Mass Desoldering

[ScuzZ]

I seem to acquire a lot of pre-loved electrical goods, most of which have very usable parts still inside.

Is there anyway short of throwing it all on a fire and retrieving what's left, to de-solder something like the entire PCB of a VCR without having to do each individual component?

 

[dknguyen]

TUrn it upside down and stick it in a toaster-oven that will never be used for food? Maybe shake the PCB somehow a bit while it is inside? Or a hot air blower?

 

[RODALCO]

Use an electric heatgun, heat the tracks and solder pads and hold the board upside down and tap the board.
The components will fall out easily.

 

[picasm]

A hot air gun works well, you can use it with a small nozzle attachment to concentrate on removing the best parts first then do a larger area after with the standard nozzle.

The fumes produced by the board are very noxious and poisonous so do it outside if possible or have plenty of ventilation.

 

[ScuzZ]

Well I know what I have on my shopping list.

Does it have to be a very hot, hot air gun? Or just one that is used to strip paint?

 

[picasm]

Does it have to be a very hot, hot air gun? Or just one that is used to strip paint?

Mine is just a DIY type intended for paint stripping. It has two heat settings (I use the hottest setting).
It came with a nozel attachments accessory kit intended for various paint removal jobs which is really useful, although I suspect this is not standard with the cheaper ones.

 

[justDIY]

I have another vote for the paint stripper gun - it works great.

Keep the gun moving at all times, especially once the solder starts to melt. If you pause too long, you'll start to burn the board, and that smells very very bad.

 

[Andy1845c]

I have never got the paint stripper gun method to work. I have a fairly decent one, gets pretty hot, but I can't get it to work to de-solder. It just makes the board smell bad

I have saved alot of components from vcr and stereo board by clamping them to the edge of a work bench and using a small brazing tip on my acetylene torch to heat an area and tapping the board with a hammer to shake the parts out. As others have said, the smell is awful and this is best done outside.

Is it really worth it though? I used to save everything. Now I have accumulated so much stuff i'll never use that I just grab things like heat sinks and switches.

1/4 watt resistors are so cheap I don't find them worth saving. Plus they are so hard to work with when the leads are clipped.

Electrolic Capacitors can be hard to save also, as they often are glued as well as soldered on a board. The leads end up so short they are hard to use, and if i'm not mistaken, they do dry up over time, so a cap out of a 25 y/o stereo might not be too prime anymore.

IC and semi conductors you find in mass manufactured goods seem to often have in house part numbers on them, making datasheets hard to find, and even when I can identify one, chances are its so special, its of no use to me.

Ceramic caps are cheap too, so I don't often save those anymore either.

Seems to me there was a pretty good topic on this subject about a year ago. If you search i'm sure you will find it.

 

[ScuzZ]

I've always been in two frames of mine when coming to 'recycling' parts..

1. The parts are old and there lifespan maybe be significantly shorter than buying new.

on the other hand,

2. When I'm prototyping, I figure most of my designs won't last very long anyway (not from poor design, but I'm still learning so I'm always changing things) therefore why buy new parts to learn on?

And I also hate seeing working components go to the rubbish heap. I don't mind spending a few hours of a weekend desoldering bits, just looking for a quicker way to do it.

 

[futz]

I use a propane torch (big pro model - I'm a plumber). Take it outside. This makes a mess and lots of smoke. A slightly breezy day and working downwind is best so you don't breath so much of it. Wear old clothes as you'll be wearing some solder. This destroys the boards, so don't do it with anything you want later. Also, don't do it over your nice sidewalks or you'll have to clean the solder off after. But do do it over an area where you can find all the tiny parts later (not grass). Ok, warnings over. On to the fun part.

Hold the board parts side down, heat areas with the torch and whack the board with a pliers or something when the solder is just melty. Almost every part just jumps out and falls on the ground. Don't whack on the pins or those parts likely won't come out.

Some cleanup is needed later on the parts. They'll have some leftover solder on them.

I sometimes do this with old computer mainboards that have nice connectors. They can be pricey to buy new sometimes.

Doing this with your average piece-o-crap consumer-level pencil tip propane torch is going to be slow going. You really need to get large areas of the board hot (but not so hot that you damage the parts) all at once or you'll be bending lots of pins and being very frustrated.

 

[Boncuk]

Hi,

I am using a stainless steel pot with heating underneath and around the pot. It is filled with plumber tin just to a level so the liquid tin doesn't flood the PCB to be desoldered. Shortly before the desoldering I use some drops of flux.

I use manual temperature control wiht a light dimmer and bricks for heat insulation in an aluminum frame work.

Putting the board into the "soup" all parts are desoldered very quickly and evenly. Even ICs with many pins are easily removed with a tweezer.

If you do the job careful you won't even burn plastic parts like connectors. Except for the old PCB that's 100% recycling.

I've tried many ways, also using a heat gun. There will never be the same temperature over a big area to remove parts as quickly as possible to prevent damage.

