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To learn how to solder wires, strip both ends, slide on heat shrink, twist the strands together, heat the wire with your iron and feed solder into it until it flows through. Then let it cool and shrink the tubing over the joint.
A good soldered splice is smooth, fully wetted and soaked through the strands. It takes about 15 minutes the first time and much less once you get the feel for it.
Most bad joints come from cold wire, dirty copper or the wrong solder. Each of those has a simple fix.
Time: about 15 minutes | Difficulty: Moderate | Tools: soldering iron, rosin-core solder, wire strippers, heat shrink tubing, heat gun, helping hands
What You’ll Need
- A temperature-controlled soldering iron with a clean, tinned tip
- Rosin-core solder: 63/37, 60/40 or a lead-free alloy such as SAC305
- Wire strippers and flush cutters
- Heat shrink tubing that fits over the finished joint
- A heat gun or a lighter to shrink the tubing
- Helping hands or a small clamp to hold the wires
- A damp sponge or brass tip cleaner
- A non-flammable work surface and good airflow
Which Solder Should You Use for Wires?
For most wire splices, 63/37 rosin-core solder is the easiest to use. It melts at a single point, 361°F (183°C), per Kester’s alloy temperature chart, so it goes from liquid to solid fast.
60/40 melts over a short range, and lead-free alloys need more heat. Use lead-free solder when the job, the code or the customer calls for it.
| Alloy | Common Name | Melting Range (Kester) | Notes |
|---|---|---|---|
| Sn63Pb37 | 63/37 | 361°F (183°C) | Single melting point, sets fast, contains lead |
| Sn60Pb40 | 60/40 | 361 to 374°F (183 to 190°C) | Short pasty range, contains lead |
| Sn96.5Ag3.0Cu0.5 | SAC305 | 422 to 428°F (217 to 220°C) | Common lead-free alloy |
| Sn99.3Cu0.7 | Tin-copper | 440°F (227°C) | Lead-free, highest melting point of the four |
Pick rosin-core or no-clean solder for electrical work. Acid-core solder and acid fluxes are corrosive, so keep them off wiring.
What Temperature Should Your Soldering Iron Be?
Weller’s Better Soldering booklet says tip temperatures are usually set between 700°F and 800°F. Its rule is to keep the temperature as low as possible and still solder the joint quickly.
Start near the low end for thin wire and 63/37 solder. Go higher for thick wire or lead-free solder, because the joint needs more heat to reach the alloy’s melting point.
Weller lists 2 to 3 seconds as the maximum heat time for electronic soldering. Thick wire splices hold more copper and take longer, so use a bigger tip instead of cranking up the heat.
How to Solder Wires: Step by Step
Follow these 8 steps for a twisted inline splice. The same method works for automotive, speaker and low-voltage DIY wiring.
Step 1: Set Up a Safe Work Area
Clear a non-flammable surface and open a window or run a fan for airflow. Turn on the iron and let it reach temperature. Disconnect power from the circuit before you cut or splice any wire.
Step 2: Strip the Wire Ends
Strip enough insulation so the strands can overlap fully when you twist them. Don’t nick the copper, because cut strands weaken the splice. Clamp one wire in each arm of your helping hands with the ends facing each other.
Step 3: Slide On the Heat Shrink First
Cut heat shrink tubing about 0.4 to 0.6 inch (10 to 15 mm) longer than one exposed wire end, per iFixit’s splice guide. Slide it onto one wire and push it well back so the iron’s heat doesn’t shrink it early.
Forget this step and you’ll have to cut the splice apart to add the tubing.
Step 4: Twist the Strands Together
Fan out the strands on both ends and push them into each other so they intermesh. Then twist them flat into one tight bundle. A tight twist gives the solder a clean path to flow through.
Step 5: Tin the Tip and Heat the Wire
Wipe the tip on a damp sponge and add a small dab of solder. Weller says to keep the tip coated with a thin layer of solder. Then press the tip against the twisted wires with as much contact area as you can.
Step 6: Feed Solder Into the Wire
Touch the solder to the wire on the side opposite the iron, not to the tip. The hot copper should melt it and pull it into the strands.
If solder sits in a ball on top, the wire isn’t hot enough yet. Move along the splice until it’s thinly coated and the strand outlines still show.
