Poly(dimethylsiloxane)-polyimide blends in the formation of thick polyimide films |
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Authors: | L J Matienzo F D Egitto |
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Affiliation: | (1) Department of Materials Science, Endicott Interconnect Technologies, Inc., 1701 North Street bldg. 46-2, Endicott, NY 13760, USA |
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Abstract: | Thick polyimide layers can be formed by using some unique properties of poly(dimethylsiloxane)-polyimide (PDMS/PMDA–ODA) blends
followed by surface modification and deposition of a second layer of polyimide precursor chemicals. The method is based on
the micro-phase separation characteristics of these blends to yield surfaces that have PDMS-like character. Upon modification
with UV/ozone treatment, a surface that is essentially SiO
x
and hydrophilic in nature is produced. This surface is amenable to reaction and deposition of a second polyimide layer from
polyimide precursors. The thicker polyimide layer has enhanced adhesion between the original layer of the blend and the new
polyimide layer and this approach finds extensive applications for products that require thick polymer layers. Changes in
surface energy for various blend compositions were monitored by measurement of advancing contact angle with de-ionized water.
Contact angle for unmodified polyimide films was on the order of 70° and it increased to about 104° after blending with PDMS
and curing. UV/ozone treatment reduced the contact angle of the doped polyimide to less than 5°. X-ray photoelectron spectroscopy
(XPS) and angle resolved XPS (ARXPS) measurements were used to monitor the chemical compositions of the various surfaces.
High-resolution XPS spectra in the Si2p region confirm the transformation of O–Si–C bonds in PDMS to SiO
x
, where x is about 2. Scanning electron microscopy (SEM) of some selected samples shows that the blends contain phase separation of
the polymers at the surfaces of the samples. Atomic force microscopy (AFM) of siloxane-free polyimide, and PDMS/PMDA–ODA blends
both prior to and after UV/ozone exposure, show that the films are essentially flat at short treatment times (less than 60 min).
AFM also reveals the separation of PDMS into micro-domains at the cured film surface and throughout the layer below the surface
of the blended films. Adhesion of a subsequently deposited polyimide layer to the modified polyimide surface was found to
be greatly improved when compared to the adhesion obtained for deposition onto a pristine polyimide surface. |
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