7100 as full frame?

Started Sep 3, 2014 | Discussions thread
trac63 Contributing Member • Posts: 769
Re: Cost of the sensor
1

Mr Gadget wrote:

trac63 wrote:

billfreedom wrote:

I cant quite figure out why the full frame cameras are so much more $$ than the DX versions.

For example, if you took the 7100 and simply swapped out the sensor and replaced with a full frame sensor and processor and mechanics, how much more $$ would the camera cost to make?

A 135 frame sensor costs up to 20x more to produce than an APS-C.

I would have to disagree. Both full frame and APS-C sensor fabrication is done on the same silicon wafers, using the same wafer processing steps, materials and chemicals, the same number of mask layers. In the past, the full frame sensor had to be stitched together due to the fact that the stepper reticle field size was smaller than the 24mm x36mm sensor size. This would add a bit to the yield loss for full frame over APS-C which is already higher due to the larger chip size at the same defect density.

Here is a great explanation of chip costs that was written by Michael Berman in 2008.
http://www.dpreview.com/forums/post/27102330

If for the sake of argument, you assume a cost of $1000 per processed 300mm wafer, then the 44 yielded full size sensors would cost $22.73 each while the 102 APS-C size sensors would cost $9.80 each. So FX sensors will cost 2.32 times more than DX.

The arithmetic is not that simple. All the current lithographic processes generate defects on every wafer, and the larger the die size the lower the percentage of defect-free chips. You may get only 2.25x more APS-C sensors from a wafer, but in terms of the number of usable sensors the multiplier is much higher, assuming they're manufactured using an identical process (which they're not).

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