let the board dry before you power it.
• Put the iron in its stand and unplug it.

A 30-minute practice plan

1. Motion: twist two scrap wires together and solder until you get three smooth joints in a row.
2. Through-hole: solder a header onto a spare board or perfboard. Aim for joints that all look the same.
3. Rework: make a bad joint on purpose, then fix it with flux and heat, and clean it up.

Cheat sheet

Before	During	After
Bright light, steady bench	Heat pad and lead together	Look for bridges and cold joints
Fumes pulled away	Feed solder into the joint	Clean off flux residue
Tip clean and tinned	Solder away, then iron	Iron in the stand, unplugged
	Hold still while it cools