A joint in which the solder does not make good contact with the component lead or printed circuit board pad is called a cold joint. It's a soldered joint that was made incorrectly as the solder was melted on to the metal,
but the metal was not hot enough to melt the solder, meaning that the solder didn't really flow and is not bonded to the metal. A cold joint is a mechanical joint at best: it may hold together for a while, but it will eventually break loose, and it will never conduct electricity very well. 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, and should be removed.
Cold joints are easily fixed, and can be recognized by a characteristic grainy, dull gray color. First, remove 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 do it right by keeping still as it cools.
SOURCE: http://www.solderinguide.com/soldering
* Make sure PCB is spotless
* Make sure all leads are spotless
* After every solder operation, tin and clean the soldering point.
* Do not rush - make sure there is enough heat to melt the solder
* Do NOT move the lead that has just been soldered.
* Cut the leads of components straight away after the joint has cooled.
http://www.wiringfordcc.com/solder.htm
No Exceptions Whatsoever!
I wish there was a way around this, but it is a law of physics - soldering is a process of bonding metals together. Not oxidation, corrosion, paint, other chemicals like chemical weathering, enamel - nothing but certain metals. I have never seen anyone who succeeded in violating any rule of physics. So save your energy; don't bother trying.
If cutting through a wire, and the side of the wire is not the same color as the end, you must clean it. Use your Dremel wire brush, a file, sandpaper - anything but a torch. (The torch leaves burned residue behind - which is not a metal!) Copper wire should be clean like a new penny or the bottom of mom's favorite pot. (Yes, the one you ruined as a child. Thank god for Corningware!) Whatever metal you are trying to join, it MUST shine! You might also want to try using the liquid flux discussed below. It will shine copper wire right before you eyes without any filing or sanding.
You might guess from this unusually laid out section that I'm trying hard to drive home a point. You are right. I am. There is simply no other way. Yet, people try anyway. I'm trying to do you a favor!
You might think that the flux contained in solder is supposed to clean surfaces to be soldered. You are right. However, it's cleaning power isn't as great as we would like it to be. Just think of it as microcleaning the surface. Dirt so small we can't see it. Okay, think of it as not cleaning a darn think at all! Whatever it's cleaning power, by the time you apply enough of it, solder, and heat, you have a blob of solder, some of which landed on your leg and is causing excruciating pain right as we speak, has melted your track, and burned your fingers.
I have been told some people have had some good luck applying flux paste from a can. You can try this before you attack your track with a Dremel wire brush.
If you have found a way to violate any of the rules of physics, please let me know. We willl be rich!
Note: Weathered rail can still be difficult to solder to after you have cleaned it with a Dremel. Try liquid flux, you will be amazed! See the section below.
RECOMMENDATION #1-5: How to Tell When You Have a Good Solder Joint.
The solder joint should be shiny. If it has wrinkles, waves, frosted, or appears dull, you probably have a cold solder joint. If the wire is loose or wiggles, you definitely have a problem. If you tug on it - which you always do to test it - and it comes loose or apart, you don't have a good solder joint. Don't be afraid to tug on it. Now is a much better time for you to find out than during an operating session or show.
RECOMMENDATION #1-6: Make Sure the Wire Has COMPLETELY Cooled Before
Moving It.
This can be difficult - especially if the wire is hot and your fingers are getting hot, too. But if the wire moves, you will get a cold solder joint. Electrical failure will eventually occur - probably very soon!
RECOMMENDATION #1-7: The Tip of Your Soldering Iron Must Be Clean & Shiny.
One of the reasons people have a hard time soldering, melting nearby plastic parts, and getting cold solder joints is because the tip of the soldering iron tip is not clean and shiny. A clean and shiny tip conducts heat best.
Keep a damp sponge nearby and wipe the tip in it. You can use a wet paper towel, too. Rub the hot tip on your benchwork, if you dare. Do something (short of using your pants or even your tongue) to clean that tip whenever it needs it.
Remember, if it is not shiny or you are having trouble getting the solder to melt, clean that tip!
RECOMMENDATION #1-8: The Metals to Be Joined Must Have Good Mechanical
Contact.
Make sure the wire you are soldering is not "swinging in the breeze." "Crimp" it onto whatever you are soldering to so it will hold still. Failure to have a good mechanical connection causes two problems. 1) A cold solder joint is certain to occur. 2) You will have poor heat transfer. You will have to try to get the parts to solder together longer and you will melt nearby plastic parts.
RECOMMENDATION #1-9: Work Quickly a.k.a. Don't Apply Any More Heat Than
Necessary.
Doing the above, that is, good mechanical contact and have a clean tip, are the most important things to ensuring you don't apply any more heat than necessary. Applying too much heat melts nearby plastic parts and your fingers.
But once the solder flow over the work as you desire, remove the soldering iron and hold that wire still until the solder hardens and becomes shiny.
RECOMMENDATION #1-10: Heat the Work, Not the Solder.
It's tempting to heat the solder and get it melted and flowing. But if you don't heat the items that you intend to solder together, you will get a cold solder joint.
Try to position the soldering iron tip so that it touches both things you are trying to solder at the same time. Then add the solder. Initially the solder won't melt. A few seconds may be necessary until everything heats up.
Be careful! You will need to practice. Remember, do not apply any more heat than necessary. You will need to practice to get the knack.
It is okay to apply a tiny amount of solder to the tip of the iron before you start. This helps the heat transfer. This will be fine where the two items to be soldered are irregular in shape and you are having trouble getting much of the surface area of the tip to make good contact.
RECOMMENDATION #1-11: Use the Right Size Soldering Iron or Gun.
