Desoldering help - big 160 leg IC

[Nexxen]

Hello!!

I have a motherboard and it came with VARTA damage.
After some work I could clean, rebuild traces and all the other nice things that go with it but I'm stuck on a very specific problem:

the big chipset's IC that was close has many legs with some "time" corrosion, but the ones that were affected by the VARTA leak are simply impossible to solder  (painted in red).

I tried scratching with:
- a blade
- fiber glass pen
- a even sharper blade
 but nothing.

While a few legs did get soldered, the other 30 didn't. I'm dying after this last thing and it's crazy, solder goes over it like if there was flux...

I need expert help because I'm stuck real bad


My idea is to desolder it and clean the legs feet were they make contact with the pads.
How though?

[DavidAlfa]

Leave in white vinegar for an hour or so, hopefully it'll remove all those deposits and corrosion.
(Clean all that flux first!)

To remove it, you'll need a hot air rework station, definitely not something you can do in a garage with few cheap tools.
A common 2KW heat gun might do it, but it will blast 800ºC heat, so you'll have to be extremely careful, preteating the entire board for 2-3 minutes to reduce warping and then blasting the main IC wih the heat.

Those old boards are not even close to today's FR4. They're junk, very delicate, they will delaminate very easily.
Too much heat for 2 seconds - popcorn! Blisters everywhere, if there were vias in the zone, now they're gone.
If it's a multilayer pcb, then you're really screwed!

And that IC package is a nightmare to work with, it's just too easy to damage the legs.

[Nexxen]

Maybe 2-3 hrs would do it too much or...?
Honest question.

Edit:  I read your edit

I only have a 400°C heatgun, the combo iron+gun.  I will preheat.

I could solder a big copper wire to the legs (if it sticks) to help absorb heat.

I could cover the IC with something to avoid all the extra heat a protect it.

I knew I was in for a surprise... 

Thanks hombre!!

[fmashockie]

You can also try ChipQuik chip remover alloy https://www.amazon.com/Fast-Chip-Removal-Temperature-Alloy/dp/B015RV4NBS/ref=asc_df_B015RV4NBS/?tag=hyprod-20&linkCode=df0&hvadid=312128028232&hvpos=&hvnetw=g&hvrand=15445900554041999093&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007317&hvtargid=pla-505397180305&psc=1

This stuff works really well.  Especially if you want to save the chip you are removing.  You usually don't have to worry about heating up the chip too much because you don't need a hot air gun to use it.

[Nexxen]

I have a syringe of Sn42Bi58 solder , melting point 138°C.

Could that do?

[DavidAlfa]

Might help, I've also used it and it stays melted for a long time.
But the thing is it's totally corroded and normal solder isn't sticking, those won't either, and you need to melt the existing solder so it dilutes in the new alloy.

You might be lucky if this is real:
https://a.aliexpress.com/_EvuvZd9

Still, try the vinegar first! Will be a way less dangerous option.
You might need to repeat the procedure several times, brushing after each one.
The fiberglass pen works great, but the  corrosion must go away first.
When done, apply some water and baking soda to neutralice any acid.

[Nexxen]

Well, I'll try things.

Thanks for ideas so far 

[fmashockie]

I can't say if the solder paste will work.  I've never seen that used to remove ICs like that before.  But the ChipQuik stuff works great.  I use it all the time.  And its cheap to buy.  It's a great alternative to a hotair gun. Plenty of vids on YouTube on how to use it.  I think Dave does a video on it as well.

[Nexxen]

I watched it.

That link goes to a 8$ item. In my country it's 22$. Import taxes I think.

I'm not going through this today, I prefer to let it seat for some time to have a clear plan.
Haste is a very bad friend with old electronics.

[Swake]

motherboard and it came with VARTA damage.

Do you mean a VARTA battery leaked and the acid is now all over the place?

The pictures show that everything is pretty dirty. If you want to clean the board: Kitchen sink, water, dish soap and dish brush + tooth brush. Rince well, dry with hair dryer. A paint stripper works too but not recommended without experience.
After that first thorough cleaning assess the board again. You might have to use an slightly more aggressive technique to clean some places.


Removing the chip is easy, putting it back is going to be another story without the right tools. And as already written before, you will certainly damage it.

