Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-08-21
2002-10-29
Martin, David (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S792000, C361S793000, C361S780000, C174S255000, C257S724000, C257S700000
Reexamination Certificate
active
06473312
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a printed circuit board, a printed circuit board module, and an electronic device adapting same, and more particularly, to a printed circuit board, a printed circuit board module, and an electronic device adapting same in which the power supply layer is divided into a plurality of lands.
2. Description of the Related Art
Electronic devices typically contain one or more printed circuit board modules, in which a variety of electronic elements are mounted atop a printed circuit board. However, in such a configuration, electromagnetic waves radiating from the printed circuit board can cause the electronic device to malfunction. Accordingly, in order to improve the reliability of such devices it is necessary to restrict the radiation of these electromagnetic waves from the printed circuit board.
In order to further an understanding of the problem the present invention attempts to solve a description will now be given of noise currents.
When the electronic elements operate, noise such as switching noise is generated. Hereinafter, the current caused by such noise is referred to as noise current.
It is known that the intensity of these electromagnetic waves is related to the size of the area of the return loop through which the noise current flows, so that the larger the area enclosed by the loop the stronger the electromagnetic wave radiation. It should be noted that the term “return loop” refers to the closed path along which the noise current flows from the noise source back to the noise source.
Accordingly, in order to suppress the electromagnetic waves radiating from the printed circuit board, it is desirable that the area enclosed by the loop-like return path through which the noise current flows be as small as possible. It should be noted that the return path through which the noise current flows is the path of least load resistance. Therefore, it is desirable that such a path enclose the smallest possible area.
Additionally, electronic devices have come to be loaded with an increasing number of functions to make data processing faster. In order to accommodate these added demands it has become necessary to mount electronic elements of different operating voltages on the printed circuit board. These operating voltages may for example be 5 V, 3 V, and 2.8 V.
An additional requirement particularly with respect to portable electronic devices is that battery power be conserved and the life of the battery extended. In order to accomplish this aim, the printed circuit board is mounted with a plurality of circuits having different functions. Power is then turned ON not to the entire printed circuit board but only to each of those circuits requiring power, and the power is turned OFF with respect to those circuits whose operations are not required, thus saving battery power.
It will be appreciated by those skilled in the art that, in order to be able to supply power selectively, that is, to selected portions of a printed circuit board mounted with electronic elements having different operating voltages, the printed circuit board must have either a plurality of power supply layers or a single power supply layer divided into a plurality of lands that are electrically insulated from each other.
Providing a plurality of power supply layers complicates the structure of the printed circuit board, and reduces the production yield of the printed circuit board. Accordingly, the conventional solution is to divide the single power supply layer on the printed circuit board into a plurality of mutually electrically insulated lands.
FIG. 1
shows perspective and cross-sectional views of a conventional printed circuit board
10
and a portion of a conventional printed circuit board module
20
. The drawing at the right of
FIG. 1
is the cross-sectional view of the printed circuit board
10
. The drawing at the left of
FIG. 1
is a schematic rendering of the printed circuit board
10
drawn to emphasize a power supply layer
11
, a dielectric layer
12
and a ground layer
13
. The drawing at the right represents a cross-sectional view along a line I—I of the drawing at the left.
As shown in the diagram, the portion of the printed circuit board
10
shown in
FIG. 1
has the power supply layer
11
divided into a plurality of mutually electrically insulated lands A, B and C. The dielectric layer
12
and the ground layer
13
are provided beneath the power supply layer
11
. Another dielectric layer
14
and a signal layer
15
are provided above the power supply layer
11
. The dielectric layer
12
disposed between the power supply layer
11
and the ground layer
13
forms the land A and the ground layer
13
into a capacitor Ca, the land B and the ground layer
13
into a capacitor Cb and the land C and the ground layer
13
into a capacitor Cc. A voltage Va is applied across the ground layer and the land A, a voltage Vb is applied across the ground layer and the land B, and a voltage Vc is applied across the ground layer and the land C.
As shown in the diagram, electronic elements are disposed atop the lands having the appropriate operating voltages. An electronic element
30
, for example, has an operating voltage Vc and is thus mounted on the land C. Similarly, an electronic element
31
has an operating voltage Va and is thus mounted on the land A.
Normally, an electronic element, like the electronic element
30
shown in
FIG. 1
, has all its terminals positioned atop the same land. However, some electronic elements, such as the electronic element
31
shown in
FIG. 1
, electrically straddle two lands, in this case land A and land B. As a result, a ground terminal Pg
31
of electronic element
31
to be connected to the ground layer
13
is positioned not so as to oppose the land A but so as to oppose the land B.
As shown in
FIG. 1
, NS
30
is the source of noise generated by the operation of the electronic elements as described above, in this case electronic element
30
. Similarly, NS
31
is the source of noise generated by the operation of the electronic elements as described above, in this case electronic element
31
. A noise current i
30
from the noise source NS
30
flows through a loop-like return circuit indicated in the drawing by reference numeral
40
via the ground layer
13
through the capacitor Cc to the
30
land C and back to the noise source NS
30
. As can be seen from the drawing, the area enclosed by this return path
40
is extremely small and hence the electromagnetic waves generated from the noise source NS
30
are weak.
By contrast, consider a noise current i
31
from the other noise source NS
31
and the path along which it returns to the noise source NS
31
. As noted above, the land B is electrically insulated from the land A. The noise current i
31
, flows along a return path indicated by reference numeral
41
, that is, from the ground layer
13
to the capacitor Ca to the land A and back to the noise source NS
31
. The area enclosed by this loop is large and hence the electromagnetic waves generated from the noise source are strong.
Accordingly, the above-described printed circuit board
10
and printed circuit board module
20
are not capable of adequately suppressing electromagnetic wave radiation.
It should be noted that although
FIG. 1
shows the capacitors Ca, Cb and Cc as a single line connecting two opposed layers, in actuality the entire areas of the opposed layers or plates form the capacitors Ca, Cb and Cc. The same holds true of
FIGS. 2 and 4
which will be described later.
Additionally, although the loop-like return path shown on the left of
FIG. 1
would appear to be three-dimensional, in actuality a direction in a thickness of the printed circuit board has been exaggerated compared to a horizontal direction of the printed circuit board for purposes of illustrative clarity only. It is understood by those of skill in the art that in actuality the direction in the thickness of the path is so small that it can be ignored and that the area enclosed by
Hiratsuka Yoshiaki
Yamaguchi Masanori
Yoshinaga Hisashi
Armstrong Westerman & Hattori, LLP.
Bui Hung
Fujitsu Limited
Martin David
LandOfFree
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