Hi all,
Anyone got any tips on how to avoid the unpleasant situation where you try to de-solder a part on an elderly board and end up removing more than just component leads? Most of the stuff I work on is at *least* 25 years old and things start to get fragile.
thanks
Preheat the board before desoldering and apply some liquid flux. Make sure to use *enough* heat as too low is just as bad as too much. You want to reduce the time it takes to finish the process more than anything.
Tip on a more powerful iron?
-- Adrian C
Been using this one professionally for years.
-- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
I used to service scopes and DVMs and other testgear in the service department of the manufacturer. At the time they did not use surface mount so any duff IC, transistor, diode etc had all its pins cut on the top of the board then each pin removed individually (using spring loaded solder sucker or vacuum device depending if in field or not).
At least you don't need fume extraction as no throat-grabbing noxious PbF stuff. Go around each blob with fresh multicore solder, heating just enough to introduce some new solder, but no great depth. Then long nose pliers on the other side of the board and as much tug as you can give, while reheating the solder. Repeat for each pad.
Then when finished, a needlepoint (steel ,not S/S needle set in a pencil or something as a handle) set point in the hole , heating the needle with soldering iron while pushing through pcb and waggling , to give good clean h
Add fresh solder and liquid flux, then solder suck or use braid.
old solder has oxides and crap on it and is a poor heat conductor, so you you can end up burning the pads off the board if you fight with it too long. Cutting Leads off the part can help too if they were wedged into the holes.
My advice tends to go against conventional wisdom and some of the other advice in this thread. The problem is that you're delivering too many joules for too long a time (Joules = watt-seconds). To avoid problems, you have to work fast. You can get the joint as hot as you want, but not for very long.
Therefore, I suggest:
I'm undecided if hot air desoldering is any better than a soldering sucker for through hole parts.
Conformal coatings such as urethane or acrylic, will either burn or vaporize before the solder melts. Using these to glue down the pad doesn't seem to work for me.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I'd add to that; make sure the end of the lead isn't bent so it struggles when you try to pull it out.
Although its my preferred method, I'm reluctant to recommend a piston type solder sucker because the recoil can knock pads off if you're not careful. Conversely; solder wick has to be kept hot while you pull it away, or the pad/track comes with it - which doesn't really help with keeping the heating to the shortest time possible.
Sometimes you have to remove the solder to inspect the end of the lead, and straighten it if required. All I can suggest is; use the method you're most comfortable with.
A single sided board is dead easy if you remove the solder, through hole takes a little more effort. Some manufacturers do sucker irons where the tip is hollow and has a receptacle for the waste solder, the expensive ones with an electric pump or the cheaper type with a rubber bulb next to the handle. It almost never removes *ALL* the solder from a through hole, but you can usually wiggle the lead free with pointy nose pliers.
In most cases more solder and the flux that comes with it is added to improve heat flow - in the case of RoHS solder, adding some 60/40 lowers the melting temperature.
I constantly am working on boards that are from the 1970s. Mostly I use a #7 tip on my Weller solder station, and a Soldapullt (sp?) solder sucker. Take great care not to push down on the solder pad, press the tip sideways. Do NOT let the solder sucker strike the tip when sucking the solder, but keep it on a 45 degree angle away from the tip, with its tip resting on the PCB.
Have the PCB well supported if possible so it doesn't bounce.
John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
OY! It depends a lot on the quality of the board, and then how much heat it has been exposed to, over its life.
If the chip is no good, I scribe the leads with an X-acto knife, running down the whole row, and then JUST BARELY snap the leads off from the body. You only have to do this on one side of a SOIC. Then scribe the other side and bend the IC up and down a few times, until it breaks off completely. Then, the individual leads can be removed in a much more gentle fashion. Avoid pressing down on the pads, they will tend to "crumple" and the edges pull up from the board.
Since you say OVER 25 years, I'm guessing none of this is SMT? If it has plated through holes, these generally are quite robust. The worst are some old paper-phenolic one-sided boards. You just look at them and the pads start coming off.
