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April 2013

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Subject:
From:
Reuven Rokah <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Reuven Rokah <[log in to unmask]>
Date:
Wed, 17 Apr 2013 13:12:18 +0300
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The yield prediction S/W is basing on real results in each organisation /
EMS and having a self correction capabilities after receiving the future
results.
When you have such S/W, you can estimate the real cost of components,
assembly labor and may change the design accordingly.
Reuven

On Wed, Apr 17, 2013 at 12:49 PM, Joyce Koo <[log in to unmask]> wrote:

> It would be very hard to bang the "real world" idea into new generation of
> designer.  15 years ago, I ran into trouble to convince someone that triple
> redundancy of three module can not be equal to one single chip with on chip
> triple redundancy.  After 1hr useless dialogue, I ask if anyone can tell me
> the single event radiation damage zone size and how many transistors will
> be impacted on that single wonder chip, guess what! The 2 chaps look at me
> like I got two heads.  I think what you don't know will not hurt you.   The
> common sense is lost in some case is scary.  Better not think about it (too
> late anyhow).   I miss the good old A-10 aircraft days.  That is real
> engineering.
> --------------------------
> Sent using BlackBerry
>
>
> ----- Original Message -----
> From: Reuven Rokah [mailto:[log in to unmask]]
> Sent: Wednesday, April 17, 2013 03:24 AM
> To: [log in to unmask] <[log in to unmask]>
> Subject: Re: [TN] Reliability Predictions
>
> Years ago, I suggested and mentored  2 students in computer science to
> yield prediction project. The project was based on history yield, density,
> technology, sides of assemblies, thickens of PCB / layers count etc. The
> S/W was was auto improved (by adding new yield results).
>
> I am suggesting  IPC to start such project, it may help the industry to
> predict PCBAs yields and improve DfA / DfM procedures.
>
> Best Regards
>
> Reuven
>
> On Wed, Apr 17, 2013 at 9:36 AM, Per-Erik Tegehall <
> [log in to unmask]> wrote:
>
> > In the Introduction part of MIL-HDBK-217F it is stated that ”A
> reliability
> > prediction (per MIL-HDBL-217) should never be assumed to represent the
> > expected field reliability as measured by the user”. It is also stated
> that
> > "Those who view the prediction only as a number which must exceed a
> > specified value can usually find a way to achieve their goal without any
> > impact on the system". I think that says all that needs to be said about
> > this type of reliability predictions.
> >
> > Per-Erik
> >
> > -----Ursprungligt meddelande-----
> > Från: TechNet [mailto:[log in to unmask]] För Blair Hogg
> > Skickat: den 16 april 2013 15:10
> > Till: [log in to unmask]
> > Ämne: Re: [TN] Reliability Predictions
> >
> > I had asked the original question regarding methods used to determine the
> > predicated reliability of an assembly, whether it be a PCB assembly, or
> the
> > product containing the PCB assembly. There are a number of software
> > packages out there that will do this, and there are differing methods
> > ranging from simple - load the BOM into the package and it sums up all of
> > the failure rates and spits out an MTBF prediction, to complex where you
> > load in observed temperatures and other stresses which then are factored
> > into the prediction (generally making the MTBF lower).
> >
> > Accompanying this are methods used to evaluate how to increase
> reliability
> > and raise the MTBF. Increasing the wattage of parts that have higher
> > stresses, heat sinking, etc. are common methods.
> >
> > I have typically been using field data to calculate reliability for our
> > customers who request an MTBF number, however, on newer designs that
> number
> > seems suspect, as the devices have not seen significant service life.
> >
> > A while back I worked for a company that produced electromechanical
> relays
> > under Mil specs. We had banks of ovens and load testers that would test
> > relays for weeks on end, and each week one group would come off and a new
> > group would go on test. As you accumulated hours of test time with no
> > failures DESC would allow you to claim a higher reliability level for the
> > parts, as I remember L was lowest, then M, P and S. A failure would need
> to
> > be factored into the calculation and could cause you to lose a rating. I
> > think we attempted to get to 100,000 operations on each group being
> tested.
> >
> > Thanks to everyone who contributed to the discussion so far. I've
> > appreciated all the responses.
> >
> > Blair
> >
> >
> > On Mon, 15 Apr 2013 17:15:48 -0400, Honsowetz, Eric <[log in to unmask]
> >
> > wrote:
> >
> > Was the question about the reliability of electronic assemblies or the
> > reliability of PCBs?
> >
> > The University of Maryland,
> >
> http://www.calce.umd.edu/general/education/physics_of_failure_and_reliabili.htm
> >
> > has been one place that research into electronic assembly reliability has
> > been ongoing for a few years...
> >
> > I seem to remember that someone there had done some work of the
> > reliability of PCB materials and did a presentation Webinar via IPC but
> it
> > has been a few years and I never have had a good memory...
> >
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>
>
> --
>
> Best Regards,
>
> *Reuven Rokah*
>
> Mobile: 972-52-6012018
> Tel:        972-3-9360688
> Fax:          076-5100674
>  <http://www.rokah-technologies.com/>[log in to unmask]
> [log in to unmask]
> www.rokah-technologies.com
>
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-- 

Best Regards,

*Reuven Rokah*

Mobile: 972-52-6012018
Tel:        972-3-9360688
Fax:          076-5100674
 <http://www.rokah-technologies.com/>[log in to unmask]
[log in to unmask]
www.rokah-technologies.com

**
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