Abstract: A method and associated structure for increasing the rate at which a chromium volume is etched when the chromium body is contacted by an acid solution such as hydrochloric acid. The etch rate is increased by a metallic or steel body in continuous electrical contact with the chromium volume, both of which are in continuous contact with the acid solution. At a temperature between about 21° C. and about 52° C., and a hydrochloric acid concentration (molarity) between about 1.2 M and about 2.4 M, the etch rate is at least a factor of about two greater than an etch rate that would occur in an absence of the steel body. In one embodiment, the chromium volume is a chromium layer that rests upon a conductive layer that includes a metal such as copper, wherein the acid solution is not in contact with the conductive layer.

Abstract: A flexible circuit board having an improved protective coverlay is provided. The product flexible circuit board comprises a flexible, dielectric substrate, one or more electrical conductors carried on the surface thereof, one or more electrical contact bumps in electrical communication with the conductors, and an improved protective coverlay electrically insulating the electrical conductors. The coverlay, which is a solid, tack-free film bonded to the surface of the dielectric substrate, is formed in situ from one or more layers of flexible, dielectric, polymeric adhesives and avoids the use of a pre-formed, self-supporting film.

Abstract: A composite laminated structure is provided which includes a thin copper or other conducting material laminated to a polyimide having a relatively high coefficient of thermal expansion which in turn is bonded to a polyimide which has a relatively low coefficient of thermal expansion (CTE). This polyimide is in turn bonded to a relatively thick base such as stainless steel. The thicknesses of the polyimide and copper and the specific coefficients of thermal expansion of all of the material are so selected that in the absence of support from the stainless steel the stresses between the various layers are balanced in such a way that the two layers of polyimide and the copper remain essentially flat. This allows for a stainless steel substrate to have a portion etched away or otherwise removed so as to form a hinge region; and when the stainless steel is removed, the remaining structure will remain essentially flat and not curl either toward the stainless steel or toward the copper.

Abstract: The present invention provides a method of forming a pattern of conductive material on dielectric material with access openings or vias through said dielectric material and such a structure. A sheet of conductive material, which is to be circuitized, is provided with a layer of a first photoimageable dielectric material on one face thereof. A layer of a second photoimageable material, such as a conventional photoresist material, is provided on the opposite face of the conductive material. The layer of said first photoimageable material is selected such that it will not be developed by the developer that develops the layer of said second material. The two layers of photoimageable material are pattern-wise exposed to radiation. The second layer of material is developed and the revealed underlying conductive material is etched to form the desired circuit pattern.

Abstract: An improved method of laminating a metal foil or sheet to a polyimide material is provided. A solution of a precursor of an intractable (i.e. thermosetting) polyimide is applied to a substrate and the solvent is removed to form a dry tack-free film. Thereafter, a solution of a precursor of a thermoplastic polyimide is applied onto the first film of polyimide and the solvent is removed to form a dry tack-free second film. Both films are then cured concomitantly at a sufficiently rapid rate and low temperature to effect substantial imidization of the polyimide precursors of both films without substantial crosslinking or densification of the polyimides in either of the films. Thereafter, a metal sheet or foil is laminated onto the thermoplastic polyimide film according to the following process. The thermoplastic film is contacted with the sheet or foil of metal to be laminated thereto.

Abstract: An improved method of laminating a metal foil or sheet to a polyimide material is provided. A solution of a precursor of an intractable (i.e. thermosetting) polyimide is applied to a substrate and the solvent is removed to form a dry tack-free film. Thereafter, a solution of a precursor of a thermoplastic polyimide is applied onto the first film of polyimide and the solvent is removed to form a dry tack-free second film. Both films are then cured concomitantly at a sufficiently rapid rate and low temperature to effect substantial imidization of the polyimide precursors of both films without substantial crosslinking or densification of the polyimides in either of the films. Thereafter, a metal sheet or foil is laminated onto the thermoplastic polyimide film according to the following process. The thermoplastic film is contacted with the sheet or foil of metal to be laminated thereto.

Abstract: A method of etching polyimide having metallization patterned thereon in which an epoxy resin system provides the etch mask for etching the polyimide and provides a resulting passivation structure overlying the metallization. The polyimide having a metallization pattern thereon is coated with the photoimageable material resists concentrated KOH etching when the epoxy is cured and adheres to the polyimide and the metallized pattern after the KOH etch providing passivation to the metallization. The process includes exposing the layer of photoimageable material to radiation to selectively pattern the material, developing the patterned material revealing the underlying polyimide to be etched, curing the remaining material and etching the revealed polyimide in concentrated KOH to remove the revealed polyimide. The remaining epoxy firmly adheres as a passivation layer for the metallization.

Abstract: A polyimide pattern is formed on a substrate by providing a layer of photosensitive polyimide precursor containing the polyimide precursor and a compound having a photosensitive group on the substrate and prebaking the layer. The layer is then exposed imagewise to actinic radiation through a photomask to form an exposed image pattern of the polyimide precursor in the layer. The unexposed areas of the layer are removed using a liquid developer and the exposed image pattern is cured by heating. In one aspect of the present invention, the prebaking step employs a judicious selection of times and temperature to eliminate the problem of formation of a white residue that occurs from using prior art prebake procedures. In another aspect of the present invention, a particular liquid developer composition is employed to facilitate the formation of sloped vias in the polyimide. In another aspect of the present invention, a particular range of exposure wavelength(s) is employed to obtain smooth walled vias.