>>> I also saw an article just a couple of days ago, stating that the cost >>> of FF sensor is 10 to 20 times larger than that of APS sized one and >>> it won't narrow. But I have a bad habit of not bookmarking. Maybe I >>> read it somewhere in this white paper. I will take a time to read it >>> more in detail later ;-). >>> >>> >> Really? *Someone* provided some info *somewhere* in the context of the >> release of the Canon 5D that suggested it had actually narrowed quite a >> bit since the release of the 1Ds, and that there was also a lot more >> room for improvement. I think it said that the yield was up from 10% to >> 25% - while it had remained stable for a while at 80% or whatever for >> smaller sensors. But perhaps your article was written after that and/or >> gave a good reason while this gap won't be reduced further? >> > > OK, I finally found where these descriptions were. [ ... ] > > Anyway, here is what the Japanese article says; > > 1. yield from 8" wafer is 200/APS-C, 46/APS-H, 20/FF > > 2. number of LSI's on a single wafer is 1000~2000. If for example, > there were 20 defects but rather uniformly distributed over the wafer, > it could be possible that "ALL" FF sized sensor could be defective. > OK. I was referring to an article someone posted when the 5D was discussed just after its launch, but of course I can't find it now (haven't tried too hard, though.) I think it included figures similar to the ones included above, but claimed that this was the (average) yield after defective units was taken into account (or counted out, if you like.) The number of units that can actually fit on a wafer was quoted as something like 250 for APS-C and 80 for FF. You may notice that the ratio between those numbers is already larger than the actual difference in area because you're bound to loose more material near the edges with larger chips (the wafer is round.) What's worse, however, is that (according to the article), out of those 80 FF units, as much as 60 on average are going to be useless. You'll loose some with the smaller size, too, but "only" about 50 out of 250.
But the article went on to say (or perhaps began by saying) that it used to be worse - around the time of the introduction of the first 1Ds only 5 to 10 of the 80 units would be usable. I don't know enough about IC production to know for sure how Canon has managed to reduce the number of defective units, but I'm assuming that the industry has learned over time how to utilise lower-quality silicon (thus reducing the effects of "bad" areas on the wafer) and also minimise the number of errors in the production itself. And I've also been assuming that the production quality will continue to improve, which will of course be most beneficial for the larger chips, thus narrowing the gap... - Toralf -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
