Note: Descriptions are shown in the official language in which they were submitted.
6~2
B~C~GROUND OF THE INVENTION
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Fabrication of gas discharge display devices
generally of the character disclosed herein have been accom-
plished in the past and typically these are one-for-one type
operations. That is, individual glass substrates and/or
ceramic substrates are provided upon which the conductor runs
are printed and then the dielectric masks are printed over
the conductor runs and in the openings in the conductor runs
for the cathode electrodes, the cathode materials which inter-
face with the gas discharge medium are printed thereon and all
of these being subsequently fired and cured. Such devices
are subsequently assembled usually by the use of a gas filling
tubulation but in some cases tubulationless devices have been
fabricated in which final hermetic seal of two spaced apart
substrates accomplished by utilization of an unfused sealing
frame, evacuating the entire unit and back filling with an
elevated temperature and then heating the assembled parts ;~
spaced between the electrode elements while retaining the gas
in the assembly until the glass parts have been softened to a
sealing temperature to result in a fusion sealing of the frame
element and thereby final assembly of the device. This process
is difficult and cumbersome and does not lend itself well to
batch processing of individual display elements.
In Boswau U.S. patent 2,142,106 issued January 3,1939,
a gaseous discharge display device having small glass discs
carrying shaped cathode elements and individual anode elements
are stacked in a disc with the interstices between the discs
sealed in a manner around the periphery *o prevent electrode
interference between each other, a small aperture being left -
at one point in the periphery by leaving out the sealing opera-
tion at this point to provide communication with the main gas
chamber formed by an overall glass envelope or bulb. In the
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soswau patent, the bulb is subsequently exhausted and filled
with the gas a-t a proper pressure, the exhausting and back
filling processes extending through and communicating through
the aperture to the individual gas chambers formed in the
spaced disc and the aperture then is filled with a suitable
sealing materlal which permits the gas to permeate during the
exhausting and filling operation thereafter this individual
seal element or plug is sealed by heating means of electronic
bombardment or other sealing means. The present invention is
a direct and distinct improvement over the sealing technique -~disclosed in the Boswau patent in that the present invention
adapts a portion of that technique of the Boswau patent and
extends same to batch processing of thousands of individual
discrete gaseous discharge panel elements in a manner and
fashion not heretofore available, with yield factors
significantly greater than those of the prior art. A sub-
stantially bubble-free glass rod, shaped generally in the
perimetrical configuration of the gas chamber is fused to the
two substrate surfaces in an air atmosphere. A small opening -
or space between the ends of the rod is provided. Large ~
numbers of the device may be stacked in trays, with a small ~;
glass rod bridging the ends of the rod and space and held in
position by the opposing substrate. The rod seal or plug is
slightly smaller in diameter to snugly fit between opposing
substrate surfaces and has a fusion temperature slighly below
that of the formed rod. Both materials are, however, of
optical quality and of substantially bubble-free edge surfaces.
This loose rod seal element or plug permits batch vacuumiza-
tion (also under bake out conditions if desired) and back
filling with any desired gas composition of large numbers of
individual devices in a single operation.
In the prior art, in making segmented electrode
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gaseous discharye display panels, particularly alphanumeric
type displays, the individual conductor runs are printed first
and fired on the substrate and subsequently, the mask and
cathode element electrodes e.g., those elements which are to ;~
be in direct conductive contact with the gas are printed and
cured, the printing of the cathode elements being through the
apertures or openings in the dielectric mask. In accordance
with this invention, instead of using a ceramic substrate,
simple, inexpensive glass substrates are used. The conductor
elements forming the cathode electrodes which interface with
the gas medium are printed first and cured at relatively
-higher temperature so as to assure that those conductor seg~
ments or elements forming the cathodes of the device have a
good hard surface at the gas interface 50 as to minimize
sputtering problems and improve the discharge properties of
such devices.
