As we know some laptops come with soldered cpus. In most cases same laptop has different variants of it e.g. one comes with i5-7300hq and other with i7-7700hq. Those cpu's are same generation. My questions are: Do two same generation soldered cpu's come with same contact pad array? Could one solder off more powerful cpu and solder it on motherboard who had same generation slower cpu? And WOULD IT WORK? e.g. soldering off i7-7700hq of donor board and soldering it in place of i5-7300hq
Physically, it works. 7300HQ and 7700HQ are both FCBGA 1440 socket, so they are in theory compatible, but the package is soldered to the PCB and changing it can be really hard due to the precision of the needed solders, as Jan mentionned.
There are still few concerns:
- Changing CPU may change power dissipation needs, which is a stumbling block on laptops.
- It may also change power consumption as well, same problem.
- Bios may prevent from changing CPU.
The first two shouldn't be problems considering that the 7300HQ and the 7700HQ have the same TDP even though the i7 may draw a bit more power and heat up a bit more too.
For the last concern, it depends on your laptop.
Soldering BGAs is hard even for machines. Reworking a new one in place of an old one manually is harder. Getting one from an old board to a new one is nigh impossible.
BGA stands for ball grid array. While many Intel documents are not public, BGA itself is an industry standard. Those devices come with tiny solder balls attached to them which then get deformed when soldered to the board. And when you put the processor on a new board it might turn out there is not enough solder on some pins.
Also: this requires superb precision. Looking at the datasheet for the i7-8650U which is also FCBGA has a minimum pitch (distance between two neighbouring balls) stated as 0.914mm. Which means you need to place the processor accurately down to about 0.5mm. With no obvious reference point. If it seems hard that's because it is.
As an anecdote: someone I know, who is the best in our company when it comes to soldering, once soldered a device with similar package. A bit finer pitch, waaaay less balls and these were brand new ICs. Out of three only one worked.