Hi Jean-Paul,
Excellent closing point
But can we focus on that aspect and predict reliability with some degree of
confidence, given that the creep models are still in a bit of flux.
Today, in order to meet the deadlines.
Regards,
LS
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, February 21, 2006 9:00 PM
To: [log in to unmask]
Subject: Re: Accelerated testing
Hi Werner,
I agree. There are two things going on for SAC and SnPb assemblies subject
to the same thermal cycle:
1) SAC and SnPb see entirely different stress/strain histories (and
different strain rates at any given time) because they have different
thermo-mechanical characteristics: SAC is more creep resitant than SnPb
under low to medium
stress; SAC creeps faster under high stress; last, at a given temperature,
SAC is always stiffer than SnPb (higher modulus).
2) Damage rates / creep-fatigue characteristics are also different for the
two alloys.
One way to get rid of possible confusions (and the risky apple to oranges
comparisons) is simply to forget about SnPb and just focus on assessing the
reliability of SAC products, which is what we were doing in the days of
SnPb
when there was no predecessor to compare to. Upfront, I have absolutely no
worry when SAC test results are inferior to SnPb results, the reason being
that
they may still be good enough. The only thing i have to demonstrate to my
customers is that their SAC assemblies meet their reliability requirements.
If
they don't, it's another story and we have to go back to the drawing board.
All the best,
Jean-Paul
In a message dated 2/21/2006 8:17:32 P.M. Eastern Standard Time,
[log in to unmask] writes:
Hi John,
You say:
> If you apply that same test to a lead free identical assembly it will
> tell you whether the unit is going to be more or less reliable given
> enough samples, but that is about it. It will not tell you whether tin
> whiskers will kill the product etc.
>
That is actually not true, unless you run the product in actual
operational
conditions. As soon as you do any acceleration, you have an apples/orages
comparison.
Werner
Quote of the month:
"I can calculate the motion of heavenly bodies, but not the madness of
people",
Isaac Newton.
_______________________________________________
Jean-Paul Clech
EPSI Inc., P.O. Box 1522, Montclair, NJ 07042, USA
tel.:+1 (973)746-3796, fax: +1 (973)655-0815
_http://www.jpclech.com_ (http://www.jpclech.com/)
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