Please note: this instructable is written for beginners, and contains lots of very basic information. If you have lots of experience soldering, please use the comments to share your knowledge. Clarifications and corrections are especially welcome.
This Instructable was the lead-off for "How to Solder" month, where we rewarded soldering tutorials with Instructables patches. See the original call for project here at submitting a How to Solder Instructable or just check out all the other soldering Instructables here at the How to Solder group.
Step 1: Tools and materials
For further information and some more technical specs on soldering check out the wikipedia article.
As with many skills, having the right tools for the job effects the quality of the work being done. When it comes to soldering you can end up using a lot of fancy tools, or just a few simple items you can pick up at the hardware store for a couple of bucks. I am going to use a couple of different soldering tools in this Instructable; there are many ways to solder, and you should use what works for you.
At the very minimum you will need the solder and a heat source to melt it - preferably something small which can get to 600-800 degrees Fahrenheit. If you've got that, your ready to make a connection. That being said, there are a wide range of soldering tools and accessories that can be really helpful if you're going to be soldering frequently. Ladyada has compiled a nice list of equipment and sources to buy the tools on her site. I got together a solid supply of soldering tools by raiding the Squid Labs soldering station. Here is the complete list of what I used...
1. Soldering iron
Most people opt for using a soldering iron to solder. It's a great heat source that heats up and cools down quickly and can maintain a pretty constant temperature. Soldering irons can be purchased from a variety of places. I have picked up some at Radioshack - evil yes, but convenient, some from the hardware store, some from garage sales and a bunch more from retailers online. Low wattage (15-40 watt) soldering irons work best for soldering components on circuit boards while more powerful (60-140 watt) soldering irons work well joining thicker materials like braided speaker wire. If you use too powerful of a soldering iron on a circuit board you might damage the components you are trying to join. I like to keep a low-wattage iron around for detail work, and a high-wattage iron that I can use when I am not too concerned about exposing the material I am working with to high temperatures. It's a real pain to solder thick wires without a powerful soldering iron.
The soldering iron in most of the pictures is made by Weller, and has a variable temperature control. This is the best of both worlds since you can set the heat exactly where you want it, but it's significantly more expensive than fixed-temperature irons. If you're just going to do some occasional soldering it isn't a must have by any means. Anyone interested in modding a soldering iron should check out DIY Hot Air Soldering Iron by charper.
There are lots of kinds of solder available. They come in different thicknesses from around .02" to some really thick stuff you would only use on copper pipe with a butane torch. You use thin solder for detailed work like putting resistors onto circuit boards and thicker solder for joining larger materials like speaker wire. I use solder around .025" for most jobs. Most solder is made from a combination of tin and lead - it's about a 60% tin, 40% lead mix depending on what solder your using. Recent international health codes from Japan and the EU (California and New York have adopted similar policies as well) mandate that lead solder be phased out of certain commercial products and substituted with a lead-free alternative. The manufacturing deadline was this past July so we should be seeing the changes now. Even if you don't live in California or New York its still worth staying away from lead solder since lead has been known to cause all kinds of a nasty health effects from birth defects to severe developmental and neurological damage. Plus it's pretty easy to find the lead-free stuff.
Some solder will contain a small amount of silver. This pushes the melting temperature up a bit, but the silver helps the solder to flow and makes a stronger joint. If you are worried about burning whatever your working with, try to stay away from solder with silver in it, but it works very well if you're just joining wires or something that won't be easily damaged. The last thing to know about solder is that you want to use a solder that has a rosin core. The rosin acts as a flux when soldering and helps the connection - it's also the kind that's most readily available at the hardware store and from electronics suppliers.
3. Soldering iron tips
Soldering irons come with a tip, so you don't have to go out and get a special one, but it's important to know the differences between them and make sure you're using the right tip for the kind of soldering you're doing. Some small-wattage irons come with conical pointed tips for detail work, while most high-wattage irons come with a flatter screwdriver-style tip that works well on wires. You want your tip to be a little smaller than whatever you are soldering so you have good control of what you heat up and what you leave alone.
4. Soldering iron holder and cleaning sponge
It's nice to have a safe place to put the soldering iron down in between soldering. A soldering stand safely holds the iron and gives you a place to clean the tip. Some soldering irons come with their own holders. If yours doesn't have one, you can buy one or make one. jaime9999 has a Homemade nearly-free Soldering Iron Stand that is pretty much identical to what you can buy. The stand isn't a necessity for learning how to solder, but it does help.
