Learning how to Solder

9/98 - Jens Moller - http://www.colomar.com/Shavano/soldering.html
Updated 10/98, 12/02 and 07/04

I prefer to make repairs of cables and connectors when at home. I can sit at a well lighted workbench and use a small vise to hold parts as I take my time to fix them. If you carry a 'bad cable bag' with you - this is where you normally will sit down to work on things when you have the time. Unfortunately, you will sometimes be in situations where your options are quite limited and you need to fix something right now, otherwise, the show will not go on. Taping connections together is often better than nothing, but its often a lousy short term correction. If possible, soldering connections then taping up results is better than twisting the wires together and taping them. Any band member that has played out for few years will have a story or 2 about wiring problems. Soldering is an easy to learn skill that can make your performance life substantially less miserable. If you want to become a "Roadie" - ie. someone who sets up/tears down and maintains equipment, its a skill thats a necessity to learn.

Choosing the right Soldering iron

For most on the road cable repairs, instrument volume/tone re-wiring and cross-over/speaker cabinet wiring, a soldering iron that is rated at 30 to 40 watts is quite effective. If you have a soldering gun (usually 100 watts or more), this is good for heavy wire (14 gauge or thicker), but typically will ruin many of the connectors, wire and components that you might be trying to wire up. I carry an inexpensive 30 watt Soldering iron in my cord case that looks like this:

Its tip (heating surface) is no more than 1/4 inch (6mm) wide. It has a plastic handle and a short wire, that allows me to plug it into an electrical outlet where ever I happen to be. There is usually a set screw on the Soldering iron that holds the Tip in (some models also have tips that screw in). You must keep the tip tightly attached to the iron - the tip will work its way loose over time & you may be forced to tighten it while its hot - have pliers and a screw driver handy to do this, otherwise the tip will not heat up enough to melt the solder.

When working correctly, the tip gets plenty hot for most connectors/wire and common electrical parts. You could use one of these on printed circuit boards (like a guitar players stomp box or any device that uses 9 volt batteries - the wires frequently break where these 9 volt battery adapters attach to the circuit board).

When you work with electrical circuits use solder that is - 60% tin 40% lead and has a Rosin core (there are others that have 63% tin and 37% lead - these have a lower melting point and are excellent for this purpose). Do not use acid core solder - it can corrode things and may damage the thing which you are trying to repair.

NOTE: While it sounds obvious, let me remind you never to attempt soldering on any circuit to which power is applied. The damage to the equipment could be severe and you may get electrocuted. Always check to make sure the equipment/cables are unplugged and if the thing you are repairing is battery operated, that the battery is removed. If its a cable, verify that both ends are disconnected.

Soldering fundamentals

• The Soldering iron tip must be clean and covered with a shiny silvery surface. Keeping this area shiny is called "tinning" it. The shiny silvery part is where the heat transfer will take place, and if you can't get an area on the soldering iron tip "Tinned", you won't be doing any repairs with it. When the Soldering iron tip has warmed up, the solder quickly oxidizes - gaining a thin skin that is not a good conductor of heat - it is easy to keep clean - On the road I normally use a dampened paper towel that I rub the tip across before using it. At home, I use a dampened sponge for the same purpose. After cleaning, touch the tip with end of a piece of solder. The solder should melt instantly and form a clean bright layer over the copper. Apply only enough solder to form this "Tinned" coating. Wipe off any excess.

  Most Soldering iron tips are made of copper, or have a copper coating that can be "tinned". You'll find over time that the copper surface gets worn (the solder actually takes a little with it for each connection soldered), and you should always carry spare Soldering iron tips. Most fit into the plastic 35mm film holders that I often have left over from my photography projects - if you don't have any, ask someone who uses 35mm film to save you a few.

• Surfaces to be soldered must be clean, free from water, dirt and any grease. I occasionally use fine sand paper/emery cloth to clean connections. Never use steel wool to clean with - small pieces of it can get lodged in places causing short circuits.

  When soldering wires, you must first remove the insulation from the end of the wire. I normally use a wire stripper for plastic insulation or a knife if I'm working with 'Bell' wire - it has an enamel surface. Very lightweight 'Bell' wire is used in pickup windings found on electric guitars. You cannot solder thru the enamel insulation, you must remove it. Normally, I remove 1/4 to 1/2 inch (6mm to 13mm) of insulation. Its hard to scrape wire that is is the thickness of a persons hair and see what you are doing when trying to reconnect broken guitar pickup windings (I have gotten many 'free' pickups with broken windings that were quite easy to repair by simply unwinding a turn of wire and re-soldering it); use a magnifying glass if you need to.