In the sealing operation described earlier herein,
it has also been found that the use of screened on sealing -
materials in an unfused state, is not as desirable as the use
of a preformed rod element fabricated from glasses having
fiber optic properties, that is to say no bubbles therein
which distort and rupture the seal upon heating and/or ~
vacuumization. ~ -
~ he typical and classical way of fabricating gaseous
discharge devices is to vacuum bake the devices so as to
remove included gaseous contaminants from the interior surfaces ;~
of the device. Vacuum baking is a very time consuming-and
expensive process. In another feature of the process of this
invention, the several thousand devices stacked in trays are
placed in a vacuum chamber. ~he vacuum is pulled over the
device without heating to remove substantially all of the free
contaminants from the individual gaseous discharge devices and
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then, at an ambient temperature, the gas filling is admitted
to the processing chamber and thereby each individual gaseous
discharge elemen-t is filled as room or ambient temperature.
This assures proper gas proportions and eliminates the need ~ -
for accurate and precise calibration at high temperatures of
the gas filling. Then, after the gas filling has been in-
troduced to the devices, the devices are heated by Calarod ~
heaters inside the chamber so as to effect a melting of small
sealing elements in the openings described earlier herein.
This technique thereby avoids the long time between the fil-
ling and heating of the chamber thereby reducing a production
run of thousands of devices in a single chamber to no more than
six hours in pumped in heating back illing with the gas and `
the like. Since this sealing process is done at a pressure ~ ~-
somewhat below ambient, and since the volume of gas in the
vacuum chamber can be greater than the cumulative gas volume
contained in the devices, there is sufficient heating under
somewhat negative pressure conditions to assure good clean up
of the device under less than perfect vacuum conditions and at -
significantly reduced cost and processing time. In still
another feature of the invention, small mercury-containing
capsules or givers are activated by the use of a laser beam.
To this end, the device is provided with laser transparent
windows in each of two glass substrates which thereby permits ~
the use of a laser beam to effectively break the mercury ~ .
capsule without damaging the device itself.
Finally, in the prior art, connections between the
anode electrodes and exterior connections to operating poten-
tials have been by means of small metal clips between the two
substrates. In accordance with this invention a conductive
epoxy is inserted between the terminals ends of the anode
electrodes and the printed conductor ends o~ the cathode plate.
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According to the invention, this epoxy is carefully cured so ~ -
as to assure that there are no bubbles in contact with the
anode elements which would tend to cause hot spots and breaking
of the anode connections.
Thus, in accordance with the present teachings, an
improvement is provided in the process for manufacturing a gas
discharge information display panel device wherein a pair of
rigid substrate members define parallel flat boundaries and a
thin glass chamber in which information can be displayed is
generated by plural discrete gas discharges between selectively
energized electrodes. The improvement resides in the sealing
of the information display panel which comprises joining the
rigid members in spaced apart relation by a sealing member having ~;
the perimetrical shape of the gas chamber and defining the
lateral boundaries of the chamber. The terminal ends of the ;
member are spaced apart to form a port so that the chamber is
in communication with its ambient temperature. The spaced ends
of the sealing member are fusibly bridged with a plugging ;~
member after the chamber has been filled with an ionizable gas.
In accordance with a further embodiment an
improvement is provided in a gas discharge information display ;
panel comprising a pair of substrate plate members, seal means
joining the plates in spaced relationship and defining a thin
gas discharge chamber, the gas in the chamber and an electrode
system for selectively ionizing a gas in the chamber to display
information. The improvement resides in rendering the panel ~ ~
tubulationless comprising a seal means which includes a first ~ ;
seal member having a configuration defining the perimeter of
the thin gas discharge chamber with the first seal member
including a pair of spaced apart ends defining a vacuumization
and gas filling port. A second seal member is provided which
comprises a plug fusibly bridging the spaced apart ends of the
first seal member and between opposing facing surfaces of the
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pair of plate members so as to seal the gas filling port.