[RoGeorge]

Desoldering Made Easy
Mr SolderFix

[Nexxen]

I already cleaned everything, VARTA isn't a problem anymore.The board is dirty because yesterday I didn't want to clean it right after all the unsuccessful soldering, it's basically just flux.
Today I'll give it another good scrub

Yeah, this one is a very difficult challenge.

Today I'll soak it in vinegar and see if it changes anything. I could solder a few legs, it might just be a matter of going nuts over it... 



I need to let all the information sit in my head.

[Nexxen]

Yep, I am subbed to his channel.
Alas it's not sticking to it, the copper wire method isn't possible yet.

I hope vinegar will help.

[DavidAlfa]

If you see any bubbles, it's the vinegar taking action - there was some residue left!
Still, the pictures are not showing any brushing marks... The fiberglass pen would definitely leave a dull surface if it did its work!
You don't have to be specially careful, if you scratch too much you'll end exposing the copper, which might be the actual objective - removing all the oxidized layer.
Then it'll solder very easily.

But anyways, you won't be able to access the area behind the legs.
As long as the old battery electrolyte is removed, shouldn't be a huge concern if you're able to solder it at the front (Unless there are damaged traces under the chip), not optimal, but this is a very delicate repair.

[Nexxen]

I put vinegar on and it's about the same, dull joints and no easy soldering to pads.

If I can't solder due to corrosion and most of the megs are in fact getting desoldered,
at this point I can concentrate on lifting each leg as it looks faster than soldering.

Low melt on the others that are in perfect shape and this should do it.

[DavidAlfa]

Doesn't scratching with the fiberglass make anything?

[Nexxen]

I'll try that later.

But if out of 80 legs, 40-50 don't make contact, at this point it could be easier to remove the IC....... IDK, for now I'm justing wtiting down ideas.

I'll report back in a few days. Today I have some back ache, age I presume  or too much leaning on the motherboard yesterday + house chores


Edit: https://www.youtube.com/shorts/Pu_5xvkh0fs

[Haenk]

Can you source a replacement? If so, carefully cut the legs and desolder leg one by one, clean, solder in the new IC.

[Nexxen]

It's hard to find a replacement.

Even if the usual issue is to find a non fake and 100% functional. Not a pull from some board.
I think that desoldering might be easier than expected, I'm not in a hurry and a solution IS there.

202% positive attitude 

[DavidAlfa]

Edit: https://www.youtube.com/shorts/Pu_5xvkh0fs

I've done that before, it's ok for 1 or 2 legs, but definitely the last thing you want in a 160-pin IC!

[Nexxen]

My IC has 80 legs good as new. They are located on the farthest sides from the Varta battery.

The other 2 sides are the ones giving me hell. They haven counted today, 57 loose legs. A few more resulting from my soldering session.

In the end I don't think it's too difficult to desolder, just patience and avoid overheating anything.

Even if a few legs "die' in the process, dremel + rebuild isn't impossible as the motherboard is rather simple but very friendly as everything is of easy access (like soldering an enameled wire).


But I didn't see any compromised legs as in the video (and this was good for me to notice).

Every suggestion pushes me a little further, I think I'm close to going the right way.

A huge thanks to everyone so far 

[DavidAlfa]

Nothing to do! Fill the legs with the SnBi alloy forming giant blobs.
As this alloy melts at 138ºC, set the temp to 280 or so, hopefully it will dissolve the original solder.
The lower temp will increase the chances of the board surviving. I would not go over 320ºC in this type of board.
Good luck! 

[Nexxen]

I retried soldering and the result was more legs desoldered... 

I then desoldered all the legs of the corroded sides and added solder to the other two. It came off pretty easily.

Glad I did as a few pads came off and were dead already, others had the trace so thin they came off just cleaning with a cotton swab.

After that I cleaned thoroughly the pads and polished them with a fiberglass pen, now they are all nice and shiny.
They looked awful, all dull and even adding solder to the tip to remove the old solder it wasn't sticking... 

In the end it was a good idea to desolder and even if a few traces need to be rebuilt it's an easy task.

Well, my inglesh sucks but it's clear enough I hope 

[Nexxen]

Traces done, pads too.

I still have to anchor them.

To resolder the chipset I'm going for solder paste + lifting a bit the legs that will land on a wire.
Maybe touch ups.

[DavidAlfa]

You need to buy UV solder resist to hold those wires a bit, specially when a stupid wire makes you lift a 160leg ic!
Edit: I see you already used it