  If working with wire, "Tin" the wire you just cleaned. To do this, put the cleaned wire up against the Soldering iron tip, getting a good mechanical connection between the "Tinned" portion of the Soldering iron tip and the wire and rub the end of the solder against the wire (not the Soldering iron tip). Place only as much as is needed to make the end shiny. If it is stranded wire, make sure that the solder flows thru completely for at approximately 1/4 of an inch (6mm), but not up into the strands that are into the plastic insulation. For solid 'Bell' wire or other types of solid copper wire, "Tin" as much as you want.

  I often "Tin" connectors before soldering wires to them - these often need to be cleaned up a little and "Pre-Tinning" them will verify that the solder will stick - if you can't get the solder to flow over these parts now, they certainly won't when you are trying to solder a wire to them. Clean any parts with light sand-paper or scrape lightly with the blade of a knife.

  I keep my solder in 35mm film holders in my cord case for 'on the road' repairs. At home, I leave the solder on a spool. solder comes in a few different thicknesses. I prefer the thinnest Rosin core solder you can get - it allows me to easily control the amount of solder applied to any joint.

  NOTE: Soldering makes stranded wire stiff. This extra stiffness too far up into the insulation tends to make the wire break there if it flexes much. Always use only as much solder as is needed.

• When connecting a wire to a another wire or a terminal, try to make a good mechanical connection by hooking or twisting the two pieces together.

• Hold the soldering iron in one hand and the solder in the other. Press the Soldering iron tip to the wire or connector (which ever is larger) and apply heat to the connection. Wipe the solder across the item to be soldered while the tip of the soldering iron is against the connection. This will cause both the solder and and the Rosin run into the connection. Keep the soldering iron in place long enough to allow the molten mixture to penetrate the joint. Remove the heat source from the connection (Soldering iron tip) Do not move the connection until the solder solidifies. Don't heat the connection any longer than necessary or apply any more solder than necessary to get a good shiny and clean flow.

  If the solder joint does not shine, or it balls up, its possible that it did not connect the parts together the way you wanted. Its probable that the surface of one of the items being soldered was not clean. I have often taken a knife blade to scrape the surface of the offending item to clean it, then re-soldered the connection. If you allow a bad solder connection to occur, the joint will eventually develop a high resistance and develop into a 'Cold Solder Joint'. Never "Blob" the solder on, these sort of connections frequently fail over time.

• Clean off the Soldering iron tip between connections. The surface will oxidize quickly and make for poor connections if you don't.

Flux

Other Thoughts

When trying to remove solder from existing holes in connectors or holes in metal, I heat the joint and quickly blow on the joint. This frequently removes the solder clogging the opening.

What to wear

Solder doesn't hurt cotton fabrics very much - you can usually just peel it off once it has cooled - not so with man-made fabrics; these usually melt when they come into contact with the hot solder. Try not to be making repairs when you are dressed in Polyester, Rayon or Spandex.

Please be careful with a hot Soldering Iron. Its easy to put it down on a carpet by accident, or drop onto your leg. Get a holder for the Soldering iron (even the cheap ones usually come with one) and use it.

Is it hot enough?

If you find that your Soldering iron is unable to heat enough to make a good solder joint, you'll notice that the joint is not shiny and not smooth. You'll also note that the smell changes. For connections that require more heat, you can use a Soldering gun, or a much larger Soldering iron (as are used by people who are doing Stained Glass work). Don't use these high powered Soldering tools to work on normal cables or printed circuit boards - they will damage things beyond repair.

Working on Printed Circuit Boards

When working on a circuit board, verify that the point that you are Soldering to is clean - I have found that some kits have copper traces that have oxidized and can't be soldered without cleaning them. In these cases, I use a fine sandpaper (220 grit or finer) to clean the surface before soldering. I always try to "Tin" a small part of the circuit board to verify that its clean enough. If you find that the circuit board has silver colored traces, it is already "Pre-Tinned". Many of these have a green or red protective coating of the areas of the circuit board that you should not be Soldering anything to. Clean copper is normally Gold in color. When it oxidizes, it begins turning a reddish color - you can't solder to it no matter how much heat you apply (the copper traces will come off it you get them too hot). Never use steel wool to clean a circuit board - little pieces of fine wire will come off and create tiny short circuits all over the place - a very bad thing.

If you accidently short out 2 or more adjoining copper traces, there are products to help clean it off. "Solder Wick" is a fine braided wire saturated with Rosin Flux that you place over the area that you want to remove solder from, then you press the tinned portion of the Soldering iron tip onto the wick until it absorbs the extra solder. Be careful using this stuff since it distributes heat to a larger area of the circuit board and can damage things if you apply too much heat for too long. There is also a tool that provides a vacuum to the area. This is useful for unsoldering integrated circuits, transistors and other components. The narrower your Soldering iron tip the better when working on printed circuit boards - it allows you better control of the heat.