DESCRIPTION OF THE DRAWINGS
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The above and other objects, advantages and
features of the invention will become more apparent from the
following description taken in conjunction with the accompanying
drawings wherein:
Figure 1 illustrates a glass substrate upon which
a first conductive pattern has been printed, one such pattern
being shown in the top left hand corner thereof with the dash
lines indicating the positions of a large number of other such ~;
patterns not shown in this drawing for purposes of clarity of
explanation,
Figure 2 illustrates the glass plate bf Figure 1 y
upon which has been printed the first dielectric mask (a
black colored dielectric but shown white in Figure 2),
Figure 3 is the plate shown in Figure 2 having the
crossover conductors printed on the mask of Figure 3 inter~
connecting the different elements shown, it being understood
that a similar printing has occurred with respect to the
other substrate elements shown in Figure 3,
In Figure 4, a further dielectric printing has
been accomplished over the crossover elements shown in Figure 3,
Figure 5 is an exploded view showing the sequence
of assembly of the different components into a device ready
for batch fill and seal operations,
Figure 6 is a top plan view of a completely
assembled device. -~
Figure 7 is an enlarged sectional view showing the -
placement of the seal rod bridging the gap on the now fused ~`
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seal frame, ~ -
Figure 8 shows the mercury capsule in position with
a laser beam directed thereto for fracturing same,
Figure 9 is a process flows chart showing the
individual printing and curing operations utilized in the
manufacture of the devices.
DETAII,ED DESCRIPTION .
Referring now to Figures 1-8 in conjunction with
Figure 9, Figure 1 shows a glass plate 10 which, in a specific
example, may be ten inches by twelve inches single strength
glass, has printed thereon individual cathode electrode patterns
11-1, 11-2, ll-N and cathode period elements 12-1, 12~N. Each
cathode pattern constitutes a digit position, the illustrated
embodiment being for a nine digit numeric display tn-9). It ~
will be appreciated that the invention is equally applicable ~-
to alphanumeric segmentation as well as crosspoint matrix dis-
play. These elements have cathode electrode segments 13A, 13B
etc. which, in the embodiment of this invention, constitute the
cathode electrode elements defining the glow discharge portions
of the display. It will be noted that certain ones of these
cathode segments 13A, for example, has a further direct con- -
ductive portion 14-A leading to a conductor pad 15-A. In the
embodiment of this invention to be described herein, each of
the corresponding segments 13-A in all of the digit positions
11-1, 11-2...11-N, are interconnected electrically, some of
which are directly interconnected in the initial electrode
printing shown in Fig. 1. For example, the center bar segment
13-C is shown as being an interconnected horizontal segment
electrode and by conductor portion 14-C to a pad 15~C.
Alternate pads are also printed at this time for subsequent
connection to the anode elements to be described later herein.
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In like manner, the cathode electrode 13-B in digit position
11-1 is interconnected to ever~ cathode segment designated with
the numeral B b~ a conductor portion 14-B and thereby to a pad
15-B.
However, in accordance with the present embodiment,
some of the cathode segments are not directly connected to
conductors extending to the individual pad elements 15. In
the illustrated embodiment, a first dielectric mask element 16
shown in Figure 2 is printed over the conductor segments leaving
openings or vias 18-1, 18-2, 18-N and 19-1, 19-2, l9-N and
20-1, 20-N, 21-1, 21-N and 22~1, through 22-N, all of which are
~ registry with an underlying conductor portions or areas.
These vias are simply opening or spaces left vacant in the
dielectric mask or layer 16. In addition to the vias or open-
ings left for crossover connections, to be described later in
connection with Figure 3, it will be noted that the individual
cathode segments 13-A, 13-B, etc. and the periods therefor
: ~.
12-1... 12-N, are left open. As has been described earlier, no ~ -
further conductive material is applied to these cathode elements ~ ~
because they have been cured at a high~r temperature to thereby ~;-` -
anneal and/or provide smooth surfaces for the discharge per se.
