My first preference is using through-holes for both the PGA-168 and PGA-132 mounts and a single PCB. I remember thinking long and hard about this years back and determined that I could even assemble it without hot air, but now that I am comfortable with solder paste and hot air, I'd likely use this to save time. I think the VRM, trimmer, header, and tantalum should be on the edge of the PCB like that shown for the commercial product above. This allows the VRM to cool some using an affixed fan. I never thought sandwiching the VRM under the CPU was a good idea. I'm not sure what the printed cost difference is between a 4, 6 and 8 layer PCB on a 10-unit order, so I cannot say which is preferred. I think using SMD sockets is not a great idea unless we have a single source [a person here] who can solder them on. Maybe some low melting temp solder paste would work, while not melting the plastic on the housing?
I do not have a preference for which edge of the PCB sticks out to receive the VRM/trimmer/header/tantalum. I think the tantalum might need to be moved to the centre if the VRM/trimmer/header consume too much real-estate. The header would be 3-pin, one for MEMW, the other two for 5 V and GND (fan). There are no multipliers which would use jumpers.
For assembly, I'd first try using rows of machine pins, as those shown above. Test the unit to ensure functionality at 80 MHz, then on a second PCB, see if I can use the proper PGA sockets w/hot air.
Someone mentioned about the possibility of needing to use same trace lengths for, I think, address and data lines. Is this needed? Max CPU operating frequency would be 100 MHz. Also mentioned, there may need to be more filtering caps underneath for each Vcc?
By the way, I should still have a dozen or so of the SXL2-66 PGA-168 chips held for me for this project.
Second overall choice is the double PCB method.
Thanks again.
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