Desoldering help - big 160 leg IC - Page 1
Forum section: electronics / repair

author: Nexxen
author_rank: Regular Contributor
timestamp: September 09, 2023, 10:38:44 pm
content: 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 bladebut 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 badMy idea is to desolder it and clean the legs feet were they make contact with the pads.How though?

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 09, 2023, 10:42:51 pm
content: 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.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 09, 2023, 10:46:24 pm
content: Maybe 2-3 hrs would do it too much or...?Honest question.Edit: I read your editI 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!!

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 09, 2023, 11:14:31 pm
content: You can also try ChipQuik chip remover alloyhttps://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=1This 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.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 09, 2023, 11:46:14 pm
content: I have a syringe of Sn42Bi58 solder , melting point 138°C.Could that do?

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 10, 2023, 01:11:48 am
content: 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/_EvuvZd9Still, 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.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 10, 2023, 01:13:51 am
content: Well, I'll try things.Thanks for ideas so far

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 10, 2023, 01:32:26 am
content: 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.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 10, 2023, 09:16:04 am
content: 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.

author: Swake
author_rank: Frequent Contributor
timestamp: September 10, 2023, 10:18:59 am
content: Quote from: Nexxen on September 09, 2023, 10:38:44 pmDo 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.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 10, 2023, 10:24:50 am
content: Desoldering Made EasyMr SolderFix

author: Nexxen
author_rank: Regular Contributor
timestamp: September 10, 2023, 10:27:34 am
content: 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 scrubYeah, 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.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 10, 2023, 10:29:22 am
content: 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.

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 10, 2023, 10:55:31 am
content: 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.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 10, 2023, 06:04:59 pm
content: 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.

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 10, 2023, 06:22:41 pm
content: Doesn't scratching with the fiberglass make anything?

author: Nexxen
author_rank: Regular Contributor
timestamp: September 10, 2023, 07:21:24 pm
content: 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 presumeor too much leaning on the motherboard yesterday + house choresEdit:https://www.youtube.com/shorts/Pu_5xvkh0fs

author: Haenk
author_rank: Super Contributor
timestamp: September 11, 2023, 05:11:47 am
content: Can you source a replacement? If so, carefully cut the legs and desolder leg one by one, clean, solder in the new IC.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 11, 2023, 09:45:56 am
content: 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

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 11, 2023, 01:54:45 pm
content: Quote from: Nexxen on September 10, 2023, 07:21:24 pmI've done that before, it's ok for 1 or 2 legs, but definitely the last thing you want in a 160-pin IC!

author: Nexxen
author_rank: Regular Contributor
timestamp: September 11, 2023, 02:02:54 pm
content: 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

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 11, 2023, 02:42:35 pm
content: 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!

author: Nexxen
author_rank: Regular Contributor
timestamp: September 13, 2023, 01:12:00 am
content: 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

author: Nexxen
author_rank: Regular Contributor
timestamp: September 14, 2023, 01:06:50 pm
content: 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.

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 14, 2023, 01:11:41 pm
content: 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

author: Nexxen
author_rank: Regular Contributor
timestamp: September 14, 2023, 01:19:52 pm
content: I have to admit that going for a long project like this in fact made me realize I have to buy a few things more (flux is a must but quality is crucial - mine is all over the place and makes a mess + it doesn't clean easy...).I could have used some chemicals, like metal polish to clean the legs. But in fact some pads were detached and others were just wainting to break off.I now have a base line to understand what to do in such cases.Necesité aprender y aprendíNow I hope the chipset IC isn't dead. But for 10€ I can get a new one shipped.Edit: legs came out pretty neat with some chemical cleaner (for copper/brass/silver...) and some fiberglass pen mechanical work to finish it off.Now solder sticks like crazy. The layer of oxidation was that thick.

author: Swake
author_rank: Frequent Contributor
timestamp: September 16, 2023, 11:54:06 am
content: Have to admit you made good progress. With those zoomed in pictures all seems big and it doesn't seem difficult, but this really is not easy.Anyhow, nothing to loose, you already won the experience part.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 16, 2023, 01:48:02 pm
content: Thanks, it took me forever to do the job.One step I made is to flatten the wire with pliers, thus looking close to a pad.See next post.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 16, 2023, 01:57:44 pm
content: I removed, with hot air, all the SMDs close to the chipset IC.Solder joints felt solid but inside most were rotten and I had a hard time removing this old solder (looked like old cavity filler before use - amalgam), cleaning and prepare the pads for good fresh solder.A few pads came off as the small trace connecting one to another was actually worn and ready to break.On my side, I bought a 10W USB UV lamp to cure solder mask. The lamp that came in the my first bundle is cheap (5€) and doen't have enough LEDs to do the work fast. Moreover, the power of the LEDs goes down to useless when it hits below a certain voltage, it dims and takes 10x the time to cure.I ordered all the SMDs, as many just look like they are about to crack and others just have the small pad gone while desoldering.Some capacitors show an ESR of 18-95 ohms, and need to be replaced.I'll replace all caps as they are all 100nf.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 17, 2023, 11:46:29 am
content: I'd like to idebtify this diode, the big white one. All others are 1N4148 (markings).This one has nothing on it, transparent

author: alligatorblues
author_rank: Regular Contributor
timestamp: September 21, 2023, 02:13:20 am
content: I would flux each pad with a dental tool. Then wet each with solder. Put a small piece of funtack or gluetack on the bottom of the IC, to hold the chip aligned. The legs should all be resting on a soldered pad. Flux up each leg with the dental tool. Put a bead of solder on the iron tip, and touch it to a joint on all 4 sides.It won't move after that. Do the same for each leg.

