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FX sensors cost 20x DX sensors? More info?

Ana Stasi , May 10, 2012; 02:59 p.m.

I read the following on Wikipedia:

Production costs for a full-frame sensor can exceed twenty times the costs for an APS-C sensor.[citation needed]

Does anyone know where I can find more detailed information on the production of camera sensors and why the above is the case?

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Jos van Eekelen , May 10, 2012; 03:05 p.m.

Search photo.net. This was discussed (more than) a couple of years ago.

Matt Laur , May 10, 2012; 03:07 p.m.

Such sensors frequently have flaws (a bad pixel or two or a hundred) as they are manufactured. It's unavoidable. They're made on large wafers, multiple chips/sensors per wafer. The odds of a given small sensor having such a flaw are much lower than the odds of a physically larger section of the parent wafer having a similar flaw.

So, you get a higher failure rate with the larger sensors during manufacturing. Combine that with the fact that smaller sensors sell many, many times more frequently than larger ones, you have the economy of scale that goes into producing millions more of the small ones. This contributes to the lower costs on the smaller sensors (or, a smaller customer base for the large sensors contributes to the higher costs, depending on how you want to look at it).

Bob Sunley , May 10, 2012; 03:07 p.m.

Yield is the name of the game. The higher the yield, or % of good parts, means lower unit prices given the same production quantities. The same applies to ALL semiconductor devices.

Try google. :)

Remco Jan Woldhuis , May 10, 2012; 03:10 p.m.

Another cost parameter is the wafer usage. Wafers have fixed dimensions (circular). The smaller the chip is, the more efficient real estate usage is possible. When producing 36x24mm chips, there's a lot of unused space on the wafers.

Michael Chang , May 10, 2012; 03:35 p.m.

Ana, here's a video description of how CCD sensors are made by Teledyne Dalsa.
http://www.youtube.com/watch?v=bqJksXwrx7U

A factory built to produce sensors can cost $500M or more, and along with its R&D costs, must be recovered through sales.
http://news.cnet.com/8301-10784_3-9747468-7.html

Full-frame sensors currently lag APS-C sensors in sales by a wide margin which in part accounts for the price-ratio difference. Another contributing factor is yield - more complex sensors of larger wafer size might have a lower yield during manufacture due to defect-rejection. The manufacturing process also takes longer than smaller sensors.

There are other contributing factors not within the normal course of business such as Sony's sensor factory flooding:
http://image-sensors-world.blogspot.ca/2011/10/sony-thailand-ccd-plant-flooded.html

This is not an exhaustive list but is generally accurate; others may input corrections or additions.

Mike Halliwell , May 10, 2012; 05:03 p.m.

So are medium format sensors, such as the one for the Pentax 645, another cost leap ahead? More expensive yes, but not such a huge leap I think?

There must be a huge 'failure' rate for such large chips and a real low number of sales relative to FX. DX or CX.

Leigh B. , May 10, 2012; 05:29 p.m.

Let me try to put the failure rate in perspective.

Semiconductor yields are based on average defects per unit of area (square inch or whatever).

Suppose your process has an average defect rate of one per square inch.
If your sensors are 1/10 square inch in size, you can expect nine good sensors out of every ten (90%).
If your sensors are 1/2 square inch, you can expect one good sensor out of every two (50%).
If the sensor is a full square inch in size, you can expect zero good sensors (0%).

Another point to consider is the quality level required for different sensor sizes.
Consumer-grade (small) sensors can tolerate a few bad pixels because consumers don't care.
Professional-grade (large) sensors have much tighter quality requirements, generally rejecting any sensor
with even one single defect. This contributes to lower usable yield.

It all boils down to economics. It costs the same to process one wafer regardless of what's on it.

- Leigh

Ilkka Nissila , May 10, 2012; 06:29 p.m.

If you have an average defect rate of one per square inch, there will still be some square inches which are defect free (and some with multiple defects). If the number of defects per area follows a Poisson distribution with expectation = 1 per square inch, then the probability of a given square inch to be defect free is about 37%. So 37% yield in this case. (Disclaimer: it's bedtime and my stats are rusty.)

Also, since dead/hot pixels can be mapped in software I doubt the sensor has to be completely defect free when it is manufactured.

Leigh B. , May 10, 2012; 06:37 p.m.

Semiconductor manufacturering operations are based on statistical methods.

When you're making parts by the hundreds of thousands, the time required to test each becomes
prohibitively expensive if the yield drops below a certain threshold, perhaps 30% or 20% or whatever.

There will always be some good parts even from a bad process, but finding them is not cost effective.

As I mentioned before, the definition of "defect" varies with the size of the sensor. A minor problem that
would pass inspection for a consumer-grade sensor might be considered a hard failure at pro-grade. So
the defect rate increases as the sensor size increases.

You can mask a bad pixel in software, but you cannot replace the information that was lost due to the error.

- Leigh


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