However, the crossover vias, 18-1...18-N, l9-1...19-N, 20
20-N and 22-1...22-N are left open for the purpose of permitting
the conductor material which is printed in a manner shown in
Figure 4 to make electrical contact with the conductor elements
exposed by the vias. These form the electrical crossover con-
nections shown in the pattern of Figure 3. It will be appreci-
ated that conductor patterns may be devised so that the printing
of such crossovers is eliminated or minimized. It should be
understood that while the dielectric mask is shown as white, it
is a black mask for highlighting the glow discharges at the
cathode segments, and that the cathode material is white or
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silver colored in appearance and, in fact, is basically a
silver in a suitable vehicle. Furthermore, clear or transparent
areas of glass have been stippled. Of course the anode glass
substrate could be translucent.
In addition to the openings or vias to make the cross-
over connections and in addition to the opening for permitting
the cathode segments to be viewed in direct conductive contact
with the gas, a pair of windows 25A and 25B are provided so
that the glass substrate 10 is directly viewable through these
openings 24 and 25. These openings are for the purpose to be
described more fully hereinafter. ~Not shown in Figures 1 or 2 are conventional reg- `~ ;
istration marks, the registration marks simply being marks
which are printed in dielectric material upon the substrate ~
10 and in any subsequent printing upon the substrate 10 when ~ -
the dielectric material is printed so as to assure registration
thereof. In like manner, in the following pace which also
follows, further printings of the registration marks are made
to assure the proper registrations are achieved. The term
printing is used principally to encompass stencil screen print- ~
ing etc,. but other forms of printing may be used. ~;
As shown in Figure 3 the crossover interconnecting
via 19-1 through via l9-N is designated with the numeral 30
and the crossovers connecting the vias 18-1...18-N are
designated 31. In like manner, crossover conductor means 32,
33 and 34 are conductor printings upon the dielectric. The
printing operations are simply screening or otherwise applying
the conductive material directly upon the dielectric surfaces
of the substrate with the conductive material entering the vias
and making the electrical contacts with the conductor pre~
viously printed. It will also be noted that a pair of cross-
overs 36 and 37 have also been printed upon the conductor solely
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for the purpose of making the crossover connections between -the
conductor elements as shown~
It will be noted that the conductive cathode segments
for each of the digit positions remains exposed and these
elements are, in effect, continuing to receive the temperature
treatments (albeit at lower temperatures) Eor the curing of the
dielectric layer 16 and the individual crossover layers as
shown.
In a final printing operation, the final dielectric
layer is applied over the crossover, the windows 25A and 25B
being maintained. The purpose of this final printing is, as `~
is well known, to avoid any glowing of conductor areas or por-
tions which it is not desired to glow.
Referring now to Figure 9, it should be noted that
an important step in the process just described in the fabrica-
tion of the back substrate is that the electrodes which form
the cathode segments for the display have been printed in an
initial printing operation. This electrode is cured in step ~ ~ ;
5 as shown in Figure 9 at a much higher temperature than could
be effected by prior art techniques in fabrication devices of
the character of the present invention. In other words, by
printing the cathode segments first and curing them at a much
higher temperature to provide an improved cathode-gas interface, ~-
the mask which is printed on at a later time, can be cured at
lower temperatures without adversely affecting the conducting
properties of the different conductor elements used in providing
exterior connections for the device. As shown in Figure 9, the
initial mask is printed in a two step operation of, first,
printing the mask a first time, drying the mask and then curing
the mask. A second mask printing, drying and curing operation
is effected but it will be appreciated that these may be done
in a single step. In some cases, the mask may be fabricated
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as a film and transferred to the substrate~ However, it is
important to assure that the mask is of a sufficient thickness
that the gap adjacent cathode segments is separated by a physi-
cal barrier of dielectric material. Thus, this second step is
an important assurance that the dielectric between the ends of
individual cathode segments is high enough to provide a barrier
which avoids or minimizes shorting between nearby cathode
segments.