author: Nexxen
author_rank: Regular Contributor
timestamp: September 21, 2023, 01:54:25 pm
content: Drag soldering isn't an option.I made the listake of using a wire to replace the broken/lifted/rotten pads thus resulting in having to "lift up" the leads of the IC. Noting special, but I need to use a fine tip there and around.Thanks for the input!I'm wainting for the components to get here, old smds are fine but I'll go with new ones for good measure as a couple "lost" a pad on one end; corrosion altered the solder to its core and I can't trust the smds pads to be good.Axial components (i.e. diodes) are fine and I have plenty of spares.I have to let it settle to get a new view on the whole matter.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 01, 2023, 02:06:25 am
content: Soldered.

author: Veketti
author_rank: Regular Contributor
timestamp: October 01, 2023, 05:32:15 am
content: You got it done already, but I'd just add my method of desoldering these IC's. Chipquick is good, but maybe better method is following. Add solder flux to all the legs and wick all the excess solder that comes off. then starting from one corner push sewing pin under the leg and keep some pressure and at same time heat the legs one by one. They pop off from the pcb nicely one at a time. Of course they do bend a bit, but the pin is so thin that the bend is very minimal and easy to restore. This way the heat input is very minimal and there shouldn't be issue of damaging the IC. You just need to find the correct pressure for the pin to not lift the traces but still have enough to bend slightly the leg.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 01, 2023, 10:57:14 am
content: The corrosion built a layer of oxide that prevented solder from bonding, it was like ice on the road.I scraped a bit to have enough solder to stick in order to avoid high temperature with the heat gun, possibly killing the already compromised IC, desoldering it fast.The solder was so corroded it basically came off as fast as I hoped.Solder paste wasn't sticking either, low melt didn't as it couldn't mix with old solder. In fact old solder looked rotten, probably the battery leak reacted in such a way (don't know how chemically speaking).When I desoldered the 1206 smds, the solder on the leads and the LM358, looked and felt ok, but was in fact rotten and barely holding. My image is of mortar that has too much sand and is brittle, at first is feels hard and holding but at the first blow it collapses.It was an interesting journey and I learnt lots of things.

author: u666sa
author_rank: Frequent Contributor
timestamp: October 01, 2023, 01:00:44 pm
content: You need a metal brush.https://aliexpress.ru/item/1005005721993119.htmlYou need high activity flux.https://aliexpress.ru/item/1005004730420277.htmlYou need low melt.https://aliexpress.ru/item/1005005963616378.htmlAgain, I throw something really quick, not best prices, first that I found. Find best prices and free shipping for your country, perhaps get it on eBay or Amazon or whatever. These are tools I use, you might have something better where you at. For example real amtek flux, or different type of low melt. (don't use kadmium based low melt it's toxic)Plus you'd need microscope and proper soldering tip.To desolder you scratch using metal brush. Put low melt paste across contacts. Blow with hot air, I'd say about 400C. Remove.To solder back, clean contacts with 63-37 solder and flux and wick. Clean chip contacts as well. Align chip under microscope. Tack 1 leg on one side, 1 leg on the opposite side. Apply flux, tack every leg with 63-37 solder using a properly sized tip, you may or may not have to apply pressure from top using tweezers. If iyou get solder on several legs use wick. Clean with flux off and brush, here hard tooth brush is preferred, tooth brushes come in soft, medium, hard. Inspect under microscope, use twizers to werify everything is soldered.

author: MathWizard
author_rank: Super Contributor
timestamp: October 02, 2023, 10:08:38 am
content: To clean some of the corrosion on the legs I would have tried sandpaper, of course it would take the green coating right off traces tho.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 02, 2023, 10:35:27 am
content: In retrospective, I should have looked for problems in the pictures I took.Look at this one: cracked joints, rotten solder, corrosion all over, under the pads, on the pads, on the traces.Sanding would have damaged it even worse, in this spscific case. It was my first on such extended damage and I learnt things on the way.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 04, 2023, 02:22:12 am
content: Populated

author: Nexxen
author_rank: Regular Contributor
timestamp: October 04, 2023, 10:32:01 pm
content: While checking for continuity from VLSI to ISA,I fond that ISA A1: I/O CH CK didn't have continuity with pin 121 of VLSI (-I/O Ch CK).A trace was going from the VLSI to ISA A1. I soldered a wire to restore continuity but now I'm wondering if that is correct.QUESTION: any idea if it was right?QUESTION2: Addresses and Data had no continuity with ISA, is that nomral?I have no idea what's righ o wrong.Thanks in advance for any help.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 07, 2023, 01:41:44 am
content: Board shorts on +12V.Guess that's the end of it.Thanks a lot for all the help and comments.

