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March 2000

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Subject:
From:
Glenn Pelkey <[log in to unmask]>
Reply To:
Date:
Mon, 20 Mar 2000 08:33:43 PST
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Hi Justin,

        Here's what we do:

1)  Fiber optic assembly:  Bellcore TR-332
2)  Military Assembly:  Mil-Std-217F
3)  An Other Assembly:  Parts count method using supplier data for active
components and any passives that are available.  Use Bellcore as first choice
for any not available, use 217 last.

        Here's some other info to keep in mind when doing reliability
estimates.  First, many people are skeptical of these methods, but I still
find there's value in them.  In the least, it opens up lines of communication
between you and the supplier so that you can be aware of limitations and
potential/past problem areas.
        Second, if you use supplier data, be sure to adjust for temperature
and confidence levels.  Many suppliers will publish 25 C failure rate numbers
and Bellcore asks for 40C.  As you probably know, the higher the temperature,
the higher the failure rate and lower MTBF.  We also like to use 90%
confidence, but you will often find 60% confidence commonly used.  The higher
the confidence, the higher the failure rate.
        Thirdly, Bellcore (Telcordia) TR-332 now costs $1,000.  Good luck
trying to sell management on that.

Some links:
http://telecom-info.telcordia.com/site-cgi/ido/index.html
http://www.enre.umd.edu/mainnojs.html
http://www.quality.org/html/reliable.html

Glenn

Justin Braime <[log in to unmask]> Wrote:
|
| What is the best method for calculating an MTBF figure for your average, run
of the mill, electronic
| assembly?
| Are Bellcore TR-332 and MIL-HDBK-217 still the most current standards in
this area, or has IPC come
| out with something?
|
| my humble thanks...
|
| Justin Braime
| ------------------------
| Process Engineer
| Compuspec Industries Ltd
| Auckland, New Zealand
| [log in to unmask]
|
|

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