Use a soldering iron of 25-35 watts to solder everything except bus wires, rail, or large switch solder tabs. Don't use anything large to install any decoders or any other electronics into your locomotives!
Use a 150-250 watt gun to solder wires to buses, car tail light bulbs (read on), track, or large switch tabs. Using enough heat is important, too. These cases have a lot of metal to heat. Without enough heat, such as when using a 25 watt soldering iron, things will get hot, but not hot enough to melt solder - but probably enough to melt plastic parts or your fingers!
SUGGESTION 1-12: Use a Resistance Soldering Station
A resistance soldering station bears some resemblance to welding. While it is not actually welding, it does pass a low-voltage, high-current, through it's tips and the work to be soldered. The high current causes the probe tips in particular to heat up. The primary reason for using a resistance soldering station is that the heat is localized. This is accomplished by applying a higher heat than you might with a standard soldering iron for a brief period of time. The solder flows before the overall temperature of the work rises too much. The bottom line is you can avoid melting ties or wheels! There are a few disadvantages, but you will happily deal with them to reap the benefits of using this type of soldering station. Ask anyone who has ever used one - they love it! For a demonstation of a resistance soldering station in action, click here. Make sure your sound is on.
Notice I call it a station rather than an iron. This is one of the disadvantages. It consists of the soldering probes, a power pack that weighs several pounds, and a foot switch. Still, for soldering track, this thing can't be beat. I've used it for HO and G. It has never been easier to solder jumpers and feeders to both of these scales! It's also great for soldering to the steel tabs found inside of Athearn locomotives like the PA-1. This has never been easier, too!
They come in several power level capabilities; typically 100W to 250W. If you are doing HO or smaller, 100 to 150W will do. If you intend to solder O or G scale track, you will definitely need a 250W unit. If you are soldering metal cars or buildings, you should get the 250W unit. Two companies that modelers are familiar with are PBL, which carries the Hotip brand ,and Micro Mark, which carries the American Beauty brand. When comparing the offerings of these two companies, you might be wondering, "What kind of soldering tool is called American Beauty?" There is no need to be scared away by this seemingly unusual name. They have been a major soldering tool supplier for many years. So pick the one that suits you.
The manual that came with mine touts the benefits of this "ultra high performance soldering" method and also warns that there is no way to know exactly what to set the power level to. They recommend trial and error. This would make you tend to think that it would be hard to learn to use it. I was smiling on the very first try! I generally start with a setting of 50% (125W). The whole soldering operation can be over in under 3 seconds, so if it does not start to go by then, I stop and crank up the power. You will find that you can get the hang of this thing quickly and a less than optimum setting doesn't spell disaster.
Here is another neat benefit. The normal soldering probes consist of something that looks like electrified tweezers. So if you are soldering a wire to track, you squeeze the wire and track between the tweezer tips, holding the two items tightly together. And unlike using a pair of pliers or something to hold the wire to the rail, and having them suck away the heat, these supply the heat! As soon as the solder flows, take your foot of the switch. When it cools, release your grip on the tweezers. Even though they may have been in contact with the solder, you will find that the tweezers did not get soldered to the work. What more could you ask for? You will love it!
If you have the bad habit of trying to solder without cleaning the work first, that habit will stop here! The reason is that this type of soldering works because of the flow of a low-voltage, high-current. Any dirt or oxidation introduces too much resistance for the necessary high-current to flow. Nothing will happen. It simply will not work. So you will have to keep the probe tips and your work (track, wheels, etc.) shiny clean. Keep a piece of 400 grit sand paper or an emory board (finger nail file) handy to clean the tip. You will probably need to clean the tip frequently, especially in the beginning.
What's the other disadvantage? Unless you build one yourself, these things are not inexpensive. They range in price from $262 to about $380.
The December 1997 issue of Garden Railways carries an article to build one from a battery charger and an old soldering iron handle. Should you want the electrified tweezers, you can buy them from one of the above. If you want to build your own tweezers, you will need to at least buy the copper clad, stainless steel tips. These are important to carry the power to the tip where the stainless steel heats up to do the soldering.
See the section on Track Wiring, DCC in the Garden, and Block Detection for specific advice on how to use a resistance soldering station as it relates to these sections.
If you do decide to get a resistance soldering station, be sure to wear safety glasses. Properly used, there are no sparks. However, if you hit the foot switch a moment sooner than when you have the tweezers ready, you will get a few. Whether you realize it or not, but often sparks are really tiny bits of burning metal. There is no point in risking getting anything in your eyes!
RECOMMENDATION #1-13: Use Liquid Flux for the Easiest, Neatest, Best Solder
Joints You Have Ever Seen.
Liquid flux is not as convenient as rosin core fluxes. Or so it would seem. H&N Electronics http://www.ccis.com/home/hn markets Supersafe flux which works as advertised. I have tried liquid fluxes before, but none impressed me enough to give up using rosin core solder until I came across this product.
Solder joints look great and are more quickly obtained. If you find soldering difficult, try this liquid flux. You are not left with a residue which contributes to cold solder joints. You will find the solder flows completely over your joint. Quicker soldering means less likelihood of melting ties.
I use their gel, which is more like a syrup than a paste, for soldering to HO track. Just dip solid (no core) solder in the gel. The drop can then be applied to the side of the rail. You will find liquid flux makes it effortless to solder to the side of weathered rail. (Weathered rail can be hard to solder even after the weathering is removed with a Dremel.)
When using liquid flux, do not use a rosin core flux. The defeats the advantages of using liquid flux. Use solid solder. H&N sells solid solder. Your local hardware store may also have it. It also can be ordered from places like Digikey and Mouser.
Their liquid works great for G nickel-silver and for attaching all feeders to buses. Go ahead and keep using rosin core flux to install decoders and other electronic work.
