Eight most common soldering errors:
1. Not enough heat.
The joint looks OK, but because you didn't apply quite enough heat, the solder didn't melt sufficiently to realign its internal molecular structure. It remained granular instead of becoming a solid, uniform blob, and you end up with a “dry joint,” also known as a “cold joint,” which will come apart when you pull the wires away from each other. Reheat the joint thoroughly and apply new solder. A leading cause of under heated solder is the temptation to use the soldering iron to carry solder to the joint. This results in the cold wires reducing the temperature of the solder. What you should do is touch the soldering iron to heat the wires first, and then apply the solder. This way, the wires are hot and help to melt the solder, which wants to stick to them. Because this is such a universal problem, I’ll repeat myself: Never melt solder on the tip of the iron and then use it to carry the solder to the joint. You don’t want to put hot solder on cold wires. You want to put cold solder on hot wires.
2. Too much heat.
This may not hurt the joint, but can damage everything around it. Vinyl insulation will melt, exposing the wire and raising the risk of short circuits. You can easily damage semiconductors, and may even melt the internal plastic components of switches and connectors. Damaged components must be desoldered and replaced, which will take time and tends to be a big hassle.
3. Not enough solder.
A thin connection between two conductors may not be strong enough. When joining two wires, always check the underside of the joint to see whether the solder penetrated completely.
4. Moving the joint before the solder solidifies.
You may create a fracture that you won’t necessarily see. It may not stop your circuit from working, but at some point in the future, as a result of vibration or thermal stresses, the fracture can separate just enough to break electrical contact. Tracking it down will then be a chore. If you clamp components before you join them, or use perforated board to hold the components steady, you can avoid this problem.
5. Dirt or grease.
Electrical solder contains rosin that cleans the metal that you’re working with, but contaminants can still prevent solder from sticking. If any component looks dirty, clean it with fine sandpaper before joining it.
6. Carbon on the tip of your soldering iron.
The iron gradually accumulates flecks of black carbon during use, and they can act as a barrier to heat transfer. Wipe the tip of the iron on the little sponge mounted in the base of your soldering iron stand or your helping hand.
7. Inappropriate materials.
Electronic solder is designed for electronic components. It will not work with aluminum, stainless steel, or various other metals. You may be able to make it sticky to chrome-plated items, but only with difficult
8. Failure to test the joint.
Don’t just assume that it’s OK. Always test it, by applying manual force if you can or, if you can’t get a grip on the joint, slip a screwdriver blade under it and flex it just a little, or use small pliers to try to pull it apart. Don’t be concerned about ruining your work. If your joint doesn't survive rough treatment, it wasn't a good joint. Of the eight errors, dry/cold joints are by far the worst, because they are easy to make and can look OK.
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