5. Tools to work with wires
I have a go-to stock of tools that I round up when working with wires or electrical components. They consist of wire cutters, a wire stripper, needle nose pliers, and an automatic wire stripper (courtesy of the Squid Labs soldering station.) The automatic wire stripper is really convenient if you're going to be stripping lots and lots of wire, but by no means necessary. I have stripped lots and lots of speaker wire using my teeth (not the best idea, I know I know.)
6. Clips to hold your work
Often called "third hands" or "helping hands," these little guys help a whole lot when soldering. You have to hold the soldering iron with one hand and the solder wire in the other, so it really helps to have something else to hold the components you're actually trying to join. You can use alligator clips, clamps, or even some tape to hold things in place if you need to. The third hand is generally a good investment if your going to be soldering regularly, and there are plenty of Instructables with with ideas to modify them if you do happen to pick one up. Check out: Make a 3 degree of freedom 'hand' to help with soldering / gluing work and make your 'helping hands' 100x more useful for soldering / gluing small parts by leevonk to start.
If you would like to make a set of helping hands of your own there are already a number of good Instructables on that too. Quick helper for surface-mount soldering by http://www.instructables.com/member/bikeNomad/bikeNomad, QuickMods - Soldering Arms by Aeshir and Build a Pair of Helping Hands by john otto should get things started.
7. Exhaust fan
I do most of my soldering at a soldering station that is equipped with an exhaust fan. It's really not such a good idea to breathe in solder fumes, and soldering does produce fumes. Any kind of ventilation/fan you can rig up will help. Vent the fumes outside or use an indoor fan with a filter if you can't vent them outdoors. Here is a Window-mounted solder fume extractor (not just for RVs!) posted by bikeNomad. Also check out Dr. Solomon's low tech, but functional Solder Fume Extractor if you're looking to build something that you can place right on your table. If you're just doing a quick soldering job, the fumes wont kill you by any means. I have certainly done my fair share of soldering without a vent, but anyone doing repetitive soldering should definitely pick one up or make one.
8. Safety goggles
I hadn't ever used goggles before while soldering, but while doing research for this post I saw it mentioned elsewhere and agree that its a good idea. Little molten bits of solder tend to fly out of the soldering joint when you're feeding in the solder, and if it landed in your eye it wouldn't feel too good.
9. The materials that you want to join together
I was just messing around, and mostly soldering for the purpose of this Instructable so my materials didn't necessarily make anything. You can solder wire, electrical components like resistors and capacitors, circuits, breadboards, electrodes, small pieces of metal and whatever else you can think of. Don't know if it can be soldered? Give it a try - you won't blow anything up.
Once I have got my tools and materials rounded up, I like to pretend that I am a pilot and begin my pre-flight/solder checklist.
Step 2: Getting ready
First things first, the tip of the soldering gets hot - up to 800 degrees Fahrenheit, so don't touch it. I know this seems obvious, but many people seem to burn themselves at some point while soldering.
If you're using a new soldering iron you will want to put a small amount of solder on the tip of the hot iron before you start working. This is called tinning the iron and you only have to do it with a new iron. Once you start using it will usually have some solder on it already and be ready to go.
Once the iron reaches temperature (some irons take minutes to do this and some irons take seconds), I like to clean the tip of my iron on a wet sponge. You can wet the sponge on your soldering base if you have one, or you can just use a damp sponge or steel wool. Gently touch the tip of the soldering iron to the sponge and clean off any old bits of solder that might be stuck to it. It will sizzle a bit; this is normal.
I asked Mitch, a soldering expert who works at the control tower by day and is numberandom by night, for some tips. Mitch showed me a good idea for how to hold solder wire: he cuts a piece of it off the roll, and then makes a coil at one end with a short lead at the other. This helps him hold it steady and apply just the right amount of solder. This is a way better idea than trying to hold the whole spool of solder or grab onto just one thin strand.
