Enclosure for an RF assembly

Details Enclosure for an RF assembly Enclosure for an RF assembly

1998-08-27

2001-11-06

Gaffin, Jeffrey (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S800000, C361S818000, C361S814000, C361S753000, C174S034000, C174S034000, C206S706000, C206S719000

Reexamination Certificate

active

06314000

ABSTRACT:

FIELD OF THE INVENTION
This invention is related to enclosures, and more particularly to enclosures for RF assemblies.
BACKGROUND OF THE INVENTION
The performance of an electronic device can be affected by the environment of the device. RF components and circuit boards for RF components face a particular problem. The enclosure for an RF circuit needs to prevent any RF energy radiated by the circuit from escaping out of the enclosure and interfering with other circuitry of the device or with other nearby devices. Additionally, in most areas the FCC has specific limitations on how much RF energy the electronic device can release into the atmosphere. These limitations are meant to prevent an RF device from interfering with other devices.
The problem of preventing interference is even more significant for circuit boards that contain both RF and digital components. The RF energy radiated from the RF component is at a much higher frequency than the frequency used by the digital component. If this high frequency reaches the digital component it interferes with the much lower frequency of the clocks of the digital component, thereby disrupting the operation of the digital component. One problem caused by RF leakage is that the RF signals create false clock signals or edges for the digital component.
In an effort to minimize the interference, the enclosures for RF components are designed to shield and to attenuate as much of the RF energy as possible. The enclosures are fabricated from a material such as aluminum that balances the desire to keep the enclosure as inexpensive and lightweight as possible and the requirement to attenuate RF radiation. The enclosures are typically cast out of the aluminum into the desired shape.
FIG. 1
shows an assembly that has both RF component
12
and digital component
14
on circuit board
16
attached to a conventional enclosure and to back plate
17
.
FIG. 2
shows a top view of enclosure
20
of FIG.
1
. Referring to
FIGS. 1 and 2
concurrently, enclosure
20
has plate
22
, wall
24
that surrounds all of the components, and wall
26
that separates RF component
12
and digital component
14
. Wall
24
has openings
15
1
,
15
2
,
15
3
through which power, ground, and any other connections are supplied to components
12
,
14
and circuit board
16
. Wall
24
has lower portion
34
and upper portion
27
. Circuit board
16
fits against lower portion
34
. Enclosure
20
has standoffs
28
1
. . .
28
15
, for fasteners, typically screws, that attach enclosure
20
to circuit board
16
. The tops of standoffs
28
1
. . .
28
15
fit through openings in circuit board
16
. Optionally, enclosure
20
also includes tuning openings
30
1
. . .
30
6
for inserting testing and tuning instruments to test and tune the components after the assembly is encased in enclosure
20
. Once the testing and tuning is complete the tuning openings
30
1
. . .
30
6
are covered with electromagnetic interference (EMI) tape, which is a thin aluminum tape used to prevent any RF energy from escaping through the tuning openings
30
1
. . .
30
6
.
Enclosure
20
should avoid any gaps between walls
24
,
26
and circuit board
16
because RF energy escapes through these gaps. To prevent gaps there is a large amount of torque on the screws that hold circuit board
16
and enclosure
20
together. Additionally, the screws are placed close to walls
24
,
26
to tightly fasten circuit board
16
to enclosure
20
. The torque on the screws is typically large enough that if the screws were not placed in standoff
28
1
. . .
28
15
that absorb some of the force of the screws, the screws could bend plate
22
of enclosure
20
.
A problem with conventional enclosures is that even if circuit board
16
is tightly pressed against enclosure
20
too much RF energy passes around each of walls
24
and
26
.
Additionally, the tolerance of the metal may still allow for gaps between walls
24
,
26
and circuit board
16
. As shown in
FIG. 3
, in an effort to eliminate these gaps, RF gasket
32
can be placed on wall
26
. RF gasket
32
is a silver filled silicone rubber gasket. Referring to
FIGS. 1 and 4
, RF gasket
32
has groove
36
. Groove
36
allows two sides
37
,
38
of RF gasket
32
to fit around, a wall or around a notch in the wall, so that RF gasket
32
surrounds an end of the wall. This prevents RF energy from escaping around any gaps between the end of the wall and circuit board
16
. Unfortunately, since lower portion
34
of wall
24
is attached to upper portion
27
and there are no notches in lower portion
34
, RF gasket
32
cannot be easily placed against lower portion
34
to assist in eliminating any gaps between wall
24
and circuit board
16
.
Referring to
FIGS. 3 and 4
, another problem with conventional enclosure
20
is that with conventional casting equipment if two shapes are not located far enough apart the area between them is filled solid. Standoffs
28
1
. . .
28
13
should be in locations where the screws through standoffs
28
28
. . .
28
13
, fasten enclosure
20
tightly enough to circuit board
16
to try to prevent gaps. This typically locates standoffs
28
1
. . .
28
13
close enough to walls
24
,
26
that the areas between standoffs
28
1
. . .
28
13
and walls
24
,
26
are filled with metal connections
36
1
. . .
36
13
. The metal connections
36
1
. . .
36
13
do not allow RF gasket
32
to be placed on the portion of wall
26
attached to the metal connections.
SUMMARY OF THE INVENTION
The invention solves the above problems by providing an enclosure with two walls perpendicular to the plate that are close to each other to increase the attenuation of energy generated by a component. In the preferred embodiment, at least one of the walls is orbitally riveted to the plate of the enclosure. Both wall can be orbitally riveted to the plate, or one of the walls can be formed by bending the outer portions of the plate to form a wall, or by casting the wall in the same cast used to form the plate, or by soldering the wall in place. Having two walls close to each other is particularly advantageous for RF components. When the two walls are placed to surround the RF component they reduce the amount of RF energy that escapes into the atmosphere. When the two walls separate the RF component from other component in the same enclosure the wall reduce the interference of the RF component with the other components.
In an alternative embodiment of the invention, a single wall orbitally riveted to plate of an enclosure can be used. Because the orbitally riveted wall can be fully stand alone and is not connected to the standoffs, an RF gasket can be attached to entire length of the wall without gaps in the length of the RF gasket, thereby reducing the amount of RF energy that is able to pass around the wall.


REFERENCES:
patent: 3816911 (1974-06-01), Knappenberger
patent: 4705916 (1987-11-01), Wadhera et al.
patent: 4868716 (1989-09-01), Taylor et al.
patent: 5252782 (1993-10-01), Cantrell et al.
patent: 5566055 (1996-10-01), Salvi, Jr.
patent: 5847317 (1998-12-01), Phelps
patent: 6037541 (2000-03-01), Bartley et al.
Tool and Manufacturing Engineers Handbook, Fourth Edition, vol. IV, Charles Wick, Editor-in-Chief, 1987, Chapter 8, p. 8-54.

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