Polyamic acid characteristics

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. 

The interaction of the polyimide chains via carboxylate type bonds is however clearly evident in spectra 7b for the cured polyimide film on polycrystalline silver. In addition to the characteristic vibrational modes of bulk polyimide we find two strong bands at 1600 cm 1 and 1440 cm 1 not present in the bulk spectra in the thick film (7c). These are interpreted as arising from the polyimide-silver carboxylate type interface bonding as discussed above for polyamic acid. The presence of both the asymmetric and symmetric V(C00 stretch could again be due to a preferential monodentate bonding configuration or to the polycrystalline nature of the substrate. 

Only one carbonyl component appears in the NR-055X spectrum after the 300 C cure treatment. Its 3.8 eV chemical shift is consistent with imide. The F binding energy and chemical shift values were identical to those observed for the polyamic acid. The most intense C Is component peak characteristics showed little change with temperature spanning 85 -400 C. 

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. 

In the IR spectrum of polyimide films of 5a, the absorption-due to hydrocarbon group of the film disappeared, and new characteristic absorptions corresponding to the imide carbonyl groups appeared at 1780 and 1720 cm. This suggested that the cyclization of the polyamic acid salt to polyimide 5a proceeded almost completely with the removal of the long chain alkylamine. 

This material is easily prepared directly from the precursor silicone polyamic acid. Properties and characteristics of this polymer system are discussed including handling, use, and practical photochemistry. 

Polymer Characterization The Tg s obtained by TMA and TBA, of polymers prepared in diglyme or other ether solvents were the same as for those polymers prepared in DMAc. Infrared analyses also proved that the polyamic acids and polyimides synthesized in diglyme were essentially identical to those made in the usual aprotic amide solvents. The infrared spectra of polymers made in diglyme and other ethers, and thermally imidized, disclosed a band of medium to low intensity at 1850 cm l which is characteristic of an anhydride... 

NASA-Langley Research Center. The characteristics of the samples in the two sets are given in Table I. The first set of samples were lap-joints of Pasa-Jell cleaned Ti-6-4 panels bonded with one polyimide resin adhesive. The resin adhesive was prepared from benzophenone tetracarboxylic acid dianhydride (BTDA) and m,m -diaminobenzophenone (m,m DABP). The structures of these compounds are given in Table II. The uncured adhesive was applied on the adherend in the polyamic acid stage from either diglyme or DMAC solution and then heat cured to the polyimide resin form. This condensation polymerization reaction is shown below. 

The molecular and conformation characteristics of a series of polyamic acids and polyester imides, obtained by high-temp. imidisation of polyamic acids in N-methylpyrrolidinone or m-cresol, were studied by viscometry and exclusion liquid chromatography. The differences in the molec.wts. of the products of polyamic acid imidisation in N-methylpyrrolidinone and m-cresol were explained by the different characters of inactivation of the anhydride groups. 20 refs. (Full translation of Vys.Soed.A, 39, No.8, 1997, p.1387-91)... 

---