Soldering Is NOT Rocket Science!

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Introduction: Soldering Is NOT Rocket Science!

About: I've been taking things apart since I was 10. My mother wasn't impressed, even though I told her I knew how to put it back together... I've been making things since I picked up my first soldering iron (By Th...

I've seen so many articles on electronic soldering that are either overly verbose and hard to read, too complex for a beginner, insist on expensive tools, or are just plain wrong, that I decided to clear the air a bit by going back to the basics. When I first started soldering, many years ago, "How To Solder" was printed on the back of the soldering iron package with room to spare. After that, it was just practice. This is not hard stuff, and it's not complicated, either. It's just a matter of a handful of basic principles:

  1. Choose the right soldering tool.
  2. Use the right solder with rosin flux.
  3. Cleanliness is essential, both for the iron and the work.
  4. Contact both parts of the work with the iron.
  5. Use the work to melt the solder, not the iron.

I learned many of these techniques on a production line in the 80s, so I've done a lot of hand soldering.

The Soldering Comic Book attached is a good quick reference.

Step 1: Choose the Right Soldering Utensil

To solder electronics, you need a soldering iron, not a soldering gun. Soldering guns are designed for large, bulky projects like copper pipe or gutters. They are too imprecise and too powerful for delicate soldering. In addition, they work by putting current directly through the tip, and that current could potentially damage sensitive semiconductors.

Your first soldering iron should be in the 25-40 Watt range. It does not need to be one of those fancy ones with temperature control. I've been using non-temperature-controlled irons for decades, and they do just fine for all but the most demanding jobs. The $10 one from Radio Hovel or WalMart will do just fine when you're starting out. You'll know when your work demands something better.

If you'll be soldering a lot of CMOS ICs (integrated circuits), they are static sensitive, and a grounded iron with a 3-prong plug will help, or just solder in IC sockets and put in the ICs when all soldering is done. This is safer, anyway, until your skills are better.

Step 2: Use Solder and Flux Designed for Electronics

You want onlyRosin Core Solder for soldering electronics. The rosin acts as flux (A substance that helps prevent oxidation and promotes bonding). Flux is essential, but the wrong kind of flux will destroy your project. Acid core solder should be paired with that soldering gun, and used only for plumbing and home repairs. The kind of solder you can buy at Radio Shack is the right kind.

Choose a diameter of solder based on the size of your soldering job. Diameters are given in Inches. For general electronic soldering, .025" or .030" is OK. For fine work like Surface Mount components, use .015 or even .010. I've been using .015 for nearly everything, but for a big connection like an AC plug, you might have to use a foot of the stuff.

Note: Lead-free solder is environmentally correct, but a lot harder to work with and requires higher temperatures. I don't recommend it. The best kind is 63% Tin/37% Lead, although 60/40 works fine also.

Step 3: Safety Concerns

I am assuming that you're grown-up enough to realize that soldering irons get Hot! Around 500-750 degrees F hot. (260-400 C for our friends across the Pond.) If you don't understand this, blow out a few more Birthday candles first.

Anyway, protect yourself from possible hot splatters with the appropriate gear. Safety glasses are a good idea. I'm not responsible if you hurt yourself, or burn your house down. And by the way, picking up a hot soldering iron by the wrong end is definitely not recommended. (Ask me how I know.)

You also don't want to breathe any more of the smoke and fumes than you have to. A small fan to keep the smoke out of your face will be sufficient for hobby work-You're not doing it 40 hours a week! Don't point the fan directly at your iron stand, though. It might blow hard enough to cool your iron off, and you'll be frustrated.

Step 4: Cleanliness Is Essential, Part 1

Soldering is a process somewhat like gluing, in that the solder has to form a tight bond between the parts. Just as clean parts glue better, they also solder better. Any mud, blood, beer, grease, oil, or especially oxidation will make the joint difficult or impossible to solder well.

How do you know it's clean enough? Clean it till it's shiny. Only bare metal will solder. Tin or Gold-plated circuit boards don't need to be cleaned unless you've been a slob and gotten crud on them, but bare Copper boards can always stand a quick buffing with fine steel wool. Anything else that looks old and gray needs some cleaning before you start to solder.

"Solder Aid" sets often include a small wire brush that's very helpful. Fiberglass "Scratch Brushes," used by jewelers, are even better.

Step 5: Cleanliness Is Essential, Part 2

Your workpiece isn't the only thing that needs to be clean. So does your soldering iron. A dirty iron won't transfer it's heat to the work very well. That's why most iron stands include a sponge. Always make sure the sponge is wet (water only) before touching it with the iron.

You clean a soldering iron by wiping it on the sponge, then tinning it. This must be done very frequently because the solder on the tip oxidizes rapidly in the heat. "Tinning" is simply the process of coating something with solder. Your tip should look silver and shiny.

My routine is, every time I pick up the iron, I give it a quick wipe on the sponge, then tin. Now I've got a clean shiny tip for maximum efficiency. The extra little blob of solder on the tip conforms to the work, increasing heat transfer.

