In a previous study, we found that moisture preconditioning strongly influenced the interfacial fracture toughness of the underfill/solder mask interface, decreasing the interfacial adhesion by approximately one-half for both classifications of underfill/solder mask interfaces after 725 h of exposure at $85°C/85%RH.$ To better understand the rate and mechanisms for moisture transport through the interfacial fracture test specimens, a diffusion analysis was implemented based on traditional, analytical solutions of Fick’s second law of diffusion. Test specimens were constructed to experimentally determine the diffusion coefficient for each underfill. Since both underfill encapsulants proved to exhibit non-Fickian behavior at $85°C/85%RH,$ the application of the analytical Fickian solution for the test specimens was limited to the associated JEDEC criteria of 168 hours for $85°C/85%RH.$ A finite element analysis was performed to illustrate the moisture concentration in the interfacial fracture test specimens for initial times of exposure to the humid environment. The results of this study demonstrate that the presence of amine functional groups considerably retard moisture penetration through underfill encapsulants.

1.
Soles
,
C.
, and
Yee
,
A.
,
2000
, “
A Discussion of the Molecular Mechanisms of Moisture Transport in Epoxy Resins
,”
J. Polym. Sci., Part B: Polymer Physics
,
38
, pp.
792
802
.
2.
Soles
,
C.
,
Chang
,
T.
,
Gidley
,
D.
, and
Yee
,
A.
,
2000
, “
Contributions of the Nanovoid Structure to the Kinetics of Moisture Transport in Epoxy Resins
,”
J. Polym. Sci., Part B: Polymer Physics
,
38
, pp.
776
791
.
3.
Ferguson
,
T.
, and
Qu
,
J.
,
2001
, “
Effect of Moisture on the Interfacial Adhesion of the Underfill/Solder Mask Interface
,”
ASME J. Electron. Packag.
124
, pp.
106
110
.
4.
Crank, J., 1956, The Mathematics of Diffusion, Clarendon Press, Oxford, UK.
5.
Shi, S., 2000, “Study on No-Flow Underfill Materials for Low-Cost Flip-Chip Applications,” doctoral thesis, Georgia Institute of Technology, School of Materials Science Engineering, Atlanta, GA.
6.
Wong, C. P., Shi, S., and Jefferson, G., 1997, “High Performance No-Flow Underfills for Low-Cost Flip-Chip Applications,” IEEE Electronic Components and Technology Conference, pp. 850–858.
7.
Vanlandingham
,
M.
,
Eduljee
,
R. F.
, and
Gillespie
,
J. W.
,
1999
, “
Moisture Diffusion in Epoxy Systems
,”
J. Appl. Polym. Sci.
,
71
, pp.
787
798
.
8.
Shen
,
C. H.
, and
Springer
,
G. S.
,
1976
, “
Moisture Absorption and Desorption of Composite Materials
,”
J. Compos. Mater.
,
10
, pp.
2
10
.
9.
Wong, E. H., Chan, K. C., Lim, T. B., and Lam, T. F., 1999, “Non-Fickian Moisture Properties Characterization and Diffusion Modeling for Electronic Packages,” Proc. 49th IEEE ECTC, pp. 302–306.