The crossover printing is done with the same conduc-
tive material as is used in the first printing o~eration of ~ ;
conductive material and it will be noted that in each case,
the conductive material is dryed and then cured at higher
temperatures. This material is a frit based thick film paste
primarily of silver. The third mask printing operation, while
it could have been limited to printing simply over the cross-
overs, was, in effect, a full printing since this further assured ~
a sufficient barrier between the individual cathode segments ~ `
on the substrate. Thus, in addition to being able to print,
dry and cure the cathode electrodes at a high enough temperature
(a typical conveyor oven being about 50 ft. long, one foot per
minute, there being about 15 heat zones with a maximum tempera-
ture of 1100C.) as to assure a good, clean, smooth silver
surface for the cathode electrode, printing the cathode elec-
- trodes in the first printing step permits the buiiding up in the
mask areas of sufficient barriers between the individual
cathode segments as to reduce the possibility of conductive
connections between the individual cathode elements due to the
sputtering, etc. and thereby enhance the active life of the
device.
As illustrated at box 18 of Figure ~, the device is
scribed along the dash-dot lines and separated to provide indi-
vidual back substrates illustrated in Figure 5 as element 50.
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Element 50 is identical to the differnet element 50 shown in
Figure 4.
Referring now to Figure 5, the back substrate now
designated as element 50, is identical to the back substrate
component shown in Figure 4. Also shown in Figure 5 is an
anode substrate 51 having printed thereon individual anode
elements 52-1, 52-2, 52-N, there being one such anode electrode
element for each digit position and adapted to overlie the indi-
vidual cathode segments and the cathods period element 12;1 at
a given digit position. The anode conductors are transparent
tin oxide which are printed and fired on a single strength glass
substrate 53. It will be appreciated that the printing and
firing of these conductors may be done in a batch process, very
much like the printing of the back substrate with cathode
elements. The use of tin oxide as a transparent anode element
is conventional in the art and is not described in detail here-
in except to say that the process of printing same with large
numbers of devices on a thin glass substrate is useful for the
purpose of batch producing devices.
The top substrate or anode plate 51 is joined to the
bottom substrate by means of a sealing element or member 55
which has been shaped so as to have the ends thereof 56 and 57
spaced by about a 1/4 inch to about 1/16 inch. The sealing
element 55 is simply placed upon the black dielectric masked
element and held in place by drying unfused dielectric. At the
same time, small spacer rods 58 and 59 at each end of the device
are likewise temporarily held in position by tacking as by the
use of unfused dielectric. Spacer rods 58 and 59 consist of a ~ ?
hard glass composition having a higher softening temperature ;
than the sealing element 55. The seal element 55 is made from
a fiber optic type glass which has no bubbles therein and which
has a fusing or seal temperature below the melting point of the ;
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glass substrate 10 and spacer rods 58 and 59 (a seal temper-
ature of about 450C is used). In addition, a small mercury
capsule 60 is held in place in position over window 25A by a
white unfused dielectric which is of essentially the same
composition as the dielectric forming the mask but which does
not have any pigmentation in it. The purpose of using a white
unfused dielectric is so that a laser energy which is used to
rupture the capsule 60 is not absorbed by the black dielectric
to create heat in the black dielectric and thereby destroy the
device. It is also for this reason that a pair of windows 25A
and 25B is provided.
After the sealing member 55 and spacer rods 58 and
59 and mercury capsule 60 have been positioned in the device,
the anode plate Sl is positioned over these elements and a
weight is applied thereto. The entire assernbly is passed -
through a heating oven to fuse or join the sealing member 55
to anode plate 51 and back substrate plate 50. The resulting
device is illustrated in Figure 6 and it will be noted that
there is a small gap 65 so the interior of the gas chamber is
accessible. A glass rod 66 having a diameter about the same
diameter as spacer rods 58 and 59 is simply laid in the gap or
crevice between back substrate plate 50 and anode plate 51 and
constitutes the glass plug illustrated in block 23 of Figure 9.
It will be appreciated that the spacer rod elements
58 and 59 need not be located in the gas chamber formed or in
the positions shown. They may be located parallel to the
horizontal runs of seal 55, parallel to all four runs, between
display positions for larger displays (see Baker et al U.S.
