PROWORKSHOP BASIC TRAINING, HOW TO SOLDER CORRECTLY

DIY = BETTER QUALITY,
MORE OPTIONS, LOWER COST

by Mark King for proworkshop.com

HOW TO SOLDER AUDIO ELECTRONICS, CABLES AND CORDS

MY FATHERS VINTAGE CRAFTSMAN SOLDERING IRON WITH WOOD HANDLE AND ASBESTOS CORD

I remember watching my father soldering when I was only five. He was building a Heathkit tube preamp and a matching tube power amp. I was totally intrigued, amazed and enthralled with the process. I did not know what he was building but it sure looked cool. 
When I was nine my Aunt (who worked in a small town hardware store) gave me a soldering gun for my birthday. I tried to solder but my connections were failing, why? 

I did not know the correct technique so I was getting cold solder joints. A cold solder joint is dull and grey, it's filled with tiny air bubbles (air does not conduct electricity). Cold solder joints are brittle and often fail mechanically by simply falling apart or separating.

My Dad started a new round of kits, he was building a Dynaco stereo tube preamp and a matching stereo 35-watt tube power amplifier, that was when he took the time to show me how to solder correctly. 

When I was 10 I picked up old TV sets that people put out for the trash, took them back to our basement where I dissected and repaired them. That was how I learned and refined my soldering techniques. Practice is what improves soldering technique. Find a broken electronic item and attack it with your soldering-iron. 

In the following I'll explain each of the techniques used to solder various electronic items together.

PROPER PROTECTIVE CLOTHING

I usually run my soldering-iron at 650-700 degrees F according to the dial. I like it hot, I solder quickly so I don't melt or damage the components I'm soldering. What this really means is that the metal solder turns into 650-700 degree molten metal, essentially a liquid which can drip off the tip of the soldering-iron right on to your bare legs or feet below causing an amazingly painful and damaging burn. I've got the scars to prove and remind me, wear pants and shoes with socks or be absolutely sure your body parts are not under your soldering work AT ALL! I was in a hurry back in 2010 and was soldering in flip flops, a large blob of solder dripped straight down on my foot and caused the nastiest burn I've ever seen in person. Save yourself, wear shoes and pants.

Wear safety glasses when you solder. You don't want a rogue bit of 700-degree molten metal hitting your fragile unprotected eyeball. Get some comfortable safety glasses that you don't mind wearing and you'll be more prone to use them.

GET THE RIGHT SOLDRING-IRON

The process of soldering requires a heating device called a soldering-iron or soldering-gun. These get dangerously hot, they can burn you badly or if you're careless you can burn down your home, don't do that.

NON TEMPERATURE REGULATED, INEXPENSIVE SOLDERING-IRON

If you're just doing a simple repair job on a guitar cable a cheap $25 soldering-iron from the hardware store can get you through, I've used these all over the world on simple repairs. But if you're going to be doing DIY and fabricating electronics for the foreseeable future I encourage you to invest in a pro soldering-iron. It will really make a big difference in the quality and the quantity of work you can do. 

WELLER WES51 SOLDERING STATION

These days my favorite soldering-iron is the Weller WES51 system. I call it a system because it consists of three parts, the power supply, the soldering-iron and the proper stand for it which has an integral sponge holder. 

A knob on the power supply sets the temperature and an LED tells you when the tip is up to temperature. As soon as you touch the tip of the soldering-iron to something you're soldering it starts to cool off, then the power supply kicks up the power and tries to keep the tip at the set temperature. How well the power supply keeps the tip at the set temperature is an important feature. This is a favorite feature of mine with the Weller, it holds it's temperature surprisingly well regardless of what I'm soldering. 

Low cost soldering-irons ($10-$50) are not temperature regulated so the tip can get very very hot, so hot it actually hurts the components you're trying to join with solder. 

The Weller WES51 is regulated so when you start trying to solder a fat speaker cable it can maintain the temperature you need, a low cost soldering-iron may cool down so much the solder won't melt if you're trying to solder 12-gauge copper wire. 

Having a proper stand for the soldering-iron is very important. You need a place to put this 600-degree metal stick when you're not using it to connect wires or components. The WES51 comes with a separate stand to hold the soldering-iron when you're not using it. At the base of this stand is a little recessed area where the included sponge goes. In use you wet the sponge with clean water, squeeze out most of the excess so the sponge is just moist. 