Important Note: Never clean your tip with steel wool or sandpaper, no matter the temptation. You'll remove the plating on the tip and it will wear out very fast. The solder will literally dissolve the tip!

Step 6: Don't Just Stand There, Solder Something!

Preliminaries out of the way, let's start soldering. The most important thing to understand about the soldering process is this: The purpose of the iron is to get the workpiece hot enough to melt the solder! Melting the solder on the iron and "dribbling" it on the work won't do at all. It just won't stick.

The proper technique is to apply the soldering iron to one side of the work, making sure it's contacting both parts to be joined. Both parts must be at soldering temperature. Then, apply the solder to the other side of the workpiece, not to the iron tip. It takes less time to do than it does to read this. After only a little practice, you can solder a PCB (Printed Circuit Board) connection in 3 to 5 seconds.

Most semiconductors are heat sensitive. Learn to solder quickly. (Another reason to use IC sockets.)

If soldering wires to wires, or wires to switches or other components, get a mechanically sound connection first. Twist wires together or wrap the wire around a terminal. If using multi-strand wire, it helps a lot to twist the end of the wire and apply a bit of solder to the wire first. Then it's easy to put a small "U" bend in the wire with your pliers and crimp that onto your terminal. Splice tiny wires, (for instance, adding long wires to an LED), by putting a "U" bend in each wire, then hooking them together and squeezing the connection down. Now they'll stay put while you solder.

Step 7: Problems and Rework

How does your solder joint look? If it's smooth and shiny, and you can't see any gap between either part and the solder, it's probably good. A good PCB joint should be shaped something like a Hershey's Kiss.

If the hole in the board isn't covered, or the joint looks dull and granular instead of smooth, reheat and add a little more solder.

If your PCB joint looks like a beach ball, you either didn't heat the pad and the wire, or you used too much solder. Try cautiously reheating and adding a tiny bit more solder. (You add more solder in this case for the flux.) If the solder is stuck to both the wire and pad, leave it alone and use less solder next time.

Solder Wick is available from the places you buy solder, and is great for soaking up excess solder if you've used too much.

If your project is a PCB, inspect it carefully, using a magnifier if necessary, for solder "Bridges." These are most likely between IC pins. It's helpful to have a diagram of what the board is supposed to look like. If you find any bridges, reheat and scrape off the excess solder with a small tool or the iron tip itself, or use solder wick and then resolder.

Step 8: Going Further

This information covers simple hobby soldering.

Surface Mount Devices (SMDs) can be hand soldered, also, and once you know the basics of soldering, it's not too hard. You just need a finer tip iron and a steady hand (and maybe a magnifier). The best way to solder surface mount stuff is to tin the PCB pads first with a film of solder. Then with the part in tweezers in one hand and the iron in the other, re-melt the solder on one pad and place the part into the melted solder. Hold it there till the solder solidifies. Now, go back to the other pad(s) and add a little solder to each one until all are done. Go back to the pad you started with and reheat it a bit to make sure it's good.

Other methods include the use of solder paste, but that's a subject for another day. Now get out there and solder something! Practice does make perfect.

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    78 Discussions

    You really shouldn't assume that the metric system is only for those 'over the pond'. 95% of the world's population is metric, including that great country to the north of you, and I assure you there is no 'pond' between us!

    1 reply

    Hmm... Never saw those before!

    I have a question for someone that actually knows. I've got a battery charger that had one of the batteries burst while being charged and as a result the acid ran down into the charger and got all over the PCB. I took it apart and cleaned it with a baking soda mixture to neutralize all the acid so it wouldn't damage it any further. My problem: The acid ate some of the coating off of the PCB, the green coating, exposing some of the ribbons of lead. What can I use to replace this coating so the ribbons won't be exposed or is this a lost cause?? Please help!! I've searched everywhere and can't find anything to tell me what to do. Thanks in advance.

    1 reply

    If it's just the green coating and not the copper (metal) on the board, don't worry about it. The green stuff is just a solder mask and not necessary to the board's function.

    I keep hearing about tining the tip but no one say's how.I tried what I think you do but when I touch the solder to the tip,the solder just rolls/melts off,what I'm I doing wrong?

    1 reply

    the idea is to have a shiny film of solder on the tip. If the solder doesn't stick at all, your tip is very dirty. You may have to clean it thoroughly before you can tin it. Unfortunately, cleaning the tip with abrasives will severely shorten the life of the tip. You might try wiping the hot tip on steel wool to see if that helps. if not, you might need a new tip.

    If you take good care of your new tip from the beginning, you shouldn't have this problem. Using the tip for anything other than soldering, such as melting plastic, will ruin it for soldering. If you need to melt/cut plastic with a soldering iron, get a second cheap iron for that.

    I really enjoyed reading your instructable! Nice humour. Oh, yes, and informative too.

