According to Tom’s Hardware reports, a Reddit user named Pi800 really wanted a Pi 400 with eight-GB of RAM. If you don’t have a RAM module that works for the custom Pi board, then Pi800 realized that Rapsberry Pi Compute Module has similar RAM circuitry to the Pi400, and it’s possible to buy one with 8GB of RAM attached. Pi800 then took the obvious step of removing the 8GB chip from the Comnputer module. It needed a lot of heat because the lead-free solder flipped on it. As the module, that was attached to the board by a ball grid array, Pi800 needed to “reball” the chip, which was done hand rather than using a BGA stencil. In total, on the chip a pair of 200 balls was melted in order to be attached to the Pi400. The old 4GB RAM module was removed and the PCB was cleaned before soldering the 8GB module in place and hoping that the transplant would work. Sure enough, the modified Pi 400 booted and recognized 8GB of RAM was available. The test performed after the RAM tested, so the operation was fine. Considering this was just a straight chip swap, it’s surprising that a Pi 400 hasn’t been offered as a choice because it has 8GB of RAM. Perhaps it is future, but with chip suppliers and prices as they are at the moment, this isn’t likely to happen for quite some time.