Next it's time to pay some attention to the material you're soldering. If you're soldering wire, you'll need to strip back about 1/2" of insulation to expose the bare wire. If your joints are going to be wire-to-wire or wire-to-lead, you can twist them together tightly before soldering. Electrical components placed on a circuit board don't need much prep work; just seat them where you want them and find a way to hold them in place with clips or by bending the leads outward slightly so they stay put when you turn the circuit board over.
Finally, place what you want to solder into the clips on the helping hand, or on a surface you don't mind getting a little burn mark on - scrap wood works well. Basically you just don't want the components moving around on you when you go to solder them. There are lots of ways to orient the wires/components so you don't have to hold them in place while you solder them. Find what works best for you.
Hopefully your soldering iron has reached temperature by now, because you're ready to solder!
Step 3: Soldering wire
With the wires you want to join twisted together and held in place, pick up your soldering iron in one hand and your solder in the other.
Touch the tip of the soldering iron to the wires and keep it there.
The wires will begin to heat up. At some point over the next 2-10 seconds (depending on how hot your iron is) the wires will be hot enough to melt the solder. You can touch the solder to the wires (not to the tip of the iron!) periodically to see if it's hot enough. It's tempting to just touch the solder to the tip of the iron and melt it right away, but don't! You will end up making what's called a cold solder joint. This occurs when you melt the solder around the joint, but you aren't melting the solder into your joint or onto your components to make a good connection. It's much better to wait the few seconds and melt the solder onto the hot wire itself.
If you touch the solder to the wire and it begins to smoke and melt, the wires are hot enough. Add the tip of your solder to the joint as necessary. You want to introduce enough solder to cover the wires, but not so much that you create a big glob of solder at the bottom of the joint.
Once you've got what you think is enough solder on the joint, pull the solder away and then remove the soldering iron. If you're using a gun style soldering iron like I was, release the trigger to turn it off. If you're using the kind that doesn't have a trigger the iron will stay hot, so just place it back into the holder.
Here is a video of wire being soldered. The whole process happens pretty fast, and isn't nearly as complicated as you may have expected.
Here is a close-up video of the same process.
Step 4: Soldering components onto a circuit board
Soldering on a circuit board takes a little more care and attention, but it's still very doable. I pushed a few of the leads from some spare LEDs and resistors that I had from my LEDs for beginners post through some open holes in a circuit board that was lying around. I soldered the leads onto the bottom of the circuit board where the electrodes push through. This is called through hole component soldering.
To solder the LEDs and the small resistors to the circuit board I switched to the adjustable temperature soldering iron. The tip was smaller so it would be easier to get the solder right where I wanted it, and using the soldering gun on a circuit board is probably way more heat than necessary and it could end up damaging the components. I set the temperature of the iron to 675 degrees Fahrenheit and waited for the tip to heat up. I then loaded the circuit board into the alligator clips and got myself ready to solder - iron in one hand, coil of solder in the other.
When soldering leads into circuit boards you want to heat the metal contact on the board and the lead itself. Applying too much heat can damage the circuit board or even your components. The surfaces being joined in this application were much smaller than the twisted wire, so things heated up a lot faster.
I touched the tip of the iron to the crack between the lead and the metal pad on the circuit board. After waiting a couple of seconds, I dipped the tip of the solder into the joint and placed a very small amount of solder at the connection - no more than the head of a pin or so.
Once the solder pooled a bit and soaked into the joint I removed the solder wire and then the iron. I remove the solder a second or two before I remove the iron so that the tip of the solder doesn't get stuck to the joint. The solder begins to harden as soon as you remove the iron.
Using the proper amount of solder is more important while soldering small components on a circuit board than when soldering wires. If you apply too much solder and it pools up outside of the metal pad, it can cause a short. Too little solder and your component won't make a good connection with the circuit board and might not work the way you want it to. When you've got the right amount of solder it looks like a small ant hill that forms right at the base of the lead and the circuit board.
Here is a video of the process.
Step 5: Cutting the leads
It's best to use a sharp wire cutter that has just one side of its cutting edge beveled. This way you can get a smooth flat cut when you cut off the lead.
It's also a good idea to cut the leads pretty close to the circuit board to minimize the risk of creating a short.
Although I didn't do it in the video below, holding onto the excess lead when you cut it off is a good way to keep the little ends from getting all over the place.
Once you've got your leads cut you're pretty much done with soldering and ready to move on.
