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15

Development of A Moisture

Soak Model For Surface

Mounted Devices

L. C. Tang and S. H. Ong

Moisture soak is a crucial step in the preconditioning test for integrated circuit pack-
ages and has a significant bearing on package quality and reliability. In this case study,
we develop a moisture soak model for molded plastic leaded chip carriers with dif-
ferent lead counts. We first give a brief description of the problem and its motivation.
Then the experimental procedure is outlined and a set of sample experimental data is
presented. We then explore various models, using regression analysis, so as to estab-
lish a model that relates the moisture soak parameter to the soak conditions. A new
model, different from those commonly in use in the reliability literature, has been
found to provide the best fit. The equivalent soak times under harsher conditions are
then estimated from the model. Finally, some comparisons are made with past results
and existing industry practice.

15.1 INTRODUCTION

In electronic assembly, a high-temperature operation, solder reflow, is used for securing
surface mounted devices (SMDs) to printed circuit boards. This operation generates a
new class of quality and reliability concerns such as package delamination and crack-
ing. The problem arises as moisture may enter the plastic molded compound through

This chapter is based on the article by L. C. Tang and S. H. Ong, ‘Development of a moisture soak model’, in
W. R. Blischke and D. N. P. Murthy (eds), Case Studies in Reliability and Maintenance, 2003, and is reproduced
by the permission of the publisher, John Wiley & Sons, Ltd
Six Sigma: Advanced Tools for Black Belts and Master Black Belts L. C. Tang, T. N. Goh, H. S. Yam and T. Yoap
C 2006 John Wiley & Sons, Ltd
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