The average melting point of solder is 700F (370C).

And your best bet is to go through a multimeter, identify dead traces, and put jumper wires over them. These boards are multiple layer, meaning traces are implanted inside the motherboard, in which case your SOL if any of those traces are foobar.

This is a task for people who know exactly what they are doing. It's sad to see these board go, but I'm not lying, this corrosion damage is probably the end of these board, The acid eats away at traces, and if too many are gone, you will likely have a completely dead or incredibly crippled board.

I think I've read or heared that boards with 4 layers only have ground in them, and this seems to be confirmed on another (dead 🙁 ) 486 board. If you look closer to that board, you'll see something that is almost everywhere underneath the board. The only place where it's "cut" is under the keyboard connector, brobably to protect the board. On the 386, there are of course headers for leds, pc speaker, etc. But on one of them there is only one trace going to one of the two pins. And i'm pretty sure that the other pin is just ground.

I might be completely wrong though, so please correct me if I am. But if I'm right, I'd like to know it too ^^

Sad to see these boards go. I recently got an all-ISA 486 that is at least this bad. It was still worth for the cpu, ram and cache but the mainboard seems unrecoverable. I'll attempt it nonetheless.
My old Compaq 386 is also showing signs of damage but it's nowhere near this level. I'll see to it asap, it would be sad to let that go.

The melting point of old solder is between 180°C and 260°C.

I did manage to fix damage like that - however I had to cut the damaged ISA slots (some pins completely eaten) to pieces to be able to unsolder them.
With an unregulated heatgun the PCB will likely start 'popcorning', then you can really throw it away.

You should first start with the vinegar treatment and see if the remaining damage is dramatic enough to justify changing the slot.

Thing is the leaked stuff really likes to drag itself into the copper ... beyond a level one would usually expect.
Which is why most repaired boards fail again after 6 months. If you're not willing to repair the board as if the parts with the leakage were actually gone you're in for a bad time.

Repair will be a lot of jumper wires, and MONTHS of painful debugging depending on the damage.

This is why people say to remove those batteries, it's not a joke. I know your not to blame, but this board is foobar.

Hm, at the moment I'm repairing my RTC card from my 8088 that still works a bit, but had also that awful varta battery. The battery was in a corner of the board and so all it really destroyed was grounding( the rest still doesn't look really healthy and there is a dip switch box that seem to be completely busted, but being an 1988 8 bit ISA card, the design is still very simple and many chips are still found standalone on eBay). That part was really crunchy so I removed excedent of corrosion with a tiny screwdriver. I discovered that there was still copper underneath (incredible considering how bad it was before), but some parts were dark. I used a product called "mirror" (I don't know if you have an equivalent to this in america, probably) that I usually use to clean connectors and stuff like that because it works really nice on these cards that don't work properly even after being cleaned with alcohol because their connector is dirty works perfectly after using that product. But I noticed that it made also some solder point looking shiny again on that card (before that, they looked grey, even a little bit greenish and they weren't shiny at all)

So yeah I might have found something better than vinegar to stop battery's acid. I'll try that on these boards and I'll tell you if it works or not (just for the cleaning, I'm not sure if those boards will work again someday ...)

@Ampera, it's not my fault at all, they were already looking like that when I got them 🙁

As long as all the other components on the board are ok, and it's just a case of patching up open traces then in short... yes, everything in this scenario is recoverable.

This is where most of my time goes. I would say success rate is around 70%-80% and has a lot to do with the health of the rest of the board. You can patch over the eaten traces and restore full connectivity as if the battery had never leaked... but if any of the IC's or ASIC's have suffered, then the board is as good as gone. Having said, these all being well, and you are able to patch up the traces then you will get the boards going once again... and when you do, it feels very rewarding.

I usually say everything is fixable. It is only the matter of time, effort and mainly money. I guess it could be fixed by jumping dead tracks with cable.

To me it not only looks repairable but also fun to do. Although 400C is way too hot. You have high chances of killing the ICs. If you are going to desolder any big through-hole components, i d strongly recommend first of all "refreshing" all solder joints with a soldering iron and some low-temp solder, that melts below 200C, all of them one by one. The best thing there is a Wood's metal that melts at 70C. Will get your through-hole components out nice and easy with a 200-250C air gun, which is very safe for the board. But you actually do not need to replace ISA slots. You can use some isopropyl alcohol to clean them, some people put boards in the dish washer that helps too (the board is already dead anyway). I would for sure not bother with replacing ISA slots.
Traces should be not too difficult to.. trace... and repair. And i wouldn't bother too much about the inner layers. They are power and ground. If the board doesn't start after resorting all visible traces, you can always check the presence of all power and ground lines on all ICs and slots with the multimeter, and if something is missing, you can route it there with a wire.

But this is definitely gonna eat a LOT of your time.

I thought about removing ISA slots not only to replace them but actually to see how traces are underneath in order to clearly see what goes where.

If the heat gun is too hot, I could also just blow air from a higher distance could I ? I don't want to remove any IC, I just want to get these slots out of my way ^^ I just need to blow on the back of these boards. What I should take care of is the board itself in that case

Deksor wrote:

I thought about removing ISA slots not only to replace them but actually to see how traces are underneath in order to clearly see what goes where.

If the heat gun is too hot, I could also just blow air from a higher distance could I ? I don't want to remove any IC, I just want to get these slots out of my way ^^ I just need to blow on the back of these boards. What I should take care of is the board itself in that case

I would highly NOT recommend using a 400C hot air gun for that at all. As for me 300C is way too hot, i never use more than 260C.

Generally removing through hole parts with a hot air gun is something I wouldn't recommend (when you have bent pins [so the parts wouldn't fall out before soldering] and a large area you need to heat up as with ISA connectors you're in for a bad time).
Soldering iron + desoldering pump or a (good) desoldering gun are the way to go. Might take more time but certainly better than adding further damage to the board.