🚀 go-pugleaf

In article <C0Co70.1ID@usenet.ucs.indiana.edu>, ntaib@silver.ucs.indiana.edu (Iskandar Taib) writes:
|> In article <sheldon.725671411@pv141b.vincent.iastate.edu> sheldon@iastate.edu (Steve Sheldon) writes:
|> > But since these are targeted for commercial usage, they're most likely
|> >only testing 1 in every 100 or so, as Mike said, a few out of each batch.
|> 
|> > Chances are also good that if any of the sample batch fails the 25 Mhz, and
|> >depending on the percent failed, they'll test all chips in that batch to see
|> >if any of them are salvageable before they go throwing them all out the
|> >door.  Of course this last one depends on the economics of how expensive it
|> >is to test all the chips vs. just making new ones.
|> 
I beg your pardon.  Ever since the Japanese IC 'revolution', *ALL* IC
chips (no matter their size, complexity or commercial grade) are
tested before they are shipped.  The tests (electrical) may vary in
completeness and stringent-ness (sp?) but the tests are performed.
 
|> Just wondering: at what point do they test the chips, and how? Do they
|> do it while at the wafer stage, before they encase it in ceramic? How
|> are the connections made?
|> 
Tests are performed at various stages to reduce the cost of buidling
an IC that is bad in the 1st place.  Many of these are sampling test. 
But at final test 100% of the chips are tested.  And it is usually
during this stage that grading is done.
 
The normal practice is to test against the highest grade, lets say 50MHz.
If it fails that, then it will be downgraded to the next and so on. If
it fails the lowest grade, 20MHz (?) then it will be scraped.

For a 33MHz grade, the chip is usually tested to pass at, say 35MHz. 
The industry calls this the guard band.   Another factor, is the
market demand at the point in time.  If the manufacturer happen to
come out with a large batch of 33MHz chips but there is great demand
for 25MHz chips, they will simply re-label these to 25MHz and ship it.
This is referred to as downgrading.  (Somewhat confusing as there are
real downgrades during final electrical test). 
 
Anyway I do not represent any IC manufacturer. Enuf said.

............................................................................
. Kyle Hor                    .    /       / _   .  Email  khor@bnr.ca     .
. Bell-Northern Research Ltd. .   /__\  / / /_\  .  Phone  (613) 763-2488  .
. Ottawa, Ontario, Canada     .  / \  \/ /  \__  .  ESN          393-2488  .
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................  standard disclaimer, 2 cents opinion  ....................
.............  searching forever, for the perfect solution  ................