Regards

Boncuk

 

[crusty]

Anyone ever try to recycle a PCB? scrap the traces off, and put your own down?

 

[Andy1845c]

haha, first circuit I ever made was a astable multivibrator, the two transistor kind. I salvaged all the parts from an old tape deck, and cut a square of its PCB, sanded the traces off and used some existing holes and drilled some of my own to mount the components and then hand wired it. Talk about crude!

I don't know how you would put down your own traces on a PCB though, seeing as you normally start with all copper and etch away what you don't need.

 

[stevez]

I used propane torch and compressed air to blow the solder off - about the stupidest thing I've done in a while. It worked well in terms of solder removal but the risk and mess arent' worth it.

For persons with some skill and experience, parts scavanged from electronics products can be a good source of supply. The risk of a recovered part having a fault is somewhat higher than one might expect from a new part. For those who don't have the experience to recognize faults it might be wise to consider the use of known good parts until you have the experience to work thru troubleshooting that might otherwise be a great source frustration.

For the beginner with little money to spare, salvaging parts isn't out of the question - just might take a little more work. Lots of parts are relatively easy to test - at least a basic test that will identify a completely failed part. My DMM has a transistor tester/lead identifier feature that's pretty handy. I don't know how reliable the test is but it would seem that a really bad device would be apparent. I've seen a number of capacitor and inductor "measuring" devices that are relatively simple to construct - again, may not be highly reliable tests but it's better than nothing.

 

[Nigel Goodwin]

haha, first circuit I ever made was a astable multivibrator, the two transistor kind. I salvaged all the parts from an old tape deck, and cut a square of its PCB, sanded the traces off and used some existing holes and drilled some of my own to mount the components and then hand wired it. Talk about crude!

I built a valve amplifier years ago when I was a kid, a guy who lived up the road drew me the circuit, and also gave me a mains transformer (as it was a part I couldn't get from the tip). The circuit used an EF80 preamp, a 6BW6 output valve, and a metal rectifier.

I wrote a list out of all the parts I required, including writing the colour code for each resistor, and went to the tip and searched old dumped TV's for all the parts I required (including valve bases).

For a 'chassis' I got a piece of hardboard off an old kitchen cupboard (on the tip), I seem to remember it was a yellow colour?.

I cut holes out for the valve bases and screwed them in place, and drilled holes for either end of every component, inserted the ends through, and bent them over to stop them falling out. I then soldered wires between all the components, and the valve bases, under the board - rather like a crude 'PCB'.

For layout I basically followed the circuit as he had drawn it, and it worked first time!

For a 'cabinet' I found an old small leather suitcase at the same tip, I mounted the 'board' in that, and cut a rectangular hole in the lid, and fitted a speaker and grill (from the tip) in that!.

I think I've still got the old suitcase somewhere, but I've no idea what happened to the insides? - it was over 40 years ago.

As kids we spent most of our days at the tip, great fun - riding old bikes with no tires and no brakes down the 1 in 6 hill that was the main road through the village! - or making carts with 20 wheels, and fifteen kids riding on it down the same road!.

Makes you wonder how you survived? - I'd kill my daughter if I thought she did half of the silly things I did.

I don't know how you would put down your own traces on a PCB though, seeing as you normally start with all copper and etch away what you don't need.

You used to be able to buy self-adhesive copper strips for just such an occurance.

 

[atferrari]

I recall an article explaining how to use oil at high temperature and the PCB inmersed upside down for the components to free themselves. Fire precautions where stressed.

I personally have used recently a vacuum desoldering tool Denon 7000. The secret is patiently pre-heating the whole PCB. Components come out EASILY.

I used the kitchen until I got a nice heating gun making my life much easier.

Before that my success was almost null.

 

[Boncuk]

Anyone ever try to recycle a PCB? scrap the traces off, and put your own down?

I said except for the PCB everything else is 100% recycling. The PCB will have to go to special junk. Sorry don't know the correct english term.

In german it is called "Sondermuell".

 

[Boncuk]

sanded the traces off and used some existing holes and drilled some of my own to mount the components and then hand wired it. Talk about crude!

I don't know how you would put down your own traces on a PCB though, seeing as you normally start with all copper and etch away what you don't need.

Hi Andy,

good to know that there is somebody who has the patience to desolder two parts of a board and use the present traces to make a new circuit.

However we're talking about mass desoldering!

Making a PCB everything has to be in the right place and function properly. Using one which was already used for another purpose won't look tidy.

Of course I etch away all the copper I don't need. A wood carver for instance, who wants to make a statue of a dog, cuts off all the wood which doesn't look like a dog.

Boncuk

 

[mneary]

I made my first CP/M (Z80) computer entirely from salvaged IC's. Wore out one solder sucker. About a hundred chips in all, only a few were bad. I also salvaged discretes, but I purchased most of the capacitors.