Electricity: conductors and insulators – Insulators – Special application
Reexamination Certificate
1999-05-28
2001-07-10
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Insulators
Special application
C174S16600R, C361S742000
Reexamination Certificate
active
06259032
ABSTRACT:
BACKGROUND OF THE INVENTION
The performance of electronic instruments often depends on how well the circuit boards within the instruments are grounded to the instruments' chassis. For example, in a measurement instrument poorly grounded circuit boards can increase noise and spurious signal levels, degrading measurement range and accuracy of the instrument. Typically, circuit boards are grounded using a series of conductive standoffs, which also provide mechanical support for the circuit boards in the instrument. In one known grounding scheme, one end of each standoff is fastened to the instrument chassis while the other end of the standoff contacts a ground plane of the circuit board and receives a fastening screw. The fastening screws ensure both adequate mechanical support for the circuit board and sufficient grounding of the circuit board to the instrument's chassis. However, the screws increase the assembly time for this type of grounding scheme because the circuit board must be accurately aligned with the series of standoffs before each of the screws is properly positioned and installed. Another known grounding scheme provides self-alignment of the circuit board with the standoffs and does not rely on screws to fasten the circuit board to the standoff. While this scheme has low assembly time, it does not provide for intimate grounding of the circuit board to the instrument chassis. The grounding provided may be inadequate for electronic instruments in which performance depends on well-grounded circuit boards. Accordingly, there is a need for a grounding scheme that achieves intimate grounding of a circuit board to an instrument chassis, that also has low assembly time.
SUMMARY OF THE INVENTION
In a grounding scheme constructed according to the preferred embodiments of the present invention, a circuit board having a series of slots is self-aligning with a series of conductive standoffs. Each standoff has a tapered head supported by a neck, and a base that is coupled to a conductive member, such as an instrument chassis. A narrow portion of the tapered head of each standoff penetrates a corresponding one of the slots in the circuit board, aligning the circuit board with the standoff. Once aligned with the standoffs, the circuit board rests on the bases of the standoffs in a neutral position. The circuit board is then biased toward the necks of the standoffs, becoming wedged in a non-uniform gap that is formed between a wide end of the tapered head and the base of each standoff. One or more ground areas on the circuit board contacts the wide end of the tapered head or the base of the standoff. According to a first preferred embodiment of the present invention, the standoffs are coupled to the conductive member using fasteners, or alternatively, the standoffs are compression fit into the conductive member. According to a second preferred embodiment of the present invention, the standoffs are continuous with the conductive member.
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Agilent Technologie,s Inc.
Imperato John L.
Nino Adolfo
Reichard Dean A.
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