Maybe lucky, maybe not - salvaging

[Mark Hammer]

Went to one of my favourite haunts yesterday, that deals in recycling all the tech crap in the region.  In a large cardboard box (and I mean *large*, you can fit 4 or 5 people in it) were boards yanked from busted monitors and similar equipment.  One of the boards I spied seemed interesting so I yanked it out.  Bingo!  A trio of MC1496 balanced modulator chips, and an SSM2210 matched NPN pair (low noise for high quality VCAs and filters), plus a ton of BC547s, electrolytic caps with leads long enough for recycling, and a bunch of other passive components.  Three bucks let me take it home.  Still don't know what it was from, but it was a sweet deal for what's on it.

I started trying to unsolder the chips, but despite my own usually reliable advice to others, no go.  Even WITH adding a bit of extra solder to the leads, my solder-sucker still could not remove everything that stood in the way of me re-using the chips.  Unfortunately, this baby is double sided and most of the component side is ground plane with ultra-thick copper.  It would seem that at least one pin of just about every desirable semi in there is nicely adhered to the ground plane.  Normally, with double-sided boards, a little extra bit of solder is sufficient to spread the heat better and  flow the solder on both sides.  In this case, the huge ground plane sinks all of that heat on the component side so the relevant pins never seem to loosen.

Although I usually have good fortune with a solder-sucker, I suspect this may be a situation for solder-wick.  Perhaps tomorrow I'll see if I can score some.  Conceivably, I may have to carve away the ground plane and form a "moat" around the components so that the heat from the iron stays localized enough to flow the solder on the component side.  For now, my "good fortune" taunts me.

[R.G.]

I have had some luck with removing chips by a mass-destruction method in the past.

I rigged my propane torch to have an exhaust about 1.5" wide. I clamp the PCB in a vise, hold the chip with a chip puller in my left hand and wave the propane torch --gently-- over the bottom area of the chip on the solder side while pulling gently with my left hand. At some point, the chips leads all get hot enough and it blips out in my left hand.

Note that this usually burns and destroys the pcb, so it's not good for repairs, only getting chips off a board you can throw away.

[ExpAnonColin]

Very interesting method, RG  Too bad I have no torch.

Mark-what kind of solder-sucker are you using?  I've been looking for a while for a pump attachment for my soldering gun because I'm convinced it will work better than a solder sucker.

-Colin

[petemoore]

I've never tried this on chips but...for pots or switches that have numerous pins soldered into the PCB, trimming the part out sith wire cutters, the cutting each pin it's one piece of PCB to be then removed with the soldering iron and steady pulling pressure...
 Perhaps a dremel could cut between the pins and save them from the bending that occurs when the wire snips blades spread the PCB pieces apart as they cut.

[Ge_Whiz]

If you haven't got a propane torch, an electric hot-air paint stripper will do just as well, and they're not expensive (well, not this side of the pond, anyhoo). The pcb itself will protect the devices from damage.

[toneman]

Removing parts from gnd-planed pcbs can B difficult *even* with a
good de-soldering tool.
Now, i'm not talking about the spring-compress-then-release "extractors",
or the "bulb" type.  These only work on "simple" pcb, and in a lot of
these cases, U can destroy the pcb, or, at minimum, lift the pad/trace.
As 4 solderwick,  4 removing parts, not a good thing.
If U don't have a de-soldering station, the suggestion for cutting the
pcb with the part on it is a good one.  Usually when i have 2 remove
an IC for an engineer, i ask him/her, "do U want to save the pcb,
or the IC?"..usually they want 2 save the pcb, and install a different
IC.  In your case, destroy the pcb 2 save the IC/component.
Solderwick works 4 removing excess solder from pot lugs.  I also use
it for the large surface-mount components.  After the component is
removed, i use solderwick 2 remove excess, left over solder, to make
the pads smooth for the new SMcomponent.
After U have the small section of pcb removed, hold the edge in a vise.
Then, allign your sucker with the pad.  Then heat pad up from opposite
side.  Tin your iron first, cause that will create a heat-bridge to get the heat 2 the pad quicker.  Sometime it might take 3 hands.
In all cases, when desoldering a component, ocassionally feel the part
with both fingers(pinch).  If U can still touch it, U probably used an OK
amount of heat.  Desolder 1 pin at a time, and feel the part and wait
for it 2 cool B4 U try again.   yes, U can blow on it.
I use a PACE2000 solderstation @ work, but the machine has everything
but brains.  I supply that along with experience.
tone

[Gilles C]

Talk about massive unsoldering...

http://www.qsl.net/iz7ath/web/02_brew/14_howto/04_rec/

Does it look like you Mark?

http://store.allstainedglass.com/solderwick.html

That's also what I like to use.


Some good info.

http://www.hillinstruments.com/electronics1.htm

[Phorhas]

But, is that REALLY WORTH all of the effort? does it save that much money?
- or is it just good for getting special parts?

[Paul Perry (Frostwave)]

, and feel the part and wait
for it 2 cool B4 U try again.   tone

Whenever you use you finger to see if a chip is hot, use a WET finger, because I find that if the chip is REALLY hot, I can hear the hiss & jerk it away befire I feel it. How do I know to do this? :oops:  :oops:  :roll:

[sirkut]

Heatgun is amazing for this sort of work. I have boards where everything on it just about is usuable for one project or another, it's a little messy with solder splatter on the components but I've never damaged ANY chip yet. Only needs a few seconds, tap it out, hell sometimes they just fall out! Give it a whirl.