Guenter,
We are facing (next month) assembly of quite a complex board (16 layers, 2.7mm, some BGAs as small as 1158 and 1441 pins, dual side reflow). I have doubts whether to test the assemblies in slow cycles (1500 cycles of -10/+60 deg C functional or -20/+70 deg C non functional), or to perform shock tests - liquid to liquid, for instance. From the job done in your lab - what would you recommend?
Regards
Ofer Cohen
Manager
Quality Assurance, Reliability and Production Technologies
SEABRIDGE Ltd. - A Siemens Company
> -----Original Message-----
> From: Leadfree [mailto:[log in to unmask]] On Behalf Of Guenter Grossmann
> Sent: Monday, January 10, 2005 15:17
> To: [log in to unmask]
> Subject: [LF] Antw: Re: [LF] Lead-Free Acceleration Factor
>
> Pascal, David
>
> Well I'm glad someone looked at my article about the concerns of
> accelerating tests of lead free solder (patting my shoulder).
> Due to the slower creep rate of lead free solder compared to tin lead and
> the strong dependency of the temperature on the creep rate dwell times
> will have to become longer if lead free solder is to be tested. Especially
> below 0°C lead free solder creeps very slow. The longer I work the more I
> am afraid that there is not much about accelerating thermal cycles.
> Another point to be mentioned is a fact I discussed with Jean Paul Clech
> lately: We have to expect that the slopes of the Nf-dT lines in a Coffin
> Manson graph are not the same for SnPb and for lead free solder. This
> means, that there must be a point where the lines cross each other. It
> could well be, that tests run with large strain amplitudes might indicate
> that one solder has a better creep fatigue resistance but a test with
> small amplitudes (or the application) will show the opposite.
> Right now we run a slow thermal cycling test -20/120°C, ramps of 2°C per
> minute and dwell times of 20 min at 120°C and 40 min at -20°C. End of
> January 4000 cycles will be done. Additionally our Phd student should be
> finished with his work about deformation behaviour of SnAgCu by the end of
> this year. This year we planed slow tests with small amplitudes. Seems all
> well so far, except that we had a cut of founding which left me all alone
> without a cent left to pay for the analysis of the specimen. I am running
> around right now to organise money to pay at least for my salary. I don't
> know if I will make it to the point where I can afford a person again
> working in my lab doing the microsections.
> However, whenever we publish new results they will be posted on our web
> site.
>
> Best regards
>
> Guenter
>
>
>
> EMPA
> Swiss Federal Laboratories for Materials Testing and Research
> Centre for Reliability
> Guenter Grossmann, Senior Engineer
>
> 8600 Duebendorf
> Switzerland
>
> Phone: xx41 1 823 4279
> Fax : xx41 1 823 4054
> mail: [log in to unmask]
>
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