NOTE LITTLE BITS OF MOLTEN SOLDER AROUND THE STAND, YOU DON'T WANT THAT DRIBBLING ON YOUR BARE LEG, IT HURTS A LOT! YOU DON'T WANT THEM IN YOUR EYES EITHER

When you withdraw the soldering-iron from the stand to make a connection get in the habit of wiping the tip clean on the moist sponge, the tip should appear to be clean and shiny. Do this every time you pull the soldering-iron out of it's stand so you don't bring along any contaminated old solder to the new connection you're about to make. Nowhere is this more critically important than when you're building large diaphragm microphones with their ultra high circuit impedances, the connections have got to be clean.

MY TRUSTY WELLER SOLDERING-IRON

HOW HOT?

I like my soldering-iron to be hot but that does not mean the parts will be heated to that temperature. The heat will flow out of the irons-tip the moment it touches the parts, introducing fresh solder to the connection will further slow down temperature rise in the components. Solder begins to melt around 350-400 degrees F so when I see the solder flow on the parts that is when I retract the soldering-iron and let it begin to cool down.

With an unregulated soldering-iron you're really just guessing about the temperature at the iron's-tip and you're stuck with whatever it turns out to be. A typical 35-40 watt unregulated soldering-iron is adequate for making basic guitar and speaker cables but it won't be good enough to build sophisticated circuits like microphones. 

GET THE RIGHT SOLDER

LEAD WARNING: I like and use lead-based solder. Lead has been linked to causing cancer. Don't put solder in your mouth. I know guys who do and they're not dead yet but personally I never put solder in my mouth. 

The solder I use is rosin-core 60/40, Kester is a big brand name for this product. The numbers refer to what the metal part is composed of, 60% tin and 40% lead. The rosin is contained in the center of the solder. 

Solder looks like shiny metal wire and it is very flexible. Because of the lead content you should minimize handling solder. I've been touching lead based solder for over 60 years and I'm still using it. 

The rosin in solder is usually a refined pine tree sap and it is there to help the solder flow on to the electronic components which are being joined together by the soldering process. 

It is critically important to your success that you have the right solder. You don't want acid-core solder which is used in other trades. You also don't want pure solder with no rosin in it (you can use this if you apply rosin manually but it's a pain to do). There are other solders like silver solder and there are new solder alloys which do not contain lead. 

Lead-free solder is more difficult to use, but might be worth the effort if you want to build products to sell to other people or if you're concerned about the health risk of being around the lead. Personally I've found lead-free solder to be difficult to work with.

.031 solder on the left, .062 on the right

Solder comes in lots of varying diameters, here are the two I use most often for electronics: 

.062" for guitar and speaker cable fabrication, building point-to-point guitar amps

.031" for building microphones and precision electronics

For making guitar and speaker cables I prefer solder that is .062" in diameter. This size works well for a lot of general purpose soldering tasks on various electronics projects like building guitar amplifiers. 

For precision electronic soldering work on printed circuit boards (like you find in building microphones) I use .031 diameter. If your solder is too thin you'll be constantly unspooling more too often. If your solder is too thick it can cool the tip of your soldering-iron, drip more often and may flow between connection points causing short circuits. 

One last note about solder, some brands are better than others. I've done emergency repair work all over the planet, in an emergency you run out, buy what you need and get back to make the repair. This means you're stuck with whatever you bought locally. I've purchased solder from Radio Shack that is labeled rosin core 60/40 solder and it just did not work right. This has happened to me so many times that I quit buying this brand entirely. I've had problems with other off brands, not sure what they sold us in a local Singapore market for solder but it was a fail too. I've never had a single problem with Kester brand so I keep buying that. 

HOW TO SOLDER CORRECTLY

When a solder connection is done correctly it appears shiny and lays flat against the parts. If the solder balls up you either used too much or there was contamination on the surface and the solder could not adhere correctly. 

There are a couple of steps involved in preparing two or more components which are to be soldered together. 

Be sure the components that are going to be joined are clean. If there is any contamination on the metal surfaces the solder may refuse to bond to the surface in which case you'll end up with a failed connection. Contamination causes the solder to ball up and not bond to the metal surface, this is one of the most frustrating situations in soldering, when it refuses to cooperate. Quality clean components makes a big difference in your potential for success.

