Stripping circuit boards with a solder bath

[Vincent]

Anyone ever gave it a try?

I did. It's terrific! 

As I don't have an actual solder bath heater, I filled a steel cup I removed from an old loudspeaker with scrap solder that I accumulated since the beginning (then topped off with a roll of plumber tin), and put the whole thing on a standard hot plate, with a metal plate inbetween.

I went through a certain learning curve (dealing with the radiated heat, order of components removal, dipping times and cooling periods inbetween, etc.), but now I can strip a computer power supply of most of its components under 30 minutes! I do pull a few resistors and diodes if the leads on the solder side are straight, making them easy and fast to grab with tweezers one after the other, but I don't waste too much time on E12 resistors and 1N4148s LOL.

Here's what I've got in roughly 5 hours of work:




It may not look like much, but keep in mind that the metal pan in both pictures is filled with very small parts tightly piled together! 

The resulting stripped boards:



And that's just the beginning. I have well over a hundred pounds of circuit boards to process. That's an enormous potential supply of very cheap parts. Of course I wouldn't use them for HiRel projects. In such case I'd order new parts. But for the rest, I'm almost worse than Uncle Scrooge, so these are all parts I don't have to buy!

[whitevamp]

cool idea i kinda thought about something like this as well. as i have been / in the process of doing the same thing, but wasn't sure if it would work or not, now i know it will. ill have to give it a go.

so just put enough solder in the pan to cover the bottom and then stick the board in and then start pulling the components out?

[Vincent]

cool idea i kinda thought about something like this as well. as i have been / in the process of doing the same thing, but wasn't sure if it would work or not, now i know it will. ill have to give it a go.

so just put enough solder in the pan to cover the bottom and then stick the board in and then start pulling the components out?

Sure, give it a try too! It's pretty much the only way to go for a large volume of (through-hole) components. Hot air would be my second option, especially for SMD parts. Many of my circuit boards have some, so I'll need an hot air station to remove those parts before taking the boards to the solder bath.

As for the amount of tin, I'll save you some time (and tries): make sure you've got enough of it! I'd melt at least a pound to be sure. Otherwise the thermal mass is too low and the tin drops too much in temperature when the board is dipped in it. The tin will stick to the board instead of melting all the solder joints at once.

I plan to make a video about this soon. It'll probably explain the thing better than words would. 

[Vgkid]

I look forward to the video. Do you need to apply any flux? I don't think you would need to.

[whitevamp]

looking forward to the vid. 

[mariush]

This one's a classic :

[T3sl4co1l]

Great!

Now you've got tons of parts to make more 3.3-5-12V 100-500W switching power supplies!

What will you build next?

(Needless to say, yes... I have some cynicism about stripping parts obsessively.  That said, perhaps your next adventure will involve stripping and rewinding those transformers and inductors -- you can make supplies with different output voltages, at least.  Maybe even, say, a class D amplifier.)



Tim

[batteksystem]

Anyone ever gave it a try?

I did. It's terrific! 

As I don't have an actual solder bath heater, I filled a steel cup I removed from an old loudspeaker with scrap solder that I accumulated since the beginning (then topped off with a roll of plumber tin), and put the whole thing on a standard hot plate, with a metal plate inbetween.

I went through a certain learning curve (dealing with the radiated heat, order of components removal, dipping times and cooling periods inbetween, etc.), but now I can strip a computer power supply of most of its components under 30 minutes! I do pull a few resistors and diodes if the leads on the solder side are straight, making them easy and fast to grab with tweezers one after the other, but I don't waste too much time on E12 resistors and 1N4148s LOL.

Here's what I've got in roughly 5 hours of work:




It may not look like much, but keep in mind that the metal pan in both pictures is filled with very small parts tightly piled together! 

The resulting stripped boards:



And that's just the beginning. I have well over a hundred pounds of circuit boards to process. That's an enormous potential supply of very cheap parts. Of course I wouldn't use them for HiRel projects. In such case I'd order new parts. But for the rest, I'm almost worse than Uncle Scrooge, so these are all parts I don't have to buy!

I have concern on what temperature you are applying and how reliable the retrieved part can be.

[obiwanjacobi]

I usually use a paint stripper... 

[Gyro]

That looks scarily close to the way 'new' parts are sourced in China for selling on ebay! 

Of course you're not properly following through with the more hazardous solder and gold recovery steps. 

