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Browse Prior Art Database

Three-Ply Foil For Fabrication Of Embedded Resistors

IP.com Disclosure Number: IPCOM000006600D
Original Publication Date: 2002-Jan-16
Included in the Prior Art Database: 2002-Jan-16
Document File: 2 page(s) / 481K

Publishing Venue

Motorola

Related People

Gregory J. Dunn: AUTHOR

Abstract

The invention is a three-ply foil comprising approximately 100 nm of highly resistive (1-20 kohm/square) Pt-SiO2 on approximately 100 nm of resistive (25-100 ohm/square) Ni-P on 5-40 micron Cu foil. The three-ply foil can be patterned selectively to yield Cu traces, Ni-P resistors, and Pt-SiO2 resistors, for a complete embedded resistor solution in one circuit board layer. The invention is not limited to Ni-P and Pt-SiO2 layers, but could comprise other resistive materials that offer high and low sheet resistances and can be patterned selectively with respect to copper and each other.

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Three-Ply Foil For Fabrication Of Embedded Resistors

Gregory J. Dunn

Abstract

The invention is a three-ply foil comprising approximately 100 nm of highly resistive (1-20 kohm/square) Pt-SiO2 on approximately 100 nm of resistive (25-100 ohm/square) Ni-P on 5-40 micron Cu foil.  The three-ply foil can be patterned selectively to yield Cu traces, Ni-P resistors, and Pt-SiO2 resistors, for a complete embedded resistor solution in one circuit board layer.  The invention is not limited to Ni-P and Pt-SiO2 layers, but could comprise other resistive materials that offer high and low sheet resistances and can be patterned selectively with respect to copper and each other.

Problem

A typical wireless product contains hundreds of surface mounted resistors.  These add significant assembly cost to the product, and take up 10-15% of the printed circuit board surface area.  Embedding the resistors in the inner layers of the circuit board would allow product cost and size reductions.

A copper/nickel-phosphorus two-ply foil is commercially available, from which embedded resistors can be fabricated by subtractive, selective etching processes.  An important limitation of this material is that it is only available in sheet resistances of 100 ohms/square or less.  Another material under development uses a platinum-silica film in place of the nickel-phosphorus as the resistive layer.  This material may be available in sheet resistances up to 10 kohms/square.  An important shortcoming of both materials is that they do not allow resistors to be fabricated on one board layer from different sheet resistances.  This is highly desirable for efficient, compact circuit designs comp...