Credit: www.youtube.com
Step 7: Let It Cool Without Moving It
Lift the iron and hold the wires still until the solder sets. iFixit suggests giving it 2 to 3 minutes to cool before you handle it. A joint that gets bumped as it sets can turn grainy and weak.
Step 8: Seal the Joint With Heat Shrink
Slide the tubing over the splice so it covers all the bare copper and overlaps the insulation on both sides. Heat it evenly with a heat gun until it shrinks tight. Adhesive-lined tubing adds a moisture seal for automotive and outdoor wiring.
What a Good Solder Joint Looks Like
A good wire splice is smooth and fully wetted, with solder soaked into the strands and their outlines still faintly visible. Weller describes good wetting as solder that quickly wicks along the metal on contact.
A bad joint looks lumpy or balled up, or has bare strands sticking out. Lead-free solder often sets a little duller than leaded solder, so judge it by shape and flow. Reheat a bad joint with a little rosin flux, or cut it out and start over.
Common Mistakes to Avoid
- Melting solder on the iron and dabbing it on. The flux burns off before it reaches the wire. Heat the wire and let the wire melt the solder.
- Too little heat. Solder balls on top and never soaks in. Use a bigger tip or hold a second longer.
- Too much heat for too long. The insulation melts and pulls back from the joint. Keep the iron as cool as works.
- Dirty or oxidized wire. Dark copper resists solder. Cut back to bright copper or add rosin flux.
- Forgetting the heat shrink. Slide it on before you twist the wires.
- Moving the wires too soon. Hold still until the solder sets.
- Using acid-core solder. Its flux keeps attacking the copper after the job is done.
- Filing the iron tip. Weller says never to file or grind its tips. Clean them on a damp sponge and keep them tinned.
Credit: www.youtube.com
Soldering Safety Tips
- Work with good airflow. Rosin flux smoke irritates the eyes and lungs, so use a fan or fume extractor to pull it away from your face.
- Wash your hands after handling leaded solder, and keep food and drinks off the bench.
- Put the iron back in its stand every time you set it down. The tip stays hot for minutes after you unplug it.
- Wear safety glasses, because hot solder and flux can spit.
- For household mains wiring, use the connectors your local electrical code requires.
Frequently Asked Questions
Can You Solder Wires Without a Soldering Iron?
Yes, for small jobs. Solder seal heat shrink connectors hold a ring of low-temperature solder inside the tubing, and a heat gun melts it around a twisted splice. A butane torch also works, but the open flame can scorch insulation fast, so keep it moving.
Is It Better to Crimp or Solder Wires?
Both work when done right. Crimping is faster and handles vibration well, so it’s common in vehicles. Soldering makes a low-resistance joint with no special crimp tool. Many installers solder, then add adhesive heat shrink for strain relief. Follow the connector maker’s instructions for either method.
What Kind of Solder Is Best for Electrical Wires?
Rosin-core solder is the right type for electrical wire. 63/37 tin-lead melts at 361°F (183°C) and sets fast, so beginners find it easiest. For lead-free work, SAC305 melts at 422 to 428°F (217 to 220°C) and needs a hotter iron. Never use acid-core solder on wiring.
Do You Need Flux to Solder Wires?
Usually you don’t need extra flux. Rosin-core solder carries flux inside the wire, and it cleans the copper as it melts. Add a little rosin flux paste when the wire is old, dark or hard to wet. Clean off heavy residue afterward with isopropyl alcohol and a brush.
Why Won’t Solder Stick to My Wire?
Solder won’t stick when the wire is too cool, dirty or oxidized. Heat the copper first and feed solder into the wire, not onto the iron. Strip back to fresh, bright copper, add a little flux, and clean and tin your iron tip so heat moves into the joint.
Final Words
Soldering wires comes down to clean copper, enough heat and a still hand. For copper pipe and heavier metal parts, brazing vs soldering comes down to joint strength and working heat. Slide on the heat shrink first, twist the strands tight, heat the wire and let it pull the solder in.
Use 63/37 or 60/40 rosin-core solder for the easiest joints, or a lead-free alloy when the job calls for it. Keep the iron as cool as works, seal the splice with heat shrink, and tug-test it before you tape up the wiring.
