Soldering….

[george gonzalez]

Eric, you’re a prince among men, a good presenter, and what you don’t know about cars wouldn’t fill a gnat’s ear.

However, I’ve now seen you solder wires and PC boards twice, and I gotta tell you, you’re teaching just about everything wrong about this technique. Everything.

How’s about you take a little advice from someone that’s been doing it for, oh, 50 years now? On thin wires, thick wires, old radios, terminal strips, connector lugs, big old PC boards, and modern PC boards? Here we go:

(1) First, you need the right soldering iron. Do NOT even consider using one of those “guns” with the wire loop or anything with a trigger. They heat up, but in a very uncontrolled way. The copper loop has almost no thermal mass, so it zooms way up and down in temperature. Much better to use a real soldering iron, one that you plug in and it takes 5 to 10 minutes to heat up.

(2) Second, it should be the right temperature and size for the job. For a couple of thin wires or a PC board with thin and narrow traces, a 30 to 50 watt iron is about right. If the wires are #14 or larger, or the PC board traces are more than 1/8th inch wide, you need like 75 to 120 watts. Too little and too much wattage is bad. Try to hit the right range.

(2.5) Now the right kind of solder. If possible find tin-lead 60/40 or 63/37 ELECTRICAL solder, rosin core. Do NOT use anything like plumber’s solder, or solder with separate plumber’s flux. Try to avoid 100% tin solder, it just does not flow smoothly or stick very well, and it gets brittle. Do not use plumber’s flux, it’s somewhat toxic and acidic and can eventually corrode electrical joints.

(3) To transfer heat, the tip has to be CLEAN and tinned with solder. If it’s really black and cruddy, it needs to be rubbed with a file or sandpaper until the copper shines. If it’s a newish tip, it may have a shiny metal coating, then don’t use something very abrasive, a little fine steel wool will do the job (but keep the steel wool far away from any PC boards!). Then wait until the tip is hot and rub some solder on it. The solder had better FLOW like water, and NOT bead up in just a few spots. Beading up means it’s being repelled and that tells you the surface is not clean. The iron and oh, the things you are going to be soldering have to be CLEAN and free of dirt, crud, oil, grease or oxides.

(4) The things you’re soldering have to be very clean. Take a knife or fine sandpaper and scrape and polish the wires to a fine coppery shine. Do NOT just go solder to an old copper wire! it may look semi-shiny, but it’s really not. In a car the old wires quite often have sucked up oil and moisture and they’re not fit for soldering. Use something like isopropyl alcohol if needed, and get the metal parts SHINY. Every time I’ve tried to save time and skipped the 20 seconds to clean the surfaces, I usually regret it. The solder just beads up and refuses to bond.

(4.5) Twist the wires tightly together. Do not fan out the strands and do not interleave them. You want firm metal-to-metal contact, not a lot of air space in there and not a chance for little strands to be flailing out. Twist the wires together 3 to 3 turns.

(5) Now for the technique. First you have to transfer heat to the things to be soldered. That means FIRM physical contact. Not the sloppy wobbly technique you may have seen in someone’s videos. Heat does not transfer unless there is close physical contact. This usually means you need a third hand, or vice-grips, to hold the objects. If you use vice-grips, it’s IMPORTANT to have soft padded surfaces on the jaws that will not carry heat away! A couple thicknesses of shop-rags will do the trick. Also do not solder free-hanging wires.

As an aid to heat transfer, you can first put like a SMALL layer of solder on the tip of the iron, that will act like a heat transfer agent.

Now make firm contact. If the iron is the right size, in about 5 to 10 seconds, the metals to be soldered will be hot enough to melt solder. Not the 30 seconds or more you might have seen in some demos. If it takes that long, the iron is either too small (too few watts), or it has too small a tip with too little thermal inertia, or it’s not making good thermal contact. Too long, like more than 15 seconds, is very bad, as that gives heat a chance to diffuse up the wires and traces and heat things that should not be heated up.

(6) BTW: NEVER use a clip-on heat sink! If you use the right 5 to 10 second time frame, the heat will not have time to migrate away. I have soldered thousands of heat-sensitive components, things that you will never encounter, including old Germanium diodes, LED’s, and old rubber wires, without a heat sink. It’s much more likely that a heat sink will make things worse than make things better.

