🚀 go-pugleaf

oldwanda (93gke@williams.edu) wrote:
: In article <1993Jan5.152504.9786@bmers95.bnr.ca> khor@bnr.ca writes:
: >For example lets take a simple switching speed from low to high.  If
: >it takes 35ns to switch (low and high voltage levels reference points
: >differs in low->high and high->low), then it will fall into the 25MHz
: >grade.  But if the switching takes only 28MHz then it will fall into
: >the 33MHz grade.
: 
: >In the actual case, the testing is a lot more complex and there are
: >hundreds of electrical tests before the chips a graded.
: 
: If this is true, then how can vendors push the 25Mhz chips to 33Mhz?
: Wouldn't they fail at the higher speeds since they were slow in
: testing?
: 

Sometimes, chip makers will test to fill orders. If they have outstanding
orders for 25Mhz parts, they will noly perform a test at 25Mhz, and ship those
that pass. When throughput is important (because of backlog), testing at
several speeds reduces the part throughput. Parts that fail may be put in a
retest bin for later testing at a slower speed rating (if they offer it) or
trashed if it failed the lowest speed rating they offer.

Also, the tests that are performed on the parts, is very rigorous. I know, my
company makes the testers that chip makers use to test these parts. The
computer makers are betting on the fact that 99.9% of the time, "pushing"
a chip will not be as rigorous as the testing that placed them in the rated
speed category, or that the part would have passed the higher speed rating,
but was simply not tested because of market demand and backlog.

In some cases, during the life of a product, newer versions of the chip may
come out, because of a die shrink, that allows production of faster parts,
but the slower parts are still the old technology. Pushing these chips is
very dangerous, because the process was never intended to yield such parts.

In any case, you do take a chance, and if at all possible, insist on a part
factory labeled to run at the speed it is being clocked at.

Russ Poffenberger               DOMAIN: poffen@sj.ate.slb.com
Schlumberger Technologies ATE   UUCP:   {uunet,decwrl,amdahl}!sjsca4!poffen
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