THANK YOU! I was waiting for someone to say this, PoP RAM wouldn't be a good idea to touch
Why touch the eMMC too anyways?? I'm an N900 owner and 32 is more than I want (and I have Android and Arch on my eMMC too).

PoP RAM can be touched. I have seen companies who have machines and ability to do so. But, what will system and SoC do about it? One is HW side, second is compatibility and so on.

N900 has 32GB + up to 64GB (or 32 only?) MicroSD card. N9 & N950 have no SD slot.

I understand what he wants to do and why. I just... use 1GB swap, it will work, even if slow. but that is not for daily usage anyway.

If I am not too late, this is definitely not what a collector does. A collector who has the rarest devices ever would not even come near 'modding' it. If you want to be a 'collector' you should have the devices intact and 'vanilla'. Do not mod them under any circumstances. Or else you won't be called a 'collector'.. That would be a monster. Please, if you want to ruin those beauties.. Give them to someone who would take good care of them.

Depends. Some collectors do modify things they collect for the sake of making it better.

Thats not collecting then. Thats modding.
I am a collector, with 1000 phones. I do plan to make a museum in Slovakia, about mobile telephony and so on. Just need some support

If one collects antique cars, do they just leave it unusable? No, most likely they will repair it and make it better. However, N950 has the devices still working, so no need for a risky mod. My better advice is to just make a swap. It has 64 gb, no?

Speaking from experience, we do these stuff regularly at work. Here some random comments:

- It is possible to replace the BGA device. The success rate is quite good but we don't do this for operational boards, we can not trust it for long term and reliable operation. We do this only for prototypes that had a mistake. The high cost can be justified there since we cannot wait 2-3 months for building another proto.

- usually we don't reuse devices. It is very difficult not to destroy the chip when it is removed. The cost of the reballing is high and in the end for most devices does cost the same as new.

- no-one uses x-ray to aligh the pins. We use the xray machine for the pre-series production to check the factory and how clean was their job.

If I were you, I wouldn't do this mod unless there was something already broken.
If you going to do it, ask the company to buy a new memory for you. Don't re-use from the other phone.

Hope it helps

Another question, Isn't the ram module built in the processor chip? just like on raspberry pi(CPU+GPU+RAM on single chip)?

no, it is no IN processor chip, it is "on" it. search about "PoP"

Yes they do repair it, okay. But unless it is very risky that you might actually ruin it instead of repairing it.