1. What yield improvement were you thinking of that is of no benefit to APS-C sized sensors? EXACTLY!
2. If it is of benefit to APS-C sized sensors, why apply it only to full frame sensors? Surely you apply the technology that improves yield to the production line that has the highest production levels (i.e. APS-C), not the one with the lowest?
Sell 100,000,000 APSC cameras and save $10 each and thats a billion dollars....
Sell 5,000,000 FF cameras and save $40 each and thats 200 million dollars....
Which pile of money do you think Canon would go for first
It depends on what the improvement is and how much it costs to implement. The rumor (although likely false) suggests an improvement in yield, which is where there's a major difference between FF and APS-C. Sensors are cut from round silicon wafers, and according to Canon
a single wafer can produce 20 FF sensors or ~200 APS-C sensors.
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
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.