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236 Development of A Moisture Soak Model For Surface Mounted Devices
an in-line process monitor. To avoid having reliability and quality issues later, it is
critical that moisture sensitive devices be properly classified, identified and packaged
in dry bags until ready for printed circuit board assembly. Several attempts have been
made to derive models, through analytic or statistical means, for predicting the soak
time and humidity condition for SMDs. In this case study, we have used a statistical
approach with physical reasoning to model the moisture absorption process so as
to derive the equivalent moisture soak time for PLCC packages. In particular, it is
found that the soak condition at 60 C/60%RH will reduce the soak time for level 3--5
◦
(30 C/60%RH) by 3.7--4.7 times.
◦
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