3
\$\begingroup\$

I've just bought new 30W soldering iron and now that I'm home, I've tried to desolder few capacitors from my MBO. Anyway, I've turned the soldering iron on, waited few minutes for it to heat up and then put the tip to the part I wanted to desolder. I was amazed - nothing happened !! Well, after let's say 30 seconds (I know, that's too long but I didn't get anything e.g. smoke or something and the capacitor didn't heat up because I was holding it on the other side) I've managed to somehow desolder it ... But now I have solder in holes, and I thought well, that's no problem.

I've used this technique: Pic

but unfortunately, this doesn't work. I can't melt remaining solder (in the holes) by applying tip of soldering iron to the one leg of capacitor. Actually, I don't think that I can do anything with this soldering iron ...

Is there something wrong with it or with how I am using it ?

Thanks !

\$\endgroup\$
  • \$\begingroup\$ Didn't tin the tip perhaps? \$\endgroup\$ – Olin Lathrop Jan 16 '12 at 13:48
  • 1
    \$\begingroup\$ The bit might be too small to transfer enough heat. What size is it? Some cheap irons are a waste of money, what have you got? \$\endgroup\$ – Leon Heller Jan 16 '12 at 14:38
  • 1
    \$\begingroup\$ Get a decent one! I use a second-hand Metcal system that cost me about $150. \$\endgroup\$ – Leon Heller Jan 16 '12 at 22:20
  • 2
    \$\begingroup\$ @LeonHeller: Well, I would love to buy something more expansive and better than what I have, but currently I don't have money for something professional, and I won't be using it every day (more like 10 times a year for some DIY projects when I find some free time) ... \$\endgroup\$ – xx77aBs Jan 16 '12 at 22:41
  • 1
    \$\begingroup\$ Just a thought: if that's soldered to a ground plane you'll have hard time desoldering it with your iron. Ground plane would take away lots of heat (plus add lead-free on top of that - just won't happen). \$\endgroup\$ – Mihailo Jan 17 '12 at 10:48
6
\$\begingroup\$

First of all: modern PCBs use lead-free solder. It has a higher melting point and a different "look" when solid. Sometimes it helps to apply a little bit of lead solder to get a better heat transfer between the soldering iron and the solder joint. After the whole soldering joint is molten, I use a vacuum plunger ("solder sucker") to remove bigger amounts of solder. Remove the soldering iron to avoid overheating the component.

Then (the component wire is still in the hole) I use some quality brand desoldering wick: I place the desoldering wick in such a way that it has a good contact to the solder joint, and then press on top of the wick. This way the wick has a good contact to the solder joint.

About heating up the capacitor: It may well be that you overheated the cap, I'm not sure if the metal case is has a good thermal coupling to the contacts.

\$\endgroup\$
  • \$\begingroup\$ Thanks ! That MBO isn't really modern (it's like 10 years old), but it could be that it uses lead-free solder. After adding my own solder to the joint, it actually melts faster (few seconds).It seems that I'll need to buy vacuum plunger and desoldering wick ... But do you have any ideas why I can't solder like in the picture ? I must put solder on the tip of the soldering iron - then it works. But when I try just to head the wire and put the solder on the joint, nothing melts. \$\endgroup\$ – xx77aBs Jan 16 '12 at 21:47
  • \$\begingroup\$ @xx77aBs: Thats because the contact area between the tip and the component wire is too small. I don't know what kind of soldering tip you use and how you position it. Adding your own solder (with a lower melting point) builds up a layer of molten tin witch conducts heat very well (as well provides some fresh flux). Note: You might want to spend some more money on your equipment. I bought a temperature controlled soldering station that I like more than my brand name soldering iron. \$\endgroup\$ – 0x6d64 Jan 16 '12 at 22:17
  • \$\begingroup\$ @ox6d64: I don't know what kind of soldering tip it is. I put the point of the tip to the wire ... I'll try to make more contact area. \$\endgroup\$ – xx77aBs Jan 16 '12 at 22:43
  • \$\begingroup\$ @xx77aBs: I avoid using the point of my tip, as it is quite pointy. Usually there is enough space to use the side of the tip, somewhat similar to these pictures: embeddedengineer.wordpress.com/category/project/… \$\endgroup\$ – 0x6d64 Jan 16 '12 at 22:57
  • \$\begingroup\$ @ox6d64: Ok, I'll try that next time ;) \$\endgroup\$ – xx77aBs Jan 17 '12 at 0:31
7
\$\begingroup\$

The solder needs to be melted and physically removed while in its molten state. Applying the soldering iron tip it will only melt it, you need something else to remove it.

Use a "solder sucker" for this job. It is a small spring loaded vacuum pump designed to, well, suck solder away from a joint. You can get them from any electronics hobby shop.

enter image description here

First, apply heat to the joint until all the solder is melted. Next bring the tip of the solder sucker right up to the joint and release the plunger. The final result should be that most of the solder is gone (some will be left behind but that is usually ok). take your iron and lightly push on the joint until you feel the lead loosen, then move onto the next joint. If a small amount of solder remains and you can't loosen the joint, apply more solder and use the solder sucker again (you need an amount of solder on the joint for the solder sucker to work).

\$\endgroup\$
  • \$\begingroup\$ Thanks for the answer :) I'll try that when I get vacuum plunger. Do you have any idea why I can't solder like in the picture I've included with my answer ? I'm trying to tin the tip, but I'm not sure if it's done properly ... \$\endgroup\$ – xx77aBs Jan 16 '12 at 21:48
  • 1
    \$\begingroup\$ @xx77aBs For small components that have a small amount of solder on them, I found these suckers to be rubbish. The wick is much better. You do need to learn to use it though; for example, it has flux on it that, once evaporated, makes that part of the wick nearly useless. \$\endgroup\$ – Roman Starkov Jan 18 '12 at 12:42

Not the answer you're looking for? Browse other questions tagged or ask your own question.