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Barrier Properties

 

Due to the physical properties of Parylene and the method of deposition, Parylene forms a pin-hole free film on the subject substrate. Therefore, it provides an excellent barrier to both liquids and gases. The table below lists the permeability characteristics of the Parylenes and also shows typical values for other types of conformal coatings.

Moisture vapor permeability values have been measured at thickness¹ below 0.1 micron. Normalized to equivalent thickness, the values are the same for all thicknesses. Assuming that parylene C at 0.001 inch is pinhole free, then parylene C films at 0.1 micron (~ x 10-6 inch) are also pinhole free.

 

Barrier Properties of Parylene C
Compared with Epoxies, Silicones, and Urethanes

 

POLYMER

GAS PERMEABILITY
cc-mil/100 in2 -  24 hours *

MOISTURE VAPOR TRANSMISSION
gm-mil/100  in2 - 24 hours **

N2

O2

CO2

H2

Parylene C

0.6

5

14

110

1

Epoxies

4

5-10

8

110

1.79-2.38

Silicones

...

50,000

300,000

45,000

4.4-7.9

Urethanes

80

200

3,000

...

2.4-8.7

 

*  ASTM D1434-63T

** ASTM E96-63T

 
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