Hi 'j,'
First, with SJs it is hardly ever the stresses one has to worry
about—well, that actually has changed somewhat with Pb-free SAC
solders, but talking only about creep-fatigue that is true for
SAC-solders as well. It is the displacement strains which are
essentially 100% plastic deformations for product applications, but
some mixture of plastic and elastic strains [in the solder and
elsewhere in the attachment arrangement] for acclerated reliability
test [Note: I did not say HAST or HASS—this severe HA/HA's are
something else again].
Second, it is the dwells that determine the completeness of the creep
process in converting all displacements into plastic deformations in
the SJs.
Third, T-change ramps are not important for product operational cycles,
because they are slow enough not to cause stresses to built up faster
than creep can reduce them AND not to allow significant thermal
gradients causing warpage of components and/or PCBs. It is the later
that by definition causes 'thermal shock', because those warpages
produce tensile strains/stresses in the SJs rather than loading in
shear.
Fourth, Good information sources are IPC-SM-785 and IPC-D-279, as well
as the reliability columns that I have been writing for Global SMT &
Packaging magazine since 2001—the later are electronically available
from GSMT&P.
Werner
-----Original Message-----
From: John Goulet <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, Dec 8, 2009 12:16 pm
Subject: Re: [TN] Engelmaier expression etc.
Hello Werner. Do you have any links to papers that you wrote or could
share with usa alittle more about the ramp and dwell stresses that you
talk about in your E-mail? Looks interesting.
Thanks J Goulet
----- Original Message -----
From: "Werner Engelmaier" <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, November 12, 2009 1:30:07 PM GMT -05:00 US/Canada
Eastern
Subject: Re: [TN] Engelmaier expression etc.
Hi Inge,
Well, you sure lay it on.
2.What is Norris-Landzberg equation? Has it to do with extrapolation of
ccelerated test results?
A: Norris and Landzberg were 2 people working for IBM who published a
paper with their equation,
developed for Pb but mis-applied for solders.
IBM distanced itself from the N-L model, and nobody ever heard from
Norris or Landzberg again to
my knowledge. That has not stopped people from using N-L to extrapolate
accelerated solder reliability
test results, because it generally gives very optimistic answers. It
biggest short-coming is thast dwell
time is not considered.
3.About damage during ramp vs. damage during dwell (temp cycling), how
do you
ecide data which mirrors real operational conditions?
A: Ramp is only important if it is rapid enough to lead to build-up of
stresses faster thqan creep can reduce them;
that mean thermal shock-type testing.
4.Is Matlab 7.6.0 useful for practical reliability calculation, or is
it just
esearch tool?
A: No idea.
5. What is the Engelmaier expression? Has it to do with Werner's face
after a
ouple of beer?
A: I do drink beer, but not enough to make any difference---single-malt
scotch, no that is another matter.
But if you really want to change my expression, give me 50 cm of virgin
powder snow on top of a nice slope---
now that is a paradign shift.
Now, I do have 2 equations with my name on it. One, for solder
creep-fatigue behavior, the Engelmaier-Wild
model [Roger wild was a researcher at IBM on who's data the model is
based]; the other to relate tensile properties
to fatigue behavior for copper, aluminum, and the like.
Anything else I can help you with, Inge. Did some consulting for Saab
last Summer---they said they would rather give me money than a ride on
one of your jet fighters---bummer.
Werner
-----Original Message-----
From: Hernefjord Ingemar <[log in to unmask]>
To: TechNet E-Mail Forum <[log in to unmask]>; Werner Engelmaier
<[log in to unmask]>
Sent: Thu, Nov 12, 2009 1:50 pm
Subject: Engelmaier expression etc.
articipated in a meeting about LGA/QFN/BGA reliability and life. Have a
couple
f qs.
1.NN (Neural Networks) often contain up to 20 parameters. Will these
models
eally be useful in practice? Seems a lot to complicated to me.
2.What is Norris-Landzberg equation? Has it to do with extrapolation of
ccelerated test results?
3.About damage during ramp vs. damage during dwell (temp cycling), how
do you
ecide data which mirrors real operational conditions?
4.Is Matlab 7.6.0 useful for practical reliability calculation, or is
it just
esearch tool?
5. What is the Engelmaier expression? Has it to do with Werner's face
after a
ouple of beer?
/Inge=
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