lists at rtty.us
Sat Aug 14 16:08:13 UTC 2010
I brought up the idea of a full spec at the time. Since we made the parts and used them it seemed like a reasonable idea. The price on the parts went from $ 0.0326 each to $ 18.56 when the major parameters were banded 2 to 1. Since we were using 4 in a $ 35 item (bom was about $6) the suggestion was not well received.
On Aug 14, 2010, at 11:50 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 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 Unpublished specs needs consistency testing or even selection testing on all components.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.
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