Creep-fatique model for SAC405/305 solder joint reliability estimation—a proposal
Werner Engelmaier
“The data bases for LF-solders have grown, and the favored LF-solders are shifting.
Nevertheless, progress has been made.”
Creep-fatigue model for
SAC405/305 solder joint
reliability estimation —a proposal
Over the years I have devoted quite a bit some of the JCAA/JG-PP/NASA No-Lead evident in Figure 8, which is based on an
of space to solder joint reliability
1-3
. In this Solder Project data
9
by CALCE at the Uni- analysis of Jean-Paul Clech of available in-
column I have frequently discussed the reli- versity of Maryland
10
. The analysis is based dustry data (see Ref. 8, Fig. 14), however with
ability of Pb-free solder joints
4-7
. Recently I on the Engelmaier-Wild model (see Refs. 1 & a significant addition of data. Also shown
updated the available reliability information 2), with four of the parameters changed by in Figure 8 is the CALCE model curve for
for lead-free solder joints in my GSMT&P regression analysis and data fitting without accelerated test results of SAC solder joints.
column in the August 2008 issue
8
. Since consideration of the solder properties or From these data and the physical
than, even more information has become the creep-fatigue behavior, other than the insights gained, the model shown in Equa-
available, making it possible to propose accelerated test results. tions 1 and 2 is proposed for SAC405 and
an accelerated creep-fatigue model for The analysis in Reference 10 initially ana- SAC305.
SAC405/305 Pb-free solder joints. lyzed the leaded components, TSOPs and This model has the same form as the
When looking at the Weibull graphs TQFPs, as compliant-leaded in violation Engelmaier-Wild model and should be
showing the results of accelerated creep-fa- of ‘Caveat 5’ in IPC-D-279
11
which dictates used like that model (see Refs. 1 to 3). Five
tigue thermal cycling tests, it is evident that that the leaded analysis be used only for parameters are different as shown in Table
the accelerated test results for SAC405/305 component with leads sufficiently compli- 1. It is likely, that these parameters will see
are no more than a factor of two (2) away ant to reduce the cyclic stress range to stress slight adjustments once data showing the
from the results for SnPb solder joints. This levels below the yield strength of the solder. independent influences of temperature and
is illustrated in Figures 1 through 6. When these components were properly ana- creep time on creep-fatigue life are available.
Additional data and analyses were pub- lyzed as leadless, the predicted results and The National Physical Laboratory, UK, and
lished showing that for results coming from the experimental results were within a factor perhaps others are working on developing
the same testing environment, a certain of two of each other, which is well within these data.
consistency and commonality can be shown. the experimental variation to be expected. In Figure 9, model predictions for both
Figure 7 shows the results of an analysis of This experimental variation is fully eutectic SnPb and SAC405/305 solder joint
Figure 1. Weibull plots for Sn37Pb and SAC405 solder joints for severe Figure 2. Weibull plots for Sn37Pb and SAC solder joints for severe
–55⇔+125°C thermal cycling showing significantly lower life and wider failure –55⇔+125°C thermal cycling showing comparable life but wider failure
distribution for SAC405. [Source: Dave Hillman, Rockwell Collins, USA]. distribution for the SAC solder. [Source: Dave Hillman, Rockwell Collins, USA].
46 – Global SMT & Packaging – December 2008
www.globalsmt.net
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