The following is from an article written by Jenny Hwang in SMT Magazine in
2002 that highlights the challenge of modeling solder.
_http://smt.pennnet.com/display_article/138260/35/ARTCL/none/none/1/Step-3:-So
ldering-Materials/_
(http://smt.pennnet.com/display_article/138260/35/ARTCL/none/none/1/Step-3:-Soldering-Materials/)
Joe
Single Model Limitations
Service conditions under which solder joints must perform in component
packages and assemblies often involve random multiaxial stresses that expose them
to creep ranges as well as cyclic strains. At this time, sufficient and
integrated data of solder joint behavior under such conditions and corresponding
damage evolution are lacking. Consequently, some important areas and
conditions are grossly ignored in the modeling scheme.
Listed are the areas that either have not been included or are not covered
adequately. They are, in turn, considered to be the reasons that contribute to
the limitations of a single model for wider applications:
1. Effect of initial microstructure
2. Effect of grain size
3. Effect of microstructure that is not homogeneous
4. Change in microstructure vs. external conditions
5. Multiaxial creep-fatigue
6. Identification of the presence or absence of crack-free materials at the
starting point
7. Size of existing cracks, if present
8. Effect of interfacial metallurgical interaction
9. Joint thickness vs. interfacial effect
10. Damage mechanism (transgranular or intergranular)
11. Potential damage mechanism shift (from transgranular or intergranular)
12. Presence or absence of grain boundary cavitation
13. Effect of fillet geometry
14. Effect of free surface condition
15. Correlation of accelerated testing conditions vs. those of actual service
16. Testing condition vs. damage mechanism
17. Service conditioned to include possible variation in chip-power
dissipation over time
18. Ambient temperature change
19. The number of on/off power cycles
20. Effect of variations in coplanarity among solder joints.
Including these areas in modeling is not only overwhelmingly time consuming
but also information demanding — it is a daunting task. Nonetheless, their
inclusion is necessary to achieve a model's ultimate utility for predicting
solder joint service life for specific applications. However, before a universal
model is validated, combining knowledge and data in conjunction with
experimentation can produce practically sound systems.
Dr. Jennie S. Hwang is an SMT editorial advisory board member and president
of H-Technologies Group Inc. For a list of references cited in this article
e-mail the author at [log in to unmask]
In a message dated 4/29/2008 6:03:34 A.M. Pacific Daylight Time,
[log in to unmask] writes:
David,
If you find software that can really do this, let us all know!
Are you thinking of Finite Element software like Ansys? There is
another big contender also with a name starting with A, but it escapes
me right now. If your company was a member of the CALCE consortium,
they also have truncated programs that sort of do the same thing.
The problem is:
1) The amount of computing power needed
2) Defining the problem properly
3) A lack of fundamental materials properties
Good luck!
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bruce, David (GB -
MAV)
Sent: Tuesday, April 29, 2008 4:08 AM
To: [log in to unmask]
Subject: [TN] Software package to perform fatigue life prediction of
solder joints
Does anyone know of a software package to perform fatigue life
prediction of solder joints.
I need to be able to predict the fatigue life of solder joints under
different thermal cycling and vibration load conditions. The PCB will
usually be FR4, the solder tin/lead, the components everything from
BGA's to chip passives. Ideally I need to provide an estimate on cycles
to failure.
We are trying to do a comparison exercise to try and specify the more
reliable component, for example, a chip capacitor in 0805 or 1206, which
one will be more reliable, from a solder joint perspective and by what
order of magnitude? And what would the expected life of the joint be
under different conditions?
We need to perform this exercise over a range of different types of
components, using different types of leaded solder and perhaps with
different board thicknesses. Predictive software would be quicker and
easier than empirical experiments.
Any ideas?
Regards
David
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