Tips for re-attaching wires to circuit boards

[GKGKGK]

Hello, I'm wondering if anyone has a good tip for the best way to reattach wires that have come lose from the solder terminals on a circuit board. As you know, there usually is very little slack and you're working with the last centimeter or so of bare wire, at best. I've found it's considerably more difficult to get these wires to reliably re-adhere to the terminal... i've resorted to a fairly sloppy technique where I try to bend the wire a bit and get it flush against the terminal, then quickly try to drop some hot solder on there. It rarely looks good and I don't feel confident that it will hold very long.

I'm particularly concerned with Farfisas but I imagine this is a problem for most combo organs.

How do other folks do this?

[Coenraads]

Unfortunately the technique you describe is almost guaranteed to yield a cold solder joint and it will eventually fail. Never drop solder onto a connection. The first rule of soldering is that both the terminal and the wire must be brought to a temperature where they will melt the solder. If you are tack soldering, as in this case, heat up the terminal until it melts the solder and leave a small amount of solder behind. Now heat the end of the wire until it too melts the solder leaving a thin coating of solder. Now, without adding more solder, touch the wire to the terminal, heat with the soldering iron until the solder flows smoothly, then remove the iron, holding the wire firmly in place while giving it a few seconds to cool.

A properly soldered connection should look shiny and if it does not look good, it is not good. May I suggest that you grab an old circuit board, some wire and practice this technique. My preference is for a 35 watt iron which lets you get in and out fast, without risking overheating a component, three to four seconds at most.

[GKGKGK]

Thank you!

[John Vanderlee]

Often novice people treat the solder like glue. It's not! As said above, the entire joint must be heated up until the solder flows over it, leaving a smooth shiny finish.

[Larason2]

I always struggled with the advice to heat the wire with the soldering iron. It's true the wire needs to be heated up for a good solder joint, but I find there isn't really a way to know if the wire is hot enough yet. So what I tend to do is hold the iron on the metal to be soldered for 3-4 seconds, then touch the solder to the tip of the soldering iron. Most of the time it works, though if it doesn't, then I know I have to remove the solder with soldering braid, and heat the metal a bit longer! Another tip is that if you're using rosin as flux, solder will only flow as long as you can see the rosin's smoke. If you heat up some old solder, it generally won't flow unless there is flux present.

If I'm trying to solder a wire that's too short, I always extend it with some more wire. I find this avoids disasters. I have a spool of green 24 gauge just for this purpose. I strip the end of each wire, form a loop on each end, then hook the two loops together, and pinch them tight with micro pliers. Then, I heat up the medal and add some solder. If necessary, I add a bit of electrical tape once it has cooled to isolate the join. This usually forms a pretty reliable joint. If you have to tack solder, then you must, but I was always taught that the first step of a reliable solder joint is a good mechanical joint. Coenraads has a good technique for tack soldering though, I think I'll try that next time I have to do it! What I usually do is heat up the blob of solder already on the board with my soldering iron until it melts, then stick the cold wire into that heated blob with micro pliers, then remove the iron, and hold the wire there until the solder sets again. It works most of the time, and is fairly reliable, but it's true I sometimes get joints that come apart this way (usually because there isn't enough solder to fully cover the wire). If that happens, I usually add some more solder, then try again. Coenraad's technique is probably better!

[John Vanderlee]

I heat the wire or the joint by touching it with the solder, holding it there while I apply the iron tip to the solder which then melts enveloping the wire/joint with hot solder thus raising everything to the right temperature. Finish the joint by continuing to feed a bit more solder. I used to teach college students how to solder as they came me with their robotic projects that "didn't work" or were "intermittent". Invariably they were cold solder joints.

[Jaim]

Several things:
1. Make sure the surface you are soldering to is clean.
2. If you are planning to do any amount of electronic repair, invest in a temperature controlled soldering station. Well worth the money.

Jim

[myorgan]

It's true the wire needs to be heated up for a good solder joint, but I find there isn't really a way to know if the wire is hot enough yet. So what I tend to do is hold the iron on the metal to be soldered for 3-4 seconds, then touch the solder to the tip of the soldering iron. Most of the time it works, though if it doesn't, then I know I have to remove the solder with soldering braid, and heat the metal a bit longer!

Did you know many of the big box stores have stopped carrying de-soldering braid, or package it with something I don't need? I looked at Lowes (discontinued) and they sent me to Harbor Freight, but HF only provided the braid (all I really need) with 2-3 solder sucker plungers (which I'll never need). They also recommended Tractor Supply, but at that point, I was wasting more money in gas than if I purchased it online–which is what I ended up doing.

When I solder, I hold the iron to the joint and wire to heat it up, and then introduce the solder to the hot connection. From a science perspective, heating "excites" the atomic bond in the pieces being soldered, thereby allowing the solder to form a proper bond with both the wire and work before they cool off as a much tighter bond than before.

I, too, like Coenraads' advice regarding soldering joints. In fact, I like it so much I think I'll go home and try his approach!

Michael

[John Vanderlee]

Coenraads is right also. My point was that if you introduce a bit of melted solder between the iron and the joint, the thermal effect that he notes takes place immediately.

[myorgan]

John,

I wasn't negating your method. In fact, I'll probably try that as well in repairing my speakers. Many heads are better than one!

Michael

[John Vanderlee]

LOL I was not questioning you! Just put in my 2c!

[myorgan]

When it comes time to de-solder, I've found that putting the braid between the iron and the solder works best for me. Once it heats up, I simply draw the braid between the wire and the soldering iron until the connection loosens up. Unfortunately, I'm correcting some REALLY BAD soldering jobs I found in the Conn Speaker Pipes I have, so even drawing 2"-3" of braid between the two is barely scratching the surface of the material put on those connections. Remember, whatever you solder (especially speakers) may sometime have to be undone, so don't overload the connection with piles of solder. Just enough to do the job works well enough.

Michael

[Larason2]

What I was taught to do is push on the end of the braid to open it up. It absorbs way more solder this way. I use 2-3 inches of braid for a whole project! I also put it between the soldering iron and the solder.

[you795a]

I use a desoldering iron myself.

[myorgan]

I use 2-3 inches of braid for a whole project!

Larason2,

You use 2-3 inches even if someone has over-soldered before? How do you soak up that much extra solder with only that amount?

you795a, Desoldering iron? I'm not sure I know what you are referring to.

Michael

[you795a]

Here is a desoldering iron. They work great for me. https://www.amazon.com/ECG-J-045-DS-...xpY2s9dHJ1ZQ==

[myorgan]

Ah, I have one of those and never had much success using it–I don't have enough hands! ;-)

Michael

[Larason2]

I also have a desoldering iron, but didn't have much success with it either! Like I said, just push on the end of the desoldering braid, maybe just 2-3 mm. The braid will open up, and go from 1 mm wide to like 3 mm wide. It takes a bit for the solder to melt, but even if it's really been over soldered, you don't need more than ~6 mm of the braid per joint.

[Jyvoipabo]

Look at this badly damaged circuit board repair.
The technique uses Teflon-insulated mini-wrap wire soldered onto what remains of the components. A socket has been added for the IC.
It was an ACE 3000 fruit machine, but I used it on Farfisa and many others.
Teflon wire is used to extend short wires (add a piece of heat shrink tubing over the splice) to find a solder attachment point in a solid location. The insulation does not melt when heated.
JP