How about a hypothetical example… Say it costs $20,000 for the raw silicon wafer and the stamping and cutting (I have no idea how wild-assed that guess is). That means a FF sensor costs $1000 and an APS-C sensor costs $100. Now, say there are on average two random local defects per wafer that result in the loss of the sensors where they occur. FF production takes a 10% hit on yield, whereas APS-C takes only a 1% hit on yield. Taking QC defects into account, the cost of a FF sensor is $1111 and an APS-C sensor is $101. Now, suppose this new process cuts the defect rate in half, to one per wafer, and increases production costs by 2% per wafer. That drops the cost of a FF sensor to $1074, a 3.3% savings. However, that 'improvement' results in an APS-C cost per sensor of $102.50, an
increase of 1.5% per sensor for APS-C production.
Sell 5,000,000 FF cameras and save $37 each and that's a 185 million dollar profit….
Sell 100,000,000 APSC cameras and spend an extra $1.50 each and that's a 150 million dollar
loss....
Now which pile of money do you think Canon would go for first?
Granted, this is only a hypothetical example. Hwever, it does demonstrate one scenario in which application of a process improvement for FF production would not be cost-effective when applied to APS-C production.