Water polyimide films

As stated, the capability of plasma deposits to reduce the access of water to corrosion-sensitive surfaces may be an important motivation for their application in corrosion protection. In order to study this property, Kapton polyimide film was selected as the substrate because of its high inherent permeability to water and its ability to resist elevated temperatures. The response of Kapton film overcoated by PPHMDSO to the permeation of water vapor is shown in Fig. 1. Clearly, the presence of the organo-silicone plasma film greatly reduces water permeation. The magnitude of the effect is much enhanced when plasma polymers are produced at high T and p. 

Extraction of Films. Cobalt modified polyimide films were extracted by one of several techniques (1) films on the casting plate were soaked in a tray of distilled water at room temperature, (2) films were soxhlett extracted with distilled water, (3) films were soaked in DMAc at room temperature, and (4) films were soxhlett extracted with DMAc. 

Each sample was evaluated by thermogravimetry to determine if the thermal stability could be enhanced by removing some residual cobalt chloride. The BTDA-ODA polyimide film thermal stability is reduced about 50 C due to the cobalt chloride dopant. Soa)cing or extraction with water has no positive effect on the thermal stability whereas soxhlett extraction with DMAc severely degrades the polymer stability. For the BDSDA-ODA polyimide films the incorporation of cobalt chloride also reduces the bul)c polymer thermal stability. Soa)cing this film in water for 24 hours, however, increased the bul)c thermal stability slightly from 512 to 532 C. 

The air-side resistivity of the cobalt chloride modified polyimide film was Increased to the value observed with a nonmodified BTDA-ODA polyimide film while, the cobalt chloride modified BDSDA-ODA polyimide film had an increase in surface resistivity of only about three orders of magnitude after soa)cing this film in water. The variable temperature air-side surface resistivity profiles for the cobalt chloride modified BDSDA-ODA polyimide film before and after a water soa)c are shown in Figure 4. 

Figure A. Comparison of air-side electrical resistivity of a cobalt chloride modified BDSDA-ODA polyimide film before and after soaking in distilled water.

The dielectric constant of polyimide films in the wet condition (50% RH atmosphere) is higher than in the dry condition. This is attributed to water absorption by the polyimides. Figure 15.5 also shows the water absorption of die polyimides, which is due to the presence of imide groups in the polymer and decreases widi increasing fluorine content because of the hydrophobic effect of fluorine atoms. The water absorption is related to the stability of the dielectric constant. The dielectric constant variability between the dry and wet conditions of highly fluorinated polyimides, P3FDA/TFDB and P6FDA/TFDB, is smaller than... 

After the PMDA-ODA films were fully cured, they were cut into 1.59 mm wide peel strips using a wafer dicer with deionized water coolant. The polyimide film was carefully cut down to the wafer, taking care that the wafer stayed intact. 

Adhesion of polyimides to inorganic substrates is of great importance to the microelectronics industry [1, 2]. The polyimide films are deposited most often by spin coating the polyamic acid (PAA) usually from a TV-methylpyrrolidone (NMP) solution onto the substrate surface followed by thermal imidization at temperatures up to 400<>C. The most studied polyimide is the pyromellitic dianhydride-oxydianiline (PMDA-ODA), which exhibits excellent mechanical and dielectric properties, but not so good adhesion characteristics. The latter has been generally overcome by application of an adhesion promoter, such as y-aminopropyltriethoxysilane [3-7]. The reactions of APS (coated from water solution) with the silicon dioxide surface as well as with polyamic acid have been well characterized by Linde and Gleason [4] however, we do not have such detailed information available on APS interaction with other ceramic surfaces. 

Y. Sano [107] described the influence of the film thickness, 8, on the drying course of water-moist polyimide films. In thick films (6 = 1 mm), the liquid-side diffusion plays an important role from the very beginning. The surface concentration quickly drops off to an equilibrium value and the temperature at the film surface increases to the drying air temperature, without reaching a constant steady-state goods temperature. A period of constant drying rate does not appear. 

TABLE 3. Results of water and methylene/iodine repellency testing of polyimide films obtained by reacting 1,2,3,4-cyclobutane tetracarboxylic dianhydride with amines described in Table 1. 