Where to start learning

If you don't have a vice to hold things, you can use pliers or a pair of vice-grips. The connectors will get pretty hot at times and you won't be able to handle them with your fingers.

Avoiding short circuits in cables or anywhere else

Expect things to fail and be prepared to make repairs if you have to. As I've mentioned before, carry spares of everything that you can. When you build new cables or wire up anything - think about what might happen to it in actual use and try to anticipate the failure modes. Shorts in cables are common and they normally occur at the connector ends. Any extra effort you can provide to avoid a short circuit when making or fixing a cable will eventually pay you back somewhere along the line. Things like power amplifiers can be destroyed by short circuits. Sometimes 5 cents worth of electrical tape can save $500.00 worth of gear.

Its often a good idea to verify that your wiring is ok using a VOM or Multi-meter - Testing for short circuits is quite easy and finding them before they cause problems is a good thing to do,

What you need to solder with

At Home:

• Quality Soldering iron (I have a Weller)
• Spool of 60/40 (or 63/37) Rosin Core Solder
• Spare Soldering iron tips
• Soldering iron holder
• Dampened Sponge on plate (to clean the tip with)
• Screw driver to tighten tip with
• Small vise to hold parts to be Soldered
• Roll of electrical Tape
• A small knife (for use as a scraper)
• A small piece of fine grit sandpaper/Emery Cloth
• Wire Cutters
• Wire Strippers
• Solder Wick
• Small wire cutter
• Scissors

In the cord case:

• Cheap Soldering iron (Under $10.00 model from Radio Shack)
• 5 feet of 60/40 (or 63/37) Rosin Core Solder in a 35mm film holder
• Spare Soldering iron tips in a 35mm film holder
• Soldering iron holder (came with the Soldering iron)
• A folded piece of paper towel (to clean the tip with once wetted)
• Screw driver to tighten tip with
• Pliers to hold parts to be Soldered
• Roll of electrical tape
• A small pocket knife
• A small piece of fine grit sandpaper/Emery Cloth
• Small wire cutter or scissors

Tinning too far up the wire, making it stiff and breaking off is caused by the effect of "heat treating" the copper - making it brittle. If you noticed, this happens usually where the copper is bare and the solder stops; the weakest part of any solder, braze, or weld.

The mistakes most people make soldering are that parts to be soldered are not clean (or even the solder its self is coated with oxides) and too much heat causing "dewetting" of the material.

If copper is heated too often it will no longer conduct electricity, a weird phenomenon that happens to copper. Also, try not to solder to gold contacts as it makes the joint very brittle, tin and gold do that to each other.

I was unable to solder - the problem was traced to my 15 year old solder having an oxidised layer. It was certainly driving me mad until I noticed how dull the spool of solder looked and it dawned on me how long I'd had it. A quick rub up and down with fine sandpaper = no more soldering problems and all audio cables repaired and tested.

Aaron Peterson writes:

1. Pick up a container of Rosin Flux at Radio Shack or wherever (just not at the plumbing store, because that will probably be acid based flux). Dip each wire to be soldered into the flux before soldering. Then if you are going to be soldering the wire to a connector, rub the flux coated wire onto the connector to spread some flux there too. Now you can tin your wire. It makes a BIG difference. The solder will flow onto just about anything that has flux applied to it. With the extra flux, it takes less heat to finish the job, and you don't wind up melting the plastic parts of your connector.

2. If you start using the flux, you'll notice that it is very sticky and hard to wash off your hands, and other things. Soap and water WON'T do the trick. Alcohol works very good for this. I carry alcohol prep pads (like they wipe on your arm before they give you a shot) in my kit for this very purpose.

3. Less is more. Most people use way too much solder when soldering. If you twist two bare wires together and then solder them, you should still be able to make out the two individual wires, and even be able to see the individual strands of wire in both of them. If you used so much solder that it looks like a big blob, you used waaay too much. The finished product should look like it was plated with silver, not encased in silver. Big blobs of solder will crack and fall off eventually. If you use extra flux, like the first suggestions, you'll find that you don't have a lot of big blobs anymore, anyway because the solder tends to spread out more.

4. Heat sinks. If you can clamp something onto the wire or connector just above the soldering point, it will conduct the heat away from the rest of the item you are soldering. I use a pair of hospital hemostats. This will keep you from melting the wire insulation above a solder joint, and keep you from burning your fingers. If you're working with connectors that have a lot of plastic in them, it can keep you from ruining a good connector with too much heat.

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