[TerraHertz]

This is probably how 'that guy' began his collection:
   https://www.eevblog.com/forum/buysellwanted/free-(aus)-world's-largest-electronics-parts-collection-as-seen-on-eevblog/
   https://www.eevblog.com/forum/buysellwanted/free-(aus)-world's-largest-electronics-parts-collection-as-seen-on-eevblog/msg954886/#msg954886

And I have to say, some of that collection is pretty... mad. I began to wonder if he had serious lead poisoning or something else well past OCD. Still on the whole it's lots of fun.

But I can't criticize. I too sometimes do parts removal from boards. Except more for relaxing basketwork kind of reasons, knowing I'm very unlikely to ever use any of the parts.
Here's pics of the most recent example - some old PC power supplies that I wanted to get rid of. An afternoon's leisure, using only an iron and for things with more than 3 leads, a solder sucker.
I wash my hands and clean the work area very thoroughly after this kind of thing. Lead solder dust everywhere. Solder pots are even worse, for the amount of lead oxide powder they make.

Anyone had any luck dissolving the lacquer used to seal the ferrite core transformers? Without decoating the wire or ruining the plastic coil formers. It would be nice to be able to reuse these.

I have concern on what temperature you are applying and how reliable the retrieved part can be.

Me too. This is why I never bothered with a solder pot. For semiconductors, if you can't hold the part with your fingers while pulling it out, there's no point pulling it out at all. Rule of thumb-ouch.

[donatas]

Anyone had any luck dissolving the lacquer used to seal the ferrite core transformers? Without decoating the wire or ruining the plastic coil formers. It would be nice to be able to reuse these.

I put my 30W soldering iron on one half of the core (right above the middle shaft) with an appropriate solder blob. Leave it for ~5mins. GENTLY wiggle it out with tweezers. If still resisting to move - repeat heating process. Works 70-80% of the time. Depends on how impatient you are while wiggling it. No pun intended.

[T3sl4co1l]

The secret to disassembling ferrite cores, transformers, etc.:
Heat and superglue.

(Not at the same time.)

If the transformer is small, you can heat it with the soldering iron.  DO NOT apply direct heat to the core.  The core is weak ceramic and will crack from thermal stress!

First, remove any tape or clips securing the core.

Set the soldering iron horizontal, and balance the transformer on the barrel of the iron.  It will heat up gently this way.  Using gloves and/or pliers, twist and wiggle the core pieces until they come loose.  The varnish should become gooey (and a bit stinky) when it's hot enough.

Larger transformers will take a long time to heat up, and may be better done in a toaster oven (you DO have a throwaway toaster oven for lab use only, right?).

The core may end up fractured, anyway.  Clean the fragments: scrape off whatever excess varnish you can, and wipe the fractured surfaces with solvent.  Line up the fractured surfaces as perfectly as possible, then mate them with a drop of superglue.  Hold until cured.

The additional air-gap of a thin superglued joint is insignificant for most cores.  (High-mu pulse transformers and common mode chokes are the most sensitive to air gap.)  If medium sized chips are missing from the fracture, try to reassemble them; don't worry about small chips.  Large chips, and crushed material, isn't practical to repair.

Inevitably, the core pieces won't line up perfectly, and the ground faces will no longer be flat and parallel; if this is desired, use carbide sandpaper (laid over a very flat surface, like plate glass) to grind the faces parallel again.

Tape and wire can be unwound from the bobbin.  Be careful with the bobbin: it is made from brittle, high temperature plastic.  Salvaged wire is sometimes reusable, but don't count on it.  (Some varnish is so strong, it peels the enamel right off the wire!)

Do invest in a roll of Scotch(R) 74 or similar polyester tape (it's usually yellow).  It's legit, it has good hold strength (better after heating!), it's strong and it's an excellent insulator.

Or polyimide (Kapton(R)) tape, which is even stronger, stiffer, and higher temperature (and more expensive).  Though I'd kind of recommend against it for general use, as it's not as well-behaved (because of the stiffness and all that).  It's good for other uses too, though -- it can withstand direct soldering heat pretty much forever.  Polyimide is one badass organic polymer!

Tim

[langwadt]

http://webecoist.momtastic.com/2009/11/28/trashy-times-where-do-recycled-gadgets-really-go/

[TerraHertz]

Do invest in a roll of Scotch(R) 74 or similar polyester tape (it's usually yellow).  It's legit, it has good hold strength (better after heating!), it's strong and it's an excellent insulator.