The surface chemical structure of several thin polyimide films formed by curing of polyamic acid resins was studied using X-ray photoelectron spectroscopy (ESCA or XPS). The surface modifications of one of the polymer systems after exposure to KOH, after exposure to temperature and humidity, after exposure to boiling water, and after exposure to O2 and 02/CF plasmas were also evaluated. The results showed imide bond formation for all cured polyimide systems. It was found that (a) K on the surface of the polyamic acid alters the "normal" imidization process, (b) cured polyimide surfaces are not invarient after T H and boiling water exposures, and (c) extensive modifications of cured polyimide surfaces occur after exposures to plasma environments. Very complex surfaces for these polymer films were illustrated by the C Is, 0 Is, N Is and F Is line characteristics. 

Mono- and multilayer films of polyimides were successfully prepared using Langmuir-Blodgett technique. Monolayer films of polyamic acid long alkylamine salts were prepared at the air-water interface. The mono-layer films were deposited on appropriate plates to produce multilayer films of the precursor to polyimide films. Finaly, the polyimide multilayer films were obtained by treatment of the multilayer films of the polyamic acid amine salts with acetic anhydride and pyridine. The polyimide multilayer films had excellent coating ability giving a very smooth surface. They also exhibited insulating characteristics as reliable as polyimide thick films. 

For these sensors, 2-nm thick Ti and 20-nm thick Au layers were deposited on 50-prn thick polyimide films by vacuum evaporation. Next, a 50 nm pentacene layer was deposited, again by vacuum sublimation. The pentacene layer was then doped p-type by exposure to a 1% solution of ferric chloride in water. 

Effect of Humidity Because the water content of Kapton polyimide film can affect its electrical properties, electrical measurements were made on 0.025 mm film after exposure to environments of varying relative humidities at 23°C.f l... 

Hydrolytic Properties Kapton polyimide film is made by a condensation reaction therefore, its properties are affected by water. Although long-term exposure to boiling water, as shown in the curves in Figs. 22-03 and 22-04, will reduce the level of film properties, sufficient tensile and elongation remain to ensure good mechanical performance. A decrease in the temperature and the water content will reduce the rate of Kapton property reduction, whereas higher temperature and pressure will increase it.t 1... 

Aqueous amylose solution (1%) was prepared by dissolving amylose powder in hot water (80°C). A 1% salt free aqueous water-soluble chitosan (WSC) was obtained by the dialysis of a WSC solution that included NaCl produced by the neutralization of a dilute hydrochloric acid solution of WSC with NaOH. Each film having a thickness of 40-50 om was prepared by casting the amylose, WSC, or their mixed solutions at 60°C. A film of fully deacetylated chitosan was obtained by casting a 0.1 M aqueous AcOH solution of fully deacetylated chitosan (1%) on a Kapton (polyimide) film. The resulting acidic chitosan film was neutralized with 1M aqueous NaOH followed by washing with water and then dried. 

The absorption of water by polymers is especially suited to the development of a capacitive humidity sensor based on the high dielectric constant of water, since capacitance depends on the area, the thickness, and the dielectric constant of a dielectric. Uptake of water causes an increase in the dielectric constant followed by an increase in capacitance. Polyimide is a suitable sensitive material, but so are certain inorganic ceramics such as AI2O3 [142] and low-density Ta205, which change their capacitance with the formation of water dipoles. Low-density Ta20s layers can be formed by anodic oxidation of sputtered tantalum films, whereas polyimide films are deposited by spin coating and subsequent polymerization. 

The resultant morphology of the s-BPDA-PDA polyimide film is also influenced by the kind of the precursors (water-releasing PAA or alcohol-releasing poly(amic alkyl ester)s, PAE), which give the same PI chemistry [40,82-85,86]. A common observation is that at < 350°C the PAE-derived PI films show a lower ordered structure than the PAA-derived ones, but this situation is reversed when Ti... 

PMMA- and poly(a-methyl-st)rrene)-PI block copolymer [9,10] blend solution containing polyurethane and PAA [11] and polyacrylamide- and PMMA-grafted PI [12]. They have achieved 10-30% decrease in a dielectric constant of polyimide films, and low-fc porous films ( fc 2.2) have been provided. Also, other methods, such as using water droplets and LiCl crystal as templates, and extracting a porogen polymer from composite PI film by supercritical CO2, have been known [47-49]. On the other hand, we have obtained ultralow-fc porous films by depositing porous PI MPs onto substrates [18,20]. 

Tohge N., Tadanaga K., Sakatani H., Minami T. Formation of Si02-based coatings by the sol-gel method and their effects on water vapour permeability of polyimide films. 1. Mater. Sci. Lett. 1996 15 1517-1519... 

---