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Ultem® Resin for Flexible Printed Circuit Applications

IP.com Disclosure Number: IPCOM000010843D
Publication Date: 2003-Jan-27
Document File: 6 page(s) / 99K

Publishing Venue

The IP.com Prior Art Database

Abstract

Thermoplastic resins can readily be formed into substrate films for flexible circuit applications. XH Ultem® resin from GE Plastics is a strong candidate for use in such films, where its physical characteristics can provide necessary performance for flex circuit assembly and function. Film dimensional stability over operating temperatures can be a distinguishing characteristic, one that can be changed by blending resin with fillers and by film processing. Keywords: XH Ultem, polyetherimide, thermoplastic film, flexible circuits, thermal expansion, fillers.

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Ultem® Resin for Flexible Printed Circuit Applications

Thermoplastic resins can readily be formed into substrate films for flexible circuit applications.� XH Ultem® resin from GE Plastics is a strong candidate for use in such films, where its physical characteristics can provide necessary performance for flex circuit assembly and function.� Film dimensional stability over operating temperatures can be a distinguishing characteristic, one that can be changed by blending resin with fillers and by film processing.

Keywords: XH Ultem, polyetherimide, thermoplastic film, flexible circuits, thermal expansion, fillers.

1.      Flexible circuit design and application.

Flexible Printed Circuits (FPC) (also known as Flexible Printed Wiring (FPW)) have found increasing use in a broad array of electrical and electronic devices, spanning a variety of market segments, e.g., Medical, Consumer Electronics, Military, Telecom, Computers, and Home Entertainment. FPC/FPW are a versatile medium for providing high density circuit interconnections. In addition, as the name implies, FPC/FPW are used to provide flexible interconnections as well, for both dynamic flex (e.g., printer ribbon connectors) or "flex-to-install" applications (e.g., circuits that fold up to be installed inside of digital cameras).

At a high level, FPC consists of circuit traces on a thin, flexible substrate. The traces can be formed by metals or other conductive medium (e.g., silver inks) and most often are formed by copper. Metallic conductive traces can be generated "subtractively" by starting with a copper coated or copper foil laminated insulator and etching away unwanted copper from between the traces or "additively" by electrolessly or electrolytically depositing copper (or other metals) in the desired locations.

The substrates in FPC (upon which these conductive traces are mounted) are most often thin (10-75 micron thick) thermoset or thermoplastic insulating films. The films themselves should be able to withstand a variety of processing operations, while maintaining very high dimensional stability. Often, the requirements for circuit preparation are more demanding than the end-use application.

By layering several pieces of substrate and conductive traces, a multilayer "stack-up" can be created that provides for extremely high density interconnection. This sort of arrangement is not only preferred but is sometimes necessary for some high-end active devices� - i.e. IC chips of various formats. To achieve high layer counts and to meet the other requirements for FPC fabrication, these substrates are supplied in a variety of metallized and unmetallized formats, sputtered, laminated to copper foils or coated with adhesives. For some types of multilayer circuit fabrication, it would be highly preferable to employ thermoplastic substrates (as opposed to thermoset substrates) since thermoplastics can be bonded to themselves (and to other materials) simply by applying adequate heat and pressure an...