Surface properties of photoablated thermostable polymers are considerably different from those of original, unexposed ones, and of mercury UV lamp exposed surfaces. They also depend on the laser exposure conditions. This paper reports such non-linear phenomena observed on polymer surfaces, caused by excimer laser exposures, like increased hydrophilicity of polymer surfaces, imagewise wetting and metallizations, and new metal compound formations on laser exposed polymer films. Because these features are limited to polymer films with high glass transition temperature, like polyimides and poly(phenylquinoxaline), photo-mechanical effects may be important. In some cases, new interfacial reactions appear between exposed polymer surfaces and deposited metal films. Swelling of polyimide in pre-photoablation irradiation is discussed.

Simultaneous mechanical and calorimetric measurements of the work and the heat of peeling have been made for polyester films bonded to rigid metal substrates with a pressure sensitive adhesive. Most of the work expended in peeling is consumed by plastic deformation and viscous dissipation. 70% to 85% of the peel energy is dissipated as heat. The peeled polyester films were tightly curled. Energy stored in the peeled polyester films was measured using solution calorimetry and a significant fraction of the peel energy not dissipated as heat was found to be stored in the peeled films.

Potential applications of a very general route to photochemically modifying a range of surfaces will be described. Surfaces which have been modified vary considerably and include polyimide, polyethylene, fluoropolymers, polyester, glass, tin oxide and aluminum. Photoactivated azides, for example 3-azidopyridine, have been found to be very effective at modifying a range of surfaces. Using this method organic type functional groups, in this case pyridine type groups, can be photografted on to the surface. As a result of photomodification the surface properties change. In the case of polyethylene for example the surface becomes more hyrophilic and shows improved adhesion to metals. These modified surfaces also display acid-base character. In the protonated form anions can be exchanged into the film. This method has been used to modify a metal oxide electrode surface to develop chemically modified electrodes. The process may also be used in lithography.

The surface properties of polyimide can be changed without altering the bulk properties. The surface layer (around 200 Å) of fully cured PMDA-ODA polyimide is chemically modified to polyamic acid which is subsequently imidized at 230 °C for 30 min to give an unordered polyimide surface. This unordered layer seems amorphous since it swells well in NMP. The modified surfaces are analyzed by surface sensitive techniques such as contact angle measurement, XPS, ISS, and external reflectance infrared (ERIR) spectroscopy. Adhesion of polyimides and chromium on the amorphous polyimides is greatly enhanced. Interdiffusion and subsequent mechanical interlocking are the major contributions to the polyimide-polyimide adhesion.

This paper presents studies of surface modifications of benzocyclobutene (BCB) using reactive ion etching (RIE), ion implantation, and combinations of those in conjunction with liftoff processing steps. It was found that O2/N2 RIE treatments of the BCB surface improve the adhesion of subsequently evaporated chromium and copper. Implant treatments with C+, O+, Si+, As+, and Sb+, were also investigated. The implant treated samples exhibited improved adhesion prior to subsequent heat treatments in the Cr/BCB structures and some improvement subsequent to heat treating in the Cu/BCB structures. Combinations of the surface modification treatments were seen to have the greatest benefit, even after heat treatments.

A polyimide (PI) surface is analyzed by XPS at each electroless-copper-plating step. Zn ions are adsorbed on the PI surface, and subsequently replaced with Pd ions. Cu is deposited on the PI surface catalyzed by these Pd ions, As the surface concentration of Pd ions increases, the adhesive strength of the plated Cu to the PI surface increases.

In the case of PI fabrication onto a plated Cu, no significant PI degradation is observed.

