Hi Gordon, 

"1. The process by which reliability distinctions get into 
    standards. 

 2. The relative merits of making the distinctions on the 
    basis of consequences vs. risk of failure."

I'll try to explain from another side of Reliability and 
Product Safety. 

Reliability - 

Bellcore is a private set of standards (in other words they 
are not enforced by law) covering telecommunications 
equipment. Technical Reference TR-NWT-000332 "Reliability 
and Quality Generic Requirements".  From this, through 
complicated math, failure rates of each component are 
used for the calculation of the entire assembly. 

FITs "Failure in Time" are used as well as MTBF "Mean Time 
Between Failures".  A FIT = 1 is one failure in 10^9 hours. 
Typically say, a 1/4W carbon composition resistor has a 
FIT = 1.  MTBF = (10^9 hours)/FITs. Unfortunately, MTBF 
doesn't say anything about MTTF "Mean Time to First Failure".
These FIT or MTBF numbers are supplied by either Bellcore 
from charts for standard parts (such as the resistor above) 
or from the mfr using accelerated tests and calculations. 

No where in this document are any calculation based on 
any flux residue analysis nor processes related to 
boards.  The construction of boards as such is covered 
in another Bellcore document TR-78 soon to be GR-78. 

The purpose of all this number chrunching is to give 
the Telco customer (like NYNEX or Ameritech to name 
some) a "reasonable" estimate that indicates how 
long a device will last. This is driven from the 
service provider handling 911 calls for example. 
Another would be simply comparison - one piece of 
equipment has a one failure in 100,000 hours, another 
one has one failure in 500,000 hours. 

Safety - 

All of the product safety testing I've had done for UL 
never addresses board construction, i.e. flux residue, etc. 
They do approve clearances between traces and CTI 
(Comparative Tracking Index) of the material used. 
Failure analysis is done at a first level stage -
something shorts, something opens, something overheats. 
It is motivated by "end user" safety. 

How all these things get into the standards be they 
public standards or private standards is driven basically 
by us - the industry.  If enough of us get on the 
bandwagon, we can pursuade ANSI or law itself to 
either rewrite an old or write a new standard. 

Think of ANSI as a clearing house for standards. If 
enough people have caused a fuss, they are charged 
with getting it written. They will turn toward an 
established organization for tha actual dirty work. 
You will see ANSI standards with a ANSI/xxxx. 
The "xxxx" is the actual commitee that performed 
the work. 


I don't know if I really answered your questions. 

Regards, Doug 

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   The comments and opinions stated herein are mine alone,
   and do not reflect those of my employer.
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