Method of etching polyimides and resulting passivation structures

• Main Authors: KINDL, THOMAS E, RICKERL, PAUL G, RUSSEL, DAVID J
• Format: Patent
• Language: English; French; German
• Published: 30.07.1997
• Edition: 6
• Subjects: BASIC ELECTRIC ELEMENTS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR; ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR; ELECTRICITY; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS; PRINTED CIRCUITS; SEMICONDUCTOR DEVICES

A method of etching polyimide material having metallization patterned thereon in which an epoxy resin system not only provides the etch mask for etching the polyimide but also provides a resulting passivation structure overlying the metallization on the polyimide substrate. The polyimide having a desired metallization pattern thereon is coated with the epoxy based photoimageable material which has the properties of resisting concentrated KOH etching when the epoxy material is cured and also the property of adhering to the polyimide substrate and the metallized pattern after exposure to the KOH etch to provide a passivation to the metallization. The process includes exposing the layer of photoimageable material to actinic radiation to selectively pattern the material, developing the patterned material to reveal the underlying polyimide to be etched, curing the remaining material and etching the revealed polyimide material in concentrated KOH to remove the revealed polyimide. The remaining epoxy material is firmly adherent as a passivation layer for the metallization. Preferably the epoxy material consists essentially of from about 10% to about 80% by weight of a polyol resin which is a condensation product of epichlorohydrin and bisphenol A having a molecular weight of between about 40,000 to 130,000, and between about 20% and 90% by weight of an epoxidized octafunctional bisphenol A formaldehyde novolak resin, having a molecular weight of between 4,000 to 10,000 and about 0.1 to about 15 parts by weight of resin of a cationic photoinitiator capable of initiating polymerization of the epoxidized resin system upon exposure to actinic radiation. The resin may optionally contain up to about 50% by weight of epoxidized di-glycidal ether of tetrabromo bisphenol A having a molecular weight of between about 600 and 2,500, if flame retardancy is required.