Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
FACEPLATE FOR A CIRCUIT BOARD IN ELECTRONIC APPARATUS
This invention relates to a faceplate for a circuit board, for
use in electronic apparatus.
Electronic apparatus is being required to meet increasingly
s-trict EMI (electromagnetic interference) standards. In order to meet
such standards, EMI shielding or screening of the apparatus is
required, the shielding typically comprising an electrically
conductive, e.g. metal, enclosure surround;ng the entire apparatus.
In order to allow an air flow for cooling the apparatus, part of such
an enclosure may comprise open metal grids or meshes.
In order to meet EMI standards in the U.S.A., it has been
determined for one type of apparatus that there must be no opening in
the EMI shielding having a length in any direction greater than about
5cm. (2 inches). This requirement poses a significant problem in the
design of the enclosure. In particular, joins in the enclosure must
be closely fitting, and opening doors provided for enabling access to
the apparatus must be sealed with EMI gaskets.
An object of this invention is to provide an improved
faceplate for a circuit board, for use in electronic apparatus in
which EMI is avoided in an advantageous and convenient manner.
In accordance with the present invention there is provided a
faceplate for a circuit board, the faceplate comprising extruded
electrically conductive material and having first and second sides,
the first side having a substantially flat surface and the second side
having a laterally open recessed slot therein laterally opposite the
substantially flat surface and extending along the length of the
faceplate. The faceplate preferably includes a plurality of
electrically conductive clip members each comprising a first portion
laterally retained in the recessed slot and a second, narrower,
portion extending substantially perpendicularly from the first portion
laterally outwardly of the slot, the clip members being spaced along
the length of the slot.
The invention also extends to the combination of a faceplate
as recited above with a circuit board attached thereto along one edge
of the circuit board.
The invention will be further understood from the following
description with reference to the accompanying drawings, in which:
Fig. 1 is a partly cut-away general illustration of
electronic apparatus;
Figs. 2 to 6 are partial cross-sectional illustrations
showing the EMI sealing provided in the apparatus at points II to VI
respectively in Fig. 1;
Fig. 7 is an enlarged cross-sectional illustration of a
known form of EMI sealing strip used in the apparatus as illustrated
in Figs. 5 and 6; and
Figs. 8 to 10 illustrate a preferred form of EMI sealing
member used in the apparatus as illustrated in Fig. 6.
The same reference numerals are used throughout the drawings
to refer to similar parts of the apparatus.
Referring to Fig. 1, the illustrated apparatus comprises a
backpanel 10 having on a front surface thereof a plurality of
parallel circuit board connectors 12 only some of which are shown.
Circuit boards (not shown separately in Fig. 1) guided by channels 14
plug into the connectors 12 in conventional manner at their back
edges, and have faceplates 16 at their front edges as described in
greater detail belowO When circuit boards are inserted in all of the
connectors 12, their faceplates 16 form a generally planar front face
of the apparatus, parallel to the backpanel 10. One or more of such
circuit boards may be dummy boards provided simply to complete this
front face. The backpanel 10 may be positioned at a back of the
apparatus, in which case it conveniently has a ground plane on its
back face, or it may be positioned centrally in the apparatus with a
second set of circuit boards, and a similar arrangement to that
illustrated, on its back face, in which case it conveniently has a
central ground plane. In either case the ground plane (not shown) of
the backpanel serves as an EMI screen. In addi-tion to being stacked
on both sides of the backpanel 10, such apparatuses can be stacked
vertically and/or side by side.
A generally rectangular electrically conductive enclosure
18 for the circuit boards extends between the backpanel 10 at a back
edge 20 of the enclosure and the faceplates 16 at a -Front edge 22 of
the enclosure. The enclosure 18 consists of top and bottom members
24 and 26 respectively, and two side members 28, which are rivetted
together along their edges by rivets 30 which are spaced apart by a
distance of about 5cm. or less. The side members 28 are of
electrically conductive material such as sheet steel, and have their
back and front edges folded as shown in Figs. 3 and 6 respectively.
