Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-09-18
2002-05-14
Paladini, Albert W. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S034000, C361S816000, C361S818000
Reexamination Certificate
active
06388205
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to printed circuit boards and electromagnetic interference (EMI). In particular, the present invention is related to printed circuit boards with shielding against electromagnetic interference.
BACKGROUND OF THE INVENTION
Printed circuit boards (PCB's), including rigid, flexible, single, double and multilayer boards have found important uses in the semi-conductor and electronic industry. A PCB typically contains metallized layers of electrical circuitry or traces separated by dielectric material. Interconnections are provided for electrical connection between the metallized layers. In certain applications, such as audio-amplifiers, microphones and mobile telephones, the electrical circuitry of the PCB generates an electromagnetic field which interfere with the normal operation of other circuitries in the vicinity.
One conventional method of reducing EMI in circuitry embedded in PCB's is to provide metal shield on the surfaces of the board. This shield may be one or more metal plates mounted around the PCB, or a layer of metallic coating plated directly onto the surface of the PCB. Another prior art method involves the plating of metallic traces internally within the inner layers of the PCB adjacent the prescribed trace or traces for which EMI shielding is needed.
FIGS. 1A
to
1
D show the traces and structures found in the prior art PCB for internal EMI shielding. A simple six-layer PCB is shown with a metal trace
20
in layer L
1
-
3
and another metal trace
22
in layer L
1
-
4
. These two traces require EMI shielding. For ease of illustration, only the traces to be shielded and the relevant shielding structures are shown in layers L
1
-
2
to L
1
-
5
. Trace
20
is interconnected to trace
22
through metal-coated via
24
. Two ground shields
26
and
28
are also plated in layer L
1
-
3
on the two opposing sides of trace
20
. Ground shield
21
, connected to traces
26
and
28
in layer L
1
-
3
, is provided for top shielding of trace
22
. Two other grounded traces
30
and
32
are plated in L
1
-
4
on the two adjacent sides of trace
22
. They are connected to trace
31
, which act as the bottom shield for trace
20
. Ground shield
33
is provided in layer L
1
-
2
directly above metal trace
20
to function as top shielding against EMI. Ground shield
35
is provided in layer L
1
-
5
directly below metal trace
22
as bottom shield therefor. Between metallic layers L
1
-
2
, L
1
-
3
, L
1
-
4
and L
1
-
5
are dielectric layers, denoted as L
1
-axb where a and b indicate the layers directly above and below it respectively. To provide partial EMI shielding at the dielectric layers, conventional PCB boards are provided with vias
34
a
and
34
b
having a coat of metal
36
thereon.
It is clear from the above description of the prior art that the shielding provided within the PCB does not provide good EMI shielding, as there are multiple gaps
38
between vias
34
a
and
34
b
that do not provide shielding.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a PCB board with improved internal EMI shielding.
Accordingly, the present invention provides PCB boards with in-board EMI shielding in which a prescribed electrical circuitry within a PCB is shielded from EMI by fabricating a uniform metal shielding enclosure therearound. The shielded circuitry may be a single metal trace, a group of interconnected traces in the same or different layers of the same PCB, or a complete electrical circuitry spanning many different layers and locations within the same PCB. Using the same technology, groups of electrical circuitry that require isolation because of EMI may be fabricated together in proximity, with each group shielded from the EMI of the others. The metal shield contains a top shield in a layer above the circuitry, a bottom shield in a layer below the circuitry, and side shields adjacent the circuitry.
According to one embodiment of the present invention, the side shields are trenches with metal coating provided adjacent the prescribed circuitry. The side trenches connect the top shield and the bottom shield without gaps. Openings of the uniform metal shield are provided at the sites where the circuitry connects to another circuitry within the same PCB board or with the exterior.
In another embodiment, the side shields are solid walls provided adjacent the prescribed circuitry. The walls are built using electroplating and/or electroless plating as described in detail below. As with the metal coated trenches, the solid walls connect the top shield and the bottom shield to form a uniform enclosure around the prescribed circuitry, except for openings where the prescribed circuitry connects to another circuitry within the same PCB board or with the exterior. The present invention not only provides complete shielding of a circuitry, but also gives substantial internal space savings.
As used herein, a uniform metallic shield refers to the a complete shield absent any non-metallic gaps within the side shields that connect the top shield and the bottom shield.
REFERENCES:
patent: 5252782 (1993-10-01), Cantrell et al.
patent: 5572408 (1996-11-01), Anhalt
patent: 5833473 (1998-11-01), Betker et al.
patent: 6180876 (2001-01-01), Holmes
patent: 404199790 (1992-07-01), None
Gul Technologies Singapore LTD
Paladini Albert W.
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