Current state of the Pi
"Now mostly dead is slightly alive"
Yesterday I started off with a functioning Pi4 1GB and an 8GB RAM chip. Today I have a Pi4 N/A GB and a 1GB and 8GB RAM chip. A lot happened.
I started this project after seeing MadEDoctor's YouTube tutorial on how to do exactly this. He helpfully linked to the RAM chips in his video, so I bought the 8GB chip and had a Pi4 1GB sitting unused.
Turns out BGA rework is pretty tricky and I have been unsuccessful so far in getting the 8GB working on the Pi.
Yesterday I removed the 1GB chip successfully - all the pads stayed on, no catastrophic visual damage. Then I cleaned it up and attempted to solder on the 8GB chip. I used a heater on the backside to preheat the board to around 80-100C, then used a hot air rework station to heat the RAM chip alot, everything else shielded with kapton tape. To get the unleaded solder to flow, I had to turn the station up to max heat (it just uses a dial, no actual temperature indication). The first attempt wasn't successful, the chip just popped off. So I tried again after verifying that no pads were lost, and it was successful in securing it to the board. But upon plugging it in, I got 8 flashes from the ACT led signalling a RAM error. That was day one.
Today I went back and reflowed it again. But no luck. Although somehow I managed to melt part of the RAM chip. Still 8 flashes. So I just decided to remove the chip and verify that everything looked alright since it wasn't working anyway. So I removed it successfully and all the pads are intact, it doesn't look like there were any solder bridges, and now I'm stuck.
It doesn't seem to be totally dead, but I don't have an X-Ray machine to inspect the internal layers, I have no way of telling if the board is borked or not. It still blinks out a RAM error, but it's also been heated to several hundred C a few times now and I have no idea what I'm doing with a hot air gun other than make chip hot, place on or take off.
So that's part 2. Maybe there will be a part 3, but it's hard to justify buying another RAM chip or stuff to try and reball the now partly melted 8GB chip. I would love to see it succeed but I just don't have the skills or all the resources to do this properly, assuming the pi is still ok internally after all it's been through. This has been a fun albeit expensive learning experience.
If anyone has any resources around how to do BGA reworking, any advice, or a spare RAM chip with the balls still on it, I'd love any support. If you made it this far, thanks!
The pi prior to getting the RAM swapped
The Pi this morning prior to the second reflow (I got ahold of flux this time!)
After some thoughts, I've created a new Pi! The Pi4 0GB! So maybe a I did do something cool after all and now have a very unique Pi.
submitted by /u/Bytepond
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Source: https://www.reddit.com/r/raspberry_pi/c ... gb_part_2/