R
Raveninghorde
- Jan 1, 1970
- 0
How do you calculate MTBF?
How do you calculate MTBF?
Get the failure rate of each part (specified in FITS, failures per
billion hours), add them up, take the reciprocal, multiply by a
billion.
John
For a component? For an entire system? 217 or Bellcore/Telcordia or ...
The Wikipedia article isn't a bad place to start. If you're tasked with
doing a full-up parts-stress reliability prediction analysis, good luck!
Thanks
The National site is good and I found the info for the their parts.
Microchip no luck, IR no luck. So where do you normally find the
information?
I suppose one also assumes perfect ESD procedures, and perfect lead
free soldering.
On Thu, 21 Jan 2010 12:43:20 -0500, Rich Webb
[snip][snip]You're new at this so, even if you're not doing a MIL-STD prediction,
I'd strongly recommend downloading MIL-HDBK-217 from the online site
<https://assist.daps.dla.mil/quicksearch/> (search on MIL-HDBK-217 in
the Document ID field) and skimming though sections 3 and 4. The
Bellcore process is similar.
Firefox give me "This Connection is Untrusted" for that site.
It's been a long time since I did any of that stuff but IIRC the MILJohn Larkin said:We use Bellcore because the calculated MTBFs come out much higher.
John
Thanks
The National site is good and I found the info for the their parts.
Microchip no luck, IR no luck. So where do you normally find the
information?
I suppose one also assumes perfect ESD procedures, and perfect lead
free soldering.
You're new at this so, even if you're not doing a MIL-STD prediction,
I'd strongly recommend downloading MIL-HDBK-217 from the online site
<https://assist.daps.dla.mil/quicksearch/> (search on MIL-HDBK-217 in
the Document ID field) and skimming though sections 3 and 4. The
Bellcore process is similar.
John's basic equation is correct. You can use the tables in 217 to
estimate the reliability of items for which the manufacturer does not
provide the info.
There are provisions to consider connections (e.g., "Quantity of Hand
Soldered PTHs [plated through holes]"). It's a hell of a lot of work to
do a full analysis.
..as long as they PAY for the info and time to compile it.
Given the customer I'll go with 217. I'm trying to avoid spending a
week doing this so I'm looking at other solutions.
I've seen a few websites that offer online calculation ($500) or send
the BOM and results in 48 hours ($1500). I've also seen some programs
that calculate MTBF.
Anyone tried these options?
Nope. They would prefer the BOM and do the calculation themselves.
Since I won't give the BOM it's down to me sort it out.
Basically it is the _statistical_ point where the root sum square failure rate
of the individual components becomes 50% probability.