There are mass desoldering tools for DIP and SOIC standard sizes that work pretty well to melt the solder on all leads simultaneously. These work great if you have the right size. I've even made some custom ones out of solid copper bar when I had a bunch of chips to pull.
And, of course, a temperatur-controlled soldering iron, run at the minimum temperature possible, is a big help.
Jon
These work, but if you have ever used a Pace desoldering station with either a vacuum pump or a venturi suction generator, you will be AMAZED at how much better a job it does. These have a hollow copper tip, so you can keep the tip on the joing while it applies the suction. You apply the tip, wait a few seconds and then wiggle the tip in an orbiting motion and step on the pedal. When the slurping sound stops, all the solder is gone, let up on the pedal and remove the tip. There is no big reaction from a flying piston as with the plugner-type solder puller, and you get enough suction time to get ALL the solder out of the joint.
(Other brands of pump-type desoldering irons are probably just as good, but I happen to have Pace brand gear.)
Jon
A Swan & Mortem scalpel is a little more precise for the smaller ICs, Usually I shear the pins off at the header - but you have to be careful not to slice tracks underneath.
With the old standard pitch DIL packages, a decent quality pair of side cutters were sufficient to nip the pins off flush with the header.
I HAVE a Pace Desoldering station (actually two of them) - however I am usually just removing one or two ICs and I can remove them with my Weller (#7!) and Soldapullt faster than the Pace will heat up!
You can get a nice rhythm going where you heat two leads at the same time (medium tip) and suck both together, then while the next pair are warming up you are reloadng the sucker with your other hand. I can pull a 40 pin chip in a minute or less typically (not that I ever time myself, it just seems to go pretty fast.).
Once the legs are unsoldered I then use a tiny screwdriver to push the bottom leads back and forth across the feed through hole. If it appears to be stuck I put a dab of solder and resuck. Then I press the bottom of each leg on the top side where they meet the PCB to again loosen them up. At this point the IC usually pulls out with my finger tips. Prying with any force at all means something is wrong...not to mention it yanks out feed through pipes!
If I am reworking a bunch of chips then the Pace is heated up. It is slightly better as you can put the tip around the IC's lead and swirl it from side to side as you heat it up, to feel if it has released, prior to suction.
John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
Yes, this is absolutely true! But, for something really expensive, or where I have a lot of pins to desolder, I take the time to warm up the Pace, and always get GREAT results. Usually the part just falls off the board when the last pin is desoldered.
With the Pace, and the technique of orbiting the tip while applying suction, I RARELY have this happen. Usually, I desolder the whole chip and it just falls off the board. That wigglign back and forth can damage the plated barrel of the hole.
Jon
Has anyone ever used pressure to blow away solder? I'm thinking that
125 psi through a tiny nozzle would clean out the solder better than a spring loaded solder sucker.Though I guess that it might send molten solder where you don't want it!
Bob
It WILL send it all over the place. Nice way though to destroy a board.......
When you are 'orbiting' I take that to mean that you are applying side pressure to the leg of the device to move it far enough away from the walls of the tube that the solder is removed completely and the leg has no sticking point to the tube. That is the same process I use.
I just like using the Soldapullt, it is faster and when done with a bit of experience (35 years in my case) gives very good consistent results when extracting one or two ICs at a time. I train students to use the Soldapullt in under a week - give them some bunged up boards to learn how to remove parts without damaging the parts or the PCB. They learn quickly and most can do a good job with only a day or so of practice.
When they get good with the Soldapullt I then train them on the Pace!
John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
I tried that once on a board that was hopeless and marked for "spare parts" only. When blowing from the bottom side, the ICs would come out full of solder residuals on the bottom side (cleaning required a longer time than using a proper desolder method). When blowing from the upper side (IC side), the action was not so effective in removing all the solder from the hole and anyway the solder residues were blown everywhere in the bench. In short, I've never tried that again.
Frank IZ8DWF
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.