1
\$\begingroup\$

Hi I have a flow soldered board with some very big capacitors on it. I was hoping to get them off but when I looked it has a very large ground plane. I was unable to get these capacitors off because it heated up the surrounding board. When I attempted to pull them off even after the solder looked like it was melted and I sucked it off. Once i did this and pulled on the cap it pulled the leads out of the cap. Do you guys have any ideas thanks

\$\endgroup\$
  • \$\begingroup\$ "flow soldered"? Do you mean wave soldered? \$\endgroup\$ – stevenvh Sep 4 '11 at 8:15
  • \$\begingroup\$ yes sorry it was a mistake \$\endgroup\$ – Not You Sep 4 '11 at 12:33
3
\$\begingroup\$

Large ground planes, or any large mass of copper make soldering/desoldering more difficult. You may want to look at getting a better soldering iron that can automatically sense load and adjust power to keep the tip at set temperature (e.g. Metcal, Weller, etc)

However desoldering with "standard" irons is usually possible, you just need more time/care taken. Good solder wick and some liquid flux is invaluable, get some of both if you have none already. Flux generously, use the solder wick to remove as much solder as you can (often with care enough can be removed to free the lead with no further heating, but almost always a little remains however you remove it) from both pads, then if any remains, heat the pad until solder is melted, then wiggle component gently and lift that side slightly, do the same with the other side to bring level, and repeat till you gradually work the component out.

One "trick" if solder will not melt due to too much copper is if you have another iron, you can try using two irons on the same joint (may need someone else to hold the other iron) but this is rarely necessary, and certainly not an alternative to getting a decent iron.

As SubZero says, if the leads come out you are certainly pulling too hard - with some components this happens more easily when they are hot, so a heatsink clamp on leads (e.g. pliers, which can be used to pull lead gently and avoid stress on body, or a dedicated clamp can be bought) is sometimes a good idea if possible. With patience pretty much anything can be removed. If you are planning on doing this a lot follow his advice about the hotplate and heat gun (soldering type, not paint removal type)

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ Thanks guys but I have a stain glass Lead iron I will try that I guess. \$\endgroup\$ – Not You Sep 4 '11 at 12:32
  • \$\begingroup\$ I have alredy tried keeping the soldering iron on it for about 10 minutes and it didnt help \$\endgroup\$ – Not You Sep 4 '11 at 12:40
2
\$\begingroup\$

If your breaking anything your probably doing it wrong.

What I would suggest is getting a pre-heater, you can even build one yourself. You didn't provide enough information as to why/what you need to remove or if you need the PCB Intact or are just getting used parts for other projects.

If your just gutting components get a hot air gun and be quick, or cut the board into multiple pieces thus allowing the heat to heat up a smaller area. It really depends on how much work your willing to put into it. Such as when I have a gigantic monitor PCB I sometimes cut the PCB up into smaller pieces so it will fit in my holder to desolder.

As for the pre-heater you want something like this: http://mightyohm.com/blog/2009/01/diy-pid-controlled-soldering-hotplate/

It's a PID (Proportional Integral Derivative) hotplate, You can use it to heat up the entire board to a temperature below solder melting and then use a heat gun/desoldering tool to remove the components.

And as I said if your pulling the leads out your either pulling too hard (Most likely), your iron isn't high power enough, or possible internal damage which you would not want to use in future projects anyway.

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ +1 for pre-heater. You won't believe this distance it makes for large ground planes. \$\endgroup\$ – mbrig Jul 20 '17 at 21:51
1
\$\begingroup\$

You need an iron that can dump a lot of heat into the joint quickly without overshooting - Metcal MX irons, with a large tip like SMTC-117 are perfect for this and can easily handle large groundplanes in a couple of seconds. If it was originally soldered with leadfree, flooding with leaded solder will also help.

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

http://www.msed.nist.gov/solder/NIST_LeadfreeSolder_v4.pdf

This has some great info if you can understand it. So you have huge ground planes, you want to add a solder that is lower in thermal conductivity to the top of your joints, just makes sure it is melted and the joint has been wel

Liquidus -temperature -Contactangle- Wetting rate -Surface Solder tension

Alloy -(ºC) -(deg) -(dyne/ sec) -(dyne/ cm)

1Sn-58Bi 138 43 350 300 1Sn-2.8Ag-20In 114 (low-temp. peak); 178 (primary peak) 44 650 390

theres also this one to try with similar to lead based Low melt P but also high density slver

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

If the bottom of the PCB doesn't have a lot of components, you can try using a hot plate to heat up the large copper area. If you don't have a hot plate, use a baking pan and some sand. Yeah, that's right, sand. It's commonly available and conducts heat extremely well.

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

For a long time now, I have successfully used a big cheap 100W hardware store soldering iron, to desolder large components. I have not yet meet a component or a ground plane so large this iron can not handle. Also with a big iron the heating time is much shorter and the component suffers less damage (for example connectors with temperature sensitive plastic on it).

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ By big you mean 'high wattage'? The bigger the tip the longer it takes to heat up \$\endgroup\$ – Voltage Spike Jul 20 '17 at 22:35
  • \$\begingroup\$ Both big 1cm width tip and high wattage, 100W. The more mass the tip has, the faster it can release it to melt all tin. Bigger tip melts large ground plane tin faster than small. More heat transfer. \$\endgroup\$ – user2604188 Jul 21 '17 at 19:21
0
\$\begingroup\$

You can also try an 858D hot-air rework tool. Ebay for lots of links. Put the large nozzle on it, crank up the air, and go in circles around the whole area to be desoldered, working the heat towards the cap in question. Once hot enough and with lead-based low-temp solder in the joints to "contaminate" them, the cap should just pull right out (gloves might be an idea, it'll be hot!) The 858D is about 700W - far more heat power than even a large iron can provide. I've done this with very stubborn terminal strips in multi-layer PCB's. Invaluable tool for today's repairs.

| improve this answer | |
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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