22 Sep

How to Solder

The one thing that most novice guitar repairmen dread is soldering. More damage is done than is repaired by inexperienced hobbyists and a hot soldering iron. But, soldering isn’t that hard if you understand the process and learn a little thermodynamics while you’re at it. Soldering is simply joining two disparate pieces of metal using elevated heat and an easily melted metal mixture.

Soldering irons are like shotguns, you just have to remember to point the working end away from your face! They are essentially ceramic heating coils encased in a metal pointed tool. Some have fixed wattages (a measure of how hot the iron will get) and more expensive professional models have variable heat/wattages. But the basic principles are the same for both types, and learning how to wield one correctly will save you a lot of money and time as well.

Soldering Irons
1. There are 15, 25, 40 and 60 watt soldering irons, with the smallest ones used in PC board work, and the larger ones used to physically ‘weld’ metal together. Variable heat irons can be digitally controlled and have adjustable wattages of 10 to 50 watts available at the twist of a knob.

2. Solder is an alloy mixture of tin and lead, along with a flux. Flux is an additive (usually rosin) that is mildly corrosive at elevated temperatures and helps the two pieces of metal bond both physically and electrically. The most common type of solder used in guitar building is composed of 60 % tin and 40 % lead. Due to environmental restrictions, there is a new type of solder that is lead free, but requires an additional 100 degrees of heat to properly melt.

Soldering Tinning Tip
3. A soldering iron is only as good as its metal tip. If you’re working with a new iron, you must ‘tin’ the tip properly, to help it transmit heat efficiently to working surfaces. When you turn on the iron for the first time, apply a liberal coating of solder and let it work its way all over the heating tip, then tap it against an edge to remove the excess solder. Now the tip of the iron is properly prepared to use for the first time. You must continually ‘wet’ the tip by applying solder to the iron while using. When you place the iron back in to its holder, it’s a good habit to touch a bit of solder to the iron.

Soldering Sponge
4. Keep a wet sponge handy to clean the rosin and impurities off the tip during use. If you use a dry rag or sponge to clean the tip, sulfur deposits can corrode the iron clad copper tip and eventually render it useless and in need of replacement way before its time. Remember that low iron temperatures will slow the rate of flow of the solder. Too high a temperature can burn the flux in the solder, creating a thick white smoke that’s not too healthy to breathe in. This will also cause what’s known as a “dry joint”. This poor connection can cause intermittent faults in the electrical connectivity of the soldered joint and is difficult to trace out. A typical working temperature for normal guitar related soldering is around 270 to 350 degrees Fahrenheit. It’s important to have the correct heat for the correct job.

Soldering Heating Joint
5. When soldering two pieces of metal together, always apply the solder directly to the joint and not to the tip of the iron itself. The solder flux is mildly caustic and will eat away at the iron’s tip over time. You want to heat up the two pieces of metal, then apply solder to the joint and let it flow readily into the connection. Don’t use excessive pressure on the tip while heating the working surfaces. It doesn’t improve heat transfer and can cause the ceramic heater coil to break, thereby ruining your soldering iron.

Soldering Cloudy Tip
6. After repeated usage, you may see a cloudy film form on the soldering iron tip. This is oxidation and can reduce the heat transfer ability of the iron and eventually cause the iron to quit working properly. To clean the tip, use some very fine grade sandpaper (800 to 1500 grit) and a small amount of Isopropyl Alcohol to buff the oxide film off carefully. Never clean the tip with a metal file or other rough abrasive materials. After buffing, turn the iron back on and re-tin the tip with copious amounts of solder.

Soldering Wrapped
7. Use a light amount of solder per connection. Too much solder can impair the connectivity and inadvertently ground or short wiring traces, especially on printed circuit boards. Too little solder in the joint can create an intermittent or non-working connection instead of a dependable one. I always try and make some sort of physical reinforcement to the connection by wrapping the wires together or tying off a component while soldering. This can relieve the stress of the physical connection and preserve the electrical continuity for a long time.

Soldering Heat Sink
8. When soldering wires in tight places, make sure your iron isn’t touching any peripheral wiring or components. The entire length of the iron barrel is hot, not just the tip, so be aware of where it’s being placed while in use. When soldering delicate electronic components such as resistors and capacitors, always use a “Heat Sink” in between the iron and the component. A heat sink is a device that allows an alternate path for the heat to disperse, rather than moving in to the delicate component. A small pair of hemostats or other clamping plier works well to divert the heat buildup away from what you’re working on.

Neatness and cleanliness do count when soldering. Remember that whatever you’re joining together may have to be un-soldered at sometime in the future, and making the connection as professional as possible when installing it makes it that much easier to uninstall later on without damaging any peripheral components or wiring. Use as little heat and solder as possible to do the job properly. A correct solder joint is shiny without pin holes or uneven breaks. If the connection’s hazy and flaky looking, it’s probably not going to hold. Be aware that too little heat or too little solder can cause just as much trouble as too much heat or solder. Take your time, and work deliberately to ensure the best possible outcome. The mantra of soldering perfection is this; do no harm and make good strong connections instead. And always remember that the best soldering job is the one that looks like no one’s done any work at all…

2 thoughts on “How to Solder

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