I believe the basis for many (most) component failures comes from
the military and the Reliability Assesment Center (RAC) - and I could have
the name slightly wrong. They ran demonstrated tests on components at
various stress levels to derive the FITS, for the Military.
I believe they are still functioning. Could be, and have been
several times, wrong about that.
Gary
-----Original Message-----
From: plaw...@west.net [mailto:plaw...@west.net]
Sent: Wednesday, August 30, 2000 8:43 AM
To: EMC-PSTC
Subject: Re: MTBF Calculations
The comments below are made in the context of the Bellcore reliability
prediction standard TR-332.
On Fri, 18 Aug 2000 12:01:09 +0200, "Gert Gremmen" <cet...@cetest.nl>
wrote:
>This MTBF calculations are interesting, and sounds logic.
>Next logical question:
>
>How to estimate the MTBF of:
>
>a component - IC - Resistor - Cap - Elco
> I suppose a component manufacturer can say something about that
The Bellcore standard was written around Bellcore's experience with
products. Presumably they kept records of what part failed after how long.
This standard does allow you to specify a different MTBF for parts if you
have more appropriate data.
>a PCB
> Adding up invers MTBF's is easy, but what does the soldering do ?
> How to manage things like "heat spread out" (f.a. VGA monitor MTBF < 1
year)
> Factors like vibration, humidity, environmental issus like external
heat, dust..
Interestingly, the Bellcore standard excludes the blank PCB board and
soldering.
>
>an apparatus
> a disk drive ( in 1980 my 5MB HDD lived less then 6 months)
Assuming that the disk drive was designed properly, that sounds like a
workmanship problem. I haven't heard of any standard that takes that into
account.
I suppose a manufacturer could specify reliability on the basis of field
return rate, which would reflect your drive failure.
>
>an equipment
> a personal computer
>
>a system
> a GSM/cellular base station or computer network
>
>a network
> the internet
>so many questions ....... and no answers ??
>
>Regards,
>
>Gert Gremmen, (Ing)
>
>ce-test, qualified testing
>
>===============================================
>Web presence http://www.cetest.nl
>CE-shop http://www.cetest.nl/ce_shop.htm
>/-/ Compliance testing is our core business /-/
>===============================================
>
>
>>>-----Original Message-----
>>>From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf
>>>Of Doug
>>>Sent: Thursday, August 17, 2000 4:06 PM
>>>To: Joel Mandel; EMC-PSTC Discussion Group
>>>Subject: Re: MTBF Calculations
>>>
>>>
>>>
>>>Guess I went a little overboard there.
>>>Some clarification is needed.
>>>
>>>MTBF is Mean Time Between Failures. This has nothing
>>>to do with repair in the strict sense. This has to
>>>do with assemblies which fail, then are replaced.
>>>MTBFs are *supposed* to be applied to things like a
>>>fuse, a resistor, ... things that don't get "repaired".
>>>
>>>MTTR is Mean Time To Repair. This does involve items
>>>that are repaired, a printed circuit board, ...
>>>
>>>You will find that MTBF is used interchangeably with
>>>MTTR quite a bit. If you're a stickler for semantics,
>>>then I guess it's important. Some vendors I've worked
>>>with make the distinction, so be careful.
>>>
>>>My experience with Bellcore 332 is this - as long
>>>as you are talking about some "thing" as the final
>>>assembly which may be composed of all sorts of
>>>sub-assemblies, you basically just add up all the
>>>FITs, invert, and you've got your MTBFs.
>>>
>>>1 FIT is 1 failure in a billion hours.
>>>
>>>- Doug
>>>
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