Last updated: October 2026

To solder a through-hole part, tin a clean iron tip, touch it so it heats both the copper pad and the component lead at the same time, then feed solder into the joint (not onto the tip) until it flows around the lead and fills the hole. Pull the solder away, then the iron, and let the joint cool without moving it. A good joint is smooth, shiny and shaped like a small cone around the lead.

This guide covers each step, the tip temperatures that solder and iron makers publish, how to tell good joints from bad ones, and how to clean up. It is written for low-voltage hobby boards and kits.

Safety first

Read this before you plug in the iron.

  • Ventilate. The University of Rhode Island soldering rules say to work in a well-ventilated area, use a fume extractor and not inhale the fumes. Kester also notes that some fluxes smoke more at the hotter tip temperatures lead-free solder needs.
  • Leaded solder means hand washing. Tin/lead solder contains lead, which is toxic. The same rules say to keep food and drink away from the work area and to wash your hands thoroughly after handling flux and solder that contains lead. Wash before you eat, drink or touch your face.
  • Protect your eyes. Wear safety glasses. SparkFun’s tutorial recommends them in case clipped leads or molten solder fly toward your eyes.
  • Park the iron. Always return the iron to its stand. The tip runs at several hundred degrees and will melt wire insulation and plastic.
  • Power off the board. Never solder a circuit that is powered or plugged in. If the board has large capacitors, discharge them before you work on it.

Step 1: Set up the bench

  1. Clear the space between the iron stand and your work.
  2. Hold the board steady with a vise, helping hands or a board holder so you are not holding hot parts with your fingers.
  3. Wet the cleaning sponge, or have a brass wire cleaner ready.
  4. Bend the component leads so the part sits flat, push them through the holes from the component side, and spread the leads slightly on the back so the part does not fall out when you flip the board.

Step 2: Choose a tip temperature

There is no single correct number. The right setting depends on the solder alloy, the tip size and how much copper the joint has to heat. These are the published starting points:

SourceGuidance
Hakko (tip care guide)Start at 330 to 350 °C if you have no other recommendation, then adjust. Use the lowest temperature that works, because high temperature wears tips faster.
Kester (lead-free hand soldering note)With 63/37 leaded solder, temperatures as low as 650 °F (about 343 °C) have been used. With lead-free SAC and SnCu, 700 to 800 °F (about 371 to 427 °C) is best. Above 800 °F, board and component damage may occur.
SparkFun (through-hole tutorial)A medium heat of 325 to 375 °C for standard through-hole work, more for large pads and ground planes.

Kester gives the melting points of the common lead-free alloys as about 217 °C for tin-silver-copper (SAC) and about 227 °C for tin-copper (SnCu). Leaded 63/37 melts lower, which is why it needs less tip heat and why many beginners find it easier.

A practical approach: start near 330 to 350 °C for leaded solder, or in Kester’s lead-free range for SAC, then go up in small steps only if the solder is slow to flow. Kester notes that too low a temperature gives cold joints, while too high a temperature can cause grainy joints, de-wetting and charred flux.

If you use a Pinecil, its maker lists an adjustable range of 100 to 400 °C. See Pinecil vs TS101 for more on small USB-C irons.

Step 3: Tin the tip

Tinning means coating the tip with a thin layer of fresh solder so heat moves into the joint quickly.

  1. Let the iron reach its set temperature.
  2. For a brand-new tip, Hakko says to melt solder onto the pre-tinned end of the tip and cover it.
  3. Wipe the tip on the sponge or brass cleaner, then add a small amount of fresh solder.
  4. Hakko recommends cleaning the tip just before soldering, not after, and keeping the pre-tinned area covered with solder at all times. A healthy tip looks wet and silver. A dull, dark tip that solder will not stick to is oxidized and transfers heat poorly.

Step 4: Heat the pad and the lead together

  1. Touch the tip so it contacts both the copper pad and the component lead at the same time. Adafruit’s soldering guide stresses heating both parts of the joint.
  2. A small bead of solder on the tip helps heat flow into the joint.
  3. Hold it for about a second or two. Larger pads and thicker leads need longer.

