Desoldering components

Question

One time, I accidentally reversed the polarity of a diode (luckily I noticed it before I powered it on), so I tried to desolder it. I tried solder pumps and solder wicks but nothing happened. I think the PCB was more damaged than the solder. Any tips on how to desolder it without overheating the component? It is a through hole diode. It looks like this (not exactly the same)

Answer 1

Recommended:

• The professional tool to use is a "desoldering station" which can both heat the joints as well as utilize a vacuum pump. It doesn't necessarily have to be a state of the art brand, all of them work similar, but some cheaper ones have a tendency to clog up.

  With a desoldering station you just aim at one hole at a time, heat until the joint starts wetting then pump. These minimize damage to the PCB and component.

Ok with skill & experience:

• You can remove them with a soldering iron too - pick as big a chisel tip as you can manage. Then heat one side and lift that leg while the joint is hot, using flat nose pliers (tweezers are too delicate for DO packages like in the picture) so that the leg is out of the solder. Then repeat on the other end.

• If you have a hot air soldering station you can also try to heat both joints at once from the solder side and then just hope gravity is your friend & that the component isn't stuck too tightly. Depending on the distance between the legs & board layout, this could either be easy or pretty hard/forget about it.

Not recommended:

• When just removing the component while heating it with the iron fails, you can try to remove all the solder using a wick braid. But they are hard to use for this particular purpose, almost always failing to remove all of the solder from inside the hole. And so they often lead to excessive heating - not really recommended.

• Another option is a hand-held desolder pump, but I have never used one which actually worked well. They suck too poorly and you tend to heat the joint far longer than you should while pumping. It's just a bad tool to avoid entirely, in my personal opinion. Others than me claim they work just fine, I haven't seen it, but I suppose it might be a matter of brand.

• "Heat the joint then tap it against the bench" seems to be a popular suggestion around here - I wouldn't recommend because of the solder splatter alone - you'll easily end up with solder in places where it shouldn't be. Also sensitive components like quartz crystals don't like physical shocks.

Answer 2

With limited equipment, the best approach is often to cut the leads off the diode and remove them individually. This may be the only way to limit damage if the leads are crimped. Diodes are usually cheap compared to board damage.

To actually desolder:

Heat the joint, remove the lead with tweezers, apply generous amount of fresh solder to the pad and employ suckage with the nozzle straight so that it is in as close contact to the board as possible and with the hole directly above the pad hole (but without much pressure, that's an easy way to damage the board). If it fails to clear the hole, clear the sucker, re-apply a blob of solder and try again. If the hole is big enough you might just be able to rap it against the bench with the solder thoroughly melted, but that won't work for holes much smaller than about 1mm.

This technically answers your question, since hacking the leads off does not overheat it, but if you want to be able to re-use the diode after removal you may have to do something else.

Answer 3

Solder wick is great for removing excess solder from the surface of boards, but it's useless for getting solder out of holes. For that you need a suction tool, ideally a heated powered one, though the plunger-based tools do work to some extent.

In general there are four strategies to removing through-hole stuff.

1. Remove the solder and then the part.
2. Remove the part "hot" in one go.
3. Remove the legs of the part "hot" one at a time without destroying the part.
4. Destroy the part and then remove the individual legs "hot".

How well the first strategy works depends very much on the board design. On a single sided board with generously sized holes it can work very well. On a plated-through-hole board with tight holes it's extremely difficult, maybe impossible.

The second strategy can be very effective if you can get the solder round all the legs to melt at the same time, but this can be difficult to pull-off. Solder tends to re-solidify almost instantly on removing the soldering iron.

Having a second person with more soldering irons can help, with two people you can apply three soldering irons and still have a hand free to pull the component out.

There are special solders with lower melting points, which are supposed to make it easier to melt the solder round all the pins at once. (chipquick is one brand), but I haven't tried them personally.

The third strategy can work well for axial parts, though ones with thick legs may be more of a struggle. You can pull on one leg with pliers and let the legs bend to accomodate the fact the other leg is still in the board.

If the parts are low-value then the fourth strategy is usually easiest. With the body of the component gone there is no impediment to removing the legs hot one at a time.