Electricity: circuit makers and breakers – Solid contact – Membrane type
Reexamination Certificate
2001-05-17
2002-08-27
Enad, Elvin (Department: 2832)
Electricity: circuit makers and breakers
Solid contact
Membrane type
C200S0050EA
Reexamination Certificate
active
06441330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a keyboard circuit, and more particularly, to a keyboard circuit using conduits within a bus for air flow.
2. Description of the Prior Art
Please refer to FIG.
1
and FIG.
2
.
FIG. 1
is an exploded diagram of a prior art circuit board
10
for a keyboard
12
, and
FIG. 2
is a cross-sectional view of the circuit board
10
. The circuit board
10
for the keyboard
12
is used to generate key signals. The keyboard
12
includes a base
14
and a plurality of key structures
16
. The circuit board
10
, disposed between the base
14
and the key structures
16
, includes a thin film switching circuit
18
for generating key signals. The thin film switching circuit
18
includes an upper circuit layer
22
and a lower circuit layer
24
.
As shown in
FIG. 2
, the upper circuit layer
22
includes a plurality of upper joints
26
corresponding to a plurality of lower joints
28
of the lower circuit layer
24
. The key structures
16
are disposed over all sets of the upper joints
26
and the lower joints
28
, and are movable in an upward and downward manner. Thus, the upper joints
26
are capable of being pressed down by the key structures
16
to cause the upper joints
26
to contact their respective lower joint
28
to generate corresponding key signals. An air-filled space
30
is between the upper joints
26
and the lower joints
28
. When the key structures
16
are pushed downward, the upper joints
26
descends and contacts the lower joints
28
; the upper joints
26
are designed to maintain or return to the original positions when the key structures
16
are not pressed or released.
Generally, there are two ways of designing the air-filled space
30
. The first method is to isolate the air-filled space
30
to prevent dust and moisture from entering the air-filled space
30
. This prolongs the life of the circuit board
10
, but the upper joints
26
may become hard to be pressed down by the key structures
16
or to revert to the original positions when the outside atmosphere pressure or temperature varies. The user, thus, may felt inconvenient. Moreover, the circuit board
10
may generate incorrect key signals. The other method is to let the air-filled space communicated with the atmosphere to equalize internal and external pressures. This, however, leaves the circuit board
10
open to the atmosphere and cannot stop effectively the entering of external dust and moisture.
Please refer to FIG.
3
.
FIG. 3
is a schematic diagram of another prior art circuit board
32
designed to overcome the aforementioned problems. As shown in
FIG. 3
, a plurality of air passageways
33
are connected to a restrictive air passageway
34
that has a superior blocking effect than a device with air passageways
33
that are directly open to the outside.
Both the air passageways
33
and the restrictive air passageway
34
have openings on the thin film switching circuit
18
, and so dust and moisture is able to enter the air-filled spaces
30
. For example, if a user spills hot liquid on the thin film switching circuit
18
, the air within the air-filled space
30
expands from the heat, leaving the air-filled spaces
30
, and returns when the liquid cools down. Therefore, the liquid may be sucked through the restrictive air passageway
34
and the air passageways
33
into the air-filled spaces
30
when the liquid cools down. Therefore, the circuit boards
10
and
32
do not always satisfy the user's wants.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a circuit board for a keyboard that not only adjusts the air pressure of the air-filled spaces within the keyboard, but also prevents dust and moisture from entering the air-filled spaces.
In accordance with the claimed invention, a thin film circuit includes a thin film switching circuit with an upper circuit layer including at least one upper joint, and a lower circuit layer with at least one lower joint corresponding to the upper joint. The lower circuit layer is set under the upper layer, and an air-filled space is disposed between the upper joint and the lower joint. The thin film switching circuit further includes at least one first air conduit set between the upper circuit layer and the lower circuit layer that is connected to the air-filled space. At least one bus structure is connected to the thin film switching circuit and extends out of the thin film switching circuit to transmit electrical signals from the thin film switching circuit. The bus structure includes at least one second air conduit. One end of the second air conduit is connected to the ambient atmosphere. The other end of the second air conduit is connected to the first air conduit so that the air in the air-filled space can flow in and out to the ambient atmosphere through the first air conduit and the second air conduit.
It is an advantage of the present invention that because the air in the air-filled spaces is able to flow in and out to the ambient atmosphere through the first air conduit and the second air conduit, the keyboard circuit is able to adjust pressure according to variations of the ambient atmosphere while preventing contaminants, such as dust or moisture, from entering the keyboard circuit.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.
REFERENCES:
patent: 4701579 (1987-10-01), Kurachi et al.
patent: 5218177 (1993-06-01), Coleman et al.
patent: 5981890 (1999-11-01), Chen
patent: 6259434 (2001-07-01), Tsai
Darfon Electronics Corp.
Enad Elvin
Fishman M.
Winseon Hsu
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