| The parylenes resist attack and are
insoluble in all organic solvents up to 150ºC. Parylene C can be
dissolved in chloro-naphthalene at 175ºC and parylene N is soluble
at the solvent boiling point of 265ºC. Both polymers are resistant
to permeation by most solvents with the exception of aromatic
hydrocarbons. They are also unaffected by stress-cracking agents
such as "Hostepal," "Igepal" and lemon oil.
The effect of a wide variety of organic solvents on parylenes N, C
and D was investigated.
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 aromatic (chlorobenzene
and o-dichlorobenzine), 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: deionized 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, 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
75ºC. Concentrated acids at room temperature (23ºC) had little
effect. Under severe conditions, 75ºC for 30 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.
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 X-chloronaphthelene
or benzoyl benzoate at temperatures above 150ºC. However, these
solvents are seldom encountered in the electronic 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). This conclusion
was confirmed by the work reported here and quantitative results
given. |
