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This is my first question, and I'm pretty new to the world of electronics, although I'm attending an Australian college course called "certificate 3 in electrotechnology".

My guitar tuner seems to have a ground problem. I think it's from the battery terminal, as it was fine but then 9V got stuck in the clips and had to be taken out with pliers. Ever since, it's been unreliable unless i put a bare foot on it. I've bought a new connector and plan on replacing the old one. One thing I am reasonably confident in is soldering, as I've wired my guitars myself for a while now. I understand that PCBs are pretty sensitive and that extra precautions should be taken when working on them. I read somewhere that alligator clips/leads should be used to dissipate the heat from the iron. If this is the case (there's a chance that some wise guy has just said it on the internet without qualification), would I connect these to the leads of the terminal or the board itself?

Also, in the past I have only used desolder wick. Should I go and get a pump for this sort of thing?

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  • \$\begingroup\$ Watch out for those pumps around delicate things, though. Mine, at least, has a pretty serious recoil. \$\endgroup\$ – Bobbi Bennett Apr 6 '13 at 13:23
  • \$\begingroup\$ I'm not sure what you are trying to desolder. If its just the battery connector leads, just heat up the pad until the solder is melted all the way through the board and pull the wire out. You will know when the joint is hot enough if you maintain just a tiny bit of pull on the wire as you are heating it. Then clean the hole and solder the new wire in. \$\endgroup\$ – Dwayne Reid Jan 28 '15 at 21:54
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I think that using anything to dissipate the heat when doing soldering is just some very nasty folklore, best forgotten unless fully understood.

On surface mount parts, you want to do exactly the opposite. When soldering or desoldering, you ideally want all parts to be at the same temperature: that's why people use preheat plates. When all things are at the same temperature, there's minimal thermal stress on the terminals.

On through-hole parts with just a few terminals and good access, you may find it possible to grab all the pins at once with pliers to sink some heat away. You'll find that in practice you're more likely to mechanically damage your part by doing that, than just quickly desoldering without any heat sinking. For desoldering leaded parts, the important things are:

  1. Have a high-powered iron. 50W would be bare minimum. Do not use fine tips. The wider the tip, the lower the thermal resistance between the heater and the tip, and the closer the tip temperature will be to your setpoint.
  2. Have an iron with temperature control based on feedback close to the tip. Otherwise your tip, in presence of a heat sink, will be cold even though you think the temperature is right.
  3. Ensure that you have good thermal contact with all the pins at the same time. This means that you need to heat up a big blob of solder with your iron, and then roll it over the pins of the device. In less than a second you should be able to pull it out.
  4. If your device has leads far apart, you will need multiple soldering irons, no way around. Yes, you can try and pull leads out one at a time, but it's a hit or miss if you want to preserve the part.
  5. Use flux-cored solder with electronics-compatible flux. That really means a rosin-core flux. I find that water based fluxes have too low boiling point for rework, and no-clean fluxes are irrelevant since you'll have to clean stuff anyway.
  6. If you can avoid it, do not play with pulling the solder out of the holes before you desolder the part. It's easy to damage the PCB and/or the part while doing so. Apply the heat, pull the part out, and only then remove the solder from the holes so that you can replace the part.
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  • \$\begingroup\$ Thanks. What you say makes sense, but goes against everything else I've learnt about soldering. Can anyone else verify this? \$\endgroup\$ – Tim Crossey Apr 20 '13 at 11:53
  • \$\begingroup\$ Think about the contact area between an alligator clip, made out of thin sheet metal, and component leads. It'll be fractions of a square millimeter of contact area in the best of the circumstances. Normally you'd really get point or line style of contact. That does nothing for thermal sinking, but you're adding an extra mechanical stress and making it harder to work on it. \$\endgroup\$ – Reinstate Monica Apr 22 '13 at 14:01
  • \$\begingroup\$ There's a lot of lore about soldering stuff that's spread about by well meaning people who demonstrably have no feel for even the most basic physics of the situation. Do yourself a favor: break open a TO-92 device to see how it's made. \$\endgroup\$ – Reinstate Monica Apr 22 '13 at 14:03
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If you're not confortable with getting in and out quick with the iron, you might try using a heat sink clip on each of the legs of the device you are soldering. Typically a 40W iron will get the job done just fine. Also, I would recommend any Craig Anderton material for learning more about this. "Electronic Projects for Musicians" is a worthy read.

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You need a heat-sink to protect heat-sensitive electronics components while you are soldering them. For example when soldering a TO-92 transistor, you might want a heatsink on its plastic body while you solder the legs.

While you are desoldering battery contacts you will not need a heatsink, unless there are some very heat-sensitive components nearby and you believe the heat will reach them via the traces/groundplanes. This is possible and how likely it is depends on your desoldering skills, but then you'd need heatsinks for all these sensitive components. The battery connector will get thrown away (no need to protect it) and will itself act as a heatsink anyhow. Depending on your soldering iron, the problem you are more likely to have is not enough heat, rather than too much.

And yes, desoldering pump will make it much easier, but nothing says you can't do this with a desoldering wick. However, the desoldering pump will actually help with protecting other components from heat: it is quicker to work with a desoldering pump than a wick. This will minimize your heating time, and therefore reduce the chance that nearby components will get heat-damaged.

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  • \$\begingroup\$ Thanks. One more thing (I'm a little nervous about wrecking my tuner - it wouldn't be the first time I've created a large problem fixing a small one). What temp is best for this sort of thing? In the past I've just used as hot as possible (around 450C) as guitar components are pretty hardy. \$\endgroup\$ – Tim Crossey Apr 6 '13 at 2:50
  • \$\begingroup\$ Start lower and go higher. Make sure that you touch the soldering gun to the PCB for as little time as possible. This is where soldering pump is much faster: heat->melt->whoosh->remove iron. \$\endgroup\$ – angelatlarge Apr 6 '13 at 2:51
  • \$\begingroup\$ Would it be possible just to wire the leads from the old terminal to the new terminal instead of desoldering? \$\endgroup\$ – Tim Crossey Apr 6 '13 at 3:15
  • \$\begingroup\$ Ah.. right.. well... you need 20 so that's not gonna happen. Anyway, yes, you can do that. You can solder the leads from the new connector to the old one, or to where the old one connects. But I'd go ahead and desolder it: you'll need to learn to do that some day. Maybe practice on some junk electronics first? \$\endgroup\$ – angelatlarge Apr 6 '13 at 3:39
  • \$\begingroup\$ Thanks heaps. I'll just jump them together for now and find some old stuff to desolder. I'd be able to ask my course instructor, but we're on Easter break. \$\endgroup\$ – Tim Crossey Apr 6 '13 at 4:04

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