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Mechanical Packaging Scheme With Considerations for Maximum ESD/EMC Protection, Efficient Cooling And Quiet Office Environment

IP.com Disclosure Number: IPCOM000119693D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 5 page(s) / 220K

Publishing Venue

IBM

Related People

Anderson, N: AUTHOR [+10]

Abstract

As the circuit speed increases and the size gets smaller, data processing equipment has to meet more and more restrictive requirements from the standpoint of radiated acoustical noise and radiated electrical energy. Your computer cannot affect the one in the next room, or make so much noise that it bothers other people in the office. The problem is to package the circuit and I/O devices so that the acoustical noise and radiated electrical noise in minimized. In addition, the package must be strong enough to withstand shipping forces and provide cooling for the circuits and I/O devices.

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Mechanical Packaging Scheme With Considerations for Maximum ESD/EMC
Protection, Efficient Cooling And Quiet Office Environment

      As the circuit speed increases and the size gets smaller,
data processing equipment has to meet more and more restrictive
requirements from the standpoint of radiated acoustical noise and
radiated electrical energy.  Your computer cannot affect the one in
the next room, or make so much noise that it bothers other people in
the office.  The problem is to package the circuit and I/O devices so
that the acoustical noise and radiated electrical noise in minimized.
In addition, the package must be strong enough to withstand shipping
forces and provide cooling for the circuits and I/O devices.

      To pass a 2800-volt ESD test, fingerstock grounds were added at
many locations on the frame of the machine.  The box was also capable
of passing a radiated emissions test. The fingerstock grounds were
added because the sheet metal covers were not screwed into position.
They wrapped around the side and over the top, resting on a metal
ledge built into the frame.  Because they were metal, they provided a
large surface to hit with the ESD simulator furniture probe. The
design also met the acoustical requirements of 5.5 bels. This was
because the three cooling fans were located on the back panel of the
frame just under the rear decorative cover.

      To provide cooling air flow over the electronics the cooling
fans were put inside the enclosure.  Making a complete metal
enclosure and putting the fans inside gave it superior ESD/EMI
hardness and acoustical levels.

      As the box design evolved, we tried to keep all slot openings
to one inch or less for EMI reasons.  This was compromised in a few
places and one was in screw spacing for holding on the side plates.
However, we use screws rather than using tabs or quarter-turn
fasteners.  The screws on the sideplate provide the box with a
structural integrity much like the stressed skin on an aircraft.

      Fig. 1 shows the frame and the cover of the machine. The frame
is constructed of four plates with side flanges that are welded
together.  The side plates are screwed on to the metal flanges of the
four plates.  This gives a completely enclosed metal box which
provides strength as well as ESD/EMI protection.  The appearance
covers are low cost, thin wall plastic and have no coating for
ESD/EMI reasons.  Fig. 2 is a view of the power supply and logic
areas of the...