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November 2005

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From:
Joyce Koo <[log in to unmask]>
Reply To:
Date:
Wed, 16 Nov 2005 17:33:58 -0500
Content-Type:
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"Some GaAs chips are so hot
that you burn your fingers when you touch them,"...

Laptop by the name of it should be able to put on your lap... how many of
lap top is cool enough to sit on your lap?  By the way, I couldn't
understand why the laptop guys always ad that "ultra-light" "compact",
meanwhile you need one of "cooling pad" to operate these ultra stuff...
http://www.maplin.co.uk/Module.aspx?ModuleNo=45656&&source=14&doy=search

As for reliability, heat dissipation sure get rid of all the MTBF prediction
(how many of prediction based on the hot location and cool location in the
same unit?)..don't get me started..
                       jk

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ingemar Hernefjord
Sent: Wednesday, November 16, 2005 4:21 PM
To: [log in to unmask]
Subject: [TN] SV: [TN] [LF] Reliability prediction of LF soldering


Exactly. A processor chip can go really hot, while other chips are
biased in a way  that they have nearly no heat dissipation at all. The
boards general temperature is another factor, starting a board at 30,000
feet or at Saudi ground is two extremes, that affect the calculations.
And the placement on the boards, we have boards mounted on a cooler
waffle, big differences in BGA temperatures. Some GaAs chips are so hot
that you burn your fingers when you touch them, others are working once
in a month etc. Some balls carry a lot of current, others just pA.
Center of superBGA differs from perimetrically placements. Warpage from
the boards have an impact. Vibration and other mechanical injections
have an impact. And so on. I'm not doing MTBF predictions myself, but I
realise that we must have to do with very complex models to be able to
predict the real life for a given number of components on a specific
board. I still believe in making tempcycling, switched life test and
life tests to failure and other practics which I call hand-on. I'm
probably rigid, conservative and too old to learn new things...

Inge

-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Ahne Oosterhof
Skickat: den 16 november 2005 21:48
Till: [log in to unmask]
Ämne: Re: [TN] [LF] Reliability prediction of LF soldering

>From my "engineering" experiences:

I used the "scientific" method to calculate an MTBF before finishing a
paper
design. Then changed the design if the number ended up too far out of
the
desired ballpark.
The changes could be made (I thought) because for most components the
demonstrated MTBF depended a lot on how they are being used. A 1W
transistor
dissipating 0.1W lives longer than one running at 1.0W. (Kind of like
comparing one solder joint on a 0402 resistor in a desktop modem (super
benign environment) to one on the corner of a BGA located close to the
shear
edge of a board that is used in a portable computer by a forester in the
Pacific NW in the middle of winter (throw it, shake it, cool it, etc.).
After building engineering samples of the design I required life cylce
tests
to find a 'demonstrated MTBF', a number that would go in the spec
document
for customers to see.

This discussion is really "fun".
Ahne.



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
(KC/EMW)
Sent: Wednesday, November 16, 2005 10:25
To: [log in to unmask]
Subject: Re: [TN] [LF] Reliability prediction of LF soldering

Agree, wasn't an answer on my question. We have complicated situation
with
mixed technology, and we have few persons with a deep understanding in
the
mystery of metallurgy and kinetics and so on. Perhaps someone else can
give
a tip. The scientific reports are sometimes too academic, and my job is
to
'strip' the report and make it understandable for those who work on the
'floor' (old fashioned expression, guess we are all standing on floor,
except for the high bosses, who are in the blue). So, again, can you
omit
the variations of lead distribution or not? It's very important that I
give
the soldering responible people a correct information.
Inge

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of John Burke
Sent: den 16 november 2005 19:09
To: [log in to unmask]
Subject: Re: [TN] [LF] Reliability prediction of LF soldering


Sharp words for Technet..........................8-)

John

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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Whittaker, Dewey
(AZ75)
Sent: Wednesday, November 16, 2005 10:04 AM
To: [log in to unmask]
Subject: Re: [TN] [LF] Reliability prediction of LF soldering


At least if he did that he could take it for granite that he was working
with cutting edge technology.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, November 16, 2005 10:59 AM
To: [log in to unmask]
Subject: Re: [TN] [LF] Reliability prediction of LF soldering

Hi Ingemar,
Well, tell us--what choice do you have? Are you a 'scientist' or an
'engineer'? Shall we stop making product? Go back to the stone
age--assuming
of course that the quartz is uniformly distributed in the blade of your
stone axe?
Since when do we live in a perfect world?

Werner

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