The Art of Soldering! (a how-to)

Ok, so I was reading a thread in Amps, and decided to compile this lil thing (internet, myself, my father (an Electrical Engineer), my tech are all sources used) on soldering... (I noticed in a quick search that nothing like this existed yet). Hopefully it'll eventually become a sticky once enough people put in their info, and we have a good "how-to" on soldering. Well, here's my start.

Equipment needed/used:
Soldering requires two main things: a soldering iron and solder. Soldering irons are the heat source used to melt solder. Irons of the 15W to 30W range are good for most electronics/printed circuit board work. Anything higher in wattage and you risk damaging either the component or the board. Note that you should not use so-called soldering guns. These are very high wattage and generate most of their heat by passing an electrical current through a wire. Because of this, the wire carries a stray voltage that could damage circuits and components.

The choice of solder is also important. One of the things to remember is to never use acid core solder. Acid core solder will corrode component leads, board traces and form conductive paths between components. The best solder for electronics work is a thin rosin core solder. I prefer a thickness of 0.75mm, but other thicknesses will also work. Just remember not to get anything too thick.

Surface Preparation:
A clean surface is very important if you want a strong, low resistance joint. All surfaces to be soldered should be cleaned with steel wool and some sort of solvent. Laquer thinner works well. Steel wool is my preference. Don't neglect to clean component leads, as they may have a built up of glue from packaging and rust from improper storage.

Appling Heat:
Apply a very small amount of solder to the tip of the iron. This helps conduct the heat to the component and board, but it is not the solder that will make up the joint. Now you are ready to actually heat the component and board. Lay the iron tip so that it rests against both the component lead and the board. Normally, it takes one or two seconds to heat the component up enough to solder, but larger components and larger soldering pads on the board can increase the time. Just be sure all parts that are being soldered are adequatly heated!


Appling Solder And Removing Heat:
Once the component lead and solder pad has heated up, you are ready to apply solder. Touch the tip of the strand of solder to the component lead and solder pad, but not the tip of the iron. If everything is hot enough, the solder should flow freely around the lead and pad. Once the surface of the pad is completely coated, you can stop adding solder and remove the soldering iron (in that order). Don't move the joint for a few seconds to allow the solder to cool. If you do move the joint, you will get what's called a "cold joint". This will be discussed shortly.


Cleanup:
After you have made all the solder joints, you may wish to clean with steel wool or solvent to remove all the left over rosin. You may also wish to coat the components with laquer. This will prevent oxidation and keep them nice and shiny.


Cold Solder Joints

A cold joint is a joint in which the solder does not make good contact with the component lead or printed circuit board pad. Cold joints occur when the component lead or solder pad moves before the solder is completely cooled. Cold joints make a really bad electrical connection and can prevent your circuit from working.

Cold joints can be recognized by a characteristic grainy, dull gray colour, and can be easily fixed. This is done by first removing the old solder with a desoldering tool or simply by heating it up and flicking it off with the iron. Once the old solder is off, you can resolder the joint, making sure to keep it still as it cools.

Tips and Tricks

Soldering is something that needs to be practiced. These tips should help you become successful so you can stop practicing and get down to some serious building.

Double check joints. It is a good idea to check all solder joints with an ohm meter after they are cooled. If the joint measures any more than a few tenths of an ohm, then it may be a good idea to resolder it.

Use the proper iron. Remember that bigger joints will take longer to heat up with an 30W iron than with a 150W iron. While 30W is good for printed circuit boards and the like, higher wattages are great when soldering to a heavy metal chassis.

Summary

1. All parts must be clean and free from dirt and grease.
2. Try to secure the work firmly.
3. "Tin" the iron tip with a small amount of solder. Do this immediately, with new tips being used for the first time.
4. Clean the tip of the hot soldering iron on a damp sponge.
   Many people then add a tiny amount of fresh solder to the cleansed tip.
5. Heat all parts of the joint with the iron for under a second or so.
6. Continue heating, then apply sufficient solder only, to form an adequate joint.
7. Remove and return the iron safely to its stand.
8. It only takes two or three seconds at most, to solder the average p.c.b. joint.
9. Do not move parts until the solder has cooled.

All input is welcome, as always!

-Ray

Edit: dang typos. Also, board is used throughout... it can mean whatever though, a pot, a ground, etc. etc.

elros said:

How about some photos?

BTW: that cheap 30W soldering iron in the photos died today, after about 17 years of service. (got it when I was about 10 years old)

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Sweet sweet! Thanks man,

-Ray

I guess one thing I can add, now that I'm thinking about it again, is that when soldering, keep in mind that the solder likes to flow *towards* the heat source.

-Ray

Zebra said:

I'm with Valenti on the wool thing. I'm no soldering expert, but steel wool could potentially leave steel dust bits in the circuitry that can screw stuff up, right?
Another question: I've been told that leaving excessive heat on your circuitry can damage the electronics, but you seem to suggest to make everything heat up.

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Yeah, steel wool is more for places where you can't get it inside of things... i.e. circuit boards etc.
You just want to heat the contact points adequatly enough to have the solder melt into it and creat a good joint. You don't want the entire circuit hot as hell . If it's not hot enough, you'll get a cold solder joint, and that's a badism. If the insulation on a wire is starting to melt, you know you're too hot. You kinda figure these things out as you do it more... I'm only 19, but since my dad is a Mr. FixIt, I learned from him long ago how to do this (among many other things). The more you do it, the better you'll do it, I just wanted to help anyone get started really.

-Ray

godraphonic said:

[snip]...and told me simply heating a wire and the point to be solderd can cause a cold joint do to voids between the actual stranded wires allowing for air pockets and corosion.

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I hate to go against you, but this isn't really neccessary. If you get the wire/contact points hot enough, and use enough solder (and watch to make sure that it goes into the wires as much as completes the connection), then you're fine. You can do it that way, it's just an extra step, IMO. I haven't had a solder join break since I first started to learn how...

-Ray

VEGANBASS said:

I find it difficult to solder ground wires to pots b/c the pot surface is too big to get hot enough to accept the solder.

suggestions?

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You don't need to get the entire surface hot. In fact, on pots, you wouldn't want to, at least I wouldn't, in fear of damaging the pot. What you just want to do is heat the area the wire will be making contact, and the wire itsself. Perhaps a tiny area outside of that also. Make sure your iron is 10-15W and it'll do the job fine. And also, sometimes it takes a minute to heat the contact surface, so give it some time. Hope this helped.

-Ray

VEGANBASS said:

thanks for the quick reply!

my solder is really old... like 15 years or more. does that matter?

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I don't ACTUALLY know. I have used solder that was a few years old, and it worked fine. Fifteen years may be pushing it, but like I said, I don't ACTUALLY know, and this is more or less a guess. There's no real reason I can think of that would make it go bad if it's stored correctly and what not. Someone with better expirence with it should chime in on that though, it's a good question.

-Ray