Why exactly do you think 3900X is much cheaper to produce?
- 3900X consists of 14nm IO die (~125mm^2) and two 7nm CCD dies (76mm^2).
- Both Zen and Zen+ dies are around 209mm^2.
- We do not know exactly how large Intel's 10-core thing is but since Skylake and derivatives have a long history, we know that 4 core die (7700K) is ~125mm^2, 6 core die (8700K) is ~175mm^2 and 8-core die (9900K) is ~200mm^2. The numbers are not exact, a few mm^2 here or there but close enough. Adding two more cores would put a 10-core die at ~225mm^2 assuming no other major changes are made.
Edit:
I messed up the sizes here. 2 additional cores add about 25mm^2 but I somehow went +50mm^2 from 4 to 6 cores. See
comment below from
@ppn . He correctly estimates 10-core CPU at 200mm^2 and 12-core CPU at 225mm^2.
200-250mm^2 is not a big die yet, it's reasonable in terms of yields and production.
3900X has smaller dies but more die size and 7nm is more expensive.
When it comes to cost also consider in case of Intel CPUs Intel is both CPU architecture designer as well as manufacturer. They can work with both design and production margins. In case of AMD, AMD designs the CPU architecture but dies are manufactured by TSMC. TSMC wants its own profit and its own margins regardless of what AMD does.
I am not saying Intel would be willing to cut into its margins - recent history shows exactly the opposite - but when shit hits the fan, they can.
Are you serious? History quite clearly shows Intel has had no intention of sitting on an older node if they can produce on a smaller one. Sandy Bridge was at 32nm, Ivy Bridge was at 22nm, Broadwell was at 14nm.
They are on 14nm because they do not have a new process node available for production, pure and simple.
Hell, Intel
is sitting on 14nm variants for 5 years even though they do have competition.