Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-08-20
2001-09-11
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S250000, C174S260000, C361S760000, C361S783000, C361S799000, C361S800000, C257S707000
Reexamination Certificate
active
06288344
ABSTRACT:
TECHNICAL FIELD
The present description generally relates to hybrid circuit boards, and more particularly to edgewise electromagnetic interference (EMI) shielding utilizing an integrated peripheral EMI shield.
BACKGROUND
In many applications, sensitive electronic circuitry and components are susceptible to electromagnetic interference (EMI) emanating from other circuits and components. Electronics designers may incorporate EMI shields to isolate the sensitive circuits from the offending circuits. For example, in the design of implantable cardioverter defibrillators, highly sensitive circuitry is in very close proximity to the pulse generating case which is a major EMI source. Such shielding may be composed of electrically conductive metal, such as copper, and may be in electrical contact with electrical ground.
Integrated circuit (IC) chip carriers are specialized circuit panel structures that are frequently used to attach IC's to circuit boards. Chip carriers provide high density, complex interconnections between the IC and the circuit board. Separately attached peripheral or edge shielding is used to address cross-wise EMI emissions. Such shielding may be in the form of conductive tape or foil. The physical size of the tape is a limiting factor for miniaturizing systems and the extra labor involved in manufacturing does not provide for an efficient manufacturing process. It is not mechanically efficient or desirable to have a separate component that takes up valuable device space and volume.
SUMMARY
The present embodiments and associated methods provide for an integrated EMI shield for effective shielding not only from emissions perpendicular to the integrated circuit (IC) chip carrier but also parallel (edgewise) to the carrier. In one embodiment, an IC chip carrier comprises an insulating ceramic substrate and at least one internal electrically conductive layer being a circuit ground, portions of which extend to the edge of the substrate, the internal electrically conductive layer in electrical contact with an electrically conductive layer applied to a portion of the substrate edge. This provides a horizontal hybrid ground plane which can be used as an EMI shield that runs horizontally to the chip as well as a hybrid edge EMI shield perpendicular along a portion of the edge. This edge shield protects internal circuitry from exterior EMI emissions directed towards the chip carrier edge portion incorporating the shield.
In one embodiment, the method of applying the edge conductive layer comprises the steps of laying-up a plurality of ceramic green sheets, at least one green sheet having an applied electrically conductive first layer, applying heat and pressure to the lay-up to consolidate the green sheets and at least one conductive layer into a monolithic structure, exposing at least a portion of the conductive layer on the structure edge, application of metallized paste (such as that used to create the first conductive layer) to at least a portion of the structure edge and in electrical contact with the first conductive layer, applying heat and pressure to the structure a second time to metalize the paste and to create a consolidated chip carrier.
In another embodiment, metalized paste is applied to the entire chip carrier edge and in electrical contact with the first conductive layer. The chip carrier is treated to heat and pressure a second time to consolidate the unit. Thus, the chip carrier has a hybrid shield which provides EMI shielding of internal circuits from external EMI emissions directed towards any part of the edge of the chip carrier.
In another embodiment, the metalized paste is applied using a printing process, such as silk-screening.
In another embodiment, the metalized paste contains molybdenum.
In another embodiment, the metalized paste contains tungsten.
In another embodiment, the edge EMI shield is applied via a plating process not requiring a second heat and pressure treatment.
In other embodiments, where the chip carrier is made of a low-temperature calcined ceramic, the metalized paste may contain either Cu, Au, Ag, Al, Ni, Pb-Sn, among others, since the heat treatments may be conducted at a lower temperature.
In another embodiment, the edge shield is applied to a printed circuit board.
In another embodiment, the edge shield is applied to a printed wiring board.
This summary is a brief overview of some embodiments of an integrated EMI shield utilizing a hybrid edge and methods of use and is not intended to be exclusive or limiting and the scope of the invention is provided by the attached claims and their equivalents.
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Blood James E.
Hansen John E.
Youker Nick A.
Cardiac Pacemakers Inc.
Gaffin Jeffrey
Patel I B
Schwegman Lundberg Woessner & Kluth P.A.
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