The top and bottom members 24 and 26 are similar to one another, only
parts of each member being illustrated in Fig. 1 for clarity. Each
of these members 24 and 26 comprises a sheet steel member, whose
back, front, and side edges are folded as shown in Figs. 2, 5, and 4
respectively, having elongate apertures 32 therein between which the
channels 14 are formed as is bes-t shown in Figs. 4 and 5. On the
outer surfaces (i.e. the upper surface of the top member 24 and the
lower surface of the bottom member 26) of these members are wire
meshes 34, which are welded to the sheet steel members around their
peripheries shown by a chained line 36 in Fig. 1.
The holes in the meshes 34 and the apertures 32 are
suf-Ficiently large to allow air to circulate or be blown vertically
through the apparatus between the circuit boards for cooling
purposes, whilst being sufFiciently small that the meshes 34 still
act as effective EMI screens. The enclosure 18 thus forms an EMI
screen around the sides, top, and bot-tom of the apparatus, the ground
plane of the backpanel 10 forming an EMI screen at the back, and the
faceplates 16, which are oF electrically conductive material such as
extruded aluminum, forming an EMI screen at the front, of the
apparatus. In order to complete this screening in an effective
manner, the apparatus includes EMI sealing between the backpanel 10
and the back edge 20 of the enclosure 18 around the periphery oF this
back edge, and between the faceplates 16 and the front edge 22 oF the
enclosure 18 around the peripheries of all of -the Faceplates 16.
The latter EMI sealing is described in greater detail below.
The former EMI sealing comprises a ground conductor 38 on the front
face of the backpanel 10 and extending around the entire periphery of
-the back edge 20 of the enclosure 18 for electrical contact
therewith. Screws 40, spaced apart by a distance of about 5cm. or
less along the back edges of the top and bottom members 24 and 26,
are screwed through the backpanel 10 and into these members as best
shown in Fig. 2. The back edges of the side members 28 are folded as
best shown in Fig. 3 to abut and electrically contact the ground
conductor 38. In this manner a good electrical contact, and hence an
ef-fective EMI seal, is ensured around the entire periphery oF the
back edge 20 of the enclosure 18. The ground conductor 38 is itself
grounded or earthed.
Figs. 2, 3, and 4, showing cross-sections at the junction
between respect-ively the top member 24 and the backpanel 10, the
left-hand side member 28 and the backpanel 10, and the left-hand side
member 28 and the bottom member 26, require no further description.
Fig. 5 shows a cross-sec-tion at the junction between the
bo-ttom member 26 and a faceplate 16 which is attached to a circuit
board part of which is shown and referenced 42. The bottom member 26
has a ~-shaped channel 44 formed at its front edge (the top member 24
has a corresponding, but inverted, shape), which channel forms a
recess for engagement of a latching lever (not shown) of the circuit
board in known manner. When the board is inserted into the
respective connector 12, its latching levers are operated in known
manner to engage the channels 44 and latch the board 42 in place,
pulling the faceplate 16 into engagement with the front edges of the
bottom and top members 24 and 26. A downwardly extending projection
46 of the front of the faceplate 16 is thereby pulled towards this
front edge, with a corresponding action at the top of the faceplate
16, to compress therebetween a resilient electrical contact strip 48
which is adhesively secured to the back of this projection 46. The
contact strip 48 ensures an electrical connection, and hence an EMI
seal, between the electrically conductive faceplace 16 and the bottom
member 26.
The contact strip 48, which is shown in greater detail in
Fig. 7, consists of a beryllium-copper strip which is segmented along
its length and which has an electrically conductive adhesive backing
50 on one part thereof. Such a strip is commerically available as
Tech-Etch type 156M32 No-Snag Fingers.
Fig, 6 shows a cross-section at the junction between
the right-hand side member 28 and a right-hand-most faceplate 16, and
at the junction between two adjacent faceplates 16. Each faceplate
16 is attached, for example by screws 52, to a respective circuit
board 42, and is of extruded aluminum with a cross-section as
illustrated in Fig. 6.