Enhanccd adhesion of Copper to spin-coated polytetrafluoroethylene PTFE.) film is achieved by employing an intermediate adhesive layer consisting of fluorinated ethylenepropylene (FEP) and metallic titanium. The peel strength of Cu on PTFE is low (1–2 g/mm) without the adhesive layer. After incorporating the Ti/FEP adhesive layer, a peel strength as high as 80 g/mm can be achieved. The overall peel strength is found to increase with the adhesive layer thickness. Thermal annealing at high temperatures strongly affects its overall peel strength. Previous XPS study indicated the formation of TiCx at the Ti/FEP and Ti/PTFE interfaces. Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy studies revealed that significant amount of Cu diffused into the FEP layer through the Ti layer when the specimens were heat treated at 375°C for various amount of time. Cu diffusion strongly affects the interfacial properties and hence results in the variation of overall peel strength. The results indicate that the thickness of Ti barrier as well as the heat treatment temperature are important for retaining the high peel strength.

Binary mixtures of a rodlike poly(p-phenylene pyromellitimide) (PMDA-PDA) and a flexible 6F-BDAF polyimide synthesized from hexafluoroisopropylidene diphthalic anhydride and 2,2-bis(4-aminophenoxy-p-phenylene) hexafluoropropane were prepared by solution-blending of the meta-PMDA-PDA poly(amic ethyl ester) and 6F-BDAF poly(amic acid) precursors, followed by solvent evaporation and thermal imidization. The size scale of the phase separation, as measured by light scattering, is ca. I μm or smaller in most cases. Dynamical mechanical thermal analysis measurements indicate that the glass transition temperature of 6F-BDAF is unaffected in all of the mixtures studied, indicating complete demixing of rodlike and flexible polyimides in agreement with theory. X-ray photoelectron spectroscopy results show a strong surface segregation of 6F-BDAF in mixtures containing as low as 10% by weight of the 6F-BDAF component in the bulk. The mixtures with PMDA-PDA as the major matrix component therefore maintain excellent bulk properties of rodlike polymers, i.e., high modulus to 500°C, and low coefficients of thermal expansion (< ca. 10 ppm/°C). On the other hand, the surface properties of the mixtures are dominated by the flexible 6F-BDAF, resulting in excellent polymer/polymer self-adhesion (lamination) properties between fully imidized films.

Thin films of poly(p-phenylene biphenyltetracarboximide), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, UV-visible, infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in-plane index n║ = 1.852 and the out-of-plane index n┴ = 1.612 at 632.8 nm wavelength, indicating a strong preference of polymer chains to orient along the film plane. No discernible effect of the film thickness on this optical anisotropy is found in the range of ca. 0.4 μm to 7.8 μm in thickness. The frequency dispersion of the in-plane refractive index to 1.06 μm wavelength is consistent with the results calculated by the Lorentz-Lorenz equation from the UV-visible spectrum. The contribution from the entire IR range from 7000 to 200 cm,−1 computed by the Spitzer-Kleinmann dispersion relations from the measured spectra, adds ca. 0.07 to the in-plane refractive index n║. Approximately the same increase is assumed for the out-of-plane index n┴, based on the tilt-angle dependent IR results. Application of the Maxwell relation leads to the out-of-plane dielectric constant ε┴≃2.8 at ca. 1013 Hz, as compared with the measured value of ca. 3.0 at 106 Hz. Assuming this small difference to remain the same for the in-plane dielectric constants ε║, we obtain a a very large anisotropy in the dielectric properties of these polyimide films with the estimated in-plane dielectric constant ε║≃3.5 at ca. 1013 Hz, and ε.≃3.7 at 106 Hz.

We have investigated the conformation – order relationships of four aromatic polyimides prepared by thermal imidization of the precursor poly(amic acids) in thin films. They are: (i) PMDA-4,4′-ODA polyimide from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) monomers; (ii) PMDA-PDA polyimide from PMDA and p-phenylene diamine (PDA); (iii) PMDA-Benzidine polyimide from PMDA and benzidine and (iv) BPDA-PDA polyirnide from biphenylene tetracarboxylicdianhydride (BPDA) and PDA. X-ray diffraction results and their analyses by molecular modeling show that all the four polyimides exhibit extended chain conformations in various smectic-type ordered structures that form monomer repeat layers but differ in the details of interchain packing. Furthermore, the polyimide chains are highly aligned along the film plane.