author: Agent24
author_rank: Regular Contributor
timestamp: October 07, 2023, 06:58:24 pm
content: Not necessarily? There are ways to find shorts...

author: Nexxen
author_rank: Regular Contributor
timestamp: October 09, 2023, 05:25:49 pm
content: Quote from: Agent24 on October 07, 2023, 06:58:24 pmYeah, I guess I was hasty out of frustration. I'll get back to it this w/e. Fresh start so to speak.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 09, 2023, 06:18:16 pm
content: I know the feeling! Enough is enough! You put it back togetheralla cazzo di cane, slam the door and proceed to drive the highway at 200mph with loud music. Happens to me a lot!No worries, after some birra and italian magic 🤌 eventually you'll give it another try!

author: Bud
author_rank: Super Contributor
timestamp: October 09, 2023, 06:38:06 pm
content: Likely one of those tantalums on the power bus.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 09, 2023, 08:53:23 pm
content: Quote from: DavidAlfa on October 09, 2023, 06:18:16 pmYou made me dieWhen you learn italian and then find that it can be reduced to just a few idioms and still get straight to the point...I'll watch some Torrente to lift my spirits up.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 09, 2023, 08:56:29 pm
content: As mentioned above I just wanted to throw everything out of the window and watch it crash... then I remembered I paid for itI think it's one of those orange 4.7µF.Question: why not 10µF? On other boards it's 10. Cheaped out on this? Or not necessary?

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 09, 2023, 09:09:08 pm
content: But how? These are decoupling caps, connected to VDD/ GND. No way this could short the address lines!

author: Nexxen
author_rank: Regular Contributor
timestamp: October 09, 2023, 09:12:39 pm
content: I'm guessing. I'll probably end up removing a bunch until I find the one... or not.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 09, 2023, 09:30:38 pm
content: But there's nothing connected the these traces now!

author: Agent24
author_rank: Regular Contributor
timestamp: October 09, 2023, 09:47:57 pm
content: I thought the short was said to be on +12v rail.What is this about shorted address lines?

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 09, 2023, 09:52:50 pm
content: Ah! I mistaken this thread with the Amiga 2000 one!Right! Tantalum like to short a lot!

author: Nexxen
author_rank: Regular Contributor
timestamp: October 09, 2023, 10:27:19 pm
content: Quote from: Agent24 on October 09, 2023, 09:47:57 pmIt's +12V rail. He posted in the wrong thread.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 09, 2023, 10:36:38 pm
content: Tantalums are usually easy to catch. Power it with 12V 1A. Something should warm up.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 09, 2023, 10:40:18 pm
content: Quote from: DavidAlfa on October 09, 2023, 10:36:38 pmWill try. The 1st tantalum +12 onnects to has some debris under it. Let's cross fingers it's just that one

author: Nexxen
author_rank: Regular Contributor
timestamp: October 10, 2023, 02:47:18 pm
content: It wasn't a tantalum shorting but a 0.1mH coil. It was orange as its neighbours, looked the same.Beware the coils!Ok, it was a tantalum. It didn't explode though. Good thing as I wasn't wearing glasses.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 14, 2023, 01:39:41 am
content: I soldered the two 3904 and 3906 that were missing from the board.Still no go. On POST card there is no IRDY. On my other boards it happens with a missing bios.Cpu can reset no problem, there must be some communication with the big VLSI, or is it me seeing things that aren't there???Now I need a 286 motherboard schematic to understand how BIOS communicates...This is a very tough one for me.

author: Agent24
author_rank: Regular Contributor
timestamp: October 14, 2023, 01:56:57 am
content: Is BIOS chip getting power/data?Scope address/data lines, do you get any activity?Do the waveforms look OK? (not badly distorted, low voltage levels etc)

author: Nexxen
author_rank: Regular Contributor
timestamp: October 14, 2023, 02:05:51 am
content: I was tired to look for a bios schematic but I I had my oscilloscope at hand.Power, I think yes. 5.xxVMany waves were indeed square, 156KHz or Hz (can't remember), but heavily "trembling". Tomorrow I'll take pics of them.Voltage I dind't care to watch.Not having a datasheet I don't know which are data lines and what should happen.When resetting waves had a change, but I wasn't paying much attention.Sorry for all the IDK....

author: Nexxen
author_rank: Regular Contributor
timestamp: October 15, 2023, 02:04:21 am
content: Well, it works. I soldered a wire to the wrong hole and a connection was missing to the VLSI I resoldered. Guess I deserve a slaphttps://youtu.be/G2uS0BaOtpM

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 15, 2023, 04:52:44 am
content: Perseverance pays off, bravo!!