For forming an EMI seal between the right-hand side mernber 28
and the adjacent faceplate l6, a contact strip 48 as shown in FigO 7
is attaclled along the entire length of a folded back portion 54 of
the side member 28, whereby it is compressed by and electrically
connects -to a flat right-hand side face 56 of the faceplate 16. An
EMI seal is thereby formed along the length of the junction between
the right-hand side member 28 and the adjacent faceplate 16. A
similar arrangement can optionally be provided between the left-hand
side member 28 and its adjacen-t faceplate 16, with or without the EMI
sealing described below.
Whilst a similar arrangement could conceivably be provided
along the junction between each pair of adjacent faceplates 16, in
practice this tends to result in excessively high lateral,
or sideways, forces being necessary in order to compress the numerous
lengths oF contact strip 48. In order to avoid such excessive
la-teral forces, in the present apparatus a different form of EMI
sealing is provided between each pair of adjacent faceplates 16.
As shown in Figs. 5 and 6, the left-hand side edge of each
facepla-te 16 includes a recessed slot 58 which, when circuit boards
42 are inserted into adjacent connectors 12 on the backpanel 10, is
positioned opposite the flat face 56 of the faceplate 16 to its left.
Electrically conductive clips 60, which are described in detail below
with reference to Figs. 8 to 10, are slid into each slot 58 from one
or both ends thereof before insertion of the circuit boards 42 into
the apparatus, and are spaced apart along the length of the slot with
a pitch of about 5cm. or less.
As shown in Figs. 8 to 10, each clip 60 comprises a heat
-treated spring strip of beryllium copper alloy which is shaped and
bent to provide a body 62 and a rounded projection 64. The body 62
has a width such that it can be accommodated in the recessed part of
-the slot 58, and is bent along bend lines 66, 68, and 70 in such a
manner and to a sufFicient degree that it can be resiliently moved in
the slot 58, but normally remains in place in the slot due to its
lateral bearing against the surfaces of the slotO The projection 64
has a narrower width than the body 62, so that it can extend through
the opening of the slot 58 when the clip 60 is inserted into the
slot, and extends approximately perpendicularly from the body 62 at
one end thereof. As shown in Fig. 6, the project-ion 64 thereby
electrically contacts the flat face 56 of -the adjacent faceplate 16,
so that the several clips 60 spaced along the length of each slot 58
provide a series of such electrical contacts and hence an effective
EMI seal between the faceplates 16. At the same -time, the lateral
forces required to compress the clips 60 in order to accommodate all
of the faceplates 16 are very much less than those required using the
contact strips 48.
The clip 60 can also include, as shown in Figs. 8 and 9, a
hole 72, conveniently positioned at the bend line 66, which can be
readily engaged by the end of a thin rod or other -tool to -Facilitate
sliding of the clip along the slot 58 ancl positioning of the clip
therein. In addition, while the clip 60 shown in Figs. 8 to 10 has
only a single projection 6~ at one end thereof, it should be
appreciated that the clip may be readily modified to provide two such
projections, one at each end of a body portion, spaced apart by a
suitable distance of, for example, up to about 5cm~ Wi-th such a
modification, a smaller number of clips may be used in each slot 58.
The above described apparatus provides effec-tive EMI
screening in a manner which is particularly convenient in the event
that many cables must be connected to the circuit boards. In this
case, cable connectors can be provided on the faceplates 16 for
establishing connections through the faceplates to the circuit
boards. In consequence, cables can be connected and clisconnected
without disturbing the e-F-Fectiveness of the EMI screening provided
by the apparatus. In addition, the routing of the cables themselves
is facilitated, because this routing is no longer constrained by
restrictive EMI screening requirements.
Numerous modificationss variations, and adaptations may be
made to the particular embodiment of the invention described above
without departing from the scope of the invention, which is defined
in the claims.