HELPING HANDS HOLDING TWO PIECES OF WIRE

Have the components well supported so they won't move around until the finished solder connection is cooled. There are various devices available for holding components while soldering. These can range from $5 up to $100 or more depending on what you're working with. 

I've used a little parts-holder called "Helping Hands" for years. The parts you're soldering can easily be clamped in the alligator clips and held very stable while you solder them together. For simplicity, low cost and function Helping-Hands is hard to beat. 

HELPING HANDS HOLDING AN XLR CONNECTOR FOR SOLDERING TO A PIECE OF  WIRE

TINNING PARTS - SOLDERING WIRES - MAKING CABLES
For making cables and connecting wires to connectors you'll want to "Tin" the components you're soldering together.

Tinning means applying a tiny bit of solder to each component you want to join. If you're going to join a wire to a plug, you'll want to put a very thin coat of solder on the exposed wire conductors (after twisting them tightly together) and a similar thin coat on the plug before trying to mate the two pieces.

Pull your soldering-iron, clean the tip on the sponge, touch your solder to the tip so it has fresh solder on it, touch the soldering-iron wetted tip to the component you want to tin, be sure the soldering-iron is getting a good physical connection to the component. As soon as you get the soldering-iron touching the component bring your solder in and touch it to the point where the soldering-iron touches the part, the solder should melt immediately, carefully flow a bit of solder on to the component and then withdraw the solder and soldering-iron. Now, do that to the other part that will be joined to the first part.

Once you have the components tinned you're ready to fuse them together. Bring the two tinned components together so the tinned surfaces are making a good solid physical contact with each other. Now all you need to do is to pull your soldering-iron (clean the tip), apply a tiny amount of fresh solder to the tip and then bring the iron's tip into position so it is touching both of the pieces you want to join together. The soldering-iron will heat the components you previously tinned, as soon as the solder on these two pieces reaches the melting point all the solder on both components will flow together and intermingle. When you see this happen withdraw the soldering-iron carefully without disturbing the connection. Solder takes time to cool, it happens quickly but if you move the freshly soldered connection too soon it will result in air bubbles and a poor connection that can break or become intermittent.

SOLDERING CIRCUIT COMPONENTS

If you want to solder components to a printed circuit board (PCB) you don't tin them first. It is of prime importance that components and the PCB itself are clean.

Soldering resistors to a PCB is an example of this type of soldering work. The legs of the resistor are bent and run through the proper hole locations on the PCB. The PCB should be mounted so you can easily get your soldering-iron to the junction point between the resistor component wire and the copper on the PCB. You don't want the PCB or component to be jostled around while the solder is hot or you'll get the dreaded cold solder joint.

Making the connection between a resistor and a PCB should be quick. Pull your soldring-iron (clean the tip), wet the tip with a bit of fresh solder, then bring the tip in to the junction point between the component and the PCB copper traces. It's vitally important that you apply heat to both pieces you're soldering, if they're both not up to temperature the solder won't stick properly and you'll get a cold solder joint. As you're heating the two parts with your soldering-iron bring a piece of fresh solder in and touch it ever so slightly to the union between the PCB and the component so that the moment the whole joint comes up to temperature the solder will flow between the component and the PCB. The moment that happens carefully withdraw the solder supply and the soldering-iron.

By applying a tiny bit of fresh solder to the tip of your soldering-iron (right after you cleaned it on the sponge) you help the heat from the soldring-iron flow to the component being soldered and the PCB. The molten solder on the tip of your soldering-iron helps conduct the heat into the resister lead wire and the PCB copper trace. Without that little bit of fresh solder on the tip assisting the thermal transfer into the two pieces being connected it's impossible to properly heat the two components. If the PCB is not hot enough the solder will just ball up on it and not make a good connection. If the resister is not hot enough it won't be joined to the PCB and the connection may become intermittent or fail all together.

POINT TO POINT WIRING AND SOLDERING

In the 1970's I built custom tube amp equipment using little brown terminal strips that had eight-to-twelve isolated terminals each. I riveted these into aluminum chassis and then wired resisters and capacitors between them. This is how my old Danelectro Sears tube bass amp is built, it's a point to point nightmare but a cool sounding amp.

