Jl. Wu et al., Evaluation and characterization of reliable non-hermetic conformal coatings for microelectromechanical system (MEMS) device encapsulation, IEEE T AD P, 23(4), 2000, pp. 721-728
The thrust of this project was to evaluate commercial conformal encapsulati
on candidates for low cost aerospace applications. The candidate conformal
coatings evaluated in this study included silicone elastomers, epoxies, and
Parylenes with bi-layer or tri-layer designs. Properties characterized in
this study included mobile ion permeation and moisture ingress resistance,
interfacial adhesion variation through thermal shock cycling and 85 degrees
C/85 % RH aging, Surface Insulation Resistance (SIR), Triple Track Resista
nce (TTR) and die shear strength were used for the corresponding electrical
and physical property characterizations. Parylene F displayed excellent pr
operties for environmental protection, Silicone elastomers displayed less r
esistance to the harsh environment as compared to the Parylene family (N, C
, D types), but it could provide advantages for low residual stress applica
tions, The change in adhesion strength between Parylene C and silicone elas
tomers after exposure to thermal shock cycling or 85 degreesC/85 %RH aging
for different time periods were conducted from die shear test in terms of t
he interfacial failure. SIR values of all the candidate materials after 100
0 h exposure to 85 degrees C/85%RH, with 100 V de for resistance measuremen
t, range from 1 x 10(8)-1 x 10(9)Omega. Leakage current values after 1000 h
exposure to 85 degrees C/85 % RH, 175 V bias, are in the range of 10(-9) t
o 10(-11) Amp, The bi- or tri-layer conformal coating combination investiga
ted in this study showed significant promise for encapsulation of the micro
electromechanical system (MEMS) devices.