Patent 3,499,167); even externally of the chamber and parallel
to the horizontal and/or vertical runs of seal member 55. As
a matter of fact, the spacer may have a perimetrical pattern
which is a twin to seal member 55, and only sliyhtly larger or
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smallerO The only size eriteria of the spacer is that it
define the discharge gap and be a high melting tempe~ature
glass and have a fiber softening point below that of seal
member 55. ; As shown in Figure 6 alternate ones of contact pads
15 are connected to the cathode electrode on cathode plate 50
and the intervening ones are connected by means of a extruded
conductive silver epoxy connectors 70~1, 70-2 as an improvement
over prior art metal insert connectors previously used for this
purpose. It is important to cure the epoxy at a temperature
such that bubbles are not formed. Bubbles tend to cause con-
centrations of current flow in the tin oxized coatings and
thereby impair or destroy the connection thereto.
As shown in Figure 8, the mercury giver 60 is a ;~
filamentary glass tube ~18 mils in outside diameter) which is
laser energy transparent~ It is positioned between a window
25~ and the cathode plate 50 and a transparent portion of the
anode plate 51 (which may also be designated as a "window")
and held in place for assembly purposes by a white dielectric.
The aluminum or copper block serves as a heat sink and should
not be highly reflective for safety reasons. Instead of a
glass capsule the giver may be any other radiant energy
actuatable device, such as SAES type 150 giver from the SAES
company of Italy. -
The gas filling may be a mixture of neon and argon,
such as 99.5% neon and 0.5% argon. As is conventional, radio- ~ ;
active Krypton (Krypton 85) may be added to the fill mixture
to lower the operating voltage. However, it will be noted that
there are two unused contact pads 15 which could be used to
operate a keep alive discharge as is also conventional in the
art.
In a preferred embodiment, the edges 75 and 76 on
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plates 50 and 51 from a slot or notch for receipt of the seal
rod or plug member 60. This permits a simple mechanical reten-
tion of the spacer in its desired position during the outgassing
and gas filling operation. If desired the top horizontal run
of seal member 55 may be located closer to the edge so that
upon softening the seal material of element 55 will be pressed
flat as shown in Figure 8 and the plug rod 66 held in position
by an adhesive such as unfused dielectric. However, the seal
member 55 may be formed flat in cross section and, as before,
slightly thicker than the spacer rods. The panel assemblies,
with seal rod 66 in the notch or space and bridging the ends -
of the seal element 55, the panels are stacked, in stainless
trays with the port of space 65 up and the glass rod 66 in place.
A high temperature glass shim, not shown, is located between
the lower edge of anode plate 51 to maintain the proper rela- ~-
tionship between the anode and cathode plates while the heating
of seal rod 66 is performed.
Seal element 55 is a bubble-free glass to avoid
"worm holes herein, a~fiber optic type glass such as Corning
type 7570 glass 033" O.D. cane formed as shown in Figure 5
works satisfactorily, it having a relatively low temperature of
about 450C. The glass plugging element or rod 66, placed
across the opening or port 65 as shown, has fiber softening
point below that of the sealing member 55; a similar glass
with a fiber softening point 20 ~o 30 degrees lower is
satisfactory.
The gas process procedure is the evacuation of the
system, the introduction of the proper gas at ambient room
temperature to the proper pressure, about 120 torr, and the
heating of the seal rod so it closes the envelope with the
desired gas condition. In the system described above, the
cycle is 6 hours with 2000 devices per cycle. Each chamber
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can be large enough to handle as many as 5000 devices. The
cycle may be reduced to 1-1/~ hours. If devices fail to seal,
they are simply recycled. System gas is reco~ered by operating
two chambers in parallel. After the sealed devices are re~
moved from the gas process system, each one is placed under a
laser which is projected through a window in the device to
crack the capsule and release mercury into the envelope. As
is conventional in the art some panel aging time may be per-
formed before releasing the mercury.
It will be appreciated that while a number of
modifications have been referred to, others will become appar-
ent to those skilled in the art and it is to be understood
that such obvious modifications may be made without departing
from the true spirit and scope of the claims appended hereto.-
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