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From:
WTSJ-Willis Tam <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, WTSJ-Willis Tam <[log in to unmask]>
Date:
Fri, 18 Nov 2005 09:49:23 +0800
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Hi Inge,



How to link to Steve?



Regards

Willis



-----原始邮件-----

发件人: TechNet [mailto:[log in to unmask]]代表 Ingemar Hernefjord

发送时间: 2005年11月18日 5:47

收件人: [log in to unmask]

主题: [TN] Reliability prediction of LF soldering LAST CALL!





Still  awaiting for an answer from the experts: can we neglect the

varying distribution of lead when soldering BGAs and other parts? If

not, how do we handle the situation on the floor. Production people want

know what to do when they do sample metallurgical investigations and see

Lead distributed many a way. See example sent to Steve, one and the same

BGA. Bright spots is Lead.

Inge



-----Ursprungligt meddelande-----

Från: TechNet [mailto:[log in to unmask]] För Ingemar Hernefjord

Skickat: den 17 november 2005 03:07

Till: [log in to unmask]

Ämne: [TN] SV: [TN] SV: [TN] [LF] Reliability prediction of LF soldering



Bingo jk,

That's what I mean with reality. Scientist being, as you are with your

background, you have to admit, however, that Arrhenius law is adaptable

on hot solder joint as well as cold, but it's a tough job to 'estimate'

all the thousand individuals because of the different life they live.



I would like to pay attention to my own central question which was

indeed a super'estimation': can we omit the various lead distribution in

BGA solder joints (and others as well)? I did not contribute with a

solution myself, because I wanted to wake up the dragons to see what

treasures they were lying on.



Our company has been working for years with the announced topic, and in

cooperation with other companies. All do the same. If you do your

'estimations' without too many of my reality factors, your MTBF

calculations give an interesting answer. As the result belongs to our

company, I can't give you the exact figure, but I can go so far as to

say this:

MTBF for LF BGA solder joints is : MTBF(LF)=MTBF(Sn/Pb) times a

multiplicand that is less than 1.0. All is confirmed by numerous tests.



Upon this number, you may build your up-and-down pyramid by putting in

all the real life factors that I mentioned. We are working on that, but

it seems to be a long working day before we have nice and reliable (!)

model.



Inge



-----Ursprungligt meddelande-----

Från: Joyce Koo [mailto:[log in to unmask]] 

Skickat: den 16 november 2005 23:34

Till: TechNet E-Mail Forum; Ingemar Hernefjord

Ämne: RE: [TN] SV: [TN] [LF] Reliability prediction of LF soldering



"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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Avanex

John Burke

Senior Manager RoHS Compliance

[log in to unmask]

40919 Encyclopedia Circle

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CA 94538

tel: 510 897 4250

fax: 510 979 0189

mobile: 510 676 6312

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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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