Browse Prior Art Database

Method for Providing Emc Protection to a Backplane With Exposed Edges

IP.com Disclosure Number: IPCOM000102215D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 6 page(s) / 234K

Publishing Venue

IBM

Related People

Aug, CJ: AUTHOR [+4]

Abstract

Described is a method which effectively extends radio frequency interference (RFI) shielding to an area of a logic cage backplane assembly that is external to the cage itself without the addition of extra parts or shields. This increases the manufacturability of the system, reducing cost and eliminating access constraints to that portion of the backplane that would occur if additional shields were mounted in the area. Protection against RFI entry is provided to both the faces and edges of the external portion of the backplane assembly.

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Method for Providing Emc Protection to a Backplane With Exposed Edges

       Described is a method which effectively extends radio
frequency interference (RFI) shielding to an area of a logic cage
backplane assembly that is external to the cage itself without the
addition of extra parts or shields.  This increases the
manufacturability of the system, reducing cost and eliminating access
constraints to that portion of the backplane that would occur if
additional shields were mounted in the area.  Protection against RFI
entry is provided to both the faces and edges of the external portion
of the backplane assembly.

      A Central Electronics Complex (CEC) contains a logic cage (Fig.
1) comprised of a backplane assembly 8 to which logic "books" 3 are
plugged.  Books 3 are guided by top and bottom castings 6,7,9,10 or
other means which are metallic or otherwise made conductive; the as
sembly is completed by sideplates 11,12 which are also metallic or
otherwise conductive.  Backplane assembly 8 (Fig. 2) is further
comprised of the backplane card itself 15, plastic stiffeners 17,18,
and thin sheet metal EMC shields 19,20--one shield on either side of
the assembly. Shields 19,20 may be of spring-grade material, as
needed. Shields 19,20 make electrical contact with cage castings
6,7,9,10 and sideplates 11,12 when all parts are assembled into a
complete logic cage.  Logic books 3 are mounted in conductive covers,
and, when plugged into the completed logic cage, make electrical
contact with EMC fingers 25 formed on shields 19,20.  With all logic
cards plugged, this construction provides protection from RFI
entry/exit to the faces and edges of the backplane assembly internal
to the logic cage.  Inspection of Fig. 1 will show that no protection
is provided to the section of backplane 60 protruding above the top
surface of the completed cage assembly, since this external area is
not covered by any of the shielding hardware described above.

      Shielding of the exposed area 60 is accomplished as follows:
As shown in Fig. 3, backplane assembly 8 is designed such that the
exposed portion 60 of backplane card 15 has added to it copper ground
planes 30 on either side that will serve as integral RFI shield
planes.  Ground planes 30 are produced in the card build process in
the normal manner of photoetching land patterns for signals, power,
and other grounds and are continuous (in the electrical sense, not
necessarily physically) across both sides of the exposed card area.
Referring to Fig. 3A, signal and other planes 50 are inside the outer
ground planes.  Holes 31 are spaced at relatively small intervals
around the inside periphery of ground planes 30 and are through-
plated, as shown.  The through-plating acts as a conductive bridge
between planes 30 at each hole 31 location.  Holes 31 at the lower
edge of planes 30 are equipped with pressed compliant or soldered
pins 32, depending on the construction of the remainder of the boar...