Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1997-08-20
2001-05-22
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S829000
Reexamination Certificate
active
06233816
ABSTRACT:
TECHNICAL FIELD
The present invention relates to fabricating electrical circuits on printed circuit boards, and in particular to a method of manufacturing printed circuit boards so as to minimize the effects of external vibration sources on circuit components attached thereto.
BACKGROUND
A typical circuit design implemented on a printed circuit board contains parts such as transistors, resistors, capacitors and integrated circuits. Assembly of circuit designs on printed circuit boards is a favored industry practice because it permits low-cost production and easy maintenance.
It is not unusual for a circuit design implemented on a printed circuit board to contain one or more vibration sensitive components, for example, a voltage controlled oscillator or resonant circuit, in addition to supporting circuitry. Furthermore, it is not unusual for a printed circuit board containing a vibration sensitive circuit or component to be placed in an environment that subjects the board to external vibration forces in an axis perpendicular to the plane of the board, for example, placement of the circuit board in an automobile or airplane. When oriented in this manner, external vibration forces, can cause deflections in the circuit board that influence the operation of vibration sensitive components attached thereto.
As the printed circuit board vibrates and deflects, a small part of the shunt capacitance between the circuit component leads and the ground plane varies in concert with the vibrational motion. Board deflection and the associated shunt capacitance variation are most severe at or near the natural resonance frequency of the printed circuit board. As is well known, this variation in shunt capacitance often causes a corresponding variation in the output oscillation frequency of vibration sensitive components or resonant circuits mounted to the vibrating circuit board.
Local oscillators used in telecommunications equipment are most susceptible to the effects of circuit board vibration and deflection. Deviations in the local frequency of oscillation caused by shunt capacitance variation resulting from circuit board vibration and deflection corrupts the output spectrum of the local oscillator. Corruption of this kind is known as incidental frequency modulation and manifests itself as phase jitter when measuring data signals. In conclusion, variable shunt capacitance effects from vibrating and deflecting circuit boards can render sophisticated and important vibration sensitive circuitry unusable or unreliable in hostile environments.
Accordingly, there is a need for an improved mounting of vibration sensitive circuit components on printed circuit boards to minimize the effects of external vibration sources on vibration sensitive circuit components.
SUMMARY OF THE INVENTION
The present invention provides for mounting circuit components on printed circuit boards to minimize the effects of external vibration sources on circuit components attached thereto by mechanically isolating vibration sensitive circuitry and components from supporting circuitry. As is well known, the natural resonance frequency of a circuit board is a function of the board's length, width and thickness. Mathematical resonance analysis discloses that the smaller the board area exposed to vibration, the higher its natural resonance frequency.
According to the preferred embodiment of the present invention, a plurality of holes, slots or other openings are cut into the printed circuit board surrounding the vibration sensitive circuitry or components to raise the natural resonant frequency of the isolated board area above the expected external vibration frequency spectrum. Furthermore, in one embodiment, a rigid cover may be attached to the isolated board area to further inhibit vibration and deflection of the isolated circuit board area.
Other advantages and applications derived from the use of the mounting of the present invention will readily suggest themselves to those skilled in the art from consideration of the following Detailed Description taken in conjunction with the accompanying Drawings.
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Crose Steven R.
Franke Earnest A.
Sheets Judd O.
Baker & Botts L.L.P.
Raytheon Company
Young Lee
LandOfFree
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