On 08/14/2010 05:08 PM, J. Forster wrote:
FWIW, IMO any engineer who uses undocumented or uncontrolled parameters or
instructions in a production design is a fool.
If you are that silly, you must fully specify the selection criteria.
Using non-spec aspects needs documentation, motivation and risc analysis.
I've designed a selection routine for a component which still ticks on
with good statistics. The main problem is that eventually that component
will be on last buy level. Obviously it seems the selection was chosen
on the conservative side, so it works in shipped products regardless of
batch. Trimming of the manual routine has lowered a certain failure mode
of testing.
Any spec should be verified. Published specs needs verification with
real components. Unpublished specs needs consistency testing or even
selection testing on all components. Cost of testing needs to be
understood and risc of low yield in future needs to be understood and
alternative approaches could be put in place before running on flat tires.
At times it may be cheaper and safer to run with more expensive
components which is within spec.
Cheers,
Magnus
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