Soldering Equipment and Setup

Solder melts; the parts being joined do not

Soldering joins metal parts with a filler metal that melts below the parts' melting temperatures. It is closer to brazing than welding: the base metals do not melt. Electrical soldering connects wires, printed circuit boards (PCBs), and electronic components.

A good connection must be mechanically secure and conduct electricity. The molten solder must wet both surfaces: spread onto and bond with them, rather than sit on top as a ball. Clean surfaces, flux, and heat at both parts make that possible.

Start here, then follow Making and Inspecting Solder Joints and Soldering Wire Splices and Through-Hole PCBs.

Choose the tip for contact, not just access

A temperature-controlled station regulates the iron's tip temperature. A basic iron may have no temperature control; a cordless iron changes how it is powered, not how a joint is made. Check the tool's instructions and choose settings suitable for the solder and components.

Tip shape and size matter. A fine point reaches small spaces, but a chisel's broad face often transfers heat more effectively. Use the largest tinned contact face that fits the joint without touching neighboring connections. Interchangeable tips let one iron handle different work; change them according to the tool's instructions.

What the iron's “sweet spot” means

Use the broad, clean, solder-coated working face of the tip against both parts. Do not interpret “side of the iron” as the barrel or an uncoated surface. The useful contact area, not the sharpest point or the highest temperature setting, delivers heat into the joint. A tiny point can be hot and still transfer heat poorly.

Match the solder and flux to electrical work

• Leaded solder: common tin-lead alloys melt at lower temperatures than common tin-copper or tin-silver-copper lead-free alloys. Leaded solder is still sold, but lead is restricted in many products. Follow the specified alloy for the work.
• Lead-free solder: common electrical alloys use tin with copper and/or silver. They may need a different heating process and can solidify with a duller finish. “Lead-free” does not mean “no fumes.”
• Diameter: fine solder wire makes it easier to meter a small amount into a small joint. Thick solder feeds more metal for the same length; it is easy to overfill a small pad.
• Flux: helps remove surface oxides during heating so solder can wet the metal. Rosin-core solder carries flux inside the wire; additional compatible electronics flux may help. Do not substitute plumbing acid flux.

Read the alloy and flux label, including any residue-cleaning instructions. See Chemicals and Safety Data Sheets for handling information.

Practice choosing solder

Support the work and control the heat and fume

Helping hands or a PCB vise hold the parts still while your hands hold the iron and solder. Keep a proper stand or cradle within reach. Use a damp soldering sponge or brass wool for tip cleaning, and have solder wick (copper braid) or a desoldering pump available for removing excess solder.

It gets hot. Really hot. Park the iron in its stand, and allow the work to cool before touching it. Use ventilation or fume extraction that keeps the plume away from your face and other people; most visible fume comes from flux. Wash your hands after handling leaded solder, and do not eat or drink at the bench.

SHOP RULE: NEVER SOLDER BATTERIES.

Why the battery rule stays absolute

Heat applied to a cell can damage its seals and internal parts. Lithium cells in particular can fail dangerously if damaged. Use the intended battery holder or connector instead of applying a soldering iron to a battery.

Work on disconnected circuits. Follow Electrical Safety and Personal Protective Equipment; flux and fume handling belongs with Chemicals and Safety Data Sheets.

Further reading on flux fume

The UK Health and Safety Executive's guidance for solderers describes rosin-based flux fume and recommends extraction and keeping your head out of the plume.

Clean, tin, and keep the working face coated

With the iron at working temperature, briefly clean the tip on brass wool or a damp soldering sponge. Apply fresh solder to coat its working face, then remove the excess on the cleaner. Leave a thin coating; do not wipe it bare and let it sit hot. Re-tin as needed and before storage as directed by the tool manufacturer.

Why tinning helps heat transfer

A hot tip oxidizes. Oxide interferes with wetting, while a solder coating protects the working face and helps make thermal contact with the joint. Tinning the tip is the time to feed solder onto the tip. Making a joint is different: feed solder into the heated joint.

See HAKKO's tip-life guidance for the construction of plated tips and the effects of oxidation.