(7) And DONT apply the solder to the iron! Yes, it’s hot, but doing that just fritters away the flux (the yellow stuff inside the solder). Solder should always be applied to the things being soldered. If the things are not hot enough to melt solder, you are allowed to put ONE small drop of solder between the iron and the things being soldered, but as soon as you do that, move the solder away, wait for that drop to flow over the things being soldered, then apply more solder to the side away fro the iron. You want the flux to flow over the pars, not the iron.

[8] The molten solder should flow like a flat wave and completely cover the parts. If the solder beads up, the surfaces are not clean enough, you need to grumble, back off and separate things and use the alcohol and/or sandpaper.

(9) Once the solder has flowed smoothly over the things to be soldered, take away the iron. Do not allow the parts to one until the solder is hard, about 10 to 20 seconds. The whole heating part of the operation from start to finish should take 5 to 10 seconds. Smile at a job well done.

(10) Use only enough solder to flow over and between the surfaces. There should be NO solder lumps, bulges, drips, or blobs or bubbles. The solder should look like it flowed like water over the surfaces, not like the beads of water on a windshield with Rain-X on it. The solder should look very shiny, not gray or rough.

(11) All the above info has been fine, I pat myself on the back, but reading some blab is not enough, you really need to practice to get good at this. Get some wires or an old PC board and practice, practice, practice, until you get good at this. Even try breaking a few of the rules, like skip cleaning the wires and see how well that works out for you. Sometimes this will “kinda” work, but it will take longer, take more heat, perhaps overheat the insulation and nearby parts, and the joint may never be very satisfactory. Try soldering THICK wires, like alternator or battery cables, with a 30 to 50 watt iron and see how that goes (it won’t). Try soldering BIG components, like alternator diodes, and notice that a 50-watt iron, unless it has a BIG copper tip, is just not up to the job. If you foresee having to solder big wires, go to estate sales and garage sales and find a biggish old heavy soldering iron. Again, do NOT use anything that has a trigger or a small wire loop at the business end. Those are NFG. I have two of those, and every year I forget and try using one of them, and I soon think, oh, yes, this is why I don’t use these. Don’t even THINK of using a tiny battery powered soldering instrument, no matter how cute the women are using it in the infomercial and how happy they look while appearing to be soldering back together the Titanic. Those things are much much worse than totally useless.

(12) You will see a lot of very small irons, at Radio Shack, like 12 to 27 watts, intended for soldering very thin traces on PC boards. These irons will probably NOT be of any use for anything other than soldering 1/32″ traces and very thin wires. The tips just don’t hold enough heat, and the heating element does not have enough backing oomph to supply more heat. Just say no.

So, to recap, right type and size of iron, right type of solder, clean surfaces, wires TWISTED, not interleaved, iron making FIRM contact, at most ONE small drop of solder between iron and things being soldered, then apply solder to the surfaces, not to the iron, in 5 to 10 seconds, then back off, and OH, IMPORTANT, do NOT allow the wires to move for 20 to 30 seconds, that will make for a poor crystallized solder joint. You can blow, lightly, on the joint to speed cooling, but if you overdo this you disturb the solder and you’ll get a gray crystalline joint that is not very good.

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And oh, you might have to sometimes first UNSOLDER a part from like a PC board. You can do this two ways:

(1) The old third-world way– heat up the solder joint and then quickly SMACK the pc board sideways against a hard surface. The solder might come right off. Or it might come off and then stick to nearby parts and traces. Or you might crack the board. You results may vary.

(2) Get a solder-sucker at Radio Shack. These will sometimes work. They work best when you can get the tip real close to the solder. Again no guarantees.

(3) Get some solder-sucking braid at Radio shack. You will need a soldering iron of about twice the usual wattage, as the braid is made of copper which will carry away the heat real well. This will kinda work. The downside is that you have to use quite a bit of heat and pressure and time, which sometimes overheats the PC board more than you’d like.

(4) If you’re really determined to do this right, yo can buy some “desoldering alloy”, which is a weird mixture of things like indium and expensium, which you melt onto the solder, and it reduces the solder melting point to as low as 130 degrees F!. There are also other alloys which make the solder super crumbly, so it has no cohesion at all. These alloys are expensive, so save this trick for doing really delicate jobs.

Topic

[kris]

heat oxides metal…. flux plus heat cleans metal, solder flows in and makes good connection.

A good iron/ stations makes worlds of difference. the best budget station I would get would be an hakko 888. It will set you back about ~100. Heat up times are almost nonexistent.

a good read for learning about lots of solder stuff
http://www.rctech.net/forum/radio-electronics/336870-how-solder-correctly-not-so-brief-lesson.html

[Author]

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