Computer system and EMI structure thereof

Details Computer system and EMI structure thereof Computer system and EMI structure thereof

2001-12-10

2004-05-11

Martin, David (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S816000, C361S800000, C361S802000, C439S377000, C174S034000

Reexamination Certificate

active

06735093

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to an electromagnetic interference (EMI) prevention structure, and more particularly, to an electromagnetic interference prevention structure for a personal computer.
(2) Description of the Prior Art
Many electronic products, especially information products such as personal computers or set-top boxes, comprise metal housings for covering a main board of a computer system, so as to protect the electronic components therein and to reduce EMI for the electronic components. It has been proven that strong EMI generated by an electronic product can cause harm to a human being, especially for electronic devices having high working frequencies. Therefore, a specified security standard to limit the level of EMI from many kinds of the electronic products is applied in many countries.
In a conventional technique, a main board in a metal housing is usually fixed into an inner side or the metal housing by screws so as to reduce the potential between the ground voltage of the main board and voltage of the metal housing. Thus, the EMI generated from the potential can be reduced. Additionally, the conductive surface can be extended because of the contact between the main board and the metal housing so that the energy of the EMI may be decreased.
FIG. 1
shows a main board of a computer system
10
according to the prior art, wherein an upper cover of the housing is removed such that the relationship between a main board
11
and a metal housing
13
is clear. A plurality of through holes
15
are formed on the main board
11
so that the main board
11
can be secured on one surface of the metal housing
13
by screws
12
. The lower portion of the screw
12
is tinned and is connected with a ground layer
14
of the main board
11
so as to reduce a potential between a voltage of the main board
11
and a voltage of the metal housing
13
. Thus, the EMI generated from the potential can be reduced. Additionally, the conductive surface can be extended because of the contact between the main board
11
and the metal housing
13
so that the energy of the EMI may also be reduced.
However, securing the screws
12
and the metal housing
13
is difficult. Moreover, the screws allow for a gap between the metal housing
13
and the main board
11
, the gap permitting electromagnetic waves to easily pass through.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide a computer system and an EMI preventing structure thereof.
To achieve the above object the present invention provides a shielding device comprising a pair of substantially parallel metal plates and a metal side plate forming an open rectangular channel, said shielding device connected to a ground layer of a main board by clamping over a periphery thereof, wherein at least one spring piece is installed on at least one of the metal plates for mating with a leading groove of a computer housing.
This object is achieved by the EMI preventing structure described below.


REFERENCES:
patent: 5055061 (1991-10-01), Lichtenwalter
patent: 5500789 (1996-03-01), Miller et al.
patent: 5777856 (1998-07-01), Phillips et al.

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