Technology Letter #10 Revised 05-85
The effect of a wide variety of organic solvents on parylenes C, N, and D was
Six classes of organic solvents were examined: alcohol
(isopropyl), ketones (acetone and 2,4-pentanedione), aliphatic hydrocarbon (iso-octane),
aromatic hydrocarbon (xylene), chlorinated olefin (trichloroethylene),
chlorinated aromatics (chlorobenzene and O-dichlorobenzene), heterocyclic base (pyridene),
and fluorinated solvent (trichlorotrifluoroethane).
These solvents had a minor swelling effect on the parylenes
with a 3% maximum increase in film thickness. The swelling was found to be
completely reversible after the solvents were removed by vacuum drying.
Some inorganic reagents were also examined. These
included the following: de-ionized water; 10% solutions of sodium hydroxide and
ammonium hydroxide; non-oxidizing acids, hydrochloric and sulfuric in
concentrated and 10% solutions; and oxidizing acids, nitric and chromic, in
concentrated and 10% solutions.
The diluted inorganic reagents had little effect on the
parylenes. The acids at 10% concentrations had virtually no effect at room
temperature and, except for chromic, no effect at 75°C.
Concentrated acids at room temperature (23°C) had
little effect. Under severe conditions, 75°C
for 90 minutes, all acids had a measurable effect ranging from 0.7% swelling
with hydrochloric to 8.2% with chromic. Additionally, nitric acid under
these same severe conditions caused severe degradation. Both concentrated
nitric and sulfuric acids caused some discoloration.
This information is not to be taken as a warranty or
representation for which we assume legal responsibility, or as permission or
recommendation to practice any patented invention without a license. It is
solely for your consideration, investigation, and verification.
This Technology Letter attempts to answer the questions, "Are
the parylenes themselves resistant to solvents, and do they protect substrates
from solvent attack? And if so, to what degree?"
Earlier experience had indicated that parylenes N, C, and D
were insoluble in all common solvents. Parylene C, it was found, could be
dissolved in high boiling liquids such as l -chloronaphthalene or benzoyl benzoate at temperatures
above 150°C. However, these solvents are seldom
encountered in the electronics industry. Of greater importance are those
solvents and reagents used in processing, especially in cleaning, of components
and assemblies. This study was undertaken to quantitatively measure the
effect of the more common solvents and reagents on the parylenes. Included
also were certain hydrocarbons serving as models for fuels. The organic
liquids chosen for this study were selected as being representative of typical
solvent classes. The protection provided to the coated substrates by the
parylenes was also observed.
It was also known that the parylenes were inert to inorganic
reagents (except for oxidizing agents). The work reported here and
quantitative results given confirmed this conclusion.
- On Parylene Films
Films of parylenes N, C, and D, between 0.5-1.5mL in
thickness, were deposited and then removed from glass plates. Applying
a water soluble release agent to the plates prior to parylene depositions
facilitated removal. Film thickness was measured optically by an
infrared (IR) technique. Film strips were immersed in the test liquids
for 90 minutes at room temperature and the thickness was re-measured by the
IR method. In every case, equilibrium (no further thickness change) was
reached before 90 minutes. The percent thickness change can either be
due to swelling or the solvent content of the film after surface drying. In
no case was there an apparent decrease in the original film thickness.