If you're physically building circuits using terminal strips or turret board your soldering technique will be a bit different. Typically when building these types of circuits you bend the wire leads of the part around the connection point and squeeze it tight with needle nose pliers. The connection needs to be solid so nothing moves while you make the solder joint. 

Tinning is not needed with this style of construction. It's most important that all the surfaces to be joined are clean. The wire parts need to be solidly attached to their destinations. 

Pull the soldering-iron, wipe it on the sponge, apply a tiny amount of fresh solder, put the tip of the soldering-iron right at the junction of the wrapped wire and the post or turret your bonding to. As soon as you get a good solid physical contact between the iron and the two parts, bring your solder in and lightly touch it to the same point as the soldering-iron tip. Once the iron has heated the two parts the solder should flow all around them quite quickly. As soon as that happens withdraw the solder and soldering-iron being careful to not physically move the parts you just soldered. 

PRACTICE

Soldering is not hard but it takes time preparing the parts you want to join together. Prepping the pieces can dramatically increase your success and reduce the frustration of failed joints. 

If you're making cables you need to be sure all the rope, cloth and rubber are removed and the bare wire is all you're trying to solder. All the strengthening material they put into audio cabling can contaminate the connection site and make it difficult to get the solder to flow right. 

Learning how to Tin your parts and get them clamped together takes practice but when you get it down you'll be making cables like a pro. Making your own cables is not always the least expensive way to go but you have the choice of what wire and plugs to use in what you make yourself. 

SOLDERING GUNS

My first soldering tool was a 100-watt Weller soldering gun. It was made out of bakelite and had a spring for the cable strain relief. That was my most prized possession until I got my first car.

MY FIRST SOLDERING GUN

The only time I use a soldering gun now is when I'm soldering thick copper wire (10, 12 or 14 gauges). Copper is an excellent conductor of heat and it can suck the heat out of a small 40-watt soldering-iron very quickly. A high wattage soldering gun can provide the heat necessary to get the wire up to temperature so it will melt the solder. You need to work as fast as possible because that wire will get so hot it begins to melt the insulation. Success comes by tinning your parts carefully, clamping the components so they have good physical contact, introducing heat at the junction between the two parts, adding extra solder if needed and then withdrawing the soldering-iron and solder without moving the freshly joined connection. 

DUAL HEADLIGHTS ON MY FIRST SOLDERING GUN

A big drawback to a soldering gun is that it has a trigger you need to pull to heat the gun, then you must wait for 8-15 seconds while the tip comes up to temperature. If you're making a lot of cables this can become a huge time suck waiting for the gun to heat up. You might be temped to tape the trigger ON so it just stays hot. I've done this in emergency situations where I had a lot of connections to make quickly but it's definitely not recommended because the guns are not rated for continuous duty. If you leave it taped on for long the gun dies, I know this from experience. This is what led me to say at the beginning, get a good soldering-iron, it will make you more productive and works better.

DESOLDERING

Sometimes you've got a solder connection that you need to undo. There are several ways to do it but I like using a simple desoldering-iron (often called a solder sucker). It is a combination device. The one I'm using has a very simple unregulated soldering-iron to heat up the solder joint and an integrated spring loaded plunger for sucking the solder off the connection. 

DESOLDERING IRON

First you cock the sucker part by pushing the plunger in all the way until it locks in place. Next, plug it in, after it comes up to temperature you mash the hot tip on the connection you want to undo, as soon as you see the solder become molten push the yellow button on the side to release the sucker. It will snap and if you got the connection well heated the solder will be gone. At worst, do it again to clean it up more. It's amazing how simple and effective a tool like this is.  

HINT: I never throw away Switchcraft audio connectors. I always desolder them from the ends of dead cables because they're such durable connectors they can be used over and over. I have some that I've been using since the 1960's. 

MAKING STUFF

I MADE A LOT OF THE WIRING THAT DRIVES OUR STUDIO PATCH BAY

Why solder your own stuff? Because you want or need things you can't buy. It's not only about saving money, it's about having things you can't buy for a reasonable price. In my recording studio I've used thousands of feet of wire in making all the connections between the electronics. If I had to buy all these cables pre-made it would never have happened. I also like quality cables made from good wire and good connectors. Making my own lets me have exactly what I want.

Soldering is a useful skill that will serve you well. Be careful!

Good music to all!