calculate MTBF
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From: John Larkin on 21 Jan 2010 11:54 On Thu, 21 Jan 2010 16:35:55 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: >On Thu, 21 Jan 2010 07:33:02 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >><raveninghorde(a)invalid> wrote: >> >>> >>>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 > >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? The two commonly used docs are MIL-HBK-217 and the Bellcore spec. We purchased the Bellcore reliability doc, about $1000 or so, and use its numbers unless we can get a specific FIT value from a vendor. That cost us about $50 a page, or $300 a page for the three pages that are useful. Occasionally a customer asks us for an MTBF value, so we grind out the numbers. Our actual field failure rates seem to be well below the values that we calculate. > >I suppose one also assumes perfect ESD procedures, and perfect lead >free soldering. > Yes. John
From: Rich Webb on 21 Jan 2010 12:43 On Thu, 21 Jan 2010 16:35:55 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: >On Thu, 21 Jan 2010 07:33:02 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >><raveninghorde(a)invalid> wrote: >> >>> >>>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 > >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. -- Rich Webb Norfolk, VA
From: Jim Thompson on 21 Jan 2010 13:05 On Thu, 21 Jan 2010 12:43:20 -0500, Rich Webb <bbew.ar(a)mapson.nozirev.ten> wrote: [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. > [snip] Firefox give me "This Connection is Untrusted" for that site. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: John Larkin on 21 Jan 2010 14:31 On Thu, 21 Jan 2010 12:43:20 -0500, Rich Webb <bbew.ar(a)mapson.nozirev.ten> wrote: >On Thu, 21 Jan 2010 16:35:55 +0000, Raveninghorde ><raveninghorde(a)invalid> wrote: > >>On Thu, 21 Jan 2010 07:33:02 -0800, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >>><raveninghorde(a)invalid> wrote: >>> >>>> >>>>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 >> >>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. One reason we paid for the Bellcore TR-332 document is that their numbers are much better. I assume it's the difference between commercial and military applications. John
From: Rich Webb on 21 Jan 2010 19:43
On Thu, 21 Jan 2010 11:05:32 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >On Thu, 21 Jan 2010 12:43:20 -0500, Rich Webb ><bbew.ar(a)mapson.nozirev.ten> wrote: > >[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. >> >[snip] > >Firefox give me "This Connection is Untrusted" for that site. Their root certificate is back in the .mil domain rather than the "normal" root authorities that are built into most current browsers. There may be some reluctance on the part of browsers or it could be a statutory limitation. -- Rich Webb Norfolk, VA |