Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1998-09-04
2001-04-24
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S707000, C361S706000
Reexamination Certificate
active
06222741
ABSTRACT:
BACKGROUND OF THE INVETION
1. Field of Invention
This invention relates in general to the mounting of microwave devices on circuit boards.
2. Description of Related Art
In power amplifiers operating at frequencies below 30 MHz, the chassis on which the amplifier is mounted effectively operates as a fixed ground reference, since its dimensions are only a fraction of a wavelength. During operation, an object affixed to the chassis may be assumed to be at ground potential. At frequencies above 30 MHz, however, the chassis dimensions and characteristics become significant and it must be considered to be the electrical equivalent of an inductor or transmission line.
In amplifier stages, it is important to have the shortest possible path between the amplifier ground and the ground of the transmission line it interfaces with. In large volume production this ground path must also be very consistent and guaranteed for proper function and reliability.
An amplifier is often mounted directly to the chassis for best heat sinking. If the amplifier's input and/or output leads connect to a circuit board transmission line, the chassis must provide the ground path between the amplifier ground and the circuit board transmission line ground. Small imperfections in the surface of the chassis, amplifier, or circuit board may create a much longer ground path and create a discontinuity between the amplifier and the transmission line. A discontinuity in a transmission line causes undesirable reflections of radio frequency signals that can adversely effect the amplifier's performance.
Surface imperfections may reduce the contact area between the amplifier and the chassis and result in reduced heat sinking for the amplifier. In order to assure the best possible contact between the transistor and chassis, a very flat and smooth surface finish is typically machined into the chassis at a location where the transistor seats. Superior flatness and surface finish provides greatest contact between mating components, which in turn, provides increased thermal and electrical conductivity between components. However, as in most machining operations where different components are manufactured or machined on different machine set-ups, post-machining is typically required of at least one component in order for its mating surface to confonn to its counterpart within the required specifications, or to merely correct imperfections in the initially machined step. Thus, prior to assembly, the location on the chassis where the transistor is seated is typically post-machined in order to meet the flatness and/or surface finish requirement of the interface. To facilitate connection to ground, a thin piece of aluminum is typically placed between the transistor, or other chassis-mounted component, which tends to conform to surface variations in both the transistor and chassis. Post-machining prior to assembly, however, is still required, and though effective in producing an adequate finish on the chassis, this practice is expensive and time consuming.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a superior contact between the amplifier (or transistor or other device), chassis, and the underside of the circuit board (ground) without the need to post-machine the chassis in order to meet the requirements of flatness and surface finish for interfacing with transistor, amplifier, or other chassis-mounted components.
The present invention provides a thin, compliant, electrically and thermally conductive aluminum shim device (hereinafter “aluminum shim”) to be inserted between a Microwave Monolithic Integrated Circuit (MMIC) amplifier and the chassis to provide a superior electrical and thermal contact to the chassis and to the underside of the circuit board. With the present invention, post-machining of the chassis prior to assembly of components is not required since the aluminum shim is sufficiently compliant to conform to both the bottom surface of the amplifier and the existent flatness and surface finish on the chassis produced from the initial machining step. Also, the aluminum shim creates an interference fit between the underside of the circuit board and chassis, which guarantees an electrical connection with the bottom of amplifier and underside of the circuit board. Thus, the aluminum shim provides a minimum distance and minimum inductance path from the bottom of the amplifier to the underside of the circuit board (ground). The aluminum shim also ensures superior electrical and thermal contact to the chassis and underside of circuit board regardless of slight imperfections in chassis flatness and surface finish at the seat location, thereby improving reliability and decreasing cost of manufacture and assembly. Another advantage of the aluminum shim is that, since the circuit path it creates does not require the chassis to complete the ground path back to the circuit board; the chassis need not be made of electrically conductive material.
It will be evident to those skilled in the art that the present invention is not limited to the use of MMIC amplifiers, but can be utilized for any component which is mounted to the chassis and requires the shortest possible guaranteed ground path while providing a superior thermal ground.
REFERENCES:
patent: 5206796 (1993-04-01), Thompson et al.
patent: 5353200 (1994-10-01), Bodin et al
Drennen William Anthony
Stillinger David C.
Brown Charles D.
Gaffin Jeffrey
Qualcomm Incorporated
Streeter Tom
Vu Phuong T.
LandOfFree
Mounting arrangement for microwave power amplifier does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mounting arrangement for microwave power amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mounting arrangement for microwave power amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2468084