Soldering Techniques for Beginners: How to Solder Properly

Good soldering is the skill that separates a circuit that works on the bench from one that keeps failing in the field. Most bad joints come from three things: the wrong temperature, dirty surfaces and moving the joint while it cools.

What you need

• A temperature-controlled soldering iron with a clean, tinned tip
• Solder wire with flux core. Leaded Sn63/Pb37 melts at about 183°C and is easier to learn on. Lead-free SAC305 melts at about 217°C and needs a hotter iron
• Flux, desoldering wick and a solder pump
• A damp sponge or brass wool to clean the tip, and a stand
• Fume extraction or good ventilation

How to solder a through-hole joint

1. Set the iron around 320°C to 350°C for leaded solder, higher for lead-free.
2. Clean and tin the tip so heat transfers properly.
3. Touch the iron to both the pad and the component lead at the same time, for 1 to 2 seconds.
4. Feed solder to the joint, not to the iron tip, until it flows around the lead.
5. Remove the solder, then the iron, and keep everything still until the joint cools.
6. Check the joint: it should be shiny and shaped like a small cone, not a ball or a dull blob.

Common soldering problems

• Cold joint: dull, grainy or cracked. Reheat with a little fresh flux and add a touch of solder.
• Solder bridge: solder connecting two pads. Remove it with desoldering wick and flux.
• Too much solder: remove with a pump or wick and redo the joint.
• Lifted pad: caused by too much heat or force. Repair with a jumper wire to the next connection point.

Soldering SMD components

For SMD parts, use flux, fine tweezers and a fine tip. Tack one corner, check alignment, then solder the remaining pins. For multi-pin ICs, drag soldering with plenty of flux works well, and a hot air station helps with removal and rework. Practise on dummy boards before touching a board you care about.

Safety

Never touch the tip, keep flammable items away, work with fume extraction and wash your hands after handling solder, especially leaded solder. Store the iron in its stand and switch it off when you leave the bench.

Soldering, SMD rework and BGA reballing are taught hands-on in Module 2 of the ProtoPulse Academy electronics course.