The common beginner mistake is heating only the lead or only the pad. Solder flows to hot metal, so whichever part is cold will not wet.

Step 5: Feed the solder into the joint

  1. Touch the solder wire to the joint where the pad and lead meet, on the side opposite the iron if you can. Feeding the wire into the joint, rather than melting it on the tip and carrying it over, puts the flux in the wire where the metal needs it.
  2. The solder should melt and flow smoothly onto both the pad and the lead, and fill the hole.
  3. Feed just enough to form a cone. Then pull the solder wire away first.
  4. Remove the iron and let the joint cool without moving it.

Step 6: Trim the leads

Use flush cutters to trim the lead close to the top of the solder joint. Point the board down or cover the lead with a finger so the clipped piece does not fly. Adafruit notes that this applies to wire-lead parts such as resistors and capacitors, not to chips or sockets.

Good joints vs bad joints

SparkFun describes a good through-hole joint as shaped like a volcano or a chocolate kiss, not a ball or clump. Adafruit adds that it should be smooth, concave and shiny, with solder wetting both the pin and the pad. Lead-free joints look less reflective than leaded ones even when they are good, according to Kester.

These are the faults Adafruit’s guide lists, with its fixes:

ProblemWhat it looks likeFix
Cold jointRough, lumpy surface; solder never fully meltedReheat with a hot iron until the solder flows
Disturbed jointFrosted or crystalline surface from movement while coolingReheat and let it cool without moving
Overheated jointPoor flow and burnt fluxClean off the residue, then rework carefully
Pad not wettedSolder sticks to the lead but not the padHeat the pad until solder flows onto it
Solder starvedToo little solderReheat and add a little more
Too much solderA large blob that hides the jointRemove excess with the iron or wick
Solder bridgeTwo neighboring joints connectedDrag the excess away or use wick
Lifted padPad has come off the boardUsually from too much heat; bridge to the trace with the lead or a jumper wire

If a joint fails twice, start over. The University of Rhode Island rules suggest removing the old solder with a desoldering pump, cleaning the flux residue, and trying again with fresh solder.

Step 7: Clean up

  1. Wipe the tip, then add a fresh coat of solder before you park or switch off the iron. Hakko says this helps prevent oxidation, and recommends turning the iron off if you will not solder for more than 5 minutes.
  2. Clean flux residue if your flux needs it. No-clean flux is designed to be left in many cases. Adafruit suggests isopropyl alcohol and a toothbrush for residue, and SparkFun says water-soluble flux should be washed off with hot deionized water and a stiff brush.
  3. Put solder scraps, clipped leads and dross in a lidded container. The University of Rhode Island rules call for labeling lead and silver solder waste for recycling.
  4. Wash your hands, especially after leaded solder.

Leaded or lead-free?

Leaded 63/37 flows more easily at lower temperatures and is often recommended for learning. Lead-free solder needs a hotter tip and, per Kester, at least 2% flux by weight in the wire, and it shortens tip life. Kester cites one manufacturer whose tips lasted 3 months with 63/37 but about 3 weeks with lead-free. If you choose leaded solder, the ventilation and hand washing steps above are not optional.

FAQ

What temperature should I set my soldering iron to? Hakko suggests starting at 330 to 350 °C when no other guidance applies. Kester recommends 700 to 800 °F (about 371 to 427 °C) for lead-free SAC and SnCu. Use the lowest setting that gives a fast, smooth flow.

Why will solder not stick to my tip? The tip is probably oxidized. Hakko notes that an oxidized tip repels solder and transfers heat poorly. Clean it, then retin it right away, and keep the tip coated with solder whenever the iron is idle.

How long should I hold the iron on a joint? Adafruit suggests a second or two of heating before feeding solder. Kester warns that long contact times and repeated rework can damage the joint, so if it takes much longer, use a bigger tip or slightly more heat.

Do I need extra flux for through-hole work? Rosin-core or flux-core wire usually carries enough for simple joints. A flux pen helps when reworking a joint or when the parts are old and oxidized.

What should I practice on first? A cheap kit with resistors and LEDs on a plain board. Check your work with a meter; this continuity and diode guide shows how. For gear choices, see best soldering iron and best solder and flux.

Sources