Polyimide surface modification process

Polyimide surface modification by a wet chemical process is described. Poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA) and poly(bisphenyl dianhydride-para-phenylenediamine) (BPDA-PDA) polyimide film surfaces are initially modified with KOH aqueous solution. These modified surfaces are further treated with aqueous HC1 solution to protonate the ionic molecules. Modified surfaces are identified with X-ray photoelectron spectroscopy (XPS), external reflectance infrared (ER IR) spectroscopy, gravimetric analysis, contact angle and thickness measurement. Initial reaction with KOH transforms the polyimide surface to a potassium polyamate surface. The reaction of the polyamate surface with HC1 yields a polyamic acid surface. Upon curing the modified surface, the starting polyimide surface is produced. The depth of modification, which is measured by a method using an absorbance-thickness relationship established with ellipsometry and ER IR, is controlled by the KOH reaction temperature and the reaction time. Surface topography and film thickness can be maintained while a strong polyimide-polyimide adhesion is achieved. Relationship between surface structure and adhesion is discussed. 

Surface modification (texturing) of polyimide through a metal clustering and migration process is reported. This process involves heat treatment of polyimide coated with a thin copper layer. Subsequent metallization of the textured surface leads to improved adhesion due to mechanical anchoring. Adhesion values of 7-10 lbs/in (ambient) and 4-6 lbs/in (after solder float) have been obtained. 

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. 

Successful commercialization of low cost, high efficiency solar cell fabrication is highly dependent on fabrication methods that employ continuous processing techniques. One major issue encountered in solar cell construction is the adhesion of thin film solar cells on polyimide substrates. Another involves the adhesion between polymer nanocomposite solar cell structures. The examination of the adhesion promotion potential of variable chemistry atmospheric plasma surface modifications against wet primer chemistry in solar cell construction has shown that APT is a viable continuous and environmentally friendly processing alternative to batch plasma and surfactant-based surface modification protocols. 

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