Polyimide conductivity

The increasing importance of multilevel interconnection systems and surface passivation in integrated circuit fabrication has stimulated interest in polyimide films for application in silicon device processing both as multilevel insulators and overcoat layers. The ability of polyimide films to planarize stepped device geometries, as well as their thermal and chemical inertness have been previously reported, as have various physical and electrical parameters related to circuit stability and reliability in use (1, 3). This paper focuses on three aspects of the electrical conductivity of polyimide (PI) films prepared from Hitachi and DuPont resins, indicating implications of each conductivity component for device reliability. The three forms of polyimide conductivity considered here are bulk electronic ionic, associated with intentional sodium contamination and surface or interface conductance. 

Table 3. Polyimide conductivity (o) depending on the type of layer formation...

Epoxies are the most commonly used adhesives (qv). Silver and gold are sometimes added to an epoxy to improve its thermal conductivity. Polyimide, also used as an adhesive, has low shrinkage as well as low viscosity and can be cured at 180°C its primary drawback is a tendency to absorb water, as much as 6% by weight. 

Adhesion of copper films to PMDA/ODA polyimide was determined by peel tests conducted on samples that were prepared by vapor-depositing a thin layer of copper onto the polyimide and then building the thickness of the metal layer to about 18 p,m by electrodeposition of copper. Results of the adhesion measurements correlated well with substrate pretreatment. When the substrate... 

Polyimides Powder, solutions Excellent high temperature properties, 400 to about 700 F. Difficult to process. High-temperature cable shielding, conductive film. 

Manufacture of Printed Wiring Boards. Printed wiring boards, or printed circuit boards, are usually thin flat panels than contain one or multiple layers of thin copper patterns that interconnect the various electronic components (e.g. integrated circuit chips, connectors, resistors) that are attached to the boards. These panels are present in almost every consumer electronic product and automobile sold today. The various photopolymer products used to manufacture the printed wiring boards include film resists, electroless plating resists (23), liquid resists, electrodeposited resists (24), solder masks (25), laser exposed photoresists (26), flexible photoimageable permanent coatings (27) and polyimide interlayer insulator films (28). Another new use of photopolymer chemistry is the selective formation of conductive patterns in polymers (29). 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

Since the m,m -DABP polyimide is known to be an outstanding adhesive, lap shear strength tests employing titanium-titanium adherends and metal ion filled polyimides were conducted. Tests were performed at room temperature, 250°C and 275°C employing either DMAC or DMAC/Diglyme as the solvent. At room temperature regardless of the metal ion employed adhesive strength is de-... 

Further work in this area is underway employing polyamic acid systems which are known to produce higher viscosity solutions (e.g. polyimides derived from 4,4 -oxydianiline and either BTDA or pyromellitic dianhydride). This is being carried out in the belief that higher viscosity solutions will give rise to higher quality, less brittle films and will, thereby, enable a broader spectrum of metal systems to be studied regarding the adhesive and electrical conductance properties of metal ion filled polyimides. 

The polyimide-CNT composites have good biocompatibility and conductive properties, which can be used to fabricate the electrode arrays, and enhance their biocompatibility. For example, they can be used as the stimulator embedded in the blind eyes, and can be used for the electrode arrays transplanted in the human body without damaging human organs and tissues (Tulevski et al., 2007). 

Miyatake, K., Zhou, H., Matsuo, T., Uchida, H. and Watanabe, M. 2004. Proton conductive polyimide electrolytes containing trifluoromethyl groups Synthesis, properties, and DMFC performance. Macromolecules 37 4961 966. 

Fang, J., Guo, X., Harada, S., Watari, T., Tanaka, K., Kita, H. and Okamoto, K. 2002. Novel sulfonated polyimides as polyelectrolytes for fuel cell applications. 1. Synthesis, proton conductivity, and water stability of polyimides from 4,4 -diaminophenyl ether-2,2 -disulfonic acid. Macromolecules 35 9022-9028. 

Zhang, Y, Litt, M., SavineU, R. R, Wainright, J. S. and Vendramini, J. 2000. Molecular design of polyimides toward high proton conducting materials. Abstracts of Papers of the American Chemical Society 220 11307-11307. 

Metal ion modified polyimide films have been prepared to obtain materials having mechanical, electrical, optical, adhesive, and surface chemical properties different from nonmodified polyimide films. For example, the tensile modulus of metal ion modified polyimide films was increased (both at room temperature and 200 0 whereas elongation was reduced compared with the nonmodif ied polyimide (i). Although certain polyimides are )cnown to be excellent adhesives 2) lap shear strength (between titanium adherends) at elevated temperature (275 0 was increased by incorporation of tris(acetylacetonato)aluminum(III) (2). Highly conductive, reflective polyimide films containing a palladium metal surface were prepared and characterized ( ). The thermal stability of these films was reduced about 200 C, but they were useful as novel metal-filled electrodes ( ). 

Much of the recent wor)c pertaining to metal ion modified polyimides has been aimed at increasing the surface electrical conductivity of condensation polyimides (6,7,8). This has been accomplished to a significant extent (surface resistivity reduced up to 11 orders of magnitude (8,9)) but in most systems the bul)c... 

Ti and To are the inner and onter radins of the fused-silica tnbe refers to the onter radins of the polyimide coating of the capillary tube Kj and are the thermal conductivities of the electrolyte solution and of the capillary wall, respectively... 

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