    Ever since I got this new 30W soldering iron, I have experienced problems regarding extremely fast oxidation rates. The last picture is of the tip about 5 seconds after cleaning and tinning. That results in the granular joints in the first picture (the imprecision is my own fault...). I am pretty sure the solder I use is rosin core because of the sweet scent of the smoke and the brownish residue on the joints.
    I'm guessing the iron may be to hot? Any ideas?

    DSC_0333.JPGDSC_0329.JPG
    4 replies

    I'm having the same problem with my 40 watt soldering iron. Should have gotten a 25 watt one.

    And what I did after getting so tired of wiping my tip on the sponge every 5 seconds, I just bought a few more cheap tips and try not to wipe it every 5 seconds to make the tip shine like a jewelry. And when I'm having hard time transfering heat, I just change my tip :D
    The tips makes better heat transfer at shinier conditions but it dosent really matter unless you are trying to do very fine work.

    That's why you wipe and tin just before soldering. And almost any soldering of modern PC boards is fine work.

    Thanks for reading! Solder does oxidize very quickly on the iron tip. Only thing I can say is:
    1. Make sure the solder is rosin core. If the solder is of questionable provenance, it might be better to acquire some new solder.
    2. That's why I wipe, then tin the iron just before I solder a joint. That way, you have a coating of fresh solder every time.
    3. If you're using lead-free solder, it's going to be much harder to make a good joint. That may be your problem. Get some new 60/40 or 63/37 tin/lead solder and see how that works for you.
    The iron is probably hotter than it needs to be, but the only cure for that is a temperature-controlled iron.

    Thanks! That was extremely quick.

    I will find some new solder of unquestionable provenance, then. It is really a pain to make one bad joint after another...

    I have to agree that this was a great job. This was a great way to put the best practices down. One thing that has plagued me recently is my tip has become literally solder repellent. I can't get any solder to stick to it when trying to prep it. I have cleaned it with the bronze mesh sponge to no avail. I have read a number of cleaning tips, man uh of which can have detrimental effects on the tip so wondering if you recommend any techniques above others? thanks

    Thank you for this. This is a great review of the basics plus a couple of tips that I did not know. This will server as a great guide for teaching my son basic soldering!

    Thank you for posting. I've watched and read several of these how-to guides and so far, I really wish I had read this first.

    "The purpose of the iron is to get the workpiece hot enough to melt the solder! Melting the solder on the iron and "dribbling" it on the work won't do at all. It just won't stick."

    That quote was the perfect way to describe the soldering technique. I am a welder by trade and was able to relate that to oxy-acetylene brazing with a silicon bronze rod..My welding instructor described brazing almost verbatim to that quote and that was my come to jesus moment in learning how to braze.

    I'm still lost in space (pun intended) on a few things however. Watching and reading other people's different opinions and techniques on soldering have muddied the water and have me second guessing myself the whole way. The only thing I can do about that is keep practicing and trying different techniques and tools until I figure out what works for me. I know that goes against the grain of your pragmatic approach to soldering but, I have always been of the opinion you can be good at anything but you can't be Great until you know all the ways you can do it wrong. I would describe that as the definition of experience but other people would probably just call that doing things the hard way. Kind of makes me miss the days of having an instructor around that could glance at a joint I welded and tell me where I messed up, what I was doing when I messed up, and what to do differently on my next attempt. I need to tell myself "I think I think too much" more often.

    On my first soldering attempt I had left the iron on for about 20 minutes or so without tinning it, unaware that would cause the tip to oxidize because the how-to I had watched and read failed to mention that I needed to tin my tip right off the bat. I picked up the iron, not realizing I already had a problem, thought I tinned the tip properly, and tried to solder two speaker wires together for practice but the iron wouldn't get the wire hot enough to melt the solder. At that point I started worrying that I should have gotten the heavy duty Weller Iron instead of the 25w standard. Or maybe it was the .050 solder wire I bought. The smallest size my local hardware store had was.050

    I keep trying to solder the wires together, wiping my tip off on the wet sponge as I go when I realized that was making my tip worse, The local hardware store only had one kind of sponge, a big thick sponge for washing cars. I was actually melting the sponge with to my tip.

    1 reply

    No, it doesn't go against the grain at all!

    "Good judgement comes from experience. Where does the experience come from? Bad judgement!" Doing things the hard way to start is the best way to learn. Then you practice, a lot. You should always learn to drive a stick shift before an automatic, and learn to use hand tools properly before graduating to power tools. Otherwise, you'll just screw things up faster than you ever could before!

    I probably should have mentioned that only a cellulose sponge is suitable for wiping soldering irons. Cellulose burns when it gets hot, but foam rubber sponges melt (Not good!). Or, use the bronze/brass wool, which doesn't need to be dampened.

    You can never tin an iron too often. I tin just before unplugging for the day, that way the tip is coated as it heats up the next time. I've seen some folks wrap a few turns of solder around the iron tip while it's cold, before plugging it in. Whatever works.