Polyimides processing

The support of colleagues Arthur Wilson in polyimide processing and helpful discussions, and Qiarles Baker in preparation and application of the sodium lauryl sulfate controlled contamination solutions is gratefully acknowledged. Mary Mayfield and James Field assisted in the processing of the samples, and Ronald Huff made some of the electrical measurements. Their careful work is much appreciated. 

The devices passivated by the polyimide process were compared for performance with similar devices using SiC passivations. In all the cases,it was found that an 0.8p cured film of polyimide derived from PMDA/0DA performed equally well as the SiO passivated devices. Bias margins (indicative of magnetic device performance) were within the specified limits. The polyimide passivated devices were compatible with standard terminal metallurgies and also chip mounting metallurgies. Device performance... 

Specifically for the passivation of temperature sensitive bubble memory devices,these ultrapure materials proved to be of great value. A cure process was optimized to obtain a reliable low temperature cure without affecting the magnetic coercivities of the bubble memory devices. A positive resist process, using a simple development step to pattern via holes in devices has been optimized and successfully used to fabricate devices. The devices fabricated using the the polyimide process have been compared with conventional SiC offers reliable passivations with thinner stress free films for passivations. The fabrications involve simple inexpensive process steps and are compatible with conventional resist processes. The reliability of the imide passivated devices can be considerably enhanced by the use of ultrapure starting materials to preclude harmful ionic mobilities through passivated layers. 

B. G. Laycock, D. G. Hawthorne, J. H. Hodgkin, and T. C. Morton. Aqueous polyimide process. US Patent 6333 391, assigned to Commonwealth Scientific and Industrial Research Organisation (Australian Ctqtital Territory, AU) The Boeing Company (Seattle, WA), December 25,2001. 

Chem. Descrip. N-Cyclohexyl pyrrolidone CAS 6837-24-7 EINECS/ELINCS 229-919-7 Uses Solvent tor plating engineering plastics, esp. EMS applies. dye penetrant tor aramid fibers photo resists gas separation elec, insulating coatings chem. synthesis absorp. of sulfur dioxide and nifric acid aromafic extraction high temp, polyimide processing aid Features Superior resist, to hydrolysis... 

Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of NOx NFPA Health 2, Flammability 2, Reactivity 0 Uses Solvent for plastics (vinyl, acrylic, cellulose, polyimide processing), resins, gums, fibers, coatings, adhesives, electrolytes, pharmaceuticals selective solvent for butadiene extraction reagent intermediate catalyst paint remover high-purity solvent for crystallization and purification reaction medium for prod, of pharmaceuticals, plasticizers... 

Laycock BG, Hawthorne DG, Hodgkin JH, Morton TC. Aqueous polyimide process. US patent 6333391, assigned to Commonwealth Scientific and Industrial Research Organisation,... 

Product brochure, PI2771 Photosensitive Polyimide Process Guidelines, HD Microsystems, LLC, Wilmington, Del., 2001. 

BiaxiaHy oriented films have excellent tensile strength properties and good tear and impact properties. They are especially well regarded for their brilliance and clarity. Essentially all poly(ethylene terephthalate) film is biaxiaHy oriented, and more than 80% of polypropylene film is biaxiaHy oriented. Polystyrene film is oriented, and a lesser amount of polyethylene, polyamide, poly(vinyl chloride), and other polymers are so processed. Some of the specialty films, like polyimides (qv), are also oriented. 

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

A number of thermally stable polymers have been synthesized, but in general the types of stmctures that impart thermal resistance also result in poor processing characteristics. Attempts to overcome this problem have largely been concentrated on the incorporation of flexible groups into the backbone or the attachment of stable pendent groups. Among the class of polymers claimed to be thermally stable only a few have achieved technological importance, some of which are polyamides, polyimides, polyquin oxalines, polyquinolines, and polybenzimidazoles. Of these, polyimides have been the most widely explored. 

The reactions of primary amines and maleic anhydride yield amic acids that can be dehydrated to imides, polyimides (qv), or isoimides depending on the reaction conditions (35—37). However, these products require multistep processes. Pathways with favorable economics are difficult to achieve. Amines and pyridines decompose maleic anhydride, often ia a violent reaction. Carbon dioxide [124-38-9] is a typical end product for this exothermic reaction (38). 

Thermosetting-encapsulation compounds, based on epoxy resins (qv) or, in some niche appHcations, organosiHcon polymers, are widely used to encase electronic devices. Polyurethanes, polyimides, and polyesters are used to encase modules and hybrids intended for use under low temperature, low humidity conditions. Modified polyimides have the advantages of thermal and moisture stabiHty, low coefficients of thermal expansion, and high material purity. Thermoplastics are rarely used for PEMs, because they are low in purity, requHe unacceptably high temperature and pressure processing conditions. 

Fig. 4. Examples of emission spectrometry as a diagnostic monitoring tool for plasma processing, (a) The removal of chlorine contamination from copper diode leads using a hydrogen—nitrogen plasma. Emissions are added together from several wavelengths, (b) The etching and eventual removal of a 50-p.m thick polyimide layer from an aluminum substrate, where (x ) and (° ) correspond to wavelengths (519.82 and 561.02 nm, respectively) for molecular CO2...

Since successful commercialization of Kapton by Du Pont Company in the 1960s (10), numerous compositions of polyimide and various new methods of syntheses have been described in the Hterature (1—5). A successful result for each method depends on the nature of the chemical components involved in the system, including monomers, intermediates, solvents, and the polyimide products, as well as on physical conditions during the synthesis. Properties such as monomer reactivity and solubiHty, and the glass-transition temperature,T, crystallinity, T, and melt viscosity of the polyimide products ultimately determine the effectiveness of each process. Accordingly, proper selection of synthetic method is often critical for preparation of polyimides of a given chemical composition. 

The two-step poly(amic acid) process is the most commonly practiced procedure. In this process, a dianhydride and a diamine react at ambient temperature in a dipolar aprotic solvent such as /V,/V-dimethy1 acetamide [127-19-5] (DMAc) or /V-methy1pyrro1idinone [872-50-4] (NMP) to form apoly(amic acid), which is then cycHzed into the polyimide product. The reaction of pyromeUitic dianhydride [26265-89-4] (PMDA) and 4,4 -oxydiani1ine [101-80-4] (ODA) proceeds rapidly at room temperature to form a viscous solution of poly(amic acid) (5), which is an ortho-carboxylated aromatic polyamide. 

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