Oh, I have a stock of all the typical stuff for making transformers, plain and fiberglass tape, rolls of various gauge enameled wire, and plenty of new cores too. It just burns me a little to have boxes full of salvaged switchmode supply transformers that I can't scavenge cores and formers from. Keep meaning to try various solvents, looking for a way to bulk-disassemble lots of them. Saving the wire isn't really important, since wire is easy to find. A wide variety of cores and their formers... that's something else.

Or polyimide (Kapton(R)) tape, which is even stronger, stiffer, and higher temperature (and more expensive).  Though I'd kind of recommend against it for general use, as it's not as well-behaved (because of the stiffness and all that).  It's good for other uses too, though -- it can withstand direct soldering heat pretty much forever.  Polyimide is one badass organic polymer!

It's curious that it smells so nice. Like it ought to be yummy-delicious to eat.
At least, the roll I have does. But it was called 'koptan tape' and came from China. Seems to be the real thing though.

I bet if someone could make kapton-scented cake, it would sell really well.

As for heat resistant, you're not kidding. Pic is of my hot air soldering tool, with one vent of a tip closed with kapton tape. It survives! I needed just one flat nozzle for a difficult desoldering task, with the temp turned right up to near maximum.

[T3sl4co1l]

Oh, I have a stock of all the typical stuff for making transformers, plain and fiberglass tape, rolls of various gauge enameled wire, and plenty of new cores too. It just burns me a little to have boxes full of salvaged switchmode supply transformers that I can't scavenge cores and formers from. Keep meaning to try various solvents, looking for a way to bulk-disassemble lots of them. Saving the wire isn't really important, since wire is easy to find. A wide variety of cores and their formers... that's something else.

(I was referring to OP there, but that's fine. )  Have you tried THF, maybe?  Probably methylene chloride is the only thing that would do anything worthwhile, but it'll turn everything to goo... probably including the bobbin.

Heat is the best thing, AFAIK.

You might occasionally come into a large stock of surplus cores e.g. on eBay.  Not that cores help much, but maybe you can get lucky and find bobbins as well.  Or order them from China -- I once picked up a couple trays worth of cores, and managed to find bobbins they fit.  I spent $50 (including shipping and money order) for qty 50 bobbins.  A lifetime supply!



So naturally, a lot of my projects use suboptimal core choices, like this 20W high voltage supply with tons of winding room to spare:
http://seventransistorlabs.com/Images/HVPower2.jpg


I also identified a TDK/EPCOS set which is equivalent in specs, and made a footprint that fits both, in case I ever develop something with these that sells.

It's curious that it smells so nice. Like it ought to be yummy-delicious to eat.
At least, the roll I have does. But it was called 'koptan tape' and came from China. Seems to be the real thing though.

Mine doesn't smell like anything -- silicone adhesive (same temp rating as the tape).  You can get it with acrylic too, which is cheaper, but not high temp.  Adhesive might smell like solvents if it wasn't fully cooked out in manufacture, or something, maybe.

I bet if someone could make kapton-scented cake, it would sell really well.

Imides are okay, but peptides are where it's at.


Tim

[CatalinaWOW]

I stopped doing this with drawers and drawers of salvaged parts when I realized two things.

One, even after spending eons sorting and storing these parts I was spending eons looking through the piles for a part close enough to use for the current project.  Wasn't unusual to spend 15 minutes per part.  Sorting by component type and nearest decade or so of value still leads to lots of drawers and lots of searching through those drawers.  Particularly as you get older and the markings get harder to see and interpret.

Two, very often wouldn't find something suitable.  Then it was off to the drawing board to redesign with something I had, or order new parts anyway.  The redesigns often resulted in another search through the parts bins.

Parts are cheap, time is short and Mouser and others are fast. 

[johansen]

I have yet to find more of those cores that I sold Tim over 5 years ago....

I've always used a propane torch to strip power supply boards and others..

before i left for the military at age 18, which was 10 years ago, i had about a 5 gallon bucket full of 200volt electrolytics, and another 5 gallon bucket full of the transformers and inductors. care to guess what my parents decided to drop off at the dump? you guessed it. but some how the other crap stayed behind..


as for taking the smps transformer apart. boiling water. put all of them in one bucket and slowly heat the water to boiling.

put latex gloves over some cotton gloves or something better, pick the transformer out of the 190F/90C water, unwind the mylar tape, the core should fall apart with a little bit of force.

[KL27x]

Digikey? Naw. I know I got that part somewhere.... Data sheet? Specs? Mechanical drawings for the pads? Who needs that junk!