De-Soldering PCB thru-hole with large copper plane - Page 1
Forum section: electronics / beginners

author: jstarr
author_rank: Regular Contributor
timestamp: November 14, 2014, 10:55:47 pm
content: I am trying to sucker desolder two solder-filled large thru holes (had a 1 or 2 watt resistor) on a PCB and my usual PCB point tip solder pencil isn't getting the job done because each hole is on either the big copper ground or 12v power plane and it just absorbs the heat. A larger tip will touch nearby smaller SMD components. I am at 300 C - do I just keep going up in temperature until she melts or should I buy some ChipQuik or other techniques? Any tips appreciated.

author: mikgntl-2013
author_rank: Regular Contributor
timestamp: November 14, 2014, 11:11:09 pm
content: ChipQuik won't help you if you can't melt the solder.What tool are you using? Try to increase the temp up to 350 or/and use desoldering braid instead of the sucker.

author: tautech
author_rank: Super Contributor
timestamp: November 14, 2014, 11:13:24 pm
content: See this recent thread:https://www.eevblog.com/forum/repair/cleaning-up-solder-from-a-stubborn-thruhole/

author: pickle9000
author_rank: Super Contributor
timestamp: November 14, 2014, 11:14:41 pm
content: A preheater is your best friend in these situations.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: November 14, 2014, 11:22:17 pm
content: In general the best way I've found to use a solder sucker [ the spring loaded , trigger type ] is to use a flat sided - long rectangle blade and then after a few seconds put the sucker as close to the board & solder as possible , but facing the hole flat onto the blade of the solder tip and have the tip well tinned .The idea being the most vacuum by holding the sucker flat on the soldering tool flat and drawing the sold onto the solder iron .Not using the sucker to suck direct from the board or component / but again to draw the solder up the tip into the sucker .This works almost as well as a vacuum desoldering gun , sometimes in one shot .I've used this technique to remove all kinds of mult-pin through hole chips & components .

author: JSnyder
author_rank: Contributor
timestamp: November 14, 2014, 11:39:28 pm
content: Quote from: pickle9000 on November 14, 2014, 11:14:41 pm^ This, closing the temperature differential between the copper plane/board and the solder joint even if just a little will make your soldering iron/de-soldering job much more effective. You don't need a special IR board pre-heater unless you’re doing production rework, a hot air station will allow you to uniformly preheat the board before attempting to de-solder.

author: EEMarc
author_rank: Regular Contributor
timestamp: November 14, 2014, 11:58:28 pm
content: Desolder braid requires a higher temperature than melting to work effectively. Preheat is helpful. I don't have a fancy unit so I use a heatgun if needed. Use the largest tip you can with the highest temperature that you can. I use Hakko and Weller tips up to 400C without issue. Try to get the maximum contact area and use as much pressure as you can to help maximize the heat transfer. A little bit of added solder melted to the braid and the hole may sound counterintuitive, but it helps with heat transfer in removing stubborn solder in the middle of the hole. It is important to work fast. Removing the solder on the top makes it harder to transfer heat to stubborn solder in the middle of the hole. This is because the solder help transfer heat and once it is gone, the remaining solder can solidify on you. The key to a good desolder braid is actually a little bit of flux in it. Once it burns off, it no longer works well. Sometimes moving onto a fresh section helps.I sometimes find it easier to remove SMD parts in the way if needed and replace them when the work is done.

author: pickle9000
author_rank: Super Contributor
timestamp: November 15, 2014, 01:10:12 am
content: There are many ways to fudge a preheater. If you do have a hot air then that is a great solution. Preheating can take a while (10 minutes or longer for example) far longer than what most people expect. A toaster oven can work not inside, use the outside top of it as the heat source check the temp to make sure it's not too hot. A chunk of steel plate (1/8 inch) on the top of the toaster oven helps even out the heat. And remember if you are fudging it use a thermometer to make sure you know the actual temp of the board.If you have a couple old computer motherboards kicking around try removing the connectors. That will give you a really good feel for what you need to do.Regardless of what you use to heat the board remember it will cool down fast once removed from a preheater. Thru-hole requires this so you can end up doing some back and forth (reheating to suck a couple more holes).

author: Richard Head
author_rank: Frequent Contributor
timestamp: November 15, 2014, 09:01:43 am
content: Very often two soldering irons with the correct large flat tip works perfectly.Don't use a solder sucker. Just heat up both pins simultaneously with a couple of largish irons and gently pull out the capacitor. It sounds a bit fiddly but works really well with no damage to the board.Forget about using a solder sucker. You generally end up pulling out the THP.

author: mikgntl-2013
author_rank: Regular Contributor
timestamp: November 15, 2014, 11:09:57 am
content: Quote from: Richard Head on November 15, 2014, 09:01:43 amThat's exactly why I suggested the desoldering braid.I usually set my JBC to 350 °C, apply a bit of additional flux on the braid and in a few seconds the TH is nice and clean, no matter how big the plane is.Never pulled out a pad with this method.