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Method for Making a Flexible Circuit

IP.com Disclosure Number: IPCOM000129246D
Publication Date: 2005-Oct-03
Document File: 6 page(s) / 37K

Publishing Venue

The IP.com Prior Art Database

Abstract

The present invention provides a copper-less flexible circuits useful for many applications, and in particular, medical applications in which copper is unsuitable. The present invention also allows for making fine pitched circuits. For example, the metal traces of the circuits may have a pitch of about 40micrometer to 50micrometer, or even less. The dielectric film may be any suitable plastic, but is typically a polymer such as polyimide, polyester, liquid crystal polymer, or polycarbonate. The thickness of the dielectric film will depend on the planned use of the article, but typically has a thickness of about 10um to about 350micrometer. In one embodiment, the dielectric web was subjected to an O2 plasma treatment, followed by application of a chrome tie layer using an argon gas medium. In at least one embodiment, the chrome was applied to a thickness to achieve a target optical density of about 30%. A first conductive layer is then deposited onto the tie layer using vacuum deposition methods known in the art, including sputtering and evaporation.Suitable metals include non-corrosive and noble metals. When the circuit will be used in medical applications, especially when the circuit will be placed inside the human body in some manner, a metal having no negative effects on the human body is desirable. In at least one embodiment, the first conductive layer is Gold (Au) or substantially Gold, e.g., a gold alloy or mixture of gold and another metal. Other suitable metals for use in the first conductive layer(s) of the present invention include noble metals Platinum (Pt), Silver (Ag), and other non-corrosive metals such as Nickel (Ni) and Palladium (Pd), and alloys thereof. The metal layer is typically about 5 nm to about 250 nm thick. An example of a suitable photoresist is a negative-acting aqueous photoresist available under the trade name Accuimage 5120 from Kolon Industries of Korea. The first conductive metal layer is then electroplated with a noble or non-corrosive metal, which may be the same as, or different from the metal in the first conductive metal layer. Suitable plating metals include, but are not limited to Gold (Au), Platinum (Pb), and Silver (Ag). Plating continues until a target thickness is achieved, typically in the range of about 250 nm to about 25 μm. For electroplating gold, suitable conditions may include a 36 inch cell, 5.0 pH, 150ºF, and 1.34 A (approximately 3.0 system volts). The target thickness is typically greater than the desired final thickness to allow for reduction in thickness during subsequent metal etching steps.

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METHOD FOR MAKING A FLEXIBLE CIRCUIT

TECHNICAL FIELD

            This invention relates to a method for making a flexible circuit; more particularly, a copperless flexible circuit.

BACKGROUND

            Flexible circuits are useful in many electrical and electronic applications.  For example, they can be used in integrated circuits, semiconductors, connectors, and medical diagnostic devices.  Most flexible circuits have copper in their conductive layers.  When used in medical diagnostic devices consideration must be given to the compatibility of the materials used in the flexible circuit with the intended use of the device.  For example, copper is incompatible with many electrochemical diagnostic applications, because it interferes with the measurements.   Accordingly, extra care and expense is often required in the design and manufacture of copper-based flexible circuits for medical diagnostic applications, including the specification of non-corrosive metal coverplates and conforming polymer covercoats, to ensure copper is not exposed in areas that would affect the diagnostic measurement functionality.

SUMMARY

The present invention features a novel method of making a copperless circuit.  By eliminating the copper in a flexible circuit, the invention eliminates the need for a non-corrosive or non-reactive coverplate and eliminates concerns of having copper in medical devices.

An advantage of at least one embodiment of the present invention is that it provides a roll-to-roll processing method.

Another advantage of at least one embodiment of the present invention is that it provides an economical way to produce thin or thick flexible circuits.

            Other features and advantages of the invention will be apparent from the following drawings, detailed description, and claims.

DETAILED DESCRIPTION

            The present invention provides a copper-less flexible circuits useful for many applications, and in particular, medical applications in which copper is unsuitable.  The present invention also allows for making fine pitched circuits.  For example, the metal traces of the circuits may have a pitch of about 40micrometers to 50micrometers, or even less. 

The flexible circuit typically consists of a dielectric layer with a patterned metal circuit on one side.  The dielectric material may be patterned or unpatterned.  The flexible circuit may further have a protective cover coat over all or a portion of the patterned metal layer.

The process of the present invention typically begins with a dielectric film in the form of a continuous sheet, often referred to as a web, to facilitate roll-to-roll processing.  The dielectric film may be any suitable plastic, but is typically a polymer such as polyimide, polyester, liquid crystal polymer, or polycarbonate.  The thickness of the dielectric film will depend on the planned use of the article, but typically has a thickness of about 10um to...