Electronic – Buying Low Volume Populated PCBs and Handling Passive PNs

The simple solution is that physical processors are identified using a wire connection. When you put your CPU into mainboard, there is a lot of pins on it. A pair of them can be simply short-connected inside CPU and used to say "I'm connected".

Additional CPU cores inside a single physical processor can be obtained by executing a special machine code instruction. CPU always know who it is and is ready to tell us when we use the "magic" machine code instruction.

The concrete solution depends on the particular computer system, BIOS, CPU family etc. The BIOS have to know exactly what different possible CPUs can it expect in the mainboard. (It is not possible to put 2-core CPU in an old mainboard which wasn't designed for 2-core CPUs.)

You can find very detailed information about x86/x64 CPUs on www.intel.com.

From my experience, one-off assembly is extremely expensive in the US. Most places would not even bother giving me a quote for a single piece. Furthermore, you're likely to have the same problem with building a breakout board, since that will have to be assembled (it just displaces the problem). However, I have found that (with some work), it is possible to do BGA parts if you have access to a reflow oven, or if you have access to a fairly good heat-gun.

For heat gun instructions: http://devbisme.webfactional.com/blogs/devbisme/2012/08/24/mounting-bga-pcb-quickly-and-cheaply

For a reflow oven: I used #186 rosin flux at 295 C for 90 seconds with a 200 C preheat (180 seconds). This is higher than most manufacturers recommend, but the oven I have access to was donated to the University and is from the early 90s, so it doesn't actually get that hot. It was not necessary for me to use a stencil or even apply any solder paste, I simply coated the footprint area with flux and carefully aligned the package to the silkscreen.

One bit of layout advice if you do not have access to an oven is to make the board as small as possible. This makes it possible to heat up the entire board to a consistent temperature.

Also remember to tent vias under the BGA, if you do not, capillary action will cause the solder to flow from the balls into the vias, which is not what you want to do. http://siliconexposed.blogspot.com/2012/07/bga-process-notes.html

Finally, if you don't have access to x-ray inspection, make sure your silkscreen outline is precise. It should be slightly bigger than the package to assist you in aligning the part. You can print out the silkscreen layer in Eagle on a conventional laser printer with 1:1 scale to make sure you can align it on paper first.