Soldering Wires - Doing It Wrong, But Getting It Right (What things are CRITICAL?)

[tsbrownie]

What are the most critical things when soldering wires for cars, boats, motorcycles, trailers, drip system wiring, low voltage outdoor lights, etc? I will do (almost) everything wrong and still come up with a workable joint. What is CRITICAL to a good joint? Watch and see.

WARNINGS:
- Soldering can be dangerous. If you do not know soldering safety, learn it or don't solder.
- Never solder live circuits of any type.
- Soldering house wiring, power wiring, etc. is outside the scope of this video. That should be left to professionals only.
- Electricity can cause damage, fires, burns and death. If you don't know about electricity, learn before doing.
- These are demonstrated for hobby work, low voltage - low amperage applications. NOT for mains voltages or currents or similar.
- Never use lead type solders where it will come in contact with food or drink or where it will come in regular contact with people.
- Lead is toxic. Take care to ensure that the byproducts / waste are contained and disposed of properly. Never hold solder in your mouth. Have proper ventilation.
- This is for hobby soldering only. Industrial users have more stringent requirements for industrial or large scale soldering operations.
- This is not all inclusive. If you don't know, get training before continuing.

[Paul Alciatore]

Electronic soldering: rights and wrongs???

I've done a lot of soldering and many wire joints on a professional basis. Not NASA, but on systems that also HAD to work. I agree with some of your points. I'm also afraid I have to disagree with you a bit.

0. I am adding this after finishing the rest, below. Wires are made both tinned and bare. The tinned wires are copper, just like the bare wires, but they have a thin coat of tin or solder on their outside. This coating helps to prevent corrosion and it also makes soldering easier. Tinned wires are almost always the better choice for electronic work and they are definitely are easier to solder. So tinned wire is always my first choice.

1. CLEAN metals to be joined? Yes, that is probably the number one thing for producing a good solder joint. I have had to fight a layer of corrosion many times and it can give you fits. A famous maker of electronics, one of the founding companies in the business, for many, many years used brass pins on circuit boards for holding components by twisting their wire leads around those pins. 99% of the joints were OK. But the other 1% had corrosion on the pins and the solder did not take. Many of those pins were staked to copper foil on the bottom side and a perfect looking layer of solder could be on top of that layer of corrosion and the joint, completely hidden from sight, was BAD. And it was the dickens to find and repair. Clean, clean, CLEAN! That is number ONE!

2. That brings up my second problem with your video. Your destructive inspection at the end. Solder is a very soft metal. It will smear when you use a pair of wire cutters to cut the joint. This is shown by the FACT that your cut did NOT show any copper. It should have shown many, small copper circles where you cut through the joint. But it did not. The solder was smeared across the ends of all those copper strands. You were NOT looking at the joint. You were looking at the smeared copper layer on top of the cut joint. That view showed and proved absolutely nothing about the joint. And even if you had cut it in a manner that showed those small copper circles with solder surrounding each and every one of them, it still would have said NOTHING about the joint. That solder may have been completely surrounding the copper strands, but was it adhering to them?

3. You said your mechanical joint was not good. A lot has been said about having a good mechanical joint when soldering. I believe this comes from MECHANICAL soldering work, where I do believe it is a very important consideration. But in electrical/electronic work, there is very little stress on the wires and other things being soldered and the importance of a good mechanical joint is not so great. I have seen electronic solder joints where a lot of stress was placed on a component on a PC board due to the weight of the component and a fast rotation of the assembly. The wires would rip out of the component before the solder joints to the board (just the wire through a hole with a donut pad) would come apart. Many times I have soldered two wires together with just a simple overlap: no twisting what-so-ever. And they lasted for many years with no problems. There is absolutely nothing wrong with your mechanical joint other than cosmetic issues. Mechanical and electronic soldering are different.

4. You did not do the single thing that I have found that helps a lot for making a good joint. APPLY FLUX to the metals being joined. If you succeed in heating a clean copper wire that does not have flux on it, what is going to happen first is a layer of oxide will form quickly due to the heat. It is the job of the flux to clean the metals and to KEEP them clean until you apply the solder. I strip the wires, then twist them together and then apply some flux. When the heat is applied that flux melts all over the wires and CLEANS them. And it keeps them clean for a reasonable amount of time.

5. The dirty tip on the soldering gun. Yes, that is a problem. All soldering irons should be CLEANED and TINNED. Tinned means they should be coated with a layer of solder. This is true for soldering guns with their wire like tips and also for the various soldering iron tips. A small wire brush is the tool of choice for this with a copper tip. Many tips are iron plated and a wet sponge can usually clean them. This layer of solder on the tip will be the first step when I talk about transferring heat, below.

6. Start in the center and avoid burning the insulation. Yes, this is a great tip. That burnt insulation will accumulate on the iron's tip and interfere with the transfer of heat. Starting and STAYING in the center will keep the insulation on both sides as cool as possible.

7. OK, back to the basics of soldering. 1 - Clean. 2 - Apply flux. 3 - Heat the joint. 4 - Apply solder to FLOW into the joint. 5 - Allow it to cool undisturbed.

8. On the third step above, Heat the joint. For mechanical soldering this usually means torch it or apply a big soldering iron to it. Drench it in heat. This may work for electronic work, but it is not the best technique. Over many years of electronic soldering I have found that you must transfer a relatively small amount of heat to the joint while not overheating the areas around it. This can be very important when soldering things like transistors and ICs, but it is also important with wires because most insulation can melt and burn completely off. I have found that this means that the heat from the soldering iron's tip must be transferred quickly to the joint. And a good way to do this is to partially break the sequence above which was developed for MECHANICAL soldering. First, that iron's tip should be clean and tinned. Corrosion on the tip will act as an insulator and prevent the heat from flowing into the joint. But the air gap between the iron and the wires also hinders that heat transfer: the best way to overcome this is to have a SMALL drop of solder on the iron's tip. With the flux on the wires, that small drop will rapidly wet the surface of the wire and heat will transfer through the drop of solder.

Once that heat transfer starts (in a second or two) more solder can be added to the WIRE near the iron's tip. This will continue the transfer of heat to the rest of the joint in a sequence and more added solder will wick into all of the joint.

9. Moving the iron tip around the joint in an effort to spread the solder. This is a mistake. The heat and flux should spread the solder. It should wick into all parts of the joint as the heat reaches them. Mopping the solder around with the tip is an invitation for it to coat the outer part of the joint only, leaving gaps on the inside.

10. SO, KEEP THE IRON IN THAT CENTER POSITION and let the solder wick into the joint. Only if the joint is large compared to the iron's tip is it necessary to move the iron around. But even then, it should FOLLOW the melted solder, not push it.

11. Too much solder. Yes, this can be a problem. I have seen this on circuit boards with small spaces between the traces and in many, many connectors where the pins are closely spaced. It can be a real problem. I do not think it was a problem with your wire joint.


Summary for a good wire joint:

1. CLEAN the wires.

2. Flux the wires.

2.5. Pre-tin the wires. This is optional but it can help a LOT.

3. A twisted joint is OK, but optional.

4. CLEAN the iron's tip. And TIN it.

5. Have a small drop of solder on the iron's tip.

6. Heat the joint from ONE, central point.

7. Apply more solder as the joint heats.

8. Let that solder WICK into the joint. Don't push it in or around. If this does not happen, you did one of the previous steps incorrectly: start over.

9. When the solder has flowed into the joint properly, remove the head and do not disturb the joint while it cools. Moving the joint while the solder hardens can lead to a "cold solder" joint which is weak and a poor electrical connection. If this happens, you should re-melt the joint and allow it to cool properly.