Here is some riveting video of the leads getting cut off:
Step 6: Surface mounting components onto a circuit board
To solder something onto the surface of a circuit requires a process called tinning. Tinning is when you apply a small amount of solder onto the materials you are joining before you connect them. In this case, it involves putting some solder on a contact on the surface of the circuit board then attaching the component to the solder pool. Mitch showed me how this process is done.
First he touched the tip of the iron onto the small pad on the top of the circuit board. He then introduced a small amount of solder onto the pad and took the iron away.
Then, a few seconds later he picked up the component he wanted to solder with a set of tweezers, heated up the small glob of solder that he had just placed down, and gently lowered the contact on the component into the pool of hot solder.
He took the iron away, held the component in place a few seconds longer, and released the component from the tweezers.
He then went to the other side of the component and finished making the connection by soldering the remaining two contacts together.
Surface soldering is done like this because you need to lower the component into place by hand, so it's hard to hold the iron, the tweezer and the solder all at the same time. Additionally, tinning is just a good thing to do while soldering small components. I didn't tin the wires before I soldered them because they were so big I was sure I was going to be apply enough solder to make a good connection. However, when soldering small components or doing surface mount soldering like this, tinning can be really helpful because you basically already have your solder applied to your pieces before you go to connect them. There is no need to glob on more solder and run the risk of getting it in a place where you don't want it to be.
The picture series below shows the process unfolding step-by-step.
Step 7: Soldering with a lighter
Bare bones soldering comes in handy when you're stuck on a desert island and you need to make a repair to your headphones so you can watch the sun go down while being serenaded by your most recent whale songs cd. It's also a cool trick to pull off next time your decide to be MacGuyver for Halloween.
I took some pieces of wire and stripped them with my teeth - the best method for doing this I have found is use my molars. I just grab the insulation with my teeth, try to sever the insulation a bit, and then pull on the wire. It's easiest to do with braided wires, and it certainly takes a little practice to apply the right tension so you don't just rip the wire apart entirely. But once you get the hang of it it's actually a pretty functional method. (WARNING: I do not encourage stripping wire your teeth at all, and it will probably lead to expensive dentistry work if you do it enough.)
Once I had the wires stripped and twisted together I got a lighter and a bit of solder and went to work heating up the wires I wanted to join. It took the lighter about as long to heat up the wires as it did when I used the iron. I then fed a little solder into the joint, continued heating the wire to smooth things out, and then turned off the flame.
It worked just as well as it would have had I used an iron. Of course it's harder, if not impossible ,to use this method on circuit boards, but it sure does the job on wire. I have heard that using matches also works well when soldering wires.
Here is some video of bare-bones soldering with a lighter.
Step 8: Desoldering, fixing mistakes and extrapolation
Desoldering is the process of removing solder at a joint to disconnect two components, wires or materials. You might have to do this if you want to replace a component that's gone bad, or if you want to change something about your design once it's already soldered into place. To desolder wires you can usually just heat up the connection and wiggle them around until they come free. Better yet, if you have the slack, just cut the wire at the connections, strip, and resolder as necessary.
With leads that are mounted through holes on a circuit board it takes a little more finesse. To desolder something delicate its best to use a desoldering pump, or bulb which will actually suck up the molten solder and remove it from the joint. Soldering wicks or braided copper wire also work well to suck up unwanted solder. For more complete guides on desoldering check out Make Magazine's Learn How To Solder Skill Building Work Shop Video and this site here.
Soldering is pretty forgiving, and its usually pretty easy to fix a mistake. If you put down a little too much solder or position something incorrectly you can usually reheat your joint, melt the solder, and then reposition your component as necessary. Solder can be heated and cooled as many times as you need to get your joint the way you want it. So don't be discouraged if it takes you a couple of tries to get it down - you will still end up with a good connection if you stick with it.
Soldering is a pretty straight forward process but there is no limit to what you could create with it. Try to join things together. It works well for making jewelery, doing basic arts and crafts with small metal objects, or re-wiring your toaster into a heating element for an infra-red sauna. If soldering has been keeping you away from experimenting with circuits or making a project, hopefully it doesn't have to anymore. Once you do it a few times you might even start to enjoy it.
If you would like to get started on a few basic soldering projects check out instructables user Makekits and the Make Magazine Store to build things like a MiniPOV or a Daisy MP3 Player.